Interleukin 1 Upregulates MicroRNA 135b to Promote Inflammation-associated Gastric Carcinogenesis in Mice.

BACKGROUND & AIMS: Gastritis is associated with development of stomach cancer, but little is known about changes in microRNA expression patterns during gastric inflammation. Specific changes in gene expression in epithelial cells are difficult to monitor due to the heterogeneity of the tissue. We investigated epithelial cell-specific changes in microRNA expression during gastric inflammation and gastritis-associated carcinogenesis in mice.

METHODS: We used laser microdissection to enrich epithelial cells from K19-C2mE transgenic mice, which spontaneously develop gastritis-associated hyperplasia, and Gan mice, which express activated prostaglandin E2 and Wnt in the gastric mucosa and develop gastric tumors. We measured expression of epithelial cell-enriched microRNAs and used bioinformatics analyses to integrate data from different systems to identify inflammation-associated microRNAs. We validated our findings in gastric tissues from mice, and evaluated protein functions in gastric cell lines (SNU-719, SNU-601, SNU-638, AGS, and GIF-14) and knockout mice. Organoids were cultured from gastric corpus tissues of wild type and miR-135b knockout C57BL/6 mice. We measured levels of microRNAs in pairs of gastric tumors and non-tumor mucosa from 28 patients in Japan.

RESULTS: We found microRNA 135b (MIR135B) to be the most over-expressed microRNA in gastric tissues from K19-C2mE and Gan mice-levels increased during early stages of gastritis-associated carcinogenesis. Levels of MIR135B were also increased in gastric tumor tissues from gp130F/F mice and patients, compared with non-tumor tissues. In gastric organoids and immortalized cell lines, expression of MIR135B was induced by interleukin 1 (IL1) signaling. K19-C2mE mice with disruption of Mir135b developed hyperplastic lesions that were 50% smaller than mice without Mir135b disruption, and had significant reductions in cell proliferation. Expression of MIR135B in gastric cancer cell lines increased their colony formation, migration, and sphere formation. We identified FOXN3 and RECK mRNAs as targets of MIR135B; their knockdown reduced migration of gastric cancer cell lines. Levels of FOXN3 and RECK mRNAs correlated inversely with levels of MIR135B in human gastric tumors and in inflamed mucosa from K19-C2mE mice.

CONCLUSIONS: We found expression of MIR135B to be upregulated by IL1 signaling in gastric cancer cells and organoids. MIR135B promotes invasiveness and stem-cell features of gastric cancer cells in culture by reducing FOXN3 and RECK mRNAs. Levels of these mRNA targets, which encode tumor suppressor, are reduced in human gastric tumors.