Abstract
The two most closely related isoenzymes of protein kinase C (PKC), PKC betaI and betaII, are distinct but highly homologous isoenzymes derived via alternative splicing of the same gene product. In this study, PKC betaII, but not PKC betaI, translocated to the actin cytoskeleton upon stimulation of cells with phorbol esters. In cells, antibodies to PKC betaII, but not to PKC betaI, co-immunoprecipitated actin. Using an actin-binding co-sedimentation assay, we show in vitro that PKC betaII, but not PKC betaI, binds to actin specifically. This binding was inhibited by peptides based on sequences unique to PKC betaII; thus defining an actin-binding site in PKC betaII that is not present in PKC betaI. The binding of PKC betaII 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 betaII with actin. On the other hand, the interaction of PKC betaII with actin resulted in marked enhancement of autophosphorylation of PKC betaII 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.
Highlights
We demonstrate that while Protein kinase C (PKC) I and II display identical enzymatic activity in vitro, they behave as unique yl-terminal region of PKC , which is involved in direct- isoenzymes with distinct properties in vitro and in vivo
This study has determined specific functions for the PKC II isoenzyme based on its unique carboxyl-terminal tail
9) the ability of F-actin to selectively alter the substrate specificity of PKC II
Summary
We demonstrate that while PKC I and II display identical enzymatic activity in vitro, they behave as unique yl-terminal region of PKC , which is involved in direct- isoenzymes with distinct properties in vitro and in vivo. Exogenously added troponin complex was even more potent (IC50 ϭ 2 M), demonstrating that the selective binding of PKC II to actin in vitro is mediated through ABS-1, which PKC II contains in its unique diverged sequence (Fig. 7A).
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