Nerve growth factor-induced differentiation of PC12 cells is accompanied by elevated adenylyl cyclase activity.

Rat pheochromocytoma (PC12) cells characteristically undergo differentiation when cultured with nerve growth factor (NGF). Here we show that NGF dramatically increased the adenylyl cyclase-activating property of forskolin in PC12 cells. This effect of NGF was well maintained even when NGF was removed after 4 days, even though the morphological features of neuronal differentiation were rapidly lost on removal of NGF. The enhanced cAMP production in response to forskolin could be due to a synergistic interaction between forskolin and endogenously released agonists acting on G(s)-coupled receptors. However, responses to forskolin were not attenuated by antagonists of adenosine A2 receptors or pituitary adenylate cyclase-activating polypeptide (PACAP) receptors, suggesting that adenosine and PACAP were not involved. Adenylyl cyclases 3, 6 and 9 were the predominant isoforms expressed in PC12 cells, but we found no evidence for NGF-induced changes in expression levels of any of the 9 adenylyl cyclase isoforms, nor in the expression of Gα(s). These findings highlight that NGF has a subtle influence on adenylyl cyclase activity in PC12 cells which may influence more than the neurite extension process classically associated with neuronal differentiation.

Gi-coupled prostanoid receptors are the likely targets for COX-1-generated prostanoids in rat pheochromocytoma (PC12) cells.

Cyclooxygenase-1 (COX-1) behaves as a delayed response gene in rat pheochromocytoma (PC12) cells exposed to nerve growth factor (NGF). To investigate the possible targets for COX-1 generated prostanoids in the early stages of neuronal differentiation, we have examined the expression of prostanoid receptors by PC12 cells using functional assays. Prostanoid receptor-specific agonists failed to activate adenylyl cyclase in undifferentiated and NGF-treated PC12 cells; neither did they stimulate phospholipase C activity. EP3 receptor agonists and PGF(2alpha) were the only active ligands, able to inhibit forskolin-stimulated adenylyl cyclase activity. PC12 cells expressed EP3 and FP receptor mRNA, but only the responses to EP3 receptor agonists were inhibited by the EP3 receptor antagonist ONO-AE3-240. The functional role of NGF-stimulated COX-1 remains to be determined since we found no strong evidence of a role for EP3 receptors in the morphological changes induced by NGF during the early stages of differentiation of PC12 cells.