Pituitary adenylate cyclase-activating polypeptide-induced differentiation of embryonic neural stem cells into astrocytes is mediated via the β isoform of protein kinase C

We have found previously that pituitary adenylate cyclase-activating polypeptide (PACAP) increases the number of astrocytes generated from cultured mouse neural stem cells (NSCs) via a mechanism that is independent of the cyclic AMP/protein kinase A pathway (Ohno et al., 2005). In the present study, the signaling pathway involved in the differentiation process was further investigated. PACAP-induced differentiation was inhibited by the phospholipase C inhibitor, U73122, the protein kinase C (PKC) inhibitor, chelerythrine, and the intracellular calcium chelator, BAPTA-AM, and was mimicked by phorbol 12-myristate 13-acetate (PMA), but not by 4a-PMA. These results suggest that the PACAP-generated signal was mediated via the PACAP receptor, PAC1 stimulated heterotrimeric G-protein, resulting in activation of phospholipase C, followed by calcium- and phospholipid-dependent protein kinase C (cPKC). To elucidate the involvement of the different isoforms of cPKC, their gene and protein expression were examined. Embryonic NSCs expressed α and βII PKC, but lacked PKCγ. When NSCs were exposed to 2 nM PACAR protein expression levels of the βII isoform transiently increased two-fold before differentiation, returning to basal levels by Day 4, whereas the level of PKCa increased line-arly up to Day 6. Overexpression of PKCβII with adenovirus vector synergistically enhanced differentiation in the presence of 1 nM PACAP, whereas expression of the dominant-negative mutant of PKCβII proved inhibitory. These results indicate that the β isoform of PKC plays a crucial role in the PACAP-induced differentiation of mouse embryonic NSCs into astrocytes.