Analysis of AND-34, A Novel p130Cas-Binding GDP Exchange Factor Implicated in the Development of Tamoxifen Resistance in Human Breast Cancer

摘要

AND-34 is a murine protein that binds by a cdc25-like GDP exchange factor domain to the focal adhesion docking protein pl3OCas. Over-expression of either of the human homologues of AND-34 and pl30Cas, BCAR3 and BCAR1, respectively, have been reported to induce resistance to antiestrogens in breast cancer cell lines. In our work over the last two years, we have ascertained that over-expression of AND-34 leads to activation of the Rho family GRPases Cdc42 and Rac. We further have found that transfection of a constitutively active form of Rac induces antiestrogen resistance in breast cancer cell lines. Further, we find that BCAR3-mediated cyclin Dl up-regulation in breast cancer cell lines is dependent on both Rac and a Rac effector protein, PAKl. This work, which is described in an accompanying Cancer Research article that is in press for Oct. 15, 2003, suggests that one mechanism by which breast carcinoma could develop antiestrogen resistance is by up- regulation of Rac and PAKl-dependent signaling pathways. In further work over the past year, we find that both the SH2 domain and the GDP exchange factor-like domain of BCAR3 are required for antiestrogen resistance, as transfection of mutants lacking these domains fails to allow growth of ZR-75-l cells in the antiestrogen ICI 182,780. Finally, we have detected by Western analysis expression of BCAR3 in primary human breast carcinomas but not in normal mammoplasy specimens. Our efforts to detect BCAR3 by immunohistochemistry are ongoing.