A novel domain mediates insulin-induced proteasomal degradation of insulin receptor substrate 1 (IRS-1).
Insulin receptor substrate-1 (IRS-1) plays a pivotal role in insulin signaling, therefore its degradation is exquisitely regulated. Here, we show that insulin-stimulated degradation of IRS-1 requires the presence of a highly conserved Ser/Thr-rich domain that we named domain involved in degradation of IRS-1 (DIDI). DIDI (amino acids 386-430 of IRS-1) was identified by comparing the intracellular degradation rate of several truncated forms of IRS-1 transfected into CHO cells. The isolated DIDI domain underwent insulin-stimulated Ser/Thr phosphorylation, suggesting that it serves as a target for IRS-1 kinases. The effects of deletion of DIDI were studied in Fao rat hepatoma and in CHO cells expressing Myc-IRS-1(WT) or Myc-IRS-1(Δ386-430). Deletion of DIDI maintained the ability of IRS-1(Δ386-434) to undergo ubiquitination while rendering it insensitive to insulin-induced proteasomal degradation, which affected IRS-1(WT) (80% at 8 h). Consequently, IRS-1(Δ386-434) mediated insulin signaling (activation of Akt and glycogen synthesis) better than IRS-1(WT). IRS-1(Δ386-434) exhibited a significant greater preference for nuclear localization, compared with IRS-1(WT). Higher nuclear localization was also observed when cells expressing IRS-1(WT) were incubated with the proteasome inhibitor MG-132. The sequence of DIDI is conserved more than 93% across species, from fish to mammals, as opposed to approximately 40% homology of the entire IRS-1. These findings implicate DIDI as a novel, highly conserved domain of IRS-1, which mediates its cellular localization, rate of degradation, and biological activity, with a direct impact on insulin signal transduction.
Boura-Halfon
Sigalit
S
Department of Molecular Cell Biology, The Weizmann Institute of Science, Rehovot, 76100, Israel.
Shuster-Meiseles
Timor
T
Beck
Avital
A
Petrovich
Katia
K
Gurevitch
Diana
D
Ronen
Denise
D
Zick
Yehiel
Y
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D019610:Cytoprotection / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins / Q000737:chemistry* / Q000378:metabolism*; D051379:Mice; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000187:drug effects; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism; D051381:Rats; D017384:Sequence Deletion; D015398:Signal Transduction / Q000187:drug effects; D013329:Structure-Activity Relationship; D054875:Ubiquitination / Q000187:drug effects
D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D050505:Mutant Proteins; D010768:Phosphoserine; D051736:Proto-Oncogene Proteins c-mdm2; D046988:Proteasome Endopeptidase Complex