Cyclic adenosine 3',5'monophosphate/protein kinase A and mitogen-activated protein kinase 3/1 pathways are involved in adenylate cyclase-activating polypeptide 1-induced common alpha-glycoprotein subunit gene (Cga) expression in mouse pituitary gonadotroph LbetaT2 cells

Abstract

Adenylate cyclase-activating polypeptide 1 (ADCYAP1) binds both Gs- and Gq-coupled receptors and stimulates adenylate cyclase/cAMP and protein kinase C/mitogen-activated protein kinase 3/1 (MAPK3/1) signaling pathways in pituitary gonadotrophs. In this study, we investigated the cAMP and MAPK3/1 signaling pathways induced by ADCYAP1 stimulation and examined the effects of ADCYAP1 on the expression of gonadotropin subunit genes using a clonal gonadotroph cell line, LbetaT2. ADCYAP1 increased intracellular cAMP accumulation up to 19-fold in LbetaT2 cells. Common alpha-glycoprotein subunit gene (Cga) promoter activity was strongly activated by both ADCYAP1 and the cyclic-AMP analog, 8-(4-chlorophenylthio) adenosine 3',5'-cyclic monophosphate (CPT-cAMP). Both had little effect on luteinizing hormone beta (Lhb) and follicle-stimulating hormone beta (Fshb) promoter activities. Cga promoter activity was significantly increased by transfection with constitutively active cAMP-dependent protein kinase (PKA). Activities of the Lhb and Fshb promoters were only modestly increased. Both ADCYAP1 and CPT-cAMP induced MAPK3/1 activation in LbetaT2 cells. The MEK inhibitor, U0126, and the PKA inhibitors, H89 and cAMP-dependent protein kinase peptide inhibitor (PKI), completely inhibited MAPK3/1 activation by either ADCYAP1 or CPT-cAMP. Using luciferase reporter constructs containing cis-elements, the cAMP response element (Cre) promoter was stimulated about 4-fold by ADCYAP1. ADCYAP1-induced Cre promoter activity was completely inhibited by H89, but not by U0126. ADCYAP1 also increased the activity of the serum response element (Sre) promoter, a target for MAPK3/1, and treatment of the cells with U0126 completely inhibited ADCYAP1-induced Sre promoter activity. ADCYAP1-increased Cga promoter activity was inhibited partially by both H89 and U0126. Although combining the inhibitors showed an additive inhibition effect, it did not result in complete inhibition. These results suggest that in LbetaT2 cells, ADCYAP1 mainly increases Cga through activation of PKA and MAPK3/1, as well as through an additional unknown pathway.