SELECTIVE ACTIVATION OF PHOSPHOLIPASE C-GAMMA-1 AND DISTINCT PROTEIN-KINASE-C SUBSPECIES IN INTRACELLULAR SIGNALING BY HEPATOCYTE GROWTH-FACTOR SCATTER FACTOR IN PRIMARY CULTURED RAT NEOCORTICAL CELLS

Hepatocyte growth factor/scatter factor (HGF) was recently reported to function as a neurotrophic factor in the CNS. To investigate the intr acellular signal pathways after activation of the HGF receptor c-Met i n primary cultured rat neocortical cells, in vitro kinase assays were performed. HGF stimulation enhances the phosphorylation of endogenous 80- and 45-kDa substrates, Studies with protein kinase inhibitors and phorbol 12-myristate 13-acetate showed that protein kinase C (PKC) is activated intracellularly, The 80-kDa protein was identified to be the major PKC substrate MARCKS. Although four PKC subspecies, PKC alpha, PKC epsilon, PKC gamma, and PKC lambda, were expressed in the cells, o nly PKC alpha, PKC epsilon, and PKC gamma were selectively translocate d in the plasma membrane after HGF stimulation. As expected from these three PKC subspecies, phosphorylation of phospholipase C gamma 1 (PLC gamma 1) but not phosphatidylinositol 3-kinase was enhanced, although the stimulation of brain-derived neurotrophic factor induced phosphor ylation of phosphatidylinositol 3-kinase, In contrast to the neocortic al cells, HGF did not enhance phosphorylation of PLC gamma 1 in primar y astrocytes. We also found that activated PKC(s) sewed as a major mit ogen-activated protein kinase activator in this pathway, These finding s suggest that HGF exerts neurotrophic effects through selective phosp horylation of PLC gamma 1 and activation of distinct PKC subspecies in neocortical cells, most likely neurons.