IL-17 SIGNALING REDUCES GASTRIC CARCINOGENESIS BY ALTERING FUNCTION OF THE HELICOBACTER CAG TYPE 4 SECRETION SYSTEM AND SUPPRESSING LRIG1 ACTIVATION

Helicobacter pylori is the strongest risk factor for gastric cancer; however, only a minority of infected individuals develop disease. One microbial cancer-linked locus is the cag type 4 secretion system (cagT4SS), which translocates the oncoprotein CagA into host cells. In addition, T lymphocyte activation, production of IL-17, and binding of IL-17 to its receptor IL-17RA alters disease risk. Finally, aberrant stem cell activation is linked to carcinogenesis, and Leucine-rich repeats and immunoglobulin-like domains 1 (Lrig1) is a marker for a population of progenitor cells with premalignant potential in the stomach. We previously reported that H. pylori significantly increased 1) levels of inflammation and 2) Lrig1⁺ cell proliferation in Il17ra^-/- versus wild-type (WT) mice. Based on these data, we hypothesized that changes in inflammation in Il17ra^-/- mice may drive in vivo adaptations of the cagT4SS that are important for disease. To address this, we infected Il17ra^-/- or WT mice with the cag⁺ H. pylori strain PMSS1, sacrificed mice 8- and 12-weeks post-challenge, and analyzed in vivo-adapted strains. There were no differences in colonization; however, H. pylori significantly increased levels of chronic inflammation in Il17ra^-/- vs. WT mice (p<0.01, mean score 2.7 vs. 1.4 at 8 weeks; p<0.001, mean score 3.6 vs. 1.9 at 12 weeks; Il17ra^-/- vs. WT, respectively). We then co-cultured in vivo-adapted strains with gastric epithelial cells and determined that 100% of output strains isolated from Il17ra^-/- mice retained the ability to translocate CagA, compared to 67% of WT output strains following 8 weeks of infection. Output strains from Il17ra^-/- mice also translocated significantly more CagA as determined by tyrosine phosphorylation than strains from WT mice (p<0.0006, 9018 vs. 4154 relative units (RU); Il17ra^-/- vs. WT, respectively). When the analysis was restricted to the subset of strains with a functional cagT4SS, strains isolated from Il17ra^-/- mice translocated significantly more CagA than strains isolated from WT mice (p<0.0002, 9319 vs. 4154 RU; Il17ra^-/- vs. WT mice, respectively). At 12 weeks, only 22% of strains isolated from WT mice retained the ability to translocate CagA, compared to 100% of output strains from Il17ra^-/- mice. Strains isolated from Il17ra^-/- mice translocated significantly more CagA than those from WT mice (P<0.0065, 6418 vs. 2246 RU; Il-17ra^-/- vs. WT, respectively). Finally, H. pylori-infected Il17ra^-/- mice harbored significantly higher numbers of proliferative Lrig1⁺ cells compared to infected WT mice at 12 weeks (p<0.0001, 4-fold vs. 2-fold over uninfected; Il17ra^-/- vs. WT, respectively). Collectively these data indicate that IL-17 signaling may exert a suppressive effect on H. pylori-induced pathogenesis via specifically altering infecting H. pylori strains and reducing stem cell proliferation.