Background: Metastasis and endocrine therapy resistance are clinical challenges in the treatment of estrogen receptor (ER) -positive breast tumors. Therefore, mechanistic exploration of tamoxifen (TAM) resistance is considered pivotal to improve the prognosis of ER positive breast cancer patients. We previously demonstrated the correlation between FE65 and ER, and subsequently explored the effects of FE65 on TAM and potential interaction between FE65 and Osteopontin (OPN) in ER-positive breast cancer.
Methods: We immunolocalized FE65 and OPN in ER-positive breast cancers and correlated the results with their clinicopathological variables. We then performed proximity ligation and proliferation assays to correlate TAM resistance with FE65 expression. The RT2 Profiler Human PCR Array Human Estrogen Receptor Signaling was also used to profile 96 ER related genes. Hoechst 33342 Staining was used to evaluate apoptosis.
Results: FE65 immunoreactivity was significantly associated with higher pathological N factor of the cases examined, and a potential correlation with tamoxifen resistance of the ER-positive patients. FE65 knockdown significantly increased the proportion of apoptotic carcinoma cells. The statistically significant positive correlation between FE65 and OPN was detected in this study. Subsequent immunohistochemical analyses revealed that OPN status was significantly associated with cancer metastasis and overall survival of 142 patients and FE65 status.
Conclusions: We firstly demonstrated the clinicopathological significance of FE65 in ER-positive breast cancer patients and results indicated that the effects of FE65 on ER-positive breast cancer patients were mediated through OPN expression. In addition, results suggested the clinical value of FE65 as potential prognostic factor and surrogate marker of TAM therapy in ER-positive breast cancer patients.
Keywords: Breast cancer; ER; FE65; OPN; Tamoxifen.
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