Palmitoylation induced activation of SMAD3 exacerbates colitis by promoting TRM cells differentiation

Tissue-resident memory T cells (TRM cells) have been shown to play an instrumental role in driving the onset and relapse of inflammatory bowel diseases (IBD). However, the underlying mechanism of TRM cells differentiation and its regulation in intestines remain to be unveiled. Mothers against decapentaplegic homolog 3 (SMAD3) is translocated from nucleus to membrane and activated in response to transforming growth factor beta (TGF-β), which is a key cytokine in the process of TRM cells polarization. Cysteine palmitoylation (S-palmitoylation) is a post-translational modification catalyzed by the DHHC family, regulating protein membrane associations. Genes associated with the classic SMAD3 signaling pathway, along with most genes in the DHHC family, were upregulated in TRM cells. Our study demonstrated that SMAD3 underwent reversible S-palmitoylation on Cys31 by DHHC6, leading to SMAD3 endomembrane recruitment and its subsequent colocalization with TGF-β receptor I (TGF-βRI) under TRM polarization conditions. The membrane recruitment of SMAD3 activated SMAD3 and subsequently upregulated the expression of its target genes, inducing the differentiation of TRM cells. In contrast, perturbation in DHHC6-induced palmitoylation with MYD-4 inhibited TRM cells differentiation and alleviated colitisin IBD model mice. Our work provides an example how the immune responses are regulated through the S-palmitoylation-dependent SMAD3 signaling in TRM cells differentiation and reveals protein S-palmitoylation as a potential target in IBD treatment, which could be of greater application considering the wide involvement of protein S-palmitoylation in the signal transduction in mammalian cells.