title: Alternative splicing of MEF2C pre-mRNA controls its activity in normal myogenesis and promotes tumorigenicity in rhabdomyosarcoma cells.
abstract: Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. Many cellular disruptions contribute to the progression of this pediatric cancer, including aberrant alternative splicing. The MEF2 family of transcription factors regulates many developmental programs, including myogenesis. MEF2 gene transcripts are subject to alternate splicing to generate protein isoforms with divergent functions. We found that MEF2Cα1 was the ubiquitously expressed isoform that exhibited no myogenic activity and that MEF2Cα2, the muscle-specific MEF2C isoform, was required for efficient differentiation. We showed that exon α in MEF2C was aberrantly alternatively spliced in RMS cells, with the ratio of α2/α1 highly down-regulated in RMS cells compared with normal myoblasts. Compared with MEF2Cα2, MEF2Cα1 interacted more strongly with and recruited HDAC5 to myogenic gene promoters to repress muscle-specific genes. Overexpression of the MEF2Cα2 isoform in RMS cells increased myogenic activity and promoted differentiation in RMS cells. We also identified a serine protein kinase, SRPK3, that was down-regulated in RMS cells and found that expression of SRPK3 promoted the splicing of the MEF2Cα2 isoform and induced differentiation. Restoration of either MEF2Cα2 or SPRK3 inhibited both proliferation and anchorage-independent growth of RMS cells. Together, our findings indicate that the alternative splicing of MEF2C plays an important role in normal myogenesis and RMS development. An improved understanding of alternative splicing events in RMS cells will potentially reveal novel therapeutic targets for RMS treatment.
authors.affiliation: From the Department of Biochemistry and Molecular Biology and Simmons Cancer Institute, Southern Illinois University, School of Medicine, Carbondale, Illinois 62901.
authors.forename: Meiling
authors.initials: M
authors.lastname: Zhang
authors.affiliation: From the Department of Biochemistry and Molecular Biology and Simmons Cancer Institute, Southern Illinois University, School of Medicine, Carbondale, Illinois 62901.
authors.forename: Bo
authors.initials: B
authors.lastname: Zhu
authors.affiliation: From the Department of Biochemistry and Molecular Biology and Simmons Cancer Institute, Southern Illinois University, School of Medicine, Carbondale, Illinois 62901 jdavie@siumed.edu.
authors.forename: Judith
authors.initials: J
authors.lastname: Davie
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D049109:Cell Proliferation; D005091:Exons; D015972:Gene Expression Regulation, Neoplastic; D057809:HEK293 Cells; D006655:Histone Deacetylases / Q000235:genetics / Q000378:metabolism; D006801:Humans; D064326:MEF2 Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D024510:Muscle Development / Q000235:genetics*; D032446:Myoblasts / Q000166:cytology / Q000378:metabolism; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000235:genetics*; D012208:Rhabdomyosarcoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D016415:Sequence Alignment; D015398:Signal Transduction; D012983:Soft Tissue Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology
chemical_list: D064326:MEF2 Transcription Factors; C578040:MEF2C protein, human; C578041:Mef2c protein, mouse; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases; C504341:SRPK3 protein, mouse; C404500:HDAC5 protein, human; D006655:Histone Deacetylases
keywords: Alternative Splicing; Histone Deacetylase (HDAC); MEF2C; Myogenesis; Rhabdomyosarcoma (RMS); SRPK3; Tumor Cell Biology; Tumor Immunology