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Downregulation of ER-?36 expression sensitizes HER2 overexpressing breast cancer cells to tamoxifen.

ABSTRACT: Tamoxifen provided a successful treatment for ER-positive breast cancer for many years. However, HER2 overexpressing breast cancer cells respond poorly to tamoxifen therapy presumably by pass. The molecular mechanisms underlying development of tamoxifen resistance have not been well established. Recently, we reported that breast cancer cells with high levels of ER-?36, a variant of ER-?, were resistant to tamoxifen and knockdown of ER-?36 expression in tamoxifen resistant cells with the shRNA method restored tamoxifen sensitivity, indicating that gained ER-?36 expression is one of the underlying mechanisms of tamoxifen resistance. Here, we found that tamoxifen induced expression of ER-?36-EGFR/HER2 positive regulatory loops and tamoxifen resistant MCF7 cells (MCF7/TAM) expressed enhanced levels of the loops. Disruption of the ER-?36-EGFR/HER2 positive regulatory loops with the dual tyrosine kinase inhibitor Lapatinib or ER-?36 down-regulator Broussoflavonol B in tamoxifen resistant MCF7 cells restored tamoxifen sensitivity. In addition, we also found both Lapatinib and Broussoflavonol B increased the growth inhibitory activity of tamoxifen in tumorsphere cells derived from MCF7/TAM cells. Our results thus demonstrated that elevated expression of the ER-?36-EGFR/HER2 loops is one of the mechanisms by which ER-positive breast cancer cells escape tamoxifen therapy. Our results thus provided a rational to develop novel therapeutic approaches for tamoxifen resistant patients by targeting the ER-?36-EGFR/HER2 loops.

SUBMITTER: Yin L

PROVIDER: S-EPMC4396031 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Downregulation of ER-α36 expression sensitizes HER2 overexpressing breast cancer cells to tamoxifen.

Yin Li L Pan Xiaohua X Zhang Xin-Tian XT Guo Yu-Ming YM Wang Zhao-Yi ZY Gong Yaoqin Y Wang Molin M

American journal of cancer research 20150115 2

Tamoxifen provided a successful treatment for ER-positive breast cancer for many years. However, HER2 overexpressing breast cancer cells respond poorly to tamoxifen therapy presumably by pass. The molecular mechanisms underlying development of tamoxifen resistance have not been well established. Recently, we reported that breast cancer cells with high levels of ER-α36, a variant of ER-α, were resistant to tamoxifen and knockdown of ER-α36 expression in tamoxifen resistant cells with the shRNA me ...[more]

PMID: 25973295

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Project description:The identification of clinically important molecular mechanisms driving endocrine resistance is a priority in estrogen receptor-positive (ER+) breast cancer. Although both genomic and non-genomic cross-talk between the ER and growth factor receptors such as human epidermal growth factor receptor 2 (HER2) has frequently been associated with both experimental and clinical endocrine therapy resistance, combined targeting of ER and HER2 has failed to improve overall survival in endocrine non-responsive disease. Herein, we questioned the role of fatty acid synthase (FASN), a lipogenic enzyme linked to HER2-driven breast cancer aggressiveness, in the development and maintenance of hormone-independent growth and resistance to anti-estrogens in ER/HER2-positive (ER+/HER2+) breast cancer. The stimulatory effects of estradiol on FASN gene promoter activity and protein expression were blunted by anti-estrogens in endocrine-responsive breast cancer cells. Conversely, an AKT/MAPK-related constitutive hyperactivation of FASN gene promoter activity was unaltered in response to estradiol in non-endocrine responsive ER+/HER2+ breast cancer cells, and could be further enhanced by tamoxifen. Pharmacological blockade with structurally and mechanistically unrelated FASN inhibitors fully impeded the strong stimulatory activity of tamoxifen on the soft-agar colony forming capacity-an in vitro metric of tumorigenicity-of ER+/HER2+ breast cancer cells. In vivo treatment with a FASN inhibitor completely prevented the agonistic tumor-promoting activity of tamoxifen and fully restored its estrogen antagonist properties against ER/HER2-positive xenograft tumors in mice. Functional cancer proteomic data from The Cancer Proteome Atlas (TCPA) revealed that the ER+/HER2+ subtype was the highest FASN protein expressor compared to basal-like, HER2-enriched, and ER+/HER2-negative breast cancer groups. FASN is a biological determinant of HER2-driven endocrine resistance in ER+ breast cancer. Next-generation, clinical-grade FASN inhibitors may be therapeutically relevant to countering resistance to tamoxifen in FASN-overexpressing ER+/HER2+ breast carcinomas.

Project description:Unlike breast cancer that is positive for estrogen receptor-? (ER?), there are no targeted therapies for triple-negative breast cancer (TNBC). ER? is silenced in TNBC through epigenetic changes including DNA methylation and histone acetylation. Restoring ER? expression in TNBC may sensitize patients to endocrine therapy. Expression of c-Src and ER? are inversely correlated in breast cancer suggesting that c-Src inhibition may lead to reexpression of ER? in TNBC. KX-01 is a peptide substrate-targeted Src/pretubulin inhibitor in clinical trials for solid tumors. KX-01 (1 mg/kg body weight-twice daily) inhibited growth of tamoxifen-resistant MDA-MB-231 and MDA-MB-157 TNBC xenografts in nude mice that was correlated with Src kinase inhibition. KX-01 also increased ER? mRNA and protein, as well as increased the ER? targets progesterone receptor (PR), pS2 (TFF1), cyclin D1 (CCND1), and c-myc (MYC) in MDA-MB-231 and MDA-MB-468, but not MDA-MB-157 xenografts. MDA-MB-231 and MDA-MB-468 tumors exhibited reduction in mesenchymal markers (vimentin, ?-catenin) and increase in epithelial marker (E-cadherin) suggesting mesenchymal-to-epithelial transition (MET). KX-01 sensitized MDA-MB-231 and MDA-MB-468 tumors to tamoxifen growth inhibition and tamoxifen repression of the ER? targets pS2, cyclin D1, and c-myc. Chromatin immunoprecipitation (ChIP) of the ER? promoter in KX-01-treated tumors demonstrated enrichment of active transcription marks (acetyl-H3, acetyl-H3Lys9), dissociation of HDAC1, and recruitment of RNA polymerase II. Methylation-specific PCR and bisulfite sequencing demonstrated no alteration in ER? promoter methylation by KX-01. These data demonstrate that in addition to Src kinase inhibition, peptidomimetic KX-01 restores ER? expression in TNBC through changes in histone acetylation that sensitize tumors to tamoxifen.Implications: Src kinase/pretubulin inhibitor KX-01 restores functional ER? expression in ER?- breast tumors, a novel treatment strategy to treat triple-negative breast cancer. Mol Cancer Res; 15(11); 1491-502. ©2017 AACR.

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Downregulation of ER-?36 expression sensitizes HER2 overexpressing breast cancer cells to tamoxifen.

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Downregulation of ER-α36 expression sensitizes HER2 overexpressing breast cancer cells to tamoxifen.

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