Lack of NFATc1 SUMOylation protects from inflammatory diseases

Post-translational modification with SUMO is known to regulate the activity of transcription factors, but how SUMOylation of individual proteins might influence immunity is mostly unexplored. NFATc1 is a transcription factor of the family of ‘Nuclear Factors of Activated T-cells’ which plays an essential role in antigen receptor-mediated gene regulation. It is expressed in multiple isoforms of which the longer isoforms can be modified by SUMOylation. SUMO modification of NFATc1 represses IL-2 in vitro, but its role in T cell-mediated immune responses in vivo is not clear. To this end, we generated a novel Nfatc1 transgenic mouse with lysine to arginine mutations, which abolish the SUMO modification within NFATc1’s C-terminal domain. Inhibition of NFATc1 SUMOylation ameliorated experimental autoimmune encephalomyelitis as well as graft-versus-host disease. This was due to elevated IL-2 production that promoted Treg expansion and suppressed autoreactive or alloreactive T cells. Mechanistically, increased IL-2 secretion counteracted IL-17 and IFN-γ expression through STAT5 and Blimp-1 induction. Blimp-1 also repressed IL-2 itself and the as well induced survival factor Bcl2A1. Still, lack of NFATc1 sumoylation fine-tunes T-cell responses towards lasting tolerance implying a novel approach to treat inflammatory diseases.