Cellular Effects Of Estrogen Research Articles

Estrogens, estrogen receptors and melanoma

The skin is the largest nonreproductive target tissue on which estrogen plays many beneficial and protective roles. Although neither exogenous hormones nor pregnancy represent significant risk factors for melanoma, epidemiological data suggest a higher survival rate in women with metastatic disease versus men and in premenopausal versus postmenopausal patients. Despite the fact that hyperestrogenic signaling has long been implicated in the initiation and progression of several tumors, the role of estrogens in malignant melanoma is still unclear. The cellular effects of estrogens are mediated by two subtypes of estrogen receptors (ERs). Estrogen receptor β (ERβ), the predominant ER in the skin, antagonizes the proliferative action mediated by estrogen receptor α. According to recent immunohistochemical studies, ERβ protein expression decreases progressively with increased Breslow thickness and results in more invasive melanomas; thus, ERβ immunophenotype may distinguish melanomas linked to poor prognosis from those with a favorable course and lead to melanoma unresponsiveness to both estrogen and anti-estrogen treatment. Therefore, if future large-scale immunohistochemical and molecular studies point towards ERβ as an important factor in malignant melanoma progression, they will open up novel and targeted prognostic and therapeutic perspectives.

Estrogens Maintain Bone Mass by Regulating Expression of Genes Controlling Function and Life Span in Mature Osteoclasts

Estrogens play a key role in regulation of bone mass and strength by controlling activity of bone-forming osteoblasts and bone-resorbing osteoclasts. Cellular effects of estrogens are mediated predominantly by the action of estrogen receptor alpha (ERalpha). In earlier studies, ablation of the ERalpha gene in mice did not result in osteoporotic phenotypes due to systemic endocrine disturbance and compensatory effects of elevated levels of testosterone. Despite the relatively well-established effects in osteoblasts, little is known about the direct action of estrogen in osteoclasts. Development in the last decade of more sophisticated genetic manipulation approaches opened new possibilities to explore cell-specific roles of nuclear receptors in bone tissue. Recently, we have generated osteoclast-specific ERalpha gene knockout mice and shown that in vivo estrogens directly regulate the life span of mature osteoclasts by inducing the expression of pro-apoptotic Fas ligand (FasL). Inhibitory effects of estrogens on osteoclast function were further studied in vitro. We observed sufficiently detectable ERalpha expression in osteoclasts differentiating from primary bone marrow cells or RAW264 cells, although levels of ERalpha were decreasing during progression of the differentiation into mature osteoclasts. Treatment with estrogens led to reduction in expression of osteoclast-specific genes controlling bone resorption activity. However, estrogens did not affect the size of multinucleated osteoclasts or number of nuclei in a mature osteoclast. In conclusion, in osteoclasts, estrogens function to inhibit bone resorption activity and vitality rather than differentiation.

Expression of the estrogen receptor during differentiation of human osteoclasts

Estrogens play a key role in bone structural integrity, which is maintained by the opposing activity of bone forming osteoblasts and bone resorbing osteoclasts. The cellular effects of estrogens are mediated by estrogen receptors, however, the detailed molecular mechanism of ER regulation in osteoclasts has not yet been elucidated. We provide here a detailed analysis of the expression profile and functionality of ER during osteoclast differentiation. We employed a human primary osteoclast cell culture model to evaluate the regulation of estrogen receptor (ER) variant expression. We characterized the expression profile of estrogen receptors and studied the regulation of the predominant estrogen receptor-alpha (ER-α) during differentiation into osteoclasts. In addition to the full-length ER-α, a shorter ER-α mRNA variant is expressed and both ER-α variants are regulated during osteoclastogenesis. Furthermore, we show that the pS2 gene is an estrogen-regulated gene in osteoclasts. Analysis of the activity of the pS2 gene throughout differentiation, using chromatin immunoprecipitation (ChIP), revealed the functionality of ER-α during differentiation and shows that the occupancy of ER-α and activated polymerase II on the pS2 promoter decrease with time and can be blocked by the ER antagonist ICI 182780. These results help to dissect the molecular events relevant to estrogen signaling and provide a better understanding of the role of ER-α regulation during bone resorption mediated by osteoclasts.

Signaling regulation of genomic and nongenomic functions of estrogen receptors

Estrogen receptors (ERs) mediate the effects of 17β-estradiol under physiologic and pathologic conditions. ERs trigger 17β-estradiol-sensitive gene transcription by binding to specific estrogen response elements (i.e. genomic mechanism). The cellular effects of estrogen are also influenced by membrane- or cytoplasm-initiated responses (i.e. nongenomic mechanism). Both ER-evoked genomic and nongenomic effects originate from a unique signaling network. Furthermore, estrogen-initiated rapid pathways and ERα interactions with specific partners (e.g. AIB1, PELP1/MNAR; MTA1, MTA1s and p130Cas) influence both ER functions. Here, we summarize the recent findings related to multiple regulatory levels of the signaling networks responsible for ERs-mediated responses in breast cancer cells.

ROLE OF OVARIAN HORMONES IN THE PATHOGENESIS OF IMPAIRED DETRUSOR CONTRACTILITY: EVIDENCE IN OVARIECTOMIZED RODENTS

Although detrusor hyperactivity with impaired contractility is a common urodynamic finding in elderly subjects, to our knowledge its pathogenesis remains unknown. Biopsy studies indicate that subjects with detrusor hyperactivity and impaired contractility have ultrastructural evidence of dysjunction and degeneration patterns in isolated detrusor hyperactivity and impaired contractility, respectively. Based on the known cellular effects of estrogen we postulated that declines in ovarian hormone production may contribute to the pathogenesis of detrusor hyperactivity with impaired contractility. Mature 13 to 14-month-old female Fisher 344 rats were studied 4 months after bilateral ovariectomy or sham surgery. Detrusor structure was evaluated by electron microscopy and contractility was evaluated by muscle strip studies. After bilateral ovariectomy detrusor smooth muscle decreased by 25% with a 12% decrease in the number of nucleated muscle profiles and degenerative changes in many axons. Muscle strips from bilaterally ovariectomized animals generated 40% to 50% less tension per strip in response to carbachol than strips of equal size from sham operated animals with no apparent change in muscarinic receptor affinity. Bilateral ovariectomy resulted in many changes of the degeneration ultrastructural pattern but in none of the characteristic features of the dysjunction pattern. Our results indicate that the mature rodent detrusor and its innervation are sensitive to prolonged ovarian hormonal deficiency, contributing to impaired contractility in rodents. Future studies are required to establish whether estrogen has a role in the degeneration ultrastructural pattern or impaired contractility in humans.

Antiestrogens--tamoxifen, SERMs and beyond.

Estrogens play a central role in reproductive physiology. The cellular effects of estrogens are mediated by binding to nuclear receptors (ER) which activate transcription of genes involved in cellular growth control. At least two such receptors, designated ERalpha and ERbeta, mediate these effects in conjunction with a number of coactivators. These receptors can directly interact with other members of the steroid receptor superfamily. A complex cross-talk exists between the estrogen-signaling pathways and the downstream signaling events initiated by growth factors, such as epidermal growth factor and insulin-like growth factors. Estrogens are also a causative factor in the pathogenesis of a variety of neoplastic and non-neoplastic diseases, including breast cancer, endometrial cancer, endometriosis, and uterine fibroids, among others. Antiestrogens, such as tamoxifen, are widely used for the treatment of breast cancer. Tamoxifen produces objective tumor shrinkage in advanced breast cancer, reduces the risk of relapse in women treated for invasive breast cancer, and prevents breast cancer in high-risk women. Although, initially developed as an antiestrogen, tamoxifen can also prevent postmenopausal osteoporosis as well as reduce cholesterol, due to its estrogen-agonist effects. Its estrogen-agonist activity, however, can lead to significant side-effects such as endometrial cancer and thromboembolic phenomena. This has led to the concept of "ideal" selective estrogen receptor modulators (SERMs), drugs that would have the desired, tissue selective, estrogen-agonist or -antagonist effects. Raloxifene is a SERM which has the desirable mixed agonist/antagonist effects of tamoxifen but does not cause uterine stimulation. "Pure" antiestrogens may provide very potent estrogen-antagonist drugs, but are likely to be devoid of beneficial effects on bone and lipids. Future drug development efforts should focus on developing superior SERMs that have a greater efficacy against ER-positive tumors and do not cause hot flashes or thromboembolism, and explore combination strategies to simultaneously target hormone-dependent as well as hormone-independent breast cancer.

Electrophysiological and cellular effects of estrogen on neuronal function.

Estrogen exerts a variety of electrophysiological, neurotrophic, and metabolic effects on neurons in the adult central nervous system. Recent epidemiological studies have suggested that estrogen, as hormone replacement therapy in postmenopausal women, may be protective against Alzheimer's disease; the biological basis for a potential neuroprotective effect of estrogen in humans is an area of intense current research. This review summarizes electrophysiological and cellular effects of estrogen on neuronal function, with particular emphasis on hypothalamic and hippocampal neurons. Classic electrophysiological studies are compared with more recent cellular and molecular analyses in an effort to illuminate significant relationships between data gathered over the last 30 years and from varied sources. Hypotheses are made for the mechanisms of estrogen action in the brain as well as the functional consequences of estrogen's effects for both normal brain function and pathological states.

Estrogen modulates the recruitment of myelopoietic cell progenitors in rat through a stromal cell-independent mechanism involving apoptosis

Loss of ovarian function leads to a significant increase in the number of bone-resorbing osteoclasts. Estrogen replacement is known to manifest bone protective effects in the treatment of postmenopausal osteoporosis. In the present study, we used ovariectomized rats to examine the effects of estrogen loss at the osteoclast progenitor colony forming unit-granulocyte macrophage (CFU-GM) level. A significant increase in CFU-GM number was observed as early as 7 days following ovariectomy, and correlated directly with an increase in the number of osteoclast-like cells generated in marrow cultures. The increase in CFU-GM following ovariectomy was abrogated in animals that received estrogen treatment in vivo. A similar suppressive effect was observed on CFU-GM number when ovariectomized rat marrow was treated with estrogen in vitro. This effect was blocked in the presence of the estrogen antihormone ICI 164,384. Thus, the data suggest the possibility that estrogen exerts a direct effect on osteoclast progenitors, and does so through the estrogen receptor-mediated mechanism. Ovariectomy also led to an increase in the early hematopoietic stem/progenitor cell population (Thy 1.1+ cells) as determined by FLOW cytometry methods. Morphological changes as well as terminal deoxynucleotidyl transferase assays revealed that estrogen treatment negated growth factor-induced proliferation of these early progenitors by promoting apoptosis. The cellular effects of estrogen in vitro together with the immunocytochemical detection of the estrogen receptor in these cells, strongly support the contention that in addition to osteoclast progenitors such as CFU-GM, earlier hematopoietic progenitors are also unique cellular targets for estrogen action.

Estrogen, progesterone, and vascular reactivity: potential cellular mechanisms.

I. Introduction FEMALE hormones are broadly recognized as affecting susceptibility to vascular disease, yet comparatively little is known about the cellular mechanisms by which they exert their effects. While clinical and epidemiological data support a protective effect of estrogen on cardiovascular function, a female predominance in other vascular disorders suggests that sex steroids influence the pathogenesis of vascular disease as well. Most of the literature on cellular effects of estrogen and progesterone has emerged from studies in the breast, uterus, and brain. Whether similar mechanisms occur in the vasculature and influence susceptibility to vascular disease is largely unknown. The purpose of this review is to provide a framework for identifying the mechanisms by which female sex steroids influence vascular function. A diverse literature encompassing clinical observations, whole animal, isolated vessel, and cell culture studies has been incorporated in the hopes of providing a common basis for co...

The cellular effects of estrogens on neuroendocrine tissues

Estrogen action on sensitive neurons in the rat diencephalon has been studied by morphologic techniques; evidence of estrogen action at every level is presented, including tracts, cells, circuitry and subcellular organelles. The demonstration in the arcuate nucleus of estrogen-induced synaptic remodelling, estrogen-induced postsynaptic membrane phenotypes, changes in intracellular membranes and rapid estrogen actions on neuronal endo-exocytosis indicates that cellular estrogen actions may underlie the neuronal control of reproduction.