Regulation of myosin and overall protein degradation in mouse C2 skeletal myotubes

Abstract

We compared the breakdown of total cellular protein with that of the contractile protein, myosin, in cultured C2 mouse skeletal myotubes. The degradation of long-lived cellular proteins (which comprise the vast majority of myotube proteins) was inhibited by serum, insulin, and rat insulin-like growth factor-2. A physiological concentration of insulin was effective, but most of the effect of insulin occurred at concentrations well above the physiological range. IGF-2 inhibited protein breakdown at concentrations well within the range of total IGF-2 known to be present in the serum of fetal and neonatal rats. The breakdown of short-lived proteins was not altered by insulin or serum. We measured myosin degradation using a monoclonal antibody directed against myosin heavy chain. The half-life of myosin was 27 hours, and myosin breakdown was not altered by serum withdrawal applies to certain proteins, but not to others.