Background & Aims Mechanisms responsible for crypt architectural distortion in chronic ulcerative colitis (CUC) are not well understood. Data indicate that Akt signaling cooperates with Wnt to activate β-catenin in intestinal stem and progenitor cells through phosphorylation at Ser552 (P-β-catenin552). We investigated whether phosphoinositide 3- kinase (PI3K) is required for Akt-mediated activation of β-catenin during intestinal inflammation. Methods The class IA subunit of PI3K was conditionally deleted from intestinal epithelial cells in mice. Acute inflammation was induced in these mice (I-pik3r1KO) and their intestines were analyzed by biochemical and histological methods. The effects of chemically blocking PI3K in colitic IL-10−/− mice were examined. Biopsy samples from patients were examined. Results Compared to wild type mice, I-pik3r1KO mice had reduced T-cell–mediated Akt and β-catenin signaling in intestinal stem and progenitor cells and limited crypt epithelial proliferation. Biochemical analyses indicated that PI3K–Akt signaling increased nuclear total β-catenin and P-β-catenin552 levels and reduced phosphorylation of N-terminal β-catenin, which is associated with degradation. PI3K inhibition in IL-10−/− mice impaired colitis-induced epithelial Akt and β-catenin activation, reduced progenitor cell expansion, and prevented dysplasia. Human samples had increased numbers of progenitor cells with P-β-catenin552 throughout expanded crypts and increased mRNA expression of β-catenin target genes in CUC, colitis-associated cancer, tubular adenomas, and sporadic colorectal cancer, compared with control samples. Conclusions PI3K–Akt signaling cooperates with Wnt to increase β-catenin signaling during inflammation. PI3K-induced and Akt-mediated β-catenin signaling are required for progenitor cell activation during the progression from CUC to CAC; these factors might be used as biomarkers of dysplastic transformation in the colon.

Colonic bacteria have been implicated in the development of colon cancer. We have previously demonstrated that toll-like receptor 4 (TLR4), the receptor for bacterial lipopolysaccharide (LPS), is over-expressed in humans with colitis-associated cancer. Genetic epidemiologic data support a role for TLR4 in sporadic colorectal cancer (CRC) as well, with over-expression favoring more aggressive disease. The goal of our study was to determine whether TLR4 played a role as a tumor promoter in sporadic colon cancer. Using immunofluorescence directed to TLR4, we found that a third of sporadic human colorectal cancers over-express this marker. To mechanistically investigate this observation, we used a mouse model that over-expresses TLR4 in the intestinal epithelium (villin-TLR4 mice). We found that these transgenic mice had increased epithelial proliferation as measured by BrdU labeling, longer colonic crypts and an expansion of Lgr5+ crypt cells at baseline. In addition, villin-TLR4 mice developed spontaneous duodenal dysplasia with age, a feature that is not seen in any wild-type (WT) mice. To model human sporadic CRC, we administered the genotoxic agent azoxymethane (AOM) to villin-TLR4 and WT mice. We found that villin-TLR4 mice showed an increased number of colonic tumors compared to WT mice as well as increased β-catenin activation in non-dysplastic areas. Biochemical studies in colonic epithelial cell lines revealed that TLR4 activates β-catenin in a PI3K-dependent manner, increasing phosphorylation of β-cateninSer552, a phenomenon associated with activation of the canonical Wnt pathway. Our results suggest that TLR4 can trigger a neoplastic program through activation of the Wnt/β-catenin pathway. Our studies highlight a previously unexplored link between innate immune signaling and activation of oncogenic pathways, which may be targeted to prevent or treat CRC.

BACKGROUND & AIMS Inflammatory bowel disease (IBD) is associated with increased apoptosis of intestinal epithelial cells (IECs). Mutations in the tumor suppressor p53 appear during early stages of progression from colitis to cancer. We investigated the role of p53 and its target, p53-upregulated modulator of apoptosis (PUMA), in inflammation-induced apoptosis of IECs. METHODS Apoptosis was induced in mouse models of mucosal inflammation. Responses of IECs to acute, T-cell activation were assessed in wild-type, p53−/−, Bid−/−, Bim−/−, Bax3−/−, Bak−/−, PUMA−/−, and Noxa−/− mice. Responses of IECs to acute and chronic colitis were measured in mice following 1 or 3 cycles of dextran sulfate sodium (DSS), respectively. Apoptosis was assessed by TUNEL staining and measuring activity of caspases 3 and 9; levels of p53 and PUMA were assessed in colon tissue from patients with and without ulcerative colitis. RESULTS Apoptosis of IECs occurred in the lower crypts of colitic tissue from humans and mice. Colitis induction with anti-CD3 or 3 cycles of DSS increased apoptosis and protein levels of p53 and PUMA in colonic crypt IECs. In p53−/− and PUMA−/− mice, apoptosis of IECs was significantly reduced but inflammation was not. Levels of p53 and PUMA were increased in inflamed mucosal tissues of mice with colitis and in patients with UC, compared with controls. Induction of PUMA in IECs of p53−/− mice indicated that PUMA-mediated apoptosis was independent of p53. CONCLUSIONS In mice and humans, colon inflammation induces apoptosis of IECs via p53-dependent and -independent mechanisms; PUMA also activates an intrinsic apoptosis pathway associated with colitis.

These results suggest that CXCL10 plays a dual role in colitis development by enhancing TH1 cell generation in inductive sites and promoting effector cell recruitment to inflamed tissue. Blockade of CXCL10 may be a useful adjunct to remission-inducing therapies in inflammatory bowel disease (IBD) by impairing disease recurrence through selective inhibition of effector cell generation and trafficking in vivo.

Chronic ulcerative colitis (CUC) is characterized by increased intestinal epithelial cell (IEC) apoptosis associated with elevated tumor necrosis factor (TNF), inducible nitric oxide synthase (iNOS), and p53. We previously showed that p53 is increased in crypt IECs in human colitis and is needed for IEC apoptosis in chronic dextran sulfate sodium-colitis. Herein, we examined the roles of TNF and iNOS in regulating p53-induced IEC apoptosis in CUC. The IEC TUNEL staining, caspases 3, 8, and 9, and p53 protein levels, induced by anti-CD3 monoclonal antibody (mAb) activation of T cells, were markedly reduced in TNF receptor 1 and 2 gene knockout mice. Induction of IEC apoptosis correlated with increased p53, which was attenuated in iNOS(-/-) mice. IEC p53 levels and apoptosis were reduced in IL-10(-/-) colitic mice treated with neutralizing TNF mAb and the iNOS inhibitor, aminoguanidine, further suggesting that TNF and iNOS are upstream of p53 during colitis-induced IEC apoptosis. IEC apoptosis and p53 levels were assessed in control versus untreated or anti-TNF-treated CUC patients with equivalent levels of inflammation. Data indicated that IEC apoptosis and p53 levels were clearly higher in untreated CUC but markedly reduced in patients treated with anti-TNF mAb. Therefore, TNF-induced iNOS activates a p53-dependent pathway of IEC apoptosis in CUC. The inhibition of IEC apoptosis may be an important mechanism for mucosal healing in anti-TNF-treated CUC patients.