Abstract 5135: Breast cancer antiestrogen resistance-3 influences breast cancer cell migration by regulating Rac and Rho GTPase signaling

Abstract

Abstract Breast Cancer Antiestrogen Resistance-3 (BCAR3) was initially identified as a gene whose expression confers resistance to endocrine therapy, such as the antiestrogen tamoxifen. However, work from our group as well as others implicate BCAR3 as a prominent regulator of cell migration and invasion. This is of interest because expression of BCAR3 is elevated in more aggressive breast cancer cell lines. In this study, we have taken both a gain-of-function and loss-of-function approach to determine the mechanism by which BCAR3 regulates cell migration and invasion. We found that overexpression of BCAR3 in less aggressive breast cancer cells resulted in enhanced cell migration and increased protrusive activity. Additionally, BCAR3 was co-localized at the cell membrane with an established scaffold protein, p130Cas (also known as BCAR1 or Cas). Conversely, siRNA-mediated depletion of BCAR3 in more aggressive breast cancer cells inhibited cell migration and decreased membrane protrusiveness, coincident with a significant reduction in Rac GTPase activity. This was accompanied by mislocalization of Cas and a decrease in Cas tyrosine phosphorylation. Loss of BCAR3 was also associated with stabilization of stress fibers, reduced adhesion turnover, and increased ROCK-dependent phosphorylation of myosin light chain, a major downstream target of Rho GTPase. Inhibition of ROCK in BCAR3-depleted cells disrupted stress fibers and restored membrane protrusions, confirming and indicating that the effect of BCAR3 depletion on stress fiber dynamics was dependent on ROCK. Furthermore, Cas localization to the cell periphery was restored and partial rescue of Cas tyrosine phosphorylation was observed. Taken together, these results suggest a model whereby BCAR3 expression influences cell migration and invasion by promoting Cas phosphorylation and Cas-mediated Rac activation, while negatively regulating Rho-mediated contractility. While the major mechanisms of BCAR3 as a critical regulator of breast cancer cell migration are addressed here, future studies will determine whether elevated BCAR3 expression promotes metastasis in animal models and is associated with clinical outcome in patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5135.