GPER Promotes Tamoxifen-resistance In ER+ Breast Cancer Through MAPK/Erk-TRIM2 Signaling Axis Reduced Bim Proteins

Objective: To investigate the role of GPER promotes tamoxifen-resistance in ER+ breast cancer by MAPK/Erk-TRIM2 signaling axis reduced Bim proteins.Methods: The expression of GPER and Bim were evaluated immunohistochemically in 106 specimens of metastases(MTs) and paired primary tumors(PTs), exploit c DNA array analysis the expression of TRIM2 by GPER activated in TAM-resistant MCF-7R cells. The expression of TRIM2 and Bim was evaluated by Western blot and QRT-PCR in wild MCF-7 cells and their TAM-resistant(MCF-7R) subclones. GPER specific agonist G1 and specific inhibitor G15 were used to verify the result of our previous c DNA microarray that expression of TRIM2 was regulated by GPER. Knockdown Bim in TAM-sensitive MCF-7 cells by si RNA and overexpression of Bim in TAM-resistant MCF-7 cells, the function of Bim was investigated in breast cancer cell by MTT and flow cytometry assays. By using immunohistochemical and Western blotting analysis, there is an adverse correlation between TRIM2 and Bim in TAM-resistant breast cancer MCF-7R cells. Moreover, the specific MAPK/ERK inhibitor U0126 and the PI3 K inhibitor were used to investigate the signaling pathway involved in GPER-induced TRIM2 expression.Results: Bim expression in MTs decreased compared to the corresponding PTs(p < 0.05); a close expression pattern of GPER were in MTs(p=0.0001). Increased TRIM2 expression was also confirmed in MCF-7R cells compared with MCF-7 cells. Bim was decreased in MCF-7R cells compased with MCF-7 cells, and we found TAM induced breast cancer cells apoptotic by Bim through altering the levels of cleaved PARP and Caspase3. Additionally, the expression of Trim2 was induced by TAM through GPER/EGFR/ERK signaling pathway in MCF-7R cells, and affected the binding between TRIM2 and Bim which resulted in a reduced Bim in TAM-resistant breast cancer cells. Interestingly, knockdown of TRIM2 partially rescued the sensitivity of MCF-7R cells to TAM.Conclusion: GPER/EGFR/ERK signaling upregulates TRIM2 expression and affected the binding between TRIM2 and Bim which resulted in a reduced Bim in MCF-7R cells. Thus, our study provides a novel insight to solve the TAM-resistance in ER positive breast cancer cells.