196

AHR

bHLHe76;aryl hydrocarbon receptor;AHR;aryl hydrocarbon receptor

AH-receptor|ah receptor|aromatic hydrocarbon receptor|class E basic helix-loop-helix protein 76

7p15

protein-coding

The aryl hydrocarbon receptor (AhR) plays a suppressive role in cecal carcinogenesis by CUL4B/AhR-mediated ubiquitylation and degradation of beta-catenin, which is activated by xenobiotics and natural ligands. AhR-deficient (AhR(-)(/-)) mice develop cecal tumors with severe inflammation. To elucidate whether the tumors develop autonomously in AhR(-/-) mice due to impaired beta-catenin degradation or in association with accelerated inflammation, we performed two kinds of experiments using germ-free (GF) AhR(-/-) mice and compound mutant mice lacking genes for AhR and apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), which plays an essential role in caspase-1 activation in inflammasomes. Both GF AhR(-/-) and AhR(-/-)*ASC(-/-) mice showed considerably reduced tumor development compared with that in AhR(-/-) mice albeit in a cancer-prone state with aberrant beta-catenin accumulation. Blocking of the interleukin (IL)-1beta signaling pathway by treatment with a caspase-1 inhibitor, YVAD, reduced cecal tumorigenesis in AhR(-/-) mice. Signal transducers and activators of transcription 3 (STAT3) activation was detected in the cecal epithelium of the AhR(-/-) mice due to enhanced IL-6 production. An inhibitor of the STAT3 signaling pathway, AG490 suppressed the tumor formation. ASC-mediated inflammation was also found to play a critical role in tumor development in Apc(Min/+) mice, a mouse model of familial adenomatous polyposis. Collectively, these results revealed an important role of the bacteria-triggered or ASC-mediated inflammation signaling pathway in the intestinal tumorigenesis of mice and suggest a possible chemical therapeutic intervention, including AhR ligands and inhibitors of the inflammation pathway.