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

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. M any studies point to a correlation between the development of type 1 diabetes (T1D) 3 and decreased Th2 responses (1– 4). Poor IL-4 production may contribute to the disease process by limiting protective Th2 responses (5), restricting the activation of nonpathogenic T cells (6), and reducing B7.2 expression on dendritic cells that would otherwise curb islet-specific CTL maturation (7). Although reduced IL-4 production is a well-established observation in T1D, the mechanisms contributing to its dysregulation are not clear. Cellular muscular aponeurotic fibrosarcoma (c-Maf) is a lin-eage-specific transcription factor that promotes Th2 cell development through direct transactivation of the IL-4 gene (8). An association between T1D and abnormal c-Maf function is suggested by previous studies performed with c-Maf transgenic, nonobese diabetic (NOD) mice where constitutive overexpression of c-Maf in T cells did not effectively increase IL-4 production nor protect NOD mice from T1D (9). These results were unique to NOD mice, because transgenic c-Maf production significantly increased T cell IL-4 production and reduced T1D onset in other transgenic, adop-tive transfer, and virally inducible mouse models of T1D on B10.D2 genetic backgrounds (9). Abnormal c-Maf function in NOD mice is further suggested by an inability to detect c-Maf binding to the IL-4 promoter (IL-4p) in Tc2 cells (10). Together, these existing data suggest a link between poor IL-4 production and the failure of c-Maf to bind the IL-4p in T cells …