title: Sam68 Regulates S6K1 Alternative Splicing during Adipogenesis.
abstract: The requirement for alternative splicing during adipogenesis is poorly understood. The Sam68 RNA binding protein is a known regulator of alternative splicing, and mice deficient for Sam68 exhibit adipogenesis defects due to defective mTOR signaling. Sam68 null preadipocytes were monitored for alternative splicing imbalances in components of the mTOR signaling pathway. Herein, we report that Sam68 regulates isoform expression of the ribosomal S6 kinase gene (Rps6kb1). Sam68-deficient adipocytes express Rps6kb1-002 and its encoded p31S6K1 protein, in contrast to wild-type adipocytes that do not express this isoform. Sam68 binds an RNA sequence encoded by Rps6kb1 intron 6 and prevents serine/arginine-rich splicing factor 1 (SRSF1)-mediated alternative splicing of Rps6kb1-002, as assessed by cross-linking and immunoprecipitation (CLIP) and minigene assays. Depletion of p31S6K1 with small interfering RNAs (siRNAs) partially restored adipogenesis of Sam68-deficient preadipocytes. The ectopic expression of p31S6K1 in wild-type 3T3-L1 cells resulted in adipogenesis differentiation defects, showing that p31S6K1 is an inhibitor of adipogenesis. Our findings indicate that Sam68 is required to prevent the expression of p31S6K1 in adipocytes for adipogenesis to occur.
authors.affiliation: Terry Fox Molecular Oncology Group and Segal Cancer Center, Bloomfield Center for Research on Aging, Lady Davis Institute for Medical Research, and Departments of Oncology and Medicine, McGill University, Montréal, Québec, Canada.
authors.forename: Jingwen
authors.initials: J
authors.lastname: Song
authors.affiliation: Terry Fox Molecular Oncology Group and Segal Cancer Center, Bloomfield Center for Research on Aging, Lady Davis Institute for Medical Research, and Departments of Oncology and Medicine, McGill University, Montréal, Québec, Canada stephane.richard@mcgill.ca.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Richard
mesh_terms: D041721:3T3-L1 Cells; D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D017667:Adipocytes / Q000502:physiology; D050156:Adipogenesis / Q000235:genetics*; D017398:Alternative Splicing / Q000235:genetics*; D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D002460:Cell Line; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D020033:Protein Isoforms / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D016601:RNA-Binding Proteins / Q000235:genetics*; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000235:genetics*; D015398:Signal Transduction / Q000235:genetics
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C513253:Khdrbs1 protein, mouse; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C512964:Rps6ka1 protein, mouse