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

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 D2 receptor in the regulation of pituitary gonadotropin gene expression using LβT2 cells, a mature, well differentiated clonal gonadotroph cell line. The presence of the dopamine D2 receptor in the LβT2 cells was confirmed by both RT-PCR and Western blot. Gonadotropin releasing hormone (GnRH) stimulation resulted in gonadotropin LHβ, FSHβ and α-subunit promoter activation, and none were inhibited by quinpirol, a specific dopamine D2 receptor agonist. Pituitary adenylate cyclase-activating polypeptide (PACAP) increased gonadotropin α-subunit promoter activity, but not LHβ and FSHβ promoter activity. The activity of PACAP was significantly inhibited in the presence of quinpirol. The protein kinase A inhibitor, H89, also inhibited PACAP-induced α-subunit gene expression. PACAP increased intracellular cAMP more than GnRH did in LβT2 cells, and the elevation of cAMP was strongly inhibited in the presence of various dopamine D2 agonists. These results suggest that in pituitary gonadotrophs, the dopamine D2 receptor is a negative regulator of gonadotropin α-subunit gene expression which is induced by cAMP-elevating factors in a cAMP-dependent pathway.