Abstract 5287: Role of Wnt-beta-catenin pathway in the control of tumor cell invasion in the triple negative subset of breast cancer

A plethora of genetic changes occurring in the triple negative (TN) breast tumors (BT) contribute to the different phenotypes exhibited by the tumor cells via deregulation of the specific signaling-pathways. Our group identified a differential upregulation of the Wnt-beta-catenin pathway in TN subset of BT (Barwick etal, 2008, BCS; Dey etal. 2009, AACR) and reported that the poor prognosis and higher incidence of metastasis is associated with this pathway in TNBT (Barwick etal., 2009; PNAS, revised). Of late, we demonstrated a role of the pathway in the control of integrin-mediated migration in TNBT cells (Dey etal. 2009, Adv. BCR). Since integrin-directed migration is instrumental for the invasion (directional movement across extracellular-matrix following matrix degradation) of the tumor cells and TN tumor cells are highly invasive in nature, we hypothesized that the upregulation of Wnt-beta-catenin pathway in TNBT is functionally connected to the control of invasion. Our hypothesis is strengthened by our recent identification of MMP7 (key target-gene of this pathway), as a selective-biomarker of TN subtype (Abramovitz etal, 2009, AACR). In an attempt to define the significance of the pathway in the regulation of invasion, we examined (a) the expression of MMP7 and CTNNB1 in tumor samples and 15 TNBT cell lines, (b) the activity of MMP7 in high MMP7-expressing TNBT cell lines, and (c) effects of pharmacological intervention of the pathway on the invasion of MMP7-expressing TNBT cells. We demonstrated that MMP7 is selectively upregulated in TNBT tumors (our data sets; Montreal-91, Georgia-137) and published data set (MSK-96). We validated the DASL-data by RT-PCR in tumors and cell lines. The expression of MMP7 and beta-catenin (mRNA) in tumor samples from TN patients was comparable to the pattern of expression of MMP7 and beta-catenin (protein) in TNBT cell lines. Zymography of MMP7 demonstrated that the secreted protein is enzymatically active. MDA-MB231, MDA-MB468 and SUM149 TNBT cell lines invaded more in vitro than non-TNBT cells. Administration of sulindac to attenuate the Wnt-beta-catenin pathway showed, 1) a decrease in the levels of beta-catenin (total and active) and MMP7, 2) an inhibition of invasion of cells which corroborated with the integrin-directed cell movement (real-time-video-microscopy), 3) an altered distribution-pattern of filamentous-actin, 4) over 50% attenuation of the activation of RAC1-GTPase and 5) a blockade of migration of TNBT cells. The status of activation of cofilin is directly related to cell migration, invasion, and metastasis in many tumor cells including mammary tumors. We are currently studying the state of phosphorylation of cofilin in the context of fibronectin-dependent activation of the RAC1 (upstream of cofilin) in TNBT cells following the intervention of Wnt-beta-catenin pathway, the results of which will be presented in the meeting. 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 5287.