Gastroenterology

Gastroenterology

Volume 127, Issue 5, November 2004, Pages 1513-1524
Gastroenterology

Basic-liver, pancreas, and biliary tract
Hepatitis C core and nonstructural 3 proteins trigger toll-like receptor 2-mediated pathways and inflammatory activation

https://doi.org/10.1053/j.gastro.2004.08.067Get rights and content

Background & Aims: Recent evidence suggests that toll-like receptors (TLRs) recognize certain viruses. We reported that hepatitis C virus (HCV) core and nonstructural 3 (NS3) proteins activate inflammatory pathways in monocytes. The aim of this study was to investigate the role of TLRs in innate immune cell activation by core and NS3 proteins. Methods: Human monocytes, human embryonic kidney cells transfected with TLR2, and peritoneal macrophages from TLR2, MyD88 knockout, and wild-type mice were studied to determine intracellular signaling and proinflammatory cytokine induction by HCV proteins. Results: HCV core and NS3 proteins triggered inflammatory cell activation via the pattern recognition receptor TLR2 and failed to activate macrophages from TLR2 or MyD88-deficient mice. HCV core and NS3 induced interleukin (IL)-1 receptor-associated kinase (IRAK) activity, phosphorylation of p38, extracellular regulated (ERK), and c-jun N-terminal (JNK) kinases and induced AP-1 activation. Activation of nuclear factor-κB by core and NS3 was associated with increased IκBα phosphorylation. TLR2-mediated cell activation was dependent on the conformation of core and NS3 proteins and required sequences in the regions of aa 2–122 in core and aa 1450–1643 in NS3. Although cellular uptake of core and NS3 proteins was independent of TLR2 expression, cell activation required TLR2. HCV core protein and TLR2 showed intracellular colocalization. The hyper-elevated TNF-α induction by TLR2 ligands in monocytes of HCV-infected patients was not due to increased TLR2 expression. Conclusions: HCV core and NS3 proteins trigger inflammatory pathways via TLR2 that may affect viral recognition and contribute to activation of the innate immune system.

Section snippets

Reagents

Phenol-purified lipopolysaccharide (pLPS) was kindly provided by Dr. Latz E. (University of Massachusetts Medical School, Worcester, MA). S aureus peptidoglycan (PGN) was purchased from Fluka (Milwaukee, WI), zymosan from Sigma (St. Louise, MO), PAM2CSK4 and PAM3CSK4 from EMC Microcollections GmbH (Germany), fetal calf serum from HyClone (Logan, UT), and cell culture media D-MEM and RPMI1640 from Gibco (Grand Island, NY). Recombinant hepatitis C core, NS3, NS4, and NS5 proteins were purchased

HCV core and NS3 proteins trigger cellular activation via toll-like receptor 2

Increasing evidence suggests that, in addition to recognition of bacterial and fungal pathogens, toll-like receptors are also involved in recognition of viral pathogens. TLR-mediated “danger” signals contribute to activation of innate immune responses to trigger viral elimination and inflammatory responses. We, and others, have reported that there is increased proinflammatory activation in patients with chronic HCV infection, including increased monocyte TNF-α production.7, 8 We have recently

Discussion

Although the mechanisms of hepatitis C viral replication have been extensively studied, little is known about the molecular mechanisms by which immune cells recognize HCV. Here we demonstrate that the pattern recognition receptor TLR2 is required to recognize components of the HCV polyprotein. Our data show that HCV core and NS3 but not E2 proteins activate innate immune cells in a TLR2-dependent fashion and result in downstream induction of TLR2-specific intracellular signaling pathways that

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    Supported by PHS grant AA12862 and by the resources of University of Massachusetts Medical School CFAR and DERC core facilities.

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