Hormonal regulation of estrogen receptor alpha and beta gene expression in human granulosa-luteal cells in vitro.

Abstract

Estrogen is one of the major sex steroid hormones that is produced from the human ovary, and its actions are established to be a receptor-mediated process. Despite the demonstration of estrogen receptor (ER) expression, little is known regarding the regulation of ER in the human ovary. In the present study we investigated the expression and hormonal regulation of ERalpha and ERbeta in human granulosa-luteal cells (hGLCs). Using RT-PCR amplification, both ERalpha and ERbeta messenger ribonucleic acid (mRNA) were detected from hGLCs. Northern blot analysis revealed that ERalpha is expressed at a relatively lower level than ERbeta. Basal expression studies indicated that ERalpha mRNA levels remain unchanged, whereas ERbeta mRNA levels increased with time in culture in vitro, suggesting that ERbeta is likely to play a dynamic role in mediating estrogen action in hGLCs. The regulation of ERalpha and ERbeta expression by hCG was examined. hCG treatment (10 IU/mL) significantly attenuated the ERalpha (45%; P < 0.01) and ERbeta (40%; P < 0.01) mRNA levels. The hCG-induced decrease in ERalpha and ERbeta expression was mimicked by 8-bromo-cAMP (1 mmol/L) and forskolin (10 micromol/L) treatment. Additional studies using a specific protein kinase A (PKA) inhibitor (adenosine 3',5'-cyclic monophosphorothioate, Rp-isomer, triethylammonium salt) and an adenylate cyclase inhibitor (SQ 22536) further implicated the involvement of the cAMP/PKA signaling pathway in hCG action in these cells. The hCG-induced decrease in ERalpha and ERbeta mRNA levels was prevented in the presence of these inhibitors. Next, the effect of GnRH on ER expression was studied. Sixty-eight percent (P < 0.001) and 60% (P < 0.001) decreases in ERalpha and ERbeta mRNA levels, respectively, were observed after treatment with 0.1 micromol/L GnRH agonist (GnRHa). Pretreatment of the cells with a protein kinase C (PKC) inhibitor (GF109203X) completely reversed the GnRHa-induced down-regulation of ERalpha and ERbeta expression, suggesting the involvement of PKC in GnRH signal transduction in hGLCs. In agreement with the semiquantitative RT-PCR results, Western blot analysis detected a decrease in ERalpha and ERbeta proteins levels in hGLCs after treatment with hCG (10 IU/mL), GnRH (0.1 micromol/L), 8-bromo-cAMP (1 mmol/L), forskolin (10 micromol/L), or phorbol 12-myristate 13 acetate (10 micromol/L). Functionally, we demonstrated an inhibition of progesterone production in hGLCs in vitro by 17beta-estradiol, and this inhibitory effect was eliminated by pretreatment of 10 IU/mL hCG or 0.1 micromol/L GnRHa for 24 h before 17beta-estradiol administration. In summary, we observed a differential expression of ERalpha and ERbeta mRNA in hGLCs in vitro. The demonstration of hCG- and GnRHa-induced down-regulation of ERalpha and ERbeta gene expression suggests that hCG and GnRH may contribute to the control of granulosa-luteal cell function. Furthermore, our data suggest that the effects of hCG and GnRH on ERalpha and ERbeta expression in hGLCs are mediated in part by activation of PKA and PKC signaling pathways, respectively.