IL-22BP is regulated by the inflammasome and modulates tumorigenesis in the intestine

Abstract

Chronic mucosal inflammation and tissue damage predisposes patients to the development of colorectal cancer. This association could be explained by the hypothesis that the same factors and pathways important for wound healing also promote tumorigenesis. A sensor of tissue damage should induce these factors to promote tissue repair and regulate their action to prevent development of cancer. Interleukin 22 (IL-22), a cytokine of the IL-10 superfamily, has an important role in colonic epithelial cell repair, and its levels are increased in the blood and intestine of inflammatory bowel disease patients. This cytokine can be neutralized by the soluble IL-22 receptor, known as the IL-22 binding protein (IL-22BP, also known as IL22RA2); however, the significance of endogenous IL-22BP in vivo and the pathways that regulate this receptor are unknown. Here we describe that IL-22BP has a crucial role in controlling tumorigenesis and epithelial cell proliferation in the colon. IL-22BP is highly expressed by dendritic cells in the colon in steady-state conditions. Sensing of intestinal tissue damage via the NLRP3 or NLRP6 inflammasomes led to an IL-18-dependent downregulation of IL-22BP, thereby increasing the ratio of IL-22/IL-22BP. IL-22, which is induced during intestinal tissue damage, exerted protective properties during the peak of damage, but promoted tumour development if uncontrolled during the recovery phase. Thus, the IL-22-IL-22BP axis critically regulates intestinal tissue repair and tumorigenesis in the colon.

Figure 1. Increased tumorigenesis in Il22bp^−/− mice in a colitis-associated colon cancer model

A: Time course of the tumor number and tumor score. Representative endoscopic view of the mouse colon at the indicated time points (B), macroscopic view and histology on day 80 (bars= 2000µm) (C). Results are cumulative from two independent experiments. D: Frequency of Ki67+ cells in tumors from wild type and Il22bp^−/− mice and representative histology are shown (bars= 200µm). Ki67-expression was analyzed in a total number of 48 KO and 28 WT tumors. Each dot represents one mouse; bars= mean +/− sem.

Figure 2. Inverse Expression of Il22bp and Il22 during chemical and mechanical intestinal tissue damage

A: Weight loss during DSS-colitis (2.5% for 5 days; mean +/− sem; n=11), and histology (bars= 500µm). B: Il22bp and Il22 mRNA (normalized to Hprt) in total colon (mean +/− sem of triplicates). C+D: Il22bp and Il22 mRNA after mechanical wounding (mean +/− sem; n=4). E: Number of BrdU-positive cells per crypt during DSS-colitis and BrdU immunohistochemistry on day 14 (bars= 200µm). Each dot represents one animal. Lines indicate mean +/− sem. Results are representative of at least 3 experiments.

Figure 3. IL-22BP controls tumorigenesis in APC^min/+ mice

Il22bp^−/− and Il22^−/− mice were crossed with Apc^min/+ mice. 6 months old mice were analyzed. Tumor number and size were measured using a dissecting microscope (size 1: < 2mm, size 2: 2–5 mm, size 3: > 5mm). Each dot present one mouse, lines indicate mean +/− sem. All mice displayed are Apc^min/+. No tumors were observed in Apc^+/+ mice regardless of the Il22 and Il22bp genotype.

Figure 4. IL-18 regulates Il22bp expression by CD11c+ cells

A–D: Il22bp expression in the colon. A: EC: epithelial cells, IEL, LPL: intraepithelial and lamina propria lymphocytes; mean of triplicates. B: Analysis of bone marrow chimeras (n=8). C: Isolation of CD11c+ cells; mean of duplicates. D: During wounding of WT and Myd88^−/−Trif^−/− mice (n=3). E: Il22bp expression (re-biopsy relative to initial biopsy; Abx: antibiotic treated WT mice). F+G: IL-22BP expression in cultured human monocyte-derived DC (n=8). (F:10ng/ml IL-18, variable time; G:24h, variable IL-18 concentration). Results are representative of two independent experiments (A–D, F, G), cumulative from 7 experiments (E). Mean+/−sem.