Estrogen-independent effects of ER-α36 in ER-negative breast cancer

► High expression of ER-α36 was observed in ER-negative breast cancers. ► ER-α36 was knocked down by artificial microRNA hairpins. ► Downregulation of ER-α36 sensitized cells to paclitaxel. ► Downregulation of ER-α36 decreased cell migration and invasion. Estrogen receptor-alpha 36 (ER-α36) is a variant of ER-α that has been found to be expressed in conventional ER (ER-α66)-negative breast cancer cell lines and human breast cancer samples. In this study, we found that, using immunohistochemical study, ER-α36 expression was significantly higher in ER-negative tumors than in ER-positive tumors although the expression was not associated with other clinicopathological characteristics. We then constructed an ER-α36-specific microRNA hairpin vector and established stable ER-α36 knockdown cells, and found that the knockdown cells were more sensitive to paclitaxel; the c-Jun N-terminal kinase pathway appeared to be involved in the mechanism. Downregulation of ER-α36 also resulted in decreased migration and invasion. These changes were estrogen independent. Our findings indicated that target ER-α36 may be a strategy for treating ER-negative breast cancers.