Search

Helicobacter pylori infection is the main risk factor for the development of gastric cancer, the third leading cause of cancer death worldwide. H. pylori colonizes the human gastric mucosa and persists for decades. The inflammatory response is ineffective in clearing the infection, leading to disease progression that may result in gastric adenocarcinoma. We have shown that polyamines are regulators of the host response to H. pylori, and that spermine oxidase (SMOX), which metabolizes the polyamine spermine into spermidine plus H2O2, is associated with increased human gastric cancer risk. We now used a molecular approach to directly address the role of SMOX, and demonstrate that Smox-deficient mice exhibit significant reductions of gastric spermidine levels and H. pylori-induced inflammation. Proteomic analysis revealed that cancer was the most significantly altered functional pathway in Smox-/- gastric organoids. Moreover, there was also less DNA damage and β-catenin activation in H. pylori-infected Smox-/- mice or gastric organoids, compared to infected wild-type animals or gastroids. The link between SMOX and β-catenin activation was confirmed in human gastric organoids that were treated with a novel SMOX inhibitor. These findings indicate that SMOX promotes H. pylori-induced carcinogenesis by causing inflammation, DNA damage, and activation of β-catenin signaling.

Dopamine and cAMP-regulated phosphoprotein, Mr 32000 (DARPP-32), is frequently overexpressed in earlt stages of gastric cancers. We utilized in vitro assays, 3D gastric gland organoid cultures, mouse models, and human tissue samples to investigate the biological and molecular impact of DARPP-32 on activation of IGF1R and STAT3 signaling and gastric tumorigenesis. DARPP-32 enhanced phosphorylation of IGF1R (Y1135), a step that was critical for STAT3 phosphorylation at Y705, nuclear localization, and transcription activation. By using proximity ligation and co-immunoprecipitation assays, we found that IGF1R and DARPP-32 co-existed in the same protein complex. Binding of DARPP-32 to IGF1R promoted IGF1R phosphorylation with subsequent activation of downstream SRC and STAT3. Analysis of gastric tissues from the TFF1 knockout (KO) mouse model of gastric neoplasia, demonstrated phosphorylation of STAT3 in the early stages of gastric tumorigenesis. By crossing the TFF1 KO mice with DARPP-32 (DP) knockout (KO) mice, that have normal stomach, we obtained double knockout (TFF1 KO/DP KO). The gastric mucosa from the double KO mice did not show phosphorylation of IGF1R or STAT3. In addition, the TFF1 KO/DP KO mice had significant delay in developing neoplastic gastric lesions. Analysis of human gastric cancer tissue microarrays, showed high levels of DARPP-32 and positive immunostaining for nuclear STAT3 in cancer tissues, as compared to non-cancer histologically normal tissues. In summary, the presence of a signaling axis mediated by DARPP-32–IGF1R is a critical step in gastric tumorigenesis, playing an important role in activation of STAT3.

CCL11, also known as eotaxin-1, is described as an eosinophil chemoattractant, which has been implicated in allergic and Th2 inflammatory diseases. We have reported that CCL11 is significantly increased in the serum of inflammatory bowel disease (IBD) patients, colonic eosinophils are increased and correlate with tissue CCL11 levels in ulcerative colitis patients, and CCL11 is increased in dextran sulfate sodium (DSS)-induced murine colitis. Here, we show that CCL11 is involved in the pathogenesis of DSS-induced colitis and in colon tumorigenesis in the azoxymethane (AOM)-DSS model of colitis-associated carcinogenesis (CAC). Ccl11(−/−) mice exposed to DSS then allowed to recover had significantly less body weight loss and a decrease in histologic injury versus wild-type (WT) mice. In the AOM-DSS model, Ccl11(−/−) mice exhibited decreased colonic tumor number and burden, histologic injury, and colonic eosinophil infiltration versus WT mice. Ccl11 is expressed by both colonic epithelial and lamina propria immune cells. Studies in bone marrow chimera mice revealed that hematopoietic- and epithelial-cell derived CCL11 were both important for tumorigenesis in the AOM-DSS model. These findings indicate that CCL11 is important in the regulation of colitis and associated carcinogenesis and thus anti-CCL11 antibodies may be useful for treatment and cancer chemoprevention in IBD.

Solute carrier family 7 member 2 (SLC7A2, also known as CAT2) is an inducible transporter of the semi-essential amino acid L-arginine (L-Arg), which has been implicated in wound repair. We have reported that both SLC7A2 expression and L-Arg availability are decreased in colonic tissues from inflammatory bowel disease patients and that mice lacking Slc7a2 exhibit a more severe disease course when exposed to dextran sulfate sodium (DSS) compared to wild-type (WT) mice. Here, we present evidence that SLC7A2 plays a role in modulating colon tumorigenesis in the azoxymethane(AOM)-DSS model of colitis-associated carcinogenesis (CAC). SLC7A2 was localized predominantly to colonic epithelial cells in WT mice. Utilizing the AOM-DSS model, Slc7a2–/– mice had significantly increased tumor number, burden, and risk of high-grade dysplasia versus WT mice. Tumors from Slc7a2–/– mice exhibited significantly increased levels of the proinflammatory cytokines/chemokines IL-1β, CXCL1, CXCL5, IL-3, CXCL2, CCL3, and CCL4, but decreased levels of IL-4, CXCL9, and CXCL10 compared to tumors from WT mice. This was accompanied by a shift toward pro-tumorigenic M2 macrophage activation in Slc7a2-deficient mice, as marked by increased colonic CD11b+F4/80+ARG1+ cells with no alteration in CD11b+F4/80+NOS2+ cells by flow cytometry and immunofluorescence microscopy. The shift toward M2 macrophage activation was confirmed in bone marrow-derived macrophages from Slc7a2–/– mice. In bone marrow chimeras between Slc7a2–/– and WT mice, the recipient genotype drove the CAC phenotype, suggesting the importance of epithelial SLC7A2 in abrogating neoplastic risk. These data reveal that SLC7A2 has a significant role in the protection from CAC in the setting of chronic colitis, and suggest that the decreased SLC7A2 in inflammatory bowel disease (IBD) may contribute to CAC risk. Strategies to enhance L-Arg availability by supplementing L-Arg and/or increasing L-Arg uptake could represent a therapeutic approach in IBD to reduce the substantial long-term risk of colorectal carcinoma.