SUMO Conjugation Contributes to Immune Deviation in Nonobese Diabetic Mice by Suppressing c-Maf Transactivation of IL-4

Abstract

It is not clear why the development of protective Th2 cells is poor in type 1 diabetes (T1D). c-Maf transactivates the IL-4 gene promoting Th2 cell development; therefore, abnormalities in c-Maf may contribute to reduced IL-4 production by CD4 cells from nonobese diabetic (NOD) mice. In this study we demonstrate that despite normal expression, c-Maf binds poorly to the IL-4 promoter (IL-4p) in NOD CD4 cells. Immunoblotting demonstrates that c-Maf can be modified at lysine 33 by SUMO-1 (small ubiquitin-like modifier 1). Sumoylation is facilitated by direct interaction with the E2-conjugating enzyme Ubc9 and increases following T cell stimulation. In transfected cells, sumoylation decreases c-Maf transactivation of IL-4p-driven luciferase reporter activity, reduces c-Maf binding to the IL-4p in chromatin immunoprecipitation assays, and enhances c-Maf localization into promyelocytic leukemia nuclear bodies. Sumoylation of c-Maf is increased in NOD CD4 cells as compared with CD4 cells from diabetes-resistant B10.D2 mice, suggesting that increased c-Maf sumoylation contributes to immune deviation in T1D by reducing c-Maf access to and transactivation of the IL-4 gene.

Ubiquitination of the transcription factor c-MAF is mediated by multiple lysine residues

“…MafA and MafB, two large Maf proteins, can be phosphorylated by P38 MAP kinase (Sii-Felice et al, 2005). Sumoylation of c-MAF is proposed to negatively regulate its transcriptional activity, such as mediating IL-4 expression (Leavenworth et al, 2009). MafA was reported to be ubiquitinated (Harmon et al, 2005).…”

“…Phosphorylation and SUMOylation regulate c-MAF function (Rocques et al, 2007;Leavenworth et al, 2009), whereas ubiquitination leads to c-MAF degradation in the proteasome (Mao et al, 2007). Ubiquitination typically occurs at one or more among various functionally redundant lysine residues in target proteins.…”

“…As a transcription factor, c-MAF function can be modified by several important chemical modifications, including phosphorylation (Rocques et al, 2007), SUMOylation (Leavenworth et al, 2009), and ubiquitination (Mao et al, 2007). Phosphorylation and SUMOylation regulate c-MAF function (Rocques et al, 2007;Leavenworth et al, 2009), whereas ubiquitination leads to c-MAF degradation in the proteasome (Mao et al, 2007).…”

The ubiquitin ligase HERC4 mediates c-Maf ubiquitination and delays the growth of multiple myeloma xenografts in nude mice

“…Post-translational modifications such as SUMOylation, phosphorylation, and ubiquitination are key methods to regulating the biological activity of c-Maf-for example, SUMOylation on c-Maf can negatively modulate its effects on IL-4 transcription, 24,25 whereas phosphorylation increases c-Maf-transforming activity in embryonic mouse cells 26 and enhances IL-4. 27 In MM cells, both c-Maf and MafB can be phosphorylated by the Ser/Thr kinase GSK3, thus increasing MM cell proliferation and colony formation.…”

Tyrosine Phosphorylation of c-Maf Enhances the Expression of IL-4 Gene

“…We and others have shown that SUMOylation of c-Maf attenuates its IL-4 transcriptional activity (4,5). The transforming activity of MafA, a member of the large Maf family, is dependent on its serine/threonine phosphorylation status (6).…”