T helper 17 (TH17) cells are critically involved in host defence, inflammation, and autoimmunity1,2,3,4,5. Transforming growth factor β (TGFβ) is instrumental in TH17 cell differentiation by cooperating with interleukin-6 (refs 6, 7). Yet, the mechanism by which TGFβ enables TH17 cell differentiation remains elusive. Here we reveal that TGFβ enables TH17 cell differentiation by reversing SKI–SMAD4-mediated suppression of the expression of the retinoic acid receptor (RAR)-related orphan receptor γt (RORγt). We found that, unlike wild-type T cells, SMAD4-deficient T cells differentiate into TH17 cells in the absence of TGFβ signalling in a RORγt-dependent manner. Ectopic SMAD4 expression suppresses RORγt expression and TH17 cell differentiation of SMAD4-deficient T cells. However, TGFβ neutralizes SMAD4-mediated suppression without affecting SMAD4 binding to the Rorc locus. Proteomic analysis revealed that SMAD4 interacts with SKI, a transcriptional repressor that is degraded upon TGFβ stimulation. SKI controls histone acetylation and deacetylation of the Rorc locus and TH17 cell differentiation via SMAD4: ectopic SKI expression inhibits H3K9 acetylation of the Rorc locus, Rorc expression, and TH17 cell differentiation in a SMAD4-dependent manner. Therefore, TGFβ-induced disruption of SKI reverses SKI–SMAD4-mediated suppression of RORγt to enable TH17 cell differentiation. This study reveals a critical mechanism by which TGFβ controls TH17 cell differentiation and uncovers the SKI–SMAD4 axis as a potential therapeutic target for treating TH17-related diseases.
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Gene Expression Omnibus
We thank E. Robertson and E. Bikoff for Smad4fl/fl mice, H. Moses for Tgfbr2fl/fl mice, D. Littman for Rorc−/− mice, F. Zhang for Cre-dependent Cas9 knock-in mice, N. Fisher for cell sorting, W. Chen and D. Zhang for discussion, and J. Massagué for the suggestion on SMAD4 ChIP–seq analysis. This study was supported by the National Natural Science Foundation of China (81402549, LJQ2015033) (G.Z.), the National Institutes of Health (NIH) (AI029564) and the National Multiple Sclerosis Society (CA10068) (J.P.Y.T.), the Intramural Research Program of the National Institute of Environmental Health Science (ES101965 to P.A.W. and ES102025 to D.N.C.), and by the NIH (AI097392; AI123193), the National Multiple Sclerosis Society (RG4654), and a Yang Family Biomedical Scholars Award (Y.Y.W.).
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Cellular & Molecular Immunology (2018)