Abstract 2370: A novel Src/Ezrin pathway regulates local invasion and metastasis of breast

Abstract

Abstract The membrane cytoskeletal crosslinker, ezrin, is frequently over-expressed in human breast cancer, and is required for motility and invasion of epithelial cells. Our group recently showed that ezrin acts co-operatively with the non-receptor tyrosine kinase, Src, in transformation of epithelial cells, requiring phosphorylation of specific tyrosines on ezrin by Src (Srivistava et al. MBC, 16:1481-90, 2005; Naba et al. EMBO J. 27:38-50, 2008). We showed that Src binds to ezrin Y190 via its SH2 domain and that ezrin Y145 and Y477 are phosphorylated by Src. Expression of Y145F or Y477F ezrin mutants, which cannot be phosphorylated by Src, delays cell spreading of epithelial cells on fibronectin substratum. Furthermore, ezrin is required for metastasis in a breast tumor xenograft model (Elliott et al. BCR 7:R365-73, 2005). We therefore examined whether Src/ezrin interaction regulates invasion and metastasis of breast cancer, using a mouse breast tumor (AC2M2) xenograft model. Transplanted tumor cells expressing vector alone rapidly infiltrated into surrounding stroma, underlying abdominal muscle, visceral organs and metastasized to lung and other sites. Interestingly, both Y145F and Y477F ezrin mutants had little effect on primary tumor growth rate. However, Y145F ezrin showed a marked attenuating effect on pulmonary metastasis. Furthermore, transplanted mouse breast carcinoma cells over-expressing Y477F ezrin formed cohesive tumors that were circumscribed by normal stroma with no detectable infiltration into underlying muscle. Marked lymphovascular involvement, a prognostic indicator of relapse in clinically advanced human breast cancers, was evident in control tumors but not in tumors expressing Y477F ezrin. In a preliminary IHC analysis, total ezrin showed strong cytoplasmic and weak membranous staining in the cortical region of control primary tumors, but showed strong membranous and weak cytoplasmic staining in Y477F ezrin-expressing primary tumors. The cohesive phenotype of Y477F ezrin is likely a consequence of a defect in cell adhesion as described by Naba et al. Thus, the precise state of ezrin phosphorylation may elicit different effects on local invasion and metastasis. Our study implicates a role of the Src/ezrin pathway in regulating local invasion and metastasis of breast carcinoma cells, and provides a clinically relevant model for assessing the Src/ezrin pathway as a potential prognostic marker and treatment target for invasive breast cancer. (Funded by CBCRA 17374 and ARC 4823) 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 2370.