Acquisition of epithelial-mesenchymal transition phenotype in the tamoxifen-resistant breast cancer cell: a new role for G protein-coupled estrogen receptor in mediating tamoxifen resistance through cancer-associated fibroblast-derived fibronectin and beta 1-integrin signaling pathway in tumor cells

作者：Yuan, Jie; Liu, Manran; Yang, Li; Tu, Gang; Zhu, Qing; Chen, Maoshan; Cheng, Hong; Luo, Haojun; Fu, Weijie; Li, Zhenhua; Yang, Guanglun^*

来源：Breast Cancer Research, 2015, 17(1): 69.

DOI：10.1186/s13058-015-0579-y

• EXTRACELLULAR-MATRIX
• GENE-EXPRESSION
• ER-ALPHA
• GROWTH
• EMT
• INTEGRIN
• MICROENVIRONMENT
• INVASIVENESS
• ANGIOGENESIS
• MODULATION

Introduction: Acquired tamoxifen resistance remains the major obstacle to breast cancer endocrine therapy. beta 1-integrin was identified as one of the target genes of G protein-coupled estrogen receptor (GPER), a novel estrogen receptor recognized as an initiator of tamoxifen resistance. Here, we investigated the role of beta 1-integrin in GPER-mediated tamoxifen resistance in breast cancer.
Methods: The expression of beta 1-integrin and biomarkers of epithelial-mesenchymal transition were evaluated immunohistochemically in 53 specimens of metastases and paired primary tumors. The function of beta 1-integrin was investigated in tamoxifen-resistant (MCF-7R) subclones, derived from parental MCF-7 cells, and MCF-7R beta 1-integrin-silenced subclones in MTT and Transwell assays. Involved signaling pathways were identified using specific inhibitors and Western blotting analysis.
Results: GPER, beta 1-integrin and mesenchymal biomarkers (vimentin and fibronectin) expression in metastases increased compared to the corresponding primary tumors; a close expression pattern of beta 1-integrin and GPER were in metastases. Increased beta 1-integrin expression was also confirmed in MCF-7R cells compared with MCF-7 cells. This upregulation of beta 1-integrin was induced by agonists of GPER and blocked by both antagonist and knockdown of it in MCF-7R cells. Moreover, the epidermal growth factor receptor/extracellular regulated protein kinase (EGFR/ERK) signaling pathway was involved in this transcriptional regulation since specific inhibitors of these kinases also reduced the GPER-induced upregulation of beta 1-integrin. Interestingly, silencing of beta 1-integrin partially rescued the sensitivity of MCF-7R cells to tamoxifen and the alpha 5 beta 1-integrin subunit is probably responsible for this phenomenon. Importantly, the cell migration and epithelial-mesenchymal transition induced by cancer-associated fibroblasts, or the product of cancer-associated fibroblasts, fibronectin, were reduced by knockdown of beta 1-integrin in MCF-7R cells. In addition, the downstream kinases of beta 1-integrin including focal adhesion kinase, Src and AKT were activated in MCF-7R cells and may be involved in the interaction between cancer cells and cancer-associated fibroblasts.
Conclusions: GPER/EGFR/ERK signaling upregulates beta 1-integrin expression and activates downstream kinases, which contributes to cancer-associated fibroblast-induced cell migration and epithelial-mesenchymal transition, in MCF-7R cells. GPER probably contributes to tamoxifen resistance via interaction with the tumor microenvironment in a beta 1-integrin-dependent pattern. Thus, beta 1-integrin may be a potential target to improve anti-hormone therapy responses in breast cancer patients.

• 出版日期2015-5-21
• 单位重庆医科大学