The stability and transactivation potential of the mammalian MafA transcription factor are regulated by serine 65 phosphorylation

Shuangli Guo, Ryan Burnette, Li Zhao, Nathan L. Vanderford, Vincent Poitout, Derek K. Hagman, Eva Henderson, Sabire Özcan, Brian E. Wadzinski, Roland Stein

Research output: Contribution to journalArticlepeer-review

34 Scopus citations

Abstract

The level of the MafA transcription factor is regulated by a variety of effectors of β cell function, including glucose, fatty acids, and insulin. Here, we show that phosphorylation at Ser 65 of mammalian MafA influences both protein stability and trans-activation potential. Replacement of Ser 65 with Glu to mimic phosphorylation produced a protein that was as unstable as the wild type, whereas Asp or Ala mutation blocked degradation. Analysis ofMafA chimeric and deletion constructs suggests that protein phosphorylation at Ser 65 alone represents the initial degradation signal, with ubiquitinylation occurring within the C terminus (amino acids 234-359). Although only wild type MafA and S65E were polyubiquitinylated, both S65D and S65E potently stimulated transactivation compared with S65A. Phosphorylation at Ser 14 also enhanced activation, although it had no impact on protein turnover. The mobility of MafA S65A was profoundly affected upon SDS-PAGE, with the S65E and S65D mutants influenced less due to their ability to serve as substrates for glycogen synthase kinase 3, which acts at neighboring N-ter-minal residues after Ser 65 phosphorylation. Our observations not only illustrate the sensitivity of the cellular transcriptional and degradation machinery to phosphomimetic mutants at Ser 65, but also demonstrate the singular importance of phos-phorylation at this amino acid in regulating MafA activity.

Original languageEnglish
Pages (from-to)759-765
Number of pages7
JournalJournal of Biological Chemistry
Volume284
Issue number2
DOIs
StatePublished - Jan 9 2009

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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