Melatonin activates PKC-alpha but not PKC-epsilon in N1E-115 cells

Previous reports have revealed that calmodulin antagonism by melatonin is f ollowed by microtubule enlargements and neurite outgrowths in neuroblastoma N1E-115 cells. In addition, activation of protein kinase C (PKC) by this n eurohormone is also followed by increased vimentin phosphorylation, and reo rganization of vimentin intermediate filaments (IFs) in N1E-115 cells. In t his work, we further characterize the activation of PKC by melatonin in neu roblastoma N1E-115 cells. We studied the Ca2+-dependent effects of melatoni n on PKC activity and distribution of PKC-a in isolated N1E-115 cell IFs. A lso, the effects of melatonin on PKC-alpha translocation in comparison to P KC-epsilon, were studied in intact N1E-115 cells. The results showed that b oth melatonin and the PKC agonist phorbol-12-myristate-13-acetate increased PKC activity in isolated IFs. The effects of the hormone were Ca2+-depende nt, while those caused by the phorbol ester were produced with or without C a2+. Also, in isolated in situ IFs, the hormone changed the distribution of PKC-alpha. In intact N1E-115 cells, melatonin elicited PKC-a translocation and no changes were detected in PKC-epsilon. Phorbol-12-myristate-13-aceta te modified the subcellular distribution of both PKC isoforms. The results showed that melatonin selectively activates the Ca2+-dependent a isoform of PKC and suggest that PKC-cc activation by melatonin underlies IF rearrange ments and participates in neurite formation in N1E-115 cells. (C) 2001 Else vier Science Ltd. All rights reserved.