Tripartite motif-containing 33 (Trim33) determines the pathogenic function of Th17 cells

We report that Tripartite motif-containing 33 (Trim33), a protein that was previously associated with TGF-beta signaling, determines the pathogenic function of Th17 cells. Trim33 deficiency in T cells resulted in resistance to an autoimmune disease model. Lack of Trim33 did not impact TGF-beta signaling in mediating Foxp3 gene expression but greatly reduced TGF-beta induction of IL-17 production during Th17 cell differentiation. Importantly, we found TGF-beta not only increased IL-17 but also suppressed IL-10 expression; absence of Trim33 or Smad2 but not Smad4 in T cells enhanced IL-10 expression. In a Smad2-dependent manner, Trim33 was recruited to Il17 and Il10 gene loci and was crucial in appropriate histone modification accompanying Th17 differentiation. Our study thus demonstrates that Trim33, a non-canonical branch of TGF-beta signaling, programs the pro-inflammatory function of Th17 differentiation by promoting IL-17 and suppressing IL-10 expression. As a critical switch of pathogenic versus regulatory phenotype of T cells, Trim33 may be targeted in treating human autoimmune diseases. WT and Trim33 KO CD4+ T cells were cultured under Th17-skewing condition. Comparison was made based on these two types of Th17 cells.