Polycystic ovary syndrome (PCOS) affects approximately 5% of reproductive-age women and is characterized by anovulation and increased androgen production. Despite the ability to correct ovulatory disorders, pregnancy rates remain paradoxically low, and spontaneous pregnancy loss rates are high. To determine whether uterine dysfunction contributed to the adverse reproductive outcomes in PCOS, we assessed the effect of the increased ovarian androgens on a well-characterized gene essential to endometrial receptivity. Up-regulation of HOXA10 in the endometrium is necessary for receptivity to embryo implantation. In vitro, HOXA10 expression was repressed by testosterone but not by dehydroepiandrosterone, dehydroepiandrosterone sulfate, or insulin. Testosterone also prevented the increased expression of HOXA10 previously reported with estradiol or progesterone. Dihydrotestosterone produced an effect similar to that of testosterone, whereas flutamide blocked the testosterone effect. Endometrial biopsies, obtained from women with PCOS, demonstrated decreased HOXA10 mRNA. Testosterone is a novel regulator of HOXA10. Diminished uterine HOXA10 expression may contribute to the diminished reproduction potential of women with PCOS.

The first known hormonal signal of the conceptus during implantation is human chorionic gonadotropin (hCG). Interestingly, increased apoptosis in human endometrium coincides with the implantation window. Factors from the fetal or placental origin as well as maternal hormonal factors are likely to have a potential role in the regulation of apoptotic signaling molecules. We hypothesized that hCG may be a placental link for the development of local maternal immunotolerance. Fas-Fas ligand (FasL) system is one of the apoptotic signaling pathways, shown to be important in the development of local immune tolerance during and after implantation. We report that hCG treatment decreases cell proliferation and increases apoptosis in endometrial cells. Moreover, hCG stimulates FasL mRNA and protein expression without affecting Fas mRNA in these cells. Interestingly, in coculture experiments, hCG-treated endometrial cells induce an increase in T cell apoptosis. Our in vivo results reveal that cells of early pregnancy decidua express strong FasL immunoreactivity, and decidual areas containing interstitial cytotrophoblasts have numerous TUNEL-positive cells. Compared with decidual areas devoid of interstitial cytotrophoblasts, we observed in decidual areas containing interstitial cytotrophoblasts clearly less amount of TUNEL-positive cells. These results suggest that hCG may be a link in the development of peritrophoblastic immune tolerance and may facilitate the trophoblast invasion by regulating proapoptotic molecules such as FasL in endometrial cells.

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HOX genes regulate cell differentiation during embryonic development. Here we demonstrate HOXA10 expression in both benign and malignant adult human breast tissue and in MCF-7, but not BT20 breast cancer cells. We have previously shown that HOXA10 mediates uterine differentiation in response to estrogens. The mechanism of action of estradiol and other estrogen receptor modulators on breast cancer cell growth is still poorly understood. MCF-7 cells, which are ER (+) and express HOXA10, were used to assay the effect of estradiol and tamoxifen on HOXA10 expression. Semi-quantitative RT-PCR and northern analysis revealed that treatment with either estradiol or tamoxifen increased HOXA10 mRNA expression. BT20 cells, which are ER (-) and do not endogenously express HOXA10, were used to assay the effect of increased HOXA10 expression on p53 expression and on the invasive phenotype. Constitutively expressing HOXA10 in BT20 cells increased p53 protein expression. Increased HOXA10 also reduced invasiveness through matrigel. The mechanism by which estrogen and other estrogen receptor modulators influence both normal breast development as well as breast cancer may involve the regulation of developmental control genes such as HOXA10; HOXA10 in turn regulates expression of key downstream genes such as p53 and regulates tumor cell functional phenotype.

Implantation involves a complex set of events, including apoptosis in endometrial cells. Apoptosis in human endometrium coincides with the implantation window, suggesting a potential role for steroid hormones in its regulation. Fas ligand (FasL) is one of the mediators of apoptosis in differentiated cells and in embryonic development. Interaction of FasL with its receptor, Fas, induces apoptosis through autocrine and paracrine signaling. We hypothesized that FasL expression in human endometrium is cycle-dependent and that sex steroid hormones regulate FasL expression. We first studied menstrual cycle-dependent expression of FasL in human endometrium by immunohistochemistry in 24 samples. We then investigated the in vitro regulation of FasL expression by ovarian steroid hormones. Throughout the menstrual cycle immunohistochemical staining intensity was stronger in the functional layer of endometrium than it was in the basal layer. FasL immunoreactivity increased gradually through the mid- and late-proliferative phases in both endometrial stromal and glandular cells. Strong FasL expression was observed throughout the late-proliferative and secretory phases. Semiquantitative reverse transcription-polymerase chain reaction analysis in cultured endometrial glandular cells demonstrated that estradiol and progesterone stimulate FasL mRNA expression. Western blot analysis in endometrial glandular and stromal cells in culture revealed that estradiol alone and in combination with progesterone up-regulated FasL protein expression. These results suggest that estradiol and progesterone may have a role in the regulation of maternal immunotolerance for the implantation of a semiallograft embryo by inducing FasL expression. We speculate that increased FasL expression may mediate the apoptosis of endometrial cells and thus may play a role in trophoblast invasion.