IGFS AND SKELETAL MUSCLE CELL DIFFERENTIATION

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In accordance with the Physician Scientist Award (PSA), the candidate, the sponsor, and the Phase I advisory committee, in conjunction with the Department of Pediatrics, have constructed a detailed 2-phase 5-year training program intended to provide the candidate with an intensive training and research experience. Phase I consists of eleven graduate division courses in 5 departments, regular attendance at various seminars, and three laboratory rotations. This experience, modeled after the graduate Ph.D. program in Biomedical Sciences at the University of California, San Francisco, will fulfill the Phase I requirements of the PSA. Phase Il is 95-lOO% laboratory research under the direct supervision of the sponsor. During phase II, the candidate's research effort will focus on the mechanisms by which the insulin-like growth-factors (IGFs) regulate muscle cell differentiation. This objective will be approached by l) studying potential target genes of IGF action which play a role in the differentiation process, 2) examining which IGF receptor subtypes mediate the myogenic effect of IGFs, and 3) exploring the potential role of IGF binding proteins (BPs) in modulating IGF-induced differentiation. During this proposal, the following three hypotheses will be tested: l) that IGFs influence the decision of skeletal muscle cells to grow or differentiate by regulating the phosphorylation of retinoblastoma protein (pRB), a key regulator of the cell cycle machinery, which when phosphorylated promotes growth but when hypo- or unphosphorylated promotes differentiation; 2) that IGF-II receptor, independently of IGF-I receptor, can signal myogenesis; and 3) that IGFBPs, which may enhance or inhibit IGF action, modulate IGF-induced differentiation in muscle cells. To test these hypotheses we propose the following specific aims: l) Examine the effects of IGFs on pRB phosphorylation and on the expression of the principal cyclin-dependent kinases (CDKs) and their regulatory subunits, the cyclins and the CDK inhibitors, which regulate pRB phosphorylation; 2) Functionally inactivate the IGF-I receptor with a dominant negative mutation to determine if the IGF-II receptor can signal muscle cell differentiation independently of the IGF-I receptor; and 3) Examine the ability of muscle cell IGFBPs to modulate IGF-induced differentiation by inhibiting their expression with antisense cRNAs. These studies should provide further understanding of the mechanisms by which IGFs regulate muscle cell differentiation. Studying the links between growth factor signaling and cell cycle regulation could have general implications for understanding the processes of normal as well as aberrant proliferation and differentiation. Successful completion of this program will equip the candidate to pursue an independent career investigating the molecular basis of endocrine function.