| Summary: | 博士 === 國立臺灣大學 === 免疫學研究所 === 98 === The function of transcription factor is tightly regulated by controlling their synthesis, activity and degradation. SUMOylation modulates target protein activity on post-translational level. c-Maf, the cellular homologue of v-Maf, is a basic-leucine zipper protein and belongs to the large Maf family. In helper T cells, c-Maf is the specific transcription factor of the IL-4 and IL-21 genes in type 2 T helper (Th2) and type 17 T helper (Th17) cells, respectively. In our study, we performed the yeast two-hybrid assay to identify the c-Maf interacting proteins. We found that c-Maf can interact with Ubc9 and PIAS1, the key enzymes of SUMOylation system. In T cells, c-Maf interacts with PIAS1 in primary T cells and also co-localizes with these two SUMO ligases in the nucleus. We also demonstrated that c-Maf can be SUMOylated in vitro and also in vivo. We identified the c-Maf SUMO acceptor site(s) by mutated the putative conjugating lysine residues. We demonstrated that N-terminal lysine-33 within the activation domain is the SUMO acceptor site for c-Maf. SUMO modification attenuates Wt-c-Maf transcriptional activity. Conversely, c-Maf SUMO deficient mutant is more potent to drive IL-4 production in Th2 cells. Furthermore, we showed that c-Maf, but not other transcription factor, transactivates IL-21 gene expression. SUMOylation also affects c-Maf dependent IL-21 production. In addition, SUMO deficient c-Maf does not alter the localization and the protein stability, but further enhances its recruitment to the Il4-promoter. We conclude that post-translational lysine-33 SUMOylation is critical for c-Maf activity in helper T cells.
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