title: The carboxy-terminus of I kappaB alpha determines susceptibility to degradation by the catalytic core of the proteasome.
abstract: The Rel/NF-kappaB family of transcription factors controls the expression of a wide variety of genes that are implicated in immune and inflammatory responses and cellular proliferation. Disregulation of NF-kappaB is associated with cellular transformation and the maintenance of a high anti-apoptotic threshold in transformed cells. NF-kappaB activity is in turn regulated by its sequestration in the cytoplasm by the inhibitor I kappaB. I kappaB alpha, the most abundant and well-characterized member of the I kappaB multiprotein family, is rapidly degraded in response to multiple physiologic stimuli. In the present study we show that not only the amino-terminus, but also the carboxy-terminus of I kappaB alpha contain transferable signals that must be simultaneously present in an unrelated protein to render it susceptible to activation-induced, proteasome-mediated degradation. We show here that I kappaB alpha amino-terminal modifications occur independently of the carboxy-terminus. Moreover, we present evidence indicating a critical role for the carboxy-terminal region in facilitating proteolysis by the catalytic core of the proteasome. When incubated with 20S proteasome extracted from rat liver, I kappaB alpha was quickly degraded while a deletion mutant lacking the carboxy-terminus was resistant to proteolysis. Likewise, chimeric proteins of beta-galactosidase with the I kappaB alpha carboxy-terminus were degraded in vitro independently of the presence of the I kappaB alpha amino-terminus, whereas chimeric proteins lacking the I kappaB alpha carboxy-terminus were stable. Our results identify the carboxy-terminus of I kappaB alpha as a domain critical for degradation through interaction with an as yet unidentified component of the proteasome.
authors.affiliation: Unité d'Immunologie Virale, Institut Pasteur, Paris, France.
authors.forename: M
authors.initials: M
authors.lastname: Kroll
authors.forename: M
authors.initials: M
authors.lastname: Conconi
authors.forename: M J
authors.initials: MJ
authors.lastname: Desterro
authors.forename: A
authors.initials: A
authors.lastname: Marin
authors.forename: D
authors.initials: D
authors.lastname: Thomas
authors.forename: B
authors.initials: B
authors.lastname: Friguet
authors.forename: R T
authors.initials: RT
authors.lastname: Hay
authors.forename: J L
authors.initials: JL
authors.lastname: Virelizier
authors.forename: F
authors.initials: F
authors.lastname: Arenzana-Seisdedos
authors.forename: M S
authors.initials: MS
authors.lastname: Rodriguez
mesh_terms: D000818:Animals; D019556:COS Cells; D002384:Catalysis; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D006868:Hydrolysis; D020672:I-kappa B Proteins; D009097:Multienzyme Complexes / Q000378:metabolism*; D000072000:NF-KappaB Inhibitor alpha; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D051381:Rats; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D014452:Ubiquitins / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D009097:Multienzyme Complexes; C000606204:NFKBIA protein, human; C000606206:Nfkbia protein, rat; D014409:Tumor Necrosis Factor-alpha; D014452:Ubiquitins; D000072000:NF-KappaB Inhibitor alpha; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex