Vaccinia Virus E3 Suppresses Expression of Diverse Cytokines through Inhibition of the PKR, NF-κB, and IRF3 Pathways

Abstract

The vaccinia virus double-stranded RNA binding protein E3 has been demonstrated to inhibit the expression of cytokines, including beta interferon (IFN-␤) and tumor necrosis factor alpha (TNF-␣). 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-␣, and inhibin beta A (INHBA) was associated with the early and late phases of virus infection. In contrast, the factor(s) which regulates IFN-␤ 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-B was required for vaccinia virus-induced INHBA expression, whereas induction of TNF-␣ required only PKR-dependent NF-B activation. In contrast, induction of IL-6 and IFN-␤ was largely PKR independent. IL-6 induction is regulated by NF-B, while IFN-␤ induction is mediated by IFN-␤ promoter stimulator 1 and IFN regulatory factor 3/NF-B. Collectively, these results indicate that E3 suppresses distinct but interlinked host signaling pathways to inhibit the expression of a diverse array of cytokines.

Inhibition of interferon gene activation by death-effector domain-containing proteins from the molluscum contagiosum virus

“…One such virus that serves as an important model for viral effects on host immune function, molluscum contagiosum virus (MCV), does not encode any obvious IFN-β antagonists (15,16). This was surprising given that related poxviruses, such as the vaccinia virus, express several intracellular proteins (E3, C6, and N2) that inhibit IFN-β (17)(18)(19)(20)(21)(22)(23). To date, only the MCV MC54 protein, a secreted interleukin binding protein (IL-18BP), is predicted to inhibit IFN expression indirectly by preventing IL-18-mediated IFN-β activation (24,25).…”

NFκB activation by modified vaccinia virus as a novel strategy to enhance neutrophil migration and HIV-specific T-cell responses

“…VACV interacts with TLR2 (16) and TLR4 (17) and produces early direct or indirect viral inhibitors of the NFκB pathway such as A46 (18), A49 (19), A52 (18), B14 (20), C4 (21), E3 (22), K1 (23), K7 (24), M2 (25), and N1 (26). New York vaccinia virus (NYVAC), a highly attenuated VACV strain used as vaccine vector, lacks most of these proteins but encodes NFκB pathway Significance Although poxvirus vectors are widely used in preclinical and clinical trials as candidate vaccines for multiple pathogens, how these vectors affect the host immune response is not clear.…”

A Nuclear Inhibitor of NF-κB Encoded by a Poxvirus

“…VACV-encoded NF-B inhibitors target cytoplasmic steps leading to activation of the IKK complex (A52R, A46R, B14, N1L, and M2L), degradation of IB␣ (K1L), or activation of the protein kinase RNA (PKR)-double-stranded RNA (dsRNA) signaling pathway (E3L) (2,11,14,24,35,43,46). Molluscum contagiosum virus (MOCV) protein MC159 prevents degradation of IB␤, while MC160 induces degradation of IKK␣ (34,38).…”