SUBNANOMOLAR CONCENTRATION OF VIP INDUCES THE NUCLEAR TRANSLOCATION OF PROTEIN-KINASE-C IN NEONATAL RAT CORTICAL ASTROCYTES

At subnanomolar concentrations, vasoactive intestinal peptide (VIP) ca n act as an astroglial mitogen and as a secretagogue for neurotrophic substances released from glia (Brenneman et al.: J Neurosci Res 25:386 -394, 1990), Here we report that treatment with subnanomolar (0.1 nM) VIP, that does not produce an increase in intracellular cAMP levels, i nduced the translocation of protein kinase C (PKC) from the cytoplasm to the nucleus in neonatal cortical astrocytes, as revealed by immunoh istochemistry, Western blot analysis, and measurements of the enzyme a ctivity, Western blot analysis of subcellular fractions, using PKC iso type-specific antisera, showed PKC alpha as well as the two novel PKC isotypes, delta and zeta immunoreactivities, whereas PKC beta or gamma immunoreactivities were not detected, PKC alpha was associated predom inantly with the cytosolic compartment, while PKC delta was found in t he plasma membrane and in nuclear fractions. In contrast, PKC zeta was distributed ubiquitously within the major subcellular fractions. Trea tment of the cells with 0.1 nM VIP caused a marked increase in nuclear PKC alpha and, to a lesser extent, PKC delta and PKC zeta immunoreact ivities. Western blot analysis showed that a low (1 nM) concentration of phorbol, 12-myristate, 13 acetate also caused the subcellular redis tribution of PKC immunoreactivities from the cytoplasm to the nuclear fraction, similar to VIP treatment. Exposure of astrocytes to high con centrations (1 mu M) of phorbol, 12-myristate, 13 acetate resulted in the down-regulation of PKC alpha and PKC delta, while distribution of PKC zeta immunoreactivities were only slightly altered. Measurements o f Ca2+ - and phospholipid-dependent PKC activities also showed a VIP-i nduced redistribution of PKC activity from the cytoplasmic to the nucl ear fractions. These results suggest that PKC may be involved in the s ignal transduction process elicited by VIP binding to the high affinit y VIP receptors present on cortical astrocytes. The observed changes i n the nuclear localization of PKC alpha and PRC delta in response to s ubnanomolar VIP may play a role in mediating the cellular response(s) to this peptide during neurodevelopment. (C) 1994 Wiley-Liss, Inc.