Transforming Growth Factor β Receptor Type II Inactivation Induces the Malignant Transformation of Intestinal Neoplasms Initiated by Apc Mutation

The transforming growth factor-β (TGF-β) signaling pathway is a tumor-suppressor pathway that is commonly inactivated in colon cancer. TGF-β is a secreted ligand that mediates its effects through a transmembrane heteromeric receptor complex, which consists of type I (TGFBR1) and type II subunits (TGFBR2). Approximately 30% of colon cancers carry TGFBR2 mutations, demonstrating that it is a common target for mutational inactivation in this cancer. To assess the functional role of TGFBR2 inactivation in the multistep progression sequence of colon cancer, we generated a mouse model that recapitulates two common genetic events observed in human colon cancer by mating Apc1638N/wt mice with mice that are null for Tgfbr2 in the intestinal epithelium, Villin-Cre;Tgfbr2E2flx/E2flx mice. In this model, we observed a dramatic increase in the number of intestinal adenocarcinomas in the Apc1638N/wt;Villin-Cre;Tgfbr2E2flx/E2flx mice (called Apc1638N/wt;Tgfbr2IEKO) compared with those mice with intact Tgfbr2 (Apc1638N/wt;Tgfbr2E2flx/E2flx). Additionally, in vitro analyses of epithelial tumor cells derived from the Apc1638N/wt;Tgfbr2IEKO mice showed enhanced expression and activity of matrix metalloproteinase MMP-2 and MMP-9, as well as increased TGF-β1 secretion in the conditioned medium. Similarly, primary tumor tissues from the Apc1638N/wt;Tgfbr2IEKO mice also showed elevated amounts of TGF-β1 as well as higher MMP-2 activity in comparison with Apc1638N/wt;Tgfbr2E2flx/E2flx–derived tumors. Thus, loss of TGFBR2 in intestinal epithelial cells promotes the invasion and malignant transformation of tumors initiated by Apc mutation, providing evidence that Wnt signaling deregulation and TGF-β signaling inactivation cooperate to drive the initiation and progression, respectively, of intestinal cancers in vivo. (Cancer Res 2006; 66(20): 9837-44)