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Rai DK, Lawrence P, Kloc A, Schafer E, Rieder E. Analysis of the interaction between host factor Sam68 and viral elements during foot-and-mouth disease virus infections. Virol J 2015; 12:224. [PMID: 26695943 PMCID: PMC4689063 DOI: 10.1186/s12985-015-0452-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2015] [Accepted: 12/10/2015] [Indexed: 12/27/2022] Open
Abstract
BACKGROUND The nuclear protein Src-associated protein of 68 kDa in mitosis (Sam68) is known to bind RNA and be involved in cellular processes triggered in response to environmental stresses, including virus infection. Interestingly, Sam68 is a multi-functional protein implicated in the life cycle of retroviruses and picornaviruses and is also considered a marker of virus-induced stress granules (SGs). Recently, we demonstrated the partial redistribution of Sam68 to the cytoplasm in FMDV infected cells, its interaction with viral protease 3C(pro), and found a significant reduction in viral titers as consequence of Sam68-specific siRNA knockdowns. Despite of that, details of how it benefits FMDV remains to be elucidated. METHODS Sam68 cytoplasmic localization was examined by immunofluorescent microscopy, counterstaining with antibodies against Sam68, a viral capsid protein and markers of SGs. The relevance of RAAA motifs in the IRES was investigated using electromobility shift assays with Sam68 protein and parental and mutant FMDV RNAs. In addition, full genome WT and mutant or G-luc replicon RNAs were tested following transfection in mammalian cells. The impact of Sam68 depletion to virus protein and RNA synthesis was investigated in a cell-free system. Lastly, through co-immunoprecipitation, structural modeling, and subcellular fractionation, viral protein interactions with Sam68 were explored. RESULTS FMDV-induced cytoplasmic redistribution of Sam68 resulted in it temporarily co-localizing with SG marker: TIA-1. Mutations that disrupted FMDV IRES RAAA motifs, with putative affinity to Sam68 in domain 3 and 4 cause a reduction on the formation of ribonucleoprotein complexes with this protein and resulted in non-viable progeny viruses and replication-impaired replicons. Furthermore, depletion of Sam68 in cell-free extracts greatly diminished FMDV RNA replication, which was restored by addition of recombinant Sam68. The results here demonstrated that Sam68 specifically co-precipitates with both FMDV 3D(pol) and 3C(pro) consistent with early observations of FMDV 3C(pro)-induced cleavage of Sam68. CONCLUSION We have found that Sam68 is a specific binding partner for FMDV non-structural proteins 3C(pro) and 3D(pol) and showed that mutations at RAAA motifs in IRES domains 3 and 4 cause a decrease in Sam68 affinity to these RNA elements and rendered the mutant RNA non-viable. Interestingly, in FMDV infected cells re-localized Sam68 was transiently detected along with SG markers in the cytoplasm. These results support the importance of Sam68 as a host factor co-opted by FMDV during infection and demonstrate that Sam68 interact with both, FMDV RNA motifs in the IRES and viral non-structural proteins 3C(pro) and 3D(pol).
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Affiliation(s)
- Devendra K Rai
- Foreign Animal Disease Research Unit, United States Department of Agriculture, Agricultural Research Service, Plum Island Animal Disease Center, USDA/ARS/NAA, P.O. Box 848, Greenport, NY, 11944, USA.
| | - Paul Lawrence
- Foreign Animal Disease Research Unit, United States Department of Agriculture, Agricultural Research Service, Plum Island Animal Disease Center, USDA/ARS/NAA, P.O. Box 848, Greenport, NY, 11944, USA.
| | - Anna Kloc
- Foreign Animal Disease Research Unit, United States Department of Agriculture, Agricultural Research Service, Plum Island Animal Disease Center, USDA/ARS/NAA, P.O. Box 848, Greenport, NY, 11944, USA.
| | - Elizabeth Schafer
- Foreign Animal Disease Research Unit, United States Department of Agriculture, Agricultural Research Service, Plum Island Animal Disease Center, USDA/ARS/NAA, P.O. Box 848, Greenport, NY, 11944, USA.
| | - Elizabeth Rieder
- Foreign Animal Disease Research Unit, United States Department of Agriculture, Agricultural Research Service, Plum Island Animal Disease Center, USDA/ARS/NAA, P.O. Box 848, Greenport, NY, 11944, USA.
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The Role of Alternative Splicing in the Control of Immune Homeostasis and Cellular Differentiation. Int J Mol Sci 2015; 17:ijms17010003. [PMID: 26703587 PMCID: PMC4730250 DOI: 10.3390/ijms17010003] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2015] [Revised: 12/11/2015] [Accepted: 12/15/2015] [Indexed: 12/21/2022] Open
Abstract
Alternative splicing of pre-mRNA helps to enhance the genetic diversity within mammalian cells by increasing the number of protein isoforms that can be generated from one gene product. This provides a great deal of flexibility to the host cell to alter protein function, but when dysregulation in splicing occurs this can have important impact on health and disease. Alternative splicing is widely used in the mammalian immune system to control the development and function of antigen specific lymphocytes. In this review we will examine the splicing of pre-mRNAs yielding key proteins in the immune system that regulate apoptosis, lymphocyte differentiation, activation and homeostasis, and discuss how defects in splicing can contribute to diseases. We will describe how disruption to trans-acting factors, such as heterogeneous nuclear ribonucleoproteins (hnRNPs), can impact on cell survival and differentiation in the immune system.
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Mayr C. Evolution and Biological Roles of Alternative 3'UTRs. Trends Cell Biol 2015; 26:227-237. [PMID: 26597575 DOI: 10.1016/j.tcb.2015.10.012] [Citation(s) in RCA: 212] [Impact Index Per Article: 23.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2015] [Revised: 10/21/2015] [Accepted: 10/22/2015] [Indexed: 12/21/2022]
Abstract
More than half of human genes use alternative cleavage and polyadenylation to generate alternative 3' untranslated region (3'UTR) isoforms. Most efforts have focused on transcriptome-wide mapping of alternative 3'UTRs and on the question of how 3'UTR isoform ratios may be regulated. However, it remains less clear why alternative 3'UTRs have evolved and what biological roles they play. This review summarizes our current knowledge of the functional roles of alternative 3'UTRs, including mRNA localization, mRNA stability, and translational efficiency. Recent work suggests that alternative 3'UTRs may also enable the formation of protein-protein interactions to regulate protein localization or to diversify protein functions. These recent findings open an exciting research direction for the investigation of new biological roles of alternative 3'UTRs.
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Affiliation(s)
- Christine Mayr
- Department of Cancer Biology and Genetics, Memorial Sloan Kettering Cancer Center, New York, NY, USA.
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The RNA-binding protein Sam68 regulates tumor cell viability and hepatic carcinogenesis by inhibiting the transcriptional activity of FOXOs. J Mol Histol 2015; 46:485-97. [PMID: 26438629 DOI: 10.1007/s10735-015-9639-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2015] [Accepted: 09/30/2015] [Indexed: 12/31/2022]
Abstract
Src associated in mitosis (Sam68; 68 kDa) is a KH domain RNA-binding protein that belongs to the signal transduction and activation of RNA family, and has been implicated in the oncogenesis and progression of several human cancers. Our study aimed to investigated the clinicopathologic significance of Sam68 expression and its role in cell proliferation and the underlying molecular mechanism in hepatocellular carcinoma (HCC). We demonstrated that Sam68 expression was significantly increased in HCC and high expression of Sam68 was significantly associated with Edmondson grade, tumor size, tumor nodule number, HBsAg status and Ki-67 expression. The Kaplan-Meier survival curves showed that increased expression of Sam68 was correlated with poor prognosis in HCC patients and served as an independent prognostic marker of overall survival in a multivariable analysis. In addition, through serum starvation and refeeding assay, we demonstrated that Sam68 was lowly expressed in serum-starved HCC cells, and was progressively increased after serum-additioning. Furthermore, siRNA knockdown of endogenous Sam68 inhibited cell proliferation and tumourigenicity of HCC cells in vitro, through blocking the G1 to S phase transition. Moreover, we reported that the anti-proliferative effect of silencing Sam68 was accompanied with up-regulated expression of cyclin-dependent kinase inhibitors, p21(Cip1) and p27(Kip1), enhanced transactivation of FOXO factors (FOXO4), and dysreuglation of Akt/GSK-3β signaling. Taken together, these findings provide a rational framework for the progression of HCC and thereby indicated that Sam68 might be a novel and useful prognostic marker and a potential target for human HCC treatment.
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Pagliarini V, Pelosi L, Bustamante MB, Nobili A, Berardinelli MG, D'Amelio M, Musarò A, Sette C. SAM68 is a physiological regulator of SMN2 splicing in spinal muscular atrophy. J Cell Biol 2015; 211:77-90. [PMID: 26438828 PMCID: PMC4602033 DOI: 10.1083/jcb.201502059] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2015] [Accepted: 08/31/2015] [Indexed: 02/05/2023] Open
Abstract
Knockout of the splicing factor SAM68 promotes SMN2 splicing, improving neuromuscular defects and viability in SMA mice. Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by loss of motor neurons in patients with null mutations in the SMN1 gene. The almost identical SMN2 gene is unable to compensate for this deficiency because of the skipping of exon 7 during pre–messenger RNA (mRNA) processing. Although several splicing factors can modulate SMN2 splicing in vitro, the physiological regulators of this disease-causing event are unknown. We found that knockout of the splicing factor SAM68 partially rescued body weight and viability of SMAΔ7 mice. Ablation of SAM68 function promoted SMN2 splicing and expression in SMAΔ7 mice, correlating with amelioration of SMA-related defects in motor neurons and skeletal muscles. Mechanistically, SAM68 binds to SMN2 pre-mRNA, favoring recruitment of the splicing repressor hnRNP A1 and interfering with that of U2AF65 at the 3′ splice site of exon 7. These findings identify SAM68 as the first physiological regulator of SMN2 splicing in an SMA mouse model.
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Affiliation(s)
- Vittoria Pagliarini
- Department of Biomedicine and Prevention, University of Rome Tor Vergata, 00133 Rome, Italy Laboratory of Neuroembryology, Fondazione Santa Lucia, 00143 Rome, Italy
| | - Laura Pelosi
- Institute Pasteur Cenci-Bolognetti Foundation, DAHFMO-Unit of Histology and Medical Embryology, IIM, University of Rome La Sapienza, 00161 Rome, Italy
| | - Maria Blaire Bustamante
- Department of Biomedicine and Prevention, University of Rome Tor Vergata, 00133 Rome, Italy Laboratory of Neuroembryology, Fondazione Santa Lucia, 00143 Rome, Italy
| | - Annalisa Nobili
- Laboratory of Molecular Neuroscience, Fondazione Santa Lucia, 00143 Rome, Italy Medical School University Campus Bio-Medico, 00128 Rome, Italy
| | - Maria Grazia Berardinelli
- Institute Pasteur Cenci-Bolognetti Foundation, DAHFMO-Unit of Histology and Medical Embryology, IIM, University of Rome La Sapienza, 00161 Rome, Italy
| | - Marcello D'Amelio
- Laboratory of Molecular Neuroscience, Fondazione Santa Lucia, 00143 Rome, Italy Medical School University Campus Bio-Medico, 00128 Rome, Italy
| | - Antonio Musarò
- Institute Pasteur Cenci-Bolognetti Foundation, DAHFMO-Unit of Histology and Medical Embryology, IIM, University of Rome La Sapienza, 00161 Rome, Italy Center for Life Nano Science@Sapienza, Istituto Italiano di Tecnologia, 00161 Rome, Italy
| | - Claudio Sette
- Department of Biomedicine and Prevention, University of Rome Tor Vergata, 00133 Rome, Italy Laboratory of Neuroembryology, Fondazione Santa Lucia, 00143 Rome, Italy
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Sam68 Promotes NF-κB Activation and Apoptosis Signaling in Articular Chondrocytes during Osteoarthritis. Inflamm Res 2015; 64:895-902. [PMID: 26350037 DOI: 10.1007/s00011-015-0872-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2015] [Revised: 08/18/2015] [Accepted: 08/19/2015] [Indexed: 12/11/2022] Open
Abstract
OBJECTIVES To investigate the expression of Sam68 in articular cartilage of knee osteoarthritis (OA) and the relationship between Sam68 and NF-κB activation and apoptosis signaling in OA articular chondrocytes. METHODS Sam68 expression in normal and osteoarthritic cartilage was assessed by immunohistochemistry and RT-PCR on both meniscal/ligamentous injury (MLI)-induced OA rat model and the clinical human OA cartilage tissues. Sam68 expression in chondrocytes under tumor necrosis factor-alpha (TNF-α) stimuli was also assessed by immunoblot. Inhibiting Sam68 in chondrocytes under TNF-α stimuli was conducted using small interfering RNA (siRNA) and its influence on the expression of apoptotic marker and catabolic genes was examined by immunoblot. The mechanism of how Sam68 stimulates NF-κB activity was determined by co-immunoprecipitation and immunoblot analysis of nuclear and cytoplasmic fractions of TNF-α-treated chondrocytes for p65 and Sam68. RESULTS Sam68 expression was increased in OA cartilage tissues and chondrocytes under TNF-α stimuli. Inhibition of Sam68 by siRNA significantly decreased the expression of apoptotic markers (cleaved caspase-3 and cleaved PARP) in chondrocytes following TNF-α-stimulation. Sam68 knockdown suppressed Iκ-B degradation and p65 nuclear transportation in TNF-α-treated chondrocytes, indicating a suppressed NF-κB activation. Upon TNF-α exposure, the nuclear transportation of Sam68 and its interaction with p65 was detected in chondrocytes. Furthermore, Sam68 knockdown also alleviated the TNF-α-induced catabolic marker (MMP13, ADAMTS5, iNOS and IL-6) expression. CONCLUSIONS The highly expressed Sam68 promotes NF-κB signaling activation, catabolic gene expression and cellular apoptosis in TNF-α-treated chondrocytes, which may provide better insights into the pathophysiology of OA and a potential target for its treatment.
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EMT-Inducing Molecular Factors in Gynecological Cancers. BIOMED RESEARCH INTERNATIONAL 2015; 2015:420891. [PMID: 26356073 PMCID: PMC4556818 DOI: 10.1155/2015/420891] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Accepted: 01/14/2015] [Indexed: 12/27/2022]
Abstract
Gynecologic cancers are the unregulated growth of neoplastic cells that arise in the cervix, ovaries, fallopian tubes, uterus, vagina, and vulva. Although gynecologic cancers are characterized by different signs and symptoms, studies have shown that they share common risk factors, such as smoking, obesity, age, exposure to certain chemicals, infection with human immunodeficiency virus (HIV), and infection with human papilloma virus (HPV). Despite recent advancements in the preventative, diagnostic, and therapeutic interventions for gynecologic cancers, many patients still die as a result of metastasis and recurrence. Since mounting evidence indicates that the epithelial-mesenchymal transition (EMT) process plays an essential role in metastatic relapse of cancer, understanding the molecular aberrations responsible for the EMT and its underlying signaling should be given high priority in order to reduce cancer morbidity and mortality.
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SAM68: Signal Transduction and RNA Metabolism in Human Cancer. BIOMED RESEARCH INTERNATIONAL 2015; 2015:528954. [PMID: 26273626 PMCID: PMC4529925 DOI: 10.1155/2015/528954] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/12/2015] [Accepted: 02/24/2015] [Indexed: 12/21/2022]
Abstract
Alterations in expression and/or activity of splicing factors as well as mutations in cis-acting
splicing regulatory sequences contribute to cancer phenotypes. Genome-wide
studies have revealed more than 15,000 tumor-associated splice variants derived from
genes involved in almost every aspect of cancer cell biology, including proliferation,
differentiation, cell cycle control, metabolism, apoptosis, motility, invasion, and
angiogenesis. In the past decades, several RNA binding proteins (RBPs) have been
implicated in tumorigenesis. SAM68 (SRC associated in mitosis of 68 kDa) belongs to
the STAR (signal transduction and activation of RNA metabolism) family of RBPs.
SAM68 is involved in several steps of mRNA metabolism, from transcription to
alternative splicing and then to nuclear export. Moreover, SAM68 participates in signaling
pathways associated with cell response to stimuli, cell cycle transitions, and viral
infections. Recent evidence has linked this RBP to the onset and progression of
different tumors, highlighting misregulation of SAM68-regulated splicing events as a
key step in neoplastic transformation and tumor progression. Here we review recent
studies on the role of SAM68 in splicing regulation and we discuss its contribution to
aberrant pre-mRNA processing in cancer.
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59
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Nuclear Protein Sam68 Interacts with the Enterovirus 71 Internal Ribosome Entry Site and Positively Regulates Viral Protein Translation. J Virol 2015. [PMID: 26202240 DOI: 10.1128/jvi.01677-15] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED Enterovirus 71 (EV71) recruits various cellular factors to assist in the replication and translation of its genome. Identification of the host factors involved in the EV71 life cycle not only will enable a better understanding of the infection mechanism but also has the potential to be of use in the development of antiviral therapeutics. In this study, we demonstrated that the cellular factor 68-kDa Src-associated protein in mitosis (Sam68) acts as an internal ribosome entry site (IRES) trans-acting factor (ITAF) that binds specifically to the EV71 5' untranslated region (5'UTR). Interaction sites in both the viral IRES (stem-loops IV and V) and the heterogeneous nuclear ribonucleoprotein K homology (KH) domain of Sam68 protein were further mapped using an electrophoretic mobility shift assay (EMSA) and biotin RNA pulldown assay. More importantly, dual-luciferase (firefly) reporter analysis suggested that overexpression of Sam68 positively regulated IRES-dependent translation of virus proteins. In contrast, both IRES activity and viral protein translation significantly decreased in Sam68 knockdown cells compared with the negative-control cells treated with short hairpin RNA (shRNA). However, downregulation of Sam68 did not have a significant inhibitory effect on the accumulation of the EV71 genome. Moreover, Sam68 was redistributed from the nucleus to the cytoplasm and interacts with cellular factors, such as poly(rC)-binding protein 2 (PCBP2) and poly(A)-binding protein (PABP), during EV71 infection. The cytoplasmic relocalization of Sam68 in EV71-infected cells may be involved in the enhancement of EV71 IRES-mediated translation. Since Sam68 is known to be a RNA-binding protein, these results provide direct evidence that Sam68 is a novel ITAF that interacts with EV71 IRES and positively regulates viral protein translation. IMPORTANCE The nuclear protein Sam68 is found as an additional new host factor that interacts with the EV71 IRES during infection and could potentially enhance the translation of virus protein. To our knowledge, this is the first report that describes Sam68 actively participating in the life cycle of EV71 at a molecular level. These studies will not only improve our understanding of the replication of EV71 but also have the potential for aiding in developing a therapeutic strategy against EV71 infection.
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Wang Y, Liang L, Zhang J, Li M, Zhu J, Gong C, Yang L, Zhu J, Chen L, Ni R. Sam68 promotes cellular proliferation and predicts poor prognosis in esophageal squamous cell carcinoma. Tumour Biol 2015; 36:8735-45. [PMID: 26050229 DOI: 10.1007/s13277-015-3631-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Accepted: 05/31/2015] [Indexed: 12/14/2022] Open
Abstract
Sam68 (Src-associated in mitosis of 68 kD) is a KH domain RNA-binding protein. The expression of Sam68 was correlated with kinds of tumors. Yet, the expression mechanisms and physiological significance of Sam68 in ESCC remains unclear. In this study, we clarified a potential role of Sam68 in the treatment of ESCC. Western blot and immunohistochemistry (IHC) analysis revealed that the protein level of Sam68 was higher in ESCC tumor tissues and cell lines. In addition, IHC stain revealed that Sam68 was positively correlated with clinical pathologic variables such as tumor grade and tumor invasion. In addition, Sam68 could be an independent prognostic indicator for patients' overall survival. In vitro studies such as starvation and refeeding assay along with Sam68-shRNA transfection assay demonstrated that Sam68 expression promoted proliferation of ESCC cells. And Sam68 downregulation caused decreased rate of cell growth and colony formation. Reasons are associated with growth arrest of cell cycle at G1/S phase. Moreover, our results clarified that Sam68 could promote ESCC cell proliferation via the activation of Akt/GSK-3β pathway. This research indicated that Sam68 might accelerate the cell cycle progression and be considered as a new therapy target in ESCC.
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Affiliation(s)
- Yayun Wang
- Department of Gastroenterology, Affiliated Hospital of Nantong University, 19 Qixiu Road, Nantong, 226001, Jiangsu, China
| | - Li Liang
- Department of Medical Oncology, Affiliated Hospital of Nantong University, 19 Qixiu Road, Nantong, 226001, Jiangsu, China
| | - Jianguo Zhang
- Department of Pathology, Affiliated Hospital of Nantong University, 19 Qixiu Road, Nantong, 226001, Jiangsu, China
| | - Mei Li
- Department of Medical Oncology, Affiliated Hospital of Nantong University, 19 Qixiu Road, Nantong, 226001, Jiangsu, China
| | - Junya Zhu
- Department of Gastroenterology, Affiliated Hospital of Nantong University, 19 Qixiu Road, Nantong, 226001, Jiangsu, China
| | - Chen Gong
- Department of Gastroenterology, Affiliated Hospital of Nantong University, 19 Qixiu Road, Nantong, 226001, Jiangsu, China
| | - Linlin Yang
- Department of Oncology, Affiliated Cancer Hospital of Nantong University, Nantong, 226361, Jiangsu, China
| | - Jia Zhu
- Department of Oncology, Affiliated Cancer Hospital of Nantong University, Nantong, 226361, Jiangsu, China
| | - Lingling Chen
- Department of Gastroenterology, Affiliated Hospital of Nantong University, 19 Qixiu Road, Nantong, 226001, Jiangsu, China
| | - Runzhou Ni
- Department of Gastroenterology, Affiliated Hospital of Nantong University, 19 Qixiu Road, Nantong, 226001, Jiangsu, China.
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Zhou J, Cheng M, Boriboun C, Ardehali MM, Jiang C, Liu Q, Han S, Goukassian DA, Tang YL, Zhao TC, Zhao M, Cai L, Richard S, Kishore R, Qin G. Inhibition of Sam68 triggers adipose tissue browning. J Endocrinol 2015; 225:181-9. [PMID: 25934704 PMCID: PMC4482239 DOI: 10.1530/joe-14-0727] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 04/22/2015] [Indexed: 12/12/2022]
Abstract
Obesity is associated with insulin resistance and type 2 diabetes; molecular mechanisms that promote energy expenditure can be utilized for effective therapy. Src-associated in mitosis of 68 kDa (Sam68) is potentially significant, because knockout (KO) of Sam68 leads to markedly reduced adiposity. In the present study, we sought to determine the mechanism by which Sam68 regulates adiposity and energy homeostasis. We first found that Sam68 KO mice have a significantly reduced body weight as compared to controls, and the difference is explained entirely by decreased adiposity. Interestingly, these effects were not mediated by a difference in food intake; rather, they were associated with enhanced physical activity. When they were fed a high-fat diet, Sam68 KO mice gained much less body weight and fat mass than their WT littermates did, and they displayed an improved glucose and insulin tolerance. In Sam68 KO mice, the brown adipose tissue (BAT), inguinal, and epididymal depots were smaller, and their adipocytes were less hypertrophied as compared to their WT littermates. The BAT of Sam68 KO mice exhibited reduced lipid stores and expressed higher levels of Ucp1 and key thermogenic and fatty acid oxidation genes. Similarly, depots of inguinal and epididymal white adipose tissue (WAT) in Sam68 KO mice appeared browner, their multilocular Ucp1-positive cells were much more abundant, and the expression of Ucp1, Cidea, Prdm16, and Ppargc1a genes was greater as compared to WT controls, which suggests that the loss of Sam68 also promotes WAT browning. Furthermore, in all of the fat depots of the Sam68 KO mice, the expression of M2 macrophage markers was up-regulated, and that of M1 markers was down-regulated. Thus, Sam68 plays a crucial role in controlling thermogenesis and may be targeted to combat obesity and associated disorders.
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MESH Headings
- Adaptor Proteins, Signal Transducing/genetics
- Adaptor Proteins, Signal Transducing/metabolism
- Adipogenesis
- Adipose Tissue, Brown/cytology
- Adipose Tissue, Brown/immunology
- Adipose Tissue, Brown/metabolism
- Adipose Tissue, Brown/pathology
- Adipose Tissue, White/cytology
- Adipose Tissue, White/immunology
- Adipose Tissue, White/metabolism
- Adipose Tissue, White/pathology
- Adiposity
- Animals
- Behavior, Animal
- Cell Size
- Disease Resistance
- Energy Intake
- Energy Metabolism
- Gene Expression Regulation
- Heterozygote
- Insulin Resistance
- Ion Channels/biosynthesis
- Macrophages/immunology
- Male
- Mice, Inbred C57BL
- Mice, Knockout
- Mitochondrial Proteins/biosynthesis
- Motor Activity
- Obesity/immunology
- Obesity/metabolism
- Obesity/pathology
- RNA-Binding Proteins/genetics
- RNA-Binding Proteins/metabolism
- Thermogenesis
- Uncoupling Protein 1
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Affiliation(s)
- Junlan Zhou
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | - Min Cheng
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | - Chan Boriboun
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | - Mariam M Ardehali
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | - Changfei Jiang
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | - Qinghua Liu
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | - Shuling Han
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | - David A Goukassian
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | - Yao-Liang Tang
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | - Ting C Zhao
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | - Ming Zhao
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | - Lu Cai
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | - Stéphane Richard
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | - Raj Kishore
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
| | - Gangjian Qin
- Department of Medicine-Cardiology Feinberg Cardiovascular Research Institute, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Tarry 14-721, Chicago, Illinois 60611, USA Department of Cardiology Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei, China Department of Biochemistry University of Ottawa, Ottawa, Ontario, Canada Institute for Medical Biology and Hubei Provincial Key Laboratory for Protection and Application of Special Plants in Wuling Area of China College of Life Sciences, South-Central University for Nationalities, Wuhan, Hubei, China GeneSys Research Institute CardioVascular Research Center, Tufts University School of Medicine, Boston, Massachusetts, USA Department of Medicine Medical College of Georgia, Vascular Biology Center, Georgia Regents University, Augusta, Georgia, USA Department of Surgery Roger Williams Medical Center, Boston University Medical School, Providence, Rhode Island, USA Kosair Children Hospital Research Institute Departments of Pediatrics, Radiation Oncology, Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA Lady Davis Institute for Medical Research McGill University, Montreal, Quebec, Canada Center for Translational Medicine Temple University School of Medicine, Philadelphia, Pennsylvania, USA
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62
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Frege T, Uversky VN. Intrinsically disordered proteins in the nucleus of human cells. Biochem Biophys Rep 2015; 1:33-51. [PMID: 29124132 PMCID: PMC5668563 DOI: 10.1016/j.bbrep.2015.03.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2015] [Accepted: 03/11/2015] [Indexed: 12/16/2022] Open
Abstract
Intrinsically disordered proteins are known to perform a variety of important functions such as macromolecular recognition, promiscuous binding, and signaling. They are crucial players in various cellular pathway and processes, where they often have key regulatory roles. Among vital cellular processes intimately linked to the intrinsically disordered proteins is transcription, an intricate biological performance predominantly developing inside the cell nucleus. With this work, we gathered information about proteins that exist in various compartments and sub-nuclear bodies of the nucleus of the human cells, with the goal of identifying which ones are highly disordered and which functions are ascribed to the disordered nuclear proteins.
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Affiliation(s)
- Telma Frege
- Department of Molecular Medicine, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA
- GenomeNext LLC, 175 South 3rd Street, Suite 200, Columbus OH 43215, USA
| | - Vladimir N. Uversky
- Department of Molecular Medicine, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA
- USF Health Byrd Alzheimer׳s Research Institute, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA
- Department of Biology, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia
- Institute for Biological Instrumentation, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia
- Laboratory of Structural Dynamics, Stability and Folding of Proteins, Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russia
- Correspondence to: Department of Molecular, Medicine, Morsani College of Medicine, University of South Florida, 12901 Bruce B. Downs Boulevard, MDC07, Tampa, FL 33612, USA. Tel.: +1 813 974 5816; fax: +1 813 974 7357.
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63
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Bielli P, Busà R, Di Stasi SM, Munoz MJ, Botti F, Kornblihtt AR, Sette C. The transcription factor FBI-1 inhibits SAM68-mediated BCL-X alternative splicing and apoptosis. EMBO Rep 2014; 15:419-27. [PMID: 24514149 PMCID: PMC3989673 DOI: 10.1002/embr.201338241] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 12/12/2013] [Accepted: 12/12/2013] [Indexed: 01/28/2023] Open
Abstract
Alternative splicing (AS) is tightly coupled to transcription for the majority of human genes. However, how these two processes are linked is not well understood. Here, we unveil a direct role for the transcription factor FBI-1 in the regulation of AS. FBI-1 interacts with the splicing factor SAM68 and reduces its binding to BCL-X mRNA. This, in turn, results in the selection of the proximal 5' splice site in BCL-X exon 2, thereby favoring the anti-apoptotic BCL-XL variant and counteracting SAM68-mediated apoptosis. Conversely, depletion of FBI-1, or expression of a SAM68 mutant lacking the FBI-1 binding region, restores the ability of SAM68 to induce BCL-XS splicing and apoptosis. FBI-1's role in splicing requires the activity of histone deacetylases, whose pharmacological inhibition recapitulates the effects of FBI-1 knockdown. Our study reveals an unexpected function for FBI-1 in splicing modulation with a direct impact on cell survival.
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Affiliation(s)
- Pamela Bielli
- Department of Biomedicine and Prevention, University of Rome Tor VergataRome, Italy
- Laboratory of Neuroembryology, Fondazione Santa LuciaRome, Italy
| | - Roberta Busà
- Department of Biomedicine and Prevention, University of Rome Tor VergataRome, Italy
- Laboratory of Neuroembryology, Fondazione Santa LuciaRome, Italy
| | - Savino M Di Stasi
- Department of Experimental Medicine and Surgery, University of Rome Tor VergataRome, Italy
| | - Manuel J Munoz
- Laboratorio de Fisiologia y Biologia Molecular, Universidad de Buenos AiresBuenos Aires, Argentina
| | - Flavia Botti
- Department of Biomedicine and Prevention, University of Rome Tor VergataRome, Italy
| | - Alberto R Kornblihtt
- Laboratorio de Fisiologia y Biologia Molecular, Universidad de Buenos AiresBuenos Aires, Argentina
| | - Claudio Sette
- Department of Biomedicine and Prevention, University of Rome Tor VergataRome, Italy
- Laboratory of Neuroembryology, Fondazione Santa LuciaRome, Italy
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64
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High Sam68 expression predicts poor prognosis in non-small cell lung cancer. Clin Transl Oncol 2014; 16:886-91. [PMID: 24522888 DOI: 10.1007/s12094-014-1160-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2013] [Accepted: 01/28/2014] [Indexed: 12/31/2022]
Abstract
BACKGROUND The nuclear protein Sam68 has been implicated in the oncogenesis and tumor growth. The aim of this study was to explore the clinical value of Sam68 in patients with non-small cell lung cancer (NSCLC). METHODS We examined Sam68 expression in 50 NSCLC tissues and matched adjacent noncancerous tissues by quantitative RT-PCR (qRT-PCR) and Western blotting. Furthermore, the Sam68 protein expression was analyzed by immunohistochemistry in 208 NSCLC samples. Kaplan-Meier method and multivariate Cox regression model were used to evaluate the prognostic value of nuclear Sam68 expression in NSCLC for disease survival. RESULTS The expression of Sam68 was significantly elevated in NSCLC tissues as compared with adjacent non-cancerous tissues (P < 0.01). The high expression of Sam68 in NSCLC was significantly correlated with lymph node metastasis and tumor TNM stage. Kaplan-Meier survival analysis revealed that high expression of Sam68 correlated with poor prognosis of NSCLC patients (P < 0.01). Multivariate analysis showed that Sam68 expression was an independent prognostic marker for overall survival of NSCLC patients (HR 2.73, 95 % CI 1.549-4.315, P = 0.002). CONCLUSION Our results suggest that high Sam68 expression predicts poor prognosis of NSCLC patients, and Sam68 may be potentially a prognostic biomarker for NSCLC.
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Miah S, Goel RK, Dai C, Kalra N, Beaton-Brown E, Bagu ET, Bonham K, Lukong KE. BRK targets Dok1 for ubiquitin-mediated proteasomal degradation to promote cell proliferation and migration. PLoS One 2014; 9:e87684. [PMID: 24523872 PMCID: PMC3921129 DOI: 10.1371/journal.pone.0087684] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Accepted: 01/02/2014] [Indexed: 12/13/2022] Open
Abstract
Breast tumor kinase (BRK), also known as protein tyrosine kinase 6 (PTK6), is a non-receptor tyrosine kinase overexpressed in more that 60% of human breast carcinomas. The overexpression of BRK has been shown to sensitize mammary epithelial cells to mitogenic signaling and to promote cell proliferation and tumor formation. The molecular mechanisms of BRK have been unveiled by the identification and characterization of BRK target proteins. Downstream of tyrosine kinases 1 or Dok1 is a scaffolding protein and a substrate of several tyrosine kinases. Herein we show that BRK interacts with and phosphorylates Dok1 specifically on Y362. We demonstrate that this phosphorylation by BRK significantly downregulates Dok1 in a ubiquitin-proteasome-mediated mechanism. Together, these results suggest a novel mechanism of action of BRK in the promotion of tumor formation, which involves the targeting of tumor suppressor Dok1 for degradation through the ubiquitin proteasomal pathway.
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Affiliation(s)
- Sayem Miah
- Department of Biochemistry, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Raghuveera Kumar Goel
- Department of Biochemistry, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Chenlu Dai
- Department of Biochemistry, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Natasha Kalra
- Department of Biochemistry, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Erika Beaton-Brown
- Department of Biochemistry, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
- Cancer Research Unit, Health Research Division, Saskatchewan Cancer Agency, and Division of Oncology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Edward T. Bagu
- Department of Biochemistry, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
- Cancer Research Unit, Health Research Division, Saskatchewan Cancer Agency, and Division of Oncology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Keith Bonham
- Department of Biochemistry, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
- Cancer Research Unit, Health Research Division, Saskatchewan Cancer Agency, and Division of Oncology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Kiven E. Lukong
- Department of Biochemistry, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
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Fu K, Sun X, Zheng W, Wier EM, Hodgson A, Tran DQ, Richard S, Wan F. Sam68 modulates the promoter specificity of NF-κB and mediates expression of CD25 in activated T cells. Nat Commun 2013; 4:1909. [PMID: 23715268 PMCID: PMC3684077 DOI: 10.1038/ncomms2916] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2012] [Accepted: 04/19/2013] [Indexed: 12/23/2022] Open
Abstract
CD25, the alpha chain of the interleukin-2 receptor, is expressed in activated T cells and has a significant role in autoimmune disease and tumorigenesis; however, the mechanisms regulating transcription of CD25 remain elusive. Here we identify the Src-associated substrate during mitosis of 68 kDa (Sam68) as a novel non-Rel component in the nuclear factor-kappaB (NF-κB) complex that confers CD25 transcription. Our results demonstrate that Sam68 has an essential role in the induction and maintenance of CD25 in T cells. T-cell receptor engagement triggers translocation of the inhibitor of NF-κB kinase alpha (IKKα) from the cytoplasm to the nucleus, where it phosphorylates Sam68, causing complex formation with NF-κB in the nucleus. These findings reveal the important roles of KH domain-containing components and their spatial interactions with IKKs in determining the binding targets of NF-κB complexes, thus shedding novel insights into the regulatory specificity of NF-κB.
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Affiliation(s)
- Kai Fu
- Department of Biochemistry and Molecular Biology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland 21025, USA
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Sánchez-Jiménez F, Sánchez-Margalet V. Role of Sam68 in post-transcriptional gene regulation. Int J Mol Sci 2013; 14:23402-19. [PMID: 24287914 PMCID: PMC3876053 DOI: 10.3390/ijms141223402] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2013] [Revised: 11/11/2013] [Accepted: 11/13/2013] [Indexed: 01/10/2023] Open
Abstract
The STAR family of proteins links signaling pathways to various aspects of post-transcriptional regulation and processing of RNAs. Sam68 belongs to this class of heteronuclear ribonucleoprotein particle K (hnRNP K) homology (KH) single domain-containing family of RNA-binding proteins that also contains some domains predicted to bind critical components in signal transduction pathways. In response to phosphorylation and other post-transcriptional modifications, Sam68 has been shown to have the ability to link signal transduction pathways to downstream effects regulating RNA metabolism, including transcription, alternative splicing or RNA transport. In addition to its function as a docking protein in some signaling pathways, this prototypic STAR protein has been identified to have a nuclear localization and to take part in the formation of both nuclear and cytosolic multi-molecular complexes such as Sam68 nuclear bodies and stress granules. Coupling with other proteins and RNA targets, Sam68 may play a role in the regulation of differential expression and mRNA processing and translation according to internal and external signals, thus mediating important physiological functions, such as cell death, proliferation or cell differentiation.
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Affiliation(s)
- Flora Sánchez-Jiménez
- Department of Medical Biochemistry and Molecular Biology and Immunology, UGC Clinical Biochemistry, Virgen Macarena University Hospital, Avenue. Sánchez Pizjuan 4, Medical School, University of Seville, Seville 41009, Spain.
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68
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Bonomi S, Gallo S, Catillo M, Pignataro D, Biamonti G, Ghigna C. Oncogenic alternative splicing switches: role in cancer progression and prospects for therapy. Int J Cell Biol 2013; 2013:962038. [PMID: 24285959 PMCID: PMC3826442 DOI: 10.1155/2013/962038] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2013] [Accepted: 08/12/2013] [Indexed: 01/30/2023] Open
Abstract
Alterations in the abundance or activities of alternative splicing regulators generate alternatively spliced variants that contribute to multiple aspects of tumor establishment, progression and resistance to therapeutic treatments. Notably, many cancer-associated genes are regulated through alternative splicing suggesting a significant role of this post-transcriptional regulatory mechanism in the production of oncogenes and tumor suppressors. Thus, the study of alternative splicing in cancer might provide a better understanding of the malignant transformation and identify novel pathways that are uniquely relevant to tumorigenesis. Understanding the molecular underpinnings of cancer-associated alternative splicing isoforms will not only help to explain many fundamental hallmarks of cancer, but will also offer unprecedented opportunities to improve the efficacy of anti-cancer treatments.
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Affiliation(s)
- Serena Bonomi
- Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche (IGM-CNR), Via Abbiategrasso 207, 27100 Pavia, Italy
| | - Stefania Gallo
- Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche (IGM-CNR), Via Abbiategrasso 207, 27100 Pavia, Italy
| | - Morena Catillo
- Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche (IGM-CNR), Via Abbiategrasso 207, 27100 Pavia, Italy
| | - Daniela Pignataro
- Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche (IGM-CNR), Via Abbiategrasso 207, 27100 Pavia, Italy
| | - Giuseppe Biamonti
- Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche (IGM-CNR), Via Abbiategrasso 207, 27100 Pavia, Italy
| | - Claudia Ghigna
- Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche (IGM-CNR), Via Abbiategrasso 207, 27100 Pavia, Italy
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Liao WT, Liu JL, Wang ZG, Cui YM, Shi L, Li TT, Zhao XH, Chen XT, Ding YQ, Song LB. High expression level and nuclear localization of Sam68 are associated with progression and poor prognosis in colorectal cancer. BMC Gastroenterol 2013; 13:126. [PMID: 23937454 PMCID: PMC3751151 DOI: 10.1186/1471-230x-13-126] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/25/2012] [Accepted: 08/02/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Src-associated in mitosis (Sam68; 68 kDa) has been implicated in the oncogenesis and progression of several human cancers. The aim of this study was to investigate the clinicopathologic significance of Sam68 expression and its subcellular localization in colorectal cancer (CRC). METHODS Sam68 expression was examined in CRC cell lines, nine matched CRC tissues and adjacent noncancerous tissues using reverse transcription (RT)-PCR, quantitative RT-PCR and Western blotting. Sam68 protein expression and localization were determined in 224 paraffin-embedded archived CRC samples using immunohistochemistry. Statistical analyses were applied to evaluate the clinicopathologic significance. RESULTS Sam68 was upregulated in CRC cell lines and CRC, as compared with normal tissues; high Sam68 expression was detected in 120/224 (53.6%) of the CRC tissues. High Sam68 expression correlated significantly with poor differentiation (P = 0.033), advanced T stage (P < 0.001), N stage (P = 0.023) and distant metastasis (P = 0.033). Sam68 nuclear localization correlated significantly with poor differentiation (P = 0.002) and T stage (P =0.021). Patients with high Sam68 expression or Sam68 nuclear localization had poorer overall survival than patients with low Sam68 expression or Sam68 cytoplasmic localization. Patients with high Sam68 expression had a higher risk of recurrence than those with low Sam68 expression. CONCLUSIONS Overexpression of Sam68 correlated highly with cancer progression and poor differentiation in CRC. High Sam68 expression and Sam68 nuclear localization were associated with poorer overall survival.
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Fitzgerald KD, Semler BL. Poliovirus infection induces the co-localization of cellular protein SRp20 with TIA-1, a cytoplasmic stress granule protein. Virus Res 2013; 176:223-31. [PMID: 23830997 PMCID: PMC3742715 DOI: 10.1016/j.virusres.2013.06.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2013] [Revised: 06/21/2013] [Accepted: 06/21/2013] [Indexed: 12/18/2022]
Abstract
Different types of environmental stress cause mammalian cells to form cytoplasmic foci, termed stress granules, which contain mRNPs that are translationally silenced. These foci are transient and dynamic, and contain components of the cellular translation machinery as well as certain mRNAs and RNA binding proteins. Stress granules are known to be induced by conditions such as hypoxia, nutrient deprivation, and oxidative stress, and a number of cellular factors have been identified that are commonly associated with these foci. More recently it was discovered that poliovirus infection also induces the formation of stress granules, although these cytoplasmic foci appear to be somewhat compositionally unique. Work described here examined the punctate pattern of SRp20 (a host cell mRNA splicing protein) localization in the cytoplasm of poliovirus-infected cells, demonstrating the partial co-localization of SRp20 with the stress granule marker protein TIA-1. We determined that SRp20 does not co-localize with TIA-1, however, under conditions of oxidative stress, indicating that the close association of these two proteins during poliovirus infection is not representative of a general response to cellular stress. We confirmed that the expression of a dominant negative version of TIA-1 (TIA-1-PRD) results in the dissociation of stress granules. Finally, we demonstrated that expression of wild type TIA-1 or dominant negative TIA-1-PRD in cells during poliovirus infection does not dramatically affect viral translation. Taken together, these studies provide a new example of the unique cytoplasmic foci that form during poliovirus infection.
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Affiliation(s)
| | - Bert L. Semler
- Corresponding author. Tel.: +1 949 824 7573; fax: +1 949 824 2694.
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71
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Aparicio LA, Abella V, Valladares M, Figueroa A. Posttranscriptional regulation by RNA-binding proteins during epithelial-to-mesenchymal transition. Cell Mol Life Sci 2013; 70:4463-77. [PMID: 23715860 PMCID: PMC3827902 DOI: 10.1007/s00018-013-1379-0] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2013] [Revised: 05/10/2013] [Accepted: 05/16/2013] [Indexed: 12/22/2022]
Abstract
Epithelial-to-mesenchymal transition (EMT), one of the crucial steps for carcinoma cells to acquire invasive capacity, results from the disruption of cell–cell contacts and the acquisition of a motile mesenchymal phenotype. Although the transcriptional events controlling EMT have been extensively studied, in recent years, several posttranscriptional mechanisms have emerged as critical in the regulation of EMT during tumor progression. In this review, we highlight the regulation of posttranscriptional events in EMT by RNA-binding proteins (RBPs). RBPs are responsible for controlling pre-mRNA splicing, capping, and polyadenylation, as well as mRNA export, turnover, localization, and translation. We discuss the most relevant aspects of RBPs controlling the metabolism of EMT-related mRNAs, and describe the implication of novel posttranscriptional mechanisms regulating EMT in response to different signaling pathways. Novel insight into posttranscriptional regulation of EMT by RBPs is uncovering new therapeutic targets in cancer invasion and metastasis.
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Affiliation(s)
- Luis A Aparicio
- Servizo de Oncología Médica, Complejo Hospitalario Universitario A Coruña (CHUAC), SERGAS, A Coruña, Spain
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72
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Martinez NM, Lynch KW. Control of alternative splicing in immune responses: many regulators, many predictions, much still to learn. Immunol Rev 2013; 253:216-36. [PMID: 23550649 PMCID: PMC3621013 DOI: 10.1111/imr.12047] [Citation(s) in RCA: 131] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Most mammalian pre-mRNAs are alternatively spliced in a manner that alters the resulting open reading frame. Consequently, alternative pre-mRNA splicing provides an important RNA-based layer of protein regulation and cellular function. The ubiquitous nature of alternative splicing coupled with the advent of technologies that allow global interrogation of the transcriptome have led to an increasing awareness of the possibility that widespread changes in splicing patterns contribute to lymphocyte function during an immune response. Indeed, a few notable examples of alternative splicing have clearly been demonstrated to regulate T-cell responses to antigen. Moreover, several proteins key to the regulation of splicing in T cells have recently been identified. However, much remains to be done to truly identify the spectrum of genes that are regulated at the level of splicing in immune cells and to determine how many of these are controlled by currently known factors and pathways versus unknown mechanisms. Here, we describe the proteins, pathways, and mechanisms that have been shown to regulate alternative splicing in human T cells and discuss what is and is not known about the genes regulated by such factors. Finally, we highlight unifying themes with regards to the mechanisms and consequences of alternative splicing in the adaptive immune system and give our view of important directions for future studies.
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Affiliation(s)
- Nicole M Martinez
- Department of Biochemistry and Biophysics, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104-6059, USA
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73
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Ehrmann I, Dalgliesh C, Liu Y, Danilenko M, Crosier M, Overman L, Arthur HM, Lindsay S, Clowry GJ, Venables JP, Fort P, Elliott DJ. The tissue-specific RNA binding protein T-STAR controls regional splicing patterns of neurexin pre-mRNAs in the brain. PLoS Genet 2013; 9:e1003474. [PMID: 23637638 PMCID: PMC3636136 DOI: 10.1371/journal.pgen.1003474] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Accepted: 03/07/2013] [Indexed: 11/18/2022] Open
Abstract
The RNA binding protein T-STAR was created following a gene triplication 520-610 million years ago, which also produced its two parologs Sam68 and SLM-1. Here we have created a T-STAR null mouse to identify the endogenous functions of this RNA binding protein. Mice null for T-STAR developed normally and were fertile, surprisingly, given the high expression of T-STAR in the testis and the brain, and the known infertility and pleiotropic defects of Sam68 null mice. Using a transcriptome-wide search for splicing targets in the adult brain, we identified T-STAR protein as a potent splicing repressor of the alternatively spliced segment 4 (AS4) exons from each of the Neurexin1-3 genes, and exon 23 of the Stxbp5l gene. T-STAR protein was most highly concentrated in forebrain-derived structures like the hippocampus, which also showed maximal Neurexin1-3 AS4 splicing repression. In the absence of endogenous T-STAR protein, Nrxn1-3 AS4 splicing repression dramatically decreased, despite physiological co-expression of Sam68. In transfected cells Neurexin3 AS4 alternative splicing was regulated by either T-STAR or Sam68 proteins. In contrast, Neurexin2 AS4 splicing was only regulated by T-STAR, through a UWAA-rich response element immediately downstream of the regulated exon conserved since the radiation of bony vertebrates. The AS4 exons in the Nrxn1 and Nrxn3 genes were also associated with distinct patterns of conserved UWAA repeats. Consistent with an ancient mechanism of splicing control, human T-STAR protein was able to repress splicing inclusion of the zebrafish Nrxn3 AS4 exon. Although Neurexin1-3 and Stxbp5l encode critical synaptic proteins, T-STAR null mice had no detectable spatial memory deficits, despite an almost complete absence of AS4 splicing repression in the hippocampus. Our work identifies T-STAR as an ancient and potent tissue-specific splicing regulator that uses a concentration-dependent mechanism to co-ordinately regulate regional splicing patterns of the Neurexin1-3 AS4 exons in the mouse brain.
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Affiliation(s)
- Ingrid Ehrmann
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Caroline Dalgliesh
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Yilei Liu
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Marina Danilenko
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Moira Crosier
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Lynn Overman
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Helen M. Arthur
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Susan Lindsay
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Gavin J. Clowry
- Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Julian P. Venables
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Philippe Fort
- Universités Montpellier 2 et 1, UMR 5237, Centre de Recherche de Biochimie Macromoléculaire, CNRS, Montpellier, France
| | - David J. Elliott
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
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74
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Ali M, Broadhurst RW. Solution structure of the QUA1 dimerization domain of pXqua, the Xenopus ortholog of Quaking. PLoS One 2013; 8:e57345. [PMID: 23520467 PMCID: PMC3592866 DOI: 10.1371/journal.pone.0057345] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2012] [Accepted: 01/21/2013] [Indexed: 11/19/2022] Open
Abstract
The STAR protein family member Quaking is essential for early development in vertebrates. For example, in oligodendrocyte cells it regulates the splicing, localization, translation and lifetime of a set of mRNAs that code for crucial components of myelin. The Quaking protein contains three contiguous conserved regions: a QUA1 oligomerization element, followed by a single-stranded RNA binding motif comprising the KH and QUA2 domains. An embryonic lethal point mutation in the QUA1 domain, E48G, is known to affect both the aggregation state and RNA-binding properties of the murine Quaking ortholog (QKI). Here we report the NMR solution structure of the QUA1 domain from the Xenopus laevis Quaking ortholog (pXqua), which forms a dimer composed of two perpendicularly docked α-helical hairpin motifs. Size exclusion chromatography studies of a range of mutants demonstrate that the dimeric state of the pXqua QUA1 domain is stabilized by a network of interactions between side-chains, with significant roles played by an intra-molecular hydrogen bond between Y41 and E72 (the counterpart to QKI E48) and an inter-protomer salt bridge between E72 and R67. These results are compared with recent structural and mutagenesis studies of QUA1 domains from the STAR family members QKI, GLD-1 and Sam68.
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Affiliation(s)
- Muzaffar Ali
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - R. William Broadhurst
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
- * E-mail:
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75
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RNA-binding protein Sam68 controls synapse number and local β-actin mRNA metabolism in dendrites. Proc Natl Acad Sci U S A 2013; 110:3125-30. [PMID: 23382180 DOI: 10.1073/pnas.1209811110] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Proper synaptic function requires the spatial and temporal compartmentalization of RNA metabolism via transacting RNA-binding proteins (RBPs). Loss of RBP activity leads to abnormal posttranscriptional regulation and results in diverse neurological disorders with underlying deficits in synaptic morphology and transmission. Functional loss of the 68-kDa RBP Src associated in mitosis (Sam68) is associated with the pathogenesis of the neurological disorder fragile X tremor/ataxia syndrome. Sam68 binds to the mRNA of β-actin (actb), an integral cytoskeletal component of dendritic spines. We show that Sam68 knockdown or disruption of the binding between Sam68 and its actb mRNA cargo in primary hippocampal cultures decreases the amount of actb mRNA in the synaptodendritic compartment and results in fewer dendritic spines. Consistent with these observations, we find that Sam68-KO mice have reduced levels of actb mRNA associated with synaptic polysomes and diminished levels of synaptic actb protein, suggesting that Sam68 promotes the translation of actb mRNA at synapses in vivo. Moreover, genetic knockout of Sam68 or acute knockdown in vivo results in fewer excitatory synapses in the hippocampal formation as assessed morphologically and functionally. Therefore, we propose that Sam68 regulates synapse number in a cell-autonomous manner through control of postsynaptic actb mRNA metabolism. Our research identifies a role for Sam68 in synaptodendritic posttranscriptional regulation of actb and may provide insight into the pathophysiology of fragile X tremor/ataxia syndrome.
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76
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Nakamura RL, Landt SG, Mai E, Nejim J, Chen L, Frankel AD. A cell-based method for screening RNA-protein interactions: identification of constitutive transport element-interacting proteins. PLoS One 2012; 7:e48194. [PMID: 23133567 PMCID: PMC3485056 DOI: 10.1371/journal.pone.0048194] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2012] [Accepted: 09/24/2012] [Indexed: 12/21/2022] Open
Abstract
We have developed a mammalian cell-based screening platform to identify proteins that assemble into RNA-protein complexes. Based on Tat-mediated activation of the HIV LTR, proteins that interact with an RNA target elicit expression of a GFP reporter and are captured by fluorescence activated cell sorting. This "Tat-hybrid" screening platform was used to identify proteins that interact with the Mason Pfizer monkey virus (MPMV) constitutive transport element (CTE), a structured RNA hairpin that mediates the transport of unspliced viral mRNAs from the nucleus to the cytoplasm. Several hnRNP-like proteins, including hnRNP A1, were identified and shown to interact with the CTE with selectivity in the reporter system comparable to Tap, a known CTE-binding protein. In vitro gel shift and pull-down assays showed that hnRNP A1 is able to form a complex with the CTE and Tap and that the RGG domain of hnRNP A1 mediates binding to Tap. These results suggest that hnRNP-like proteins may be part of larger export-competent RNA-protein complexes and that the RGG domains of these proteins play an important role in directing these binding events. The results also demonstrate the utility of the screening platform for identifying and characterizing new components of RNA-protein complexes.
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Affiliation(s)
- Robert L. Nakamura
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
| | - Stephen G. Landt
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
| | - Emily Mai
- Department of Biology, San Francisco State University, San Francisco, California, United States of America
| | - Jemiel Nejim
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
| | - Lily Chen
- Department of Biology, San Francisco State University, San Francisco, California, United States of America
| | - Alan D. Frankel
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
- * E-mail:
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77
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Abstract
Alternative splicing is well known to be tissue-specific. Although several genes have been shown to undergo alternative splicing in adipocytes, little is known about the mechanism that regulates alternative splicing during adipogenesis. We recently reported that Sam68−/− mice exhibit a lean phenotype and are protected against diet-induced obesity. Our genome-wide exon array analysis in white adipose tissue (WAT) from wild-type and Sam68−/− mice revealed that Sam68 deficiency leads to an abnormal splicing of the mTOR gene. This has been shown to reduce the overall mTOR protein content and activity during in vitro adipose differentiation. In Sam68−/− mice, this situation leads to an increased energy expenditure, decreased adipogenesis and WAT formation.
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78
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Vogel G, Richard S. Emerging roles for Sam68 in adipogenesis and neuronal development. RNA Biol 2012; 9:1129-33. [PMID: 23018781 DOI: 10.4161/rna.21409] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Sam68, the Src-associated substrate during mitosis of 68 kDa, belongs to the large class of heteronuclear ribonucleoprotein particle K (hnRNP K) homology (KH) domain family of RNA-binding proteins. Sam68 contains a single KH domain harboring conserved N- and C-terminal sequences required for RNA binding and homodimerization. The KH domain is one of the most prevalent RNA binding domains that directly contacts single-stranded RNA. Sam68 has been implicated in numerous aspects of RNA metabolism including alternative splicing and polysomal recruitment of mRNAs. Studies in mice have revealed physiological roles linking Sam68 to osteoporosis, obesity, cancer, infertility and ataxia. Recent publications have greatly enhanced our understanding of Sam68 mechanism of action in addition to its cellular role. Herein, we will discuss the latest advances in the literature pertaining to obesity and neuronal development.
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Affiliation(s)
- Gillian Vogel
- Bloomfield Center for Research on Aging, Lady Davis Institute for Medical Research and Departments of Oncology and Medicine, McGill University, Montréal, QC Canada
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79
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Asbach B, Ludwig C, Saksela K, Wagner R. Comprehensive analysis of interactions between the Src-associated protein in mitosis of 68 kDa and the human Src-homology 3 proteome. PLoS One 2012; 7:e38540. [PMID: 22745667 PMCID: PMC3379994 DOI: 10.1371/journal.pone.0038540] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Accepted: 05/07/2012] [Indexed: 11/19/2022] Open
Abstract
The protein Sam68 is involved in many cellular processes such as cell-cycle regulation, RNA metabolism, or signal transduction. Sam68 comprises a central RNA-binding domain flanked by unstructured tails containing docking sites for signalling proteins including seven proline-rich sequences (denoted P0 to P6) as potential SH3-domain binding motifs. To comprehensively assess Sam68-SH3-interactions, we applied a phage-display screening of a library containing all approx. 300 human SH3 domains. Thereby we identified five new (from intersectin 2, the osteoclast stimulating factor OSF, nephrocystin, sorting nexin 9, and CIN85) and seven already known high-confidence Sam68-ligands (mainly from the Src-kinase family), as well as several lower-affinity binders. Interaction of the high-affinity Sam68-binders was confirmed in independent assays in vitro (phage-ELISA, GST-pull-down) and in vivo (FACS-based FRET-analysis with CFP- and YFP-tagged proteins). Fine-mapping analyses with peptides established P0, P3, P4, and P5 as exclusive docking-sites for SH3 domains, which showed varying preferences for these motifs. Mutational analyses identified individual residues within the proline-rich motifs being crucial for the interactions. Based on these data, we generated a Sam68-mutant incapable of interacting with SH3 domains any more, as subsequently demonstrated by FRET-analyses. In conclusion, we present a thorough characterization of Sam68's interplay with the SH3 proteome. The observed interaction between Sam68 and OSF complements the known Sam68-Src and OSF-Src interactions. Thus, we propose, that Sam68 functions as a classical scaffold protein in this context, assembling components of an osteoclast-specific signalling pathway.
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Affiliation(s)
- Benedikt Asbach
- Institute of Medical Microbiology and Hygiene, University of Regensburg, Regensburg, Germany
| | - Christine Ludwig
- Institute of Medical Microbiology and Hygiene, University of Regensburg, Regensburg, Germany
| | - Kalle Saksela
- Department of Virology, Haartman Institute, University of Helsinki, Helsinki, Finland
| | - Ralf Wagner
- Institute of Medical Microbiology and Hygiene, University of Regensburg, Regensburg, Germany
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Abstract
Interference with stress granule (SG) accumulation is gaining increased appreciation as a common strategy used by diverse viruses to facilitate their replication and to cope with translational arrest. Here, we examined the impact of infection by herpes simplex virus 2 (HSV-2) on SG accumulation by monitoring the localization of the SG components T cell internal antigen 1 (TIA-1), Ras-GTPase-activating SH3-domain-binding protein (G3BP), and poly(A)-binding protein (PABP). Our results indicate that SGs do not accumulate in HSV-2-infected cells and that HSV-2 can interfere with arsenite-induced SG accumulation early after infection. Surprisingly, SG accumulation was inhibited despite increased phosphorylation of eukaryotic translation initiation factor 2α (eIF2α), implying that HSV-2 encodes previously unrecognized activities designed to maintain translation initiation downstream of eIF2α. SG accumulation was not inhibited in HSV-2-infected cells treated with pateamine A, an inducer that works independently of eIF2α phosphorylation. The SGs that accumulated following pateamine A treatment of infected cells contained G3BP and PABP but were largely devoid of TIA-1. We also identified novel nuclear structures containing TIA-1 that form late in infection. These structures contain the RNA binding protein 68-kDa Src-associated in mitosis (Sam68) and were noticeably absent in infected cells treated with inhibitors of viral DNA replication, suggesting that they arise as a result of late events in the virus replicative cycle.
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81
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Versatility of RNA-Binding Proteins in Cancer. Comp Funct Genomics 2012; 2012:178525. [PMID: 22666083 PMCID: PMC3359819 DOI: 10.1155/2012/178525] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Accepted: 02/28/2012] [Indexed: 01/22/2023] Open
Abstract
Posttranscriptional gene regulation is a rapid and efficient process to adjust the proteome of a cell to a changing environment. RNA-binding proteins (RBPs) are the master regulators of mRNA processing and translation and are often aberrantly expressed in cancer. In addition to well-studied transcription factors, RBPs are emerging as fundamental players in tumor development. RBPs and their mRNA targets form a complex network that plays a crucial role in tumorigenesis. This paper describes mechanisms by which RBPs influence the expression of well-known oncogenes, focusing on precise examples that illustrate the versatility of RBPs in posttranscriptional control of cancer development. RBPs appeared very early in evolution, and new RNA-binding domains and combinations of them were generated in more complex organisms. The identification of RBPs, their mRNA targets, and their mechanism of action have provided novel potential targets for cancer therapy.
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82
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Miah S, Martin A, Lukong KE. Constitutive activation of breast tumor kinase accelerates cell migration and tumor growth in vivo. Oncogenesis 2012; 1:e11. [PMID: 23552639 PMCID: PMC3412638 DOI: 10.1038/oncsis.2012.11] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Breast tumor kinase (BRK) is a non-receptor tyrosine kinase overexpressed in most human breast tumors, including lymph node metastases, but undetected in normal mammary tissue or in fibroadenomas. The activity of BRK-like Src family tyrosine kinase, is regulated negatively by phosphorylation of C-terminal tyrosine 447. Although the kinase that regulates BRK activation has not been identified, we and others have previously shown that BRK-Y447F is a constitutively active variant. Because BRK-Y447F significantly enhances the catalytic activity of the enzyme, we investigated the role of the constitutively active BRK variant in tumor formation and metastasis. Using stable breast cancer cell MDA-MB-231 we observed significantly enhanced rates of cell proliferation, migration and tumor formation in BRK-Y447F stable cells compared with wild-type stable cell lines. Our results indicate full activation of BRK is an essential component in the tumorigenic role of BRK.
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Affiliation(s)
- S Miah
- Department of Biochemistry, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
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83
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Wang J, Xu M, Zhu K, Li L, Liu X. The N-terminus of FILIA forms an atypical KH domain with a unique extension involved in interaction with RNA. PLoS One 2012; 7:e30209. [PMID: 22276159 PMCID: PMC3261892 DOI: 10.1371/journal.pone.0030209] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2011] [Accepted: 12/12/2011] [Indexed: 01/07/2023] Open
Abstract
FILIA is a member of the recently identified oocyte/embryo expressed gene family in eutherian mammals, which is characterized by containing an N-terminal atypical KH domain. Here we report the structure of the N-terminal fragment of FILIA (FILIA-N), which represents the first reported three-dimensional structure of a KH domain in the oocyte/embryo expressed gene family of proteins. The structure of FILIA-N revealed a unique N-terminal extension beyond the canonical KH region, which plays important roles in interaction with RNA. By co-incubation with the lysates of mice ovaries, FILIA and FILIA-N could sequester specific RNA components, supporting the critical roles of FILIA in regulation of RNA transcripts during mouse oogenesis and early embryogenesis.
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Affiliation(s)
- Juke Wang
- State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Nankai University, Tianjin, China
| | - Mengyuan Xu
- State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Nankai University, Tianjin, China
| | - Kai Zhu
- State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
| | - Lei Li
- State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
- * E-mail: (LL); (XL)
| | - Xinqi Liu
- State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Nankai University, Tianjin, China
- * E-mail: (LL); (XL)
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84
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Independent recruitments of a translational regulator in the evolution of self-fertile nematodes. Proc Natl Acad Sci U S A 2011; 108:19672-7. [PMID: 22106259 DOI: 10.1073/pnas.1108068108] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Pleiotropic developmental regulators have been repeatedly linked to the evolution of anatomical novelties. Known mechanisms include cis-regulatory DNA changes that alter regulator transcription patterns or modify target-gene linkages. Here, we examine the role of another form of regulation, translational control, in the repeated evolution of self-fertile hermaphroditism in Caenorhabditis nematodes. Caenorhabditis elegans hermaphrodites initiate spermatogenesis in an otherwise female body through translational repression of the gene tra-2. This repression is mediated by GLD-1, an RNA-binding protein also required for oocyte meiosis and differentiation. By contrast, we show that in the convergently hermaphroditic Caenorhabditis briggsae, GLD-1 acts to promote oogenesis. The opposite functions of gld-1 in these species are not gene-intrinsic, but instead result from the unique contexts for its action that evolved in each. In C. elegans, GLD-1 became essential for promoting XX spermatogenesis via changes in the tra-2 mRNA and evolution of the species-specific protein FOG-2. C. briggsae GLD-1 became an essential repressor of sperm-promoting genes, including Cbr-puf-8, and did not evolve a strong association with tra-2. Despite its variable roles in sex determination, the function of gld-1 in female meiotic progression is ancient and conserved. This conserved role may explain why gld-1 is repeatedly recruited to regulate hermaphroditism. We conclude that, as with transcription factors, spatially localized translational regulators play important roles in the evolution of anatomical novelties.
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85
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Liu J, Henao-Mejia J, Liu H, Zhao Y, He JJ. Translational regulation of HIV-1 replication by HIV-1 Rev cellular cofactors Sam68, eIF5A, hRIP, and DDX3. J Neuroimmune Pharmacol 2011; 6:308-21. [PMID: 21360055 DOI: 10.1007/s11481-011-9265-8] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Accepted: 02/14/2011] [Indexed: 10/18/2022]
Abstract
Nuclear export and translation of HIV-1 RNA are two important posttranscriptional events for HIV-1 gene expression and replication. HIV-1 Rev functions to export unspliced and incompletely spliced HIV-1 RNA from the nucleus to the cytoplasm; it requires interaction with several cellular cofactors such as Sam68, eIF5A, hRIP, and DDX3. Meanwhile, some studies have also implicated Rev and some of its cofactors such as Sam68 in HIV-1 RNA translation. Thus, in this study, we aimed to characterize the potential function of all these four Rev cofactors in HIV-1 RNA translation. Ectopic expression, siRNA knockdown, and trans-complementation assays confirmed that all these cofactors were very important for HIV-1 gene expression and production through Rev and, accordingly, Rev-dependent reporter gene expression. Importantly, these studies revealed for the first time that each of these cofactors also regulated Rev-independent reporter gene expression. To directly determine the roles of these cofactors in HIV-1 RNA translation, we designed and synthesized a full-length capped HIV-1 RNA in vitro, transfected it into cells to bypass the RNA nuclear export step, and determined HIV-1 Gag expression from the cytoplasmic RNA in the cells that had ectopically expressed or siRNA knocked down cofactors. Gag expression was found to closely correlate with the expression levels of all these cofactors. Furthermore, we took advantage of a HIV-1 internal ribosomal entry site (IRES)-based bicistronic reporter gene assay and determined the effects of these cofactors on cap-independent IRES-mediated HIV-1 translation. The results showed that DDX3, eIF5A, and hRIP enhanced HIV-1 IRES-mediated translation, whereas Sam68 did not. Taken together, these results show that HIV-1 Rev cofactors Sam68, eIF5A, hRIP, and DDX3 also function in the translation of HIV-1 RNA and suggest that the regulatory mechanisms of HIV-1 RNA translation are likely different among these cofactors.
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Affiliation(s)
- Jinfeng Liu
- The First Affiliated Hospital, Xi'an Jiaotong University College of Medicine, Xi'an, Shaanxi 710061, People's Republic of China
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86
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Ramakrishnan P, Baltimore D. Sam68 is required for both NF-κB activation and apoptosis signaling by the TNF receptor. Mol Cell 2011; 43:167-79. [PMID: 21620750 DOI: 10.1016/j.molcel.2011.05.007] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2010] [Revised: 03/14/2011] [Accepted: 05/09/2011] [Indexed: 12/15/2022]
Abstract
The RNA-binding protein Sam68 is implicated in various cellular processes including RNA metabolism, apoptosis, and signal transduction. Here we identify a role of Sam68 in TNF-induced NF-κB activation and apoptosis. We found that Sam68 is recruited to the TNF receptor, and its deficiency dramatically reduces RIP recruitment and ubiquitylation. It also impairs cIAP1 recruitment and maintenance of recruited TRAF2 at the TNF receptor. In its absence, activation of the TAK1-IKK kinase complex is defective, greatly reducing signal transduction. Sam68 is also found as a part of the TNF-induced cytoplasmic caspase-8-FADD complex. RIP is not recruited to this complex in Sam68 knockout cells, and caspase activation is virtually absent. These findings delineate previously unknown functions for Sam68 in the TNF signaling pathway, where it acts as a signaling adaptor both in the membrane-associated complex I and in the cytoplasmic complex II, regulating both NF-κB activation and apoptosis.
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87
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Cheung N, So CWE. Transcriptional and epigenetic networks in haematological malignancy. FEBS Lett 2011; 585:2100-11. [DOI: 10.1016/j.febslet.2011.03.068] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Revised: 03/28/2011] [Accepted: 03/28/2011] [Indexed: 12/16/2022]
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88
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Brockmeyer C, Paster W, Pepper D, Tan CP, Trudgian DC, McGowan S, Fu G, Gascoigne NRJ, Acuto O, Salek M. T cell receptor (TCR)-induced tyrosine phosphorylation dynamics identifies THEMIS as a new TCR signalosome component. J Biol Chem 2011; 286:7535-47. [PMID: 21189249 PMCID: PMC3045008 DOI: 10.1074/jbc.m110.201236] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2010] [Revised: 12/06/2010] [Indexed: 11/24/2022] Open
Abstract
Stimulation of the T cell antigen receptor (TCR) induces formation of a phosphorylation-dependent signaling network via multiprotein complexes, whose compositions and dynamics are incompletely understood. Using stable isotope labeling by amino acids in cell culture (SILAC)-based quantitative proteomics, we investigated the kinetics of signal propagation after TCR-induced protein tyrosine phosphorylation. We confidently assigned 77 proteins (of 758 identified) as a direct or indirect consequence of tyrosine phosphorylation that proceeds in successive "signaling waves" revealing the temporal pace at which tyrosine kinases activate cellular functions. The first wave includes thymocyte-expressed molecule involved in selection (THEMIS), a protein recently implicated in thymocyte development but whose signaling role is unclear. We found that tyrosine phosphorylation of THEMIS depends on the presence of the scaffold proteins Linker for activation of T cells (LAT) and SH2 domain-containing lymphocyte protein of 76 kDa (SLP-76). THEMIS associates with LAT, presumably via the adapter growth factor receptor-bound protein 2 (Grb2) and with phospholipase Cγ1 (PLC-γ1). RNAi-mediated THEMIS knock-down inhibited TCR-induced IL-2 gene expression due to reduced ERK and nuclear factor of activated T cells (NFAT)/activator protein 1 (AP-1) signaling, whereas JNK, p38, or nuclear factor κB (NF-κB) activation were unaffected. Our study reveals the dynamics of TCR-dependent signaling networks and suggests a specific role for THEMIS in early TCR signalosome function.
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Affiliation(s)
| | | | | | | | - David C. Trudgian
- Proteomics Facility, Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford, OX1 3RE, United Kingdom
| | - Simon McGowan
- the Computational Biology Research Group, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DS, United Kingdom, and
| | - Guo Fu
- the Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, California 92037
| | - Nicholas R. J. Gascoigne
- the Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, California 92037
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89
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Paronetto MP, Messina V, Barchi M, Geremia R, Richard S, Sette C. Sam68 marks the transcriptionally active stages of spermatogenesis and modulates alternative splicing in male germ cells. Nucleic Acids Res 2011; 39:4961-74. [PMID: 21355037 PMCID: PMC3130265 DOI: 10.1093/nar/gkr085] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Sam68 plays an essential role in mouse spermatogenesis and male fertility. Herein, we report an interaction between Sam68 and the phosphorylated forms of the RNA polymerase II (RNAPII) in meiotic spermatocytes. RNase treatment decreased but did not abolish the interaction, consistently with in vitro binding of RNAPII to the Sam68 carboxyl-terminal region. Sam68 retention in the spermatocyte nucleus was dependent on the integrity of cellular RNAs, suggesting that the protein is recruited to transcriptionally active chromatin. Mouse knockout models characterized by stage-specific arrest of spermatogenesis and staining with the phosphorylated form of RNAPII documented that Sam68 expression is confined to the transcriptionally active stages of spermatogenesis. Furthermore, Sam68 associates with splicing regulators in germ cells and we report that alternative splicing of Sgce exon 8 is regulated in a Sam68-dependent manner during spermatogenesis. RNA and chromatin crosslink immunoprecipitation experiments showed that Sam68 binds in vivo to sequences surrounding the intron 7/exon 8 boundary, thereby affecting the recruitment of the phosphorylated RNAPII and of the general splicing factor U2AF65. These results suggest that Sam68 regulates alternative splicing at transcriptionally active sites in differentiating germ cells and provide new insights into the regulation of Sam68 expression during spermatogenesis.
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Affiliation(s)
- Maria Paola Paronetto
- Department of Public Health and Cell Biology, Section of Anatomy, University of Rome, 00133 Rome, Italy
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90
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Regulatory mechanisms that mediate tenascin C-dependent inhibition of oligodendrocyte precursor differentiation. J Neurosci 2010; 30:12310-22. [PMID: 20844127 DOI: 10.1523/jneurosci.4957-09.2010] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Here, we present mechanisms for the inhibition of oligodendendrocyte precursor cell (OPC) differentiation, a biological function of neural extracellular matrix (ECM). The differentiation of oligodendrocytes is orchestrated by a complex set of stimuli. In the present study, we investigated the signaling pathway elicited by the ECM glycoprotein tenascin C (Tnc). Tnc substrates inhibit myelin basic protein (MBP) expression of cultured rat oligodendrocytes, and, conversely, we found that the emergence of MBP expression is accelerated in forebrains of Tnc-deficient mice. Mechanistically, Tnc interfered with phosphorylation of Akt, which in turn reduced MBP expression. At the cell surface, Tnc associates with lipid rafts in oligodendrocyte membranes, together with the cell adhesion molecule contactin (Cntn1) and the Src family kinase (SFK) Fyn. Depletion of Cntn1 in OPCs by small interfering RNAs (siRNAs) abolished the Tnc-dependent inhibition of oligodendrocyte differentiation, while Tnc exposure impeded the activation of the tyrosine kinase Fyn by Cntn1. Concomitant with oligodendrocyte differentiation, Tnc antagonized the expression of the signaling adaptor and RNA-binding molecule Sam68. siRNA-mediated knockdown or overexpression of Sam68 delayed or accelerated oligodendrocyte differentiation, respectively. Inhibition of oligodendrocyte differentiation with the SFK inhibitor PP2 could be rescued by Sam68 overexpression, which may indicate a regulatory role for Sam68 downstream of Fyn. Our study therefore uncovers the first signaling pathways that underlie Tnc-induced, ECM-dependent maintenance of the immature state of OPCs.
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91
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Valacca C, Bonomi S, Buratti E, Pedrotti S, Baralle FE, Sette C, Ghigna C, Biamonti G. Sam68 regulates EMT through alternative splicing-activated nonsense-mediated mRNA decay of the SF2/ASF proto-oncogene. ACTA ACUST UNITED AC 2010; 191:87-99. [PMID: 20876280 PMCID: PMC2953442 DOI: 10.1083/jcb.201001073] [Citation(s) in RCA: 137] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Expression levels of SF2/ASF are controlled by Sam68 mediated activation of splicing-induced mRNA decay. Epithelial-to-mesenchymal transition (EMT) and its reversal (MET) are crucial cell plasticity programs that act during development and tumor metastasis. We have previously shown that the splicing factor and proto-oncogene SF2/ASF impacts EMT/MET through production of a constitutively active splice variant of the Ron proto-oncogene. Using an in vitro model, we now show that SF2/ASF is also regulated during EMT/MET by alternative splicing associated with the nonsense-mediated mRNA decay pathway (AS-NMD). Overexpression and small interfering RNA experiments implicate the splicing regulator Sam68 in AS-NMD of SF2/ASF transcripts and in the choice between EMT/MET programs. Moreover, Sam68 modulation of SF2/ASF splicing appears to be controlled by epithelial cell–derived soluble factors that act through the ERK1/2 signaling pathway to regulate Sam68 phosphorylation. Collectively, our results reveal a hierarchy of splicing factors that integrate splicing decisions into EMT/MET programs in response to extracellular stimuli.
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Affiliation(s)
- Cristina Valacca
- Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche (IGM-CNR), 27100 Pavia, Italy
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92
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Wang Y, Lacroix G, Haines J, Doukhanine E, Almazan G, Richard S. The QKI-6 RNA binding protein localizes with the MBP mRNAs in stress granules of glial cells. PLoS One 2010; 5. [PMID: 20862255 PMCID: PMC2941464 DOI: 10.1371/journal.pone.0012824] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2010] [Accepted: 08/12/2010] [Indexed: 12/23/2022] Open
Abstract
Background The quaking viable (qkv) mouse has several developmental defects that result in rapid tremors in the hind limbs. The qkI gene expresses three major alternatively spliced mRNAs (5, 6 and 7 kb) that encode the QKI-5, QKI-6 and QKI-7 RNA binding proteins that differ in their C-terminal 30 amino acids. The QKI isoforms are known to regulate RNA metabolism within oligodendrocytes, however, little is known about their roles during cellular stress. Methodology/Principal Findings In this study, we report an interaction between the QKI-6 isoform and a component of the RNA induced silencing complex (RISC), argonaute 2 (Ago2). We show in glial cells that QKI-6 co-localizes with Ago2 and the myelin basic protein mRNA in cytoplasmic stress granules. Conclusions Our findings define the QKI isoforms as Ago2-interacting proteins. We also identify the QKI-6 isoform as a new component of stress granules in glial cells.
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Affiliation(s)
- Yunling Wang
- Terry Fox Molecular Oncology Group, Lady Davis Institute for Medical Research and Departments of Oncology and Medicine, Bloomfield Center for Research on Aging, McGill University, Montréal, Québec, Canada
| | - Geneviève Lacroix
- Terry Fox Molecular Oncology Group, Lady Davis Institute for Medical Research and Departments of Oncology and Medicine, Bloomfield Center for Research on Aging, McGill University, Montréal, Québec, Canada
| | - Jeffery Haines
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada
| | - Evgueni Doukhanine
- Terry Fox Molecular Oncology Group, Lady Davis Institute for Medical Research and Departments of Oncology and Medicine, Bloomfield Center for Research on Aging, McGill University, Montréal, Québec, Canada
| | - Guillermina Almazan
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada
| | - Stéphane Richard
- Terry Fox Molecular Oncology Group, Lady Davis Institute for Medical Research and Departments of Oncology and Medicine, Bloomfield Center for Research on Aging, McGill University, Montréal, Québec, Canada
- * E-mail:
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93
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Meyer NH, Tripsianes K, Vincendeau M, Madl T, Kateb F, Brack-Werner R, Sattler M. Structural basis for homodimerization of the Src-associated during mitosis, 68-kDa protein (Sam68) Qua1 domain. J Biol Chem 2010; 285:28893-901. [PMID: 20610388 DOI: 10.1074/jbc.m110.126185] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sam68 (Src-associated during mitosis, 68 kDa) is a prototypical member of the STAR (signal transducer and activator of RNA) family of RNA-binding proteins. STAR proteins bind mRNA targets and modulate cellular processes such as cell cycle regulation and tissue development in response to extracellular signals. Sam68 has been shown to modulate alternative splicing of the pre-mRNAs of CD44 and Bcl-xL, which are linked to tumor progression and apoptosis. Sam68 and other STAR proteins recognize bipartite RNA sequences and are thought to function as homodimers. However, the structural and functional roles of the self-association are not known. Here, we present the solution structure of the Sam68 Qua1 homodimerization domain. Each monomer consists of two antiparallel alpha-helices connected by a short loop. The two subunits are arranged perpendicular to each other in an unusual four-helix topology. Mutational analysis of Sam68 in vitro and in a cell-based assay revealed that the Qua1 domain and residues within the dimerization interface are essential for alternative splicing of a CD44 minigene. Together, our results indicate that the Qua1 homodimerization domain is required for regulation of alternative splicing by Sam68.
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Affiliation(s)
- N Helge Meyer
- Institute of Structural Biology, Helmholtz Zentrum München, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany
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94
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Busà R, Sette C. An emerging role for nuclear RNA-mediated responses to genotoxic stress. RNA Biol 2010; 7:390-6. [PMID: 20639695 DOI: 10.4161/rna.7.4.12466] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Defects in the regulation of alternative splicing have strong relevance in the onset and progression of several types of human cancer. Modulation of alternative splicing allows cancer cells to adapt to hostile environments through production of specific mRNA variants. In particular, genotoxic stress exerted by chemotherapeutic drugs or irradiation strongly affects splicing of many genes. A key role in this aberrant regulation is played by the unbalanced expression of several splicing factors in cancer cells. Among them, the RNA-binding protein Sam68, which is overexpressed in various tumors, was shown to accumulate in nuclear foci of active transcription, together with other splicing regulators, and to affect splicing of target mRNAs in response to genotoxic stress. We suggest that subcellular redistribution of splicing factors is guided by changes in chromatin conformation elicited by DNA-damaging drugs. This event might represent an escape mechanism used by cancer cells to survive to genotoxic insults through expression of pro-survival, cancer-specific gene products.
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Affiliation(s)
- Roberta Busà
- Department of Public Health and Cell Biology, University of Rome Tor Vergata, Rome, Italy
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95
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Carmel AB, Wu J, Lehmann-Blount KA, Williamson JR. High-affinity consensus binding of target RNAs by the STAR/GSG proteins GLD-1, STAR-2 and Quaking. BMC Mol Biol 2010; 11:48. [PMID: 20573244 PMCID: PMC2905418 DOI: 10.1186/1471-2199-11-48] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2010] [Accepted: 06/23/2010] [Indexed: 11/16/2022] Open
Abstract
Background STAR/GSG proteins regulate gene expression in metazoans by binding consensus sites in the 5' or 3' UTRs of target mRNA transcripts. Owing to the high degree of homology across the STAR domain, most STAR proteins recognize similar RNA consensus sequences. Previously, the consensus for a number of well-characterized STAR proteins was defined as a hexameric sequence, referred to as the SBE, for STAR protein binding element. C. elegans GLD-1 and mouse Quaking (Qk-1) are two representative STAR proteins that bind similar consensus hexamers, which differ only in the preferred nucleotide identities at certain positions. Earlier reports also identified partial consensus elements located upstream or downstream of a canonical consensus hexamer in target RNAs, although the relative contribution of these sequences to the overall binding energy remains less well understood. Additionally, a recently identified STAR protein called STAR-2 from C. elegans is thought to bind target RNA consensus sites similar to that of GLD-1 and Qk-1. Results Here, a combination of fluorescence-polarization and gel mobility shift assays was used to demonstrate that STAR-2 binds to a similar RNA consensus as GLD-1 and Qk-1. These assays were also used to further delineate the contributions of each hexamer consensus nucleotide to high-affinity binding by GLD-1, Qk-1 and STAR-2 in a variety of RNA contexts. In addition, the effects of inserting additional full or partial consensus elements upstream or downstream of a canonical hexamer in target RNAs were also measured to better define the sequence elements and RNA architecture recognized by different STAR proteins. Conclusions The results presented here indicate that a single hexameric consensus is sufficient for high-affinity RNA binding by STAR proteins, and that upstream or downstream partial consensus elements may alter binding affinities depending on the sequence and spacing. The general requirements determined for high-affinity RNA binding by STAR proteins will help facilitate the identification of novel regulatory targets in vivo.
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Affiliation(s)
- Andrew B Carmel
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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96
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The splicing regulator Sam68 binds to a novel exonic splicing silencer and functions in SMN2 alternative splicing in spinal muscular atrophy. EMBO J 2010; 29:1235-47. [PMID: 20186123 DOI: 10.1038/emboj.2010.19] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2009] [Accepted: 01/26/2010] [Indexed: 12/24/2022] Open
Abstract
Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by loss of motor neurons in patients with null mutations in the SMN1 gene. An almost identical SMN2 gene is unable to compensate for this deficiency because a single C-to-T transition at position +6 in exon-7 causes skipping of the exon by a mechanism not yet fully elucidated. We observed that the C-to-T transition in SMN2 creates a putative binding site for the RNA-binding protein Sam68. RNA pull-down assays and UV-crosslink experiments showed that Sam68 binds to this sequence. In vivo splicing assays showed that Sam68 triggers SMN2 exon-7 skipping. Moreover, mutations in the Sam68-binding site of SMN2 or in the RNA-binding domain of Sam68 completely abrogated its effect on exon-7 skipping. Retroviral infection of dominant-negative mutants of Sam68 that interfere with its RNA-binding activity, or with its binding to the splicing repressor hnRNP A1, enhanced exon-7 inclusion in endogenous SMN2 and rescued SMN protein expression in fibroblasts of SMA patients. Our results thus indicate that Sam68 is a novel crucial regulator of SMN2 splicing.
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97
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Sellier C, Rau F, Liu Y, Tassone F, Hukema RK, Gattoni R, Schneider A, Richard S, Willemsen R, Elliott DJ, Hagerman PJ, Charlet-Berguerand N. Sam68 sequestration and partial loss of function are associated with splicing alterations in FXTAS patients. EMBO J 2010; 29:1248-61. [PMID: 20186122 DOI: 10.1038/emboj.2010.21] [Citation(s) in RCA: 286] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2009] [Accepted: 01/20/2010] [Indexed: 01/22/2023] Open
Abstract
Fragile X-associated Tremor/Ataxia Syndrome (FXTAS) is a neurodegenerative disorder caused by expansion of 55-200 CGG repeats in the 5'-UTR of the FMR1 gene. FXTAS is characterized by action tremor, gait ataxia and impaired executive cognitive functioning. It has been proposed that FXTAS is caused by titration of RNA-binding proteins by the expanded CGG repeats. Sam68 is an RNA-binding protein involved in alternative splicing regulation and its ablation in mouse leads to motor coordination defects. Here, we report that mRNAs containing expanded CGG repeats form large and dynamic intranuclear RNA aggregates that recruit several RNA-binding proteins sequentially, first Sam68, then hnRNP-G and MBNL1. Importantly, Sam68 is sequestered by expanded CGG repeats and thereby loses its splicing-regulatory function. Consequently, Sam68-responsive splicing is altered in FXTAS patients. Finally, we found that regulation of Sam68 tyrosine phosphorylation modulates its localization within CGG aggregates and that tautomycin prevents both Sam68 and CGG RNA aggregate formation. Overall, these data support an RNA gain-of-function mechanism for FXTAS neuropathology, and suggest possible target routes for treatment options.
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Affiliation(s)
- Chantal Sellier
- Department of Neurobiology and Genetics, IGBMC, INSERM U964, CNRS UMR7104, University of Strasbourg, Illkirch, France
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98
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Stable formation of compositionally unique stress granules in virus-infected cells. J Virol 2010; 84:3654-65. [PMID: 20106928 DOI: 10.1128/jvi.01320-09] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Stress granules are sites of mRNA storage formed in response to a variety of stresses, including viral infections. Here, the mechanisms and consequences of stress granule formation during poliovirus infection were examined. The results indicate that stress granules containing T-cell-restricted intracellular antigen 1 (TIA-1) and mRNA are stably constituted in infected cells despite lacking intact RasGAP SH3-domain binding protein 1 (G3BP) and eukaryotic initiation factor 4G. Fluorescent in situ hybridization revealed that stress granules in infected cells do not contain significant amounts of viral positive-strand RNA. Infection does not prevent stress granule formation in response to heat shock, indicating that poliovirus does not block de novo stress granule formation. A mutant TIA-1 protein that prevents stress granule formation during oxidative stress also prevents formation in infected cells. However, stress granule formation during infection is more dependent upon ongoing transcription than is formation during oxidative stress or heat shock. Furthermore, Sam68 is recruited to stress granules in infected cells but not to stress granules formed in response to oxidative stress or heat shock. These results demonstrate that stress granule formation in poliovirus-infected cells utilizes a transcription-dependent pathway that results in the appearance of stable, compositionally unique stress granules.
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99
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Busà R, Geremia R, Sette C. Genotoxic stress causes the accumulation of the splicing regulator Sam68 in nuclear foci of transcriptionally active chromatin. Nucleic Acids Res 2010; 38:3005-18. [PMID: 20110258 PMCID: PMC2875014 DOI: 10.1093/nar/gkq004] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
DNA-damaging agents cause a multifaceted cellular stress response. Cells set in motion either repair mechanisms or programmed cell death pathways, depending on the extent of the damage and on their ability to withstand it. The RNA-binding protein (RBP) Sam68, which is up-regulated in prostate carcinoma, promotes prostate cancer cell survival to genotoxic stress. Herein, we have investigated the function of Sam68 in this cellular response. Mitoxantrone (MTX), a topoisomerase II inhibitor, induced relocalization of Sam68 from the nucleoplasm to nuclear granules, together with several other RBPs involved in alternative splicing, such as TIA-1, hnRNP A1 and the SR proteins SC35 and ASF/SF2. Sam68 accumulation in nuclear stress granules was independent of signal transduction pathways activated by DNA damage. Using BrU labelling and immunofluorescence, we demonstrate that MTX-induced nuclear stress granules are transcriptionally active foci where Sam68 and the phosphorylated form of RNA polymerase II accumulate. Finally, we show that MTX-induced relocalization of Sam68 correlates with changes in alternative splicing of its mRNA target CD44, and that MTX-induced CD44 splicing depends on Sam68 expression. These results strongly suggest that Sam68 is part of a RNA-mediated stress response of the cell that modulates alternative splicing in response to DNA damage.
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Affiliation(s)
- Roberta Busà
- Department of Public Health and Cell Biology, University of Rome Tor Vergata, Via Montpellier 1, 00133 Rome, Italy
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100
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Paronetto MP, Cappellari M, Busà R, Pedrotti S, Vitali R, Comstock C, Hyslop T, Knudsen KE, Sette C. Alternative splicing of the cyclin D1 proto-oncogene is regulated by the RNA-binding protein Sam68. Cancer Res 2009; 70:229-39. [PMID: 20028857 DOI: 10.1158/0008-5472.can-09-2788] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Human cyclin D1 is expressed as two isoforms derived by alternate RNA splicing, termed D1a and D1b, which differ for the inclusion of intron 4 in the D1b mRNA. Both isoforms are frequently upregulated in human cancers, but cyclin D1b displays relatively higher oncogenic potential. The splicing factors that regulate alternative splicing of cyclin D1b remain unknown despite the likelihood that they contribute to cyclin D1 oncogenicity. In this study, we report that Sam68, an RNA-binding protein frequently overexpressed in prostate cancer cells, enhances splicing of cyclin D1b and supports its expression in prostate cancer cells. Chromatin immunoprecipitation and RNA coimmunoprecipitation experiments showed that Sam68 is recruited to the human CCND1 gene encoding cyclin D1 and that it binds to cyclin D1 mRNA. Transient overexpression and RNAi knockdown experiments indicated that Sam68 acts to enhance endogenous expression of cyclin D1b. Minigene reporter assays showed that Sam68 directly affected alternative splicing of CCND1 message, with a preference for the A870 allele that is known to favor cyclin D1b splicing. Sam68 interacted with the proximal region of intron 4, and its binding correlated inversely with recruitment of the spliceosomal component U1-70K. Sam68-mediated splicing was modulated by signal transduction pathways that elicit phosphorylation of Sam68 and regulate its affinity for CCND1 intron 4. Notably, Sam68 expression positively correlates with levels of cyclin D1b, but not D1a, in human prostate carcinomas. Our results identify Sam68 as the first splicing factor to affect CCND1 alternative splicing in prostate cancer cells, and suggest that increased levels of Sam68 may stimulate cyclin D1b expression in human prostate cancers.
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Affiliation(s)
- Maria Paola Paronetto
- Department of Public Health and Cell Biology, University of Rome Tor Vergata, Rome, Italy
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