Down-regulation of protein kinase C in Swiss 3T3 fibroblasts is independent of its phosphorylating activity

The phorbol ester TPA induces down-regulation of protein kinase C (PKC) in Swiss-3T3 fibroblasts, as determined by the use of an α,β,γPKC-specific antiserum. PKC is almost completely degraded 10 hours after TPA treatment of the cells and recovers within 72 hours. The staurosporine derivative K252a, known to inhibit PKC activity, causes strong suppression of TPA-induced (PKC-catalyzed) protein phosphorylation in Swiss-3T3 cells. Inhibition of protein phosphorylation by K252a is still effective when the process of down-regulation is completed. However, K252a does not influence TPA-induced down-regulation of PKC at all. Thus, down-regulation of PKC is not dependent on the enzyme's phosphorylating activity and, therefore, most likely not on its autophosphorylation as has been suggested by Ohno et al. [J. Biol. Chem. 265 , 6296–6300 (1990)] .