雌激素信号通路概述

过去几十年,人们一直认为雌激素信号通路是雌激素与细胞核中的雌激素受体(ER)结合,作用于雌激素受体反应元件调节基因表达,从而改变细胞功能。雌激素不但与核ER结合,也能与膜ER结合激活PI3K信号通路。G蛋白偶联受体(GPR30)也能与雌激素结合,激活PI3K信号通路。雌激素通过结合不同雌激素受体改变细胞生理功能。我们对雌激素信号通路做简要综述。     

Human estrogen receptor forms multiple protein-DNA complexes

A baculovirus expression system was used to overproduce the human estrogen receptor in insect cells. The estrogen receptor made in this system is full-length, binds estrogen specifically, and is recognized by a monoclonal antibody to the human estrogen receptor. The recombinant estrogen receptor binds the estrogen response element (ERE) in both the absence and presence of estrogen if the binding is carried out in the absence of Mg2+. In the presence of Mg2+, the estrogen receptor binds the ERE in a hormone-dependent fashion. This effect is more pronounced at higher temperatures. Tamoxifen, a nonsteroidal anti-estrogen, is able to stimulate ERE binding to the same extent and under the same conditions as estradiol. Estradiol stimulates formation of an estrogen receptor-ERE complex with an increased mobility in native gels as compared with the complex formed without hormone or with tamoxifen. These results demonstrate that specific DNA binding of the estrogen receptor is not absolutely dependent on the presence of hormone and that estradiol but not tamoxifen is able to induce a change in the estrogen receptor. This differential effect of estradiol and tamoxifen may be important in understanding the role of the receptor to activate target genes differentially.     

Insulin-like growth factor-I receptors and estrogen receptors interact in the promotion of neuronal survival and neuroprotection

Several in vitro and in vivo studies have shown that estrogen has neuroprotective properties. The neuroprotective effects of estrogen are probably exerted through several mechanisms. It is established that estrogen can provide neuroprotection by actions that are independent of estrogen receptor activation. In addition, in several experimental models, activation of estrogen receptors appears to be indispensable for neuroprotection. This review focuses on neuroprotection mediated by estrogen receptors. The interaction of estrogen with growth factor receptor signaling to induce neuroprotection is discussed. Evidence is presented that estrogen receptors and insulin-like growth factor-I receptors interact in the promotion of neuronal survival and neuroprotection.     

Subcellular distribution of native estrogen receptor alpha and beta isoforms in rabbit uterus and ovary

The association of estrogen receptors with non-nuclear/cytoplasmic compartments in target tissues has been documented. However, limited information is available on the distribution of estrogen receptor isoforms, specially with regard to the newly described beta isotype. The subcellular localization of estrogen receptor alpha and beta isoforms was investigated in rabbit uterus and ovary. Native alpha and beta subtypes were immunodetected using specific antibodies after subjecting the tissue to fractionation by differential centrifugation. The ovary expressed alpha and beta estrogen receptors in predominant association to cytosolic components. However, in the uterus, a substantial proportion of the total estrogen binding capacity and coexpression of the two isoforms was detected in mitochondria and microsomes. The mitochondrial-enriched subfraction represented an important source of 17beta-estradiol binding, where the steroid was recognized in a stereospecific and high affinity manner. The existence of mitochondrial and membrane estrogen binding sites correlated with the presence of estrogen receptor alpha but mainly with estrogen receptor beta proteins. Using macromolecular 17beta-estradiol derivatives in Ligand Blot studies, we could confirm that both alpha and beta isoforms were expressed as the major estrogen binding proteins in the uterus, while estrogen receptor alpha was clearly the dominant isoform in the ovary. Other low molecular weight estrogen receptor alpha-like proteins were found to represent an independent subpopulation of uterine binding sites, expressed to a lesser extent. This differential cellular partitioning of estrogen receptor alpha and beta forms may contribute to the known diversity of 17beta-estradiol effects in target organs. Both estrogen receptor alpha and beta expression levels and cellular localization patterns among tissues, add complexity to the whole estrogen signaling system, in which membrane and mitochondrial events could also be implicated.     

不同雌激素水平下大鼠颏舌肌肌电反应的研究

目的：通过比较不同雌激素水平下大鼠颏舌肌的肌电反应,探讨雌激素在预防及降低阻塞性睡眠呼吸暂停低通气综合征（OSAHS）发病过程中的作用机制。方法：选择30只6周龄SD大鼠建立不同雌激素水平模型,用电子称评估术前、术后和雌激素替代治疗后大鼠的体重变化;放射免疫法检测血清雌激素水平;电生理方法检测不同雌激素水平颏舌肌的肌电反应。结果：与假手术组（SHAM）相比,去势组（OVX）大鼠术后6周体重明显增加（P〈0．01）,雌激素替代治疗组（OVX＋E2）与SHAM组体重相当。血清雌激素检测结果显示OVX组雌激素水平最低,与SHAM组相比具有显著差异（P〈0．01）;OVX＋E2组雌激素水平高于OVX组（P〈0．01）,但仍未恢复到SHAM组水平。电生理检测结果显示,与SHAM组相比,OVX组颏舌肌肌电强度最低（P〈0．05）,OVX＋E2组颏舌肌的肌电强度显著高于OVX组（P〈0．05）,但仍低于SHAM组。结论：血清雌激素水平可以直接影响大鼠颏舌肌肌电强度．这可能是雌激素保护OSAHS的原因之一。     

雌激素的非基因组途径在哺乳动物雌性生殖过程中的作用机制

雌激素的非基因组调节模式在雌性生殖系统中广泛存在．雌激素通过基因组、非基因组及两种调节模式的整合在不同组织中行使多种生理功能．卵巢中雌激素能通过非基因组效应对卵细胞起到保护作用．子宫中雌激素对多种基因的表达都是通过非基因组模式．对雌激素非基因组效应的研究将有利于进一步了解雌激素的作用机制．     

Interacting effects of estrogen, progesterone and catecholamines on rat uterine cyclic AMP and glycogen phosphorylase.

Ovariectomized rats were treated with estrogen, progesterone or a combination of estrogen plus progesterone. Rats were anesthetized with sodium pentobarbital and uteri were frozen $\text{in situ}$, uterine extracts were prepared and assayed for cyclic AMP and phosphorylase. Uterine cyclic AMP levels were highest in estrogen treated uteri and were significantly reduced when estrogen was withdrawn for two days. Addition of progesterone to the estrogen regimen for two days or changing from estrogen to progesterone for two days produced results comparable to those obtained when estrogen was withdrawn. Similar experiments were done except that 30 seconds before tissue freezing epinephrine was injected intravenously. Both cyclic AMP and glycogen phosphorylase increased markedly in response to epinephrine. The magnitude of the responses were greatest in the uteri pretreated with estrogen. The magnitudes of both the cyclic AMP and phosphorylase responses were significantly reduced by withdrawing estrogen for two days, by adding progesterone to the estrogen treatment or by changing to progesterone from estrogen. Isoproterenol-stimulated cyclic AMP responses were affected by the steroid state of the uterus in the same way as the epinephrine responses.     

Calmodulin enhances the stability of the estrogen receptor

The estrogen receptor mediates breast cell proliferation and is the principal target for chemotherapy of breast carcinoma. Previous studies have demonstrated that the estrogen receptor binds to calmodulin-Sepharose in vitro. However, the association of endogenous calmodulin with endogenous estrogen receptors in intact cells has not been reported, and the function of the interaction is obscure. Here we demonstrate by co-immunoprecipitation from MCF-7 human breast epithelial cells that endogenous estrogen receptors bind to endogenous calmodulin. Estradiol treatment of the cells had no significant effect on the interaction. However, incubation of the cells with tamoxifen enhanced by 5-10-fold the association of calmodulin with the estrogen receptor and increased the total cellular content of estrogen receptors by 1.5-2-fold. In contrast, the structurally distinct calmodulin antagonists trifluoperazine and CGS9343B attenuated the interaction between calmodulin and the estrogen receptor and dramatically reduced the number of estrogen receptors in the cell. Neither of these agents altered the amount of estrogen receptor mRNA, suggesting that calmodulin stabilizes the protein. This hypothesis is supported by the observation that, in the presence of Ca2+, calmodulin protected estrogen receptors from in vitro proteolysis by trypsin. Furthermore, overexpression of wild type calmodulin, but not a mutant calmodulin incapable of binding Ca2+, increased the concentration of estrogen receptors in MCF-7 cells, whereas transient expression of a calmodulin inhibitor peptide reduced the estrogen receptor concentration. These data demonstrate that calmodulin binds to the estrogen receptor in intact cells in a Ca2+-dependent, but estradiol-independent, manner, thereby modulating the stability and the steady state level of estrogen receptors.     

Differential roles of estrogen receptors α and β in control of B-cell maturation and selection

It is clear that estrogen can accelerate and exacerbate disease in some lupus-prone mouse strains. It also appears that estrogen can contribute to disease onset or flare in a subset of patients with lupus. We have previously shown estrogen alters B-cell development to decrease lymphopoiesis and increase the frequency of marginal zone B cells. Furthermore, estrogen diminishes B-cell receptor signaling and allows for the increased survival of high-affinity DNA-reactive B cells. Here, we analyze the contribution of estrogen receptor α or β engagement to the altered B-cell maturation and selection mediated by increased exposure to estrogen. We demonstrate that engagement of either estrogen receptor α or β can alter B-cell maturation, but only engagement of estrogen receptor α is a trigger for autoimmunity. Thus, maturation and selection are regulated differentially by estrogen. These observations have therapeutic implications.     

Effects of estrogen on thermoregulatory tail vasomotion and heat-escape behavior in freely moving female rats

Effects of estrogen on thermoregulatory vasomotion and heat-escape behavior were investigated in ovariectomized female rats supplemented with estrogen (replaced estrogen rats) or control saline (low estrogen rats). First, we measured tail temperature of freely moving rats at ambient temperatures (T(a)) between 13 and 31 degrees C. Tail temperature of the low estrogen rats was higher than that of the replaced estrogen rats at T(a) between 19 and 25 degrees C, indicating that the low estrogen rats exhibit more skin vasodilation than the replaced estrogen rats. There was no significant difference in oxygen consumption and core temperature between the two groups. Second, we analyzed heat-escape behaviors in a hot chamber where rats could obtain cold air by moving in and out of a reward area. The low estrogen rats kept T(a) at a lower level than did the replaced estrogen rats. These results imply that the lack of estrogen facilitates heat dissipation both by skin vasodilation and by heat-escape behavior. Ovariectomized rats may mimic climacteric hot flushes not only for autonomic skin vasomotor activity but also for thermoregulatory behavior.     

Mechanisms of estrogen receptor action in the myocardium. Rapid gene activation via the ERK1/2 pathway and serum response elements

We have previously shown that the myocardium is a target tissue for estrogen. Here, we have identified rapid non-nuclear estrogen effects on the expression of the early growth response gene-1 (Egr-1) in cardiomyocytes. Egr-1 mRNA and protein were rapidly and strongly induced by estrogen in an estrogen receptor-dependent manner via the extracellular signal-regulated kinase, ERK1/2. A promoter analysis study of a 1.2-kilobase Egr-1 promoter fragment revealed that the serum response elements (SREs) but not the estrogen response elements or AP-1 sites are responsible for Egr-1 induction by estrogen, identifying a novel mechanism of estrogen receptor-dependent gene activation in the myocardium. Both estrogen receptor-alpha and -beta induced the Egr-1 promoter via the SREs as well as an artificial promoter consisting of only five SREs in cardiomyocytes. Electrophoretic mobility shift assays showed that a protein complex containing serum response factor or an antigenically related protein was recruited to the SREs by estrogen treatment of primary cardiomyocytes. The recruitment of the protein complex was inhibited by the specific estrogen receptor antagonist ICI 182,780 as well as the MEK inhibitor PD 98059. Taken together, these results identify SREs as important promoter control elements for an estrogen receptor-dependent mechanism of gene activation in the myocardium.     

Estrogen metabolism, not biosynthesis, in rabbit articular cartilage and isolated chondrocytes: a preliminary study.

Because serum estrogen levels are associated with the presence of osteoarthritis, and cartilage tissue is known to contain estrogen receptors, it is of interest to determine the extent to which estrogen is biosynthesized and/or metabolized in cartilage tissue or isolated chondrocytes. In this preliminary study, using a sensitive assay method, estrogen synthetase (aromatase) was undetectable in articular cartilage or isolated chondrocytes in culture from immature female rabbits. However, estrogen metabolism, specifically estrogen 17 beta-hydroxysteroid dehydrogenase activity, was detected in homogenized cartilage tissue, and at substantially higher specific activities in freshly isolated chondrocytes. These fresh chondrocytes, assayed in culture without any exogenous cofactor, demonstrated a significantly higher activity for converting the weak estrogen, estrone, to the more potent estrogen, estradiol. Chondrocytes grown to confluence in culture had very low estrogen 17 beta-hydroxysteroid dehydrogenase specific activity. Homogenized cartilage tissue, tested only with added NADPH as cofactor, also showed a preference for estradiol as the principal product, but this may have been primarily due to the use of reduced cofactor. If subsequent experiments confirm the presence of estrogen 17 beta-hydroxysteroid dehydrogenase activity, and its preference for converting estrone into estradiol, in human cartilage tissue and chondrocytes, this could have substantial implications in the estrogen dependency of osteoarthritis.     

Global analysis of gene expression in the estrogen induced pituitary tumor of the F344 rat

The F344 rat rapidly forms large prolactinomas in response to chronic estrogen treatment. To identify genes expressed in the course of this estrogen induced pituitary tumor growth, we performed microarray analysis on the F344 rat pituitary after chronic estrogen treatment and on untreated controls. At a significance level set to minimize type I error, some 72 genes were found to be differentially expressed between estrogen treated and untreated. Of those genes, 70 have not been reported previously as being affected by estrogen in the F344 rat pituitary. Since many other investigators have studied the effect of estrogen on specific gene expression in rat pituitary, we also examined the mRNA expression of the 36 genes that have been previously reported as having their expression affected by estrogen in the rat pituitary. Of these, 13 were found to have their expression affected by estrogen treatment in the same direction as had been reported by others.     

Estrogen regulation of agonistic and proceptive responses in the golden hamster

The role of estrogen in modulation of agonistic (attack-chase) and proceptive (vaginal-marking) responses of the female hamster toward a male was examined in relation to time course of induction and duration of response. In addition, the sex-specific nature of the vaginal-marking response was examined. Cycling females showed a significantly higher frequency of attack-chase when endogenous estrogen levels were minimal in comparison to that at peak estrogen levels during the estrous cycle. Removal of estrogen (ovariectomy) resulted in a significant increase in attack-chase scores compared to high endogenous estrogen. Addition of exogenous estrogen (Silastic capsule) resulted in a significant decrease in attack-chase scores compared to ovariectomized animals. The inverse effect was found for vaginal marking with the lowest frequency of vaginal marking at low endogenous estrogen levels or following ovariectomy. During high endogenous estrogen levels or following treatment with exogenous estrogen vaginal-marking scores were maximal. Maximal induction of vaginal-marking responses and reduction of attack-chase were found between 6 and 48 hr of estrogen treatment. Both behaviors then returned to the prehormonal treatment level. Failure to detect effects beyond 48 hr was not due to repeated testing, as animals lacking hormone, or animals first tested at 96 hr of estrogen exposure, showed no effect of the treatment. Males gonadectomized as adults never showed vaginal marking, whereas males gonadectomized neonatally showed a low level of vaginal marking which was increased significantly following estrogen treatment. Thus both attack-chase and vaginal marking in the presence of a male are modulated by estrogen. Further, since vaginal marking is estrogen sensitive in the neonatally gonadectomized male, expression of vaginal marking is determined by the hormonal environment during the neonatal period. However, peripheral feedback may be important for frequency of occurrence.     

Down regulation of c-myc, c-fos and erb-B during estrogen induced proliferation of the chick oviduct

Oncogenes c-myc, H-ras, c-fos and erb-B were constitutively expressed in immature chick oviduct withdrawn from estrogen administration for 2.5 weeks after 10 d of primary estrogen stimulation. Following secondary estrogen stimulation of the withdrawn chicks, synthesis of egg white proteins is rapidly induced and remaining non-functioning tubular gland cells are stimulated to proliferate with a doubling time of 24 h. During first 12 h of secondary estrogen stimulation, H-ras mRNA levels doubled and did not increase further at 24 h and 48 h. The steady state levels of c-myc, erb-B and c-fos mRNA decreased 24 h following secondary estrogen stimulation. The levels of these oncogene RNAs in oviduct were similar at 48 h following secondary estrogen stimulation to those from immature chicks administered 10 d of primary estrogen stimulation. Thus elevated expression of c-myc and c-fos mRNA does not appear to be necessary components for sustained estrogen induced cell proliferation in the chick oviduct.     

Apoptotic action of estrogen

Estrogen as a mitogen stimulates cell proliferation and prevents cell death in many cell types. In patients, estrogen is known to stimulate breast and uterus cancer development. Ironically, high doses of estrogen can induce regression of hormone-dependent breast cancer in postmenopausal women. The comprehensive mechanism by which estrogen induces tumor recession in breast cancer is still unknown, but activation of the Fas/FasL pathways plays a key role in this process. Laboratory studies show that the apoptotic action of estrogen is the major factor leading to cell number decreases in several cell types. The effects of estrogen are estrogen-receptor dependent. In this mini review, we will focus on the latest findings regarding estrogen apoptotic effects in several cell models, including breast cancer cells, and summarize the possible mechanisms involved in these estrogen mediated processes. New potential implications for the pharmacological control of breast cancer with estrogen in post-menopausal women are also discussed.