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Sunatani Y, Kamdar RP, Sharma MK, Matsui T, Sakasai R, Hashimoto M, Ishigaki Y, Matsumoto Y, Iwabuchi K. Caspase-mediated cleavage of X-ray repair cross-complementing group 4 promotes apoptosis by enhancing nuclear translocation of caspase-activated DNase. Exp Cell Res 2017; 362:450-460. [PMID: 29233683 DOI: 10.1016/j.yexcr.2017.12.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2017] [Revised: 12/06/2017] [Accepted: 12/08/2017] [Indexed: 11/17/2022]
Abstract
X-ray repair cross-complementing group 4 (XRCC4), a repair protein for DNA double-strand breaks, is cleaved by caspases during apoptosis. In this study, we examined the role of XRCC4 in apoptosis. Cell lines, derived from XRCC4-deficient M10 mouse lymphoma cells and stably expressing wild-type XRCC4 or caspase-resistant XRCC4, were established and treated with staurosporine (STS) to induce apoptosis. In STS-induced apoptosis, expression of wild-type, but not caspase-resistant, XRCC4 in XRCC4-deficient cells enhanced oligonucleosomal DNA fragmentation and the appearance of TUNEL-positive cells by promoting nuclear translocation of caspase-activated DNase (CAD), a major nuclease for oligonucleosomal DNA fragmentation. CAD activity is reportedly regulated by the ratio of two inhibitor of CAD (ICAD) splice variants, ICAD-L and ICAD-S mRNA, which, respectively, produce proteins with and without the ability to transport CAD into the nucleus. The XRCC4-dependent promotion of nuclear import of CAD in STS-treated cells was associated with reduction of ICAD-S mRNA and protein, and enhancement of phosphorylation and nuclear import of serine/arginine-rich splicing factor (SRSF) 1. These XRCC4-dependent, apoptosis-enhancing effects were canceled by depletion of SRSF1 or SR protein kinase (SRPK) 1. In addition, overexpression of SRSF1 in XRCC4-deficient cells restored the normal level of apoptosis, suggesting that SRSF1 functions downstream of XRCC4 in activating CAD. This XRCC4-dependent, SRPK1/SRSF1-mediated regulatory mechanism was conserved in apoptosis in Jurkat human leukemia cells triggered by STS, and by two widely used anti-cancer agents, Paclitaxel and Vincristine. These data imply that the level of XRCC4 expression could be used to predict the effects of apoptosis-inducing drugs in cancer treatment.
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Affiliation(s)
- Yumi Sunatani
- Department of Biochemistry I, School of Medicine, Kanazawa Medical University, Kahoku-gun, Ishikawa 920-0293, Japan
| | - Radhika Pankaj Kamdar
- Laboratory for Advanced Nuclear Energy, Institute of Innovative Research, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8550, Japan
| | - Mukesh Kumar Sharma
- Laboratory for Advanced Nuclear Energy, Institute of Innovative Research, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8550, Japan; Department of Zoology, SPC Government College, Ajmer, Rajasthan 305001, India
| | - Tadashi Matsui
- Department of Biochemistry I, School of Medicine, Kanazawa Medical University, Kahoku-gun, Ishikawa 920-0293, Japan
| | - Ryo Sakasai
- Department of Biochemistry I, School of Medicine, Kanazawa Medical University, Kahoku-gun, Ishikawa 920-0293, Japan
| | - Mitsumasa Hashimoto
- Department of Physics, General Education Department, Kanazawa Medical University, Kahoku-gun, Ishikawa 920-0293, Japan
| | - Yasuhito Ishigaki
- Division of Molecular and Cell Biology, Medical Research Institute, Kanazawa Medical University, Kahoku-gun, Ishikawa 920-0293, Japan
| | - Yoshihisa Matsumoto
- Laboratory for Advanced Nuclear Energy, Institute of Innovative Research, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8550, Japan
| | - Kuniyoshi Iwabuchi
- Department of Biochemistry I, School of Medicine, Kanazawa Medical University, Kahoku-gun, Ishikawa 920-0293, Japan.
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Lee G, Zheng Y, Cho S, Jang C, England C, Dempsey JM, Yu Y, Liu X, He L, Cavaliere PM, Chavez A, Zhang E, Isik M, Couvillon A, Dephoure NE, Blackwell TK, Yu JJ, Rabinowitz JD, Cantley LC, Blenis J. Post-transcriptional Regulation of De Novo Lipogenesis by mTORC1-S6K1-SRPK2 Signaling. Cell 2017; 171:1545-1558.e18. [PMID: 29153836 DOI: 10.1016/j.cell.2017.10.037] [Citation(s) in RCA: 152] [Impact Index Per Article: 21.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2017] [Revised: 10/03/2017] [Accepted: 10/23/2017] [Indexed: 01/08/2023]
Abstract
mTORC1 is a signal integrator and master regulator of cellular anabolic processes linked to cell growth and survival. Here, we demonstrate that mTORC1 promotes lipid biogenesis via SRPK2, a key regulator of RNA-binding SR proteins. mTORC1-activated S6K1 phosphorylates SRPK2 at Ser494, which primes Ser497 phosphorylation by CK1. These phosphorylation events promote SRPK2 nuclear translocation and phosphorylation of SR proteins. Genome-wide transcriptome analysis reveals that lipid biosynthetic enzymes are among the downstream targets of mTORC1-SRPK2 signaling. Mechanistically, SRPK2 promotes SR protein binding to U1-70K to induce splicing of lipogenic pre-mRNAs. Inhibition of this signaling pathway leads to intron retention of lipogenic genes, which triggers nonsense-mediated mRNA decay. Genetic or pharmacological inhibition of SRPK2 blunts de novo lipid synthesis, thereby suppressing cell growth. These results thus reveal a novel role of mTORC1-SRPK2 signaling in post-transcriptional regulation of lipid metabolism and demonstrate that SRPK2 is a potential therapeutic target for mTORC1-driven metabolic disorders.
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Affiliation(s)
- Gina Lee
- Meyer Cancer Center, Weill Cornell Medicine, New York, NY 10065, USA; Department of Pharmacology, Weill Cornell Medicine, New York, NY 10065, USA
| | - Yuxiang Zheng
- Meyer Cancer Center, Weill Cornell Medicine, New York, NY 10065, USA; Department of Medicine, Weill Cornell Medicine, New York, NY 10065, USA
| | - Sungyun Cho
- Meyer Cancer Center, Weill Cornell Medicine, New York, NY 10065, USA
| | - Cholsoon Jang
- Lewis-Sigler Institute for Integrative Genomics and Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
| | - Christina England
- Meyer Cancer Center, Weill Cornell Medicine, New York, NY 10065, USA
| | - Jamie M Dempsey
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Yonghao Yu
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Xiaolei Liu
- Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA
| | - Long He
- Meyer Cancer Center, Weill Cornell Medicine, New York, NY 10065, USA; Department of Pharmacology, Weill Cornell Medicine, New York, NY 10065, USA
| | - Paola M Cavaliere
- Meyer Cancer Center, Weill Cornell Medicine, New York, NY 10065, USA
| | - Andre Chavez
- Meyer Cancer Center, Weill Cornell Medicine, New York, NY 10065, USA
| | - Erik Zhang
- Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA
| | - Meltem Isik
- Joslin Diabetes Center and Department of Genetics, Harvard Medical School, Boston, MA 02215, USA
| | | | - Noah E Dephoure
- Meyer Cancer Center, Weill Cornell Medicine, New York, NY 10065, USA
| | - T Keith Blackwell
- Joslin Diabetes Center and Department of Genetics, Harvard Medical School, Boston, MA 02215, USA
| | - Jane J Yu
- Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA
| | - Joshua D Rabinowitz
- Lewis-Sigler Institute for Integrative Genomics and Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
| | - Lewis C Cantley
- Meyer Cancer Center, Weill Cornell Medicine, New York, NY 10065, USA; Department of Medicine, Weill Cornell Medicine, New York, NY 10065, USA
| | - John Blenis
- Meyer Cancer Center, Weill Cornell Medicine, New York, NY 10065, USA; Department of Pharmacology, Weill Cornell Medicine, New York, NY 10065, USA.
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53
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Sánchez-Hernández N, Prieto-Sánchez S, Moreno-Castro C, Muñoz-Cobo JP, El Yousfi Y, Boyero-Corral S, Suñé-Pou M, Hernández-Munain C, Suñé C. Targeting proteins to RNA transcription and processing sites within the nucleus. Int J Biochem Cell Biol 2017; 91:194-202. [DOI: 10.1016/j.biocel.2017.06.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Revised: 05/26/2017] [Accepted: 06/01/2017] [Indexed: 12/26/2022]
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54
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Wang ZH, Liu P, Liu X, Manfredsson FP, Sandoval IM, Yu SP, Wang JZ, Ye K. Delta-Secretase Phosphorylation by SRPK2 Enhances Its Enzymatic Activity, Provoking Pathogenesis in Alzheimer's Disease. Mol Cell 2017; 67:812-825.e5. [PMID: 28826672 DOI: 10.1016/j.molcel.2017.07.018] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Revised: 06/28/2017] [Accepted: 07/19/2017] [Indexed: 01/06/2023]
Abstract
Delta-secretase, a lysosomal asparagine endopeptidase (AEP), simultaneously cleaves both APP and tau, controlling the onset of pathogenesis of Alzheimer's disease (AD). However, how this protease is post-translationally regulated remains unclear. Here we report that serine-arginine protein kinase 2 (SRPK2) phosphorylates delta-secretase and enhances its enzymatic activity. SRPK2 phosphorylates serine 226 on delta-secretase and accelerates its autocatalytic cleavage, leading to its cytoplasmic translocation and escalated enzymatic activities. Delta-secretase is highly phosphorylated in human AD brains, tightly correlated with SRPK2 activity. Overexpression of a phosphorylation mimetic (S226D) in young 3xTg mice strongly promotes APP and tau fragmentation and facilitates amyloid plaque deposits and neurofibrillary tangle (NFT) formation, resulting in cognitive impairment. Conversely, viral injection of the non-phosphorylatable mutant (S226A) into 5XFAD mice decreases APP and tau proteolytic cleavage, attenuates AD pathologies, and reverses cognitive defects. Our findings support that delta-secretase phosphorylation by SRPK2 plays a critical role in aggravating AD pathogenesis.
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Affiliation(s)
- Zhi-Hao Wang
- Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA; Department of Pathophysiology, Key Laboratory of Ministry of Education of Neurological Diseases, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Pai Liu
- Emory College of Arts and Sciences, Emory University, Atlanta, GA 30322, USA
| | - Xia Liu
- Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Fredric P Manfredsson
- Department of Translational Science and Molecular Medicine, Michigan State University, 333 Bostwick Avenue NE, Grand Rapids, MI 49503, USA
| | - Ivette M Sandoval
- Department of Translational Science and Molecular Medicine, Michigan State University, 333 Bostwick Avenue NE, Grand Rapids, MI 49503, USA
| | - Shan Ping Yu
- Department of Anesthesiology, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Jian-Zhi Wang
- Department of Pathophysiology, Key Laboratory of Ministry of Education of Neurological Diseases, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China; Co-innovation Center of Neuroregeneration, Nantong 226001, China.
| | - Keqiang Ye
- Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA; Translational Center for Stem Cell Research, Tongji Hospital, Tongji University School of Medicine, Shanghai 200065, China.
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55
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Latorre E, Harries LW. Splicing regulatory factors, ageing and age-related disease. Ageing Res Rev 2017; 36:165-170. [PMID: 28456680 DOI: 10.1016/j.arr.2017.04.004] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Revised: 04/21/2017] [Accepted: 04/21/2017] [Indexed: 12/12/2022]
Abstract
Alternative splicing is a co-transcriptional process, which allows for the production of multiple transcripts from a single gene and is emerging as an important control point for gene expression. Alternatively expressed isoforms often have antagonistic function and differential temporal or spatial expression patterns, yielding enormous plasticity and adaptability to cells and increasing their ability to respond to environmental challenge. The regulation of alternative splicing is critical for numerous cellular functions in both pathological and physiological conditions, and deregulated alternative splicing is a key feature of common chronic diseases. Isoform choice is controlled by a battery of splicing regulatory proteins, which include the serine arginine rich (SRSF) proteins and the heterogeneous ribonucleoprotein (hnRNP) classes of genes. These important splicing regulators have been implicated in age-related disease, and in the ageing process itself. This review will outline the important contribution of splicing regulator proteins to ageing and age-related disease.
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56
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Chatrikhi R, Wang W, Gupta A, Loerch S, Maucuer A, Kielkopf CL. SF1 Phosphorylation Enhances Specific Binding to U2AF 65 and Reduces Binding to 3'-Splice-Site RNA. Biophys J 2017; 111:2570-2586. [PMID: 28002734 DOI: 10.1016/j.bpj.2016.11.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Revised: 11/02/2016] [Accepted: 11/08/2016] [Indexed: 12/25/2022] Open
Abstract
Splicing factor 1 (SF1) recognizes 3' splice sites of the major class of introns as a ternary complex with U2AF65 and U2AF35 splicing factors. A conserved SPSP motif in a coiled-coil domain of SF1 is highly phosphorylated in proliferating human cells and is required for cell proliferation. The UHM kinase 1 (UHMK1), also called KIS, double-phosphorylates both serines of this SF1 motif. Here, we use isothermal titration calorimetry to demonstrate that UHMK1 phosphorylation of the SF1 SPSP motif slightly enhances specific binding of phospho-SF1 to its cognate U2AF65 protein partner. Conversely, quantitative fluorescence anisotropy RNA binding assays and isothermal titration calorimetry experiments establish that double-SPSP phosphorylation reduces phospho-SF1 and phospho-SF1-U2AF65 binding affinities for either optimal or suboptimal splice-site RNAs. Domain-substitution and mutagenesis experiments further demonstrate that arginines surrounding the phosphorylated SF1 loop are required for cooperative 3' splice site recognition by the SF1-U2AF65 complex (where cooperativity is defined as a nonadditive increase in RNA binding by the protein complex relative to the individual proteins). In the context of local, intracellular concentrations, the subtle effects of SF1 phosphorylation on its associations with U2AF65 and splice-site RNAs are likely to influence pre-mRNA splicing. However, considering roles for SF1 in pre-mRNA retention and transcriptional repression, as well as in splicing, future comprehensive investigations are needed to fully explain the requirement for SF1 SPSP phosphorylation in proliferating human cells.
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Affiliation(s)
- Rakesh Chatrikhi
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine, Rochester, New York
| | - Wenhua Wang
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine, Rochester, New York
| | - Ankit Gupta
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine, Rochester, New York
| | - Sarah Loerch
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine, Rochester, New York
| | | | - Clara L Kielkopf
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine, Rochester, New York.
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57
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Deka B, Singh KK. Multifaceted Regulation of Gene Expression by the Apoptosis- and Splicing-Associated Protein Complex and Its Components. Int J Biol Sci 2017; 13:545-560. [PMID: 28539829 PMCID: PMC5441173 DOI: 10.7150/ijbs.18649] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Accepted: 02/24/2017] [Indexed: 11/24/2022] Open
Abstract
The differential deposition of RNA-binding proteins (RBPs) on pre-mRNA mediates the processes of gene expression. One of the complexes containing RBPs that play a crucial part in RNA metabolism is the apoptosis-and splicing-associated protein (ASAP) complex. In this review, we present a summary of the structure of ASAP complex and its localization. Also, we discuss the findings by different groups on various functions of the subunits of the ASAP complex in RNA metabolism. The subunits of the ASAP complex are RNPS1, Acinus and SAP18. Originally, the ASAP complex was thought to link RNA processing with apoptosis. Further studies have shown the role of these components in RNA metabolism of cells, including transcription, splicing, translation and nonsense-mediated mRNA decay (NMD). In transcription, RNPS1 is involved in preventing the formation of R-loop, while Acinus and SAP18 suppress transcription with the help of histone deacetylase. On the one hand, individual components of the ASAP complex, namely RNPS1 and Acinus act as splicing activators, whereas on the other hand, in-vitro assay shows that the ASAP complex behaves as splicing repressor. In addition, the individual members of the ASAP complex associates with the exon junction complex (EJC) to play roles in splicing and translation. RNPS1 increases the translation efficiency by participating in the 3'end processing and polysome association of mRNAs. Similarly, during NMD RNPS1 aids in the recruitment of decay factors by interacting with EJC.
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Affiliation(s)
| | - Kusum Kumari Singh
- Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati-781039, Assam, India
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58
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Blue GM, Humphreys D, Szot J, Major J, Chapman G, Bosman A, Kirk EP, Sholler GF, Harvey RP, Dunwoodie SL, Winlaw DS. The promises and challenges of exome sequencing in familial, non-syndromic congenital heart disease. Int J Cardiol 2016; 230:155-163. [PMID: 27989580 DOI: 10.1016/j.ijcard.2016.12.024] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 11/30/2016] [Accepted: 12/11/2016] [Indexed: 12/27/2022]
Abstract
BACKGROUND Exome sequencing is an established strategy to identify causal variants in families with two or more members affected by congenital heart disease (CHD). This unbiased approach, in which both rare and common variants are identified, makes it suitable to research complex, heterogeneous diseases such as CHD. METHODS AND RESULTS Exome sequencing was performed on two affected members of a three generation family with atrial septal defects (ASD), suggesting a dominant inheritance pattern. Variants were filtered using two bioinformatics pipelines and prioritised according to in silico prediction programs. Segregation studies and functional analyses were used to assess co-segregation with disease and effects on protein function, respectively. Following the data and in silico analyses, ten candidate variants were prioritised. Of these, SRPK2 (c.2044C>T[p.Arg682Trp]) and NOTCH1 (c.3835C>T[p.Arg1279Cys]), co-segregated with disease in the family; however, previous functional analyses on SRPK2 make this an unlikely candidate. Functional analyses in the variant (c.3835C>T[p.Arg1279Cys]) of the known CHD gene NOTCH1 demonstrated a non-significant decrease in signalling activity. CONCLUSION This study demonstrates both the potential, as well as the challenges, of applying exome sequencing to complex diseases such as CHD. While in silico evidence and segregation analyses in the NOTCH1 p.Arg1279Cys variant are highly suggestive of pathogenicity, the minimal change in signalling capacity suggests that other variants may be required for CHD development. This study highlights the difficulties of applying exome sequencing in familial, non-syndromic CHD in the clinical environment and a cautionary note in the interpretation of apparently causal abnormalities in silico without supportive functional data.
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Affiliation(s)
- Gillian M Blue
- Kids Heart Research, The Children's Hospital at Westmead, Sydney, Australia; The Heart Centre for Children, The Children's Hospital at Westmead, Sydney, Australia; Sydney Medical School, University of Sydney, Australia
| | - David Humphreys
- Victor Chang Cardiac Research Institute, Darlinghurst, Sydney, Australia; St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, Australia
| | - Justin Szot
- Victor Chang Cardiac Research Institute, Darlinghurst, Sydney, Australia; School of Biotechnology and Biomolecular Sciences, Faculty of Science, University of New South Wales, Sydney, Australia
| | - Joelene Major
- Victor Chang Cardiac Research Institute, Darlinghurst, Sydney, Australia
| | - Gavin Chapman
- Victor Chang Cardiac Research Institute, Darlinghurst, Sydney, Australia; St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, Australia
| | - Alexis Bosman
- Victor Chang Cardiac Research Institute, Darlinghurst, Sydney, Australia
| | - Edwin P Kirk
- Department of Medical Genetics, Sydney Children's Hospital, Sydney, Australia; School of Women's and Children's Health, Faculty of Medicine, University of New South Wales, Sydney, Australia
| | - Gary F Sholler
- The Heart Centre for Children, The Children's Hospital at Westmead, Sydney, Australia; Sydney Medical School, University of Sydney, Australia
| | - Richard P Harvey
- Victor Chang Cardiac Research Institute, Darlinghurst, Sydney, Australia; St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, Australia; School of Biotechnology and Biomolecular Sciences, Faculty of Science, University of New South Wales, Sydney, Australia
| | - Sally L Dunwoodie
- Victor Chang Cardiac Research Institute, Darlinghurst, Sydney, Australia; St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, Australia; School of Biotechnology and Biomolecular Sciences, Faculty of Science, University of New South Wales, Sydney, Australia
| | - David S Winlaw
- Kids Heart Research, The Children's Hospital at Westmead, Sydney, Australia; The Heart Centre for Children, The Children's Hospital at Westmead, Sydney, Australia; Sydney Medical School, University of Sydney, Australia.
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Abstract
Tumor-associated alterations in RNA splicing result either from mutations in splicing-regulatory elements or changes in components of the splicing machinery. This review summarizes our current understanding of the role of splicing-factor alterations in human cancers. We describe splicing-factor alterations detected in human tumors and the resulting changes in splicing, highlighting cell-type-specific similarities and differences. We review the mechanisms of splicing-factor regulation in normal and cancer cells. Finally, we summarize recent efforts to develop novel cancer therapies, based on targeting either the oncogenic splicing events or their upstream splicing regulators.
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Affiliation(s)
- Olga Anczuków
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA
| | - Adrian R Krainer
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA
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60
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Aubol BE, Wu G, Keshwani MM, Movassat M, Fattet L, Hertel KJ, Fu XD, Adams JA. Release of SR Proteins from CLK1 by SRPK1: A Symbiotic Kinase System for Phosphorylation Control of Pre-mRNA Splicing. Mol Cell 2016; 63:218-228. [PMID: 27397683 DOI: 10.1016/j.molcel.2016.05.034] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2015] [Revised: 04/26/2016] [Accepted: 05/25/2016] [Indexed: 11/26/2022]
Abstract
Phosphorylation has been generally thought to activate the SR family of splicing factors for efficient splice-site recognition, but this idea is incompatible with an early observation that overexpression of an SR protein kinase, such as the CDC2-like kinase 1 (CLK1), weakens splice-site selection. Here, we report that CLK1 binds SR proteins but lacks the mechanism to release phosphorylated SR proteins, thus functionally inactivating the splicing factors. Interestingly, CLK1 overcomes this dilemma through a symbiotic relationship with the serine-arginine protein kinase 1 (SRPK1). We show that SRPK1 interacts with an RS-like domain in the N terminus of CLK1 to facilitate the release of phosphorylated SR proteins, which then promotes efficient splice-site recognition and subsequent spliceosome assembly. These findings reveal an unprecedented signaling mechanism by which two protein kinases fulfill separate catalytic features that are normally encoded in single kinases to institute phosphorylation control of pre-mRNA splicing in the nucleus.
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Affiliation(s)
- Brandon E Aubol
- Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093, USA
| | - Guowei Wu
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093, USA
| | - Malik M Keshwani
- Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093, USA
| | - Maliheh Movassat
- Department of Microbiology and Molecular Genetics, University of California, Irvine, Irvine, CA 92697, USA
| | - Laurent Fattet
- Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093, USA
| | - Klemens J Hertel
- Department of Microbiology and Molecular Genetics, University of California, Irvine, Irvine, CA 92697, USA
| | - Xiang-Dong Fu
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093, USA
| | - Joseph A Adams
- Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093, USA.
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61
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Wang J, Wu HF, Shen W, Xu DY, Ruan TY, Tao GQ, Lu PH. SRPK2 promotes the growth and migration of the colon cancer cells. Gene 2016; 586:41-7. [PMID: 27041240 DOI: 10.1016/j.gene.2016.03.051] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2015] [Revised: 03/09/2016] [Accepted: 03/18/2016] [Indexed: 10/21/2022]
Abstract
Colon cancer is one of the major causes of cancer-related death in the world. Understanding the molecular mechanism underlying this malignancy will facilitate the diagnosis and treatment. Serine-arginine protein kinase 2 (SRPK2) has been reported to be upregulated in several cancer types. However, its expression and functions in colon cancer remains unknown. In this study, it was found that the expression of SRPK2 was up-regulated in the clinical colon cancer samples. Overexpression of SRPK2 promoted the growth and migration of colon cancer cells, while knocking down the expression of SRPK2 inhibited the growth, migration and tumorigenecity of colon cancer cells. Molecular mechanism studies revealed that SRPK2 activated ERK signaling in colon cancer cells. Taken together, our study demonstrated the tumor promoting roles of SRPK2 in colon cancer cells and SRPK2 might be a promising therapeutic target for colon cancer.
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Affiliation(s)
- Jian Wang
- Department of Gastrointestinal Surgery, Huai'an Hospital Affiliated of Xuzhou Medical College and Huai'an Second People's Hospital, No. 62, Huai-hai South Road, Hua'an, 223200, Jiangsu, China
| | - Hai-Feng Wu
- Department of Critical Care Medicine, Affiliated Yixing People's Hospital, Jiangsu University, No. 75, Tongzhenguan Road, Yixing, 214200, Jiangsu, China
| | - Wei Shen
- Department of General Surgery, Wuxi People's Hospital Affiliated to Nanjing Medical University, Wuxi 214023, Jiangsu Province, China
| | - Dong-Yan Xu
- Department of Gastroenterology, Huai'an Hospital Affiliated of Xuzhou Medical College and Huai'an Second People's Hospital, No. 62, Huai-hai South Road, Huai'an, 223200, Jiangsu, China
| | - Ting-Yan Ruan
- Department of Medical Oncology, Wuxi People's Hospital Affiliated to Nanjing Medical University, Wuxi, 214023, Jiangsu Province, China
| | - Guo-Qing Tao
- Department of General Surgery, Wuxi People's Hospital Affiliated to Nanjing Medical University, Wuxi 214023, Jiangsu Province, China
| | - Pei-Hua Lu
- Department of Medical Oncology, Wuxi People's Hospital Affiliated to Nanjing Medical University, Wuxi, 214023, Jiangsu Province, China.
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Radhakrishnan A, Nanjappa V, Raja R, Sathe G, Chavan S, Nirujogi RS, Patil AH, Solanki H, Renuse S, Sahasrabuddhe NA, Mathur PP, Prasad TSK, Kumar P, Califano JA, Sidransky D, Pandey A, Gowda H, Chatterjee A. Dysregulation of splicing proteins in head and neck squamous cell carcinoma. Cancer Biol Ther 2016; 17:219-29. [PMID: 26853621 DOI: 10.1080/15384047.2016.1139234] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Signaling plays an important role in regulating all cellular pathways. Altered signaling is one of the hallmarks of cancers. Phosphoproteomics enables interrogation of kinase mediated signaling pathways in biological systems. In cancers, this approach can be utilized to identify aberrantly activated pathways that potentially drive proliferation and tumorigenesis. To identify signaling alterations in head and neck squamous cell carcinoma (HNSCC), we carried out proteomic and phosphoproteomic analysis of HNSCC cell lines using a combination of tandem mass tag (TMT) labeling approach and titanium dioxide-based enrichment. We identified 4,920 phosphosites corresponding to 2,212 proteins in six HNSCC cell lines compared to a normal oral cell line. Our data indicated significant enrichment of proteins associated with splicing. We observed hyperphosphorylation of SRSF protein kinase 2 (SRPK2) and its downstream substrates in HNSCC cell lines. SRPK2 is a splicing kinase, known to phosphorylate serine/arginine (SR) rich domain proteins and regulate splicing process in eukaryotes. Although genome-wide studies have reported the contribution of alternative splicing events of several genes in the progression of cancer, the involvement of splicing kinases in HNSCC is not known. In this study, we studied the role of SRPK2 in HNSCC. Inhibition of SRPK2 resulted in significant decrease in colony forming and invasive ability in a panel of HNSCC cell lines. Our results indicate that phosphorylation of SRPK2 plays a crucial role in the regulation of splicing process in HNSCC and that splicing kinases can be developed as a new class of therapeutic target in HNSCC.
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Affiliation(s)
- Aneesha Radhakrishnan
- a Institute of Bioinformatics, International Technology Park , Bangalore , India.,b Department of Biochemistry and Molecular Biology , Pondicherry University , Puducherry , India
| | - Vishalakshi Nanjappa
- a Institute of Bioinformatics, International Technology Park , Bangalore , India.,c Amrita School of Biotechnology, Amrita University , Kollam , India
| | - Remya Raja
- a Institute of Bioinformatics, International Technology Park , Bangalore , India
| | - Gajanan Sathe
- a Institute of Bioinformatics, International Technology Park , Bangalore , India.,d Manipal University , Madhav Nagar, Manipal , India
| | - Sandip Chavan
- a Institute of Bioinformatics, International Technology Park , Bangalore , India.,d Manipal University , Madhav Nagar, Manipal , India
| | - Raja Sekhar Nirujogi
- a Institute of Bioinformatics, International Technology Park , Bangalore , India.,e Centre of Excellence in Bioinformatics, School of Life Sciences, Pondicherry University , Puducherry , India
| | - Arun H Patil
- a Institute of Bioinformatics, International Technology Park , Bangalore , India.,f School of Biotechnology, KIIT University , Bhubaneswar , India
| | - Hitendra Solanki
- a Institute of Bioinformatics, International Technology Park , Bangalore , India.,f School of Biotechnology, KIIT University , Bhubaneswar , India
| | - Santosh Renuse
- a Institute of Bioinformatics, International Technology Park , Bangalore , India.,c Amrita School of Biotechnology, Amrita University , Kollam , India
| | | | - Premendu P Mathur
- b Department of Biochemistry and Molecular Biology , Pondicherry University , Puducherry , India.,f School of Biotechnology, KIIT University , Bhubaneswar , India
| | - T S Keshava Prasad
- a Institute of Bioinformatics, International Technology Park , Bangalore , India.,c Amrita School of Biotechnology, Amrita University , Kollam , India.,e Centre of Excellence in Bioinformatics, School of Life Sciences, Pondicherry University , Puducherry , India.,g YU-IOB Center for Systems Biology and Molecular Medicine, Yenepoya University , Mangalore , India
| | - Prashant Kumar
- a Institute of Bioinformatics, International Technology Park , Bangalore , India
| | - Joseph A Califano
- h Milton J Dance Head and Neck Center, Greater Baltimore Medical Center , Baltimore , MD , USA.,i Department of Otolaryngology-Head and Neck Surgery , Johns Hopkins University School of Medicine , Baltimore , MD , USA
| | - David Sidransky
- i Department of Otolaryngology-Head and Neck Surgery , Johns Hopkins University School of Medicine , Baltimore , MD , USA
| | - Akhilesh Pandey
- j McKusick-Nathans Institute of Genetic Medicine , Baltimore , MD , USA.,k Departments of Biological Chemistry , Baltimore , MD , USA.,l Oncology and Pathology, Johns Hopkins University School of Medicine , Baltimore , MD , USA.,m Pathology, Johns Hopkins University School of Medicine , Baltimore , MD , USA
| | - Harsha Gowda
- a Institute of Bioinformatics, International Technology Park , Bangalore , India.,g YU-IOB Center for Systems Biology and Molecular Medicine, Yenepoya University , Mangalore , India
| | - Aditi Chatterjee
- a Institute of Bioinformatics, International Technology Park , Bangalore , India.,g YU-IOB Center for Systems Biology and Molecular Medicine, Yenepoya University , Mangalore , India
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Post-Translational Modifications and RNA-Binding Proteins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 907:297-317. [PMID: 27256391 DOI: 10.1007/978-3-319-29073-7_12] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
RNA-binding proteins affect cellular metabolic programs through development and in response to cellular stimuli. Though much work has been done to elucidate the roles of a handful of RNA-binding proteins and their effect on RNA metabolism, the progress of studies to understand the effects of post-translational modifications of this class of proteins is far from complete. This chapter summarizes the work that has been done to identify the consequence of post-translational modifications to some RNA-binding proteins. The effects of these modifications have been shown to increase the panoply of functions that a given RNA-binding protein can assume. We will survey the experimental methods that are used to identify the presence of several protein modifications and methods that attempt to discern the consequence of these modifications.
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Nuclear protein kinase CLK1 uses a non-traditional docking mechanism to select physiological substrates. Biochem J 2015; 472:329-38. [PMID: 26443864 DOI: 10.1042/bj20150903] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Accepted: 10/06/2015] [Indexed: 01/22/2023]
Abstract
Phosphorylation-dependent cell communication requires enzymes that specifically recognize key proteins in a sea of similar, competing substrates. The protein kinases achieve this goal by utilizing docking grooves in the kinase domain or heterologous protein adaptors to reduce 'off pathway' targeting. We now provide evidence that the nuclear protein kinase CLK1 (cell division cycle2-like kinase 1) important for splicing regulation departs from these classic paradigms by using a novel self-association mechanism. The disordered N-terminus of CLK1 induces oligomerization, a necessary event for targeting its physiological substrates the SR protein (splicing factor containing a C-terminal RS domain) family of splicing factors. Increasing the CLK1 concentration enhances phosphorylation of the splicing regulator SRSF1 (SR protein splicing factor 1) compared with the general substrate myelin basic protein (MBP). In contrast, removal of the N-terminus or dilution of CLK1 induces monomer formation and reverses this specificity. CLK1 self-association also occurs in the nucleus, is induced by the N-terminus and is important for localization of the kinase in sub-nuclear compartments known as speckles. These findings present a new picture of substrate recognition for a protein kinase in which an intrinsically disordered domain is used to capture physiological targets with similar disordered domains in a large oligomeric complex while discriminating against non-physiological targets.
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65
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Lu YY, Xu W, Ji J, Feng D, Sourbier C, Yang Y, Qu J, Zeng Z, Wang C, Chang X, Chen Y, Mishra A, Xu M, Lee MJ, Lee S, Trepel J, Linehan WM, Wang XW, Yang Y, Neckers L. Alternative splicing of the cell fate determinant Numb in hepatocellular carcinoma. Hepatology 2015; 62:1122-31. [PMID: 26058814 PMCID: PMC4589429 DOI: 10.1002/hep.27923] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/02/2014] [Accepted: 06/01/2015] [Indexed: 12/30/2022]
Abstract
UNLABELLED The cell fate determinant Numb is aberrantly expressed in cancer. Numb is alternatively spliced, with one isoform containing a long proline-rich region (PRR(L) ) compared to the other with a short PRR (PRR(S) ). Recently, PRR(L) was reported to enhance proliferation of breast and lung cancer cells. However, the importance of Numb alternative splicing in hepatocellular carcinoma (HCC) remains unexplored. We report here that Numb PRR(L) expression is increased in HCC and associated with early recurrence and reduced overall survival after surgery. In a panel of HCC cell lines, PRR(L) generally promotes and PRR(S) suppresses proliferation, migration, invasion, and colony formation. Knockdown of PRR(S) leads to increased Akt phosphorylation and c-Myc expression, and Akt inhibition or c-Myc silencing dampens the proliferative impact of Numb PRR(S) knockdown. In the cell models explored in this study, alternative splicing of Numb PRR isoforms is coordinately regulated by the splicing factor RNA-binding Fox domain containing 2 (RbFox2) and the kinase serine/arginine protein-specific kinase 2 (SRPK2). Knockdown of the former causes accumulation of PRR(L) , while SRPK2 knockdown causes accumulation of PRR(S) . The subcellular location of SRPK2 is regulated by the molecular chaperone heat shock protein 90, and heat shock protein 90 inhibition or knockdown phenocopies SRPK2 knockdown in promoting accumulation of Numb PRR(S) . Finally, HCC cell lines that predominantly express PRR(L) are differentially sensitive to heat shock protein 90 inhibition. CONCLUSION Alternative splicing of Numb may provide a useful prognostic biomarker in HCC and is pharmacologically tractable.
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Affiliation(s)
- Yin Ying Lu
- Center for Therapeutic Research of Hepatocarcinoma, Beijing 302 Hospital, 100 Xi Si Huan Middle Road, Beijing 100039, China
- Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD, 20892
| | - Wanping Xu
- Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD, 20892
| | - Junfang Ji
- Liver Carcinogenesis Section, Laboratory of Human Carcinogenesis, Center for Cancer Research, National Cancer Institute, Bethesda, MD, 20892
| | - Dechun Feng
- Laboratory of Liver Diseases, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD, 20892
| | - Carole Sourbier
- Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD, 20892
| | - Youfeng Yang
- Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD, 20892
| | - Jianhui Qu
- Center for Therapeutic Research of Hepatocarcinoma, Beijing 302 Hospital, 100 Xi Si Huan Middle Road, Beijing 100039, China
| | - Zhen Zeng
- Center for Therapeutic Research of Hepatocarcinoma, Beijing 302 Hospital, 100 Xi Si Huan Middle Road, Beijing 100039, China
| | - Chunping Wang
- Center for Therapeutic Research of Hepatocarcinoma, Beijing 302 Hospital, 100 Xi Si Huan Middle Road, Beijing 100039, China
| | - Xiujuan Chang
- Center for Therapeutic Research of Hepatocarcinoma, Beijing 302 Hospital, 100 Xi Si Huan Middle Road, Beijing 100039, China
| | - Yan Chen
- Center for Therapeutic Research of Hepatocarcinoma, Beijing 302 Hospital, 100 Xi Si Huan Middle Road, Beijing 100039, China
| | - Alok Mishra
- Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD, 20892
| | - Max Xu
- Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD, 20892
| | - Min-Jung Lee
- Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892
| | - Sunmin Lee
- Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892
| | - Jane Trepel
- Developmental Therapeutics Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892
| | - W. Marston Linehan
- Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD, 20892
| | - Xin Wei Wang
- Liver Carcinogenesis Section, Laboratory of Human Carcinogenesis, Center for Cancer Research, National Cancer Institute, Bethesda, MD, 20892
| | - Yongping Yang
- Center for Therapeutic Research of Hepatocarcinoma, Beijing 302 Hospital, 100 Xi Si Huan Middle Road, Beijing 100039, China
| | - Len Neckers
- Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD, 20892
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Nirujogi RS, Wright JD, Manda SS, Zhong J, Na CH, Meyerhoff J, Benton B, Jabbour R, Willis K, Kim MS, Pandey A, Sekowski JW. Phosphoproteomic analysis reveals compensatory effects in the piriform cortex of VX nerve agent exposed rats. Proteomics 2015; 15:487-99. [PMID: 25403869 DOI: 10.1002/pmic.201400371] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Revised: 10/01/2014] [Accepted: 11/12/2014] [Indexed: 01/15/2023]
Abstract
To gain insights into the toxicity induced by the nerve agent VX, an MS-based phosphoproteomic analysis was carried out on the piriform cortex region of brains from VX-treated rats. Using isobaric tag based TMT labeling followed by titanium dioxide enrichment strategy, we identified 9975 unique phosphosites derived from 3287 phosphoproteins. Temporal changes in the phosphorylation status of peptides were observed over a time period of 24 h in rats exposed to a 1× LD50, intravenous (i.v.) dose with the most notable changes occurring at the 1 h postexposure time point. Five major functional classes of proteins exhibited changes in their phosphorylation status: (i) ion channels/transporters, including ATPases, (ii) kinases/phosphatases, (iii) GTPases, (iv) structural proteins, and (v) transcriptional regulatory proteins. This study is the first quantitative phosphoproteomic analysis of VX toxicity in the brain. Understanding the toxicity and compensatory signaling mechanisms will improve the understanding of the complex toxicity of VX in the brain and aid in the elucidation of novel molecular targets that would be important for development of improved countermeasures. All MS data have been deposited in the ProteomeXchange with identifier PXD001184 (http://proteomecentral.proteomexchange.org/dataset/PXD001184).
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Affiliation(s)
- Raja Sekhar Nirujogi
- Institute of Bioinformatics, International Tech Park, Bangalore, India; School of Life Sciences, Centre for Bioinformatics, Pondicherry University, Puducherry, India; Department of Neuroscience, School of Medicine, Johns Hopkins University, Baltimore, MD, USA
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67
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Siebert M, Böhme MA, Driller JH, Babikir H, Mampell MM, Rey U, Ramesh N, Matkovic T, Holton N, Reddy-Alla S, Göttfert F, Kamin D, Quentin C, Klinedinst S, Andlauer TF, Hell SW, Collins CA, Wahl MC, Loll B, Sigrist SJ. A high affinity RIM-binding protein/Aplip1 interaction prevents the formation of ectopic axonal active zones. eLife 2015; 4. [PMID: 26274777 PMCID: PMC4536467 DOI: 10.7554/elife.06935] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2015] [Accepted: 07/24/2015] [Indexed: 12/17/2022] Open
Abstract
Synaptic vesicles (SVs) fuse at active zones (AZs) covered by a protein scaffold, at Drosophila synapses comprised of ELKS family member Bruchpilot (BRP) and RIM-binding protein (RBP). We here demonstrate axonal co-transport of BRP and RBP using intravital live imaging, with both proteins co-accumulating in axonal aggregates of several transport mutants. RBP, via its C-terminal Src-homology 3 (SH3) domains, binds Aplip1/JIP1, a transport adaptor involved in kinesin-dependent SV transport. We show in atomic detail that RBP C-terminal SH3 domains bind a proline-rich (PxxP) motif of Aplip1/JIP1 with submicromolar affinity. Pointmutating this PxxP motif provoked formation of ectopic AZ-like structures at axonal membranes. Direct interactions between AZ proteins and transport adaptors seem to provide complex avidity and shield synaptic interaction surfaces of pre-assembled scaffold protein transport complexes, thus, favouring physiological synaptic AZ assembly over premature assembly at axonal membranes. DOI:http://dx.doi.org/10.7554/eLife.06935.001 To pass on information, the neurons that make up the nervous system connect at structures known as synapses. Chemical messengers called neurotransmitters are released from one neuron, and travel across the synapse to trigger a response in the neighbouring cell. The formation of new synapses plays an important role in learning and memory, but many aspects of this process are not well understood. In a specific region of the synapse called the active zone, a scaffold of proteins helps to release the neurotransmitters. These proteins are made in the cell body of the neuron, and are then transported to the end of the long, thin axons that protrude from the cell body. This presents a challenge for the cell, because the components of the active zone scaffold must be correctly targeted to the synapse at the end of the axon, ensuring the active zone scaffold assembles only at its proper location. Siebert, Böhme et al. studied how some of the proteins that are found in the active zone scaffold of the fruit fly Drosophila are transported along axons. Labelling the proteins with fluorescent markers allowed their movement to be examined under a microscope in living Drosophila larvae. The results showed that two of the proteins—known as BRP and RBP—are transported along the axons together. Further investigation revealed that a transport adaptor protein called Aplip1, which binds to RBP, is required for this movement. Siebert, Böhme et al. established the structure of the part of RBP where this interaction occurs, and found that mutating this region causes premature active zone scaffold assembly in the axonal part of the neuron. The interaction between RBP and Aplip1 is very strong, and this helps to prevent the scaffold assembling before it has reached the correct part of the neuron. Exactly how the transport adaptor and active zone protein are separated once they reach their final destination (the synapse) remains to be discovered. DOI:http://dx.doi.org/10.7554/eLife.06935.002
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Affiliation(s)
- Matthias Siebert
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
| | - Mathias A Böhme
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
| | - Jan H Driller
- Institute of Chemistry and Biochemisty/Structural Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Husam Babikir
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
| | - Malou M Mampell
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
| | - Ulises Rey
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
| | - Niraja Ramesh
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
| | - Tanja Matkovic
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
| | - Nicole Holton
- Institute of Chemistry and Biochemisty/Structural Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Suneel Reddy-Alla
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
| | - Fabian Göttfert
- Department of Nanobiophotonics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Dirk Kamin
- Department of Nanobiophotonics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Christine Quentin
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
| | - Susan Klinedinst
- Department of Molecular Cellular and Developmental Biology, University of Michigan, Ann Arbor, United States
| | - Till Fm Andlauer
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
| | - Stefan W Hell
- Department of Nanobiophotonics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Catherine A Collins
- Department of Molecular Cellular and Developmental Biology, University of Michigan, Ann Arbor, United States
| | - Markus C Wahl
- Institute of Chemistry and Biochemisty/Structural Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Bernhard Loll
- Institute of Chemistry and Biochemisty/Structural Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Stephan J Sigrist
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
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Potential Antileukemia Effect and Structural Analyses of SRPK Inhibition by N-(2-(Piperidin-1-yl)-5-(Trifluoromethyl)Phenyl)Isonicotinamide (SRPIN340). PLoS One 2015; 10:e0134882. [PMID: 26244849 PMCID: PMC4526641 DOI: 10.1371/journal.pone.0134882] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2015] [Accepted: 07/14/2015] [Indexed: 12/20/2022] Open
Abstract
Dysregulation of pre-mRNA splicing machinery activity has been related to the biogenesis of several diseases. The serine/arginine-rich protein kinase family (SRPKs) plays a critical role in regulating pre-mRNA splicing events through the extensive phosphorylation of splicing factors from the family of serine/arginine-rich proteins (SR proteins). Previous investigations have described the overexpression of SRPK1 and SRPK2 in leukemia and other cancer types, suggesting that they would be useful targets for developing novel antitumor strategies. Herein, we evaluated the effect of selective pharmacological SRPK inhibition by N-(2-(piperidin-1-yl)-5-(trifluoromethyl)phenyl)isonicotinamide (SRPIN340) on the viability of lymphoid and myeloid leukemia cell lines. Along with significant cytotoxic activity, the effect of treatments in regulating the phosphorylation of the SR protein family and in altering the expression of MAP2K1, MAP2K2, VEGF and FAS genes were also assessed. Furthermore, we found that pharmacological inhibition of SRPKs can trigger early and late events of apoptosis. Finally, intrinsic tryptophan fluorescence emission, molecular docking and molecular dynamics were analyzed to gain structural information on the SRPK/SRPIN340 complex. These data suggest that SRPK pharmacological inhibition should be considered as an alternative therapeutic strategy for fighting leukemias. Moreover, the obtained SRPK-ligand interaction data provide useful structural information to guide further medicinal chemistry efforts towards the development of novel drug candidates.
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69
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Splicing Regulators and Their Roles in Cancer Biology and Therapy. BIOMED RESEARCH INTERNATIONAL 2015; 2015:150514. [PMID: 26273588 PMCID: PMC4529883 DOI: 10.1155/2015/150514] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Revised: 03/10/2015] [Accepted: 04/01/2015] [Indexed: 12/17/2022]
Abstract
Alternative splicing allows cells to expand the encoding potential of their genomes. In this elegant mechanism, a single gene can yield protein isoforms with even antagonistic functions depending on the cellular physiological context. Alterations in splicing regulatory factors activity in cancer cells, however, can generate an abnormal protein expression pattern that promotes growth, survival, and other processes, which are relevant to tumor biology. In this review, we discuss dysregulated alternative splicing events and regulatory factors that impact pathways related to cancer. The SR proteins and their regulatory kinases SRPKs and CLKs have been frequently found altered in tumors and are examined in more detail. Finally, perspectives that support splicing machinery as target for the development of novel anticancer therapies are discussed.
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Corkery DP, Holly AC, Lahsaee S, Dellaire G. Connecting the speckles: Splicing kinases and their role in tumorigenesis and treatment response. Nucleus 2015; 6:279-88. [PMID: 26098145 PMCID: PMC4615201 DOI: 10.1080/19491034.2015.1062194] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Alternative pre-mRNA splicing in higher eukaryotes enhances transcriptome complexity and proteome diversity. Its regulation is mediated by a complex RNA-protein network that is essential for the maintenance of cellular and tissue homeostasis. Disruptions to this regulatory network underlie a host of human diseases and contribute to cancer development and progression. The splicing kinases are an important family of pre-mRNA splicing regulators, , which includes the CDC-like kinases (CLKs), the SRSF protein kinases (SRPKs) and pre-mRNA splicing 4 kinase (PRP4K/PRPF4B). These splicing kinases regulate pre-mRNA splicing via phosphorylation of spliceosomal components and serine-arginine (SR) proteins, affecting both their nuclear localization within nuclear speckle domains as well as their nucleo-cytoplasmic shuttling. Here we summarize the emerging evidence that splicing kinases are dysregulated in cancer and play important roles in both tumorigenesis as well as therapeutic response to radiation and chemotherapy.
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Affiliation(s)
- Dale P Corkery
- a Department of Biochemistry & Molecular Biology ; Dalhousie University ; Halifax , Nova Scotia , Canada
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Nancy MM, Nora RM, Rebeca MC. Peptidic tools applied to redirect alternative splicing events. Peptides 2015; 67:1-11. [PMID: 25748022 DOI: 10.1016/j.peptides.2015.02.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/14/2014] [Revised: 02/05/2015] [Accepted: 02/26/2015] [Indexed: 01/25/2023]
Abstract
Peptides are versatile and attractive biomolecules that can be applied to modulate genetic mechanisms like alternative splicing. In this process, a single transcript yields different mature RNAs leading to the production of protein isoforms with diverse or even antagonistic functions. During splicing events, errors can be caused either by mutations present in the genome or by defects or imbalances in regulatory protein factors. In any case, defects in alternative splicing have been related to several genetic diseases including muscular dystrophy, Alzheimer's disease and cancer from almost every origin. One of the most effective approaches to redirect alternative splicing events has been to attach cell-penetrating peptides to oligonucleotides that can modulate a single splicing event and restore correct gene expression. Here, we summarize how natural existing and bioengineered peptides have been applied over the last few years to regulate alternative splicing and genetic expression. Under different genetic and cellular backgrounds, peptides have been shown to function as potent vehicles for splice correction, and their therapeutic benefits have reached clinical trials and patenting stages, emphasizing the use of regulatory peptides as an exciting therapeutic tool for the treatment of different genetic diseases.
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Affiliation(s)
- Martínez-Montiel Nancy
- Laboratorio de Ecología Molecular Microbiana, Centro de Investigaciones en Ciencias Microbiológicas, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Mexico
| | - Rosas-Murrieta Nora
- Laboratorio de Bioquímica y Biología Molecular, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Mexico
| | - Martínez-Contreras Rebeca
- Laboratorio de Ecología Molecular Microbiana, Centro de Investigaciones en Ciencias Microbiológicas, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Mexico.
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Induced transcription and stability of CELF2 mRNA drives widespread alternative splicing during T-cell signaling. Proc Natl Acad Sci U S A 2015; 112:E2139-48. [PMID: 25870297 DOI: 10.1073/pnas.1423695112] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Studies in several cell types have highlighted dramatic and diverse changes in mRNA processing that occur upon cellular stimulation. However, the mechanisms and pathways that lead to regulated changes in mRNA processing remain poorly understood. Here we demonstrate that expression of the splicing factor CELF2 (CUGBP, Elav-like family member 2) is regulated in response to T-cell signaling through combined increases in transcription and mRNA stability. Transcriptional induction occurs within 6 h of stimulation and is dependent on activation of NF-κB. Subsequently, there is an increase in the stability of the CELF2 mRNA that correlates with a change in CELF2 3'UTR length and contributes to the total signal-induced enhancement of CELF2 expression. Importantly, we uncover dozens of splicing events in cultured T cells whose changes upon stimulation are dependent on CELF2 expression, and provide evidence that CELF2 controls a similar proportion of splicing events during human thymic T-cell development. Taken together, these findings expand the physiologic impact of CELF2 beyond that previously documented in developing neuronal and muscle cells to T-cell development and function, identify unappreciated instances of alternative splicing in the human thymus, and uncover novel mechanisms for CELF2 regulation that may broadly impact CELF2 expression across diverse cell types.
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Chang Y, Wu Q, Tian T, Li L, Guo X, Feng Z, Zhou J, Zhang L, Zhou S, Feng G, Han F, Yang J, Huang F. The influence of SRPK1 on glioma apoptosis, metastasis, and angiogenesis through the PI3K/Akt signaling pathway under normoxia. Tumour Biol 2015; 36:6083-93. [PMID: 25833691 DOI: 10.1007/s13277-015-3289-2] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Accepted: 02/24/2015] [Indexed: 01/15/2023] Open
Abstract
Gliomas, the most common primary brain tumors, have low survival rates and poorly defined molecular mechanisms to target for treatment. Serine/arginine SR protein kinases 1 (SRPK1) can highly and specifically phosphorylate the SR protein found in many tumors, which can influence cell proliferation and angiogenesis. However, the roles and regulatory mechanisms of SRPK1 in gliomas are not understood. The aim of this study was to determine the functions and regulation of SRPK1 in gliomas. We found that SRPK1 inhibition induces early apoptosis and significantly inhibits xenograft tumor growth. Our results indicate that SRPK1 affects Akt and eIF4E phosphorylation, Bax and Bcl-2 activation, and HIF-1 and VEGF production in glioma cells. Moreover, transfection of SRPK1 siRNA strongly reduced cell invasion and migration by regulating the expression of MMP2 and MMP9 and significantly decreased the volume of tumors and angiogenesis. We show here that a strong link exists among SRPK1, Akt, eIF4E, HIF-1, and VEGF activity that is functionally involved in apoptosis, metastasis, and angiogenesis of gliomas under normoxic conditions. Thus, SRPK1 may be a potential anticancer target to inhibit glioma progression.
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Affiliation(s)
- Yingwei Chang
- Institute of Human Anatomy and Histology and Embryology, Otology & Neuroscience Center, Binzhou Medical University, 346 Guanhai Road, Laishan District, Shandong Province, 264003, China
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74
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Saal L, Briese M, Kneitz S, Glinka M, Sendtner M. Subcellular transcriptome alterations in a cell culture model of spinal muscular atrophy point to widespread defects in axonal growth and presynaptic differentiation. RNA (NEW YORK, N.Y.) 2014; 20:1789-802. [PMID: 25246652 PMCID: PMC4201830 DOI: 10.1261/rna.047373.114] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2014] [Accepted: 08/22/2014] [Indexed: 05/19/2023]
Abstract
Neuronal function critically depends on coordinated subcellular distribution of mRNAs. Disturbed mRNA processing and axonal transport has been found in spinal muscular atrophy and could be causative for dysfunction and degeneration of motoneurons. Despite the advances made in characterizing the transport mechanisms of several axonal mRNAs, an unbiased approach to identify the axonal repertoire of mRNAs in healthy and degenerating motoneurons has been lacking. Here we used compartmentalized microfluidic chambers to investigate the somatodendritic and axonal mRNA content of cultured motoneurons by microarray analysis. In axons, transcripts related to protein synthesis and energy production were enriched relative to the somatodendritic compartment. Knockdown of Smn, the protein deficient in spinal muscular atrophy, produced a large number of transcript alterations in both compartments. Transcripts related to immune functions, including MHC class I genes, and with roles in RNA splicing were up-regulated in the somatodendritic compartment. On the axonal side, transcripts associated with axon growth and synaptic activity were down-regulated. These alterations provide evidence that subcellular localization of transcripts with axonal functions as well as regulation of specific transcripts with nonautonomous functions is disturbed in Smn-deficient motoneurons, most likely contributing to the pathophysiology of spinal muscular atrophy.
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Affiliation(s)
- Lena Saal
- Institute for Clinical Neurobiology, University of Wuerzburg, D 97078 Wuerzburg, Germany
| | - Michael Briese
- Institute for Clinical Neurobiology, University of Wuerzburg, D 97078 Wuerzburg, Germany
| | - Susanne Kneitz
- Department of Physiological Chemistry I, Biocenter, University of Wuerzburg, D 97074 Wuerzburg, Germany
| | - Michael Glinka
- Institute for Clinical Neurobiology, University of Wuerzburg, D 97078 Wuerzburg, Germany
| | - Michael Sendtner
- Institute for Clinical Neurobiology, University of Wuerzburg, D 97078 Wuerzburg, Germany
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75
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Primary structural features of SR-like protein acinusS govern the phosphorylation mechanism by SRPK2. Biochem J 2014; 459:181-91. [PMID: 24444330 DOI: 10.1042/bj20131091] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
SRPKs (serine/arginine protein kinases) are highly specific kinases that recognize and phosphorylate RS (Arg-Ser) dipeptide repeats. It has been shown previously that SRPK1 phosphorylates the RS domain of SRSF1 (serine/arginine splicing factor 1) at multiple sites using a directional and processive mechanism. Such ability to processively phosphorylate substrates is proposed to be an inherent characteristic of SRPKs. SRPK2 is highly related to SRPK1 in sequence and in vitro properties, yet it has been shown to have distinct substrate specificity and physiological function in vivo. To study the molecular basis for substrate specificity of SRPK2, we investigated the roles of the non-kinase regions and a conserved docking groove of SRPK2 in the recognition and phosphorylation of different substrates: SRSF1 and acinusS. Our results reveal that a conserved electronegative docking groove in SRPK2, but not its non-kinase regions, is responsible for substrate binding regardless of their identities. Although SRPK2 phosphorylates SRSF1 in a processive manner as predicted, an electronegative region on acinusS restricts SRPK2 phosphorylation to a single specific site despite the presence of multiple RS dipeptides. These results suggest that primary structural elements on the substrates serve as key regulatory roles in determining the phosphorylation mechanism of SRPK2.
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76
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Both decreased and increased SRPK1 levels promote cancer by interfering with PHLPP-mediated dephosphorylation of Akt. Mol Cell 2014; 54:378-91. [PMID: 24703948 DOI: 10.1016/j.molcel.2014.03.007] [Citation(s) in RCA: 96] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Revised: 01/24/2014] [Accepted: 02/27/2014] [Indexed: 01/07/2023]
Abstract
Akt activation is a hallmark of human cancers. Here, we report a critical mechanism for regulation of Akt activity by the splicing kinase SRPK1, a downstream Akt target for transducing growth signals to regulate splicing. Surprisingly, we find that SRPK1 has a tumor suppressor function because ablation of SRPK1 in mouse embryonic fibroblasts induces cell transformation. We link the phenotype to constitutive Akt activation from genome-wide phosphoproteomics analysis and discover that downregulated SRPK1 impairs the recruitment of the Akt phosphatase PHLPP1 (pleckstrin homology (PH) domain leucine-rich repeat protein phosphatase) to Akt. Interestingly, SRPK1 overexpression is also tumorigenic because excess SRPK1 squelches PHLPP1. Thus, aberrant SRPK1 expression in either direction induces constitutive Akt activation, providing a mechanistic basis for previous observations that SRPK1 is downregulated in some cancer contexts and upregulated in others.
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77
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Structural basis for nuclear import of splicing factors by human Transportin 3. Proc Natl Acad Sci U S A 2014; 111:2728-33. [PMID: 24449914 DOI: 10.1073/pnas.1320755111] [Citation(s) in RCA: 103] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Transportin 3 (Tnpo3, Transportin-SR2) is implicated in nuclear import of splicing factors and HIV-1 replication. Herein, we show that the majority of cellular Tnpo3 binding partners contain arginine-serine (RS) repeat domains and present crystal structures of human Tnpo3 in its free as well as GTPase Ran- and alternative splicing factor/splicing factor 2 (ASF/SF2)-bound forms. The flexible β-karyopherin fold of Tnpo3 embraces the RNA recognition motif and RS domains of the cargo. A constellation of charged residues on and around the arginine-rich helix of Tnpo3 HEAT repeat 15 engage the phosphorylated RS domain and are critical for the recognition and nuclear import of ASF/SF2. Mutations in the same region of Tnpo3 impair its interaction with the cleavage and polyadenylation specificity factor 6 (CPSF6) and its ability to support HIV-1 replication. Steric incompatibility of the RS domain and RanGTP engagement by Tnpo3 provides the mechanism for cargo release in the nucleus. Our results elucidate the structural bases for nuclear import of splicing factors and the Tnpo3-CPSF6 nexus in HIV-1 biology.
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78
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Iqbal K, Liu F, Gong CX. Alzheimer disease therapeutics: focus on the disease and not just plaques and tangles. Biochem Pharmacol 2014; 88:631-9. [PMID: 24418409 DOI: 10.1016/j.bcp.2014.01.002] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Revised: 12/26/2013] [Accepted: 01/02/2014] [Indexed: 12/13/2022]
Abstract
The bulk of AD research during the last 25 years has been Aβ-centric based on a strong faith in the Amyloid Cascade Hypothesis which is not supported by the data on humans. To date, Aβ-based therapeutic clinical trials on sporadic cases of AD have been negative. Although most likely the major reason for the failure is that Aβ is not an effective therapeutic target for sporadic AD, initiation of the treatment at mild to moderate stages of the disease is blamed as too late to be effective. Clinical trials on presymptomatic familial AD cases have been initiated with the logic that Aβ is a trigger of the disease and hence initiation of the Aβ immunotherapies several years before any clinical symptoms would be effective. There is an urgent need to explore targets other than Aβ. There is now increasing interest in inhibiting tau pathology, which does have a far more compelling rationale than Aβ. AD is multifactorial and over 99% of the cases are the sporadic form of the disease. Understanding of the various etiopathogenic mechanisms of sporadic AD and generation of the disease-relevant animal models are required to develop rational therapeutic targets and therapies. Treatment of AD will require both inhibition of neurodegeneration and regeneration of the brain.
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Affiliation(s)
- Khalid Iqbal
- Department of Neurochemistry, Inge Grundke-Iqbal Research Floor, New York State Institute for Basic Research in Developmental Disabilities, 1050 Forest Hill Road, Staten Island, NY 10314, USA.
| | - Fei Liu
- Department of Neurochemistry, Inge Grundke-Iqbal Research Floor, New York State Institute for Basic Research in Developmental Disabilities, 1050 Forest Hill Road, Staten Island, NY 10314, USA
| | - Cheng-Xin Gong
- Department of Neurochemistry, Inge Grundke-Iqbal Research Floor, New York State Institute for Basic Research in Developmental Disabilities, 1050 Forest Hill Road, Staten Island, NY 10314, USA
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79
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Wu Q, Chang Y, Zhang L, Zhang Y, Tian T, Feng G, Zhou S, Zheng Q, Han F, Huang F. SRPK1 Dissimilarly Impacts on the Growth, Metastasis, Chemosensitivity and Angiogenesis of Glioma in Normoxic and Hypoxic Conditions. J Cancer 2013; 4:727-35. [PMID: 24312143 PMCID: PMC3842442 DOI: 10.7150/jca.7576] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Accepted: 10/19/2013] [Indexed: 12/12/2022] Open
Abstract
Glioma is among the ten most common causes of cancer-related death and has no effective treatment for it, so we are trying to find a new target for anticancer treatment. This study investigates the different expression of SRPK1 as a novel protein in glioma, which can influence tumor cells biological characteristics in normoxic and hypoxic environment. The expression levels of SRPK1 protein in glioma cell lines transfected with siSRPK1 or not were examined using immunofluorescence, RT-PCR and Western blot analysis, respectively. The impact of SRPK1 on the biological characteristics of U251 cells was further studied using methylthiazol tetrazolium assays, flow cytometry, and Transwell invasion chamber assays. The results showed that knockdown of SRPK1 inhibited tumor cells growth, invasion and migration in normoxic condition, but portion of the effect could be reversed in hypoxia. SRPK1 expression was induced in glioma cells by DDP treated, but not TMZ, in both normoxia and hypoxia conditions. We propose SRPK1 as a new molecular player contributing to the early treatment of glioma.
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Affiliation(s)
- Qianqian Wu
- Institute of Human Anatomy and Histology and Embryology, Otology & Neuroscience Center, Binzhou Medical University, 346 Guanhai Road, Laishan, Shandong Province, 264003, China
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80
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Nousiainen L, Sillanpää M, Jiang M, Thompson J, Taipale J, Julkunen I. Human kinome analysis reveals novel kinases contributing to virus infection and retinoic-acid inducible gene I-induced type I and type III IFN gene expression. Innate Immun 2013; 19:516-30. [PMID: 23405030 DOI: 10.1177/1753425912473345] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2023] Open
Abstract
Activation of host innate antiviral responses are mediated by retinoic-acid inducible gene I (RIG-I)-like receptors, RIG-I and melanoma differentiation-associated gene 5, and TLRs 3, 7, 8 and 9, recognising different types of viral nucleic acids. The major components of the RIG-I- and TLR pathways have putatively been identified, but previously unrecognised kinases may contribute to virus infection-induced activation of the IFN response. Here, we screened a human kinase cDNA library, termed the kinome, using an IFN-λ1 promoter-driven luciferase reporter assay in HEK293 cells during Sendai virus infection. Of the 568 kinases analysed, nearly 50 enhanced IFN-λ1 gene expression at least twofold in response to Sendai virus infection. The best activators were FYN (FYN oncogene related to SRC, FGR, YES), serine/threonine kinase 24, activin A receptor type 1 and SRPK1 (SFRS protein kinase 1). These kinases enhanced RIG-I-dependent IFN-λ1 promoter activation via IFN-stimulated response and NF-κB elements, as confirmed using mutant IFN-λ1 promoter constructs. FYN and SRPK1 enhanced IFN-λ1 and CXCL10 protein production via the RIG-I pathway, and stimulated RIG-I and MyD88-dependent phosphorylation of IRF3 and IRF7 transcription factors, respectively. We conclude that several previously unrecognised kinases, particularly FYN and SRPK1, positively regulate IFN-λ1 and similarly regulated cytokine and chemokine genes during viral infection.
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Affiliation(s)
- Laura Nousiainen
- 1Department of Infectious Disease Surveillance and Control, National Institute for Health and Welfare (THL), Helsinki, Finland
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81
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Cyclic AMP-dependent protein kinase enhances SC35-promoted Tau exon 10 inclusion. Mol Neurobiol 2013; 49:615-24. [PMID: 24037441 DOI: 10.1007/s12035-013-8542-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Accepted: 08/19/2013] [Indexed: 01/10/2023]
Abstract
Alternative splicing of tau exon 10 generates tau with three or four microtubule-binding repeats (3R-tau or 4R-tau). The ratio of 3R-tau to 4R-tau is approximately 1:1 in the adult normal human brain. Disturbances in the ratio result in neurodegenerative tauopathies. Splicing factor SC35 acts on a SC35-like element located at the 5' end of tau exon 10 and promotes tau exon 10 inclusion. Here, we report that protein kinase (PKA) was able to interact and phosphorylate SC35. Activation or overexpression of PKA catalytic subunits promoted SC35-mediated tau exon 10 inclusion. Four PKA catalytic subunits, α1, α2, β1, and β2, all enhanced SC35-promoted tau exon 10 inclusion. SC35 has four putative PKA phosphorylation sites, Ser121, Ser128, Ser130, and Ser171. Pseudophosphorylation (SC354E) and blockage (SC354A) of phosphorylation of SC35 at these four sites increased and decreased, respectively, SC35's ability to promote tau exon 10 inclusion. Moreover, PKA catalytic subunits no longer further enhanced tau exon 10 inclusion when these four were mutated to either alanine or glutamate. These results suggest that PKA interacts with and phosphorylates SC35 and enhances SC35-promoted tau exon 10 inclusion. In Alzheimer's brain, down-regulation of the PKA pathway could lead to dysregulation of tau exon 10, contributing to tau pathogenesis.
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82
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Li X, Johansson C, Glahder J, Mossberg AK, Schwartz S. Suppression of HPV-16 late L1 5'-splice site SD3632 by binding of hnRNP D proteins and hnRNP A2/B1 to upstream AUAGUA RNA motifs. Nucleic Acids Res 2013; 41:10488-508. [PMID: 24013563 PMCID: PMC3905901 DOI: 10.1093/nar/gkt803] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Human papillomavirus type 16 (HPV-16) 5′-splice site SD3632 is used exclusively to produce late L1 mRNAs. We identified a 34-nt splicing inhibitory element located immediately upstream of HPV-16 late 5′-splice site SD3632. Two AUAGUA motifs located in these 34 nt inhibited SD3632. Two nucleotide substitutions in each of the HPV-16 specific AUAGUA motifs alleviated splicing inhibition and induced late L1 mRNA production from episomal forms of the HPV-16 genome in primary human keratinocytes. The AUAGUA motifs bind specifically not only to the heterogeneous nuclear RNP (hnRNP) D family of RNA-binding proteins including hnRNP D/AUF, hnRNP DL and hnRNP AB but also to hnRNP A2/B1. Knock-down of these proteins induced HPV-16 late L1 mRNA expression, and overexpression of hnRNP A2/B1, hnRNP AB, hnRNP DL and the two hnRNP D isoforms hnRNP D37 and hnRNP D40 further suppressed L1 mRNA expression. This inhibition may allow HPV-16 to hide from the immune system and establish long-term persistent infections with enhanced risk at progressing to cancer. There is an inverse correlation between expression of hnRNP D proteins and hnRNP A2/B1 and HPV-16 L1 production in the cervical epithelium, as well as in cervical cancer, supporting the conclusion that hnRNP D proteins and A2/B1 inhibit HPV-16 L1 mRNA production.
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Affiliation(s)
- Xiaoze Li
- Department of Laboratory Medicine, Section of Medical Microbiology, Lund University, 221 84 Lund, Sweden
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83
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Naro C, Sette C. Phosphorylation-mediated regulation of alternative splicing in cancer. Int J Cell Biol 2013; 2013:151839. [PMID: 24069033 PMCID: PMC3771450 DOI: 10.1155/2013/151839] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Accepted: 07/26/2013] [Indexed: 12/12/2022] Open
Abstract
Alternative splicing (AS) is one of the key processes involved in the regulation of gene expression in eukaryotic cells. AS catalyzes the removal of intronic sequences and the joining of selected exons, thus ensuring the correct processing of the primary transcript into the mature mRNA. The combinatorial nature of AS allows a great expansion of the genome coding potential, as multiple splice-variants encoding for different proteins may arise from a single gene. Splicing is mediated by a large macromolecular complex, the spliceosome, whose activity needs a fine regulation exerted by cis-acting RNA sequence elements and trans-acting RNA binding proteins (RBP). The activity of both core spliceosomal components and accessory splicing factors is modulated by their reversible phosphorylation. The kinases and phosphatases involved in these posttranslational modifications significantly contribute to AS regulation and to its integration in the complex regulative network that controls gene expression in eukaryotic cells. Herein, we will review the major canonical and noncanonical splicing factor kinases and phosphatases, focusing on those whose activity has been implicated in the aberrant splicing events that characterize neoplastic transformation.
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Affiliation(s)
- Chiara Naro
- Department of Biomedicine and Prevention, University of Rome “Tor Vergata”, 00133 Rome, Italy
- Laboratories of Neuroembryology and of Cellular and Molecular Neurobiology, Fondazione Santa Lucia IRCCS, 00143 Rome, Italy
| | - Claudio Sette
- Department of Biomedicine and Prevention, University of Rome “Tor Vergata”, 00133 Rome, Italy
- Laboratories of Neuroembryology and of Cellular and Molecular Neurobiology, Fondazione Santa Lucia IRCCS, 00143 Rome, Italy
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84
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Alternatively spliced tissue factor promotes breast cancer growth in a β1 integrin-dependent manner. Proc Natl Acad Sci U S A 2013; 110:11517-22. [PMID: 23801760 DOI: 10.1073/pnas.1307100110] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Full-length tissue factor (flTF), the coagulation initiator, is overexpressed in breast cancer (BrCa), but associations between flTF expression and clinical outcome remain controversial. It is currently not known whether the soluble alternatively spliced TF form (asTF) is expressed in BrCa or impacts BrCa progression. We are unique in reporting that asTF, but not flTF, strongly associates with both tumor size and grade, and induces BrCa cell proliferation by binding to β1 integrins. asTF promotes oncogenic gene expression, anchorage-independent growth, and strongly up-regulates tumor expansion in a luminal BrCa model. In basal BrCa cells that constitutively express both TF isoforms, asTF blockade reduces tumor growth and proliferation in vivo. We propose that asTF plays a major role in BrCa progression acting as an autocrine factor that promotes tumor progression. Targeting asTF may comprise a previously unexplored therapeutic strategy in BrCa that stems tumor growth, yet does not impair normal hemostasis.
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85
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Paraquat modulates alternative pre-mRNA splicing by modifying the intracellular distribution of SRPK2. PLoS One 2013; 8:e61980. [PMID: 23613995 PMCID: PMC3628584 DOI: 10.1371/journal.pone.0061980] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Accepted: 03/16/2013] [Indexed: 11/24/2022] Open
Abstract
Paraquat (PQ) is a neurotoxic herbicide that induces superoxide formation. Although it is known that its toxic properties are linked to ROS production, the cellular response to PQ is still poorly understood. We reported previously that treatment with PQ induced genome-wide changes in pre-mRNA splicing. Here, we investigated the molecular mechanism underlying PQ-induced pre-mRNA splicing alterations. We show that PQ treatment leads to the phosphorylation and nuclear accumulation of SRPK2, a member of the family of serine/arginine (SR) protein-specific kinases. Concomitantly, we observed increased phosphorylation of SR proteins. Site-specific mutagenesis identified a single serine residue that is necessary and sufficient for nuclear localization of SRPK2. Transfection of a phosphomimetic mutant modified splice site selection of the E1A minigene splicing reporter similar to PQ-treatment. Finally, we found that PQ induces DNA damage and vice versa that genotoxic treatments are also able to promote SRPK2 phosphorylation and nuclear localization. Consistent with these observations, treatment with PQ, cisplatin or γ-radiation promote changes in the splicing pattern of genes involved in DNA repair, cell cycle control, and apoptosis. Altogether, our findings reveal a novel regulatory mechanism that connects PQ to the DNA damage response and to the modulation of alternative splicing via SRPK2 phosphorylation.
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86
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Regulation of splicing by SR proteins and SR protein-specific kinases. Chromosoma 2013; 122:191-207. [PMID: 23525660 DOI: 10.1007/s00412-013-0407-z] [Citation(s) in RCA: 320] [Impact Index Per Article: 29.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2013] [Revised: 03/04/2013] [Accepted: 03/06/2013] [Indexed: 12/21/2022]
Abstract
Genomic sequencing reveals similar but limited numbers of protein-coding genes in different genomes, which begs the question of how organismal diversities are generated. Alternative pre-mRNA splicing, a widespread phenomenon in higher eukaryotic genomes, is thought to provide a mechanism to increase the complexity of the proteome and introduce additional layers for regulating gene expression in different cell types and during development. Among a large number of factors implicated in the splicing regulation are the SR protein family of splicing factors and SR protein-specific kinases. Here, we summarize the rules for SR proteins to function as splicing regulators, which depend on where they bind in exons versus intronic regions, on alternative exons versus flanking competing exons, and on cooperative as well as competitive binding between different SR protein family members on many of those locations. We review the importance of cycles of SR protein phosphorylation/dephosphorylation in the splicing reaction with emphasis on the recent molecular insight into the role of SR protein phosphorylation in early steps of spliceosome assembly. Finally, we highlight recent discoveries of SR protein-specific kinases in transducing growth signals to regulate alternative splicing in the nucleus and the connection of both SR proteins and SR protein kinases to human diseases, particularly cancer.
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87
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Abstract
Serine-arginine protein kinases 2 (SRPK2) is a cell cycle-regulated kinase that phosphorylates serine/arginine domain-containing proteins and mediates pre-mRNA splicing with unclear function in neurons. Here, we show that SRPK2 phosphorylates tau on S214, suppresses tau-dependent microtubule polymerization, and inhibits axonal elongation in neurons. Depletion of SRPK2 in dentate gyrus inhibits tau phosphorylation in APP/PS1 mouse and alleviates the impaired cognitive behaviors. The defective LTP in APP/PS1 mice is also improved after SRPK2 depletion. Moreover, active SRPK2 is increased in the cortex of APP/PS1 mice and the pathological structures of human Alzheimer's disease (AD) brain. Therefore, our study suggests SRPK2 may contribute to the formation of hyperphosphorylated tau and the pathogenesis of AD.
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88
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Li SJ, Qi Y, Zhao JJ, Li Y, Liu XY, Chen XH, Xu P. Characterization of nuclear localization signals (NLSs) and function of NLSs and phosphorylation of serine residues in subcellular and subnuclear localization of transformer-2β (Tra2β). J Biol Chem 2013; 288:8898-909. [PMID: 23396973 DOI: 10.1074/jbc.m113.456715] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The serine/arginine-rich (SR) proteins are one type of major actors in regulation of pre-mRNA splicing. Their functions are closely related to the intracellular spatial organization. The RS domain and phosphorylation status of SR proteins are two critical factors in determining the subcellular distribution. Mammalian Transformer-2β (Tra2β) protein, a member of SR proteins, is known to play multiple important roles in development and diseases. In the present study, we characterized the subcellular and subnuclear localization of Tra2β protein and its related mechanisms. The results demonstrated that in the brain the nuclear and cytoplasmic localization of Tra2β were correlated with its phosphorylation status. Using deletional mutation analysis, we showed that the nuclear localization of Tra2β was determined by multiple nuclear localization signals (NLSs) in the RS domains. The point-mutation analysis disclosed that phosphorylation of serine residues in the NLSs inhibited the function of NLS in directing Tra2β to the nucleus. In addition, we identified at least two nuclear speckle localization signals within the RS1 domain, but not in the RS2 domain. The nuclear speckle localization signals determined the localization of RS1 domain-contained proteins to the nuclear speckle. The function of the signals did not depend on the presence of serine residues. The results provide new insight into the mechanisms by which the subcellular and subnuclear localization of Tra2β proteins are regulated.
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Affiliation(s)
- Shu-Jing Li
- Laboratory of Genomic Physiology, State Key Laboratory of Medical Neurobiology, Institutes of Brain Science, School of Basic Medical Sciences, Shanghai Medical College, Fudan University, Shanghai, 200032 China
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89
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SRPK1 inhibition in vivo: modulation of VEGF splicing and potential treatment for multiple diseases. Biochem Soc Trans 2012; 40:831-5. [PMID: 22817743 DOI: 10.1042/bst20120051] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
SRPK1 (serine-arginine protein kinase 1) is a protein kinase that specifically phosphorylates proteins containing serine-arginine-rich domains. Its substrates include a family of SR proteins that are key regulators of mRNA AS (alternative splicing). VEGF (vascular endothelial growth factor), a principal angiogenesis factor contains an alternative 3' splice site in the terminal exon that defines a family of isoforms with a different amino acid sequence at the C-terminal end, resulting in anti-angiogenic activity in the context of VEGF165-driven neovascularization. It has been shown recently in our laboratories that SRPK1 regulates the choice of this splice site through phosphorylation of the splicing factor SRSF1 (serine/arginine-rich splicing factor 1). The present review summarizes progress that has been made to understand how SRPK1 inhibition may be used to manipulate the balance of pro- and anti-angiogenic VEGF isoforms in animal models in vivo and therefore control abnormal angiogenesis and other pathophysiological processes in multiple disease states.
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90
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Abstract
Persistent infection with cancer risk-related viruses leads to molecular, cellular and immune response changes in host organisms that in some cases direct cellular transformation. Alternative splicing is a conserved cellular process that increases the coding complexity of genomes at the pre-mRNA processing stage. Human and other animal tumour viruses use alternative splicing as a process to maximize their transcriptomes and proteomes. Medical therapeutics to clear persistent viral infections are still limited. However, specific lessons learned in some viruses [e.g. HIV and HCV (hepatitis C virus)] suggest that drug-directed inhibition of alternative splicing could be useful for this purpose. The present review describes the basic mechanisms of constitutive and alternative splicing in a cellular context and known splicing patterns and the mechanisms by which these might be achieved for the major human infective tumour viruses. The roles of splicing-related proteins expressed by these viruses in cellular and viral gene regulation are explored. Moreover, we discuss some currently available drugs targeting SR (serine/arginine-rich) proteins that are the main regulators of constitutive and alternative splicing, and their potential use in treatment for so-called persistent viral infections.
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91
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Yin X, Jin N, Gu J, Shi J, Zhou J, Gong CX, Iqbal K, Grundke-Iqbal I, Liu F. Dual-specificity tyrosine phosphorylation-regulated kinase 1A (Dyrk1A) modulates serine/arginine-rich protein 55 (SRp55)-promoted Tau exon 10 inclusion. J Biol Chem 2012; 287:30497-506. [PMID: 22767602 PMCID: PMC3436298 DOI: 10.1074/jbc.m112.355412] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2012] [Revised: 06/10/2012] [Indexed: 11/06/2022] Open
Abstract
Tau exon 10, which encodes the second microtubule-binding repeat, is regulated by alternative splicing. Its alternative splicing generates Tau isoforms with three- or four-microtubule-binding repeats, named 3R-tau and 4R-tau. Adult human brain expresses equal levels of 3R-tau and 4R-tau. Imbalance of 3R-tau and 4R-tau causes Tau aggregation and neurofibrillary degeneration. In the present study, we found that splicing factor SRp55 (serine/arginine-rich protein 55) promoted Tau exon 10 inclusion. Knockdown of SRp55 significantly promoted Tau exon 10 exclusion. The promotion of Tau exon 10 inclusion by SRp55 required the arginine/serine-rich region, which was responsible for the subnucleic speckle localization. Dyrk1A (dual specificity tyrosine-phosphorylated and regulated kinase 1A) interacted with SRp55 and mainly phosphorylated its proline-rich domain. Phosphorylation of SRp55 by Dyrk1A suppressed its ability to promote Tau exon 10 inclusion. Up-regulation of Dyrk1A as in Down syndrome could lead to neurofibrillary degeneration by shifting the alternative splicing of Tau exon 10 to an increase in the ratio of 3R-tau/4R-tau.
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Affiliation(s)
- Xiaomin Yin
- From the Jiangsu Key Laboratory of Neuroregeneration and
- the Department of Biochemistry and Molecular Biology, Medical School, Nantong University, Nantong, Jiangsu, 226001, China and
| | - Nana Jin
- From the Jiangsu Key Laboratory of Neuroregeneration and
| | - Jianlan Gu
- From the Jiangsu Key Laboratory of Neuroregeneration and
- the Department of Biochemistry and Molecular Biology, Medical School, Nantong University, Nantong, Jiangsu, 226001, China and
| | - Jianhua Shi
- From the Jiangsu Key Laboratory of Neuroregeneration and
- the Department of Biochemistry and Molecular Biology, Medical School, Nantong University, Nantong, Jiangsu, 226001, China and
| | - Jianhua Zhou
- From the Jiangsu Key Laboratory of Neuroregeneration and
| | - Cheng-Xin Gong
- From the Jiangsu Key Laboratory of Neuroregeneration and
- the Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, New York 10314
| | - Khalid Iqbal
- the Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, New York 10314
| | - Inge Grundke-Iqbal
- the Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, New York 10314
| | - Fei Liu
- From the Jiangsu Key Laboratory of Neuroregeneration and
- the Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, New York 10314
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92
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The Akt-SRPK-SR axis constitutes a major pathway in transducing EGF signaling to regulate alternative splicing in the nucleus. Mol Cell 2012; 47:422-33. [PMID: 22727668 DOI: 10.1016/j.molcel.2012.05.014] [Citation(s) in RCA: 199] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2012] [Revised: 04/09/2012] [Accepted: 05/10/2012] [Indexed: 11/21/2022]
Abstract
Pre-mRNA splicing is regulated by developmental and environmental cues, but little is known about how specific signals are transduced in mammalian cells to regulate this critical gene expression step. Here, we report massive reprogramming of alternative splicing in response to EGF signaling. By blocking individual branches in EGF signaling, we found that Akt activation plays a major role, while other branches, such as the JAK/STAT and ERK pathways, make minor contributions to EGF-induced splicing. Activated Akt next branches to SR protein-specific kinases, rather than mTOR, by inducing SRPK autophosphorylation that switches the splicing kinases from Hsp70- to Hsp90-containing complexes. This leads to enhanced SRPK nuclear translocation and SR protein phosphorylation. These findings reveal a major signal transduction pathway for regulated splicing and place SRPKs in a central position in the pathway, consistent with their reputed roles in a large number of human cancers.
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93
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Saitoh N, Sakamoto C, Hagiwara M, Agredano-Moreno LT, Jiménez-García LF, Nakao M. The distribution of phosphorylated SR proteins and alternative splicing are regulated by RANBP2. Mol Biol Cell 2012; 23:1115-28. [PMID: 22262462 PMCID: PMC3302738 DOI: 10.1091/mbc.e11-09-0783] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
SR splicing factors are distributed in the speckled pattern in the nucleus. Alternative pre-mRNA splicing is regulated through nuclear distribution of phosphorylated SR splicing factors, which is specifically regulated by the RANBP2 system in mammalian cell lines, as well as in mouse tissues. The mammalian cell nucleus is functionally compartmentalized into various substructures. Nuclear speckles, also known as interchromatin granule clusters, are enriched with SR splicing factors and are implicated in gene expression. Here we report that nuclear speckle formation is developmentally regulated; in certain cases phosphorylated SR proteins are absent from the nucleus and are instead localized at granular structures in the cytoplasm. To investigate how the nuclear architecture is formed, we performed a phenotypic screen of HeLa cells treated with a series of small interfering RNAs. Depletion of Ran-binding protein 2 induced cytoplasmic intermediates of nuclear speckles in G1 phase. Detailed analyses of these structures suggested that a late step in the sequential nuclear entry of mitotic interchromatin granule components was disrupted and that phosphorylated SR proteins were sequestered in an SR protein kinase–dependent manner. As a result, the cells had an imbalanced subcellular distribution of phosphorylated and hypophosphorylated SR proteins, which affected alternative splicing patterns. This study demonstrates that the speckled distribution of phosphorylated pre-mRNA processing factors is regulated by the nucleocytoplasmic transport system in mammalian cells and that it is important for alternative splicing.
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Affiliation(s)
- Noriko Saitoh
- Department of Medical Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University, 2-2-1 Honjo, Kumamoto 860-0811, Japan.
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94
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Chen C, Wang JCY, Zlotnick A. A kinase chaperones hepatitis B virus capsid assembly and captures capsid dynamics in vitro. PLoS Pathog 2011; 7:e1002388. [PMID: 22114561 PMCID: PMC3219723 DOI: 10.1371/journal.ppat.1002388] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2011] [Accepted: 10/04/2011] [Indexed: 12/14/2022] Open
Abstract
The C-terminal domain (CTD) of Hepatitis B virus (HBV) core protein is involved in regulating multiple stages of the HBV lifecycle. CTD phosphorylation correlates with pregenomic-RNA encapsidation during capsid assembly, reverse transcription, and viral transport, although the mechanisms remain unknown. In vitro, purified HBV core protein (Cp183) binds any RNA and assembles aggressively, independent of phosphorylation, to form empty and RNA-filled capsids. We hypothesize that there must be a chaperone that binds the CTD to prevent self-assembly and nonspecific RNA packaging. Here, we show that HBV capsid assembly is stalled by the Serine Arginine protein kinase (SRPK) binding to the CTD, and reactivated by subsequent phosphorylation. Using the SRPK to probe capsids, solution and structural studies showed that SRPK bound to capsid, though the CTD is sequestered on the capsid interior. This result indicates transient CTD externalization and suggests that capsid dynamics could be crucial for directing HBV intracellular trafficking. Our studies illustrate the stochastic nature of virus capsids and demonstrate the appropriation of a host protein by a virus for a non-canonical function. A virus particle is a molecular machine that has evolved to self-assemble within the confines of a living cell. For hepatitis B virus (HBV), outside of a cell, the self-assembly process is very aggressive and consequently not specific for viral RNA. Here we show that HBV takes advantage of a host protein, SRPK, which acts like a molecular chaperone, to prevent the HBV core protein from binding RNA and to prevent the core protein from assembling at the wrong time and place. At the right time, SRPK can be removed in a regulated reaction to allow assembly. Once a virus is assembled, it must traffic to the right intracellular locale. Using SRPK, we show that HBV cores can transiently expose a segment of protein, normally inside the virus, that carries a signal for transport to the host nucleus. This is the first example we know of where a virus repurposes an enzyme for an alternative function. This sort of interplay between virus and host, where the virus hijacks and repurposes host proteins, is likely to be a common feature of viral infection.
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Affiliation(s)
- Chao Chen
- Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana, United States of America
| | - Joseph Che-Yen Wang
- Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana, United States of America
| | - Adam Zlotnick
- Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana, United States of America
- * E-mail:
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95
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Biselli-Chicote PM, Oliveira ARCP, Pavarino EC, Goloni-Bertollo EM. VEGF gene alternative splicing: pro- and anti-angiogenic isoforms in cancer. J Cancer Res Clin Oncol 2011; 138:363-70. [PMID: 22045472 DOI: 10.1007/s00432-011-1073-2] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2011] [Accepted: 09/21/2011] [Indexed: 12/28/2022]
Abstract
Tumor growth and progression depend on angiogenesis, a process of new blood vessels formation from a preexisting vascular endothelium. Tumors promote angiogenesis by secreting or activating angiogenic factors that stimulate endothelial proliferation and migration and capillary morphogenesis. The newly formed blood vessels provide nutrients and oxygen to the tumor, increasing its growth. Thus, angiogenesis plays a key role in cancer progression and development of metastases. An important growth factor that promotes angiogenesis and participates in a variety of physiological and pathological processes is the vascular endothelial growth factor (VEGF-A or VEGF). Overexpression of VEGF results in increased angiogenesis in normal and pathological conditions. The existence of an alternative site of splicing at the 3' untranslated region of the mRNA results in the expression of isoforms with a C-terminal region which are downregulated in tumors and may have differential inhibitory effects. This suggests that control of splicing can be an important regulatory mechanism of angiogenesis in cancer.
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Affiliation(s)
- P M Biselli-Chicote
- Genetics and Molecular Biology Research Unit - UPGEM, Medical School of Sao Jose do Rio Preto - FAMERP, Av. Brigadeiro Faria Lima, 5416, Bloco U6, Sao Jose do Rio Preto, SP 15090-000, Brazil
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96
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Daubner GM, Cléry A, Jayne S, Stevenin J, Allain FHT. A syn-anti conformational difference allows SRSF2 to recognize guanines and cytosines equally well. EMBO J 2011; 31:162-74. [PMID: 22002536 DOI: 10.1038/emboj.2011.367] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2011] [Accepted: 09/12/2011] [Indexed: 11/09/2022] Open
Abstract
SRSF2 (SC35) is a key player in the regulation of alternative splicing events and binds degenerated RNA sequences with similar affinity in nanomolar range. We have determined the solution structure of the SRSF2 RRM bound to the 5'-UCCAGU-3' and 5'-UGGAGU-3' RNA, both identified as SRSF2 binding sites in the HIV-1 tat exon 2. RNA recognition is achieved through a novel sandwich-like structure with both termini forming a positively charged cavity to accommodate the four central nucleotides. To bind both RNA sequences equally well, SRSF2 forms a nearly identical network of intermolecular interactions by simply flipping the bases of the two consecutive C or G nucleotides into either anti or syn conformation. We validate this unusual mode of RNA recognition functionally by in-vitro and in-vivo splicing assays and propose a 5'-SSNG-3' (S=C/G) high-affinity binding consensus sequence for SRSF2. In conclusion, in addition to describe for the first time the RNA recognition mode of SRSF2, we provide the precise consensus sequence to identify new putative binding sites for this splicing factor.
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Affiliation(s)
- Gerrit M Daubner
- Institute of Molecular Biology and Biophysics, ETH Zürich, Zürich, Switzerland
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97
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Abstract
Serine-arginine (SR) proteins commonly designate a family of eukaryotic RNA binding proteins containing a protein domain composed of several repeats of the arginine-serine dipeptide, termed the arginine-serine (RS) domain. This protein family is involved in essential nuclear processes such as constitutive and alternative splicing of mRNA precursors. Besides participating in crucial activities in the nuclear compartment, several SR proteins are able to shuttle between the nucleus and the cytoplasm and to exert regulatory functions in the latter compartment. This review aims at discussing the properties of shuttling SR proteins with particular emphasis on their nucleo-cytoplasmic traffic and their cytoplasmic functions. Indeed, recent findings have unravelled the complex regulation of SR protein nucleo-cytoplasmic distribution and the diversity of cytoplasmic mechanisms in which these proteins are involved.
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Affiliation(s)
- Laure Twyffels
- Laboratoire de Biologie Moléculaire du Gène, Faculté des Sciences, Université Libre de Bruxelles, Gosselies, Belgium
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98
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Qian W, Liang H, Shi J, Jin N, Grundke-Iqbal I, Iqbal K, Gong CX, Liu F. Regulation of the alternative splicing of tau exon 10 by SC35 and Dyrk1A. Nucleic Acids Res 2011; 39:6161-71. [PMID: 21470964 PMCID: PMC3152345 DOI: 10.1093/nar/gkr195] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Revised: 03/16/2011] [Accepted: 03/17/2011] [Indexed: 12/16/2022] Open
Abstract
Abnormal alternative splicing of tau exon 10 results in imbalance of 3R-tau and 4R-tau expression, which is sufficient to cause neurofibrillary degeneration. Splicing factor SC35, a member of the superfamily of the serine/arginine-rich (SR) proteins, promotes tau exon 10 inclusion. The molecular mechanism by which SC35 participates in tau exon 10 splicing remains elusive. In the present study, we found that tau pre-mRNA was coprecipitated by SC35 tagged with HA. Mutation of the SC35-like exonic splicing enhancer located at exon 10 of tau affected both the binding of SC35 to tau pre-mRNA and promotion of tau exon 10 inclusion, suggesting that SC35 acts on the SC35-like exonic splicing enhancer to promote tau exon 10 inclusion. Dyrk1A (dual-specificity tyrosine-phosphorylated and regulated kinase 1A) phosphorylated SC35 in vitro and interacted with it in cultured cells. Overexpression of Dyrk1A suppressed SC35's ability to promote tau exon 10 inclusion. Downregulation of Dyrk1A promoted 4R-tau expression. Therefore, upregulation of Dyrk1A in Down syndrome brain or Alzheimer's brain may cause dysregulation of tau exon 10 splicing through SC35, and probably together with other splicing factors, leading to the imbalance in 3R-tau and 4R-tau expression, which may initiate or accelerate tau pathology and cause neurofibrillary degeneration in the diseases.
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Affiliation(s)
- Wei Qian
- Jiangsu Key Laboratory of Neuroregeneration, Department of Biochemistry, Medical School, Nantong University, Nantong, Jiangsu, P. R. China and Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA
| | - Hongwei Liang
- Jiangsu Key Laboratory of Neuroregeneration, Department of Biochemistry, Medical School, Nantong University, Nantong, Jiangsu, P. R. China and Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA
| | - Jianhua Shi
- Jiangsu Key Laboratory of Neuroregeneration, Department of Biochemistry, Medical School, Nantong University, Nantong, Jiangsu, P. R. China and Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA
| | - Nana Jin
- Jiangsu Key Laboratory of Neuroregeneration, Department of Biochemistry, Medical School, Nantong University, Nantong, Jiangsu, P. R. China and Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA
| | - Inge Grundke-Iqbal
- Jiangsu Key Laboratory of Neuroregeneration, Department of Biochemistry, Medical School, Nantong University, Nantong, Jiangsu, P. R. China and Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA
| | - Khalid Iqbal
- Jiangsu Key Laboratory of Neuroregeneration, Department of Biochemistry, Medical School, Nantong University, Nantong, Jiangsu, P. R. China and Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA
| | - Cheng-Xin Gong
- Jiangsu Key Laboratory of Neuroregeneration, Department of Biochemistry, Medical School, Nantong University, Nantong, Jiangsu, P. R. China and Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA
| | - Fei Liu
- Jiangsu Key Laboratory of Neuroregeneration, Department of Biochemistry, Medical School, Nantong University, Nantong, Jiangsu, P. R. China and Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA
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99
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Aubol BE, Adams JA. Applying the brakes to multisite SR protein phosphorylation: substrate-induced effects on the splicing kinase SRPK1. Biochemistry 2011; 50:6888-900. [PMID: 21728354 DOI: 10.1021/bi2007993] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To investigate how a protein kinase interacts with its protein substrate during extended, multisite phosphorylation, the kinetic mechanism of a protein kinase involved in mRNA splicing control was investigated using rapid quench flow techniques. The protein kinase SRPK1 phosphorylates ~10 serines in the arginine--serine-rich domain (RS domain) of the SR protein SRSF1 in a C- to N-terminal direction, a modification that directs this essential splicing factor from the cytoplasm to the nucleus. Transient-state kinetic experiments illustrate that the first phosphate is added rapidly onto the RS domain of SRSF1 (t(1/2) = 0.1 s) followed by slower, multisite phosphorylation at the remaining serines (t(1/2) = 15 s). Mutagenesis experiments suggest that efficient phosphorylation rates are maintained by an extensive hydrogen bonding and electrostatic network between the RS domain of the SR protein and the active site and docking groove of the kinase. Catalytic trapping and viscosometric experiments demonstrate that while the phosphoryl transfer step is fast, ADP release limits multisite phosphorylation. By studying phosphate incorporation into selectively pre-phosphorylated forms of the enzyme-substrate complex, the kinetic mechanism for site-specific phosphorylation along the reaction coordinate was assessed. The binding affinity of the SR protein, the phosphoryl transfer rate, and ADP exchange rate were found to decline significantly as a function of progressive phosphorylation in the RS domain. These findings indicate that the protein substrate actively modulates initiation, extension, and termination events associated with prolonged, multisite phosphorylation.
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Affiliation(s)
- Brandon E Aubol
- Department of Pharmacology, University of California, San Diego, La Jolla, California 92093-0636, United States
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100
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Shi J, Qian W, Yin X, Iqbal K, Grundke-Iqbal I, Gu X, Ding F, Gong CX, Liu F. Cyclic AMP-dependent protein kinase regulates the alternative splicing of tau exon 10: a mechanism involved in tau pathology of Alzheimer disease. J Biol Chem 2011; 286:14639-48. [PMID: 21367856 DOI: 10.1074/jbc.m110.204453] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Hyperphosphorylation and deposition of tau into neurofibrillary tangles is a hallmark of Alzheimer disease (AD). Alternative splicing of tau exon 10 generates tau isoforms containing three or four microtubule binding repeats (3R-tau and 4R-tau), which are equally expressed in adult human brain. Dysregulation of exon 10 causes neurofibrillary degeneration. Here, we report that cyclic AMP-dependent protein kinase, PKA, phosphorylates splicing factor SRSF1, modulates its binding to tau pre-mRNA, and promotes tau exon 10 inclusion in cultured cells and in vivo in rat brain. PKA-Cα, but not PKA-Cβ, interacts with SRSF1 and elevates SRSF1-mediated tau exon 10 inclusion. In AD brain, the decreased level of PKA-Cα correlates with the increased level of 3R-tau. These findings suggest that a down-regulation of PKA dysregulates the alternative splicing of tau exon 10 and contributes to neurofibrillary degeneration in AD by causing an imbalance in 3R-tau and 4R-tau expression.
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Affiliation(s)
- Jianhua Shi
- Jiangsu Key Laboratory of Neuroregeneration, Medical School, Nantong University, Nantong, Jiangsu 226001, China
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