Effects of growth arrest and DNA damage-inducible protein 34 (GADD34) on inflammation-induced colon cancer in mice

Background: Growth arrest and DNA damage-inducible protein 34 (GADD34/Ppp1r15a) is a family of GADD proteins that are induced by DNA damage. GADD34 protein has been suggested to regulate inflammation or host defense systems. However, the in vivo function of GADD34 in inflammation is still unclear. Long lasting inflammation, such as that seen in Crohn's disease and ulcerative colitis, is associated with a higher incidence of colorectal cancer (CRC). Methods: Using a colitis-associated cancer model, we analysed GADD34-deficient (KO) mice to study the effect of GADD34 on colitis and colorectal tumorigenesis. Results: We found a higher incidence of CRC in wild-type (WT) mice than in GADD34KO mice. Moreover, dextran sodium sulfate (DSS)-induced inflammatory responses were downregulated by GADD34 deficiency. The expression of pro-inflammatory mediators such as TNF alpha, IL-6, and iNOS/NOS2 was higher in the colons of WT mice than GADD34KO mice. IL-6 is known to activate STAT3 signalling in colonic epithelial cells and subsequently induced epithelial proliferation. We found that IL-6-STAT3 signalling and epithelial proliferation were higher in WT mice compared with GADD34KO mice. Conclusions: These results indicated that GADD34 upregulated pro-inflammatory mediator production leading to a higher tumour burden following azoxymethane (AOM)/DSS treatment.