Estradiol regulates gonadotropin-releasing hormone (GnRH) and its receptorgene expression and antagonizes the growth inhibitory effects of GnRH in human ovarian surface epithelial and ovarian cancer cells

In the present study, we investigated the expression of estrogen receptors (ER alpha and ER beta) in human ovarian surface epithelial(hOSE) cells and the ovarian cancer cell Line, OVCAR-3, and provided novel evidence that est rogen may have a growth regulatory effect in these cells. Expression levels of ER alpha messenger RNA (mRNA) were 1.5-fold higher in OVCAR-3 cells tha n in hOSE cells, as revealed by semiquantitative RT-PCR and Southern blot a nalysis. A significant increase (3.3-fold) in ER beta mRNA levels was obser ved in OVCAR-3 cells compared with hOSE cells. In parallel with mRNA levels , expression levels of ER alpha and ER beta proteins were also higher in OV CAR-3 cells compared with hOSE cells. We recently proposed that GnRH and it s receptor may have an autocrine role in hOSE and ovarian cancer cells. To determine whether estrogen regulates GnRH and GnRH receptor (GnRHR), hOSE a nd OVCAR-3 cells were treated with various concentrations of 17 beta -estra diol for 24 h. Expression levels of GnRH and GnRHR mRNA were examined using quantitative and competitive RT-PCR, respectively. Treatment with 17 beta -estradiol induced a significant down-regulation of GnRH mRNA in OVCAR-3 ce lls, but not in hOSE cells and of GnRHR mRNA in both hOSE and OVCAR-3 cells . Tamoxifen, an estrogen antagonist, prevented the effects of 17 beta -estr adiol, suggesting that estradiol action is mediated via the ER. Finally, th e effect of estrogen on the growth of hOSE and OVCAR-3 cells was investigat ed. The cells were treated with various concentrations of 17 beta -estradio l, and the proliferative index of cells was measured using [H-3]thymidine i ncorporation and DNA fluorometric assays. 17 beta -Estradiol stimulated the growth of OVCAR-3 cells in a dose-and time-dependent manner. In contrast, 17 beta- estradiol failed to stimulate the growth of hOSE cells. As estroge n down-regulated GnRH and GnRHR mRNA, we investigated whether estrogen trea tment blocks the growth inhibitory effect of a GnRH agonist in OVCAR-3 and hOSE cells. Cells were treated with 17 beta -estradiol(10(-7) M) together w ith (D-Ala(6))-GnRH (10-7 M), and the proliferative index of cells was meas ured. Pre- or cotreatment of cells with 17 beta -estradiol significantly at tenuated the growth inhibitory effect of the GnRH agonist in OVCAR-3 cells, whereas no effect of 17 beta -estradiol treatment was observed in hOSE cel ls. To our knowledge, these results provide the first demonstration of a po tential interaction between the estradiol/ER and GnRH/GnRHR systems, which may be important in the growth regulation of normal and neoplastic hOSE cel ls .