An inhibitory fragment derived from protein kinase Cε prevents enhancement of nerve growth factor responses by ethanol and phorbol esters

Abstract

We have studied nerve growth factor (NGF)-induced differentiation of PC12 cells to identify PKC isozymes important for neuronal differentiation. Previous work showed that tumor-promoting phorbol esters and ethanol enhance NGF-induced mitogen-activated protein (MAP) kinase activation and neurite outgrowth by a PKC-dependent mechanism. Ethanol also increases expression of PKCδ and PKCε, suggesting that one these isozymes regulates responses to NGF. To examine this possibility, we established PC 12 cell lines that express a fragment encoding the first variable domain of PKCε (amino acids 2-144), which acts as an isozyme-specific inhibitor of PKCε in cardiac myocytes. Phorbol ester-stimulated translocation of PKCε was markedly reduced in these PC12 cell lines. In addition, phorbol ester and ethanol did not enhance NGF-induced MAP kinase activation or neurite outgrowth in these cells. In contrast, phorbol ester and ethanol increased neurite outgrowth and MAP kinase phosphorylation in cells expressing a fragment derived from the first variable domain of PKCδ. These results demonstrate that PKCε mediates enhancement of NGF-induced signaling and neurite outgrowth by phorbol esters and ethanol in PC12 cells.