Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP38) regulate anterior pituitary cell secretion and proliferation. In the somatolactotrope GH4C1 cell line, these effects are mediated through the type-II-like PACAP receptor (VPAC2) coupled to the cAMP pathway. In this study, the control of the extracellularly responsive kinases (ERKs) by VIP and PACAP38 was investigated in GH4C1 cells. VIP and PACAP38 increased ERK1 and ERK2 phosphorylation and were equipotent stimulators of both kinases. ERK activation was mimicked by cholera toxin, forskolin and 8bromo-cAMP. VIP and PACAP38 activation of ERK2 was blocked by the protein kinase A inhibitor H89, whereas the protein kinase C inhibitor GF109203X, or prior PMA-induced depletion of the protein kinases C, failed to inhibit VIP and PACAP38 activation of ERK2. In contrast, thyrotropin-releasing hormone (TRH) elicited ERK activation by a PKC-dependent process. ERK activation by VIP or PACAP38 and TRH were additive and both sensitive to the MEK inhibitors PD98059 and U0126. In parallel, U0126 reduced prolactin (PRL) mRNA levels induced by VIP. These results demonstrate for the first time that VIP and PACAP38 activate ERK in GH4C1 cells. Cyclic AMP increase is sufficient to elicit ERK activation in these cells and thus likely to represent the transduction pathway underlying VIP- and PACAP38-dependent ERK activation. This mechanism seems to be involved in VIP-induced PRL gene regulation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.