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

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 PKC delta and PKC epsilon, suggesting that one these isozymes regulates responses to NGF. To examine this possibility, we established PC12 cell lines that express a fragment encoding the first variable domain of PKC epsilon (amino acids 2-144), which acts as an isozyme-specific inhibitor of PKC epsilon in cardiac myocytes. Phorbol ester-stimulated translocation of PKC epsilon 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 PKC delta. These results demonstrate that PKC epsilon mediates enhancement of NGF-induced signaling and neurite outgrowth by phorbol esters and ethanol in PC12 cells.