Regulation Of Estrogen Receptor Research Articles

Histone Deacetylase 6 Regulates Estrogen Receptor α in Uterine Leiomyoma

Histone deacetylase 6 (HDAC) 6 is a regulatory factor in the endocrine traffic network that controls growth factor receptor stability. Histone deacetylase 6 expression and its pathogenic role in the uterine leiomyoma have not been studied. Here, we demonstrated that there was a consistent pattern of increasing HDAC6 and estrogen receptor (ER) α expression in leiomyoma samples. For all individual cases, expression of HDAC6 in the normal myometrium or leiomyoma positively correlated with ERα expression. The spearman's rho (ρ) was .53 (P = .008) between HDAC6 and ERα in normal myometrium and, more significantly, the spearman rho was .80 (P < .001) between HDAC6 and ERα in leiomyoma. In ELT-3 leiomyoma cells, silencing HDAC6 expression substantially reduced ERα expression, lowered estrogen response, and inhibited ELT-3 cell growth. Our results, taken together, are the first to provide experimental evidence suggesting that HDAC6 may be an essential molecular therapeutic target in controlling leiomyoma growth.

Testosterone administration to adult rats differentially modulates androgen and oestrogen receptor-α expression in reproductive organs and pituitary

Regulation of androgen receptor (AR) and oestrogen receptor α (ERα) expression has direct bearing on the physiology of male reproductive organs. With the help of three independent tools of immunohistochemistry, western blotting and RT-PCR, AR and ER α receptor expression was examined in the testis, epididymis, prostate, seminal vesicle and pituitary of adult rats following testosterone enanthate (TE, 3 mg/100 μl of olive oil/rat per week) intervention for 15 and 30 days. TE administration reduced AR immunoexpression which coincided well with the decline in the receptor protein and transcript levels. In contrast, ERα was found overexpressed in all the organs. While weights of testis and epididymis decreased significantly, those of prostate, seminal vesicle and pituitary demonstrated an upward trend. Spermatogenesis was adversely affected with decline in number of germ cells per tubule and increased prevalence of germ cell apoptosis. Increase in serum and decrease in intra-testicular levels of testosterone were found significant (P < 0.001) in both 15 and 30 days treatment groups. Serum follicle stimulating hormone declined significantly (P < 0.001) at the end of 30 days treatment. Taken together, the above findings indicate that the testosterone intervention differentially modulates, AR ERα expression, which is associated with hypospermatogenesis and increased germ cell apoptosis.

Fli1 Is a Negative Regulator of Estrogen Receptor α in Dermal Fibroblasts

Estrogen is an important regulator of dermal fibroblast functions, including extracellular matrix (ECM) synthesis. Estrogen mediates its effects through estrogen receptors (ERs), ERα and ERβ; however, regulation of ERs in dermal fibroblasts remains poorly understood. Friend leukemia integration factor 1 (Fli1), a member of the Ets transcription factor family, has been shown to play a pivotal role in regulation of the ECM genes in dermal fibroblasts. The aim of this study was to examine a possible interaction between Fli1 and estrogen pathways, focusing on ERα. We show that treatment of human dermal fibroblasts with transforming growth factor-β (TGF-β) increases ERα protein and mRNA levels. Similarly, ERα expression was increased in response to small interfering RNA (siRNA)-mediated depletion of Fli1, suggesting that Fli1 is a mediator of the TGF-β effects on ERα expression. Accordingly, we showed that Fli1 binds to the most proximal region of the ERα promoter, and dissociates from the promoter upon TGF-β treatment. An inverse correlation between Fli1 and ERα expression levels was confirmed in cultured skin fibroblasts obtained from Fli1(+/-) mice and in the skin of Fli1(+/-) mice in vivo. This study supports a role of Fli1 as a negative regulator of the ERα gene in dermal fibroblasts.

Comparison of several early drug interventions in postmenopausal women with osteopenia

Two hundreds postmenopausal women with osteopenia, aged 45-80, were randomly divided into 4 groups, and received different drug interventions. After treatment for 12 months, the lumbar spine bone mineral density(BMD)and total hip BMD in alendronate group increased significantly(3.5% and 2.6%, both P＜0.05), the lumbar spine BMD raised 2.0% in selective estrogen receptor regulator group(P＜0.05). Bone turnover indices improved in both groups(all P＜0.05). No change in BMD or bone turnover indices was found in patients treated with active vitamin D3and calcium. Key words: Osteopenia; Bone mineral density; Osteoporosis, postmenopausal

P53 Binds to Estrogen Receptor 1 Promoter in Human Breast Cancer Cells

p53 is a tumor suppressor protein that regulates estrogen receptor 1 (ESR1) expression. To investigate the mechanism of ESR1 gene regulation by p53, chromatin immunoprecipitation was applied to assess the binding of p53, DNMT1, HDAC1 and MeCP2 to both silenced ESR1 promoter in MDA-MB-468 cells and active ESR1 promoter in MCF-7 breast cancer cells. The results of chromatin immunoprecipitation experiments showed that p53 protein binds to both unmethylated CpG island of the ESR1 promoter in the ER-positive MCF-7 and the hypermethylated ESR1 promoter in the ER-negative MDA-MB-468 cells. However, repression complex including DNMT1, HDAC1 and MeCP2 is only associated with silenced ESR1 in ER-negative MDA-MB-468 human breast cancer cells. In addition, ectopically expressed wild type p53 failed to reactivate the ESR1 gene in these cells. These results suggest that specific p53 mutations may contribute to loss of estrogen receptor α expression in breast tumors and also support the hypothesis that mutant p53 is likely to impact DNA methylation.

Reciprocal roles of DBC1 and SIRT1 in regulating estrogen receptor α activity and co-activator synergy

Estrogen receptor α (ERα) plays critical roles in development and progression of breast cancer. Because ERα activity is strictly dependent upon the interaction with coregulators, coregulators are also believed to contribute to breast tumorigenesis. Cell Cycle and Apoptosis Regulator 1 (CCAR1) is an important co-activator for estrogen-induced gene expression and estrogen-dependent growth of breast cancer cells. Here, we identified Deleted in Breast Cancer 1 (DBC1) as a CCAR1 binding protein. DBC1 was recently shown to function as a negative regulator of the NAD-dependent protein deacetylase SIRT1. DBC1 associates directly with ERα and cooperates synergistically with CCAR1 to enhance ERα function. DBC1 is required for estrogen-induced expression of a subset of ERα target genes as well as breast cancer cell proliferation and for estrogen-induced recruitment of ERα to the target promoters in a gene-specific manner. The mechanism of DBC1 action involves inhibition of SIRT1 interaction with ERα and of SIRT1-mediated deacetylation of ERα. SIRT1 also represses the co-activator synergy between DBC1 and CCAR1 by binding to DBC1 and disrupting its interaction with CCAR1. Our results indicate that DBC1 and SIRT1 play reciprocal roles as major regulators of ERα activity, by regulating DNA binding by ERα and by regulating co-activator synergy.

Identification of miR-193b Targets in Breast Cancer Cells and Systems Biological Analysis of Their Functional Impact

Identification of protein targets for microRNAs (miRNAs) is a significant challenge due to the complexity of miRNA-mediated regulation. We have previously demonstrated that miR-193b targets estrogen receptor-α (ERα) and inhibits estrogen-induced growth of breast cancer cells. Here, we applied a high-throughput strategy using quantitative iTRAQ (isobaric tag for relative and absolute quantitation) reagents to identify other target proteins regulated by miR-193b in breast cancer cells. iTRAQ analysis of pre-miR-193b transfected MCF-7 cells resulted in identification of 743 unique proteins, of which 39 were down-regulated and 44 up-regulated as compared with negative control transfected cells. Computationally predicted targets of miR-193b were highly enriched (sevenfold) among the proteins whose level of expression decreased after miR-193b transfection. Only a minority of these (13%) showed similar effect at the mRNA level illustrating the importance of post-transcriptional regulation. The most significantly repressed proteins were selected for validation experiments. These data confirmed 14-3-3ζ (YWHAZ), serine hydroxyl transferase (SHMT2), and aldo-keto reductase family 1, member C2 (AKR1C2) as direct, previously uncharacterized, targets of miR-193b. Functional RNAi assays demonstrated that specific combinations of knockdowns of these target genes by siRNAs inhibited growth of MCF-7 cells, mimicking the effects of the miR-193b overexpression. Interestingly, the data imply that besides targeting ERα, the miR-193b effects include suppression of the local production of estrogens and other steroid hormones mediated by the AKR1C2 gene, thus provoking two separate molecular mechanisms inhibiting steroid-dependent growth of breast cancer cells. In conclusion, we present here a proteomic screen to identify targets of miR-193b, and a systems biological approach to mimic its effects at the level of cellular phenotypes. This led to the identification of multiple genes whose combinatorial knock-down likely mediates the strong anti-cancer effects observed for miR-193b in breast cancer cells.

Letrozole and Fulvestrant Combination in Second Line or More for Estrogen Receptor Positive Metastatic Breast Cancer; Efficacy and Predictive Factors of Response

Background: Preclinical data show that complete estrogen blockade by both down regulating estrogen receptor and inhibiting estrogen synthesis, has greater effect on tumor growth than either treatment alone. Combination of an aromatase inhibitor and fulvestrant may be an optimal second line therapy by preventing activation of growth factor pathways and possible cross talk with ER. One clinical study has shown no benefit of adding anastrozole to fulvestrant at first relapse. No clinical data on combination letrozole and fulvestrant in the second line or more metastatic beast cancer setting is available. Methods: Estrogen receptor (ER) positive, progesterone receptor (PgR) positive or negative metastatic breast cancer patients with prior chemo and/or non-aromatase inhibitor (non-AI) endocrine therapy were treated with letrozole and fulvestrant. Patients with complete response(CR) partial response(PR), or stable disease(SD) were considered to have clinical benefit (CR+PR+SD). The predictive effects of age, number of prior regimens, ER/PgR status, histology, sites of metastatic disease were examined using Chi-square test. Results: Thirty-two patients received oral letrozole 2.5 mg daily plus fulvestrant 250 mg intramuscular injection monthly. Mean age was 70 (range: 35-92), median number of prior treatments was 2 (range2-6). 25 pts had ER+/ PgR+, 7 pts had ER+/PgR- tumors. Twenty-five patients had prior non-AI endocrine therapy. Eight patients had lobular histology. Overall clinical benefit rate was 71% (3 CR, 7 PR, and 13 SD). Mean duration of the clinical benefit was 15 months (range 2-38). Nine patients progressed under therapy. Age more than 65 versus younger (89% vs 46%, P=0.007), prior treatments less than 4 versus more (87% vs 25%, P=0.0007) and ER+/PgR+ versus ER+/PgR- (84% versus 42%, P 0.05) . Conclusions: In previously treated metastatic breast cancer patients, combination of letrozole and fulvestrant can be effective with a mean clinical benefit duration of 15 months. Older age, less than four prior lines of therapy, and expression of both ER/PgR are predictive of clinical benefit while lobular histology, site of metastatic disease and prior non-AI endocrine therapy are not. Letrozole and fulvestrant combination can be a reasonable option in selected group of previously treated metastatic breast cancer patients and should be further evaluated in larger studies utilizing recently approved high dose (500 mg) fulvestrant schedule.

Novel Stromal Biomarkers in Human Breast Cancer Tissues Provide Evidence for the More Malignant Phenotype of Estrogen Receptor‐Negative Tumors

Research efforts were focused on genetic alterations in epithelial cancer cells. Epithelial-stromal interactions play a crucial role in cancer initiation, progression, invasion, angiogenesis, and metastasis; however, the active role of stroma in human breast tumorigenesis in relation to estrogen receptor (ER) status of epithelial cells has not been explored. Using proteomics and biochemical approaches, we identified two stromal proteins in ER-positive and ER-negative human breast cancer tissues that may affect malignant transformation in breast cancer. Two putative biomarkers, T-cell receptor alpha (TCR-α) and zinc finger and BRCA1-interacting protein with a KRAB domain (ZBRK1), were detected in leukocytes of ER-positive and endothelial cells of ER-negative tissues, respectively. Our data suggest an immunosuppressive role of leukocytes in invasive breast tumors, propose a multifunctional nature of ZBRK1 in estrogen receptor regulation and angiogenesis, and demonstrate the aggressiveness of ER-negative human breast carcinomas. This research project may identify new stromal drug targets for the treatment of breast cancer patients.

Mdm2 Regulates Estrogen Receptor and Estrogen-responsiveness in Breast Cancer Cells

Murine double minute clone 2 (MDM2) is a multifunctional protein, which modulates nuclear receptor-mediated transactivation. In this study, we show that MDM2 significantly enhanced estrogen receptor α (ERα) and ERα/specificity protein-mediated transactivation in MCF-7 and ZR-75 breast cancer cells. This was demonstrated by both MDM2 overexpression and knockdown experiments by RNA interference. ERα interacted with wild-type MDM2 and deletion mutants of MDM2 containing amino acids 1-342 (C-terminal deletion) and 134-490 (N-terminal deletion), but not 134-342. In contrast, only wild-type but not mutant MDM2 enhanced ERα-mediated transactivation. Protein-protein interactions in vitro were 17β-estradiol (E(2)) independent, whereas fluorescent resonance energy transfer experiments in living cells showed that E(2) enhanced ERα-MDM2 interactions. Subsequent RNA interference and mammalian two-hybrid experiments suggested that MDM2 did not directly interact with endogenous coactivators such as the steroid receptor coactivators but played a role in enhancing ERα-mediating gene expression and estrogen responsiveness through interactions with ERα.

Identification of novel splicing events and post-transcriptional regulation of human estrogen receptor α F isoforms

The 5′-untranslated regions (5′-UTRs) of the estrogen receptor α (ERα) mRNAs play important roles in the modulation of translation. To elucidate the mechanisms regulating human ERα gene expression, it is necessary to determine its genomic organization and the roles of the multiple 5′-UTRs. We therefore examined the splicing and expression profiles of the human ERα F isoforms. A novel non-coding exon E3 was found in the 5′-region of the human ERα gene and six F isoform mRNA variants were identified. The variants revealed the preferred expression patterns. Post-transcriptional regulation was also investigated. The 5′-UTRs of the F isoforms decreased the translation efficiency but had no effect on mRNA stability. The results indicate that the organization and splicing patterns of the human ERα gene are more complex than previously reported, and that the 5′-UTRs of the F isoforms contribute to the post-transcriptional control of human ERα gene expression through translation repression.

Steroid receptor and microRNA regulation in cancer

Steroid hormone receptors (SHR) are crucial regulators of disease and the basis for clinical intervention in cancers. Recent evidence confirms that microRNAs (miRNAs) impact the pathobiology of hormone-regulated malignancies. Therefore, elucidating miRNA regulation of SHR expression and modulation of miRNAs by SHRs may provide diagnostic biomarkers or therapeutic targets. Estrogen receptor status has been established as a key factor in breast cancer prognosis and treatment. Recent studies detail the interactions between estrogen receptor and miRNAs in cancers. New evidence indicates involvement of miRNAs in the regulation of androgen receptor, progesterone receptor, glucocorticoid receptor in hormone responsive cancers. Several miRNAs regulate the expression of the SHRs, while other miRNAs are themselves regulated by SHR signaling in cancer. Cancers have distinct miRNA expression profiles that contribute to the pathobiology of the disease. In hormone-responsive cancers, the regulatory interactions between the SHR and miRNA may contribute to disease progression. The miRNA regulation of estrogen receptor in cancer has been established in estrogen-dependent cancers. The role of miRNAs in regulating progesterone receptor, androgen receptor and glucocorticoid receptor is under investigation with new insights emerging. These interactions can provide prognostic utility as well as the potential for therapeutic intervention in the future.

The antidepressant-like effect of the 3β-hydroxysteroid dehydrogenase inhibitor trilostane involves a regulation of β-type estrogen receptors

Trilostane is a competitive inhibitor of 3β-hydroxysteroid dehydrogenase (3β-HSD), which notably converts pregnenolone into progesterone or dehydroepiandrosterone into androstenedione. Trilostane shows antidepressant-like properties in the forced swimming test (FST). The compound, however, induced only moderate effects on neuroactive steroid levels that could be related to its behavioral efficacy. We compared the behavioral effect of trilostane with the other 3β-HSD inhibitor, cyanoketone, and analyzed the putative involvement of the β-type estrogen receptor (ERβ) in its antidepressant effect. Trilostane reduced immobility in the FST significantly at 12.5 and 25 mg/kg subcutaneously (s.c.), whereas cyanoketone (0-100 mg/kg s.c.) was ineffective. The negative ER modulator fulvestrant (ICI 182780) dose-dependently blocked the effect of trilostane (25 mg/kg). Trilostane increased circulating estradiol levels in the 12.5-50 mg/kg dose-range, and this effect was unaffected by stress and not shared by cyanoketone (25 mg/kg). The trilostane (25 mg/kg) treatment increased the ERβ mRNA expression in adrenals (+100%) and centrally, in the hippocampus (+330%). Stress and cyanoketone failed to affect ERβ mRNA levels in periphery or in the brain. These data demonstrate that the antidepressant-like potential of trilostane is not due to its 3β-HSD inhibiting activity, since it is not shared by cyanoketone, but rather to its estrogenic activity. The compound, which releases estradiol and up-regulates ERβ receptors, could be used as a therapeutic tool to allow an estrogenic facilitation of antidepressant efficacy.

Resveratrol enhances anti-proliferative effect of VACM-1/cul5 in T47D cancer cells

Vasopressin-activated calcium-mobilizing (VACM-1) protein is a cul-5 gene product that forms complexes with a subclass of ubiquitin E3 ligases involved in proteasomal protein degradation. The expression of VACM-1 cDNA in the T47D breast cancer cell line inhibits growth and decreases phosphorylation of mitogen activated protein kinase. Factors that regulate expression or stability of VACM-1 protein have not been identified, however. In our search to identify drugs/substances that may control VACM-1 protein expression, we examined the effects of resveratrol (trans-3,5,4'-trihydroxystilbene), a natural component in the human diet which inhibits tumor initiation and promotion. CMV vector and VACM-1 cDNA stably transfected T47D breast cancer-derived cells were treated with resveratrol and cell growth and VACM-1 protein concentrations were measured. Since the cellular mechanism of resveratrol-dependent inhibition of cell growth also involves the regulation of estrogen receptors, the effect of 17-β-estradiol and resveratrol on ERα levels and on cell growth was examined in control and in VACM-1 cDNA transfected cells. Our results demonstrate that antiproliferative effect of resveratrol observed in the control T47D cancer cells was significantly enhanced in VACM-1 cDNA transfected T47D cells. Western blot results indicated that resveratrol increased VACM-1 protein concentration. Finally, treatment with resveratrol for 24 and 48h attenuated 17-β-estradiol induced increase in cell growth both in control and in VACM-1 cDNA transfected cells. The effect was significantly higher in the VACM-1 cDNA transfected cells when compared to controls. These results indicate that the antiproliferative effect of resveratrol may involve induction of VACM-1/cul5.

The Effects of Dexamethasone, Ascorbic Acid, and β-Glycerophosphate on Osteoblastic Differentiation by Regulating Estrogen Receptor and Osteopontin Expression

Ascorbic acid (AA), β-glycerophosphate (GP), and dexamethasone (DEX) are the compounds known to favor the expression of the osteoblastic phenotype in several bone cell systems. In this report, the combination effects of differentiation agents on osteoprecursor cells were evaluated. The effect on cell proliferation was determined by a cell viability test with morphologic analysis. Differentiation and mineralization were evaluated using an alkaline phosphatase activity test and alizarin red-S staining. Protein expressions related to bone formation, such as transforming growth factor-beta (TGF-β), estrogen receptor-alpha (ER-α), and osteopontin (OPN) were evaluated by using a Western blot analysis. AA and GP provided an inductive effect for differentiation of osteoprecusor cells, while short-term application of DEX seemed to lead to a dose-dependent increase of cellular differentiation. Long-term use of DEX seemed to reduce mineralization. These effects may seem to be regulated by the expression of ER-α, OPN, and TGF-β. Further studies related to this mechanism within the in vivo model may be necessary to ascertain greater detail.

Thyroid hormone and reproduction: Regulation of estrogen receptors in goldfish gonads

There is increasing evidence that thyroid hormones influence reproduction in vertebrates. However, little information is available on the mechanisms by which this happens. As a first step in determining these mechanisms, we test the hypothesis that the estrogen receptor subtypes (ERalpha, ERbeta-1, and ERbeta-2) are regulated by the thyroid hormone, (T(3)), in the gonads of goldfish. All three subtypes were down-regulated by T(3) in the testis or ovary. We also found evidence that T(3) decreased pituitary gonadotropin expression and decreased transcript for gonadal aromatase. Collectively, it appears that T(3) acts to diminish estrogen signaling by (1) decreasing pituitary LH expression and thus steroidogenesis, (2) down-regulating gonadal aromatase expression and thus decreasing estrogen synthesis from androgens, and (3) decreasing sensitivity to estrogen by down-regulating the ER subtypes. Goldfish are seasonal breeders, spawning once a year, and thus have two distinct periods of growth: somatic and reproductive. Circulating thyroid hormone levels have been found to increase just after spawning. Therefore, we propose that this may be an endocrine mechanism that goldfish use to switch their energy expenditure from reproductive to growth efforts in the goldfish.

The Role of Peroxisome Proliferator-Activated Receptor-γ and Estrogen Receptors in Genistein-Induced Regulation of Vascular Tone in Female Rat Aortas

Background: Genistein (GST) is a phytoestrogen that binds estrogen receptors (ER) to produce a protective cardiovascular effect. It also has been shown binding peroxisome proliferator-activated receptor-γ (PPAR-γ). Methods: In the present study, we assessed the role of PPAR-γ and ER in GST-mediated regulation of vascular tone in female rat aortas by in vitro tension measurement, immunohistochemistry, immunofluorescence, immunoprecipitation and Western blot analysis. Results: In aortas pretreated with GW9662 (inhibitor of PPAR-γ), ICI182780 (inhibitor of ER) and a combination of GW9662 and ICI182780, the magnitudes of GST-induced dilatation were attenuated. N(G)-nitro-L-arginine methyl ester had a similar effect. ER-β and PPAR-γ colocalized in all 3 layers of the aortas, while ER-α and PPAR-γ colocalized only in the vascular endothelium and adventitia. In GST-treated whole-cell protein samples, we demonstrated coimmunoprecipitation of ER-β (not ER-α) and PPAR-γ. The expression of ER-β and PPAR-γ in nuclear protein from GST-treated samples increased, which was partially reversed by either GW9662 or ICI182780 and more efficiently reversed using a combination of GW9662 and ICI182780. Conclusion: Our findings suggest that GST can relax phenylephrine-induced vascular contraction in female rat aortas, which is mediated by PPAR-γ and ER-β.

The liver receptor homolog-1 regulates estrogen receptor expression in breast cancer cells

Estrogen receptor-α (ER) is expressed in the great majority of breast cancers, and the inhibition of ER action is a key part of breast cancer treatment. The inhibition of ER action is achieved using anti-estrogens, primarily tamoxifen, and with aromatase inhibitors that inhibit estrogen biosynthesis, thereby preventing ER activation. However, resistance to these therapies is common. With the aim of identifying new molecular targets for breast cancer therapy, we have identified the liver receptor homolog-1 (LRH-1) as an estrogen-regulated gene. RNA interference and over-expression studies were used to investigate the role of the LRH-1 in regulating breast cancer growth and to identify the targets of an LRH-1 action. Promoter recruitment was determined using reporter gene and chromatin immunoprecipitation (ChIP) assays. We show that LRH-1 regulates breast cancer cell growth by regulating the ER expression. Reporter gene and in vitro DNA-binding assays identified an LRH-1-binding site in the ER gene promoter, and ChIP assays have demonstrated in vivo binding at this site. We also provide evidence for new LRH-1 variants in breast cancer cells arising from the use of alternative promoters. Previous studies have shown that LRH-1 functions in estrogen biosynthesis by regulating aromatase expression. Our findings extend this by highlighting LRH-1 as a key regulator of the estrogen response in breast cancer cells through the regulation of ER expression. Hence, inhibition of LRH-1 could provide a powerful new approach for the treatment of endocrine-resistant breast cancer.

Let-7 family miRNAs regulate estrogen receptor alpha signaling in estrogen receptor positive breast cancer

In order to understand how microRNAs (miRNAs) regulate breast cancer tumorigenesis, a miRNA expression microarray screening was performed using RNA from formalin-fixed paraffin-embedded (FFPE) breast tissues, which included benign (n = 13), ductal carcinoma in situ (DCIS) (n = 16), and invasive ductal carcinoma (IDC) (n = 15). Twenty-five differentially expressed miRNAs (P < 0.01) were identified, of which let-7 family miRNAs were down-regulated in human breast cancer tissues at stages of DCIS and IDC compared to benign stage. We further found that there was an inverse correlation between ER-α expression and several members of let-7 family in the FFPE tissues. Next, we performed bioinformatics analysis and found that let-7 miRNA sequences match sequence in the 3'-UTR of estrogen receptor alpha (ER-α), suggesting ER-α may be a target of let-7, which was further confirmed by a number of experimental assays, including luciferase assay, protein expression, and mRNA expression. Overexpression of let-7 miRNAs in ER-positive breast cancer MCF7 cell line negatively affected ER-α activity. As expected, dampening of the ER-α signaling by let-7 miRNAs inhibited cell proliferation, and subsequently triggered the cell apoptotic process in MCF7 cells. In conclusion, our findings indicate a new regulatory mechanism of let-7 miRNAs in ER-α mediated cellular malignant growth of breast cancer.

721 Aromatase inhibitor resistance; a role for estrogen receptor and AIB1 in differential gene regulation

721 Aromatase inhibitor resistance; a role for estrogen receptor and AIB1 in differential gene regulation