Abstract
APC mutations cause activation of Wnt/beta-catenin signaling, which invariably leads to colorectal cancer. Similarly, overexpressed Dvl proteins are potent activators of beta-catenin signaling. Screening a large tissue microarray of different staged colorectal tumors by immunohistochemistry, we found that Dvl2 has a strong tendency to be overexpressed in colorectal adenomas and carcinomas, in parallel to nuclear beta-catenin and Axin2 (a universal transcriptional target of Wnt/beta-catenin signaling). Furthermore, deletion of Dvl2 reduced the intestinal tumor numbers in a dose-dependent way in the Apc(Min) model for colorectal cancer. Interestingly, the small intestines of Dvl2 mutants are shortened, reflecting in part a reduction of their crypt diameter and cell size. Consistent with this, mammalian target of rapamycin (mTOR) signaling is highly active in normal intestinal crypts in which Wnt/beta-catenin signaling is active, and activated mTOR signaling (as revealed by staining for phosphorylated 4E-BP1) serves as a diagnostic marker of Apc(Min) mutant adenomas. Inhibition of mTOR signaling in Apc(Min) mutant mice by RAD001 (everolimus) reduces their intestinal tumor load, similarly to Dvl2 deletion. mTOR signaling is also consistently active in human hyperplastic polyps and has a significant tendency for being active in adenomas and carcinomas. Our results implicate Dvl2 and mTOR in the progression of colorectal neoplasia and highlight their potential as therapeutic targets in colorectal cancer.