PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE STIMULATES BOTH C-FOS GENE-EXPRESSION AND CELL-SURVIVAL IN RAT CEREBELLAR GRANULE NEURONS THROUGH ACTIVATION OF THE PROTEIN-KINASE A PATHWAY

A high density of pituitary adenylate cyclase-activating polypeptide ( PACAP) receptors coupled to both adenylyl cyclase and phospholipase C is found in the external granule cell layer of the rat cerebellum duri ng postnatal development. It has recently been reported that synthetic PACAP promotes cell survival and neurite outgrowth in immature granul e cells. In the present study, we have investigated the transduction p athways that mediate the neurotrophic activity of PACAP in cultured gr anule cells from eight-day-old rat cerebellum. The effect of PACAP on cell survival was mimicked by dibutyryladenosine 3', 5'-cyclic-monopho sphate but not phorbol 12-myristate 13-acetate suggesting that only th e adenylyl cyclase pathway is involved in the neurotrophic activity of PACAP. PACAP also induced a transient increase in c-fos messenger RNA level. The ability of PACAP to stimulate c-fos gene expression was mi micked by dibutyryladenosine 3', 5'-cyclic-monophosphate but not phorb ol 12-myristate 13-acetate. Similar effects of PACAP on granule cell s urvival were observed whether the cells were continuously incubated wi th PACAP for 48 h or only exposed to PACAP during 1 h. The protein kin ase A inhibitor H89 significantly reduced the effect of PACAP on c-fos messenger RNA level whereas the specific protein kinase C inhibitor c helerythrine did not modify c-fos gene expression. These data indicate that the action of PACAP on cerebellar granule cell survival and c-fo s gene expression are both mediated through the adenylyl cyclase/prote in kinase A pathway. The observation that a short-term stimulation by PACAP can be converted into a long-lasting response indicates that the effect of the peptide an cell survival must involve immediate-early g ene activation. The fact that a brief exposure to PACAP causes both c- fos gene expression and promotes cell survival strongly suggests that c-fos is involved in the trophic effect of PACAP on immature cerebella r granule cells. (C) 1998 IBRO. Published by Elsevier Science Ltd.