TRAF5 Deficiency Ameliorates the Severity of Dextran Sulfate Sodium Colitis by Decreasing TRAF2 Expression in Nonhematopoietic Cells

TNFR-associated factor 5 (TRAF5) is a cytosolic adaptor protein and functions as an inflammatory regulator. However, the in vivo function of TRAF5 remains unclear, and how TRAF5 controls inflammatory responses in the intestine is not well understood. In this study, we found that intestinal epithelial cells from Traf5^2/2 mice expressed a significantly lower level of NF-kB–regulated proinflammatory genes, such as Tnf, Il6, and Cxcl1, as early as day 3 after dextran sulfate sodium (DSS) exposure when compared with wild-type mice. The intestinal barrier integrity of DSS-treated Traf5^2/2 mice remained intact at this early time point, and Traf5^2/2 mice showed decreased body weight loss and longer colon length at later time points. Surprisingly, the protein level of TRAF2, but not TRAF3, was reduced in colon tissues of Traf5^2/2 mice after DSS, indicating the requirement of TRAF5 for TRAF2 protein stability in the inflamed colon. Experiments with bone marrow chimeras confirmed that TRAF5 deficiency in nonhematopoietic cells caused the attenuated colitis. Our in vitro experiments demonstrated that proinflammatory cytokines significantly promoted the degradation of TRAF2 protein in Traf5^2/2 nonhematopoietic cells in a proteasome-dependent manner.