Estrogen receptor β selective agonists reduce invasiveness of triple-negative breast cancer cells

Abstract

Metastasis to bone is a frequent problem of advanced breast cancer. Particularly breast cancers, which do not express estrogen receptor α (ERα) and progesterone receptor (PR) and which have no overexpression of human epidermal growth factor receptor 2 (HER 2), so-called triple-negative breast cancers (TN BCs), are considered as very aggressive and have a poor prognosis. Recently we have shown that breast cancer cell invasion was dramatically increased when co-cultured with MG63 osteoblast-like cells. Using this model we have now analyzed whether estrogen receptor β (ERβ) plays a role in TN BC cell invasion in vitro. ER α and ER β protein expression was analyzed using western blot analysis. Invasion was quantified by assessment of TNBC cell migration rate through an artificial basement membrane in a modified Boyden chamber during co-culture with MG63 osteoblast-like cells. The effects of ER β agonist treatment on CXC motif chemokine receptor 4 (CXCR 4) protein expression during co-culture with MG64 cells was quantified using western blot analysis. Proliferation was measured using alamarBlue assay. TN BC cell lines HCC 1806 and HCC 1937 showed no ER α but high ER β protein expression. Cell invasion of HCC 1806 and HCC1937 TNBC cells was significantly increased when co-cultured with MG63 osteoblast-like cells. Treatment with ERβ selective estrogen agonists liquiritigenin and ER B-041 reduced the ability to invade a reconstituted basement membrane and to migrate in response to the cellular stimulus. During co-culture CXCR 4 protein expression of TN BC cell lines HCC1806 and HCC1937 was significantly increased. Treatment with liquiritigenin resulted in a significant decrease of CXCR 4 protein expression. Both ER β agonists showed no effect on TNBC cell proliferation. Our findings suggest that ERβ plays a major role in TN BC invasion. Bone-directed invasion can be inhibited by ER β agonists.