Hepatitis C virus NS2 and NS3/4A proteins are potent inhibitors of host cell cytokine/chemokine gene expression.
BACKGROUND
Hepatitis C virus (HCV) encodes several proteins that interfere with the host cell antiviral response. Previously, the serine protease NS3/4A was shown to inhibit IFN-beta gene expression by blocking dsRNA-activated retinoic acid-inducible gene I (RIG-I) and Toll-like receptor 3 (TLR3)-mediated signaling pathways.


RESULTS
In the present work, we systematically studied the effect of all HCV proteins on IFN gene expression. NS2 and NS3/4A inhibited IFN gene activation. NS3/4A inhibited the Sendai virus-induced expression of multiple IFN (IFN-alpha, IFN-beta and IFN-lambda1/IL-29) and chemokine (CCL5, CXCL8 and CXCL10) gene promoters. NS2 and NS3/4A, but not its proteolytically inactive form NS3/4A-S139A, were found to inhibit promoter activity induced by RIG-I or its adaptor protein Cardif (or IPS-1/MAVS/VISA). Both endogenous and transfected Cardif were proteolytically cleaved by NS3/4A but not by NS2 indicating different mechanisms of inhibition of host cell cytokine production by these HCV encoded proteases. Cardif also strongly colocalized with NS3/4A at the mitochondrial membrane, implicating the mitochondrial membrane as the site for proteolytic cleavage. In many experimental systems, IFN priming dramatically enhances RNA virus-induced IFN gene expression; pretreatment of HEK293 cells with IFN-alpha strongly enhanced RIG-I expression, but failed to protect Cardif from NS3/4A-mediated cleavage and failed to restore Sendai virus-induced IFN-beta gene expression.


CONCLUSIONS
HCV NS2 and NS3/4A proteins were identified as potent inhibitors of cytokine gene expression suggesting an important role for HCV proteases in counteracting host cell antiviral response.
Kaukinen
Pasi
P
Department of Viral Diseases and Immunology, National Public Health Institute, Helsinki, Finland. pasi.kaukinen@ktl.fi
Sillanpää
Maarit
M
Kotenko
Sergei
S
Lin
Rongtuan
R
Hiscott
John
J
Melén
Krister
K
Julkunen
Ilkka
I
D048868:Adaptor Proteins, Signal Transducing / Q000032:analysis / Q000378:metabolism; D002460:Cell Line; D016207:Cytokines / Q000235:genetics; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases; D015870:Gene Expression / Q000187:drug effects; D005786:Gene Expression Regulation; D016174:Hepacivirus / Q000737:chemistry* / Q000276:immunology*; D006801:Humans; D016898:Interferon-alpha / Q000494:pharmacology; D016899:Interferon-beta / Q000235:genetics*; D051336:Mitochondrial Membranes / Q000737:chemistry; D011401:Promoter Regions, Genetic; D020365:RNA Helicases / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D011971:Receptors, Immunologic; D015398:Signal Transduction; D051196:Toll-Like Receptor 3 / Q000235:genetics / Q000276:immunology; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000276:immunology; D015533:Transcriptional Activation; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D017361:Viral Nonstructural Proteins / Q000032:analysis / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D000085242:Viral Proteases
D048868:Adaptor Proteins, Signal Transducing; D016207:Cytokines; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases; D016898:Interferon-alpha; D016899:Interferon-beta; D020365:RNA Helicases; D011971:Receptors, Immunologic; D051196:Toll-Like Receptor 3; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D017361:Viral Nonstructural Proteins; C505371:MAVS protein, human; C097010:NS2 protein, Hepatitis C virus; C084422:NS3 protein, hepatitis C virus; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D000085242:Viral Proteases; C495344:TLR3 protein, human; C495345:TLR4 protein, human; C452820:RIGI protein, human