title: Mechanism for biphasic rel A. NF-kappaB1 nuclear translocation in tumor necrosis factor alpha-stimulated hepatocytes.
abstract: The proinflammatory cytokine, tumor necrosis factor alpha (TNFalpha), is a potent activator of angiotensinogen gene transcription in hepatocytes by activation of latent nuclear factor-kappaB (NF-kappaB) DNA binding activity. In this study, we examine the kinetics of TNFalpha-activated translocation of the 65-kDa (Rel A) and 50-kDa (NF-kappaB1) NF-kappaB subunits mediated by inhibitor (IkappaB) proteolysis in HepG2 hepatoblastoma cells. HepG2 cells express the IkappaB members IkappaBalpha, IkappaBbeta, and IkappaBgamma. In response to TNFalpha, Rel A.NF-kappaB1 translocation and DNA binding activity follows a biphasic profile, with an "early" induction (15-30 min), followed by a nadir to control levels at 60 min, and a "late" induction (>120 min). The early phase of Rel A.NF-kappaB1 translocation depends on simultaneous proteolysis of both IkappaBalpha and IkappaBbeta isoforms; IkappaBgamma is inert to TNFalpha treatment. The 60-min nadir is due to a rapid IkappaBalpha resynthesis that reassociates with Rel A and completely inhibits its DNA binding activity; the 60-min nadir is not observed when IkappaBalpha resynthesis is prevented by cycloheximide treatment. By contrast, selective inhibition of IkappaBbeta proteolysis by pretreatment of HepG2 cells with the peptide aldehyde N-acetyl-Leu-Leu-norleucinal completely blocks the late phase of Rel A.NF-kappaB1 translocation. These studies indicate the presence of inducible and constitutive cytoplasmic NF-kappaB pools in hepatocytes. TNFalpha induces a coordinated proteolysis and resynthesis of IkappaB isoforms to produce dynamic changes in NF-kappaB nuclear abundance.
authors.affiliation: Department of Internal Medicine and Sealy Center for Molecular Science, University of Texas Medical Branch, Galveston, Texas 77555-1060, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Han
authors.forename: A R
authors.initials: AR
authors.lastname: Brasier
mesh_terms: D002467:Cell Nucleus / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D006801:Humans; D020672:I-kappa B Proteins; D007976:Leupeptins / Q000494:pharmacology; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D052002:NF-kappa B p50 Subunit; D011498:Protein Precursors / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D020569:Proto-Oncogene Proteins c-rel; D011994:Recombinant Proteins / Q000378:metabolism; D051996:Transcription Factor RelA; D051841:Transcription Factor RelB; D014157:Transcription Factors; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; C083487:I kappa B beta protein; D020672:I-kappa B Proteins; D007976:Leupeptins; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; C000606204:NFKBIA protein, human; D011498:Protein Precursors; D011518:Proto-Oncogene Proteins; D020569:Proto-Oncogene Proteins c-rel; C497593:RELB protein, human; D011994:Recombinant Proteins; D051996:Transcription Factor RelA; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; C063261:acetylleucyl-leucyl-norleucinal; D000072000:NF-KappaB Inhibitor alpha; D051841:Transcription Factor RelB; D004247:DNA