Paracrine regulation of epithelial progesterone receptor by estradiol in the mouse female reproductive tract

Regulation of progesterone receptor (PR) by estradiol-17beta (E(2)) in mouse uterine and vaginal epithelia was studied. In ovariectomized mice, PR expression was low in both vaginal stroma and epithelium, but high in uterine epithelium. E(2) induced PR in vaginal epithelium and stroma, but down-regulated PR in uterine epithelium. Analysis of estrogen receptor alpha (ERalpha) knockout (ERKO) mice showed that ERalpha is essential for E(2)-induced PR expression in both vaginal epithelium and stroma, and for E(2)-induced down-regulation, but not constitutive expression of PR in uterine epithelium. Regulation of PR by E(2) was studied in vaginal and uterine tissue recombinants made with epithelium and stroma from wild-type and ERKO mice. In the vaginal tissue recombinants, PR was induced by E(2) only in wild-type epithelium and/or stroma. Hence, in vagina, E(2) induces PR directly via ERalpha within the tissue. Conversely, E(2) down-regulated epithelial PR only in uterine tissue recombinants constructed with wild-type stroma. Therefore, down-regulation of uterine epithelial PR by E(2) requires stromal, but not epithelial, ERalpha. In vitro, isolated uterine epithelial cells retained a high PR level with or without E(2), which is consistent with an indirect regulation of uterine epithelial PR in vivo. Thus, E(2) down-regulates PR in uterine epithelium through paracrine mechanisms mediated by stromal ERalpha.     

Regulation of progesterone receptors and decidualization in uterine stroma of the estrogen receptor-alpha knockout mouse

Regulation of progesterone receptor (PR) in uterine stroma (endometrial stroma plus myometrium) by estrogen was investigated in estrogen receptor-alpha (ERalpha) knockout (alphaERKO) mice. 17 beta-Estradiol (E(2)) increased PR levels in uterine stroma of ovariectomized alphaERKO mice, and ICI 182 780 (ICI) inhibited this E(2)-induced PR expression. Estrogen receptor-beta(ER beta) was detected in both uterine epithelium and stroma of wild-type and alphaERKO mice by immunohistochemistry. In organ cultures of alphaERKO uterus, both E(2) and diethylstilbestrol induced stromal PR, and ICI inhibited this induction. These findings suggest that estrogen induces stromal PR via ERbeta in alphaERKO uterus. However, this process is not mediated exclusively by ERbeta+, because in ERbeta knockout mice, which express ERalpha, PR was up-regulated by E(2) in uterine stroma. In both wild-type and alphaERKO mice, progesterone and mechanical traumatization were essential and sufficient to induce decidual cells, even though E(2) and ERalpha were also required for increase in uterine weight. Progesterone receptor was strongly expressed in decidual cells in alphaERKO mice, and ICI did not inhibit decidualization or PR expression. This study suggests that up-regulation of PR in endometrial stroma is mediated through at least three mechanisms: 1) classical estrogen signaling through ERalpha, 2) estrogen signaling through ERbeta, and 3) as a result of mechanical stimulation plus progesterone, which induces stromal cells to differentiate into decidual cells. Each of these pathways can function independently of the others.     

The activation function-1 domain of estrogen receptor alpha in uterine stromal cells is required for mouse but not human uterine epithelial response to estrogen

The activation function-1 (AF-1) domain of the estrogen receptor alpha (ERalpha) in stromal cells has been shown to be required for epithelial responses to estrogen in the mouse uterus. To investigate the role of the stroma in estrogenic responses of human uterine epithelium (hUtE), human/mouse chimeric uteri composed of human epithelium and mouse stroma were prepared as tissue recombinants (TR) that were grown in vivo under the renal capsule of female nude mouse hosts. In association with mouse uterine stroma (mUtS), hUtE formed normal glands surrounded by mouse endometrial stroma and the human epithelium influenced the differentiation of stroma into myometrium, such that a histologically normal appearing uterine tissue was formed. The hUtE showed a similar proliferative response and increase in progesterone receptors (PR) in response to 17beta-estradiol (E2) in association with either human or mUtS, as TRs. However, under identical endocrine and micro-environmental conditions, hUtE required 5-7 days exposure to E2 rather than 1 day, as shown for mouse uterine epithelium, to obtain a maximal proliferative response. Moreover, this extended length of E2 exposure inhibited mouse epithelial proliferation in the presence of mouse stroma. In addition, unlike the mouse epithelium, which does not proliferate or show regulation of PR expression in response to E2 in association with uterine stroma derived from mice that are null for the AF-1 domain of ERalpha, hUtE proliferates and PR are up-regulated in response to E2 in association genetically identical ERalpha knock-out mouse stromal cells. These results clearly demonstrate fundamental differences between mouse and human uterine epithelia with respect to the mechanisms that regulate estrogen-induced proliferation and expression of PR. Moreover, we show that genetically engineered mouse models could potentially aid in dissecting molecular pathways of stromal epithelial interactions in the human uterus.     

Epithelial-stromal tissue interaction in paramesonephric (Müllerian) epithelial differentiation.

During organogenesis, the middle to caudal portion of Müllerian epithelium differentiates into uterine and vaginal epithelia in females. Functional differentiation of uterine and vaginal epithelia occurs in adulthood, and is regulated by 17beta-estradiol (E(2)) and progesterone. In this report, the roles of mesenchyme/stroma in differentiation of uterine and vaginal epithelia were studied in tissue recombination experiments. At birth, Müllerian epithelium was negative for uterine and vaginal epithelial markers. Tissue recombinant experiments showed that uterine and vaginal gene expression patterns were induced in neonatal Müllerian epithelium by the respective mesenchymes. Differentiated adult uterine and vaginal epithelia did not change their original gene expression in response to heterotypic mesenchymal induction. In the adult vagina, E(2) induced expression of involucrin, a CCAAT/enhancer-binding protein beta and cytokeratin 1 via estrogen receptor alpha (ERalpha). Tissue recombination experiments with wild-type and ERalpha knockout mice demonstrated that epithelial gene expression is regulated by E(2) via epithelial-stromal tissue interactions. Uterine/vaginal heterotypic tissue recombinations demonstrated that functional differentiation of uterine and vaginal epithelia required organ-specific stromal factors. In contrast, stromal signals regulating epithelial proliferation appeared to be nonspecific in the uterus and vagina.     

Effect of estradiol on estrogen receptor expression in rat uterine cell types

In rodent uterus, both up- and down-regulation of estrogen receptor alpha (ERalpha) messenger ribonucleic acid (mRNA) and protein levels by estradiol has been demonstrated; however, it is not known which of the uterine compartments (endometrial epithelium, stroma, myometrium) respond to estradiol with autoregulation of ERalpha. The purpose of the present study was to investigate and compare the kinetics and cell type-specific effects of estradiol on uterine ERalpha expression in immature and adult rats. Ovariectomized female rats were injected s.c. with sesame oil or estradiol-17beta. Uteri were collected and analyzed for changes in ERalpha mRNA using RNase protection assays (RPA) and in situ hybridization using radiolabeled probes specific for ERalpha. Immunohistochemical analysis was performed with a polyclonal antibody specific to ERalpha. Expression of ERalpha in the uterine epithelial cells decreased at 3 and 6 h after estradiol administration to immature and adult rats, respectively. At 24 h, ERalpha mRNA levels in the immature and mature rat uterus were higher than pretreatment levels but returned to baseline by 72 h. Pretreatment with cycloheximide did not block the 3-h repressive effect of estradiol, suggesting that the estradiol-induced decrease in ERalpha mRNA occurs independent of new protein synthesis. A decrease in ERalpha mRNA and protein was also observed in uterine epithelia at 3 and 6 h after an estradiol injection to immature and adult rats, and intensity of both the in situ hybridization signal and the immunostaining in the epithelium increased at 24 and 72 h. However, the periluminal stromal cells in the adult uterus and the majority of stromal cells of the immature uterus appeared to have increased ERalpha expression. The results indicate that down-regulation of ERalpha in the epithelia and up-regulation of stromal ERalpha play a role in early events associated with estradiol-induced cell proliferation of the uterine epithelia.     

Coumestrol antagonizes neuroendocrine actions of estrogen via the estrogen receptor alpha

The phytoestrogen coumestrol has estrogenic actions on peripheral reproductive tissues. Yet in the brain this compound has both estrogenic and anti-estrogenic effects. We used estrogen receptor alpha knockout mice (ERalphaKO) to determine whether coumestrol has estrogenic actions in mice and also if these effects are mediated by the classic ERalpha. Female wild-type (WT) and ERalphaKO mice were ovariectomized and treated with estradiol (E2), dietary coumestrol, both, or neither compound. Ten days later the animals were sacrificed, blood was collected, and brain tissues were perfused. Fixed brains were sectioned and immunocytochemistry was employed to quantify progesterone receptors (PR) in the medial preoptic (POA) and ventromedial nucleus of the hypothalamus (VMN). Plasma was assayed for luteinizing hormone (LH). Estrogen treatment induced PR immunoreactivity in both regions in brains of WT females. In ERalphaKO mice, lower levels of PR were induced. The stimulatory effects of E2 on PR were attenuated in the POA by cotreatment with coumestrol, and the same trend was noted in the VMN. WT ovariectomized females treated with E2 had low levels of LH, while LH was high in untreated females and even higher in ovariectomized females treated with coumestrol. ERalphaKO females in all treatment groups had high levels of LH. Taken together, the results show that coumestrol has anti-estrogenic actions in the brain and pituitary and that ERalpha mediates these effects.     

Establishment of a primary culture model of mouse uterine and vaginal stroma for studying in vitro estrogen effects

Effects of 17beta-estradiol (E2) on uterine and vaginal epithelial cell proliferation could be mediated by stromal cell-derived paracrine factors. To study the epithelial-stromal interactions in mice, an in vitro model of uterine and vaginal stromal cells of immature mice is essential. Therefore, we established a primary culture model of stromal cells both from uterus and vagina and examined the effect of E2 on proliferation of cultured stromal cells. We found that E2 stimulated proliferation of stromal cells from both organs in vitro, showing an increase in the number of cells and the percentage of 5-bromo-2'-deoxyuridine (BrdU)-labeled cells. Interestingly, vaginal stromal cells responded to lower E2 than uterine stromal cells in proliferation (10(-12) M vs. 10(-8) M) and BrdU labeling (10(-14) - 10(-10) M vs. 10(-10) - 10(-6) M). To examine the effect of E2 in vivo, cells were grafted into the subrenal capsule of the host mice and grown for 2 weeks. The BrdU labeling in cultured stromal cells was increased by E2 in vivo. To examine the effect of cultured stromal cells on epithelial cell proliferation, uterine and vaginal epithelium of adult mice were separated, recombined with the cultured stromal cells, and grafted under the renal capsule of hosts for 3 weeks. Epithelial cells recombined with cultured stromal cells showed simple columnar morphology in uterine grafts and stratified and keratinized morphology in vaginal grafts under the influence of the hormonal environment of the hosts. The BrdU labeling in epithelial cells was increased by E2, suggesting that cultured stromal cells can stimulate epithelial cell proliferation. In conclusion, we established a primary culture model of uterine and vaginal stromal cells, which can be mitogenically stimulated by E2 in vitro and in vivo after being grafted under the renal capsule. This culture system will be useful for investigating the underlying molecular mechanisms of uterine and vaginal epithelial-stromal interactions.     

Paracrine regulation of apoptosis by steroid hormones in the male and female reproductive system

In males, androgens are essential in maintaining the integrity of the prostate. Androgen-ablation induces apoptosis of the prostatic epithelium. In females, ovariectomy induces apoptosis in uterine epithelium while progesterone inhibits this process. The objective of this study was to determine whether androgen and progesterone inhibit apoptosis, respectively, in mouse prostatic and uterine epithelia via steroid receptors in the epithelium or in the stroma. To address this question, prostatic tissue recombinants were prepared with rat urogenital sinus mesenchyme plus bladder epithelium from wild-type or testicular feminization mutant (Tfm) mice. Thus, prostatic tissue was generated having androgen receptor (AR) in both epithelium and stroma or in the stroma only. Castration of hosts induced apoptosis in the AR-negative Tfm prostatic epithelium with an epithelial apoptotic index virtually identical to prostatic tissue recombinants containing wild-type epithelium. Moreover, this castration-induced prostatic epithelial apoptosis was blocked by testosterone and dihydrotestosterone in both wild-type and Tfm prostatic tissue recombinants. Likewise, uterine tissue recombinants were prepared in which epithelium and/or stroma was devoid of progesterone receptor (PR) by using uterine epithelium and stroma of wild-type and PR knockout mice. Progesterone inhibited uterine epithelial apoptosis only in tissue recombinants prepared with PR-positive stroma. The PR status of the epithelium did not affect epithelial apoptotic index. Therefore, the apoptosis in prostatic and uterine epithelia is regulated by androgen and progesterone via stromal AR and PR, respectively. In both cases, epithelial AR or PR is not required for hormonal regulation of epithelial apoptosis in prostatic and uterine epithelium.     

Testosterone prevents orchidectomy-induced bone loss in estrogen receptor-alpha knockout mice.

To examine the role of the estrogen receptor-alpha (ERalpha) during male skeletal development, bone density and structure of aged ERalphaKO mice and wild-type (WT) littermates were analyzed and skeletal changes in response to sex steroid deficiency and replacement were also studied. In comparison to WT, ERalphaKO mice had smaller and thinner bones, arguing for a direct role of ERalpha to obtain full skeletal size in male mice. However, male ERalphaKO mice had significantly more trabecular bone as assessed both by pQCT and histomorphometry, indicating that ERalpha is not essential to maintain cancellous bone mass. Six weeks following orchidectomy (ORX), both WT and ERalphaKO mice showed high-turnover osteoporosis as revealed by increases in serum osteocalcin and decreases in trabecular (-38% and -58% in WT and ERalphaKO, respectively) and cortical bone density (-5% and -4% in WT and ERalphaKO, respectively). Administration of testosterone propionate (T, 5 mg/kg/day) completely prevented bone loss both in ERalphaKO and in WT mice. As expected, estradiol (E2, 60 microg/kg/day) replacement did not prevent cancellous bone loss in ORX ERalphaKO mice. However, E2 stimulated bone formation at the endocortical surface in ORX ERalphaKO, suggesting that osteoblasts may respond to nonERalpha-mediated estrogen action. In conclusion, although functional ERalpha may play a significant role during male skeletal development, this receptor does not seem essential for androgen-mediated skeletal maintenance in older male mice.     

Additional effects of postpuberal estrogen injections on the vaginal epithelium in neonatally estrogenized mice

In the ovariectomized mice given 10 injections of 100 micrograms 17 beta-estradiol at intervals of 2 weeks from 60 days of age, the vaginal epithelium was atrophic when killed more than 2 months after the last injection. If mice given 3 daily injections of 20 micrograms 17 beta-estradiol from the day of birth were similarly treated with estradiol after postpuberal ovariectomy, the vaginal epithelium was stratified and hyperplastic at autopsy performed more than 2 months later. These changes in the epithelium persisted for at least 30 days after transplantation of the vaginae to normal ovariectomized hosts. Neonatal treatments only did not produce such persistent vaginal changes. In view of these results, additional effects of neonatal and postpuberal injections of estrogen on the vaginal epithelium are evident. However, effects of such neonatal and postpuberal injections of estrogen might be transient on the uterine epithelium, since abnormal proliferation was not observed in it.     

Stromal cell-derived factor 1, a novel target of estrogen receptor action,mediates the mitogenic effects of estradiol in ovarian and breast cancer cells

Recent clinical studies estimate that 60-70% of human ovarian and breast cancers overexpress the estrogen receptor (ER). However, despite the established mitogenic effects of estrogen in these tumors, proliferative markers of hormone action are limited. In the current study, we report that the growth stimulatory cytokine stromal cell-derived factor 1 (SDF-1) is a bona fide target of estrogen action in ERalpha-positive human ovarian and breast cancer cells. Notably, estradiol treatment of BG-1 (ovarian carcinoma) and MCF-7 (breast carcinoma) cells leads to rapid and robust induction of the SDF-1alpha and beta isoforms. This response is blocked by the pure ER antagonist ICI 182,780 and is not apparent in ER-negative ovarian cells, indicating that SDF-1 regulation is ERalpha mediated. Treatment with the protein synthesis inhibitor cycloheximide had no effect on estradiol induction of induction of SDF-1 mRNA levels mRNA levels, demonstrating that SDF-1 is a direct target of ERalpha. SDF-1 protein levels, although undetectable under basal conditions, were strikingly increased by hormone both intracellularly and in the media of cultured BG-1 and MCF-7 cells. In cell proliferation assays, the mitogenic effects of estradiol were neutralized by addition of an SDF-1 antibody and mimicked by the addition of exogenous SDF-1 protein, indicating that SDF-1 mediates the proliferative actions of hormone. Furthermore, activation of the SDF-1 receptor CXCR4 stimulated BG-1 and MCF-7 cell proliferation in a manner comparable to estradiol. Taken together, these results demonstrate a novel estrogen-mediated paracrine pathway for inducing cancer cell proliferation and suggest that SDF-1 and CXCR4 may represent novel therapeutic targets in ERalpha-positive ovarian and breast tumors.     

Effect of estradiol and progesterone on phosphatidylinositol metabolism in the uterine epithelium of the mouse

The effect of estradiol and progesterone on uterine phosphatidylinositol (PtdIns) metabolism was examined in whole uteri and separated uterine luminal epithelium of ovariectomized mice. Incorporation of [3H]myo-inositol in vitro, into inositol-containing phospholipids extracted from whole uteri, increased in mice injected with estradiol, with maximal incorporation at 9-12 h. The breakdown of PtdIns to inositol polyphosphates was also stimulated in whole uteri by estrogen, with an abrupt increase between 6 and 9 h. Comparable increases in both processes occurred in the uterine epithelium after estrogen stimulation and were inhibited by progesterone pretreatment which by itself had little or no effect. These results suggest that PtdIns metabolism is involved in the stimulation of uterine epithelial cell proliferation by estrogens, and its inhibition by progesterone.     

Estrogen receptor-alpha mediates estrogen protection from angiotensin II-induced hypertension in conscious female mice

It has been shown that the female sex hormones have a protective role in the development of angiotensin II (ANG II)-induced hypertension. The present study tested the hypotheses that 1) the estrogen receptor-alpha (ERalpha) is involved in the protective effects of estrogen against ANG II-induced hypertension and 2) central ERs are involved. Blood pressure (BP) was measured in female mice with the use of telemetry implants. ANG II (800 ng.kg(-1).min(-1)) was administered subcutaneously via an osmotic pump. Baseline BP in the intact, ovariectomized (OVX) wild-type (WT) and ERalpha knockout (ERalphaKO) mice was similar; however, the increase in BP induced by ANG II was greater in OVX WT (23.0 +/- 1.0 mmHg) and ERalphaKO mice (23.8 +/- 2.5 mmHg) than in intact WT mice (10.1 +/- 4.5 mmHg). In OVX WT mice, central infusion of 17beta-estradiol (E(2); 30 microg.kg(-1).day(-1)) attenuated the pressor effect of ANG II (7.0 +/- 0.4 mmHg), and this protective effect of E(2) was prevented by coadministration of ICI-182,780 (ICI; 1.5 microg.kg(-1).day(-1), 18.8 +/- 1.5 mmHg), a nonselective ER antagonist. Furthermore, central, but not peripheral, infusions of ICI augmented the pressor effects of ANG II in intact WT mice (17.8 +/- 4.2 mmHg). In contrast, the pressor effect of ANG II was unchanged in either central E(2)-treated OVX ERalphaKO mice (19.0 +/- 1.1 mmHg) or central ICI-treated intact ERalphaKO mice (19.6 +/- 1.6 mmHg). Lastly, ganglionic blockade on day 7 after ANG II infusions resulted in a greater reduction in BP in OVX WT, central ER antagonist-treated intact WT, central E(2) + ICI-treated OVX WT, ERalphaKO, and central E(2)- or ICI-treated ERalphaKO mice compared with that in intact WT mice given just ANG II. Together, these data indicate that ERalpha, especially central expression of the ER, mediates the protective effects of estrogen against ANG II-induced hypertension.     

The effects of the selective estrogen receptor modulators, methyl-piperidino-pyrazole (MPP), and raloxifene in normal and cancerous endometrial cell lines and in the murine uterus

Since estrogens have vital functions in the uterus but might also contribute to endometrial cancer, we sought to determine the in vitro effects of methyl-piperidino-pyrazole (MPP), raloxifene, and beta-estradiol on Ishikawa and RL-95 endometrial cancer, and ovine luminal endometrial (oLE) cell lines and the in vivo effects of these compounds in the rodent uterus. MPP and raloxifene (1 nM) induced significant apoptosis in the endometrial cancer and oLE cell lines compared to beta-estradiol treated and control cells (P 相似文献   

Regulation of nitric oxide-dependent vasodilation in coronary arteries of estrogen receptor-alpha-deficient mice

Estrogen has been shown to increase endothelium-dependent vasodilation and expression of endothelial nitric oxide (NO) synthase (eNOS); however, the role of estrogen receptors in mediating estrogen effects on endothelial function remains to be elucidated. The purpose of this study was to test the hypothesis that estrogen modulates NO-dependent vasodilation of coronary arteries through its action on estrogen receptor-alpha (ER-alpha) to increase protein levels of eNOS and Cu/Zn superoxide dismutase (SOD-1). Vasodilation to acetylcholine (ACh) and sodium nitroprusside was assessed in isolated coronary arteries from intact and ovariectomized female wild-type (WT) and ER-alpha knockout (ERalphaKO) mice. Protein levels for eNOS and SOD-1 were also evaluated. Vasodilation to ACh was not significantly altered in ERalphaKO mice compared with WT mice. Ovariectomy reduced responsiveness to ACh in ERalphaKO mice but not WT mice. Responses to sodium nitroprusside were not altered by disruption of ER-alpha or by ovariectomy. Supplementation with estrogen restored ACh-induced vasodilation in ovariectomized ERalphaKO mice. eNOS protein was reduced in ERalphaKO mice compared with WT mice. Ovariectomy caused a further reduction in eNOS protein in ERalphaKO mice, but this reduction was reversed by estrogen treatment. SOD-1 protein levels were increased by disruption of ER-alpha. Ovariectomy reduced SOD-1 protein in ERalphaKO mice, but this reduction was partially reversed by estrogen replacement. These results suggest that estrogen modulation of eNOS protein content is mediated in part through ER-alpha. NO-dependent responses are preserved in ERalphaKO mice, possibly through increased SOD-1 expression and enhanced bioavailability of NO.     

Cellular turnover in the rat uterine cervix and its relationship to estrogen and progesterone receptor dynamics

Histoarchitectural changes of the uterine cervix allow its successful adaptation to different physiological conditions. In this study, we evaluated cell turnover in each cellular compartment of the uterine cervix in association with steroid hormone receptor expression in order to establish the range of physiological changes. Proliferation, apoptosis, and progesterone receptor (PR) and estrogen receptor alpha (ERalpha) expression were evaluated in cycling, pregnant, and postpartum rats. In estrus and diestrus II, ERalpha and PR expression exhibited variations according to the region evaluated. Proliferation and apoptosis showed a reciprocal pattern, the epithelium being the region with higher cell turnover. High apoptotic index (AI) in estrus was associated with the lowest ERalpha and the highest PR scores. During pregnancy, proliferation of the epithelium was the predominant event and AI was low. On Postpartum Day 1 (PPD1), proliferation decreased while apoptosis increased. As described for the estrous cycle, during pregnancy and PPD1, AI and ERalpha were negatively correlated. In the fibroblastic stroma, low proliferation was observed throughout pregnancy; however, there was a net increase in cell number because very few cells underwent apoptosis. No difference in ERalpha was observed in fibroblastic cells during pregnancy and postpartum; however, a great decrease of this receptor in the epithelial compartment was observed after delivery. Unlike cervical epithelium, PR was highly expressed in stromal cells. At term, a dramatic increase in epithelial PR was observed. While epithelial PR remained high on PPD1, a decrease was observed in muscle stroma. These results show that, in all stages studied, 1) ERalpha and PR have different patterns of expression with differential responses to signals that modulate proliferation and/or apoptosis depending on the cellular compartment, and 2) even though the epithelium is the region with the highest cell turnover, the fibroblastic and muscle stroma are active regions that have their own patterns of behavior.     

Natural killer cells express estrogen receptor-alpha and estrogen receptor-beta and can respond to estrogen via a non-estrogen receptor-alpha-mediated pathway

Natural killer (NK) cells play a crucial role in host defense against pathogens and immune surveillance against cancer. Given that estrogens have been reported to suppress NK cell activity, we sought to elucidate the mechanisms by which estrogen mediates this effect. We demonstrate by immunocytochemical staining with estrogen receptor-alpha (ERalpha)- and estrogen receptor-beta (ERbeta)-specific antibodies that both ERalpha and ERbeta are expressed in murine NK cells. We also compared the ability of high doses of 17beta-estradiol ( approximately 800 pg/ml) to regulate NK cell activity in wild-type and estrogen receptor-alpha-deficient (ERalphaKO) mice. 17beta-estradiol elicited a significant decrease in NK cell activity in both wild-type and ERalphaKO mice (P < 0.001). These data suggest that ERbeta or possibly a novel receptor is involved in mediating estrogen action on NK cell activity and raise the potential for therapeutic modulation of NK cell activity with selective estrogen receptor modulators (SERMS).