The Role of BCAR3 in the Promotion of Migration and Invasion of Breast Cancer Cells

Abstract

Proc Amer Assoc Cancer Res, Volume 47, 2006 1813 BCAR-3 (Breast Cancer Antiestrogen Resistance-3) is a protein recently shown in both fibroblasts and breast cancer cells to be involved in migration and invasion. While mRNA expression of BCAR-3 is reported to be undetectable in non-malignant breast tissues, elevated mRNA levels have been detected in breast tumors, particularly those that do not express the estrogen receptor (ER). Recently, our group showed that BCAR-3 functions synergistically with the adapter protein p130Cas (Cas) to increase migration of C3H10T½ murine fibroblasts. This synergy may be particularly relevant in light of our finding that Cas is co-overexpressed with BCAR-3 in a large number of breast cancer cells. The goals of this study were to determine 1) whether BCAR3 expression contributes to breast cancer cell migration and invasion and 2) if Cas recruitment to the cell periphery is a mechanism for BCAR-3-mediated motility. To address these goals, a panel of breast cancer cells was used that vary in their invasive and metastatic potential. We found that BCAR-3 expression was greater in cells with increased invasive potential. This expression pattern corresponded with increased BCAR-3 localization at the plasma membrane, most often in lamellipodia. Endogenous Cas, which was found in complex with BCAR-3 in these cells, co-localized with BCAR-3 at the cell membrane. RNA interference was used to investigate the contribution of BCAR-3 to breast cancer cell migration and invasion. BCAR-3 protein was specifically depleted from BT549 and MDA-MB-231 breast cancer cell lines, which express high levels of endogenous BCAR-3. The effect of reduced BCAR-3 expression on cell migration and invasion was then measured using Boyden chamber assays. Migration and invasion were found to be reduced 40-60% in cells treated with BCAR-3 small interfering RNAs (siRNAs) as compared to control siRNAs. This effect was shown to be due to BCAR-3 knockdown because re-expression of BCAR-3 in siRNA-treated cells rescued the defect in migration. As a corollary to these studies, we are in the process of determining if BCAR-3 overexpression in breast cancer cell lines that naturally express low levels of BCAR-3 enhances migration, and if so, whether this also requires Cas overexpression, as was the case for C3H10T½ fibroblasts. Future studies will focus on further elucidating functional relationships between BCAR-3, Cas, and other cellular factors that regulate cell migration and invasion. In conclusion, we find that BCAR-3 expression corresponds to the invasive potential of numerous breast cancer cell lines. BCAR-3/Cas complexes can be detected in invasive cells coincident with co-localization of both proteins at the leading edge of migrating cells. Depletion of BCAR-3 in cells with high invasive potential results in a significant impairment of migration and invasion, indicating that this protein plays an important role in these cellular processes.