Isoform-specific translocation of protein kinase C following glutamate administration in primary hippocampal neurons

High concentrations of glutamate, the major excitatory neurotransmitter in the mammalian brain, lead to intracellular calcium overload resulting in ex citotoxic damage and death of neurons. Since protein kinase C (PKC) is invo lved in neuronal degeneration resulting from cerebral ischemia and from glu tamate excitotoxicity, we investigated the effect of glutamate on changes i n the cellular distribution of various PKC isoforms in cultured hippocampal neurons in comparison with the effects elicited by the PKC activator phorb ol ester, Out of the expressed PKC isoforms alpha,gamma,epsilon,zeta and la mbda only the conventional isoforms PKC alpha and gamma responded to glutam ate. Using subcellular fractionation and Western blotting with isoform-spec ific antibodies and immunocytochemical localization with confocal laser sca nning microscopy, we observed that phorbol ester and glutamate have differe nt effects on PKC isoform redistribution: Whereas phorbol ester resulted in translocation of PKC alpha and PKC gamma toward a membrane fraction, the g lutamate-mediated rise in intracellular calcium concentration induced a tra nslocation mainly toward a detergent-insoluble, cytoskeletal fraction. Immu nocytochemical analysis revealed an isoform-specific translocation followin g glutamate treatment: PKC gamma was translocated mainly to cytoplasmic, or ganelle-like structures, whereas PKC alpha redistributed to the plasma memb rane and into the cell nucleus. The latter result is of special interest, a s it indicates that nuclear PKC may play a role in processes of excitotoxic cell damage. (C) 1999 Elsevier Science B.V. All rights reserved.