ERβ1 Expression Patterns Have Different Effects On EGFR TKIs Treatment Response in EGFR Mutant Lung Adenocarcinomas.

Abstract

Background: Estrogen receptor β (ERβ) can regulate cellular signaling through non-genomic mechanisms, potentially promoting resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs). However, the mechanisms underlying the ERβ-mediated resistance to EGFR TKIs remain poorly understood. Methods: qRT-PCR was performed to investigate ERβ1 and ERβ5 expression levels in cell lines. The localization of ERβ and ERβ1 within cells was assessed using immunocytochemistry and immunofluorescence. The effect of estradiol and/or gefitinib on EGFR signaling pathways was determined by western blot. Cell viability and colony formation assays were used to assess gefitinib response for different cell lines. The apoptosis was verified by tunel and western blot. Immunohistochemistry was used to assess the expression of ERβ1 in lung adenocarcinoma tissues. Patient survival was estimated using the Kaplan-Meier method, and comparisons between groups were conducted using log-rank tests. Results: PC9 cell lines stably overexpressing ERβ1 or ERβ1/ERβ5 were established successfully. Immunofluorescence revealed that ERβ5 overexpression partly retained ERβ1 in the cytoplasm. Immunoblotting analyses revealed that EGFR pathway activation levels were higher in PC9/ERβ1/5 cells than those in PC9/ERβ1 or control PC9 cells. In the presence of estradiol, PI3K/AKT/mTOR pathway activation levels were higher in ERβ1/5-expressing cells than those in ERβ1-expressing cells. Additionally, PC9/ERβ1/5 cells were less prone to the cytotoxic and pro-apoptotic effects of gefitinib compared with PC9/ERβ1 or control PC9 cells. Conclusion: Cytoplasmic ERβ1 was associated with poor progression-free survival in lung cancer patients treated with EGFR TKIs. These results suggest that anti-estrogen therapy might reverse EGFR TKI treatment resistance to some extent in selected patients.