2099

ESR1

The estrogen receptor alpha (ER alpha) is key in regulating normal breast development and function and is closely involved in the onset and progress of cancers. ER alpha transcriptional activity is mediated through two activation functions, AF1 and AF2, whose activity is tightly regulated in a cell-specific manner through yet unknown processes. Here, we demonstrate that cell-cell junctions generate cell permissiveness to AF1 through an up-regulation of the activity of an AF1 sub-region termed box 1. Moreover, the loss of E-cadherin expression is shown to silence the AF1 activity of ER alpha, allowing the receptor to mainly act through its AF2. This switch from an AF1 to an AF2 cell permissiveness also consequently results in the attenuation of ER alpha activity. Therefore, a loss of cell-cell junctions, a key process that occurs during the epithelial-mesenchymal transition, should have a broad impact on ER alpha transcriptional functions.

Here, we report that lipocalin 2 (Lcn2) promotes breast cancer progression, and we identify the mechanisms underlying this function. We first found that Lcn2 levels were consistently associated with invasive breast cancer in human tissue and urine samples. To investigate the function of Lcn2 in breast cancer progression, Lcn2 was overexpressed in human breast cancer cells and was found to up-regulate mesenchymal markers, including vimentin and fibronectin, down-regulate the epithelial marker E-cadherin, and significantly increase cell motility and invasiveness. These changes in marker expression and cell motility are hallmarks of an epithelial to mesenchymal transition (EMT). In contrast, Lcn2 silencing in aggressive breast cancer cells inhibited cell migration and the mesenchymal phenotype. Furthermore, reduced expression of estrogen receptor (ER) alpha and increased expression of the key EMT transcription factor Slug were observed with Lcn2 expression. Overexpression of ERalpha in Lcn2-expressing cells reversed the EMT and reduced Slug expression, suggesting that ERalpha negatively regulates Lcn2-induced EMT. Finally, orthotopic studies demonstrated that Lcn2-expressing breast tumors displayed a poorly differentiated phenotype and showed increased local tumor invasion and lymph node metastasis. Taken together, these in vitro, in vivo, and human studies demonstrate that Lcn2 promotes breast cancer progression by inducing EMT through the ERalpha/Slug axis and may be a useful biomarker of breast cancer.

epithelial mesenchymal transition (EMT) plays a major role in cancer metastasis. Several genes have been shown to play a role in EMT, and one of these is Amplified-in-breast cancer 1 (AIB1), which has oncogenic function and is known to be amplified in breast cancer. However, the role of AIB1 in EMT remains largely undefined at the molecular level. In this study, the effect of AIB1 overexpression on the EMT of the breast cancer cell line T47D was investigated. Overexpression of AIB1 disrupted the epithelial morphology of the cells. At the same time, the cells displayed a strong metastasis and reduced level of the epithelial marker E-cadherin. In contrast, knockdown of AIB1 in T47D cells increased cell-cell adhesion and produced weak metastasis, as well as a higher level of E-cadherin expression. We proposed that the regulation of EMT by AIB1 occurred through the action of the transcription factor SNAI1, and demonstrated that such interaction required the participation of ERalpha and the presence of ERalpha-binding site on SNAI1 promoter. The expression level of E-cadherin and the extent of cell migration and invasion in SNAI1-knocked down T47D cells that overexpressed AIB1 were similar to those of T47D cells that did not overexpress AIB1 and had no SNAI1 knockdown. Taken together, these results suggested that AIB1 exerted its effect on EMT through its interaction with ERalpha, which could directly bind to the ERalpha-binding site on the SNAI1 promoter, allowing the AIB1-ERalpha complex to promote the transcription of SNAI1 and eventually led to repression of E-cadherin expression, consistent with the loss of E-cadherin being a hallmark of EMT.

The 17beta-estradiol (E2)/estrogen receptor alpha (ERalpha) signaling pathway is one of the most important pathways in hormone-dependent breast cancer. E2 plays pivotal roles in cancer cell growth, survival, and architecture as well as in gene expression regulatory mechanisms. In this study, we established stably transfected MCF-7 cells by knocking down the ERalpha gene (designated as MCF-7/SP10+ cells), using specific shRNA lentiviral particles, and compared them with the control cells (MCF-7/c). Interestingly, ERalpha silencing in MCF-7 cells strongly induced cellular phenotypic changes accompanied by significant changes in gene and protein expression of several markers typical of epithelial to mesenchymal transition (EMT). Notably, these cells exhibited enhanced cell proliferation, migration and invasion. Moreover, ERalpha suppression strongly affected the gene and protein expression of EGFR and HER2 receptor tyrosine kinases, and various extracellular matrix (ECM) effectors, including matrix metalloproteinases and their endogenous inhibitors (MMPs/TIMPs) and components of the plasminogen activation system. The action caused by E2 in MCF-7/c cells in the expression of HER2, MT1-MMP, MMP1, MMP9, uPA, tPA, and PAI-1 was abolished in MCF-7/SP10+ cells lacking ERalpha. These data suggested a regulatory role for the E2/ERalpha pathway in respect to the composition and activity of the extracellular proteolytic molecular network. Notably, loss of ERalpha promoted breast cancer cell migration and invasion by inducing changes in the expression levels of certain matrix macromolecules (especially uPA, tPA, PAI-1) through the EGFR-ERK signaling pathway. In conclusion, loss of ERalpha in breast cancer cells results in a potent EMT characterized by striking changes in the expression profile of specific matrix macromolecules highlighting the potential nodal role of matrix effectors in breast cancer endocrine resistance.CI - Copyright (c) 2015. Published by Elsevier B.V.

The development of breast cancer is linked to the loss of estrogen receptor (ER) during the course of tumor progression, resulting in loss of responsiveness to hormonal treatment. The mechanisms underlying dynamic ERalpha gene expression change in breast cancer remain unclear. A range of physiological and biological changes, including increased adipose tissue hypoxia, accompanies obesity. Hypoxia in adipocytes can establish a pro-malignancy environment in breast tissues. Epidemiological studies have linked obesity with basal-like breast cancer risk and poor disease outcome, suggesting that obesity may affect the tumor phenotype by skewing the microenvironment toward support of more aggressive tumor phenotypes. In the present study, human SGBS adipocytes were co-cultured with ER-positive MCF7 cells for 24 h. After co-culture, HIF1alpha, TGF-beta, and lectin-type oxidized LDL receptor 1 (LOX1) mRNA levels in the SGBS cells were increased. expression levels of the epithelial-mesenchymal transition (EMT)-inducing transcription factors FOXC2 and TWIST1 were increased in the co-cultured MCF7 cells. In addition, the E-cadherin mRNA level was decreased, while the N-cadherin mRNA level was increased in the co-cultured MCF7 cells. ERalpha mRNA levels were significantly repressed in the co-cultured MCF7 cells. ERalpha gene expression in the MCF7 cells was decreased due to increased HIF1alpha in the SGBS cells. These results suggest that adipocytes can modify breast cancer cell ER gene expression through hypoxia and also can promote EMT processes in breast cancer cells, supporting an important role of obesity in aggressive breast cancer development.

In human breast cancer, estrogen receptor-alpha (ERalpha) suppresses epithelial-mesenchymal transition (EMT) and stemness, two crucial parameters for tumor metastasis; however, the underlying mechanism by which ERalpha regulates these two processes remains largely unknown. Bmi1, the polycomb group protein B lymphoma Mo-MLV insertion region 1 homolog, regulates EMT transition, maintains the self-renewal capacity of stem cells, and is frequently overexpressed in human cancers. In the present study, ERalpha upregulated the expression of the epithelial marker, E-cadherin, in breast cancer cells through the transcriptional down-regulation of Bmi1. Furthermore, ERalpha overexpression suppressed the migration, invasion, and EMT of breast cancer cells. Notably, overexpression of ERalpha significantly decreased the CD44high/CD24low cell population and inhibited the capacity for mammosphere formation in ERalpha-negative breast cancer cells. In addition, overexpression of Bmi1 attenuated the ERalpha-mediated suppression of EMT and cell stemness. Immunohistochemistry revealed an inverse association of ERalpha and Bmi1 expression in human breast cancer tissue. Taken together, our findings suggest that ERalpha inhibits EMT and stemness through the downregulation of Bmi1.

Tamoxifen resistance presents a prominent clinical challenge in endocrine therapy for hormone sensitive breast cancer. However, the underlying mechanisms that contribute to tamoxifen resistance are not fully understood. In this study, we established a tamoxifen resistant MCF-7 cell line (MCF-7-Tam-R) by continuously incubating MCF-7 cells with 4-OH-tamoxifen. We found that melanoma cell adhesion molecule (MCAM/CD146), a unique epithelial-to-mesenchymal transition (EMT) inducer, was significantly up-regulated at both mRNA and protein levels in MCF-7-Tam-R cells compared to parental MCF-7 cells. Mechanistic research demonstrated that MCAM promotes tamoxifen resistance by transcriptionally suppressing ERalpha expression and activating the AKT pathway, followed by induction of EMT. Elevated MCAM expression was inversely correlated with recurrence-free and distant metastasis-free survival in a cohort of 4142 patients with breast cancer derived from a public database, particularly in the subgroup only treated with tamoxifen. These results demonstrate a novel function of MCAM in conferring tamoxifen resistance in breast cancer. Targeting MCAM might be a promising therapeutic strategy to overcome tamoxifen resistance in breast cancer patients.CI - Copyright (c) 2016 The Authors. Published by Elsevier Ireland Ltd.. All rights reserved.

BACKGROUND: Estrogen promotes breast cancer development and progression mainly through estrogen receptor (ER). However, blockage of estrogen production or action prevents development of and suppresses progression of ER-negative breast cancers. How estrogen promotes ER-negative breast cancer development and progression is poorly understood. We previously discovered that deletion of cell cycle inhibitors p16(Ink4a) (p16) or p18(Ink4c) (p18) is required for development of Brca1-deficient basal-like mammary tumors, and that mice lacking p18 develop luminal-type mammary tumors. METHODS: A genetic model system with three mouse strains, one that develops ER-positive mammary tumors (p18 single deletion) and the others that develop ER-negative tumors (p16;Brca1 and p18;Brca1 compound deletion), human BRCA1 mutant breast cancer patient-derived xenografts, and human BRCA1-deficient and BRCA1-proficient breast cancer cells were used to determine the role of estrogen in activating epithelial-mesenchymal transition (EMT), stimulating cell proliferation, and promoting ER-negative mammary tumor initiation and metastasis. RESULTS: Estrogen stimulated the proliferation and tumor-initiating potential of both ER-positive Brca1-proficient and ER-negative Brca1-deficient tumor cells. Estrogen activated EMT in a subset of Brca1-deficient mammary tumor cells that maintained epithelial features, and enhanced the number of cancer stem cells, promoting tumor progression and metastasis. Estrogen activated EMT independent of ER in Brca1-deficient, but not Brca1-proficient, tumor cells. Estrogen activated the AKT pathway in BRCA1-deficient tumor cells independent of ER, and pharmaceutical inhibition of AKT activity suppressed EMT and cell proliferation preventing BRCA1 deficient tumor progression. CONCLUSIONS: This study reveals for the first time that estrogen promotes BRCA1-deficient tumor initiation and progression by stimulation of cell proliferation and activation of EMT, which are dependent on AKT activation and independent of ER.