No abstract

As a key signaling molecule in the cytokine-mediated transcriptional activation STATs are shown to undergo PTMs including phosphorylation, acetylation, methylation, ubiquitination and SUMOylation. The SUMO-modification of STAT1 has been implicated in the regulation of protein stability, nuclear translocation, and transcriptional activation, probably through the reduction of the formation and life-span of the active dimer. As a part of regulation of IL-4 signaling mechanism, we have investigated the role of SUMOylation on STAT6 activation. We have identified potential SUMOylation sites on STAT6 by SUMOplot prediction program analysis and observed the IL-4-induced SUMOlyation of STAT6 in HeLa cells. The introduction of mutation at a potential SUMO site K636 and transfection of shRNA of SUMO-conjugating enzyme UBC9 resulted in the inhibition of tyrosine phosphorylation at Y641 induced by IL-4. The results indicate that endogenous SUMOylation reaction of STAT6 is critical for IL-4-induced STAT6 phosphorylation. Conversely, the forced expression of SUMO-1 and STAT6 caused cytosolic relocalization of both STAT6 and phospho-STAT6 induced by IL-4 as demonstrated by Western blot and confocal analysis. Our data suggest that SUMO-modification of STAT6 may play dual roles in the regulation of phosphorylation and nuclear translocation of STAT6 during IL-4 signal transduction.