title: A novel NF-kappaB pathway involving IKKbeta and p65/RelA Ser-536 phosphorylation results in p53 Inhibition in the absence of NF-kappaB transcriptional activity.
abstract: Nuclear factor kappaB (NF-kappaB) plays an important role in regulating cellular transformation and apoptosis. The human T-cell lymphotropic virus type I protein, Tax, which is critical for viral transformation, modulates the transcription of several cellular genes through activation of NF-kappaB. We have demonstrated previously that Tax inhibits p53 activity through the p65/RelA subunit of NF-kappaB. We now present evidence that suggests that the upstream kinase IKKbeta plays an important role in Tax-induced p53 inhibition through phosphorylation of p65/RelA at Ser-536. First, mouse embryo fibroblast (MEF) IKKbeta-/-cells did not support Tax-mediated p53 inhibition, whereas MEFs lacking IKKalpha allowed Tax inhibition of p53. Second, transfection of IKKbeta wild type (WT), but not a kinase-dead mutant, into IKKbeta-/-cells rescued p53 inhibition by Tax. Third, the IKKbeta-specific inhibitor SC-514 decreased the ability of Tax to inhibit p53. Fourth, we show that phosphorylation of p65/RelA at Ser-536 is important for Tax inhibition of p53 using MEF p65/RelA-/-cells transfected with p65/RelA WT or mutant plasmids. Moreover, Tax induced p65/RelA Ser-536 phosphorylation in WT or IKKalpha-/- cells but failed to induce the phosphorylation of p65/RelA Ser-536 in IKKbeta-/-cells, suggesting a link between IKKbeta and p65/RelA phosphorylation. Consistent with this observation, blocking IKKbeta kinase activity by SC-514 decreases the phosphorylation of p65/RelA at Ser-536 in the presence of Tax in human T-cell lymphotropic virus type I-transformed cells. Finally, the ability of Tax to inhibit p53 is distinguished from the NF-kappaB transcription activation pathway. Our work, therefore, describes a novel Tax-NF-kappaB p65/RelA pathway that functions to inhibit p53 but does not require NF-kappaB transcription activity.
authors.affiliation: Virus Tumor Biology Section, Laboratory of Cellular Oncology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892-5055, USA.
authors.forename: Soo-Jin
authors.initials: SJ
authors.lastname: Jeong
authors.forename: Cynthia A
authors.initials: CA
authors.lastname: Pise-Masison
authors.forename: Michael F
authors.initials: MF
authors.lastname: Radonovich
authors.forename: Hyeon Ung
authors.initials: HU
authors.lastname: Park
authors.forename: John N
authors.initials: JN
authors.lastname: Brady
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002460:Cell Line; D005347:Fibroblasts / Q000378:metabolism; D016356:Gene Products, tax / Q000378:metabolism; D051550:I-kappa B Kinase; D047468:Immunoprecipitation; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D009154:Mutation; D016328:NF-kappa B / Q000378:metabolism*; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012694:Serine / Q000737:chemistry*; D013601:T-Lymphocytes / Q000378:metabolism; D013876:Thiophenes / Q000494:pharmacology; D051996:Transcription Factor RelA; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D019076:Transgenes; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D016356:Gene Products, tax; D016328:NF-kappa B; C477523:SC 514; D013876:Thiophenes; D051996:Transcription Factor RelA; D016159:Tumor Suppressor Protein p53; D012694:Serine; D008156:Luciferases; D017346:Protein Serine-Threonine Kinases; C496564:Chuk protein, mouse; D051550:I-kappa B Kinase; C496562:Ikbkb protein, mouse; C496566:Ikbke protein, mouse