The transcriptional regulator Sin3A balances IL-17A and Foxp3 expression in primary CD4 T cells

The Sin3 transcriptional regulator homolog A (Sin3A) is the core member of a multi-protein chromatin-modifying complex known to control gene transcription via epigenetic mechanisms. Its inactivation in developing thymocytes halts T cell maturation. We and others had previously shown that Sin3A controls STAT3 transcriptional activity. Given the role of STAT3 in the differentiation of T helper 17 cells critical in inflammatory disorders and against opportunistic infections, we asked whether Sin3A could also contribute to their differentiation. To this aim, we exploited CD4-Cre and CD4-CreER T2 deleter strains for conditional and inducible Sin3A deletion in CD4 cell subsets. We report that Sin3A inactivation in vivo arrested thymocyte development at the double positive stage, hindering the characterization of mature T cells. At difference, tamoxifen-inducible Sin3A deletion proved permissive for in vitro proliferation of T cells in Th17 skewing conditions and the acquisition of memory markers. Transcriptional profiling indicated that while Sin3A inactivation imprinted T cells with a mTORC1 signaling gene signature, Sin3A deficient cells lacked the expression of IL-17A, the signature Th17 cytokine. This reflected a defective induction of Il17a , and also of the Il23R and Il22 genes, which occurred in spite of proper upregulation of the lineage defining transcription factor RORγt. We found that Sin3A inactivation was paralleled by increased STAT3 phosphorylation and nuclear representation, and by higher fractions of IL-2 and FoxP3 expressing cells. Such events proved causally linked as inhibiting Foxp3 partially rescued IL-17A expression, and neutralizing IL-2 simultaneously lowered the representation of FoxP3 + cells, while rescuing IL- 17A + ones. Thus, together our data underline a previously unappreciated role for Sin3A in Th17 differentiation and the shaping of their immunoregulatory potential. Statement This study identifies a new role for the transcriptional regulator Sin3A in the shaping of Th17 cell differentiation. Data indicate that by controlling IL-2 expression, and mTORC1 signaling, it balances IL-17A and Foxp3 levels, shaping Th17 inflammatory potentials.