title: Degradation of the Id2 developmental regulator: targeting via N-terminal ubiquitination.
abstract: Degradation of cellular proteins via the ubiquitin-proteasome system (UPS) involves: (i) generation of a substrate-anchored polyubiquitin degradation signal and (ii) destruction of the tagged protein by the 26S proteasome with release of free and reusable ubiquitin. For most substrates, it is believed that the first ubiquitin moiety is conjugated to a epsilon-NH(2) group of an internal Lys residue. Recent findings indicate that for several proteins, the first ubiquitin moiety is fused, in a linear manner, to the free alpha-NH(2) group of the protein. Here, we demonstrate that the inhibitor of differentiation (or inhibitor of DNA binding) 2, Id2, that downregulates gene expression in undifferentiated and self-renewing cells, is degraded by the UPS following ubiquitination at its N-terminal residue. Lysine-less (LL) Id2 is degraded efficiently by the proteasome following ubiquitination. Fusion of a Myc tag to the N-terminal but not to the C-terminal residue of Id2 stabilizes the protein. Furthermore, deletion of the first 15 N-terminal residues of Id2 stabilizes the protein, suggesting that this domain serves as a recognition element, possibly for the ubiquitin ligase, E3. The mechanisms and structural motives that govern Id2 stability may have important implications to the regulation of the protein during normal differentiation and malignant transformation.
authors.affiliation: Department of Biochemistry and the Rappaport Family Institute for Research in the Medical Sciences, the Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, 31096 Haifa, Israel.
authors.forename: Ifat
authors.initials: I
authors.lastname: Fajerman
authors.forename: Alan L
authors.initials: AL
authors.lastname: Schwartz
authors.forename: Aaron
authors.initials: A
authors.lastname: Ciechanover
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D002454:Cell Differentiation; D002471:Cell Transformation, Neoplastic; D002474:Cell-Free System; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D017353:Gene Deletion; D006367:HeLa Cells; D006801:Humans; D051797:Inhibitor of Differentiation Protein 2; D008239:Lysine / Q000737:chemistry; D009097:Multienzyme Complexes / Q000378:metabolism; D010447:Peptide Hydrolases / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D025821:Polyubiquitin / Q000737:chemistry; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D025801:Ubiquitin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D018076:DNA, Complementary; D004268:DNA-Binding Proteins; C497450:ID2 protein, human; D051797:Inhibitor of Differentiation Protein 2; D009097:Multienzyme Complexes; D012097:Repressor Proteins; D014157:Transcription Factors; D025801:Ubiquitin; D025821:Polyubiquitin; D000255:Adenosine Triphosphate; D004247:DNA; D010447:Peptide Hydrolases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D008239:Lysine