The small heat shock protein alphaB-crystallin inhibits differentiation-induced caspase 3 activation and myogenic differentiation.

Myoblasts respond to growth factor deprivation either by diffentiation into multinucleated myotubes or by undergoing apoptosis. The induction of apoptosis and differentiation in myogenic lineage may use overlapping cellular mechanisms. Here we demonstrate that the expression of the small heat shock protein alphaB-crystallin as well as MyoD and myogenin is induced during myogenic differentiation in C2C12 cells, and these inductions occur at an early stage in the differentiation in vitro. To investigate the effect of alphaB-crystallin on myogenic differentiation and apoptosis, C2C12 cells were infected with adenovirus vector bearing full-length alphaB-crystallin cDNA. Overexpression of alphaB-crystallin in C2C12 cells suppressed differentiation-induced apoptosis and activation of caspase 3, and also decreased the expression of MyoD and myogenin during myogenic differentiation of C2C12 cells induced by the differentiation medium. Our findings suggest that stress such as growth factor deprivation plays an important role in triggering apoptosis associated with myogenic differentiation and alphaB-crystallin suppressed the differentiation, apoptosis and caspase 3 activity.