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Regulation of Gonadotropin Subunit Gene Expression by Dopamine D₂ Receptor Agonist in Clonal Mouse Gonadotroph T3-1 Cells¹

^a Department of Obstetrics and Gynecology, Shimane Medical University, Izumo 693-8501, Japan ^b Department of Pharmacology, Kumamoto University School of Medicine, Kumamoto 860-0811, Japan

Pituitary prolactin biosynthesis is negatively regulated by hypothalamic dopamine through D₂ receptors in pituitary lactotrophs, but little is known about the direct effect of dopamine on gonadotrophs. In this study, the clonal gonadotroph-derived cell line, T3-1, was used to examine whether gene expression of the pituitary gonadotropin subunit, stimulated with GnRH or pituitary adenylate cyclase-activating polypeptide (PACAP), was controlled by dopamine D₂ receptor. Western blotting and reverse transcription-polymerase chain reaction analysis demonstrated the presence of dopamine D₂ receptors in T3-1 cells. Both GnRH and PACAP increased subunit gene expression. GnRH-induced subunit gene expression was not affected by quinpirol, a specific dopamine D₂ receptor agonist. In contrast, PACAP-induced gene expression was significantly lower in the presence of quinpirol. The roles of extracellular signal-regulated kinase (ERK) and cAMP in the expression of the subunit gene were examined. GnRH activated ERK, but PACAP did not, and the activation was not inhibited by quinpirol. GnRH-induced subunit gene expression was completely inhibited by an ERK inhibitor, PD098059. Cyclic AMP accumulation in T3-1 cells was increased by treatment with PACAP, and quinpirol inhibited this effect. GnRH did not affect cAMP production in these cells. These results suggest that in T3-1 cells, dopamine D₂ receptors negatively regulate pituitary subunit gene expression in association with the cAMP-dependent pathway, but not with the ERK pathway.

¹ This work was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Science, Sports, and Culture of Japan to H.K. and K.M. and by a grant from the Ministry of Health and Welfare to K.M.

² Correspondence. FAX: 81-853-20-2264; kawa45{at}shimane-med.ac.jp

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