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The Stability and Transactivation Potential of the Mammalian MafA Transcription Factor Are Regulated by Serineí 65 PhosphorylationS
Ist Teil von
The Journal of biological chemistry, 2009-01, Vol.284 (2), p.759-765
Ort / Verlag
American Society for Biochemistry and Molecular Biology
Erscheinungsjahr
2009
Link zum Volltext
Quelle
Free E-Journal (出版社公開部分のみ)
Beschreibungen/Notizen
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 transactivation 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 of MafA 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-terminal 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 phosphorylation at this amino acid in regulating MafA
activity.