GnRH-induced PACAP and PAC1 receptor expression in pituitary gonadotrophs: A possible role in the regulation of gonadotropin subunit gene expression

We examined the expression of pituitary adenylate cyclase-activating polypeptide (PACAP) and the PACAP type 1 receptor (PAC1-R) mRNA following gonadotropin-releasing hormone (GnRH) stimulation using the gonadotroph cell line LβT2. GnRH stimulation increased PACAP and PAC1-R mRNA expression in a static culture. Increase in the cell surface density of the PAC1-R following transfection with PAC1-R expression vectors significantly increased gonadotropin LHβ and FSHβ subunit promoter activities following 100 nM PACAP stimulation. In addition, increasing concentrations of PACAP stimulation augmented the promoter activities for both LHβ and FSHβ in PAC-1R overexpressing cells. In the cells with PAC1-R, the effect of GnRH was further potentiated in the presence of PACAP from 5.31 ± 0.93 to 9.89 ± 0.38-fold for LHβ and for FSHβ subunit, respectively; from 2.58 ± 0.31-fold by GnRH alone to 10.90 ± 2.79-fold with PACAP. The combination treatment with GnRH and PACAP did not augment the ERK phosphorylation induced by GnRH alone. PACAP expectedly increased cAMP accumulation and this effect was significantly attenuated in the presence of GnRH. PACAP gene expression was more prominent following lower frequency GnRH pulses (every 120 min) in a perifused culture. Our results suggest that PACAP and PAC1-R are produced locally within the gonadotrophs following GnRH stimulation. They subsequently affect the gonadotrophs in an autocrine manner and modulate the GnRH pulse-dependent specific regulation of gonadotropin subunits.