RESUMO
We describe a novel function for the interferon (IFN)-induced protein 44-like (IFI44L) gene in negatively modulating innate immune responses induced after virus infections. Furthermore, we show that decreasing IFI44L expression impairs virus production and that IFI44L expression negatively modulates the antiviral state induced by an analog of double-stranded RNA (dsRNA) or by IFN treatment. The mechanism likely involves the interaction of IFI44L with cellular FK506-binding protein 5 (FKBP5), which in turn interacts with kinases essential for type I and III IFN responses, such as inhibitor of nuclear factor kappa B (IκB) kinase alpha (IKKα), IKKß, and IKKε. Consequently, binding of IFI44L to FKBP5 decreased interferon regulatory factor 3 (IRF-3)-mediated and nuclear factor kappa-B (NF-κB) inhibitor (IκBα)-mediated phosphorylation by IKKε and IKKß, respectively. According to these results, IFI44L is a good target for treatment of diseases associated with excessive IFN levels and/or proinflammatory responses and for reduction of viral replication.IMPORTANCE Excessive innate immune responses can be deleterious for the host, and therefore, negative feedback is needed. Here, we describe a completely novel function for IFI44L in negatively modulating innate immune responses induced after virus infections. In addition, we show that decreasing IFI44L expression impairs virus production and that IFI44L expression negatively modulates the antiviral state induced by an analog of dsRNA or by IFN treatment. IFI44L binds to the cellular protein FKBP5, which in turn interacts with kinases essential for type I and III IFN induction and signaling, such as the kinases IKKα, IKKß, and IKKε. IFI44L binding to FKBP5 decreased the phosphorylation of IRF-3 and IκBα mediated by IKKε and IKKß, respectively, providing an explanation for the function of IFI44L in negatively modulating IFN responses. Therefore, IFI44L is a candidate target for reducing virus replication.
Assuntos
Quinase I-kappa B/metabolismo , Imunidade Inata/imunologia , Interferons/farmacologia , Proteínas de Ligação a Tacrolimo/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Replicação Viral , Sequência de Aminoácidos , Antivirais/farmacologia , Retroalimentação Fisiológica , Humanos , Quinase I-kappa B/genética , Imunidade Inata/efeitos dos fármacos , Influenza Humana/imunologia , Influenza Humana/patologia , Influenza Humana/virologia , NF-kappa B , Neoplasias/imunologia , Neoplasias/patologia , Neoplasias/virologia , Orthomyxoviridae/efeitos dos fármacos , Orthomyxoviridae/imunologia , Fosforilação , Homologia de Sequência , Transdução de Sinais , Proteínas de Ligação a Tacrolimo/genética , Células Tumorais Cultivadas , Proteínas Supressoras de Tumor/genéticaRESUMO
Hepatitis E virus (HEV) causes predominantly acute and self-limiting hepatitis. However, in HEV-infected pregnant women, the case fatality rate because of fulminant hepatitis can be up to 30%. HEV infection is zoonotic for some genotypes. The HEV genome contains three open reading frames: ORF1 encodes the non-structural polyprotein involved in viral RNA replication; ORF2 encodes the capsid protein; ORF3 encodes a small multifunctional protein. Interferons (IFNs) play a significant role in the early stage of the host antiviral response. In this study, we discovered that the capsid protein antagonizes IFN induction. Mechanistically, the capsid protein blocked the phosphorylation of IFN regulatory factor 3 (IRF3) via interaction with the multiprotein complex consisting of mitochondrial antiviral-signaling protein (MAVS), TANK-binding kinase 1 (TBK1), and IRF3. The N-terminal domain of the capsid protein was found to be responsible for the inhibition of IRF3 activation. Further study showed that the arginine-rich-motif in the N-terminal domain is indispensable for the inhibition as mutations of any of the arginine residues abolished the blockage of IRF3 phosphorylation. These results provide further insight into HEV interference with the host innate immunity.
Assuntos
Proteínas do Capsídeo/metabolismo , Vírus da Hepatite E/fisiologia , Hepatite E/metabolismo , Hepatite E/virologia , Interações Hospedeiro-Patógeno , Interferons/biossíntese , Domínios e Motivos de Interação entre Proteínas , Proteínas do Capsídeo/genética , Genótipo , Humanos , Fator Regulador 3 de Interferon/metabolismo , Interferons/química , Modelos Biológicos , Fatores de Crescimento Neural , Fosforilação , Poli I-C/metabolismo , Ligação Proteica , Proteínas Serina-Treonina Quinases/metabolismoRESUMO
Innate immunity is the first line of defense against virus infections and is marked by production of type I interferons (IFN), a family of cytokines that includes IFN-ß and several IFN-αs. For the filoviruses and many other RNA viruses that replicate in the cytoplasm, the RIG-I-like pattern recognition receptors (RLRs) are potential triggers of IFN production. To counteract such innate antiviral responses, many viruses encode proteins that antagonize RLR signaling. Ebola virus (EBOV) and other filoviruses produce VP35 proteins that block IFN induction via RLR signaling. We describe here cell-based reporter gene assays that quantify the IFN-antagonist function of filovirus VP35 proteins by assessing activation of the IFN-ß promoter.