AND-34/BCAR3 differs from other NSP homologs in induction of anti-estrogen resistance, cyclin D1 promoter activation and altered breast cancer cell morphology

Over-expression of AND-34/BCAR3/NSP2 (BCAR3) or its binding-partner p 1 30Cas/BCAR I generates anti-estrogen resistance in human breast cancer lines. Here, we have compared BCAR3 to two related homologs, NSP I and NSP3/CHAT/SHEP, with regards to expression, anti-estrogen resistance, and signaling. BCAR3 is expressed at higher levels in ER alpha-negative, mesenchymal, than in ER alpha-positive, epithelial, breast cancer cell lines. Characterization of intermediate epithelial-like cell lines with variable ER-a expression reveals that BCAR3 expression correlates with both mesenchymal and ER(x-negative phenotypes. Levels of the BCAR3/p 1 30Cas complex correlate more strongly with the ER alpha-negative, mesenchymal phenotype than levels of either protein alone. NSP I and NSP3 are expressed at lower levels than BCAR3 and without correlation to ER(alpha/mesenchymal status. Among NSP-transfectants, only BCAR3 transfectants induce anti-estrogen resistance and augment transcription of cyclin D I promoter constructs. Over-expression of all homologs results in activation of Rac, Cdc42 and Akt, suggesting that these signals are insufficient to induce anti-estrogen resistance. BCAR3 but not NSP I nor NSP3 transfectants show altered morphology, transitioning from polygonal cell groups to rounded, single cells with numerous blebs. Whereas stable over-expression of BCAR3 in MCF-7 cells does not lead to classic epithelial-to-mesenchymal transition, it does result in down-regulation of cadherin-mediated adhesion and augmentation of fibronectin expression. These studies suggest that BCAR's ability to induce anti-estrogen resistance is greater than that of other NSP homologs and may result from altered interaction of breast cancer cells with each other and the extracellular matrix.