Expression of the pituitary adenylate cyclase-activating polypeptide (PACAP) type 1 receptor (PAC1R) potentiates the effects of GnRH on gonadotropin subunit gene expression.

We examined the effect of the pituitary adenylate cyclase-activating polypeptide (PACAP) type 1 receptor (PAC1R) on gonadotropin-releasing hormone (GnRH)-induced gonadotropin subunit promoter activities using the LβT2 gonadotroph cell line. In mock transfected cells, GnRH-increased LHβ and FSHβ promoters up to 2.74 ± 0.15-fold and 1.6 ± 0.05-fold respectively. When cells were transfected with PAC1R, both LHβ and FSHβ promoter activities were further increased up to 6.1 ± 0.87-fold and 2.22 ± 0.43-fold following GnRH stimulation. ERK phosphorylation, serum response element (SRE) promoters, and cAMP response element (CRE) promoters stimulated by GnRH were also potentiated in the presence of increasing amounts of PAC1R. The EC50 values for LHβ and FSHβ gene transcription by GnRH were significantly decreased by overexpression of PAC1R. PACAP 6-38, a PACAP receptor antagonist, failed to reduce the effect of GnRH on gonadotropin promoter activities in PAC1R overexpressing cells, suggesting that the potentiation of the effects of GnRH by PAC1R expression was not related to an autocrine mechanism of PACAP produced in the gonadotrophs. Our current results show that the action of GnRH in the regulation of gonadotropin subunit expression is enhanced by the presence of PAC1Rs.