Dopamine D2 receptor expression and regulation of gonadotropin α-subunit gene in clonal gonadotroph LβT2 cells

Abstract

This study investigated the role of dopamine on the regulation of gonadotropin secretion at the gonadotroph cell line. We examined the function of the dopamine D(2) receptor in the regulation of pituitary gonadotropin gene expression using LbetaT2 cells, a mature, well differentiated clonal gonadotroph cell line. The presence of the dopamine D(2) receptor in the LbetaT2 cells was confirmed by both RT-PCR and Western blot. Gonadotropin releasing hormone (GnRH) stimulation resulted in gonadotropin LHbeta, FSHbeta and alpha-subunit promoter activation, and none were inhibited by quinpirol, a specific dopamine D(2) receptor agonist. Pituitary adenylate cyclase-activating polypeptide (PACAP) increased gonadotropin alpha-subunit promoter activity, but not LHbeta and FSHbeta promoter activity. The activity of PACAP was significantly inhibited in the presence of quinpirol. The protein kinase A inhibitor, H89, also inhibited PACAP-induced alpha-subunit gene expression. PACAP increased intracellular cAMP more than GnRH did in LbetaT2 cells, and the elevation of cAMP was strongly inhibited in the presence of various dopamine D(2) agonists. These results suggest that in pituitary gonadotrophs, the dopamine D(2) receptor is a negative regulator of gonadotropin alpha-subunit gene expression which is induced by cAMP-elevating factors in a cAMP-dependent pathway.