title: The MCV MC159 protein inhibits late, but not early, events of TNF-α-induced NF-κB activation.
abstract: Tumor necrosis factor (TNF-alpha) triggers biphasic activation of the NF-kappaB transcriptional regulator. This process consists of an initial, IkappaBalpha-mediated transient phase and a later, persistent phase dependent on IkappaBbeta degradation. To presumably interfere with the fulfillment of this immunity-associated event in cells infected with the molluscum contagiosum virus (MCV), this pathogen produces the intracellular MC159 protein. To define the mode of action of MC159, the impact of TNF-alpha on HEK 293T cells ectopically expressing the MC159 protein was examined. In this regard, TNF-alpha-induced expression of an NF-kappaB-regulated luciferase reporter gene was partially inhibited by the MC159 protein. This ability was attributed to blockage of the persistent phase of TNF-alpha-induced NF-kappaB activation for the following reasons: (1) the initial phase of NF-kappaB transcriptional activation was not affected by the MC159 protein; (2) the MC159 protein inhibited TNF-alpha-directed degradation of IkappaBbeta, but not IkappaBalpha; and (3) expression of the late NF-kappaB-regulated cell genes, TNF-alpha and CCL2, was decreased in the presence of the MC159 protein while transcription of the early NF-kappaB-regulated cell gene, CXCL1, was not altered. Previously reported MC159-RIP interactions appear to be irrelevant for the MC159 inhibitory function. In contrast, MC159-TRAF2 associations are more relevant for inhibitory function since mutant MC159 proteins unable to bind TRAF2 also cannot inhibit TNF-mediated NF-kappaB activation. In vivo, the MC159 protein may act to prolong virus survival by preventing the infected cell from responding to TNF-alpha, ultimately preventing the cellular production of proinflammatory and immunoattractant molecules.
authors.affiliation: Department of Microbiology, College of Medicine, University of Illinois, C222 CLSL, Urbana, 61801, USA.
authors.forename: Lyre Espada
authors.initials: LE
authors.lastname: Murao
authors.forename: Joanna L
authors.initials: JL
authors.lastname: Shisler
mesh_terms: D002460:Cell Line; D005786:Gene Expression Regulation / Q000187:drug effects; D017930:Genes, Reporter; D006801:Humans; D008156:Luciferases / Q000235:genetics; D008954:Models, Biological; D008977:Molluscum contagiosum virus / Q000502:physiology*; D016328:NF-kappa B / Q000187:drug effects / Q000378:metabolism*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000494:pharmacology; D012097:Repressor Proteins / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors* / Q000494:pharmacology*; D014764:Viral Proteins / Q000494:pharmacology*
chemical_list: D016328:NF-kappa B; D011994:Recombinant Proteins; D012097:Repressor Proteins; D014409:Tumor Necrosis Factor-alpha; D014764:Viral Proteins; D008156:Luciferases