Glycogen synthase kinase-3-mediated phosphorylation of serine 73 targets sterol response element binding protein-1c (SREBP-1c) for proteasomal degradation

Qingming Dong, Francesco Giorgianni, Sarka Beranova, Xiong Deng, Robert N. O'Meally, Dave Bridges, Edwards Park, Robert N. Cole, Marshall Elam, Rajendra Raghow

Research output: Contribution to journalArticle

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Abstract

Sterol regulatory element binding protein-1c (SREBP-1c) is a key transcription factor that regulates genes involved in the de novo lipid synthesis and glycolysis pathways. The structure, turnover and transactivation potential of SREBP-1c are regulated by macronutrients and hormones via a cascade of signalling kinases. Using MS, we have identified serine 73 as a novel glycogen synthase kinase-3 (GSK-3) phosphorylation site in the rat SREBP-1c purified from McA-RH7777 hepatoma cells. Our site-specific mutagenesis strategy revealed that the turnover of SREBP-1c, containing wild type, phospho-null (serine to alanine) or phospho-mimetic (serine to aspartic acid) substitutions, was differentially regulated. We show that the S73D mutant of pSREBP-1c, that mimicked a state of constitutive phosphorylation, dissociated from the SREBP-1c-SCAP complex more readily and underwent GSK-3-dependent proteasomal degradation via SCFFbw7 ubiquitin ligase pathway. Pharmacologic inhibition of GSK-3 or knockdown of GSK-3 by siRNA prevented accelerated degradation of SREBP-1c. As demonstrated by MS, SREBP-1c was phosphorylated in vitro by GSK-3â at serine 73. Phosphorylation of serine 73 also occurs in the intact liver. We propose that GSK-3-mediated phosphorylation of serine 73 in the rat SREBP-1c and its concomitant destabilization represents a novel mechanism involved in the inhibition of de novo lipid synthesis in the liver.

Original languageEnglish (US)
Article numbere00284
JournalBioscience Reports
Volume36
Issue number1
DOIs
StatePublished - Feb 1 2016

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Glycogen Synthase Kinase 3
Phosphorylation
Response Elements
Sterols
Serine
Carrier Proteins
Degradation
Liver
Rats
Sterol Regulatory Element Binding Protein 1
Lipids
Mutagenesis
Glycolysis
Ligases
Ubiquitin
Site-Directed Mutagenesis
Aspartic Acid
Alanine
Small Interfering RNA
Transcriptional Activation

All Science Journal Classification (ASJC) codes

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Cell Biology

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Glycogen synthase kinase-3-mediated phosphorylation of serine 73 targets sterol response element binding protein-1c (SREBP-1c) for proteasomal degradation. / Dong, Qingming; Giorgianni, Francesco; Beranova, Sarka; Deng, Xiong; O'Meally, Robert N.; Bridges, Dave; Park, Edwards; Cole, Robert N.; Elam, Marshall; Raghow, Rajendra.

In: Bioscience Reports, Vol. 36, No. 1, e00284, 01.02.2016.

Research output: Contribution to journalArticle

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