Interaction of protein kinase C with filamentous actin: isozyme specificity resulting from divergent phorbol ester and calcium dependencies.
The mechanism of activation of protein kinase C isoforms by filamentous actin (F-actin) was investigated with respect to isozyme specificity and phorbol ester and Ca(2+) dependencies. It was found that the "conventional" (cPKC), alpha, betaI, betaII, and gamma, "novel" (nPKC) delta and epsilon, and "atypical" (aPKC) zeta isoforms were each activated by F-actin with varying potencies. The level of activity along with the affinity for binding to F-actin was further potentiated by the phorbol ester 4beta-12-O-tetradecanoylphorbol 13-acetate (TPA), the potency of which again varied for each isoform. By contrast to the other cPKC isoforms, the level of cPKC-gamma activity was unaffected by TPA, as was also the case for aPKC-zeta. It was found that whereas in the absence of F-actin the soluble form of cPKC-betaI contained two phorbol ester binding sites of low and high affinity, respectively, as previously reported for cPKC-alpha [Slater et al. (1998) J. Biol. Chem. 273, 23160-23168], the F-actin-bound form of the isozyme contained only a single site of relatively low affinity. The level of TPA required to induce cPKC-alpha, -betaI, and -betaII activity and the binding of these isozymes to F-actin was reduced in the presence of Ca(2+). By contrast, the activity of cPKC-gamma was unaffected by Ca(2+), as were the activities of nPKC-delta and -epsilon and aPKC-zeta, as expected. Thus, the interaction with F-actin appears to be a general property of each of the seven PKC isozymes tested. However, isoform specificity may, in part, be directed by differences in the phorbol ester and Ca(2+) dependences, which, with the notable exception of cPKC-gamma, appear to resemble those observed for the activation of each isoform by membrane association. The observation that cPKC isoforms may translocate to F-actin as well as the membrane as a response to an elevation of Ca(2+) levels may allow for the functional coupling of fluctuations of intracellular Ca(2+) levels through cPKC to F-actin cytoskeleton-mediated processes.
Slater
S J
SJ
Department of Pathology, Cell Biology and Anatomy, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Milano
S K
SK
Stagliano
B A
BA
Gergich
K J
KJ
Curry
J P
JP
Taddeo
F J
FJ
Stubbs
C D
CD
D000199:Actins / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D007527:Isoenzymes / Q000378:metabolism; D011485:Protein Binding; D011493:Protein Kinase C / Q000096:biosynthesis / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D013379:Substrate Specificity; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D000199:Actins; D007527:Isoenzymes; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium