290-OR: Acetylation Induces a SUMOylation–Phosphorylation Switch to Enhance MafA Transactivation

MAF bZIP transcription factor A (MafA) transactivates multiple genes involved in β-cell maturity function. MafA transactivation is increased by recruitment and binding of multiple lysine acetyltransferases, Kat2b and CBP, but mechanisms underlying this phenomenon are unclear. We performed a LC-MS/MS screen and validation experiments that revealed that Kat2b and CBP increased MafA acetylation at lysines (K) 32, 33 and 255. To understand functional consequences of MafA acetylation, we mutated all three to glutamine (3KQ) or arginine (3KR) to mimic constitutively acetylated and deacetylated MafA, respectively, and performed luciferase assays with these mimetics that showed increased transactivation ability at the insulin promoter by 3KQ, independent of stability, DNA binding or MafA localization. Intriguingly, 3KQ MafA also showed retarded mobility on SDS-PAGE, suggesting that acetylation induced another post-translational modification (PTM). In a second LC-MS/MS screen followed by alanine scanning, we identified that acetylation increased MafA phosphorylation at serine (S) 14. Thus, S14A mutation attenuated the effects of acetylation. Simultaneously, MafA acetylation at K32 prevents SUMOylation at the same site; thus, inhibition of SUMOylation increased MafA acetylation and activity. Overall, our findings suggest that acetylation induces a novel PTM switch in MafA - enhancing S14 phosphorylation and blocking K32 SUMOylation, to potentiate transactivation at target promoters.