Apoptosis signal-regulating kinase 1 regulates colitis and colitis-associated tumorigenesis by the innate immune responses.

BACKGROUND & AIMS: Mitogen-activated protein kinase (MAPK) signaling pathways regulate multiple cellular functions and are implicated in the pathogenesis of inflammatory bowel disease and colitis-associated cancer (CAC). Apoptosis signal-regulating kinase 1 (ASK1) is a MAPK kinase kinase; little is known about the role of ASK1 in colonic disease. We assessed the involvement of ASK1 in the development of intestinal inflammation and CAC.

METHODS: Dextran sodium sulfate (DSS) or Citrobacter rodentium was used to induce colitis in wild-type (WT) and ASK1 knock-out (ASK1(-/-)) mice; CAC was induced by azoxymethane injection followed by repeated intake of DSS by the mice. Primary macrophages were isolated from WT and ASK1(-/-) mice and used to investigate the involvement of ASK1 in innate immune responses. Bone marrow chimeric mice were used to study the contribution of myeloid cells to colitis activity.

RESULTS: ASK1 deficiency increased susceptibility to colonic inflammation in both models of colitis. In vitro, ASK1(-/-) macrophages were impaired in their ability to kill bacteria and had increased susceptibility to bacterial-induced apoptosis, because p38 was inactivated. Expression of antiapoptotic genes was greatly reduced in ASK1(-/-) macrophages. WT mice given transplants of ASK1(-/-) mouse-derived bone marrow cells developed more severe DSS-induced colitis than mice with WT-derived bone marrow cells. In the CAC model, ASK1(-/-) mice developed more numerous and larger tumors than WT mice through increased colonic inflammation.

CONCLUSIONS: ASK1 controls the development of intestinal inflammation and CAC through the regulation of innate immunity.