Abstract 3106: Intestinal mesenchymal fibroblasts promote early epithelial tumorigenesis through activation of integrin beta4 and receptor tyrosine kinases, bypassing common mutational mechanisms

Abstract

Abstract Cancer cells communicate extensively with their stroma, exchanging signals that influence growth and metastasis. Intestinal sub-epithelial myofibroblasts (ISEMFs) direct organogenesis and constitute the colorectal cancer (CRC) microenvironment. ISEMFs from the mouse small intestine and colon express regional characteristics and different cytokines. In line with these regional patterns, ApcMin mice develop adenomas principally in the small intestine but not in the colon; conversely, humans develop tumors mainly in the colon and rarely in the small bowel. We hypothesize that intestinal ISEMFs influence tumor regionality through cell-cell communication. Murine ileal ISEMFs supported growth of human CRC cells markedly better than those originating in the colon in NOD/SCID xenografts and in vitro. We traced this effect to a single secreted factor, matrix metalloproteinase 9 (MMP9), which is exclusively mesenchymal in expression and substantially enriched in native ileal over colonic ISEMFs. Actively cycling intestinal epithelial progenitors and Lgr5+ stem cells showed selectively reduced bromodeoxyuridine uptake in Mmp9-/- mouse ileum, revealing that Mmp9 deficiency impairs epithelial self-renewal. Moreover, ApcMin mice developed fewer ileal adenomas upon treatment with an Mmp9 inhibitor or on the Mmp9-/- genetic background. MMP9 immunohistochemistry revealed expression in 106 of 642 (16.5%) human CRC samples; expression was confined to stromal fibroblasts and considerably enriched among CRCs that lack characteristic KRAS mutations and harbor the CpG island methylator phenotype. Gene expression in epithelial cells interacting with ileal fibroblasts pointed to activation of cytoskeletal remodeling and integrin ß4 signaling pathways, signatures absent in cells cultured with colonic ISEMFs. Biochemical assays verified that stromal MMP9 activates epithelial integrin ß4 and, in turn, ErbB and c-Met receptor tyrosine kinases (RTKs) in adjoining epithelial, including human CRC, cells. This activation is mediated by MMP9 cleavage of the integrin ligand laminin alpha4. Activation of epithelial integrin ß4 and RTKs and the paucity of KRAS mutations in CRCs with stromal MMP9 expression together suggest that potent MMP9-mediated microenvironment signals can help bypass common mutational mechanisms of constitutive growth factor pathway activation in CRC. These results define a novel and therapeutically tractable pathway of tumor-stromal interaction in early CRC pathogenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3106. doi:10.1158/1538-7445.AM2011-3106