Estrogen induction of progestophilins in rat estrogen-sensitive cells grown in media supplemented with sera from castrated rats and from rats bearing an α-fetoprotein-secreting hepatoma

The purpose of this work was to study the effect of α-fetoprotein (AFP) over cell multiplication and the induction of an estradiol-17β (E₂)-dependent marker, i.e., progestophilins in E-sensitive cells C₂9RAP derived from a W/Fu rat pituitary tumor. These cells proliferate in isogeneic hosts under the influence of E₂, while they proliferate in culture regardless of the presence of E₂. C₂9RAP cells were grown in medium supplemented with 10% horse serum. Progestophilin levels were measured 48 h after adding serum (20% horse, or castrated rat, or AFP-secreting tumor-bearing rat) and estrogen to the 10% horse serum-supplemented medium in which the cells were growing. Maximal induction of progestophilins was obtained at 3 × 10⁻¹⁰ M E₂ in cells grown in medium containing horse or castrated rat serum. In contrast, maximal induction of progestophilins required 3 × 10⁻⁸ M E₂ in cells grown in medium supplemented with the serum of Morris hepatoma 7777-bearing rats. This serum contained AFP levels comparable to those present at birth in the rat. 11-Methoxy-17β ethynylestradiol (R₂₈₅₈), a synthetic estrogen with little affinity for AFP, was also tested for its ability to induce progestophilins. The degree of maximal induction of progestophilins expressed as percentage of the respective control, was similar for all experimental groups, both with E₂ and with R₂₈₅₈.In addition, we compared the free E₂ levels in the culture medium with the progestophilin levels and the cell proliferation rate. We found that the progestophilin levels were maximal at free E₂ concentrations above 11 pg E₂/ml, whereas there was no correlation between the free E₂ levels and the proliferation rate. Moreover, the proliferation rate of cells in medium supplemented with horse or castrated rat serum was maximal at concentrations of free E₂ below 0.4 pg/ml, whereas cell proliferation was inhibited with hepatoma serum even at concentrations of free E₂ of 44 pg/ml. We conclude that the effect of hepatoma serum on the E₂ induction of progestophilins seems to be mediated by the effect of AFP on the availability of free estrogen, since it is abolished by the addition of both natural and synthetic estrogens. The inhibitory effect of hepatoma serum upon cell proliferation is not reversed by estrogens and thus seems to be mediated by mechanisms other than E₂ trapping by AFP.     

Estrogen receptor alpha is essential for the proliferation of prostatic smooth muscle cells stimulated by 17β-estradiol and insulin-like growth factor 1

Estradiol (E₂) and its receptor estrogen receptor alpha (ERα) are implicated in the pathology of stromal‐predominant benign prostatic hyperplasia (BPH). Insulin‐like growth factor 1(IGF1) is produced primarily by stromal cells in the prostate. Recent study showed that E₂‐mediated regulation of IGF1 in mouse uterus requires the DNA binding ability of ERα. However, the crosstalk between ERα and IGF1 in the prostate has not been addressed yet. Therefore, in this study we employed mouse prostatic smooth muscle cells (PSMCs) as a model to demonstrate that E₂ stimulated the proliferation of PSMCs and up‐regulated the expression of IGF1 and its receptor IGF1R as well as cyclin D1 in PSMCs, all of which could be inhibited by shRNA‐mediated knockdown of ERα. Furthermore, we found that exogenous IGF1 could not promote cell proliferation and cyclin D1 expression in PSMCs subjected to shRNA‐mediated knockdown of ERα. Interestingly, blockage of IGF1R by antibody could inhibit E₂‐stimulated PSMCs proliferation. Altogether our present study provides the first line of evidence that there is crosstalk between ERα and IGF1 signaling in PSMCs proliferation in which ERα up‐regulates the expression of IGF1 and IGF1R, and IGF1 signaling is indispensable to mediate downstream effects of E₂ and ERα. Copyright © 2011 John Wiley & Sons, Ltd.     

Region‐specific effects of oestradiol on adipose‐derived stem cell differentiation in post‐menopausal women

The goal of this study was to determine the effect of acute transdermal 17β‐oestradiol (E₂) on the adipogenic potential of subcutaneous adipose‐derived stem cells (ASC) in post‐menopausal women. Post‐menopausal women (n = 11; mean age 57 ± 4.5 years) were treated for 2 weeks, in a randomized, cross‐over design, with transdermal E₂ (0.15 mg) or placebo patches. Biopsies of abdominal (AB) and femoral (FEM) subcutaneous adipose tissue (SAT) were obtained after each treatment and mature adipocytes were analysed for cell size and ASC for their capacity for proliferation (growth rate), differentiation (triglyceride accumulation) and susceptibility to tumour necrosis factor alpha‐induced apoptosis. Gene expression of oestrogen receptors α and β (ESR1 and ESR2), perilipin 1 and hormone‐sensitive lipase (HSL), was also assessed. In FEM SAT, but not AB SAT, 2 weeks of E₂ significantly (P = 0.03) increased ASC differentiation and whole SAT HSL mRNA expression (P = 0.03) compared to placebo. These changes were not associated with mRNA expression of oestrogen receptors α and β, but HSL expression was significantly increased in FEM SAT with transdermal E₂ treatment. Adipose‐derived stem cells proliferation and apoptosis did not change in either SAT depot after E₂ compared with placebo. Short‐term E₂ appeared to increase the adipogenic potential of FEM, but not AB, SAT in post‐menopausal women with possible implications for metabolic disease. Future studies are needed to determine longer term impact of E₂ on regional SAT accumulation in the context of positive energy imbalance.     

17β-estradiol downregulates angiotensin-II-induced endothelin-1 gene expression in rat aortic smooth muscle cells

It is well documented that 17-estradiol (E₂) exerts a cardiovascular protective effect. A possible role of E₂ in the regulation of endothelin-1 (ET-1) production has been reported. However, the complex mechanisms by which E₂ inhibits ET-1 expression are not completely understood. The aims of this study were to examine whether E₂ may alter angiotensin II (Ang II)-induced cell proliferation and ET-1 gene expression and to identify the putative underlying signaling pathways in rat aortic smooth muscle cells. Cultured rat aortic smooth muscle cells were preincubated with E₂, then stimulated with Ang II, and [³H]thymidine incorporation and ET-1 gene expression were examined. The effect of E₂ on Ang-II-induced extracellular signal-regulated kinase (ERK) phosphorylation was tested to elucidate the intracellular mechanism of E₂ in proliferation and ET-1 gene expression. Ang II increased DNA synthesis which was inhibited with E₂ (1–100 nM). E₂, but not 17-estradiol, inhibited the Ang-II-induced ET-1 gene expression as revealed by Northern blotting and promoter activity assay. This effect was prevented by coincubation with the estrogen receptor antagonist ICl 182,780 (1 µM). E₂ also inhibited Ang-II-increased intracellular reactive oxygen species (ROS) as measured by a redox-sensitive fluorescent dye, 2,7-dichlorofluorescin diacetate, and ERK phosphorylation. Furthermore, E₂ and antioxidants, such as N-acetyl cysteine and diphenylene iodonium, decreased Ang-II-induced cell proliferation, ET-1 promoter activity, ET-1 mRNA, ERK phosphorylation, and activator protein-1-mediated reporter activity. In summary, our results suggest that E₂ inhibits Ang-II-induced cell proliferation and ET-1 gene expression, partially by interfering with the ERK pathway via attenuation of ROS generation. Thus, this study provides important new insight regarding the molecular pathways that may contribute to the proposed beneficial effects of estrogen on the cardiovascular system.     

p38α MAPK mediates 17β-estradiol inhibition of MMP-2 and -9 expression and cell migration in human lovo colon cancer cells

Epidemiological studies demonstrate that the incidence and mortality rates of colorectal cancer in women are lower than in men. However, it is unknown if 17β‐estradiol (E₂) treatment is sufficient to inhibit cell proliferation and cell migration in human colon cancer cells. Up‐regulation of urokinase plasminogen activator (uPA), tissue plasminogen activator (tPA), and matrix metallopeptidases (MMPs) is reported to associate with the development of cancer cell mobility, metastasis, and subsequent malignant tumor. In the present study, we treated human LoVo colon cancer cells with E₂ to explore whether E₂ down‐regulates cell proliferation and migration, and to identify the precise molecular and cellular mechanisms behind the down‐regulatory responses. Here, we found that E₂ treatment decreased cell proliferation and cell cycle‐regulating factors such as cyclin A, cyclin D1 and cyclin E. At the same time, E₂ significantly inhibited cell migration and migration‐related factors such as uPA, tPA, MMP‐2, and MMP‐9. However, E₂ treatment showed no effects on upregulating expression of plasminogen activator inhibitor‐1 (PAI‐1), tissue inhibitor of metalloproteinase‐1, ‐2, ‐3, and ‐4 (TIMP‐1, ‐2, ‐3, and ‐4). After administration of inhibitors including QNZ (NFκB inhibitor), LY294002 (Akt activation inhibitor), U0126 (ERK1/2 inhibitor), SB203580 (p38 MAPK inhibitor) or SP600125 (JNK1/2 inhibitor), E₂‐downregulated cell migration and expression of MMP‐2 and MMP‐9 in LoVo cells is markedly inhibited only by p38 MAPK inhibitors, SB203580. Application of specific target gene siRNA (ERα, ERβ, p38α, and p38β) to LoVo cells further confirmed that p38 MAPK mediates E₂/ERs inhibition of MMP‐2 and ‐9 expression and cell motility in LoVo cells. Collectively, these results suggest that E₂ treatment down‐regulates cell proliferation by modulating the expression of cyclin A, cyclin D1 and cyclin E. E₂ treatment simultaneously impaired cell migration by inhibiting the expression of uPA, tPA, MMP‐2, and MMP‐9 through E₂/ERs ? p38α MAPK signaling pathway in human LoVo colon cancer cells. J. Cell. Physiol. 227: 3648–3660, 2012. © 2012 Wiley Periodicals, Inc.     

Endogenous prostaglandin E2 synthesis inhibits growth of polyoma virus-transformed 3T3 fibroblasts.

Indomethacin lowered the cellular content of adenosine 3 ′: 5 ′-monophosphate (cAMP) and stimulated growth of polyoma virus-transformed 3T3 fibroblasts. Exogenous prostaglandin E₂, at concentrations produced in the absence of inhibitor, reversed the effects of indomethacin on cAMP levels and cell proliferation. Therefore, endogenously produced prostaglandin E₂ decreases cell growth and raises the levels of cAMP in these cells.     

Regucalcin is under‐expressed in human breast and prostate cancers: Effect of sex steroid hormones

Regucalcin plays an important role in maintenance of intracellular Ca²⁺ homeostasis, suppresses cell proliferation, inhibits expression of oncogenes, and increases the expression of tumour suppressor genes. This suggests that regucalcin functions may be altered in cancer tissues. In this study the regucalcin expression in breast and prostate cancer cases was analysed by RT‐PCR and immunohistochemistry showing that the mRNA and/or protein are under‐expressed in these tumors. The effect of sex steroid hormones on regucalcin expression in breast and prostate cancer cells was determined by real‐time PCR. MCF‐7 and LNCaP cells were stimulated with 0, 1, and 10 nM of 17β‐estradiol (E₂) or 5α‐dihydrotestosterone (DHT), respectively, for 0, 6, 12, 24, and 48 h. MCF‐7 cells were also stimulated with E₂ conjugated to BSA (E₂‐BSA). To explore the mechanisms underlying the sex steroid regulation of regucalcin expression, control treatments with ICI 182,780, flutamide and cyclohexamide were carried out. E₂ effects regulating regucalcin expression were not abrogated in the presence of ICI 182,780, and were similar to those observed with E₂‐BSA, which suggests the involvement of a membrane‐bound estrogen receptor. In LNCaP cells, DHT down‐regulated regucalcin expression, an effect inhibited by the presence of both flutamide and cyclohexamide, suggesting the involvement of androgen receptor and de novo protein synthesis. The loss of regucalcin expression in breast and prostate cancer cases and the regulation of its expression by sex steroid hormones suggest that it may be associated with development and progression of these human tumors. J. Cell. Biochem. 107: 667–676, 2009. © 2009 Wiley‐Liss, Inc.     

Effects of estrogen deprivation on brain estrogen and progestin receptor levels and the activation of female sexual behavior

Ovariectomy (OVX) in rats is followed by a decline in behavioral sensitivity to combined estrogen and progesterone therapy. The purpose of this study was to further characterize this behavioral change, and to explore its biochemical basis in terms of estrogen and progesterone receptor concentrations in the brain. Sexually inexperienced female rats were used 5 (short-term) or 35 (long-term) days after OVX. Short- and long-term OVX animals were injected with estradiol-17β (E₂; 36 μg/kg body wt, iv) then subjected to one of the following three treatment schedules. (1) Animals were treated with progesterone (1 mg, sc in oil) 20–21 hr after E₂ injection, then tested at 24 hr for female sexual behavior. (2) One or twelve hours after the E₂, cell nuclear estrogen receptors (ER_n) were measured in the pituitary (PIT) and pooled preoptic area and mediobasal hypothalamus (POA-MBH). (3) Twenty-four hours after E₂, progestin receptor (PR_c) concentrations were measured in cytoplasmic fractions prepared from PIT and POA-MBH. Long-term OVX animals showed a reduced capacity to exhibit proceptive and receptive sexual behavior, and a lower PR_c level in the PIT and POA-MBH 24 hr after E₂ injection than animals that had been OVX for only 5 days. However, no differences were observed between long- and short-term OVX rats with respect to ER_n concentrations in PIT and POA-MBH cell nuclei 1 or 12 hr after E₂. Thus, it appears that the decline in behavioral responsiveness to E₂ which occurs after ovariectomy cannot be attributed to a decrease in the ability of E₂ to translocate estrogen receptors into POA-MBH cell nuclei, but is more probably associated with a change in the biochemical processes subsequent to ER_n binding. One of these processes may well be the induction of cytoplasmic progestin receptors.     

Estradiol-17β and 2-hydroxyestradiol-17β-induced differential production of prostaglandins by cells dispersed from human intrauterine tissues at parturition

Prostaglandin (PGE, 6-keto PGF_1α) output by cells dispersed from human amnion and decidua in the presence of increasing levels (0–5000 ng/ml) of estradiol-17β (E₂) or 2-hydroxyestradiol-17β (2-OH E₂) was studied in relation to parturition. Tissues were obtained from women at term either before (CS) or after (SL) spontaneous labor and vaginal delivery. In the absence of estrogens, the output of both PGs from amnion increased significantly with labor. No significant increase in decidua PG output occurred with labor. Neither estrogen influenced CS amnion PG output. However, both E₂ and 2-OH E₂ stimulated SL amnion PGE output (2-OH E₂>E₂) while having no affect on 6-keto PGF_1α output. Only the highest dose of 2-OH E₂ stimulated PGE output in CS decidua, but both estrogens significantly inhibited 6-keto PGF_1α output in this tissue. In SL decidua only 2-OH E₂ significantly stimulated PGE, and neither estrogen affected 6-keto PGF_1α output. These results might suggest that estrogens modulate PG biosynthesis at the level of endoperoxide to primary PG conversion.     

Estrogen induces cell proliferation by promoting ABCG2-mediated efflux in endometrial cancer cells

Recently, it has reported that overeating of lipid-food has led to increase the amount of estrogen in vivo and the incidence of endometrial carcinomas. It is well-known that ATP-binding cassette transporter sub-family G2 (ABCG2) is highly expressed in cancer stem cells (CSCs). CSCs possess the ability for differentiation, tumorigenesis, stem cell self-renewal, and the efflux of anti-cancer drug and these abilities affect malignancy of cancer cells. However, little is known about the relationship between the expression of ABCG2 and malignancy of cancer cells. The present study aimed at understanding the regulatory mechanism underlying 17-β-estradiol (E₂)-induced cell proliferation under the control of ABCG2. E₂ increased cell viability with a peak at 1 μM and facilitated ABCG2 mRNA expression followed by the increase of ABCG2 expression level at plasma membrane. E₂-induced cell proliferation was inhibited by reserpine, an inhibitor of ABCG2, and the ABCG2 siRNA treatment. Thus, these results imply that ABCG2 plays an important role in the promotion of E₂-induced cell proliferation in Ishikawa cells.     

Synthetic Chalcone Derivatives as Inhibitors of Cathepsins K and B,and Their Cytotoxic Evaluation

A series of chalcone derivatives, 1 – 15 , were prepared by Claisen? Schmidt condensation and evaluated for their cytotoxicities on tumor cell lines and also against proteolytic enzymes such as cathepsins B and K. Of the compounds synthesized, (E)‐3‐(3,4‐dimethoxyphenyl)‐1‐phenylprop‐2‐en‐1‐one ( 12 ), (E)‐3‐(4‐chlorophenyl)‐1‐phenylprop‐2‐en‐1‐one ( 13 ), (E)‐3‐(4‐methoxyphenyl)‐1‐phenylprop‐2‐en‐1‐one ( 14 ), and (E)‐3‐(4‐nitrophenyl)‐1‐phenylprop‐2‐en‐1‐one ( 15 ) showed significant cytotoxicities. The most effective compound was 15 , which showed high cytotoxic activity with an IC₅₀ value lower than 1 μg/ml, and no selectivity on the tumor cells evaluated. Substituents at C(4) of ring B were found to be essential for cytotoxicity. In addition, it was also demonstrated that some of these chalcones are moderate inhibitors of cathepsin K and have no activity against cathepsin B.     

17β‐estradiol supplementation attenuates ovariectomy‐induced increases in ATGL signaling and reduced perilipin expression in visceral adipose tissue

Adipocytes from post‐menopausal females have higher basal lipolytic rates than pre‐menopausal females, which contributes to increased risk of developing dyslipidemia following menopause. The purpose of this study was to delineate cellular mechanisms affecting adipose tissue function in the ovariectomized (OVX) mouse and also determine if physical activity or estrogen supplementation alter any detected changes. Female C57/Bl6 mice were placed into SHAM, OVX sedentary (OVX), OVX exercise (OVX‐Ex), and OVX sedentary + 17β‐estradiol (OVX + E₂) groups. Visceral fat mass, glycerol, and NEFA levels were significantly higher in OVX mice compared to SHAM animals, but were not elevated in the E₂‐treated animals. Voluntary running failed to change circulating levels of glycerol or NEFA in OVX mice, but did partially attenuate the increase in visceral fat mass. Adipose triglyceride lipase (ATGL) protein content was significantly elevated in visceral fat from OVX and OVX‐Ex groups compared to SHAM, while ATGL–CGI‐58 interaction was significantly higher in OVX than SHAM and OVX + E₂ mice. No significant differences in HSL phosphorylation were detected between groups, however, ERK1/2 phosphorylation was significantly elevated in the OVX mice. To determine if ERK1/2 function was critical for the increased glycerol levels, visceral fat was treated with MEK inhibitor PD98059, with no differences in glycerol release detected. Perilipin protein content was decreased significantly in OVX and OVX‐Ex mice compared to SHAM. Thus, these data suggest that increased ATGL signaling and reduced perilipin protein content may contribute to increased NEFA and glycerol levels in OVX mice, which are attenuated with E₂ treatment, but not by exercise. J. Cell. Biochem. 110: 420–427, 2010. © 2010 Wiley‐Liss, Inc.     

Activation of brain steroidogenesis and neurogenesis during the gonadal differentiation in protandrous black porgy,Acanthopagrus schlegelii

The early brain development, at the time of gonadal differentiation was investigated using a protandrous teleost, black porgy. This natural model of monosex juvenile fish avoids the potential complexity of sexual dimorphism. Brain neurogenesis was evaluated by histological analyses of the diencephalon, at the time of testicular differentiation (in fish between 90 and 150 days after hatching). Increases in the number of both Nissl‐stained total brain cells, and Pcna‐immunostained proliferative brain cells were observed in specific area of the diencephalon, such as ventromedialis thalami and posterior preoptic area, revealing brain cell proliferation. qPCR analyses showed significantly higher expression of the radial glial cell marker blbp and neuron marker bdnf. Strong immunohistochemical staining of Blbp and extended cellular projections were observed. A peak expression of aromatase (cyp19a1b), as well as an increase in estradiol (E₂) content were also detected in the early brain. These data demonstrate that during gonadal differentiation, the early brain exhibits increased E₂ synthesis, cell proliferation, and neurogenesis. To investigate the role of E₂ in early brain, undifferentiated fish were treated with E₂ or aromatase inhibitor (AI). E₂ treatment upregulated brain cyp19a1b and blbp expression, and enhanced brain cell proliferation. Conversely, AI reduced brain cell proliferation. Castration experiment did not influence the brain gene expression patterns and the brain cell number. Our data clearly support E₂ biosynthesis in the early brain, and that brain E₂ induces neurogenesis. These peak activity patterns in the early brain occur at the time of gonad differentiation but are independent of the gonads. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 121–136, 2016     

Reciprocal regulation of 17β-estradiol, interleukin-6 and interleukin-8 during growth and progression of epithelial ovarian cancer

Estrogens have been associated with risk for epithelial ovarian cancer (OVCA). Both IL-6 and IL-8 are also likely involved in the progression of OVCA. In order to discover the underline molecular mechanism, we investigated the modulation of estrogen and two cytokines in the growth and progression of epithelial OVCA. In these studies, the effect of 17β-estradiol (E₂) on the expression levels of IL-6, IL-8 and their receptors was investigated. The effect of IL-6 and IL-8 on activation of estrogen-responsive promoter as well as estrogen receptor (ER)α and ERβ expression was also analyzed. Gene expression profile analysis revealed that CAOV-3 and OVCAR-3 cells, which express ER, IL-6 and IL-8 receptors, are suitable model for this study. We found that E₂ not only enhanced IL-6 and IL-8 production via NF-κB signaling pathway, but also modulated their respective receptor expression. Tamoxifen (Txf), an ER antagonist, completely abolished E₂-stimulated cell growth and the expression of IL-6 and IL-8. IL-6/IL-8-induced cell proliferation was completely blocked by their specific neutralizing antibodies, which partially inhibited E₂-induced cell growth. In the absence of estrogen, both cytokines activated estrogen-responsive promoter, which was completely blocked by Txf, and caused a dose-dependent ERα increase and ERβ decrease. Pretreatment of OVCAR-3 with p38 MAPK, MEK1/2 or ErbB2 MAPK inhibitors, respectively, blocked IL-6-mediated induction of estrogen-responsive promoter while Src inhibitor blocked IL-8-induced activation of estrogen-responsive promoter. These results provide a novel mechanism that estrogens, IL-6 and IL-8 may form a common amplifying signaling cascade to modulate OVCA growth and progression. Estrogen-induced OVCA proliferation is partially occurring via enhanced IL-6 and IL-8 production and modulated their receptors, and IL-6/IL-8 could also promote OVCA growth through an ERα pathway.     

Estrogen regulates DNA methyltransferase 3B expression in Ishikawa endometrial adenocarcinoma cells

It is well-known that exposure to unopposed estrogen is considered as an important risk factor for endometrial cancer. Recent studies have shown that over-expression of DNA methyltransferases (DNMTs) are involved in the development of endometrial cancer. Therefore, the present study was undertaken to elucidate the impact of estrogen on the expression of DNMTs in endometrial cancer. Ishikawa cell line was used. Flow cytometry analysis demonstrated that 17 β-estradiol (E₂) enhanced the cell proliferation with a peak at 10⁻⁸ M. Over-expression of DNMT3B treated with E₂ was confirmed by real-time PCR and western blotting analysis. Furthermore, the up-regulation of DNMT3B expression induced by E₂ was suppressed by the addition of ICI182780. However, we did not observe changes in the expression of DNMT1. Our study suggests that estrogen up-regulating the expression of DNMT3B in an ER-dependent pathway may be a possible mechanism for estrogen facilitates the malignant transformation of endometrial cancer cells.     

Stimulation of the estrogen synthesizing system of the immature rat ovary by exogenous and endogenous gonadotropins

Immature rat ovaries increase their secretion of estradiol (E₂) when stimulated by gonadotropins but only after a lag period of several hours. Once established, estrogen secretion can be maintained, or increased, by the continued presence of gonadotropin. A combination of ovine FSH+LH given at 2 hr intervals stimulated the estrogen synthesizing system ($\text{ESS}$) of the ovary and serum E₂ showed a pronounced rise between 16 and 20 hrs after the initial injection. When given every 2 hrs for 5 doses (0–8 hrs) serum E₂ was undetectable. However, it was increased if 20 IU PMS was injected at the time of the last dose of FSH+ LH. Endogenous FSH&LH, increased by hourly injections of LH-releasing hormone for a period of 8 hrs, stimulated the $\text{ESS}$; serum E₂ increased at the expected time when this treatment was followed by an injection of PMS.Anti-PMS antiserum given 12 hrs after PMS, prevented the expected rise in serum E₂ at 24 hrs. However, FSH, LH or a combination of the two given every 2 hrs beginning at the time of the anti-PMS produced an increase in E₂ secretion; the combination was more effective than either hormone alone.These results are consistent with the interpretation that a combined FSH-LH action is responsible for induction of the $\text{ESS}$ in the immature rat ovary. The combination of hormones is also very effective in maintaining estrogen secretion but some function appears possible with FSH or LH alone.     

Selective estrogen-induced apoptosis in breast cancer

Antihormone therapy remains the gold standard of care in the treatment of estrogen receptor (ER) positive breast cancer. However, development of acquired long term antihormone resistance exposes a vulnerability to estrogen that induces apoptosis. Laboratory and clinical studies indicate that successful therapy with estrogens is dependent on the duration of estrogen withdrawal and menopausal status of a woman. Interrogation of estradiol (E₂) induced apoptosis using molecular studies indicate treatment of long term estrogen deprived MCF-7 breast cancer cells with estrogen causes an endoplasmic reticulum stress response that induces an unfolded protein response signal to inhibit protein translation. E₂ binds to the ER and mediates apoptosis through the classical genomic pathway. Furthermore, the induction of apoptosis by estrogens is dependent on the conformation of the estrogen–ER complex. In this review, we explore the mechanism and the processes involved in the paradox of estrogen induced apoptosis and the new selectivity of estrogen action on different cell populations that is correctly been deciphered for clinical practice.     

Kinetic Analysis of Estrogen and Antiestrogen Competition for Hypothalamic Cytosol Estrogen Receptors. Evidence for Noncompetitive Ligand-Receptor Interactions

Abstract

The binding of (³H)-estradiol (E₂) to cytoplasmic estrogen receptors isolated from female rat hypothalamus-preoptic area by unlabeled estrogen and antiestrogens (nafoxidine and tamoxifen) was examined when the concentrations of both the agonist (³H)-E₂) and unlabeled competitors were varied over a wide range. Concentrations of unlabeled E₂ up to 10^-10M decreased the affinity of the labeled steroid for its receptor; at higher E₂ concentrations, the apparent number of binding sites (B_max) began to decline. Thus at some concentrations, E₂ may act as a mixed competitive and noncompetitive inhibitor of its own binding to hypothalamic cytosol receptors. The antiestrogens differed markedly from E2 in their interactions with hypothalamic estrogen receptors. Only at relatively high competitor concentrations (e.g., > 10^-9M) did the antagonists appear to competitively inhibit (³H)-E₂-receptor binding. The most striking observation was that tamoxifen and nafoxidine significantly inhibited (³H)-E₂-receptor binding at very low competitor concentrations (e.g., 1 pM), but only slightly inhibited estrogen binding at intermediate concentrations (e.g., 10^-10M). It was proposed that the non-linear, concentration-dependent effects of antiestrogens on the neural estrogen receptors might be due to complex interactions of the antagonists with a non-estrogen binding site.     

Potassium chloride released from contracting skeletal muscle may stimulate development of its hypertrophy

The effects of potassium chloride on the expression of IGF-1 splice forms and myoblast proliferation were investigated. KCl at the concentrations of 7–12 mM stimulated the synthesis of IGF-1 and mechano growth factor (MGF) in murine myoblasts as well as in myotubes both at the mRNA and protein levels. Pan-calcium channel blocker CdCl₂ completely abolished stimulation of growth factor expression, whereas blocker of HCN and Na_v1.4 channels ZD7288 drastically reduced it. In addition, potassium chloride stimulated myoblast proliferation, while IGF-1 autocrine signaling inhibition partially suppressed these mitogenic effects.