title: Poxvirus MC160 protein utilizes multiple mechanisms to inhibit NF-kappaB activation mediated via components of the tumor necrosis factor receptor 1 signal transduction pathway.
abstract: Poxviruses express proteins that limit host immune responses to infection. For example, the molluscum contagiosum virus MC160 protein inhibits tumor necrosis factor alpha (TNF-alpha)-induced NF-kappaB activation. This event correlates with MC160-induced IKK1 protein degradation, suggesting a mechanism for the above-mentioned phenotype. IKK1 is stabilized when it associates with the cellular heat shock protein 90 (Hsp90). Here, Hsp90 overexpression restored IKK1 levels in MC160-expressing cells, suggesting that MC160 competitively interacted with Hsp90. In support of this, further investigation showed that a mutant MC160 protein comprising only the C-terminal region (C protein) immunoprecipitated with Hsp90. In contrast, Hsp90 IP with a mutant MC160 protein consisting of only the N-terminal tandem death effector domains (DEDs) (N protein) was dramatically decreased. Since cells expressing either the N or C mutant MC160 protein remained similarly resistant to TNF-alpha-induced NF-kappaB activation, the N mutant protein probably utilized a different mechanism for inhibiting NF-kappaB. One likely mechanism for the N protein lies in its association with the DED-containing procaspase-8 protein, a cellular apoptosis precursor protein that regulates NF-kappaB activation. Here, IPs revealed that this association relied on the presence of the DED-containing N terminus of the MC160 protein but not the C-terminal portion. These interactions appear to have relevance with NF-kappaB activation, since the expression of the viral DEDs strongly inhibited procaspase-8-mediated NF-kappaB activation, an event not substantially altered by the C protein. Thus, the MC160 protein utilizes at least two distinct mechanisms for impeding NF-kappaB activation, association with Hsp90 to result in IKK1 protein degradation or interaction with procaspase-8.
authors.affiliation: Department of Microbiology, College of Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
authors.forename: Daniel Brian
authors.initials: DB
authors.lastname: Nichols
authors.forename: Joanna L
authors.initials: JL
authors.lastname: Shisler
mesh_terms: D053181:Caspase 8 / Q000378:metabolism; D002460:Cell Line; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism; D047468:Immunoprecipitation; D008977:Molluscum contagiosum virus / Q000276:immunology / Q000502:physiology*; D016328:NF-kappa B / Q000037:antagonists & inhibitors*; D011485:Protein Binding; D025941:Protein Interaction Mapping; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism*; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: D018841:HSP90 Heat-Shock Proteins; D016328:NF-kappa B; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; D014764:Viral Proteins; C496559:CHUK protein, human; D051550:I-kappa B Kinase; D053181:Caspase 8