The present study demonstrates the action of pituitary adenylate cyclase-activating polypeptide (PACAP) on gonadotropin-releasing hormone (GnRH)-producing neuronal cells, GT1-7. Because we found the expression levels of PACAP type 1 receptor (PAC1R) to be low in these cells, we transfected them with PAC1R expression vector and observed the outcome. PACAP increased the activity of the serum response element (Sre) promoter, a target of extracellular signal-regulated kinase (ERK), as well as the cAMP response element (Cre) promoter in GT1-7 cells overexpressing PAC1R. We also observed ERK phosphorylation and cAMP accumulation upon PACAP stimulation. PACAP stimulated the promoter activity of GnRH receptor (GnRHR) with increasing levels of GnRHR proteins. Notably, the increase in GnRHR promoter activity from kisspeptin was potentiated in the presence of PACAP. A similar increasing effect of PACAP on the action of kisspeptin was observed for Cre promoter activity. On the other hand, the Sre promoter activated by kisspeptin was inhibited by co-treatment with kisspeptin and PACAP. Likewise, kisspeptin-increased GnRHR promoter activity and Cre promoter activity were both potentiated in the presence of cAMP, whereas the Sre promoter activated by kisspeptin was inhibited in the presence of cAMP. Our observations show that PACAP increases GnRHR expression and stimulates kisspeptin's effect on GnRHR expression in association with the cAMP/PKA signaling pathway in GT1-7 cells overexpressing PAC1R. In addition, PACAP was shown to have an inhibitory effect on ERK-mediated kisspeptin action.
Keywords: GnRH; GnRH receptor; Kisspeptin; PACAP.
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