Protein kinase C beta II specifically binds to and is activated by F-actin

The two most closely related isoenzymes of protein kinase C (PRC), PKC beta I and beta II, are distinct but highly homologous isoenzymes derived via alternative splicing of the same gene product. In this study, PKC beta II, but not PKC beta I, translocated to the actin cytoskeleton upon stimulation of cells with phorbol esters. In cells, antibodies to PKC beta II, but not to PKC beta I, co-immunoprecipitated actin. Using an actin-binding co-sedimentation assay, we show in vitro that PKC beta II, but not PKC beta I, binds to actin specifically, This binding was inhibited by peptides based on sequences unique to PKC beta II; thus defining an actin-binding site in PKC beta II that is not present in PKC beta I. The binding of PKC beta II to actin was not inhibited by kinase inhibitors of PKC (sphingosine and staurosporine), suggesting that prior activation and/or substrate phosphorylation are not required for the interaction of PKC beta II with actin. On the other hand, the interaction of PKC beta II with actin resulted in marked enhancement of autophosphorylation of PKC beta II and in an alteration in substrate specificity. These studies serve to define a novel functional domain in the carboxyl-terminal region of PKC beta, which is involved in directing isoenzyme-specific protein-protein interactions, and consequently, isoenzyme-specific functions in vivo.