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Estrogen receptor alpha is cell cycle-regulated and regulates the cell cycle in a ligand-dependent fashion.

ABSTRACT: Estrogen receptor alpha (ER?) has been implicated in several cell cycle regulatory events and is an important predictive marker of disease outcome in breast cancer patients. Here, we aimed to elucidate the mechanism through which ER? influences proliferation in breast cancer cells. Our results show that ER? protein is cell cycle-regulated in human breast cancer cells and that the presence of 17-?-estradiol (E2) in the culture medium shortened the cell cycle significantly (by 4.5 hours, P < 0.05) compared with unliganded conditions. The alterations in cell cycle duration were observed in the S and G2/M phases, whereas the G1 phase was indistinguishable under liganded and unliganded conditions. In addition, ER? knockdown in MCF-7 cells accelerated mitotic exit, whereas transfection of ER?-negative MDA-MB-231 cells with exogenous ER? significantly shortened the S and G2/M phases (by 9.1 hours, P < 0.05) compared with parental cells. Finally, treatment of MCF-7 cells with antiestrogens revealed that tamoxifen yields a slower cell cycle progression through the S and G2/M phases than fulvestrant does, presumably because of the destabilizing effect of fulvestrant on ER? protein. Together, these results show that ER? modulates breast cancer cell proliferation by regulating events during the S and G2/M phases of the cell cycle in a ligand-dependent fashion. These results provide the rationale for an effective treatment strategy that includes a cell cycle inhibitor in combination with a drug that lowers estrogen levels, such as an aromatase inhibitor, and an antiestrogen that does not result in the degradation of ER?, such as tamoxifen.

SUBMITTER: JavanMoghadam S

PROVIDER: S-EPMC4934046 | biostudies-literature | 2016 Jun

REPOSITORIES: biostudies-literature

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Estrogen receptor alpha is cell cycle-regulated and regulates the cell cycle in a ligand-dependent fashion.

JavanMoghadam Sonia S Weihua Zhang Z Hunt Kelly K KK Keyomarsi Khandan K

Cell cycle (Georgetown, Tex.) 20160406 12

Estrogen receptor alpha (ERα) has been implicated in several cell cycle regulatory events and is an important predictive marker of disease outcome in breast cancer patients. Here, we aimed to elucidate the mechanism through which ERα influences proliferation in breast cancer cells. Our results show that ERα protein is cell cycle-regulated in human breast cancer cells and that the presence of 17-β-estradiol (E2) in the culture medium shortened the cell cycle significantly (by 4.5 hours, P < 0.05) ...[more]

PMID: 27049344

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Project description:PurposeIn early stage, ERα-positive breast cancer, concurrent use of endocrine therapy and chemotherapy has not been shown to be superior to sequential use. We hypothesized that genetic biomarkers can aid in selecting patients who would benefit from chemo-endocrine therapy. Our previous studies revealed that ZNF423 is a transcription factor for BRCA1 and an intronic single nucleotide polymorphism (SNP) in ZNF423, rs9940645, determines tamoxifen response. Here, we identified mitosis-related genes that are regulated by ZNF423 which led us to investigate taxane response in a rs9940645 SNP- and tamoxifen-dependent fashion.MethodsThe Cancer Genome Atlas (TCGA) breast cancer dataset was used to identify genes correlated with ZNF423. Quantitative reverse transcription PCR, chromatin immunoprecipitation, and luciferase reporter assays were used to validate the gene regulation. We used CRISPR/Cas9 to engineer paired ZR-75-1 cells which differ only in ZNF423 rs9940645 SNP genotype to test SNP-dependent phenotypes including cell cycle and cell viability. We validated our findings in an additional two breast cancer cell lines, Hs578T-ERα and HCC1500.ResultsMitosis-related genes VRK1 and PBK, which encode histone H3 kinases, were experimentally validated to be regulated by ZNF423. ZNF423 knockdown decreased VRK1 and PBK expression and activity. Additionally, ZNF423 knockdown enhanced docetaxel-induced G2/M arrest and cytotoxicity through VRK1 or PBK regulation. Lastly, cells carrying the rs9940645 variant genotype had increased G2/M arrest and decreased cell viability when treated with docetaxel in combination with estradiol and 4-OH-TAM.ConclusionsWe identified ZNF423 regulated genes involved in the G2/M phase of the cell cycle. 4-OH-TAM sensitized ERα-positive breast cancer cells to docetaxel in a ZNF423 SNP-dependent manner. Our findings suggest that patients with rs9940645 variant genotype may benefit from concurrent tamoxifen and docetaxel. This would impact a substantial proportion of patients because this SNP has a minor allele frequency of 0.47.

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: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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Estrogen receptor alpha is cell cycle-regulated and regulates the cell cycle in a ligand-dependent fashion.

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Estrogen receptor alpha is cell cycle-regulated and regulates the cell cycle in a ligand-dependent fashion.

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