Interactions between the epithelium and surrounding mesenchyme/stroma play an important role in normal gut morphogenesis, the epithelial response to injury, and epithelial carcinogenesis. The tumor microenvironment, composed of stromal cells including myofibroblasts and immune cells, regulates tumor growth and the cancer stem cell niche. Deletion of epimorphin (Epim), a syntaxin family member expressed in myofibroblasts and macrophages, results in partial protection from colitis and from inflammation-induced colon cancer in mice. We sought to determine whether epimorphin deletion protects from polyposis in the Apcmin/+ mouse model of intestinal carcinogenesis. Epim-/- mice were crossed to Apcmin/+ mice; Apcmin/+ and Apcmin/+/Epim-/- mice were killed at 3 mo of age. Polyp numbers and sizes were quantified in small intestine and colon, and gene expression analyses for pathways relevant to epithelial carcinogenesis were performed. Primary myofibroblast cultures were isolated, and expression and secretion of selected growth factors from Apcmin/+ and Apcmin/+/Epim-/- myofibroblasts were examined by ELISA. Small bowel polyposis was significantly inhibited in Apcmin/+/Epim-/- compared with Apcmin/+ mice. Apcmin/+/Epim-/- compared with Apcmin/+ polyps and adjacent uninvolved intestinal mucosa had increased transforming growth factor-β (TGF-β) expression and signaling with increased P-Smad2/3 expression. Myofibroblasts isolated from Apcmin/+/Epim-/- vs. Apcmin/+ mice had markedly decreased hepatocyte growth factor (HGF) expression and secretion. We concluded that Epim deletion inhibits polyposis in Apcmin/+ mice, associated with increased mucosal TGF-β signaling and decreased myofibroblast HGF expression and secretion. Our data suggest that Epim deletion reduces tumorigenicity of the stromal microenvironment.
Keywords: colon cancer; hepatocyte growth factor; myofibroblasts; stem cell niche; tumor microenvironment.