Differential expression of estrogen receptor subtypes in ovarian high‐grade serous carcinoma and clear cell carcinoma

PURPOSE: To investigate the role of estrogen receptors (ERs) in high‐grade serous carcinoma (HGSC) and clear cell carcinoma (CCC) of the ovary and evaluate ERs as prognostic biomarkers for ovarian cancer. METHODS: This study included 79 patients with HGSC (n = 38) or CCC (n = 41) treated at our institution between 2005 and 2014. Immunohistochemistry examined protein expression of ERα, ERβ, and G protein‐coupled estrogen receptor‐1 (GPER‐1); relationships between ERα, ERβ, and GPER‐1 with patient survival were evaluated. Additionally, cell proliferation assay and phosphokinase proteome profiling were performed. RESULTS: In HGSC patients, expression of ERα, cytoplasmic GPER‐1, or nuclear GPER‐1 was associated with poor progression‐free survival (PFS) (P = .041, P = .010, or P = .013, respectively). Cytoplasmic GPER‐1 was an independent prognostic factor for PFS in HGSC patients (HR = 2.83, 95% CI = 1.03‐9.16, P = .007). ER expressions were not associated with prognosis in CCC patients. GPER‐1 knockdown by siRNA reduced the cells number to 60% of siRNA‐control‐treated cells (P < .05), and GPER‐1 antagonist, G‐15 inhibited two HGSC cell lines proliferation (KF and UWB1.289) in a dose‐dependent manner. Phosphoprotein array revealed that GPER‐1 silencing decreased relative phosphorylation of glycogen synthase kinase‐3. CONCLUSIONS: High GPER‐1 expression is an independent prognostic factor for PFS in HGSC patients, and GPER‐1 may play a role in HGSC cell proliferation.