Ozz-E3, A Muscle-Specific Ubiquitin Ligase, Regulates b-Catenin Degradation during Myogenesis

The identities of the ubiquitin-ligases active during myogenesis are largely unknown. Here we describe a RING-type E3 ligase complex specified by the adaptor protein, Ozz, a novel SOCS protein that is developmentally regulated and expressed exclusively in striated muscle. In mice, the absence of Ozz results in overt maturation defects of the sarcomeric apparatus. We identified b-catenin as one of the target substrates of the Ozz-E3 in vivo. In the differentiating myofibers, Ozz-E3 regulates the levels of sarcolemma-associated b-catenin by mediating its degradation via the proteasome. Expression of b-catenin mutants that reduce the binding of Ozz to endogenous b-catenin leads to Mb-b-catenin accumulation and myofibrillogenesis defects similar to those observed in Ozz null myocytes. These findings reveal a novel mechanism of regulation of Mb-b-catenin and the role of this pool of the protein in myofibrillogenesis, and implicate the Ozz-E3 ligase in the process of myofiber differentiation.