SMAD2 S-palmitoylation promotes its linker region phosphorylation and TH17 cell differentiation in a mouse model of multiple sclerosis

Abstract

The transcriptional regulators SMAD2 and SMAD3 share the same primary signaling pathway in response to the cytokine TGFβ. However, whereas SMAD2 stimulates the differentiation of naive CD4⁺ T cells into proinflammatory T helper 17 cells (T_H17 cells), SMAD3 stimulates the differentiation of anti-inflammatory regulatory T cells (T_reg cells). Here, we report a dynamic SMAD2-specific posttranslational modification important for T_H17 cell differentiation. SMAD2, but not SMAD3, was reversibly S-palmitoylated at cysteine-41 and cysteine-81 by the palmitoyltransferase DHHC7 and depalmitoylated by the acyl protein thioesterase APT2. As a result, SMAD2 was recruited to intracellular membranes where its linker region was phosphorylated, leading to its interaction with the transcriptional regulator STAT3. Nuclear translocation of the SMAD2-STAT3 complex induced the expression of their target genes that promoted T_H17 cell differentiation. Perturbation of SMAD2-STAT3 binding by inhibiting the palmitoylation-depalmitoylation cycle suppressed T_H17 cell differentiation and reduced disease severity in mice with experimental autoimmune encephalomyelitis, a model of multiple sclerosis (MS). Thus, the S-palmitoylation–depalmitoylation cycle mediated by DHHC7 and APT2 specifically regulates SMAD2, providing insights into the functional differences between SMAD2 and SMAD3 and the distinct role of SMAD2 in T_H17 cell differentiation. The findings further highlight DHHC7 and APT2 as potential therapeutic targets for the treatment of T_H17 cell–mediated inflammatory diseases, including MS.