TGF-beta-independent function of SMAD4 preconditions naïve CD8 T-cells to prevent severe microbiota-driven chronic intestinal inflammation [ChIPseq]

SMAD4, a key mediator of TGF-beta signaling, plays a crucial role in T cells to prevent chronic intestinal inflammation through unknown mechanisms. We reveal that SMAD4 in CD8 T cells prevents chronic intestinal inflammation primarily in a TGF-beta-independent manner. Mechanistically, SMAD4, in CD8 T cells, acts as a basal and tonic repressor of TGF-beta-target genes at the transcriptional and epigenetic level, prior to any TGF-beta signal. SMAD4 deletion affects aberrantly a wide range of TGF-beta-target genes, thereby promoting accumulation and epithelial retention of CD8.alpha.beta T cells inversely to total TGF-beta signaling disruption. Moreover, SMAD4 deletion unleashes the expression of TGF-beta-signaling-repressors and hampers TGF-ß-mediated CD8 T cell immunosuppression, eliciting their chronic activation. Hence, in a feedforward mechanism, SMAD4 both blocks the TGF-beta signature in CD8 T cells and pre-sensitizes them to TGF-beta. Overall design: We used the CD4-CRE conditional deletion system to establish several mouse strains lacking one or several TGF-ß signaling pathways. We established mice with a deletion of SMAD4 (SKO), TGF-beta RII (R2KO), and double deletion of TGF-beta RII and SMAD4 (R2SKO) in T cells. We next performed SMAD4 ChIPseq of CD8 T cells from WT, SKO and R2KO mice. In order to rule out any potential side effects of the inflammatory environment, we used F5 transgenic CD8 T cells in a RAG2KO background, because these mice do not develop any inflammation.