Acetylation as a novel post-translational modification of MafA

PROJECT SUMMARY/ABSTRACT β-cell dysfunction is one of the hallmark determinants of Type II Diabetes (T2D) which is characterized by impaired insulin secretion and subsequent hyperglycemia. Identifying mechanisms to preserve and enhance β-cell function is therefore crucial to ameliorate T2D pathogenesis. Data from knockout animals has established that the MAF bZIP transcription factor A (MafA) is a critical regulator of β-cell functional capacity to adapt to insulin resistance. MafA directly activates insulin transcription, but also regulates a wide array of genes necessary for glucose sensing and insulin secretion. Commensurately, MafA is downregulated in islets of people and mice with T2D. Preserving MafA expression in islets from diabetic animals restores proper glucose regulation, suggesting that finding mechanisms to protect and enhance MafA expression may mitigate βcell dysfunction in T2D. MafA binds lysine acetyltransferases, Kat2b and CBP, leading to increased transactivation of MafA target genes, but the underlying mechanism is not known. Testing the hypothesis that Kat2b/CBP may acetylate MafA , I performed a LC/MS-MS screen that revealed MafA acetylation at lysines 32, 33 and 255. Based on this result, I mutated these lysines to glutamine (3KQ) and arginine (3KR) to mimic constitutively acetylated and deacetylated MafA, respectively. Using these mimetics, I found that 3KQ MafA has significantly increased transactivation ability at the insulin promoter. As a first step to understanding mechanism of this increased transactivation ability, I observed that MafA acetylation prompts hyperphosphorylation at serine 14 and competes with SUMOylation at lysine 32. These data suggest a novel form of PTM crosstalk between MafA acetylation, phosphorylation and SUMOylation. In Aim 1, I use my recently generated 3KQ and 3KR knock-in mice, and human beta cell lines, to determine whether MafA acetylation may affect GSIS and improve the β-cell response to obesity-induced insulin resistance. In Aim 2, I explore the complex relationship between MafA PTMs, and test whether acetylation- induced hyperphosphorylation is necessary for activity (Aim 2a) and whether a SUMOylation-acetylation switch occurs in response to rising glucose levels (Aim 2b).