Background & Aims: Chronic inflammation is a risk factor for colon cancer in patients with ulcerative colitis (UC). The molecular mechanisms linking inflammation and colon carcinogenesis are incompletely understood. We tested the hypothesis that Toll-like receptor 4 (TLR4) is involved in tumorigenesis in the setting of chronic inflammation. Methods: Tissues from UC patients with cancer were examined for TLR4 expression. Colitis-associated neoplasia was induced using azoxymethane injection followed by dextran sodium sulfate treatment in TLR4-deficient or wild-type mice. Inflammation, polyps, and microscopic dysplasia were scored. Cyclooxygenase (Cox)-2 and prostaglandin E₂ production were analyzed by real-time polymerase chain reaction, immunohistochemistry, or enzyme immunoassay. Epidermal growth factor receptor (EGFR) phosphorylation and amphiregulin production were examined by Western blot analysis and enzyme-linked immunosorbent assay, respectively. Results: We show that TLR4 is overexpressed in human and murine inflammation-associated colorectal neoplasia. TLR4-deficient mice were protected markedly from colon carcinogenesis. Mechanistically, we show that TLR4 is responsible for induction of Cox-2, increased prostaglandin E₂ production, and activation of EGFR signaling in chronic colitis. Amphiregulin, an EGFR ligand, was induced in a TLR4, Cox-2–dependent fashion and contributes to activation of EGFR phosphorylation in colonic epithelial cells. Conclusions: TLR4 signaling is critical for colon carcinogenesis in chronic colitis. TLR4 activation appears to promote the development of colitis-associated cancer by mechanisms including enhanced Cox-2 expression and increased EGFR signaling. Inhibiting TLR4 signaling may be useful in the prevention or treatment of colitis-associated cancer.

Inflammatory bowel disease (IBD) arises from a dysregulated mucosal immune response to luminal bacteria. Toll-like receptor (TLR)4 recognizes LPS and transduces a proinflammatory signal through the adapter molecule myeloid differentiation marker 88 (MyD88). We hypothesized that TLR4 participates in the innate immune response to luminal bacteria and the development of colitis. TLR4−/− and MyD88−/− mice and littermate controls were given 2.5% dextran sodium sulfate (DSS) for 5 or 7 days followed by a 7-day recovery. Colitis was assessed by weight loss, rectal bleeding, and histopathology. Immunostaining was performed for macrophage markers, chemokine expression, and cell proliferation markers. DSS treatment of TLR4−/− mice was associated with striking reduction in acute inflammatory cells compared with wild-type mice despite similar degrees of epithelial injury. TLR4−/− mice experienced earlier and more severe bleeding than control mice. Similar results were seen with MyD88−/− mice, suggesting that this is the dominant downstream pathway. Mesenteric lymph nodes from TLR4−/− and MyD88−/− mice more frequently grew gram-negative bacteria. Altered neutrophil recruitment was due to diminished macrophage inflammatory protein-2 expression by lamina propria macrophages in TLR4−/− and MyD88−/− mice. The similarity in crypt epithelial damage between TLR4−/− or MyD88−/− and wild-type mice was seen despite decreased epithelial proliferation in knockout mice. TLR4 through the adapter molecule MyD88 is important in intestinal response to injury and in limiting bacterial translocation. Despite the diversity of luminal bacteria, other TLRs do not substitute for the role of TLR4 in this acute colitis model. A defective innate immune response may result in diminished bacterial clearance and ultimately dysregulated response to normal flora.

Background & Aims: We recently showed that mice deficient in Toll-like receptor 4 (TLR4) or its adapter molecule MyD88 have increased signs of colitis compared with wild-type (WT) mice after dextran sodium sulfate (DSS)-induced injury. We wished to test the hypothesis that cyclooxygenase 2 (Cox-2)–derived prostaglandin E₂ (PGE₂) is important in TLR4-related mucosal repair. Methods: Cox-2 expression was analyzed by real-time polymerase chain reaction, immunohistochemistry, Western blotting, and luciferase reporter constructs. Small interfering RNA was used to inhibit expression of MyD88. TLR4−/− or WT mice were given 2.5% DSS for 7 days. Proliferation and apoptosis were assessed using bromodeoxyuridine staining and terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate nick-end labeling assays, respectively. PGE₂ was given orally to DSS-treated mice. Results: Intestinal epithelial cell lines up-regulated Cox-2 expression in a TLR4- and MyD88-dependent fashion. Lipopolysaccharide-mediated stimulation of PGE₂ production was blocked by a selective Cox-2 inhibitor or small interfering RNA against MyD88. After DSS injury, Cox-2 expression increased only in WT mice. TLR4−/− mice have significantly reduced proliferation and increased apoptosis after DSS injury compared with WT mice. PGE₂ supplementation of TLR4−/− mice resulted in improvement in clinical signs of colitis and restoration of proliferation and apoptosis to WT values. The mechanism for improved epithelial repair may be through PGE₂-dependent activation of the epidermal growth factor receptor. Conclusions: We describe an important link between TLR4 signaling and Cox-2 expression in the gut. TLR4 and MyD88 signaling are required for optimal proliferation and protection against apoptosis in the injured intestine. Although TLR4 signaling is beneficial in the short term, chronic signaling through TLR4 may lower the threshold for colitis-associated cancer.

GPR15 Gets T _regs to Guard the Gut: The large intestine is the site that is typically most inflamed in Crohn's disease and ulcerative colitis, which are thought to result when the immune system is not able to keep the peace with trillions of resident gut microbes. The immune system does this by recruiting specific cell populations, like regulatory T cells (T _regs ), to the gut. Kim et al. (p. 1456 , published online 9 May) now suggest that the orphan G protein–coupled receptor GPR15 is expressed by T _regs and required for T _reg homing to the large intestine in mice.

Pancreatic ductal adenocarcinoma (PDAC) is one of the most fatal human cancers due to its complicated genomic instability. PDAC frequently presents at an advanced stage with extensive metastasis, which portends a poor prognosis. The known risk factors associated with PDAC include advanced age, smoking, long-standing chronic pancreatitis, obesity, and diabetes. Its association with genomic and somatic mutations is the most important factor for its aggressiveness. The most common gene mutations associated with PDAC include KRas2, p16, TP53, and Smad4. Among these, Smad4 mutation is relatively specific and its inactivation is found in more than 50% of invasive pancreatic adenocarcinomas. Smad4 is a member of the Smad family of signal transducers and acts as a central mediator of transforming growth factor beta (TGF-β) signaling pathways. The TGF-β signaling pathway promotes many physiological processes, including cell growth, differentiation, proliferation, fibrosis, and scar formation. It also plays a major role in the development of tumors through induction of angiogenesis and immune suppression. In this review, we will discuss the molecular mechanism of TGF-β/Smad4 signaling in the pathogenesis of pancreatic adenocarcinoma and its clinical implication, particularly potential as a prognostic factor and a therapeutic target.

Background. Patients with ulcerative colitis are at increased risk for developing colorectal cancer. We have shown that Toll-like receptor-4 (TLR4) is overexpre