title: Degradation of transcription factor IRF-1 by the ubiquitin-proteasome pathway. The C-terminal region governs the protein stability.
abstract: Interferon regulatory factor-1(IRF-1) is a transcriptional activator of interferon genes and interferon-inducible genes. It has been shown that IRF-1 functions not only as a regulator of the interferon-responsive system but also as a regulator of cell growth and apoptosis. In addition, it is known that IRF-1 is a short-lived protein, but the mechanism that regulates its stability has not yet been clarified. Here, we show that IRF-1 is degraded via the ubiquitin-proteasome pathway. IRF-1 protein degradation in HeLa and NIH3T3 cells was inhibited by treatment with proteasome-specific inhibitors. Overexpression of IRF-1 protein and ubiquitin in COS7 cells revealed specific multiubiquitination of IRF-1. Although the full-length IRF-1 was unstable, IRF-1 mutants with C-terminal truncations larger than 39 amino acids were found to be almost stable, suggesting that the 39-residue C-terminal region controls the stability of IRF-1. Further analysis of the stability of a green fluorescent protein-fusion protein containing the 39-residue C-terminal region of IRF-1 showed that this C-terminal region confers instability on green fluorescent protein, a normally stable protein, suggesting that this region functions as a protein-degradation signal. Taking the results together, it can be concluded that the 39-residue C-terminal region is necessary and sufficient to control the stability of the IRF-1 protein.
authors.affiliation: Department of Biochemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Nakagawa
authors.forename: H
authors.initials: H
authors.lastname: Yokosawa
mesh_terms: D016475:3T3 Cells; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D050856:Interferon Regulatory Factor-1; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017384:Sequence Deletion; D014162:Transfection; D014452:Ubiquitins / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; C494257:IRF1 protein, human; D050856:Interferon Regulatory Factor-1; C494258:Irf1 protein, mouse; D009097:Multienzyme Complexes; D009363:Neoplasm Proteins; D010446:Peptide Fragments; D010750:Phosphoproteins; D011480:Protease Inhibitors; D011993:Recombinant Fusion Proteins; D014452:Ubiquitins; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex