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Zheng B, Zhou B, Ye D, Wang Y, Zheng W, Wang X, Liu D, Qian F, Zhou X, Yan T, Li Y, Fang L. LINC01572 promotes triple-negative breast cancer progression through EIF4A3-mediated β-catenin mRNA nuclear exportation. ENVIRONMENTAL TOXICOLOGY 2024; 39:3026-3039. [PMID: 38317508 DOI: 10.1002/tox.24171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Revised: 01/08/2024] [Accepted: 01/26/2024] [Indexed: 02/07/2024]
Abstract
Long noncoding RNAs have been reported to be involved in the development of breast cancer. LINC01572 was previously reported to promote the development of various tumors. However, the potential biological function of LINC01572 in breast cancer remains largely unknown. R language was used to perform bioinformatic analysis of The Cancer Genome Atlas data. The expression level of RNAs was examined by RT-qPCR. The effect of knocking down or overexpression LINC01572 in triple-negative breast cancer (TNBC) cell lines was evaluated by detecting cell proliferation, migrant action. RNA immunoprecipitation assay and RNA pull-down assay were performed to explore the regulatory relationship between LINC01572, EIF4A3, and β-catenin. Bioinformatics analysis identifies LINC01572 as an oncogene of breast cancer. LINC01572 is over-expressed in TNBC tissues and cell lines, correlated with poor clinical prognosis in BC patients. Cell function studies confirmed that LINC01572 facilitated the proliferation and migration of TNBC cells in both vivo and vitro. Mechanistically, β-catenin mRNA and EIF4A3 combine spatially to form a complex, LINC01572 helps transport this complex from the nucleus to the cytoplasm, thereby facilitating the translation of β-catenin. Our findings confirm that LINC01572 acts as a tumor promoter and may act as a biomarker in TNBC. In addition, novel molecular regulatory relationships involving LINC01572/EIF4A3/β-catenin are critical to the development of TNBC, which led to a new understanding of the mechanisms of TNBC progression and shows a new target for precision treatment for TNBC.
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Affiliation(s)
- Bowen Zheng
- Department of Breast and Thyroid Surgery, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai, People's Republic of China
| | - Baian Zhou
- Department of Breast and Thyroid Surgery, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai, People's Republic of China
| | - Danrong Ye
- Department of Breast and Thyroid Surgery, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai, People's Republic of China
| | - Yuying Wang
- Department of Breast and Thyroid Surgery, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai, People's Republic of China
| | - Wenfang Zheng
- Department of Breast and Thyroid Surgery, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai, People's Republic of China
| | - Xuehui Wang
- Department of Breast and Thyroid Surgery, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai, People's Republic of China
| | - Diya Liu
- Department of Breast and Thyroid Surgery, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai, People's Republic of China
| | - Fengyuan Qian
- Department of Breast and Thyroid Surgery, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai, People's Republic of China
| | - Xiqian Zhou
- Department of Breast and Thyroid Surgery, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai, People's Republic of China
| | - Tao Yan
- Department of Breast and Thyroid Surgery, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai, People's Republic of China
- Medical College, Anhui University of Science and Technology, Huainan, People's Republic of China
| | - Yating Li
- Department of Breast and Thyroid Surgery, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai, People's Republic of China
- Medical College, Anhui University of Science and Technology, Huainan, People's Republic of China
| | - Lin Fang
- Department of Breast and Thyroid Surgery, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai, People's Republic of China
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Huang X, Tan W, Liu Z, Fu X, Li Z, Lai S, Li Q, Zhong X, Qu F, Zhang H, Li H. EIF4A3-induced circZFAND6 promotes breast cancer proliferation and metastasis through the miR-647/FASN axis. Life Sci 2023; 324:121745. [PMID: 37127184 DOI: 10.1016/j.lfs.2023.121745] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Revised: 04/19/2023] [Accepted: 04/24/2023] [Indexed: 05/03/2023]
Abstract
AIMS Circular RNAs (circRNAs) are important regulators in breast cancer progression. However, the underlying mechanism of circRNAs functions in breast cancer remain largely unclear. MAIN METHODS To investigate the circRNAs expression pattern in breast cancer, high-throughput circRNA microarray assay was used. The top up-regulated circRNA, circZFAND6, was submitted to further experiments, including cell counting kit-8 (CCK-8) assay, colony formation assay, transwell assay and mouse xenograft assay. To investigate the underlying mechanism of circZFAND6 function in breast cancer progression, luciferase reporter assay and RNA immunoprecipitation (RIP) assay were conducted. KEY FINDINGS We found a novel circRNA, circZFAND6, was up-regulated in breast cancer tissues and cell lines. Inhibition of circZFAND6 reduced proliferation and metastasis of breast cancer. Mechanically, circZFAND6 acted as a competing endogenous RNA (ceRNA) to sponge miR-647 and increase fatty acid synthase (FASN) expression. And eukaryotic translation initiation factor 4A3 (EIF4A3) was found to bind to circZFAND6 pre-mRNA transcript upstream region, leading to the high expression of circZFAND6 in breast cancer. Inhibition of EIF4A3 also suppressed proliferation and metastasis of breast cancer. SIGNIFICANCE EIF4A3-induced circZFAND6 up-regulation promoted proliferation and metastasis of breast cancer through the miR-647/FASN axis. Our results uncovered a possible mechanism underlying breast cancer progression and might provide a breast cancer treatment target.
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Affiliation(s)
- Xiaojia Huang
- Department of Breast Surgery, Guangdong Provincial Key Laboratory of Colorectal and Pelvic Floor Diseases, The Sixth Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, 510655, China; Department of Breast Oncology Surgery, Affiliated Cancer Hospital & Institute of Guangzhou Medical University, Guangzhou, Guangdong 510095, China
| | - Weige Tan
- The First Affiliated Hospital of Guangzhou Medical University, The First Clinical School of Guangzhou Medical University, Guangzhou, Guangdong 510120, China
| | - Ziteng Liu
- Department of Breast Surgery, Guangdong Provincial Key Laboratory of Colorectal and Pelvic Floor Diseases, The Sixth Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, 510655, China
| | - Xiaoyan Fu
- Department of Breast Surgery, Guangdong Provincial Key Laboratory of Colorectal and Pelvic Floor Diseases, The Sixth Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, 510655, China
| | - Zongyan Li
- Department of Breast Surgery, Guangdong Provincial Key Laboratory of Colorectal and Pelvic Floor Diseases, The Sixth Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, 510655, China
| | - Shengqing Lai
- Department of Breast Surgery, Guangdong Provincial Key Laboratory of Colorectal and Pelvic Floor Diseases, The Sixth Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, 510655, China
| | - Qian Li
- Department of Breast Surgery, Guangdong Provincial Key Laboratory of Colorectal and Pelvic Floor Diseases, The Sixth Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, 510655, China
| | - Xiaofang Zhong
- Department of Breast Surgery, Guangdong Provincial Key Laboratory of Colorectal and Pelvic Floor Diseases, The Sixth Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, 510655, China
| | - Fanli Qu
- Department of Breast Surgery, Guangdong Provincial Key Laboratory of Colorectal and Pelvic Floor Diseases, The Sixth Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, 510655, China
| | - Huayao Zhang
- Department of Breast and Thyroid Surgery, SSL Central Hospital of Dongguan City, Dongguan, Guangdong 523325, China
| | - Haiyan Li
- Department of Breast Surgery, Guangdong Provincial Key Laboratory of Colorectal and Pelvic Floor Diseases, The Sixth Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, 510655, China.
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Mahmoudian RA, Akhlaghipour I, Lotfi M, Shahidsales S, Moghbeli M. Circular RNAs as the pivotal regulators of epithelial-mesenchymal transition in gastrointestinal tumor cells. Pathol Res Pract 2023; 245:154472. [PMID: 37087995 DOI: 10.1016/j.prp.2023.154472] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/06/2023] [Revised: 04/11/2023] [Accepted: 04/18/2023] [Indexed: 04/25/2023]
Abstract
Gastrointestinal (GI) cancers, as the most common human malignancies are always considered one of the most important health challenges in the world. Late diagnosis in advanced tumor stages is one of the main reasons for the high mortality rate and treatment failure in these patients. Therefore, investigating the molecular pathways involved in GI tumor progression is required to introduce the efficient markers for the early tumor diagnosis. Epithelial-mesenchymal transition (EMT) is one of the main cellular mechanisms involved in the GI tumor metastasis. Non-coding RNAs (ncRNAs) are one of the main regulatory factors in EMT process. Circular RNAs (circRNAs) are a group of covalently closed loop ncRNAs that have higher stability in body fluids compared with other ncRNAs. Considering the importance of circRNAs in regulation of EMT process, in the present review we discussed the role of circRNAs in EMT process during GI tumor invasion. It has been reported that circRNAs mainly affect the EMT process through the regulation of EMT-specific transcription factors and signaling pathways such as WNT, PI3K/AKT, TGF-β, and MAPK. This review can be an effective step in introducing a circRNA/EMT based diagnostic panel marker for the early tumor detection among GI cancer patients.
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Affiliation(s)
- Reihaneh Alsadat Mahmoudian
- Basic Sciences Research Institute, Mashhad University of Medical Sciences, Mashhad, Iran; Cancer Research Center, Mashhad University of Medical Sciences, Mashhad, Iran
| | - Iman Akhlaghipour
- Student Research Committee, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
| | - Malihe Lotfi
- Medical Genetics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran
| | | | - Meysam Moghbeli
- Medical Genetics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran; Department of Medical Genetics and Molecular Medicine, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
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Liu Q, Dong H. EIF4A3-mediated hsa_circ_0088088 promotes the carcinogenesis of breast cancer by sponging miR-135-5p. J Biochem Mol Toxicol 2021; 35:e22909. [PMID: 34463003 DOI: 10.1002/jbt.22909] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 08/14/2021] [Accepted: 08/20/2021] [Indexed: 11/07/2022]
Abstract
Circular RNAs have participated in oncology progress. Nevertheless, the potential mechanisms are not completely understood. We intended to inspect the functions of hsa_circ_0088088 on breast malignancy, together with the possible mechanism(s). hsa_circ_0088088 expression in breast malignancy was studied using quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR). The overall survival was studied by the Kaplan-Meier curve. The biological functions of hsa_circ_0088088 aberrant expression on cell growth and metastasis were evaluated in MDA-MB-231 cells. Bioinformatics analysis, RNA immunoprecipitation (RIP), and qRT-PCR were accomplished to confirm the possible regulatory effects of eukaryotic initiation factor 4A3 (EIF4A3) on the biogenesis of hsa_circ_0088088. Furthermore, a dual-luciferase reporter assay, qRT-PCR, and RNA pull-down assay were used to confirm the association between the hsa_circ_0088088 and miR-135-5p in MDA-MB-231 cells. hsa_circ_0088088 was upregulated in the tumor tissues and cells, and higher expression presented an unfavorable prognosis. hsa_circ_0088088 overexpression promoted cell growth and metastasis in MDA-MB-231 cells. EIF4A3 was found to positively regulate hsa_circ_0088088. Furthermore, we confirmed that hsa_circ_0088088 sponges miR-135-5p and directly targets miR-135-5p with respect to the cell growth and metastasis in MDA-MB-231 cells. Our data suggest that EIF4A3-induced hsa_circ_0088088 stimulates the carcinogenic effects of breast tumors by sponging miR-135-5p.
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Affiliation(s)
- Qun Liu
- Department of Breast Surgery, The First Affiliated Hospital of China Medical University, Shenyang, Liaoning, China
| | - Huiting Dong
- Department of Breast Surgery, The First Affiliated Hospital of China Medical University, Shenyang, Liaoning, China
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Wang G, Sun D, Li W, Xin Y. CircRNA_100290 promotes GC cell proliferation and invasion via the miR-29b-3p/ITGA11 axis and is regulated by EIF4A3. Cancer Cell Int 2021; 21:324. [PMID: 34182990 PMCID: PMC8240270 DOI: 10.1186/s12935-021-01964-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2021] [Accepted: 05/04/2021] [Indexed: 12/29/2022] Open
Abstract
Background Circular RNAs (circRNAs) have been reported to be important regulators of the development and progression of various carcinomas. However, the role of circRNA_100290 in gastric cancer (GC) is still unclear. This study aimed to investigate the role of circRNA_100290 in GC invasion and metastasis and the possible underlying mechanism. Methods The expression of circRNA_100290 in GC cells and tissues was examined using quantitative real-time polymerase chain reaction (qRT-PCR). The role of circRNA_100290 in cell proliferation, migration, and invasion was evaluated in the AGS and HGC-27 cell lines in vitro. Bioinformatics tools, dual-luciferase reporter assays, Western blot assays and qRT-PCR were used to explore the pathways downstream of circRNA_100290. The mechanism underlying the regulation of circRNA_100290 expression was explored using RNA immunoprecipitation, qRT-PCR, and Western blot assays. Results The expression of circRNA_100290 was significantly upregulated in GC cells and 102 GC tissues, and high circRNA_100290 expression in GC was closely related to Borrmann’s type, lymph node metastasis and tumour-node-metastasis stage. In vitro, knockdown of circRNA_100290 in AGS and HGC-27 cells significantly inhibited cell proliferation, migration, and invasion. Mechanistically, a dual-luciferase reporter assay confirmed the direct interaction between circRNA_100290 and miR-29b-3p, which targets ITGA11, an oncogene that is closely related to epithelial–mesenchymal transition (EMT). In addition, EIF4A3, an RNA-binding protein (RBP), could inhibit the formation of circRNA_100290 by binding to the flanking sites of circRNA_100290. Low EIF4A3 expression in GC was related to a poor prognosis. Conclusions Elevated circRNA_100290 expression in GC promotes cell proliferation, invasion and EMT via the miR-29b-3p/ITGA11 axis and might be regulated by EIF4A3. CircRNA_100290 might be a promising biomarker and target for GC therapy. Graphical abstract ![]()
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Affiliation(s)
- Gang Wang
- Laboratory of Gastrointestinal Onco-Pathology, Cancer Institute, The First Affiliated Hospital of China Medical University, 155 Nanjing North Street, Heping District, Shenyang, Liaoning Province, China.,Department of Oncology, The First Affiliated Hospital of Shandong First Medical University & Shandong Provincial Qianfoshan Hospital, Shandong Key Laboratory of Rheumatic Disease and Translational Medicine, Shandong Lung Cancer Institute, 16766 Jingshi Road, Lixia District, Jinan, Shandong Province, China
| | - Dan Sun
- Laboratory of Gastrointestinal Onco-Pathology, Cancer Institute, The First Affiliated Hospital of China Medical University, 155 Nanjing North Street, Heping District, Shenyang, Liaoning Province, China
| | - Wenhui Li
- Laboratory of Gastrointestinal Onco-Pathology, Cancer Institute, The First Affiliated Hospital of China Medical University, 155 Nanjing North Street, Heping District, Shenyang, Liaoning Province, China
| | - Yan Xin
- Laboratory of Gastrointestinal Onco-Pathology, Cancer Institute, The First Affiliated Hospital of China Medical University, 155 Nanjing North Street, Heping District, Shenyang, Liaoning Province, China.
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The exon junction complex core factor eIF4A3 is a key regulator of HPV16 gene expression. Biosci Rep 2021; 41:228142. [PMID: 33760064 PMCID: PMC8026852 DOI: 10.1042/bsr20203488] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 03/04/2021] [Accepted: 03/24/2021] [Indexed: 01/06/2023] Open
Abstract
High-risk human papillomavirus (hrHPVs), particularly HPV16 and HPV18, are the etiologic factors of ano-genital cancers and some head and neck squamous cell carcinomas (HNSCCs). Viral E6 and E7 oncoproteins, controlled at both transcriptional and post-transcriptional levels, drive hrHPVs-induced carcinogenesis. In the present study, we investigated the implication of the DEAD-box helicase eukaryotic translation initiation factor 4A3 (eIF4A3,) an Exon Junction Complex factor, in the regulation of HPV16 gene expression. Our data revealed that the depletion of the factor eIF4A3 up-regulated E7 oncoprotein levels. We also showed that the inhibition of the nonsense-mediated RNA decay (NMD) pathway, resulted in the up-regulation of E7 at both RNA and protein levels. We therefore proposed that HPV16 transcripts might present different susceptibilities to NMD and that this pathway could play a key role in the levels of expression of these viral oncoproteins during the development of HPV-related cancers.
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7
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The exon junction complex: structural insights into a faithful companion of mammalian mRNPs. Biochem Soc Trans 2018; 46:153-161. [PMID: 29351963 DOI: 10.1042/bst20170059] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2017] [Revised: 12/13/2017] [Accepted: 12/18/2017] [Indexed: 12/21/2022]
Abstract
During splicing, the exon junction complex (EJC) is deposited upstream of exon-exon boundaries. The EJC and its peripheral bound proteins play an essential role in mediating mRNA export, translation and turnover. However, the exact sequence of EJC assembly and the involved factors during splicing remain elusive. Recently published structures of the human C* spliceosome clarified the position of the EJC at this phase of splicing and have given insight into previously unidentified interactions between the EJC and spliceosomal proteins. Here, these new observations are presented and the significance for EJC assembly is discussed. Furthermore, the vast landscape of EJC interacting proteins and their manifold functions are described. Finally, the factors involved in EJC disassembly and recycling are recapitulated. This review aims to integrate structural, biochemical and physiological data to obtain a comprehensive picture of EJC components during the lifetime of the EJC.
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Shaul O. How introns enhance gene expression. Int J Biochem Cell Biol 2017; 91:145-155. [PMID: 28673892 DOI: 10.1016/j.biocel.2017.06.016] [Citation(s) in RCA: 223] [Impact Index Per Article: 31.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2017] [Revised: 06/26/2017] [Accepted: 06/30/2017] [Indexed: 01/18/2023]
Abstract
In many eukaryotes, including mammals, plants, yeast, and insects, introns can increase gene expression without functioning as a binding site for transcription factors. This phenomenon was termed 'intron-mediated enhancement'. Introns can increase transcript levels by affecting the rate of transcription, nuclear export, and transcript stability. Moreover, introns can also increase the efficiency of mRNA translation. This review discusses the current knowledge about these processes. The role of splicing in IME and the significance of intron position relative to the sites of transcription and translation initiation are elaborated. Particular emphasis is placed on the question why different introns, present at the same location of the same genes and spliced at a similar high efficiency, can have very different impacts on expression - from almost no effect to considerable stimulation. This situation can be at least partly accounted for by the identification of splicing-unrelated intronic elements with a special ability to enhance mRNA accumulation or translational efficiency. The many factors that could lead to the large variation observed between the impact of introns in different genes and experimental systems are highlighted. It is suggested that there is no sole, definite answer to the question "how do introns enhance gene expression". Rather, each intron-gene combination might undergo its own unique mixture of processes that lead to the perceptible outcome.
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Affiliation(s)
- Orit Shaul
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 5290002, Israel.
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Nabih A, Sobotka JA, Wu MZ, Wedeles CJ, Claycomb JM. Examining the intersection between splicing, nuclear export and small RNA pathways. Biochim Biophys Acta Gen Subj 2017; 1861:2948-2955. [PMID: 28578161 DOI: 10.1016/j.bbagen.2017.05.027] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 05/25/2017] [Accepted: 05/29/2017] [Indexed: 01/06/2023]
Abstract
BACKGROUND Nuclear Argonaute/small RNA pathways in a variety of eukaryotic species are generally known to regulate gene expression via chromatin modulation and transcription attenuation in a process known as transcriptional gene silencing (TGS). However, recent data, including genetic screens, phylogenetic profiling, and molecular mechanistic studies, also point to a novel and emerging intersection between the splicing and nuclear export machinery with nuclear Argonaute/small RNA pathways in many organisms. SCOPE OF REVIEW In this review, we summarize the field's current understanding regarding the relationship between splicing, export and small RNA pathways, and consider the biological implications for coordinated regulation of transcripts by these pathways. We also address the importance and available approaches for understanding the RNA regulatory logic generated by the intersection of these particular pathways in the context of synthetic biology. MAJOR CONCLUSIONS The interactions between various eukaryotic RNA regulatory pathways, particularly splicing, nuclear export and small RNA pathways provide a type of combinatorial code that informs the identity ("self" versus "non-self") and dictates the fate of each transcript in a cell. Although the molecular mechanisms for how splicing and nuclear export impact small RNA pathways are not entirely clear at this early stage, the links between these pathways are widespread across eukaryotic phyla. GENERAL SIGNIFICANCE The link between splicing, nuclear export, and small RNA pathways is emerging and establishes a new frontier for understanding the combinatorial logic of gene regulation across species that could someday be harnessed for therapeutic, biotechnology and agricultural applications. This article is part of a Special Issue entitled "Biochemistry of Synthetic Biology - Recent Developments" Guest Editor: Dr. Ilka Heinemann and Dr. Patrick O'Donoghue.
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Affiliation(s)
- Amena Nabih
- Dept. of Molecular Genetics, University of Toronto, Canada
| | | | - Monica Z Wu
- Dept. of Molecular Genetics, University of Toronto, Canada
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Carvalho T, Martins S, Rino J, Marinho S, Carmo-Fonseca M. Pharmacological inhibition of the spliceosome subunit SF3b triggers exon junction complex-independent nonsense-mediated decay. J Cell Sci 2017; 130:1519-1531. [PMID: 28302904 DOI: 10.1242/jcs.202200] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Accepted: 03/06/2017] [Indexed: 12/12/2022] Open
Abstract
Spliceostatin A, meayamycin, and pladienolide B are small molecules that target the SF3b subunit of the spliceosomal U2 small nuclear ribonucleoprotein (snRNP). These compounds are attracting much attention as tools to manipulate splicing and for use as potential anti-cancer drugs. We investigated the effects of these inhibitors on mRNA transport and stability in human cells. Upon splicing inhibition, unspliced pre-mRNAs accumulated in the nucleus, particularly within enlarged nuclear speckles. However, a small fraction of the pre-mRNA molecules were exported to the cytoplasm. We identified the export adaptor ALYREF as being associated with intron-containing transcripts and show its requirement for the nucleo-cytoplasmic transport of unspliced pre-mRNA. In contrast, the exon junction complex (EJC) core protein eIF4AIII failed to form a stable complex with intron-containing transcripts. Despite the absence of EJC, unspliced transcripts in the cytoplasm were degraded by nonsense-mediated decay (NMD), suggesting that unspliced transcripts are degraded by an EJC-independent NMD pathway. Collectively, our results indicate that although blocking the function of SF3b elicits a massive accumulation of unspliced pre-mRNAs in the nucleus, intron-containing transcripts can still bind the ALYREF export factor and be transported to the cytoplasm, where they trigger an alternative NMD pathway.
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Affiliation(s)
- Teresa Carvalho
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal
| | - Sandra Martins
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal
| | - José Rino
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal
| | - Sérgio Marinho
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal
| | - Maria Carmo-Fonseca
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal
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Woodward LA, Mabin JW, Gangras P, Singh G. The exon junction complex: a lifelong guardian of mRNA fate. WILEY INTERDISCIPLINARY REVIEWS-RNA 2016; 8. [PMID: 28008720 DOI: 10.1002/wrna.1411] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Revised: 10/27/2016] [Accepted: 11/09/2016] [Indexed: 12/28/2022]
Abstract
During messenger RNA (mRNA) biogenesis and processing in the nucleus, many proteins are imprinted on mRNAs assembling them into messenger ribonucleoproteins (mRNPs). Some of these proteins remain stably bound within mRNPs and have a long-lasting impact on their fate. One of the best-studied examples is the exon junction complex (EJC), a multiprotein complex deposited primarily 24 nucleotides upstream of exon-exon junctions as a consequence of pre-mRNA splicing. The EJC maintains a stable, sequence-independent, hold on the mRNA until its removal during translation in the cytoplasm. Acting as a molecular shepherd, the EJC travels with mRNA across the cellular landscape coupling pre-mRNA splicing to downstream, posttranscriptional processes such as mRNA export, mRNA localization, translation, and nonsense-mediated mRNA decay (NMD). In this review, we discuss our current understanding of the EJC's functions during these processes, and expound its newly discovered functions (e.g., pre-mRNA splicing). Another focal point is the recently unveiled in vivo EJC interactome, which has shed new light on the EJC's location on the spliced RNAs and its intimate relationship with other mRNP components. We summarize new strides being made in connecting the EJC's molecular function with phenotypes, informed by studies of human disorders and model organisms. The progress toward understanding EJC functions has revealed, in its wake, even more questions, which are discussed throughout. WIREs RNA 2017, 8:e1411. doi: 10.1002/wrna.1411 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Lauren A Woodward
- Department of Molecular Genetics, The Ohio State University, Columbus, OH, USA
| | - Justin W Mabin
- Department of Molecular Genetics, The Ohio State University, Columbus, OH, USA
| | - Pooja Gangras
- Department of Molecular Genetics, The Ohio State University, Columbus, OH, USA
| | - Guramrit Singh
- Department of Molecular Genetics, The Ohio State University, Columbus, OH, USA
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Abstract
Several studies propose an influence of chromatin on pre-mRNA splicing, but it is still unclear how widespread and how direct this phenomenon is. We find here that when assembled in vivo, the U2 snRNP co-purifies with a subset of chromatin-proteins, including histones and remodeling complexes like SWI/SNF. Yet, an unbiased RNAi screen revealed that the outcome of splicing is influenced by a much larger variety of chromatin factors not all associating with the spliceosome. The availability of this broad range of chromatin factors impacting splicing further unveiled their very context specific effect, resulting in either inclusion or skipping, depending on the exon under scrutiny. Finally, a direct assessment of the impact of chromatin on splicing using an in vitro co-transcriptional splicing assay with pre-mRNAs transcribed from a nucleosomal template, demonstrated that chromatin impacts nascent pre-mRNP in their competence for splicing. Altogether, our data show that numerous chromatin factors associated or not with the spliceosome can affect the outcome of splicing, possibly as a function of the local chromatin environment that by default interferes with the efficiency of splicing. Splicing is an RNA editing step allowing to produce multiple transcripts from a single gene. The gene itself is organized in chromatin, associating DNA and multiple proteins. Some proteins regulating the compaction of the chromatin also affect RNA splicing. Yet, it was unclear whether these chromatin proteins were exceptions or whether chromatin very generally affected the outcome of splicing. Here, we show that a subset of chromatin proteins is physically in interaction with the enzyme responsible for RNA splicing. In addition, several chromatin proteins not found directly associated with the splicing machinery were also able to influence RNA splicing, suggesting that chromatin compaction very globally plays a role in splicing. This finding was confirmed using the first in vitro assay combining transcription and splicing in the context of chromatin; this assay showed that assembling DNA with chromatin proteins influences the efficiency of splicing.
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13
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Boehm V, Gehring NH. Exon Junction Complexes: Supervising the Gene Expression Assembly Line. Trends Genet 2016; 32:724-735. [PMID: 27667727 DOI: 10.1016/j.tig.2016.09.003] [Citation(s) in RCA: 85] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Revised: 08/23/2016] [Accepted: 09/01/2016] [Indexed: 12/16/2022]
Abstract
The exon junction complex (EJC) is an RNA-binding protein complex that is assembled and deposited onto mRNAs during splicing. The EJC comprises four core components that bind to not only canonical sites upstream of exon-exon junctions, but also to noncanonical sites at other positions in exons. EJC-associated proteins are recruited by the EJC at different steps of gene expression to execute the multiple functions of the EJC. Recently, new insights have been obtained into how EJCs stimulate pre-mRNA splicing, and mRNA export, translation, and degradation. Furthermore, mutations in EJC core components were shown to result in severe disorders in humans, demonstrating the critical physiological role of the EJC. Hence, the EJC has been identified as an important player in post-transcriptional gene regulation in metazoans.
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Affiliation(s)
- Volker Boehm
- Institute for Genetics, University of Cologne, 50674 Cologne, Germany
| | - Niels H Gehring
- Institute for Genetics, University of Cologne, 50674 Cologne, Germany.
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14
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Zhang Q, Li H, Zhao X, Zheng Y, Meng H, Jia Y, Xue H, Bo S. Analysis on the preference for sequence matching between mRNA sequences and the corresponding introns in ribosomal protein genes. J Theor Biol 2016; 392:113-21. [DOI: 10.1016/j.jtbi.2015.12.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2015] [Accepted: 12/10/2015] [Indexed: 10/22/2022]
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15
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Hir HL, Saulière J, Wang Z. The exon junction complex as a node of post-transcriptional networks. Nat Rev Mol Cell Biol 2015; 17:41-54. [DOI: 10.1038/nrm.2015.7] [Citation(s) in RCA: 167] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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16
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Nomakuchi TT, Rigo F, Aznarez I, Krainer AR. Antisense oligonucleotide-directed inhibition of nonsense-mediated mRNA decay. Nat Biotechnol 2015; 34:164-6. [PMID: 26655495 PMCID: PMC4744113 DOI: 10.1038/nbt.3427] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2015] [Accepted: 11/09/2015] [Indexed: 12/12/2022]
Abstract
Nonsense-mediated mRNA decay (NMD) is a cellular quality-control mechanism that is thought to exacerbate the phenotype of certain pathogenic nonsense mutations by preventing the expression of semi-functional proteins. NMD also limits the efficacy of read-through compound (RTC)-based therapies. Here, we report a gene-specific method of NMD inhibition using antisense oligonucleotides (ASOs), and combine this approach with an RTC to effectively restore the expression of full-length protein from a nonsense-mutant allele.
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Affiliation(s)
- Tomoki T Nomakuchi
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, USA.,Stony Brook University School of Medicine, Stony Brook, New York, USA
| | - Frank Rigo
- Isis Pharmaceuticals, Carslbad, California, USA
| | - Isabel Aznarez
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, USA
| | - Adrian R Krainer
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, USA
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17
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Steckelberg AL, Altmueller J, Dieterich C, Gehring NH. CWC22-dependent pre-mRNA splicing and eIF4A3 binding enables global deposition of exon junction complexes. Nucleic Acids Res 2015; 43:4687-700. [PMID: 25870412 PMCID: PMC4482076 DOI: 10.1093/nar/gkv320] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Accepted: 03/27/2015] [Indexed: 11/17/2022] Open
Abstract
In metazoan cells, spliced mRNAs are marked by the exon junction complex (EJC), a multi-protein complex that serves as a key regulator of post-transcriptional mRNA metabolism. Deposition of EJCs on mRNA is intimately linked to the splicing process. The spliceosomal protein CWC22 directly binds the core EJC-protein eIF4A3, guides it to the spliceosome and initiates EJC assembly. In addition, CWC22 is involved in the splicing process itself, but the molecular details of its dual function remain elusive. Here we analyze the mechanisms, by which CWC22 co-regulates pre-mRNA splicing and EJC assembly. We show that the core of CWC22 is sufficient to mediate both pre-mRNA splicing and EJC assembly. Nonetheless, both processes can be functionally uncoupled with an eIF4A3-binding deficient mutant of CWC22, which impedes EJC assembly. A C-terminal domain of CWC22 strongly enhances its spliceosomal interaction and likely regulates its function. High-throughput RNA-sequencing identifies global defects of pre-mRNA splicing and downregulation of diverse gene expression pathways in CWC22-depleted cells. We propose a model, in which CWC22 represents an integral component of the spliceosome and orchestrates pre-mRNA splicing and eIF4A3 binding to achieve global assembly of exon junction complexes.
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Affiliation(s)
| | - Janine Altmueller
- Cologne Center for Genomics (CCG), University of Cologne, D-50931 Cologne, Germany Institute of Human Genetics, University of Cologne, D-50931 Cologne, Germany
| | - Christoph Dieterich
- Max Planck Institute for Biology of Ageing, Joseph-Stelzmann-Straße 9b, D-50931 Cologne, Germany
| | - Niels H Gehring
- Institute for Genetics, University of Cologne, D-50674 Cologne, Germany
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18
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Singh G, Pratt G, Yeo GW, Moore MJ. The Clothes Make the mRNA: Past and Present Trends in mRNP Fashion. Annu Rev Biochem 2015; 84:325-54. [PMID: 25784054 DOI: 10.1146/annurev-biochem-080111-092106] [Citation(s) in RCA: 272] [Impact Index Per Article: 30.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Throughout their lifetimes, messenger RNAs (mRNAs) associate with proteins to form ribonucleoproteins (mRNPs). Since the discovery of the first mRNP component more than 40 years ago, what is known as the mRNA interactome now comprises >1,000 proteins. These proteins bind mRNAs in myriad ways with varying affinities and stoichiometries, with many assembling onto nascent RNAs in a highly ordered process during transcription and precursor mRNA (pre-mRNA) processing. The nonrandom distribution of major mRNP proteins observed in transcriptome-wide studies leads us to propose that mRNPs are organized into three major domains loosely corresponding to 5' untranslated regions (UTRs), open reading frames, and 3' UTRs. Moving from the nucleus to the cytoplasm, mRNPs undergo extensive remodeling as they are first acted upon by the nuclear pore complex and then by the ribosome. When not being actively translated, cytoplasmic mRNPs can assemble into large multi-mRNP assemblies or be permanently disassembled and degraded. In this review, we aim to give the reader a thorough understanding of past and current eukaryotic mRNP research.
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Affiliation(s)
- Guramrit Singh
- Department of Molecular Genetics, Center for RNA Biology, The Ohio State University, Columbus, Ohio 43210;
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19
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Abstract
The human spliceosome is a large ribonucleoprotein complex that catalyzes pre-mRNA splicing. It consists of five snRNAs and more than 200 proteins. Because of this complexity, much work has focused on the Saccharomyces cerevisiae spliceosome, viewed as a highly simplified system with fewer than half as many splicing factors as humans. Nevertheless, it has been difficult to ascribe a mechanistic function to individual splicing factors or even to discern which are critical for catalyzing the splicing reaction. We have identified and characterized the splicing machinery from the red alga Cyanidioschyzon merolae, which has been reported to harbor only 26 intron-containing genes. The U2, U4, U5, and U6 snRNAs contain expected conserved sequences and have the ability to adopt secondary structures and form intermolecular base-pairing interactions, as in other organisms. C. merolae has a highly reduced set of 43 identifiable core splicing proteins, compared with ∼90 in budding yeast and ∼140 in humans. Strikingly, we have been unable to find a U1 snRNA candidate or any predicted U1-associated proteins, suggesting that splicing in C. merolae may occur without the U1 small nuclear ribonucleoprotein particle. In addition, based on mapping the identified proteins onto the known splicing cycle, we propose that there is far less compositional variability during splicing in C. merolae than in other organisms. The observed reduction in splicing factors is consistent with the elimination of spliceosomal components that play a peripheral or modulatory role in splicing, presumably retaining those with a more central role in organization and catalysis.
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20
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eIF4AIII enhances translation of nuclear cap-binding complex-bound mRNAs by promoting disruption of secondary structures in 5'UTR. Proc Natl Acad Sci U S A 2014; 111:E4577-86. [PMID: 25313076 DOI: 10.1073/pnas.1409695111] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
It has long been considered that intron-containing (spliced) mRNAs are translationally more active than intronless mRNAs (identical mRNA not produced by splicing). The splicing-dependent translational enhancement is mediated, in part, by the exon junction complex (EJC). Nonetheless, the molecular mechanism by which each EJC component contributes to the translational enhancement remains unclear. Here, we demonstrate the previously unappreciated role of eukaryotic translation initiation factor 4AIII (eIF4AIII), a component of EJC, in the translation of mRNAs bound by the nuclear cap-binding complex (CBC), a heterodimer of cap-binding protein 80 (CBP80) and CBP20. eIF4AIII is recruited to the 5'-end of mRNAs bound by the CBC by direct interaction with the CBC-dependent translation initiation factor (CTIF); this recruitment of eIF4AIII is independent of the presence of introns (deposited EJCs after splicing). Polysome fractionation, tethering experiments, and in vitro reconstitution experiments using recombinant proteins show that eIF4AIII promotes efficient unwinding of secondary structures in 5'UTR, and consequently enhances CBC-dependent translation in vivo and in vitro. Therefore, our data provide evidence that eIF4AIII is a specific translation initiation factor for CBC-dependent translation.
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21
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Zhang Q, Li H, Zhao X, Zheng Y, Zhou D. Distribution bias of the sequence matching between exons and introns in exon joint and EJC binding region in C. elegans. J Theor Biol 2014; 364:295-304. [PMID: 25234235 DOI: 10.1016/j.jtbi.2014.09.009] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2014] [Revised: 08/30/2014] [Accepted: 09/04/2014] [Indexed: 11/17/2022]
Abstract
We propose a mechanism that there are matching relations between mRNA sequences and corresponding post-spliced introns, and introns play a significant role in the process of gene expression. In order to reveal the sequence matching features, Smith-Waterman local alignment method is used on C. elegans mRNA sequences to obtain optimal matched segments between exon-exon sequences and their corresponding introns. Distribution characters of matching frequency on exon-exon sequences and sequence characters of optimal matched segments are studied. Results show that distributions of matching frequency on exon-exon junction region have obvious differences, and the exon boundary is revealed. Distributions of the length and matching rate of optimal matched segments are consistent with sequence features of siRNA and miRNA. The optimal matched segments have special sequence characters compared with their host sequences. As for the first introns and long introns, matching frequency values of optimal matched segments with high GC content, rich CG dinucleotides and high λCG values show the minimum distribution in exon junction complex (EJC) binding region. High λCG values in optimal matched segments are main characters in distinguishing EJC binding region. Results indicate that EJC and introns have competitive and cooperative relations in the process of combining on protein coding sequences. Also intron sequences and protein coding sequences do have concerted evolution relations.
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Affiliation(s)
- Qiang Zhang
- Laboratory of Theoretical Biophysics, School of Physical Science and Technology, Inner Mongolia University, Hohhot, 010021, China
| | - Hong Li
- Laboratory of Theoretical Biophysics, School of Physical Science and Technology, Inner Mongolia University, Hohhot, 010021, China.
| | - Xiaoqing Zhao
- Biotechnology Research Centre, Inner Mongolia Academy of Agricultural and Animal Husbandry Science, Hohhot, 010021, China
| | - Yan Zheng
- Laboratory of Theoretical Biophysics, School of Physical Science and Technology, Inner Mongolia University, Hohhot, 010021, China
| | - Deliang Zhou
- Laboratory of Theoretical Biophysics, School of Physical Science and Technology, Inner Mongolia University, Hohhot, 010021, China
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22
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Steckelberg AL, Gehring NH. Studying the composition of mRNPs in vitro using splicing-competent cell extracts. Methods 2014; 65:342-9. [DOI: 10.1016/j.ymeth.2013.08.033] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2013] [Revised: 08/27/2013] [Accepted: 08/30/2013] [Indexed: 10/26/2022] Open
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23
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Favaro F, Alvizi L, Zechi-Ceide R, Bertola D, Felix T, de Souza J, Raskin S, Twigg S, Weiner A, Armas P, Margarit E, Calcaterra N, Andersen G, McGowan S, Wilkie A, Richieri-Costa A, de Almeida M, Passos-Bueno M. A noncoding expansion in EIF4A3 causes Richieri-Costa-Pereira syndrome, a craniofacial disorder associated with limb defects. Am J Hum Genet 2014; 94:120-8. [PMID: 24360810 DOI: 10.1016/j.ajhg.2013.11.020] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Accepted: 11/22/2013] [Indexed: 01/31/2023] Open
Abstract
Richieri-Costa-Pereira syndrome is an autosomal-recessive acrofacial dysostosis characterized by mandibular median cleft associated with other craniofacial anomalies and severe limb defects. Learning and language disabilities are also prevalent. We mapped the mutated gene to a 122 kb region at 17q25.3 through identity-by-descent analysis in 17 genealogies. Sequencing strategies identified an expansion of a region with several repeats of 18- or 20-nucleotide motifs in the 5' untranslated region (5' UTR) of EIF4A3, which contained from 14 to 16 repeats in the affected individuals and from 3 to 12 repeats in 520 healthy individuals. A missense substitution of a highly conserved residue likely to affect the interaction of eIF4AIII with the UPF3B subunit of the exon junction complex in trans with an expanded allele was found in an unrelated individual with an atypical presentation, thus expanding mutational mechanisms and phenotypic diversity of RCPS. EIF4A3 transcript abundance was reduced in both white blood cells and mesenchymal cells of RCPS-affected individuals as compared to controls. Notably, targeting the orthologous eif4a3 in zebrafish led to underdevelopment of several craniofacial cartilage and bone structures, in agreement with the craniofacial alterations seen in RCPS. Our data thus suggest that RCPS is caused by mutations in EIF4A3 and show that EIF4A3, a gene involved in RNA metabolism, plays a role in mandible, laryngeal, and limb morphogenesis.
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24
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Allemand E, Hastings ML. Expression and purification of splicing proteins from mammalian cells. Methods Mol Biol 2014; 1126:205-16. [PMID: 24549667 DOI: 10.1007/978-1-62703-980-2_16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Pre-mRNA splicing is a complex process that is carried out by a large ribonucleoprotein enzyme, termed the spliceosome, which comprises up to 200 proteins. Despite this complexity, the role of individual spliceosomal proteins in the splicing reaction has been successfully investigated using cell-free assays. In many cases, the splicing factor of interest must be expressed and purified in order to study its function in vitro. Posttranslational modifications such as phosphorylation, methylation, acetylation, and ubiquitination of splicing factors are important for activity. Thus, their purification from mammalian cells presents numerous advantages. Here, we describe a method for expression and purification of splicing proteins from mammalian cells.
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Affiliation(s)
- Eric Allemand
- Unité de Régulation Epigénétique, Département de Biologie du Développement, Institut Pasteur, Paris, France
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25
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Crystal structure of the human eIF4AIII-CWC22 complex shows how a DEAD-box protein is inhibited by a MIF4G domain. Proc Natl Acad Sci U S A 2013; 110:E4611-8. [PMID: 24218557 DOI: 10.1073/pnas.1314684110] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
DEAD-box proteins are involved in all aspects of RNA processing. They bind RNA in an ATP-dependent manner and couple ATP hydrolysis to structural and compositional rearrangements of ribonucleoprotein particles. Conformational control is a major point of regulation for DEAD-box proteins to act on appropriate substrates and in a timely manner in vivo. Binding partners containing a middle domain of translation initiation factor 4G (MIF4G) are emerging as important regulators. Well-known examples are eIF4G and Gle1, which bind and activate the DEAD-box proteins eIF4A and Dbp5. Here, we report the mechanism of an inhibiting MIF4G domain. We determined the 2.0-Å resolution structure of the complex of human eIF4AIII and the MIF4G domain of the splicing factor Complexed With Cef1 (CWC22), an essential prerequisite for exon junction complex assembly by the splicing machinery. The CWC22 MIF4G domain binds both RecA domains of eIF4AIII. The mode of RecA2 recognition is similar to that observed in the activating complexes, yet is specific for eIF4AIII. The way the CWC22 MIF4G domain latches on the eIF4AIII RecA1 domain is markedly different from activating complexes. In the CWC22-eIF4AIII complex, the RNA-binding and ATP-binding motifs of the two RecA domains do not face each other, as would be required in the active state, but are in diametrically opposite positions. The binding mode of CWC22 to eIF4AIII reveals a facet of how MIF4G domains use their versatile structural frameworks to activate or inhibit DEAD-box proteins.
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26
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Akua T, Shaul O. The Arabidopsis thaliana MHX gene includes an intronic element that boosts translation when localized in a 5' UTR intron. JOURNAL OF EXPERIMENTAL BOTANY 2013; 64:4255-70. [PMID: 24006416 PMCID: PMC3808313 DOI: 10.1093/jxb/ert235] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
The mechanisms that underlie the ability of some introns to increase gene expression, a phenomenon called intron-mediated enhancement (IME), are not fully understood. It is also not known why introns localized in the 5'-untranslated region (5' UTR) are considerably longer than downstream eukaryotic introns. It was hypothesized that this extra length results from the presence of some functional intronic elements. However, deletion analyses studies carried out thus far were unable to identify specific intronic regions necessary for IME. Using deletion analysis and a gain-of-function approach, an internal element that considerably increases translational efficiency, without affecting splicing, was identified in the 5' UTR intron of the Arabidopsis thaliana MHX gene. Moreover, the ability of this element to enhance translation was diminished by a minor downstream shift in the position of introns containing it from the 5' UTR into the coding sequence. These data suggest that some of the extra length of 5' UTR introns results from the presence of elements that enhance translation, and, moreover, from the ability of 5' UTR introns to provide preferable platforms for such elements over downstream introns. The impact of the identified intronic element on translational efficiency was augmented upon removal of neighbouring intronic elements. Interference between different intronic elements had not been reported thus far. This interference may support the bioinformatics-based idea that some of the extra sequence of 5' UTR introns is also necessary for separating different functional intronic elements.
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Affiliation(s)
- Tsofit Akua
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel
| | - Orit Shaul
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel
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27
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Human spliceosomal protein CWC22 plays a role in coupling splicing to exon junction complex deposition and nonsense-mediated decay. Proc Natl Acad Sci U S A 2012; 109:21313-8. [PMID: 23236153 DOI: 10.1073/pnas.1219725110] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The multiprotein exon junction complex (EJC) that is deposited upstream of spliced junctions orchestrates downstream events in the life of a metazoan mRNA, including its surveillance via the nonsense-mediated decay (NMD) pathway. However, the mechanism by which the spliceosome mediates EJC formation is not well understood. We show that human eIF4G-like spliceosomal protein (h)CWC22 directly interacts with the core EJC component eIF4AIII in vitro and in vivo; mutations at the predicted hCWC22/eIF4AIII interface disrupt association. In vivo depletion of hCWC22, as for yeast Cwc22p, causes a splicing defect, resulting in decreased levels of mature cellular mRNAs. Nonetheless, hCWC22 depletion yields increased levels of spliced RNA from the unusual nonsense codon-containing U22 host gene, which is a natural substrate of NMD. To test whether hCWC22 acts in NMD through coupling splicing to EJC deposition, we searched for mutations in hCWC22 that affect eIF4AIII deposition without affecting splicing. Addition of hCWC22(G168Y) with a mutation at the putative hCWC22/eIF4AIII interface exacerbates the defect in splicing-dependent deposition of eIF4AIII(T334V) with a mutation reported to be in direct contact with mRNA, linking hCWC22 to the process of EJC deposition in vitro. Importantly, the addition of hCWC22(G168Y) affects deposition of eIF4AIII(T334V) without inhibiting splicing or the efficiency of deposition of the endogenous eF4AIII(WT) in the same reaction, demonstrating hCWC22's specific role in eIF4AIII deposition in addition to its role in splicing. The essential splicing factor CWC22 has, therefore, acquired functions in EJC assembly and NMD during evolution from single-celled to complex eukaryotes.
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28
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Intimate liaison with SR proteins brings exon junction complexes to unexpected places. Nat Struct Mol Biol 2012; 19:1209-11. [DOI: 10.1038/nsmb.2454] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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29
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CLIP-seq of eIF4AIII reveals transcriptome-wide mapping of the human exon junction complex. Nat Struct Mol Biol 2012; 19:1124-31. [PMID: 23085716 DOI: 10.1038/nsmb.2420] [Citation(s) in RCA: 149] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2012] [Accepted: 09/21/2012] [Indexed: 12/14/2022]
Abstract
The exon junction complex (EJC) is a central effector of the fate of mRNAs, linking nuclear processing to mRNA transport, translation and surveillance. However, little is known about its transcriptome-wide targets. We used cross-linking and immunoprecipitation methods coupled to high-throughput sequencing (CLIP-seq) in human cells to identify the binding sites of the DEAD-box helicase eIF4AIII, an EJC core component. CLIP reads form peaks that are located mainly in spliced mRNAs. Most expressed exons harbor peaks either in the canonical EJC region, located ~24 nucleotides upstream of exonic junctions, or in other noncanonical regions. Notably, both of these types of peaks are preferentially associated with unstructured and purine-rich sequences containing the motif GAAGA, which is a potential binding site for EJC-associated factors. Therefore, EJC positions vary spatially and quantitatively between exons. This transcriptome-wide mapping of human eIF4AIII reveals unanticipated aspects of the EJC and broadens its potential impact on post-transcriptional regulation.
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30
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Singh G, Kucukural A, Cenik C, Leszyk JD, Shaffer SA, Weng Z, Moore MJ. The cellular EJC interactome reveals higher-order mRNP structure and an EJC-SR protein nexus. Cell 2012; 151:750-764. [PMID: 23084401 DOI: 10.1016/j.cell.2012.10.007] [Citation(s) in RCA: 246] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Revised: 08/24/2012] [Accepted: 10/03/2012] [Indexed: 01/12/2023]
Abstract
In addition to sculpting eukaryotic transcripts by removing introns, pre-mRNA splicing greatly impacts protein composition of the emerging mRNP. The exon junction complex (EJC), deposited upstream of exon-exon junctions after splicing, is a major constituent of spliced mRNPs. Here, we report comprehensive analysis of the endogenous human EJC protein and RNA interactomes. We confirm that the major "canonical" EJC occupancy site in vivo lies 24 nucleotides upstream of exon junctions and that the majority of exon junctions carry an EJC. Unexpectedly, we find that endogenous EJCs multimerize with one another and with numerous SR proteins to form megadalton sized complexes in which SR proteins are super-stoichiometric to EJC core factors. This tight physical association may explain known functional parallels between EJCs and SR proteins. Further, their protection of long mRNA stretches from nuclease digestion suggests that endogenous EJCs and SR proteins cooperate to promote mRNA packaging and compaction.
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Affiliation(s)
- Guramrit Singh
- Howard Hughes Medical Institute, University of Massachusetts Medical School, Worcester, MA 01605; Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605
| | - Alper Kucukural
- Howard Hughes Medical Institute, University of Massachusetts Medical School, Worcester, MA 01605; Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605
| | - Can Cenik
- Howard Hughes Medical Institute, University of Massachusetts Medical School, Worcester, MA 01605; Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605
| | - John D Leszyk
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605
| | - Scott A Shaffer
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605
| | - Zhiping Weng
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605; Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, Worcester, MA 01605
| | - Melissa J Moore
- Howard Hughes Medical Institute, University of Massachusetts Medical School, Worcester, MA 01605; Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605.
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31
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Human CWC22 escorts the helicase eIF4AIII to spliceosomes and promotes exon junction complex assembly. Nat Struct Mol Biol 2012; 19:983-90. [DOI: 10.1038/nsmb.2380] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2012] [Accepted: 08/08/2012] [Indexed: 01/09/2023]
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32
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Daguenet E, Baguet A, Degot S, Schmidt U, Alpy F, Wendling C, Spiegelhalter C, Kessler P, Rio MC, Le Hir H, Bertrand E, Tomasetto C. Perispeckles are major assembly sites for the exon junction core complex. Mol Biol Cell 2012; 23:1765-82. [PMID: 22419818 PMCID: PMC3338441 DOI: 10.1091/mbc.e12-01-0040] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The exon junction complex (EJC) allows the spliceosome to communicate with other cellular machinery. This study shows that assembled EJC cores are enriched in nuclear regions around speckles, called perispeckles. Speckles and perispeckles may represent specialized nuclear regions for messenger ribonucleoprotein maturation. The exon junction complex (EJC) is loaded onto mRNAs as a consequence of splicing and regulates multiple posttranscriptional events. MLN51, Magoh, Y14, and eIF4A3 form a highly stable EJC core, but where this tetrameric complex is assembled in the cell remains unclear. Here we show that EJC factors are enriched in domains that we term perispeckles and are visible as doughnuts around nuclear speckles. Fluorescence resonance energy transfer analyses and EJC assembly mutants show that perispeckles do not store free subunits, but instead are enriched for assembled cores. At the ultrastructural level, perispeckles are distinct from interchromatin granule clusters that may function as storage sites for splicing factors and intermingle with perichromatin fibrils, where nascent RNAs and active RNA Pol II are present. These results support a model in which perispeckles are major assembly sites for the tetrameric EJC core. This subnuclear territory thus represents an intermediate region important for mRNA maturation, between transcription sites and splicing factor reservoirs and assembly sites.
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Affiliation(s)
- Elisabeth Daguenet
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Unité Mixte de Recherche 7104, Centre National de la Recherche Scientifique/U964 Institut National de Santé et de Recherche Médicale/Université de Strasbourg, 67404 Illkirch, France
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33
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Hwang J, Maquat LE. Nonsense-mediated mRNA decay (NMD) in animal embryogenesis: to die or not to die, that is the question. Curr Opin Genet Dev 2012; 21:422-30. [PMID: 21550797 DOI: 10.1016/j.gde.2011.03.008] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2011] [Revised: 03/24/2011] [Accepted: 03/25/2011] [Indexed: 11/28/2022]
Abstract
Nonsense-mediated mRNA decay (NMD) is a well-studied cellular quality-control pathway. It decreases the half-lives of eukaryotic mRNAs that aberrantly contain premature termination codons and additionally regulates an estimated 10-20% of normal transcripts. NMD factors play crucial roles during embryogenesis in many animals. Here, we review data indicating that NMD factors are required for proper embryogenesis by discussing the abnormal developmental phenotypes that result when the abundance of individual NMD factors is either downregulated or completely eliminated. We conclude that while NMD per se affects the embryogenesis of all animals, it is required to avoid embryonic lethality in only some animals. The critical roles of many NMD factors in other metabolic pathways undoubtedly also contribute to embryonic development if not viability.
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Affiliation(s)
- Jungwook Hwang
- Department of Biochemistry and Biophysics and the Center for RNA Biology, School of Medicine and Dentistry, 601 Elmwood Avenue, Box 712, University of Rochester, Rochester, NY 14642, USA
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34
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Alexandrov A, Colognori D, Steitz JA. Human eIF4AIII interacts with an eIF4G-like partner, NOM1, revealing an evolutionarily conserved function outside the exon junction complex. Genes Dev 2011; 25:1078-90. [PMID: 21576267 DOI: 10.1101/gad.2045411] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Despite the lack of an exon junction complex (EJC), Saccharomyces cerevisiae contains Fal1p, a DEAD-box helicase highly homologous to eIF4AIII. We show that yeast Fal1p is functionally orthologous to human eIF4AIII, since expression of human eIF4AIII complements both the lethal phenotype and the 18S rRNA biogenesis defect of fal1Δ(null) yeast. We further show that yeast Fal1p interacts genetically with an eIF4G-like protein, Sgd1p: One allele of sgd1 acts as a dominant extragenic suppressor of a mutation in a predicted RNA-binding residue of Fal1p, whereas another synthetically exacerbates the growth defect of this fal1 mutation. Both sgd1 mutations map to a single, short, evolutionarily conserved patch that matches key eIF4A-interacting residues of eIF4G when superimposed on the X-ray structure of the eIF4A/eIF4G complex. We demonstrate direct physical interactions between yeast Sgd1p and Fal1p, and between their human orthologs (NOM1 and eIF4AIII) in vitro and in vivo, identifying human NOM1 as a missing eIF4G-like interacting partner of eIF4AIII. Knockdown of eIF4AIII and NOM1 in human cells demonstrates that this novel conserved eIF4A/eIF4G-like complex acts in pre-rRNA processing, adding to the established functions of eIF4A/eIF4G in translation initiation and of eIF4AIII as the core component of the EJC.
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Affiliation(s)
- Andrei Alexandrov
- Department of Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06536, USA
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35
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Maquat LE, Hwang J, Sato H, Tang Y. CBP80-promoted mRNP rearrangements during the pioneer round of translation, nonsense-mediated mRNA decay, and thereafter. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2011; 75:127-34. [PMID: 21447822 DOI: 10.1101/sqb.2010.75.028] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
In mammalian cells, two different messenger ribonucleoproteins (mRNPs) serve as templates for protein synthesis. Newly synthesized mRNPs bound by the cap-binding protein heterodimer CBP80-CBP20 (CBC) initially undergo a pioneer round of translation. One purpose of this round of translation is to ensure the quality of gene expression, as exemplified by nonsense-mediated messenger RNA (mRNA) decay (NMD). NMD largely functions to eliminate mRNAs that prematurely terminate translation, although NMD also contributes to proper gene control, and it targets CBC-bound mRNPs. CBC-bound mRNPs are remodeled to eukaryotic translation initiation factor (eIF)4E-bound mRNPs in steps that (1) are a consequence of the pioneer round of translation and (2) occur independently of translation. Rather than supporting NMD, eIF4E-bound mRNPs provide for the bulk of cellular protein synthesis and are the primary targets of mRNA decay mechanisms that conditionally regulate gene expression. Here, we overview cellular processes by which CBC-bound mRNPs are remodeled to eIF4E-bound mRNPs. We also describe the molecular movements of certain factors during NMD in view of the influential role of CBP80.
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Affiliation(s)
- L E Maquat
- Department of Biochemistry and Biophysics, The Center for RNA Biology, School of Medicine and Dentistry, University of Rochester, Rochester, New York 14642, USA.
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36
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Belaya K, St Johnston D. Using the mRNA-MS2/MS2CP-FP system to study mRNA transport during Drosophila oogenesis. Methods Mol Biol 2011; 714:265-283. [PMID: 21431747 DOI: 10.1007/978-1-61779-005-8_17] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Asymmetric mRNA localisation to specific compartments of the cell is a fundamental mechanism of -spatial and temporal regulation of gene expression. It is used by a variety of organisms and cell types to achieve different cellular functions. However, the mechanisms of mRNA localisation are not well understood. An important advance in this field has been the development of techniques that allow the visualisation of mRNA movements in living cells in real time. In this paper, we describe one approach to visualising mRNA localisation in vivo, in which RNAs containing MS2 binding sites are labelled by the MS2 coat protein fused to fluorescent reporters. We discuss the use of this mRNA-MS2/MS2CP-FP system to study mRNA localisation during Drosophila oogenesis, and provide a detailed explanation of the steps required for this approach, including the design of the mRNA-MS2 and MS2CP-FP constructs, the preparation of fly oocytes for imaging, the optimal microscope configurations for live cell imaging, and strategies for image processing and analysis.
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37
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Bono F, Gehring NH. Assembly, disassembly and recycling: the dynamics of exon junction complexes. RNA Biol 2011; 8:24-9. [PMID: 21289489 DOI: 10.4161/rna.8.1.13618] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Efficient gene expression requires that, during their lifetime, mRNAs associate with different sets of RNA binding proteins to form messenger ribonucleoprotein particles (mRNPs). The protein components of mRNPs are essential for the correct post-transcriptional function and regulation of mRNAs. mRNPs are constitutively remodeled during the maturation of the mRNA in the nucleus and downstream steps in the cytoplasm, and can also change depending on the cellular environment. Here we review the current understanding of the biochemical and structural aspects of a central mRNP component and regulator, the exon junction complex (EJC).
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Affiliation(s)
- Fulvia Bono
- Max-Planck-Institute for Developmental Biology, Tübingen, Germany.
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38
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Exon junction complex subunits are required to splice Drosophila MAP kinase, a large heterochromatic gene. Cell 2010; 143:238-50. [PMID: 20946982 DOI: 10.1016/j.cell.2010.09.036] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2009] [Revised: 08/04/2010] [Accepted: 09/02/2010] [Indexed: 02/04/2023]
Abstract
The exon junction complex (EJC) is assembled on spliced mRNAs upstream of exon-exon junctions and can regulate their subsequent translation, localization, or degradation. We isolated mutations in Drosophila mago nashi (mago), which encodes a core EJC subunit, based on their unexpectedly specific effects on photoreceptor differentiation. Loss of Mago prevents epidermal growth factor receptor signaling, due to a large reduction in MAPK mRNA levels. MAPK expression also requires the EJC subunits Y14 and eIF4AIII and EJC-associated splicing factors. Mago depletion does not affect the transcription or stability of MAPK mRNA but alters its splicing pattern. MAPK expression from an exogenous promoter requires Mago only when the template includes introns. MAPK is the primary functional target of mago in eye development; in cultured cells, Mago knockdown disproportionately affects other large genes located in heterochromatin. These data support a nuclear role for EJC components in splicing a specific subset of introns.
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39
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Odho Z, Southall SM, Wilson JR. Characterization of a novel WDR5-binding site that recruits RbBP5 through a conserved motif to enhance methylation of histone H3 lysine 4 by mixed lineage leukemia protein-1. J Biol Chem 2010; 285:32967-32976. [PMID: 20716525 DOI: 10.1074/jbc.m110.159921] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Histone modification is well established as a fundamental mechanism driving the regulation of transcription, replication, and DNA repair through the control of chromatin structure. Likewise, it is apparent that incorrect targeting of histone modifications contributes to misregulated gene expression and hence to developmental disorders and diseases of genomic instability such as cancer. The KMT2 family of SET domain methyltransferases, typified by mixed lineage leukemia protein-1 (MLL1), is responsible for histone H3 lysine 4 methylation, a marker of active genes. To ensure that this modification is correctly targeted, a multiprotein complex associates with the methyltransferase and directs activity. We have identified a novel interaction site on the core complex protein WD repeat protein-5 (WDR5), and we mapped the complementary site on its partner retinoblastoma-binding protein-5 (RbBP5). We have characterized this interaction by x-ray crystallography and show how it is fundamental to the assembly of the complex and to the regulation of methyltransferase activity. We show which region of RbBP5 contributes directly to mixed lineage leukemia activation, and we combine our structural and biochemical data to produce a model to show how WDR5 and RbBP5 act cooperatively to stimulate activity.
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Affiliation(s)
- Zain Odho
- From the Section of Structural Biology, Institute of Cancer Research, Chester Beatty Laboratories, London SW3 6JB, United Kingdom
| | - Stacey M Southall
- From the Section of Structural Biology, Institute of Cancer Research, Chester Beatty Laboratories, London SW3 6JB, United Kingdom
| | - Jon R Wilson
- From the Section of Structural Biology, Institute of Cancer Research, Chester Beatty Laboratories, London SW3 6JB, United Kingdom.
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40
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Bono F, Cook AG, Grünwald M, Ebert J, Conti E. Nuclear import mechanism of the EJC component Mago-Y14 revealed by structural studies of importin 13. Mol Cell 2010; 37:211-22. [PMID: 20122403 DOI: 10.1016/j.molcel.2010.01.007] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2009] [Revised: 12/02/2009] [Accepted: 01/06/2010] [Indexed: 11/28/2022]
Abstract
Mago and Y14 are core components of the exon junction complex (EJC), an assembly central to nonsense-mediated mRNA decay in humans and mRNA localization in flies. The Mago-Y14 heterodimer shuttles between the nucleus, where it is loaded onto specific mRNAs, and the cytoplasm, where it functions in translational regulation. The heterodimer is imported back into the nucleus by Importin 13 (Imp13), a member of the karyopherin-beta family of transport factors. We have elucidated the structural basis of the Mago-Y14 nuclear import cycle. The 3.35 A structure of the Drosophila Imp13-Mago-Y14 complex shows that Imp13 forms a ring-like molecule, reminiscent of Crm1, and encircles the Mago-Y14 cargo with a conserved interaction surface. The 2.8 A structure of human Imp13 bound to RanGTP reveals how Mago-Y14 is released in the nucleus by a steric hindrance mechanism. Comparison of the two structures suggests how this unusual karyopherin might function in bidirectional nucleocytoplasmic transport.
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Affiliation(s)
- Fulvia Bono
- Max-Planck-Institute of Biochemistry, Department of Structural Cell Biology, Am Klopferspitz 18, 82152 Martinsried, Germany
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41
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Abstract
hnRNP A1 binds to RNA in a cooperative manner. Initial hnRNP A1 binding to an exonic splicing silencer at the 3' end of human immunodeficiency virus type 1 (HIV-1) tat exon 3, which is a high-affinity site, is followed by cooperative spreading in a 3'-to-5' direction. As hnRNP A1 propagates toward the 5' end of the exon, it antagonizes binding of a serine/arginine-rich (SR) protein to an exonic splicing enhancer, thereby inhibiting splicing at that exon's alternative 3' splice site. tat exon 3 and the preceding intron of HIV-1 pre-mRNA can fold into an elaborate RNA secondary structure in solution, which could potentially influence hnRNP A1 binding. We report here that hnRNP A1 binding and splicing repression can occur on an unstructured RNA. Moreover, hnRNP A1 can effectively unwind an RNA hairpin upon binding, displacing a bound protein. We further show that hnRNP A1 can also spread in a 5'-to-3' direction, although when initial binding takes place in the middle of an RNA, spreading preferentially proceeds in a 3'-to-5' direction. Finally, when two distant high-affinity sites are present on the same RNA, they facilitate cooperative spreading of hnRNP A1 between the two sites.
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42
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Gehring NH, Lamprinaki S, Hentze MW, Kulozik AE. The hierarchy of exon-junction complex assembly by the spliceosome explains key features of mammalian nonsense-mediated mRNA decay. PLoS Biol 2009; 7:e1000120. [PMID: 19478851 PMCID: PMC2682485 DOI: 10.1371/journal.pbio.1000120] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2008] [Accepted: 04/17/2009] [Indexed: 11/19/2022] Open
Abstract
Protein complexes deposited on messenger RNAs during their maturation are able to recruit components of a cellular RNA surveillance pathway, thereby linking RNA maturation to subsequent steps in RNA quality control. Exon junction complexes (EJCs) link nuclear splicing to key features of mRNA function including mRNA stability, translation, and localization. We analyzed the formation of EJCs by the spliceosome, the physiological EJC assembly machinery. We studied a comprehensive set of eIF4A3, MAGOH, and BTZ mutants in complete or C-complex–arrested splicing reactions and identified essential interactions of EJC proteins during and after EJC assembly. These data establish that EJC deposition proceeds through a defined intermediate, the pre-EJC, as an ordered, sequential process that is coordinated by splicing. The pre-EJC consists of eIF4A3 and MAGOH-Y14, is formed before exon ligation, and provides a binding platform for peripheral EJC components that join after release from the spliceosome and connect the core structure with function. Specifically, we identified BTZ to bridge the EJC to the nonsense-mediated messenger RNA (mRNA) decay protein UPF1, uncovering a critical link between mRNP architecture and mRNA stability. Based on this systematic analysis of EJC assembly by the spliceosome, we propose a model of how a functional EJC is assembled in a strictly sequential and hierarchical fashion, including nuclear splicing-dependent and cytoplasmic steps. The first step in the expression of eukaryotic protein-coding genes is transcription into a messenger RNA (mRNA) precursor in the nucleus. These precursor mRNAs then undergo maturation through the removal of introns in a process termed splicing. During splicing, the splicing machinery or “spliceosome” deposits a complex of proteins onto the mRNA that accompanies it during post-transcriptional steps in gene expression, including the regulation of mRNA stability, transport out of the nucleus, cellular localisation, and translation. This complex, the exon junction complex (EJC), represents a molecular memory of the splicing process. Understanding the biogenesis of EJCs and their downstream effects helps reveal the basic principles by which the primary steps of mRNA synthesis are coupled to the regulation of gene expression. Here we show that EJCs are assembled in a strictly splicing-dependent manner through an unexpected, coordinated, and hierarchical assembly pathway. Importantly, we show that the EJC recruits the cytoplasmic protein BTZ, which then bridges the complex to an mRNA quality-control machinery called the nonsense-mediated decay pathway that degrades mRNAs containing premature stop codons. This finding suggests that the EJC and bridging by BTZ help determine the stability of mRNA and thus are essential for proper cellular surveillance of mRNA quality.
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Affiliation(s)
- Niels H. Gehring
- Molecular Medicine Partnership Unit, University of Heidelberg and European Molecular Biology Laboratory, Heidelberg, Germany
- Department of Pediatric Oncology, Hematology and Immunology, University of Heidelberg, Heidelberg, Germany
- European Molecular Biology Laboratory, Heidelberg, Germany
- * E-mail: (NHG); (AEK)
| | - Styliani Lamprinaki
- Molecular Medicine Partnership Unit, University of Heidelberg and European Molecular Biology Laboratory, Heidelberg, Germany
- European Molecular Biology Laboratory, Heidelberg, Germany
| | - Matthias W. Hentze
- Molecular Medicine Partnership Unit, University of Heidelberg and European Molecular Biology Laboratory, Heidelberg, Germany
- European Molecular Biology Laboratory, Heidelberg, Germany
| | - Andreas E. Kulozik
- Molecular Medicine Partnership Unit, University of Heidelberg and European Molecular Biology Laboratory, Heidelberg, Germany
- Department of Pediatric Oncology, Hematology and Immunology, University of Heidelberg, Heidelberg, Germany
- * E-mail: (NHG); (AEK)
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43
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Schmidt U, Im KB, Benzing C, Janjetovic S, Rippe K, Lichter P, Wachsmuth M. Assembly and mobility of exon-exon junction complexes in living cells. RNA (NEW YORK, N.Y.) 2009; 15:862-876. [PMID: 19324961 PMCID: PMC2673070 DOI: 10.1261/rna.1387009] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2008] [Accepted: 01/30/2009] [Indexed: 05/27/2023]
Abstract
The exon-exon junction complex (EJC) forms via association of proteins during splicing of mRNA in a defined manner. Its organization provides a link between biogenesis, nuclear export, and translation of the transcripts. The EJC proteins accumulate in nuclear speckles alongside most other splicing-related factors. We followed the establishment of the EJC on mRNA by investigating the mobility and interactions of a representative set of EJC factors in vivo using a complementary analysis with different fluorescence fluctuation microscopy techniques. Our observations are compatible with cotranscriptional binding of the EJC protein UAP56 confirming that it is involved in the initial phase of EJC formation. RNPS1, REF/Aly, Y14/Magoh, and NXF1 showed a reduction in their nuclear mobility when complexed with RNA. They interacted with nuclear speckles, in which both transiently and long-term immobilized factors were identified. The location- and RNA-dependent differences in the mobility between factors of the so-called outer shell and inner core of the EJC suggest a hypothetical model, in which mRNA is retained in speckles when EJC outer-shell factors are missing.
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Affiliation(s)
- Ute Schmidt
- Division of Molecular Genetics, Deutsches Krebsforschungszentrum, 69120 Heidelberg, Germany
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44
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Moore MJ, Proudfoot NJ. Pre-mRNA processing reaches back to transcription and ahead to translation. Cell 2009; 136:688-700. [PMID: 19239889 DOI: 10.1016/j.cell.2009.02.001] [Citation(s) in RCA: 648] [Impact Index Per Article: 43.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The pathway from gene activation in the nucleus to mRNA translation and decay at specific locations in the cytoplasm is both streamlined and highly interconnected. This review discusses how pre-mRNA processing, including 5' cap addition, splicing, and polyadenylation, contributes to both the efficiency and fidelity of gene expression. The connections of pre-mRNA processing to upstream events in transcription and downstream events, including translation and mRNA decay, are elaborate, extensive, and remarkably interwoven.
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Affiliation(s)
- Melissa J Moore
- Howard Hughes Medical Institute, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605, USA.
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45
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Garapaty S, Xu CF, Trojer P, Mahajan MA, Neubert TA, Samuels HH. Identification and characterization of a novel nuclear protein complex involved in nuclear hormone receptor-mediated gene regulation. J Biol Chem 2009; 284:7542-52. [PMID: 19131338 DOI: 10.1074/jbc.m805872200] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
NRC/NCoA6 plays an important role in mediating the effects of ligand-bound nuclear hormone receptors as well as other transcription factors. NRC interacting factor 1 (NIF-1) was cloned as a novel factor that interacts in vivo with NRC. Although NIF-1 does not directly interact with nuclear hormone receptors, it enhances activation by nuclear hormone receptors presumably through its interaction with NRC. To further understand the cellular and biological function of NIF-1, we identified NIF-1-associated proteins by in-solution proteolysis followed by mass spectrometry. The identified components revealed factors involved in histone methylation and cell cycle control and include Ash2L, RbBP5, WDR5, HCF-1, DBC-1, and EMSY. Although the NIF-1 complex contains Ash2L, RbBP5, and WDR5, suggesting that the complex might methylate histone H3-Lys-4, we found that the complex contains a H3 methyltransferase activity that modifies a residue other than H3-Lys-4. The identified components form at least two distinctly sized NIF-1 complexes. DBC-1 and EMSY were identified as integral components of an NIF-1 complex of approximately 1.5 MDa and were found to play an important role in the regulation of nuclear receptor-mediated transcription. Stimulation of the Sox9 and HoxA1 genes by retinoic acid receptor-alpha was found to require both DBC-1 and EMSY in addition to NIF-1 for maximal transcriptional activation. Interestingly, NRC was not identified as a component of the NIF-1 complex, suggesting that NIF-1 and NRC do not exist as stable in vitro purified complexes, although the separate NIF-1 and NRC complexes appear to functionally interact in the cell.
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Affiliation(s)
- Shivani Garapaty
- Department of Pharmacology, New York University School of Medicine, New York, New York 10016, USA
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46
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Mishler DM, Christ AB, Steitz JA. Flexibility in the site of exon junction complex deposition revealed by functional group and RNA secondary structure alterations in the splicing substrate. RNA (NEW YORK, N.Y.) 2008; 14:2657-2670. [PMID: 18952819 PMCID: PMC2590960 DOI: 10.1261/rna.1312808] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2008] [Accepted: 09/02/2008] [Indexed: 05/27/2023]
Abstract
The exon junction complex (EJC) is critical for mammalian nonsense-mediated mRNA decay and translational regulation, but the mechanism of its stable deposition on mRNA is unknown. To examine requirements for EJC deposition, we created splicing substrates containing either DNA nucleotides or RNA secondary structure in the 5' exon. Using RNase H protection, toeprinting, and coimmunoprecipitation assays, we found that EJC location shifts upstream when a stretch of DNA or RNA secondary structure appears at the canonical deposition site. These upstream shifts occur prior to exon ligation and are often accompanied by decreases in deposition efficiency. Although the EJC core protein eIF4AIII contacts four ribose 2'OH groups in crystal structures, we demonstrate that three 2'OH groups are sufficient for deposition. Thus, the site of EJC deposition is more flexible than previously appreciated and efficient deposition appears spatially limited.
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Affiliation(s)
- Dennis M Mishler
- Department of Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute, Yale University, New Haven, Connecticut 06536, USA
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47
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Conservation of the protein composition and electron microscopy structure of Drosophila melanogaster and human spliceosomal complexes. Mol Cell Biol 2008; 29:281-301. [PMID: 18981222 DOI: 10.1128/mcb.01415-08] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Comprehensive proteomics analyses of spliceosomal complexes are currently limited to those in humans, and thus, it is unclear to what extent the spliceosome's highly complex composition and compositional dynamics are conserved among metazoans. Here we affinity purified Drosophila melanogaster spliceosomal B and C complexes formed in Kc cell nuclear extract. Mass spectrometry revealed that their composition is highly similar to that of human B and C complexes. Nonetheless, a number of Drosophila-specific proteins were identified, suggesting that there may be novel factors contributing specifically to splicing in flies. Protein recruitment and release events during the B-to-C transition were also very similar in both organisms. Electron microscopy of Drosophila B complexes revealed a high degree of structural similarity with human B complexes, indicating that higher-order interactions are also largely conserved. A comparison of Drosophila spliceosomes formed on a short versus long intron revealed only small differences in protein composition but, nonetheless, clear structural differences under the electron microscope. Finally, the characterization of affinity-purified Drosophila mRNPs indicated that exon junction complex proteins are recruited in a splicing-dependent manner during C complex formation. These studies provide insights into the evolutionarily conserved composition and structure of the metazoan spliceosome, as well as its compositional dynamics during catalytic activation.
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48
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Wachsmuth M, Caudron-Herger M, Rippe K. Genome organization: Balancing stability and plasticity. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1783:2061-79. [DOI: 10.1016/j.bbamcr.2008.07.022] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2008] [Revised: 07/21/2008] [Accepted: 07/24/2008] [Indexed: 12/18/2022]
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49
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Palazzo AF, Springer M, Shibata Y, Lee CS, Dias AP, Rapoport TA. The signal sequence coding region promotes nuclear export of mRNA. PLoS Biol 2008; 5:e322. [PMID: 18052610 PMCID: PMC2100149 DOI: 10.1371/journal.pbio.0050322] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2007] [Accepted: 10/19/2007] [Indexed: 11/19/2022] Open
Abstract
In eukaryotic cells, most mRNAs are exported from the nucleus by the transcription export (TREX) complex, which is loaded onto mRNAs after their splicing and capping. We have studied in mammalian cells the nuclear export of mRNAs that code for secretory proteins, which are targeted to the endoplasmic reticulum membrane by hydrophobic signal sequences. The mRNAs were injected into the nucleus or synthesized from injected or transfected DNA, and their export was followed by fluorescent in situ hybridization. We made the surprising observation that the signal sequence coding region (SSCR) can serve as a nuclear export signal of an mRNA that lacks an intron or functional cap. Even the export of an intron-containing natural mRNA was enhanced by its SSCR. Like conventional export, the SSCR-dependent pathway required the factor TAP, but depletion of the TREX components had only moderate effects. The SSCR export signal appears to be characterized in vertebrates by a low content of adenines, as demonstrated by genome-wide sequence analysis and by the inhibitory effect of silent adenine mutations in SSCRs. The discovery of an SSCR-mediated pathway explains the previously noted amino acid bias in signal sequences and suggests a link between nuclear export and membrane targeting of mRNAs. In eukaryotic cells, precursors of messenger RNAs (mRNAs) are synthesized and processed in the nucleus. During processing, noncoding introns are spliced out, and a cap and poly-adenosine sequence are added to the beginning and end of the transcript, respectively. The resulting mature mRNA is exported from the nucleus to the cytoplasm by crossing the nuclear pore. Both the introns and the cap help to recruit factors that are necessary for nuclear export of an mRNA. Here we provide evidence for a novel mRNA export pathway that is specific for transcripts coding for secretory proteins. These proteins contain signal sequences that target them for translocation across the endoplasmic reticulum membrane. We made the surprising observation that the signal sequence coding region (SSCR) can serve as a nuclear export signal of an mRNA that lacks an intron or functional cap. Even the export of an intron-containing natural mRNA was enhanced by its SSCR. The SSCR export signal appears to be characterized in vertebrates by a low content of adenines. Our discovery of an SSCR-mediated pathway explains the previously noted amino acid bias in signal sequences, and suggests a link between nuclear export and membrane targeting of mRNAs. Signal sequences, which target newly synthesized secretory proteins to the endoplasmic reticulum, are encoded by adenine-depleted nucleotide sequences that promote the nuclear export of the mRNAs.
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Affiliation(s)
- Alexander F Palazzo
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Michael Springer
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Yoko Shibata
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Chung-Sheng Lee
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Anusha P Dias
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Tom A Rapoport
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
- * To whom correspondence should be addressed. E-mail:
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PYM binds the cytoplasmic exon-junction complex and ribosomes to enhance translation of spliced mRNAs. Nat Struct Mol Biol 2007; 14:1173-9. [PMID: 18026120 DOI: 10.1038/nsmb1321] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2007] [Accepted: 09/21/2007] [Indexed: 11/08/2022]
Abstract
Messenger RNAs produced by splicing are translated more efficiently than those produced from similar intronless precursor mRNAs (pre-mRNAs). The exon-junction complex (EJC) probably mediates this enhancement; however, the specific link between the EJC and the translation machinery has not been identified. The EJC proteins Y14 and magoh remain bound to spliced mRNAs after their export from the nucleus to the cytoplasm and are removed only when these mRNAs are translated. Here we show that PYM, a 29-kDa protein that binds the Y14-magoh complex in the cytoplasm, also binds, via a separate domain, to the small (40S) ribosomal subunit and the 48S preinitiation complex. Furthermore, PYM knockdown reduces the translation efficiency of a reporter protein produced from intron-containing, but not intronless, pre-mRNA. We suggest that PYM functions as a bridge between EJC-bearing spliced mRNAs and the translation machinery to enhance translation of the mRNAs.
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