The N-terminal truncated isoform of SOCS3 translated from an alternative initiation AUG codon under stress conditions is stable due to the lack of a major ubiquitination site, Lys-6

J Biol Chem. 2003 Jan 24;278(4):2432-6. doi: 10.1074/jbc.C200608200. Epub 2002 Nov 28.


The suppressor of cytokine signaling-3 (SOCS3/CIS-33/SSI-3) is an important negative regulator of cytokine signaling. Here, we show that an N-terminal truncated isoform (DeltaN-SOCS3) translated from the internal AUG codon 12 was profoundly induced by endoplasmic reticulum (ER) stress- or active double-stranded RNA-activated protein kinase PKR, as a result of induction of eukaryotic initiation factor 2alpha phosphorylation. DeltaN-SOCS3 exhibited a stronger cytokine-inhibitory activity and a higher stability than WT-SOCS3 in Ba/F3 hematopoietic cells. A potential ubiquitination residue, Lys-6, at the N terminus is evolutionary conserved among SOCS3 species. The K6Q-SOCS3 mutant showed a much longer half-life than WT-SOCS3 in Ba/F3 cells. Furthermore, inhibition of the 26 S proteasome pathway increased both ubiquitination and protein levels of WT-SOCS3 but had no effect on K6Q-SOCS3. SOCS3 mutant lacking the carboxyl-terminal SOCS-box exhibited the same stability as K6Q-SOCS3. These observations suggest that the short form of SOCS3 is a naturally occurring stabilized inhibitory protein, whereas WT-SOCS3 is a short-lived protein modulated by Lys-6 ubiquitination and proteasome-dependent degradation. Our findings provide strong evidence for the first time that translational control plays an important role in stabilization and function of SOCS3.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line
  • Codon
  • Endoplasmic Reticulum / metabolism
  • Gene Expression Regulation*
  • Humans
  • Lysine / chemistry
  • Mice
  • Mutation
  • Peptide Hydrolases / metabolism
  • Proteasome Endopeptidase Complex*
  • Protein Biosynthesis*
  • Protein Isoforms
  • Protein Structure, Tertiary
  • Proteins / chemistry*
  • Proteins / genetics*
  • Repressor Proteins*
  • Suppressor of Cytokine Signaling 3 Protein
  • Suppressor of Cytokine Signaling Proteins
  • Time Factors
  • Transcription Factors*
  • Transfection
  • Ubiquitin / metabolism


  • Codon
  • Protein Isoforms
  • Proteins
  • Repressor Proteins
  • SOCS3 protein, human
  • Socs3 protein, mouse
  • Suppressor of Cytokine Signaling 3 Protein
  • Suppressor of Cytokine Signaling Proteins
  • Transcription Factors
  • Ubiquitin
  • Peptide Hydrolases
  • Proteasome Endopeptidase Complex
  • ATP dependent 26S protease
  • Lysine