Requirement of NOX2 and Reactive Oxygen Species for Efficient RIG-I-Mediated Antiviral Response through Regulation of MAVS Expression

The innate immune response is essential to the host defense against viruses, through restriction of virus replication and coordination of the adaptive immune response. Induction of antiviral genes is a tightly regulated process initiated mainly through sensing of invading virus nucleic acids in the cytoplasm by RIG-I like helicases, RIG-I or Mda5, which transmit the signal through a common mitochondria-associated adaptor, MAVS. Although major breakthroughs have recently been made, much remains unknown about the mechanisms that translate virus recognition into antiviral genes expression. Beside the reputed detrimental role, reactive oxygen species (ROS) act as modulators of cellular signaling and gene regulation. NADPH oxidase (NOX) enzymes are a main source of deliberate cellular ROS production. Here, we found that NOX2 and ROS are required for the host cell to trigger an efficient RIG-I-mediated IRF-3 activation and downstream antiviral IFNβ and IFIT1 gene expression. Additionally, we provide evidence that NOX2 is critical for the expression of the central mitochondria-associated adaptor MAVS. Taken together these data reveal a new facet to the regulation of the innate host defense against viruses through the identification of an unrecognized role of NOX2 and ROS

Binding of Kaposi's Sarcoma-Associated Herpesvirus K-bZIP to Interferon-Responsive Factor 3 Elements Modulates Antiviral Gene Expression▿

Kaposi's sarcoma-associated herpesvirus encodes numerous regulatory proteins capable of modulating viral and cellular gene expression and affecting host cell functions. K-bZIP, a leucine zipper-containing transcription factor encoded by ORFK8, is one such protein. During infection, transcription of the ORFK8 early gene is turned on by the immediate-early replication and transcription factor activator (RTA). One described function of the K-bZIP nuclear protein is to interact with and repress RTA-mediated transactivation of viral promoters, including that of the K8 gene. In the present work, we provide evidence that the expression of K-bZIP results in the activation of the ifn-β gene. Of interest, ifn-β gene activation by K-bZIP is independent of interferon (IFN)-responsive factor 3 (IRF-3) and nuclear factor κB (NF-κB) activation. Using a DNA binding affinity assay and electromobility shift assay, we report that K-bZIP binds efficiently to the PRDIII-I region of the beta IFN (IFN-β) promoter, and, in doing so, it prevents the attachment of activated IRF-3 but not that of NF-κB or ATF2/c-Jun to the IFN-β promoter sequence. As a consequence, ifn-β gene activation in response to IFN inducers such as Sendai virus infection or expression of retinoic acid-inducible gene I, mitochondrial antiviral signaling protein, or TANK-binding kinase 1 (TBK-1) is severely impaired (>90%) by the presence of K-bZIP. K-bZIP also prevents the activation of RANTES and CXCL11, whose promoters are also regulated by IRF-3. Lysine 158 (target for SUMO conjugation), threonine 111, and serine 167 (targets for phosphorylation) mutants of K-bZIP were equally effective as wild-type K-bZIP in mediating the repression of TBK-1-activated ifn-β gene expression. Lastly, the overexpression of CREB binding protein could not reverse the K-bZIP repression of TBK-1-activated ifn-β gene expression. In all, our results indicate that K-bZIP binds directly to the PRDIII-I region of the IFN-β promoter and, as a consequence, causes a low level of ifn-β gene transcription. In doing so, K-bZIP prevents IRF-3 from binding to the IFN-β promoter and precludes the formation of the enhanceosome, which is required for maximal ifn-β gene transcription. A new role for K-bZIP as a protein involved in immune evasion is therefore uncovered