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Effects of estrogen on breast cancer development: Role of estrogen receptor independent mechanisms.

ABSTRACT: Development of breast cancer involves genetic factors as well as lifetime exposure to estrogen. The precise molecular mechanisms whereby estrogens influence breast tumor formation are poorly understood. While estrogen receptor alpha (ERalpha) is certainly involved, nonreceptor mediated effects of estradiol (E(2)) may also play an important role in facilitating breast tumor development. A "reductionist" strategy allowed us to examine the role of ERalpha independent effects of E(2) on mammary tumor development in ERalpha knockout (ERKO) mice bearing the Wnt-1 oncogene. Exogenous E(2) "clamped" at early follicular and midluteal phase levels (i.e., 80 and 240 pg/ml) accelerated tumor formation in a dose-related fashion in ERKO/Wnt-1 animals (p = 0.0002). Reduction of endogenous E(2) by oophorectomy (p < 0.001) or an aromatase inhibitor (AI) (p = 0.055) in intact ERKO/Wnt-1 animals delayed tumorigenesis as further evidence for an ER-independent effect. The effects of residual ERalpha or beta were not involved since enhancement of tumor formation could not be blocked by the antiestrogen fulvestrant. 17alpha-OH-E(2), a metabolizable but ER-impeded analogue of E(2) stimulated tumor development without measurable uterine stimulatory effects. Taken together, our results suggest that ER-independent actions of E(2) can influence breast tumor development in concert with ER dependent effects. These observations suggest 1 mechanism whereby AIs, which block E(2) synthesis, would be more effective for breast cancer prevention than use of antiestrogens, which only block ER-mediated effects.

SUBMITTER: Yue W

PROVIDER: S-EPMC4775086 | biostudies-literature | 2010 Oct

REPOSITORIES: biostudies-literature

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Effects of estrogen on breast cancer development: Role of estrogen receptor independent mechanisms.

Yue Wei W Wang Ji-Ping JP Li Yuebai Y Fan Ping P Liu Guijian G Zhang Nan N Conaway Mark M Wang Hongkun H Korach Kenneth S KS Bocchinfuso Wayne W Santen Richard R

International journal of cancer 20101001 8

Development of breast cancer involves genetic factors as well as lifetime exposure to estrogen. The precise molecular mechanisms whereby estrogens influence breast tumor formation are poorly understood. While estrogen receptor alpha (ERalpha) is certainly involved, nonreceptor mediated effects of estradiol (E(2)) may also play an important role in facilitating breast tumor development. A "reductionist" strategy allowed us to examine the role of ERalpha independent effects of E(2) on mammary tumo ...[more]

PMID: 20104523

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Project description:Breast cancer resistance to the antiestrogens tamoxifen (OHT) and fulvestrant is accompanied by alterations in both estrogen-dependent and estrogen-independent signaling pathways. Consequently, effective inhibition of both pathways may be necessary to block proliferation of antiestrogen-resistant breast cancer cells. In this study, we examined the effects of apigenin, a dietary plant flavonoid with potential anticancer properties, on estrogen-responsive, antiestrogen-sensitive MCF7 breast cancer cells and two MCF7 sublines with acquired resistance to either OHT or fulvestrant. We found that apigenin can function as both an estrogen and an antiestrogen in a dose-dependent manner. At low concentrations (1 mumol/L), apigenin stimulated MCF7 cell growth but had no effect on the antiestrogen-resistant MCF7 sublines. In contrast, at high concentrations (>10 mumol/L), the drug inhibited growth of MCF7 cells and the antiestrogen-resistant sublines, and the combination of apigenin with either OHT or fulvestrant showed synergistic, growth-inhibitory effects on both antiestrogen-sensitive and antiestrogen-resistant breast cancer cells. To further elucidate the molecular mechanism of apigenin as either an estrogen or an antiestrogen, effects of the drug on estrogen receptor-alpha (ERalpha); transactivation activity, mobility, stability, and ERalpha-coactivator interactions were investigated. Low-dose apigenin enhanced receptor transcriptional activity by promoting interaction between ERalpha and its coactivator amplified in breast cancer-1. However, higher doses (>10 mumol/L) of apigenin inhibited ERalpha mobility (as determined by fluorescence recovery after photobleaching assays), down-regulated ERalpha and amplified in breast cancer-1 expression levels, and inhibited multiple protein kinases, including p38, protein kinase A, mitogen-activated protein kinase, and AKT. Collectively, these results show that apigenin can function as both an antiestrogen and a protein kinase inhibitor with activity against breast cancer cells with acquired resistance to OHT or fulvestrant. We conclude that apigenin, through its ability to target both ERalpha-dependent and ERalpha-independent pathways, holds promise as a new therapeutic agent against antiestrogen-resistant breast cancer.

Project description:BackgroundNumerous studies have implicated the aryl hydrocarbon receptor (AhR) as a potential therapeutic target for several human diseases, including estrogen receptor alpha (ER?) positive breast cancer. Aminoflavone (AF), an activator of AhR signaling, is currently undergoing clinical evaluation for the treatment of solid tumors. Of particular interest is the potential treatment of triple negative breast cancers (TNBC), which are typically more aggressive and characterized by poorer outcomes. Here, we examined AF's effects on two TNBC cell lines and the role of AhR signaling in AF sensitivity in these model cell lines.MethodsAF sensitivity in MDA-MB-468 and Cal51 was examined using cell counting assays to determine growth inhibition (GI50) values. Luciferase assays and qPCR of AhR target genes cytochrome P450 (CYP) 1A1 and 1B1 were used to confirm AF-mediated AhR signaling. The requirement of endogenous levels of AhR and AhR signaling for AF sensitivity was examined in MDA-MB-468 and Cal51 cells stably harboring inducible shRNA for AhR. The mechanism of AF-mediated growth inhibition was explored using flow cytometry for markers of DNA damage and apoptosis, cell cycle analysis, and ?-galactosidase staining for senescence. Luciferase data was analyzed using Student's T test. Three-parameter nonlinear regression was performed for cell counting assays.ResultsHere, we report that ER?-negative TNBC cell lines MDA-MB-468 and Cal51 are sensitive to AF. Further, we presented evidence suggesting that neither endogenous AhR expression levels nor downstream induction of AhR target genes CYP1A1 and CYP1B1 is required for AF-mediated growth inhibition in these cells. Between these two ER? negative cell lines, we showed that the mechanism of AF action differs slightly. Low dose AF mediated DNA damage, S-phase arrest and apoptosis in MDA-MB-468 cells, while it resulted in DNA damage, S-phase arrest and cellular senescence in Cal51 cells.ConclusionsOverall, this work provides evidence against the simplified view of AF sensitivity, and suggests that AF could mediate growth inhibitory effects in ER?-positive and negative breast cancer cells, as well as cells with impaired AhR expression and signaling. While AF could have therapeutic effects on broader subtypes of breast cancer, the mechanism of cytotoxicity is complex, and likely, cell line- and tumor-specific.

Project description:BACKGROUND:Breast cancer (BC) is highly heterogeneous with ~?60-70% of estrogen receptor positive BC patient's response to anti-hormone therapy. Estrogen receptors (ERs) play an important role in breast cancer progression and treatment. Estrogen related receptors (ERRs) are a group of nuclear receptors which belong to orphan nuclear receptors, which have sequence homology with ERs and share target genes. Here, we investigated the possible role and clinicopathological importance of ERR? in breast cancer. METHODS:Estrogen related receptor ? (ERR?) expression was examined using tissue microarray slides (TMA) of Breast Carcinoma patients with adjacent normal by immunohistochemistry and in breast cancer cell lines. In order to investigate whether ERR? is a direct target of ER?, we investigated the expression of ERR? in short hairpin ribonucleic acid knockdown of ER? breast cancer cells by western blot, qRT-PCR and RT-PCR. We further confirmed the binding of ER? by electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation (ChIP), Re-ChIP and luciferase assays. Fluorescence-activated cell sorting analysis (FACS) was performed to elucidate the role of ERR? in cell cycle regulation. A Kaplan-Meier Survival analysis of GEO dataset was performed to correlate the expression of ERR? with survival in breast cancer patients. RESULTS:Tissue microarray (TMA) analysis showed that ERR? is significantly down-regulated in breast carcinoma tissue samples compared to adjacent normal. ER?+?ve breast tumors and cell lines showed a significant expression of ERR? compared to ER-ve tumors and cell lines. Estrogen treatment significantly induced the expression of ERR? and it was ER? dependent. Mechanistic analyses indicate that ER? directly targets ERR? through estrogen response element and ERR? also mediates cell cycle regulation through p18, p21cip and cyclin D1 in breast cancer cells. Our results also showed the up-regulation of ERR? promoter activity in ectopically co-expressed ER? and ERR? breast cancer cell lines. Fluorescence-activated cell sorting analysis (FACS) showed increased G0/G1 phase cell population in ERR? overexpressed MCF7 cells. Furthermore, ERR? expression was inversely correlated with overall survival in breast cancer. Collectively our results suggest cell cycle and tumor suppressor role of ERR? in breast cancer cells which provide a potential avenue to target ERR? signaling pathway in breast cancer. CONCLUSION:Our results indicate that ERR? is a negative regulator of cell cycle and a possible tumor suppressor in breast cancer. ERR? could be therapeutic target for the treatment of breast cancer.

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Effects of estrogen on breast cancer development: Role of estrogen receptor independent mechanisms.

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Effects of estrogen on breast cancer development: Role of estrogen receptor independent mechanisms.

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