Protein kinase C V3 domain mutants with differential sensitivities to m‐calpain are not resistant to phorbol‐ester‐induced down‐regulation

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Abstract
Distinct linker sequences were introduced into the protease‐sensitive V3 domain of protein kinase C‐α and the mutant proteins were expressed in COS‐1 cells. Partially purified preparations of these mutants were functionally similar to wild‐type protein kinase C‐α, however their susceptibility to m‐calpain was quite distinct, with one mutant being insensitive to cleavage. The three mutants, after expression in COS‐1 cells, were found to behave in a manner indistinguishable from wild‐type protein kinase C‐α with respect to subcellular distribution, acute responses to 12‐O‐tetradecanoyl‐phorbol 13‐acetate and 12‐O‐tetradecanoyl‐phorbol‐13‐acetate‐induced down‐regulation. The data imply that down‐regulation of protein kinase C‐α is likely to involve a general degradative process rather than cleavage by a site‐specific protease.