BINDING OF PROTEIN-KINASE-C ISOFORMS TO ACTIN IN APLYSIA

Recently, two of the 10 vertebrate protein kinase C (PKC) isoforms, PK C beta II and PKC epsilon, have been shown to bind specifically to act in filaments, suggesting that these kinases may regulate cytoskeletal dynamics. Here, we present evidence that two PKCs from the marine moll usk Aplysia californica, PKC Apl I, a Ca2+-activated PKC, and PKC Apl II, a Ca2+-independent PKC most similar to PKC epsilon and eta, also b ind F-actin. First, they both cosedimented with purified actin filamen ts in a phorbol ester-dependent manner. Second, they both translocated to the Triton-insoluble fraction of the nervous system after phorbol ester treatment. PKC Apl II could also partially translocate to actin filaments and associate with the Triton-insoluble fraction in the abse nce of phorbol asters. Translocation to purified actin filaments was i ncreased in the presence of a PKC inhibitor, suggesting that PKC phosp horylation reduces PKC bound to actin. Although both kinases bound F-a ctin, actin was not sufficient to activate the kinases. In support of a physiological role for actin-PKC interactions, immunochemical locali zation of PKC Apl II in neuronal growth cones revealed a striking colo calization with F-actin. Our results are consistent with a role for ac tin-PKC interactions in regulating cytoskeletal dynamics in Aplysia.