Glycogen synthase kinase 3? represses MYOGENIN function in alveolar rhabdomyosarcoma.

ABSTRACT: MYOGENIN is a member of the muscle regulatory factor family that orchestrates an obligatory step in myogenesis, the terminal differentiation of skeletal muscle cells. A paradoxical feature of alveolar rhabdomyosarcoma (ARMS), a prevalent soft tissue sarcoma in children arising from cells with a myogenic phenotype, is the inability of these cells to undergo terminal differentiation despite the expression of MYOGENIN. The chimeric PAX3-FOXO1 fusion protein which results from a chromosomal translocation in ARMS has been implicated in blocking cell cycle arrest, preventing myogenesis from occurring. We report here that PAX3-FOXO1 enhances glycogen synthase kinase 3? (GSK3?) activity which in turn represses MYOGENIN activity. MYOGENIN is a GSK3? substrate in vitro on the basis of in vitro kinase assays and MYOGENIN is phosphorylated in ARMS-derived RH30 cells. Constitutively active GSK3?(S9A) increased the level of a phosphorylated form of MYOGENIN on the basis of western blot analysis and this effect was reversed by neutralization of the single consensus GSK3? phosphoacceptor site by mutation (S160/164A). Congruently, GSK3? inhibited the trans-activation of an E-box reporter gene by wild-type MYOGENIN, but not MYOGENIN with the S160/164A mutations. Functionally, GSK3? repressed muscle creatine kinase (MCK) promoter activity, an effect which was reversed by the S160/164A mutated MYOGENIN. Importantly, GSK3? inhibition or exogenous expression of the S160/164A mutated MYOGENIN in ARMS reduced the anchorage independent growth of RH30 cells in colony-formation assays. Thus, sustained GSK3? activity represses a critical regulatory step in the myogenic cascade, contributing to the undifferentiated, proliferative phenotype in alveolar rhabdomyosarcoma (ARMS).

SUBMITTER: Dionyssiou MG 

PROVIDER: S-EPMC3944270 | biostudies-literature | 2014 Feb

REPOSITORIES: biostudies-literature