Stimulatory Effect Of Estrogen Research Articles

Interaction among estrogen, IGF-1, and H2S on smooth muscle cell proliferation.

Both estrogen and hydrogen sulfide (H2S) inhibit the proliferation of vascular smooth muscle cells (SMCs) and development of atherosclerosis. In the absence of endogenous H2S as occurred in CSE-knockout (KO) mouse, however, estrogen stimulates the proliferation of vascular SMCs. The underlying mechanisms for this seemingly controversial vascular effect of estrogen are unclear. In the present study, we demonstrated that the stimulatory effect of estrogen on the proliferation of CSE-KO SMCs was suppressed by the inhibitor of insulin-like growth factor-1 receptor (IGF-1R) or knockdown of IGF-1R protein expression. Estrogen downregulated the expression of insulin-like growth factor-1 (IGF-1) and IGF-1R in aortic tissues or aortic SMCs isolated from WT and CSE-KO mice. Furthermore, endogenous H2S downregulated IGF-1R, but upregulated estrogen receptor (ER)-α, in aortic tissues or SMCs. ER-α and IGF-1R were co-located in SMCs and co-immunoprecipitated, which was decreased by H2S. Finally, both endogenous and exogenous H2S induced the S-sulfhydration of IGF-1R, but not ER-α, in WT-SMCs and CSE-KO SMCs, which underlies the decreased formation of IGF-1R/ER-α hybrid in the presence of H2S. Thus, the absence of H2S favors the interaction of estrogen with IGF-1R/ER-α hybrid to stimulate SMCs proliferation. The appreciation of a critical role of H2S in preventing estrogen-induced SMCs proliferation will help better understand the regulation of complex vascular effects of estrogen and sex-related cardiovascular diseases.

Gynecomastia in Infants, Children, and Adolescents.

Gynecomastia may occur physiologically in the neonatal period, during puberty, and in old age. It may also develop in association with various pathologic states. The challenge for the physician is to distinguish physiological gynecomastia from those with an underlying pathology. To review in depth the pathophysiology, clinical manifestations, and treatment of gynecomastia. A PubMed search was completed in Clinical Queries using the key term "gynecomastia". Patents were searched using the key term "gynecomastia" from www.google.com/patents, www.uspto.gov, and www.freepatentsonline.com. Gynecomastia is caused by an imbalance between the stimulatory effect of estrogen and the inhibitory effect of androgen at the breast tissue level. Clinically, gynecomastia is characterized by the presence of a firm or rubbery, discrete, subareolar ridge of glandular tissue that is symmetrical in shape, freely movable, and nonadherent to skin or underlying tissue. Since most cases of physiological gynecomastia regress spontaneously with time, reassurance is all that is necessary. For pathological gynecomastia, treatment should be directed at the underlying cause, if possible. If gynecomastia persists in spite of the above measures, pharmacologic therapy and reduction mammoplasty may be considered. Recent patents related to the management of gynecomastia are discussed. The majority of cases are physiological and do not require treatment other than reassurance. For pathological cases, the underlying cause should be treated if possible. If gynecomastia persists in spite of the above measures and treatment becomes necessary, tamoxifen is the treatment of choice. Reduction mammoplasty may be considered for resistant cases.

The endometrial and breast safety of menopausal hormone therapy containing micronised progesterone: A short review.

For a significant minority of women, menopausal symptoms can be very unpleasant; however, many are worried about taking menopausal hormone therapy (MHT) for fear of causing breast cancer. Micronised progesterone (mP4) has been available in Europe since the 1990s and clinical trials have shown that 100mg oral daily, 200mg oral sequentially or 100mg vaginal every second day effectively protect the endometrium from the stimulatory effects of oestrogen. MHT containing mP4 has a significantly lower breast cancer risk than those containing progestins. Micronised progesterone does not appear to attenuate the cardiovascular benefits of oestrogen. Pharmaceutical grade, body identical MHT is now available in Australia.

A clinical approach to gynecomastia

Gynecomastia is the commonest breast condition in male, which can cause significant psychological distress and anxiety to the patient. It refers to the benign enlargement of the male breast caused by proliferation of glandular breast tissue due to an imbalance between the inhibitory effect of androgen and stimulatory effect of estrogen. Gynecomastia can be physiological during neonatal period, puberty or old age. Various drugs, systemic disorders, benign or malignant tumours and hypogonadism can also lead to gynecomastia, while about 25% of cases are idiopathic. Gynecomastia should be differentiated from pseudogynecomastia (adipomastia), which is characterized by excessive accumulation of adipose tissue without glandular proliferation. A detailed history and examination helps to exclude differential diagnosis, identify the underlying etiology and to assess the severity of the disease and the concerns of the patient. The management of gynecomastia depends on the underlying etiology and the concerns of the patient. This may include interventions for relief of pain or discomfort, restoration of normal appearance and reassurance regarding cancer. Treatment options include watchful waiting, pharmacotherapy and surgery. Sri Lanka Journal of Diabetes, Endocrinology and Metabolism 2015; 5: 23-27

Abstract 3343: Anomalous expression of claudin 16 in ovarian cancer: Role of PKC, PI3K and estrogen

Abstract Background: We have demonstrated that 63% of primary epithelial ovarian cancer (EOC) anomalously overexpressed CLDN16 in the cell cytoplasm, regardless of tumor histological type or grade, thus suggesting that this is an early event in EOC development, and might serve as an EOC marker. The present work aimed to enlighten cellular mechanisms that modulate CLDN16 expression in EOC. Methods: PKA, PKC, and PI3K pathways affect CLDNs cellular localization and function, cancer development and progression. We investigated the effect of the pathways, and of intra-tumoral estrogen (0.5, 5, 50 and 500 nM), on CLDN16 expression in the serous and platinum-resistant EOC model, the OVCAR3 cell line. Immunofluorescence experiments were carried out to determine the cellular localization of CLDN16 in OVCAR3. CLDN16 expression was assessed by real-time RT-PCR, in the presence or absence of the pathway modulators cAMP (PKA activator, 10-6M), KT5720 (PKA inhibitor, 10-7M), PMA (PKC activator, 10-8M), and Wortmannin (WORT: PI3K activator, 10-7M). CLDN16 relative expression analyses followed the CT method of Pffalf, using the REST program (Version 2.0.13, 2009). Data, expressed as mean ± SE, were analyzed by Bonferroni and Dunnet multiple comparisons tests. Findings: OVCAR3 expressed CLDN16 exclusively in the cytoplasm compartment, resembling primary tumors, so being a reliable in vitro model to our expression study. While the PKA pathway did not affect CLDN16 expression in OVCAR3, the PKC pathway lead to an increase of the transcript by1.95-fold (PMA; p <0.001). Likewise, the PI3K pathway modulated CLDN16 expression, as seen by the 2.32-fold decrease on its expression in the presence of WORT (p <0.001). Whereas estrogen 0.5 and 5 nM did not change CLDN16 expression, but increased its expression by 6.57-fold at 50 nM. The stimulatory effect of estrogen was abolished at 500 nM, thus suggesting a biphasic effect of the hormone in CLDN16 expression in EOC. Estrogen effects in EOC result, in part, from the intra-tumoral production of the hormone by aromatases, as corroborated by the 10.31-fold inhibition of CLDN16 expression by the aromatase inhibitor anastrozole (IC50 2.5 x 10-4M). Conclusions: Our data strongly suggest that the expression of CLDN16 is stimulated by the PKC and PI3K, and intra-tumoral aromatase-produced estrogen in EOC. Whereas the anomalous cytoplasm overexpression of CLDN16 still puzzles us, we speculate that fragments of the molecule could be possibly secreted. If this is the case, screening for circulatory portions of the protein could serve as an EOC screening molecule, considering that it is overexpressed early in disease course. Despite the fact that more studies are necessary to elighten the mechanisms that control the expression and function of CLDN16 in EOC, our study opens a new avenue to overcome EOC dramatic epidemiological scenario, bringing hope to improve patients overall outcome and quality of life. Citation Format: Nayara G. Tessarollo, Marcela Paes, Murilo Cerri, Alice Herlinger, Klesia Madeira, Renata Daltoé, Ian Silva, Leticia Rangel. Anomalous expression of claudin 16 in ovarian cancer: Role of PKC, PI3K and estrogen. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3343. doi:10.1158/1538-7445.AM2014-3343

Osteoporosis: Current review

Although hormone therapy using estrogens plus progestogens (EPT) is effective for the management of menopausal symptoms (e.g., vasomotor symptoms and vulvar/vaginal atrophy) and prevention/treatment of postmenopausal osteoporosis, EPT is associated with safety and tolerability concerns. A new alternative to EPT is the tissue selective estrogen complex (TSEC), which partners a selective estrogen receptor modulator (SERM) with one or more estrogens and is designed to treat menopausal symptoms and prevent postmenopausal osteoporosis without the tolerability concerns associated with EPT. The first TSEC to reach advanced clinical development is a combination of the SERM bazedoxifene (BZA) with conjugated estrogens (CE). BZA has been shown to inhibit the stimulatory activity of CE on uterine tissue and breast in vitro and in vivo. In clinical studies, BZA/CE treatment has been associated with significant improvements in menopausal symptoms including hot flushes and vulvar/vaginal atrophy and significant increases in bone mineral density, coupled with reductions in bone turnover marker levels and improvements in sleep and health-related quality of life. Additionally, BZA/CE has been shown to have a neutral effect on endometrial and breast tissue because BZA inhibits the stimulatory effects of estrogens in selective tissue fashion in these two organs. Taken together, results of these preclinical and clinical studies indicate that the benefits of estrogens for treating menopausal symptoms are maintained with BZA/CE without endometrial or breast stimulation, resulting in a safe and effective treatment for symptomatic postmenopausal women.

Unilateral Gynecomastia in a Tennis Player

Unilateral Gynecomastia in a Tennis Player

The Involvement of Angiotensin Type 1 and Type 2 Receptors in Estrogen-Induced Cell Proliferation and Vascular Endothelial Growth Factor Expression in the Rat Anterior Pituitary

The aim of our study was to examine the involvement of renin-angiotensin system (RAS) in estrogen-induced lactotropes proliferation and vascular endothelial growth factor (VEGF) expression in rat pituitary. The study was performed on Fisher 344 rats underwent 8-day treatment with diethylstilboestrol (DES). The proliferation index (PCNA) and VEGF expression in pituitary sections were estimated using immunohistochemical methods. Treatment with DES increased the number of PCNA-positive cells, VEGF-positive cells, and VEGF-positive blood vessels in pituitary. Stimulatory effect of estrogen on cell proliferation and VEGF expression in blood vessels was attenuated by losartan, PD123319, and captopril. VEGF immunoreactivity in pituitary cells of DES-treated rats was decreased by AT1 antagonist and not changed by AT2 blocker and ACE inhibitor. Our findings suggest the involvement of RAS in DES-induced cell proliferation and VEGF expression in pituitary. Both the AT1 and AT2 receptors appear to mediate the estrogen-dependent mitogenic and proangiogenic effects in rat pituitary.

Estrogen-induced upregulation of Sftpb requires transcriptional control of neuregulin receptor ErbB4 in mouse lung type II epithelial cells

Estrogen is known for its positive stimulatory effects on surfactant proteins. ErbB4 receptor and its ligand neuregulin (NRG) positively stimulate lung development. ErbB receptors interact with nuclear receptors and ErbB4 co-regulates estrogen receptor (ER)α expression in breast cells. ERβ is highly expressed in pneumocytes and its deletion leads to fewer alveoli and reduced elastic recoil. A similar picture was seen in ErbB4-deleted lungs. We hypothesized that estrogen signals its effect on surfactant protein B (Sftpb) expression through interactions of ERβ and ErbB4. Estrogen and NRG treatment decreased cell numbers and stimulated Sftpb expression in type II cells. Estrogen and NRG both stimulated phosphorylation of ERβ and co-localization of both receptors. Overexpression of ERβ increased the cell number and Sftpb expression, which was further augmented by estrogen and NRG. Finally, estrogen and NRG stimulated ERβ and ErbB4 binding to the Sftpb promoter. Overexpression of these receptors stimulated Sftpb promoter activation, which was further enhanced by estrogen and NRG. The stimulatory effect of estrogen and NRG was abolished in ErbB4 deletion and reconstituted by re-expression of full-length ErbB4 in fetal ErbB4-deleted type II cells. Estrogen-induced nuclear translocation of ErbB4 required the intact γ-secretase cleavage site but not the nuclear localization sequence of the ErbB4 receptor, suggesting that ERβ might function as a nuclear chaperone for ErbB4. These studies demonstrate that estrogen effects on Sftpb expression require an interaction of ERβ and ErbB4. We speculate that the stimulatory effects of estrogen on Sftpb are under transcriptional control of ErbB4.

Mechanisms of gender-specific regulation of mouse sulfotransferases (Sults)

Marked gender differences in the expression of sulfotransferases (Sults) are known to exist in several species including rats, mice and hamsters. However, the mechanism for this gender difference is not known. Therefore, in the present study, it was determined whether sex and/or growth hormone (GH) are responsible for the gender difference in the expression of Sults using gonadectomized (GNX), hypophysectomized (HX) and GH-releasing hormone receptor-deficient little (lit/lit) mouse models.Sult1a1 and Papss2 in liver and kidney, and Sult1d1 in liver are female-predominant in mice because of suppressive effects of both androgens and male-pattern GH secretion. Sult2a1/a2 is the most markedly female-predominant Sult in mouse liver due to suppressive effects of androgens and male-pattern GH secretion, as well as stimulatory effects by estrogens and female-pattern GH secretion. Sult3a1 is female-predominant in mouse liver due to suppressive effects of androgens as well as stimulatory effects of estrogens and female-pattern GH secretion. Sult1c1 expression is male-predominant in mouse liver and kidney because of stimulatory effects of androgens in males. Sult4a1 expression is female-predominant in mouse brain due to stimulatory effects of estrogens.In conclusion, gender-divergent Sults are mostly female-predominant and Sult1c1 is the only male-dominant Sult. The gender differences in expression of various mouse Sults are influenced by various mechanisms involving sex and/or GHs.

Oestrogenic Compounds Modulate Cytokine-induced Nitric Oxide Production in Mouse Osteoblast-like Cells

Nitric oxide (NO) is a mediator of bone metabolism with effects on both bone resorption and formation. Its production by both the constitutive and inducible isoforms of nitric oxide synthase (NOS) is affected by oestrogen in several types of cell and in tissues other than bone cells. Recently, oestrogens were found to increase basal NO production by osteoblasts via enhanced activity or expression, or both, of NOS-3. Inflammatory cytokines, however, increase NO by increasing the expression of NOS-2. In this study we have examined whether cytokine-induced NO production by osteoblastic cells was affected by oestrogenic compounds by studying the effect of 17beta-oestradiol and the anti-oestrogens ICI164,384 and 4-hydroxytamoxifen on cytokine-induced NO production in oestrogen receptor positive MC3T3-E1 osteoblast-like cells. Combinations of the inflammatory cytokines interleukin-1beta, tumour necrosis factor-alpha, and interferon-gamma with lipopolysaccharide stimulated NO production up to 11-fold. This cytokine-induced NO production was further increased dose-dependently by the anti-oestrogens ICI164,384 and 4-hydroxytamoxifen (133.3 +/- 3.2% and 146.0 +/- 13.2%, respectively). 17Beta-oestradiol either had no effect on or slightly inhibited cytokine-induced NO production. It did, however, dose-dependently counteract the stimulatory effect of the anti-oestrogens. Concentrations of 17beta-oestradiol needed to prevent the stimulatory effect of 4-hydroxytamoxifen were ca tenfold that of ICI164,384. These findings show that, in addition to the stimulatory effect of oestrogen on basal NO production by NOS-3, cytokine-induced NO production is also affected by oestrogenic compounds in osteoblasts.

Abstract CN02-02: Epigenetic targets in endometrial cancer

Abstract CN02-02: Epigenetic targets in endometrial cancer

A New MAP Kinase Protein Involved in Estradiol-Stimulated Reproduction of the Helminth ParasiteTaenia crassiceps

MAP kinases (MAPK) are involved in the regulation of cellular processes such as reproduction and growth. In parasites, the role of MAPK has been scarcely studied. Here, we describe the participation of an ERK-like protein in estrogen-dependent reproduction of the helminth parasite Taenia crassiceps. Our results show that 17β-estradiol induces a concentration-dependent increase in the bud number of in vitro cultured cysticerci. If parasites are also incubated in presence of an ERK-inhibitor, the stimulatory effect of estrogen is blocked. The expression of ERK-like mRNA and its corresponding protein was detected in the parasite. The ERK-like protein was over-expressed by all treatments. Nevertheless, a strong induction of phosphorylation of this protein was observed only in response to 17β-estradiol. Cross-contamination by host cells was discarded by flow cytometry analysis. Parasite cells expressing the ERK-like protein were exclusively located at the subtegument tissue by confocal microscopy. Finally, the ERK-like protein was separated by bidimensional electrophoresis and then sequenced, showing the conserved TEY activation motif, typical of all known ERK 1/2 proteins. Our results show that an ERK-like protein is involved in the molecular signalling during the interaction between the host and T. crassiceps, and may be considered as target for anti-helminth drugs design.

Stimulatory effect of estrogen on the growth of endometrial cancer cells is regulated by cell-cycle regulators

Estrogen is known as a major risk factor in tumorigenesis of the endometrium. The aim of this study is to establish stable estrogen-responsive endometrial cancer cell lines and to investigate the mechanism of estrogen action, focusing on cell-cycle regulation. Human wild-type estrogen receptor cDNA was transfected into endometrial cancer cells (Ishikawa) and estrogen-responsive cell lines were cloned. Their estrogen responsiveness was evaluated by the effect of estrogen on cellular growth and progesterone receptor expression. It was quantitatively estimated by immunocytochemistry or immunoblotting how the expression of cell-cycle regulators such as cyclin D1, cyclin E, Cyclin A, p53, p21 and p27 was regulated by estrogen. A cell line stably responsive to estrogen was established, and cells proliferated and the glandular structure was formed by estrogen stimulation. Cyclin D1 expression increased at 6–24 h and cyclin A gradually increased until 48 h of estrogen treatment compared with untreated cells. On the other hand, p53 and p21 expressions decreased at 6–24 h, and p27 gradually decreased until 24 h by estrogen. Our results show that the stimulatory effect of estrogen on cell proliferation may be regulated by the up-regulation of cyclin D1 and cyclin A, and down-regulation of p53, p21 and p27. This cell line is useful to clarify the molecular mechanism of estrogen action on endometrial cancer.

Update on the use of aromatase inhibitors in breast cancer

Estrogens are biosynthesised from androgens by the CYP450 enzyme complex called aromatase. Aromatase is expressed in the ovary, placenta, brain, bone, adipose tissue and breast tissue. In breast cancer, intratumoural aromatase is the source for local estrogen production in the tissue. Inhibition of aromatase is an important approach for reducing growth stimulatory effects of estrogens in estrogen-dependent breast cancer. The potent and selective third-generation aromatase inhibitors anastrozole, letrozole and exemestane were introduced to the market as endocrine therapy in postmenopausal patients failing anti-estrogen therapy alone, or multiple hormonal therapies. Anastrozole and letrozole are both non-steroidal aromatase inhibitors that compete with the substrate for binding to the enzyme active site. Exemestane is a mechanism-based steroidal inhibitor that mimics the substrate, is converted by the enzyme to a reactive intermediate, and results in inactivation of aromatase. These third-generation aromatase inhibitors are currently approved as first-line therapy for the treatment of postmenopausal women with metastatic estrogen-dependent breast cancer. The use of an aromatase inhibitor as initial therapy, or after treatment with tamoxifen, is now recommended as adjuvant hormonal therapy for postmenopausal women with hormone-dependent breast cancer. Several clinical studies of aromatase inhibitors focus on the use of these agents in the adjuvant setting, for the treatment of early breast cancer. Recently published results show improved responses with these agents compared with tamoxifen.

Dehydroepiandrosterone, androgens and the mammary gland

Mainly through the transformation of dehydroepiandrosterone (DHEA) into androgens in peripheral tissues by intracrine mechanisms, women synthesize at least two-thirds of the androgens found in men. Such data strongly suggest that androgens exert very important but so far underestimated physiological functions in women, including in the breast. In fact, the mammary gland possesses all the enzymatic machinery required to transform DHEA into both androgens and estrogens, although androgens are the predominant steroids synthesized from DHEA in the mammary gland. Early clinical studies have shown beneficial effects of androgens on breast cancer which are comparable to those observed with other hormonal therapies. In fact, a long series of preclinical and clinical data clearly indicate that proliferation of both the normal mammary gland and breast cancer results from the balance between the stimulatory effect of estrogens and the inhibitory effect of androgens. Moreover, the data showing the additive inhibitory effects of antiestrogens and androgens suggest that taking advantage of the inhibitory effect of androgens on breast cancer proliferation could well improve the efficacy of the currently used estrogen deprivation therapies for the treatment and prevention of breast cancer, the best and most physiological candidate being DHEA that limits the androgenic exposure to the tissues which possess the required enzymatic intracrine machinery.

Valproic acid increases the stimulatory effect of estrogens on proliferation of human endometrial adenocarcinoma cells.

Long-term use of valproic acid (VA), a well-tolerated anticonvulsant agent widely used for treating epilepsia, has been recently shown to inhibit histone deacetylases, which in turn are involved in the regulation of the expression of estrogen receptor alpha (ERalpha) by suppressing gene transcription. Because estrogens are known to increase cell proliferation of human endometrial tumors, in this study we investigated whether treatment with VA may increase the proliferative response of human endometrial adenocarcinoma cells to 17-beta-estradiol through induction of ERalpha. The results clearly show that VA, at concentrations of clinical interest, significantly enhanced the proliferative activity exerted by 17-beta-estradiol in the endometrial adenocarcinoma Ishikawa cell line. Moreover, in these cells treatment with VA resulted in increased ERalpha gene expression. Similar effects of VA on cell proliferation were also observed in an ERalpha-positive breast cancer cell line (MCF-7). These findings indicate that VA might favor proliferation of estrogen-dependent human tumors.

Intracellular pathways mediating estrogen-induced cholangiocyte proliferation in the rat

The aim of this study was to explore the intracellular signaling pathways involved in the stimulatory effects of estrogens on cholangiocyte proliferation. We investigated the tyrosine kinase–receptor pathway by evaluating the protein expression of total and phosphorylated mitogen-activated protein kinase (MAPK) isoform p44/p42 ( e.g., extracellular signal-regulated kinase [ERK]1/2), the steroid-receptor coactivator Src and Shc (Src-homology/collagen protein). The study was performed in 3-week-old bile duct–ligated (BDL) rats, BDL rats treated with the antiestrogens, tamoxifen or Ici 182,780, and normal control rats. Proliferation was also evaluated in normal purified cholangiocytes treated with 17β estradiol in the presence or absence of tamoxifen, Ici 182,780, ERK, or Src inhibitors. After bile duct ligation, cholangiocyte proliferation was associated with a marked immunohistochemical nuclear positivity for phosphorylated (p)-ERK1/2, which was inhibited by in vivo treatment with tamoxifen or Ici 182,780. Protein expression of total and p-ERK1/2, and Shc in cholangiocytes isolated from BDL rats was markedly increased compared with controls and was inhibited by in vivo treatment with antiestrogens. In vitro, 17β estradiol–induced proliferation of isolated normal cholangiocyte was associated with increased ( P < .01) protein expression of p-ERK1/2, Src, and Shc. Specific inhibitors of ER (Ici 182,780), ERK (U0125), and Src (PP2) inhibited in vitro 17β estradiol–induced cholangiocyte proliferation. In conclusion, this study showed that estrogens induced cholangiocyte proliferation by activating the Src/Shc/ERK pathway. This might suggest that pharmacologic modulation of ER, ERK, and/or Src could be proposed for the treatment of human pathology characterized by dysregulation of cholangiocyte proliferation. (H EPATOLOGY 2002;36:297-304.)

Impairment of stimulation by estrogen of insulin-activated nitric oxide synthase in human breast cancer.

Nitric oxide (NO) is reported to have several important effects in the control of neoplasm. We have reported before the presence of an insulin-activated constitutive form of membrane-bound nitric oxide synthase (IANOS) in various cells. Since the insulin-induced NO synthesis by IANOS could have important consequences on the pathophysiology of neoplastic cells, the role of estrogen on the activity of IANOS in malignant and nonmalignant breast tissue as well as in erythrocytes in breast cancer patients was determined. It was found that the IANOS activity of nonmalignant breast tissue was maximally stimulated by 4-fold over the basal activity in the presence of physiologic amounts of estrogen (8-32 nM). The enzymic activity was, however, inhibited by estrogen both below and above this range when compared to appropriate controls. In contrast, both the basal IANOS activity and the stimulatory effect of estrogen was markedly impaired in malignant breast tissue and in erythrocytes in these patients. It was also noted that tamoxifen, a widely used nonsteroidal compound in breast cancer, mimicked estrogen both in the stimulation and in the inhibition of IANOS activity in both of the tissues. These results indicated the probable existence of a novel pathway for estrogen effect independent of nuclear receptor for the stimulation of IANOS activity that might have important consequences in breast cancer and suggested that some of the beneficial effects of tamoxifen could be related to its estrogen-mimicking effect on IANOS independent of hormone-responsive elements sequence in the DNA.

Intrapituitary Regulatory System of Mammotrophs in the Mouse

Estrogen stimulates the proliferation of pituitary cells, in particular mammotrophs. The present study was designed to clarify involvement of transforming growth factor a (TGF-a) in the estrogen-induced growth of mouse pituitary cells in vitro. Anterior pituitary cells obtained from ICR male mice were cultured in a primary, serum-free culture system. Proliferation of pituitary cells was detected by monitoring the cellular uptake of a thymidine analogue, bromodeoxyuridine. Secretory cell types were immunocytochemically determined. Treatment with TGF-a (0.1 and 1 ng/ml) for 5 days stimulated cell proliferation. Since TGF-a binds to the epidermal growth factor (EGF)-receptor, this action may be exerted through this receptor. Estradiol-17β (E2, 10 -9 M) stimulated proliferation of mammotrophs. RG-13022, an EGF receptor inhibitor, reduced the cell proliferation induced by EGF or E2, showing that the EGF receptor was involved in this induction of mammotroph growth. Treatment with TGF-a antisense oligodeoxynucleotide (ODN) inhibited the cell proliferation induced by E2, but treatment with EGF antisense ODN did not. Dual detection of TGF-a mRNA and growth hormone by in situ hybridization and fluorescence-immunocytochemistry demonstrated that TGF-a mRNA was detected in most somatotrophs. Our recent RT-PCR analysis revealed that E2 stimulated TGF-a-mRNA and EGF-receptor mRNA expression. These results indicate that TGF-a produced in somatotrophs mediates the stimulatory effect of estrogen on pituitary cell proliferation in a paracrine manner, and that EGF-receptor expression is stimulated by estrogen. These findings indicate that intrapituitary cell-to-cell interaction plays an important role in the control of pituitary secretory cells.