Vaccinia virus E3 suppresses expression of diverse cytokines through inhibition of the PKR, NF-kappaB, and IRF3 pathways.
The vaccinia virus double-stranded RNA binding protein E3 has been demonstrated to inhibit the expression of cytokines, including beta interferon (IFN-beta) and tumor necrosis factor alpha (TNF-alpha). However, few details regarding the molecular mechanisms of this inhibition have been described. Using real-time PCR arrays, we found that E3 suppressed the induction of a diverse array of cytokines representing members of the IFN, interleukin (IL), TNF, and transforming growth factor cytokine families. We discovered that the factor(s) responsible for the induction of IL-6, TNF-alpha, and inhibin beta A (INHBA) was associated with the early and late phases of virus infection. In contrast, the factor(s) which regulates IFN-beta induction was associated with the late phase of replication. We have found that expression of these cytokines can be induced by transfection of cells with RNA isolated from vaccinia virus-infected cells. Moreover, we provide evidence that E3 antagonizes both PKR-dependent and PKR-independent pathways to regulate cytokine expression. PKR-dependent activation of p38 and NF-kappaB was required for vaccinia virus-induced INHBA expression, whereas induction of TNF-alpha required only PKR-dependent NF-kappaB activation. In contrast, induction of IL-6 and IFN-beta was largely PKR independent. IL-6 induction is regulated by NF-kappaB, while IFN-beta induction is mediated by IFN-beta promoter stimulator 1 and IFN regulatory factor 3/NF-kappaB. Collectively, these results indicate that E3 suppresses distinct but interlinked host signaling pathways to inhibit the expression of a diverse array of cytokines.
Myskiw
Chad
C
Department of Medical Microbiology, University of Manitoba, Winnipeg, MB, Canada R3T 2N2.
Arsenio
Janilyn
J
van Bruggen
Rebekah
R
Deschambault
Yvon
Y
Cao
Jingxin
J
D000818:Animals; D006224:Cricetinae; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D028322:Inhibin-beta Subunits / Q000378:metabolism; D050838:Interferon Regulatory Factor-3 / Q000378:metabolism*; D015850:Interleukin-6 / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism*; D010766:Phosphorylation; D016601:RNA-Binding Proteins / Q000378:metabolism*; D015398:Signal Transduction; D014158:Transcription, Genetic; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D014616:Vaccinia virus / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000378:metabolism*; D019892:eIF-2 Kinase / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
C081374:E3L protein, Vaccinia virus; C508600:IL6 protein, human; C494232:IRF3 protein, human; D050838:Interferon Regulatory Factor-3; D015850:Interleukin-6; D016328:NF-kappa B; D016601:RNA-Binding Proteins; D014409:Tumor Necrosis Factor-alpha; D014764:Viral Proteins; C103008:inhibin beta A subunit; D028322:Inhibin-beta Subunits; D019892:eIF-2 Kinase; D048051:p38 Mitogen-Activated Protein Kinases