Alternative Splicing of MEF2C pre-mRNA Controls Its Activity in Normal Myogenesis and Promotes Tumorigenicity in Rhabdomyosarcoma Cells

• Published in: The Journal of biological chemistry Vol. 290; no. 1; pp. 310 - 324
• Main Authors: Zhang, Meiling, Zhu, Bo, Davie, Judith
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 02.01.2015; American Society for Biochemistry and Molecular Biology
• Subjects: Alternative Splicing; Amino Acid Sequence; Animals; Cell Biology; Cell Differentiation; Cell Line; Cell Proliferation; Exons; Gene Expression Regulation, Neoplastic; HEK293 Cells; Histone Deacetylase (HDAC); Histone Deacetylases - genetics; Histone Deacetylases - metabolism; Humans; MEF2 Transcription Factors - chemistry; MEF2 Transcription Factors - genetics; MEF2 Transcription Factors - metabolism; MEF2C; Mice; Molecular Sequence Data; Muscle Development - genetics; Myoblasts - cytology; Myoblasts - metabolism; Myogenesis; Protein Isoforms - chemistry; Protein Isoforms - genetics; Protein Isoforms - metabolism; Protein-Serine-Threonine Kinases - deficiency; Protein-Serine-Threonine Kinases - genetics; Rhabdomyosarcoma (RMS); Rhabdomyosarcoma - genetics; Rhabdomyosarcoma - metabolism; Rhabdomyosarcoma - pathology; Sequence Alignment; Signal Transduction; Soft Tissue Neoplasms - genetics; Soft Tissue Neoplasms - metabolism; Soft Tissue Neoplasms - pathology; SRPK3; Tumor Cell Biology; Tumor Immunology; SRPK3; MEF2C; Tumor Cell Biology; Alternative Splicing; Histone Deacetylase (HDAC); Tumor Immunology; Rhabdomyosarcoma (RMS); Myogenesis
• DOI: 10.1074/jbc.M114.606277
• ISSN: 0021-9258; 1083-351X

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.MEF2C is an important regulator of many developmental programs. Alternative splicing of the α exon of MEF2C regulates myogenesis. Loss of SRPK3 in rhabdomyosarcoma cells inhibits this splicing and blocks differentiation. MEF2Cα2 promotes myogenesis, and restoration of MEF2Cα2 in rhabdomyosarcoma cells inhibits growth. Defining the function and deregulation of MEF2Cα2 enhances the understanding of normal myogenesis and RMS tumorigenesis.