Arkadia-SKI/SnoN signaling differentially regulates TGF-ß-induced iTreg and Th17 cell differentiation.

TGF-ß signaling is fundamental for both Th17 and regulatory T (Treg) cell differentiation. However, these cells differ in requirements for downstream signaling components, such as SMAD effectors. To further characterize mechanisms that distinguish TGF-ß signaling requirements for Th17 and Treg cell differentiation, we investigated the role of Arkadia (RNF111), an E3 ubiquitin ligase that mediates TGF-ß signaling during development. Inactivation of Arkadia in CD4+ T cells resulted in impaired Treg cell differentiation in vitro and loss of RORγt+FOXP3+ iTreg cells in the intestinal lamina propria, which increased susceptibility to microbiota-induced mucosal inflammation. In contrast, Arkadia was dispensable for Th17 cell responses. Furthermore, genetic ablation of two Arkadia substrates, the transcriptional corepressors SKI and SnoN, rescued Arkadia-deficient iTreg cell differentiation both in vitro and in vivo. These results reveal distinct TGF-ß signaling modules governing Th17 and iTreg cell differentiation programs that could be targeted to selectively modulate T cell functions.