Expression of a phosphorylated p130^Cas substrate domain attenuates the phosphatidylinositol 3‐kinase/Akt survival pathway in tamoxifen resistant breast cancer cells

Abstract

Elevated expression of p130Cas/BCAR1 (breast cancer anti estrogen resistance 1) in human breast tumors is a marker of poor prognosis and poor overall survival. Specifically, p130Cas signaling has been associated with antiestrogen resistance, for which the mechanism is currently unknown. TAM-R cells, which were established by long-term exposure of estrogen (E2)-dependent MCF-7 cells to tamoxifen, displayed elevated levels of total and activated p130Cas. Here we have investigated the effects of p130Cas inhibition on growth factor signaling in tamoxifen resistance. To inhibit p130Cas, a phosphorylated substrate domain of p130Cas, that acts as a dominant-negative (DN) p130Cas molecule by blocking signal transduction downstream of the p130Cas substrate domain, as well as knockdown by siRNA was employed. Interference with p130Cas signaling/expression induced morphological changes, which were consistent with a more epithelial-like phenotype. The phenotypic reversion was accompanied by reduced migration, attenuation of the ERK and phosphatidylinositol 3-kinase/Akt pathways, and induction of apoptosis. Apoptosis was accompanied by downregulation of the expression of the anti-apoptotic protein Bcl-2. Importantly, these changes re-sensitized TAM-R cells to tamoxifen treatment by inducing cell death. Therefore, our findings suggest that targeting the product of the BCAR1 gene by a peptide which mimics the phosphorylated substrate domain may provide a new molecular avenue for treatment of antiestrogen resistant breast cancers.

Targeting Cas Family Proteins as a Novel Treatment for Breast Cancer

“…In feline and canine breast cancers the levels of p130 Cas positively correlate with advanced breast disease as well (Scibelli et al 2003). Furthermore, our in vitro studies have shown increased p130 Cas levels in the tamoxifen resistant breast cancer cells TAM-R (Soni et al 2009), which were derived from tamoxifen sensitive MCF-7 cells (Knowlden et al 2003). In 2000, Brinkman and colleagues identified the gene of p130 Cas , in a retroviral insertion screen as a factor that mediates resistance to tamoxifen in breast cancer cell lines (Brinkman et al 2000;Dorssers et al 1993).…”

“…Consistently, interference with p130 Cas signaling results in the attenuation of the ERK and PI3K/Akt survival pathways in breast cancer cells (Soni et al 2009). Moreover, overexpression of p130 Cas mediates resistance to the chemotherapeutic drug adriamycin in mammary tumor cells by activating c-Src, Akt, and ERK1/2 growth and survival pathways (Ta et al 2008).…”

“…Chimeric p130 Cas /HEF1 proteins generated by exchange of defined domains, identified the SD of p130 Cas as the region contributing to anti-estrogen resistance in breast cancer cells (Brinkman et al 2009). Accordingly, disruption of the p130 Cas signaling node by ectopic expression of an isolated constitutively tyrosine phosphorylated SD of p130 Cas in the cytoplasm (as described in detail in Section 3) led to reduced proliferation and re-sensitization of tamoxifen resistant breast cancer cells to tamoxifen (Kirsch et al 2002;Soni et al 2009). The mechanisms by which Cas proteins may promote mammary carcinomas and acquired tamoxifen resistance are manifold and under extensive investigation.…”

“…Importantly, overexpression of p130 Cas as well as shortinterfering (si) RNA-mediated reduction of p130 Cas experiments in T47D breast cancer cells indicated that p130 Cas enhances the estrogen-dependent Src and Erk1/2 activities (and accelerates the kinetics in response to stimulation) (Cabodi et al 2004). Long-term treatment of estrogen-dependent mammary carcinoma cells with the estrogen antagonist tamoxifen led to increased phosphorylation levels of p130 Cas (Cowell et al 2006;Soni et al 2009), suggesting that anti-estrogens modulate intrinsic mechanisms to deregulate Cas protein function.…”

“…Resistance to the anti-estrogens tamoxifen and fulvestrant, is associated with enhanced growth factor signaling involving the upregulation of epidermal growth factor receptor (EGFR) family and alteration of the AKT signaling pathway (Knowlden et al 2003;Soni et al 2009;Zhang et al 2009;Frogne et al 2009). Consistently, interference with p130 Cas signaling results in the attenuation of the ERK and PI3K/Akt survival pathways in breast cancer cells (Soni et al 2009).…”