2026 Theses Doctoral

Acetylation as a Novel Post-Translational Modification of MafA

Chirikjian, Margot

MAF bZIP transcription factor A (MafA) is a key transcriptional regulator of β-cell maturity and function, and thus essential for proper insulin release. Recruitment and binding of lysine acetyltransferases increase MafA transactivation ability, but mechanisms underlying this phenomenon are unclear. We performed a LC-MS/MS screen and validation experiments to identify acetylated lysines of MafA: K32, K33 and K255. We mutated lysines (K) to glutamine (Q) to mimic constitutively acetylated MafA and measured their transcriptional activity. 3KQ MafA significantly increased transactivation ability at the insulin promoter in mouse β-cell lines. Mechanistically, we uncovered a novel form of post-translational modification (PTM) crosstalk, where MafA acetylation simultaneously blocks SUMOylation at K32 and enhances phosphorylation at S14 to increase activity at the insulin promoter.

We next generated 3KQ MafA knock-in mice to study the in vivo consequences of MafA acetylation. RNA sequencing analysis revealed that 3KQ MafA significantly upregulated the expression of the L-amino acid transporter Lat2/𝘚𝘭𝘤7𝘢8, which we confirmed to be a novel transcriptional target of MafA. Given that Lat2 has a high affinity for branched chain amino acids (BCAAs), we tested whether 3KQ MafA would be more sensitive to BCAA-stimulated insulin secretion. Indeed, while 3KQ MafA mice showed mildly impaired glucose tolerance compared to WT mice in response to glucose, they had improved glucose tolerance and insulin secretion when stimulated with BCAA. Ultimately, 3KQ MafA induced a switch in beta cell nutrient sensitivity from glucose to amino acids. These data provide new insights into β-cell amino acid sensing, which may be provide novel therapeutic targets for when traditional glucose sensing mechanisms fail.