Degradation of protein kinase Mα by μ-calpain in a μ-calpain-protein kinase Cα complex

Abstract In previous studies, we isolated and identified a μ-calpain-PKCα complex from rabbit skeletal muscle. At the same time we pointed out that an association between μ-calpain and PKCα could occur at the level of the plasma membrane of muscle cells, and that PKCα could thus be considered as a potential μ-calpain substrate. In the present study, using the μ-calpain-PKCα complex as a model, we report that μ-calpain is activated in the combined presence of physiological calcium concentrations (less than 1 μM) and phosphatidylserine. Furthermore our data also show that: (1) there exists a correlation between the appearance of autolyzed μ-calpain forms and PKCα hydrolysis which leads to the formation of PKMα; (2) in certain experimental conditions, autolyzed μ-calpain forms are able to hydrolyze PKMα independently of the presence of diacylglycerol.