title: Hepatitis C virus NS4B induces unfolded protein response and endoplasmic reticulum overload response-dependent NF-kappaB activation.
abstract: Hepatitis C virus nonstructural protein 4B (NS4B) is an endoplasmic reticulum (ER) membrane associated protein and a potent causative factor of ER stress. Here we reported that unfolded protein response (UPR) can be activated by HCV NS4B through inducing both XBP1 mRNA splicing and ATF6 cleavage in human hepatic cells. Flow cytometric analysis revealed that HCV NS4B stimulates the production of reactive oxygen species (ROS) by perturbing intracellular Ca(2+) homeostasis. Luciferase assay showed that HCV NS4B also activates the multifunctional transcription factor, NF-kappaB, in a dose-dependent manner through Ca(2+) signaling and ROS. Further immunoblot analysis showed that HCV NS4B promotes NF-kappaB translocation into the nucleus via protein-tyrosine kinase (PTK) mediated phosphorylation and subsequent degradation of IkappaBalpha. These studies provide an important insight into the implication of NS4B in HCV life cycle and HCV-associated liver disease by affecting host intracellular signal transduction pathways.
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China.
authors.forename: Shanshan
authors.initials: S
authors.lastname: Li
authors.forename: Linbai
authors.initials: L
authors.lastname: Ye
authors.forename: Xilan
authors.initials: X
authors.lastname: Yu
authors.forename: Bo
authors.initials: B
authors.lastname: Xu
authors.forename: Kuntai
authors.initials: K
authors.lastname: Li
authors.forename: Xiangdong
authors.initials: X
authors.lastname: Zhu
authors.forename: Haoju
authors.initials: H
authors.lastname: Liu
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Wu
authors.forename: Lingbao
authors.initials: L
authors.lastname: Kong
mesh_terms: D051702:Activating Transcription Factor 6 / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000737:chemistry; D003593:Cytoplasm / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D016174:Hepacivirus / Q000502:physiology*; D022781:Hepatocytes / Q000821:virology*; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000096:biosynthesis*; D017382:Reactive Oxygen Species / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors / Q000378:metabolism; D017361:Viral Nonstructural Proteins / Q000378:metabolism*; D000071717:X-Box Binding Protein 1
chemical_list: C497111:ATF6 protein, human; D051702:Activating Transcription Factor 6; D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; C080107:NS4B protein, flavivirus; D017382:Reactive Oxygen Species; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D017361:Viral Nonstructural Proteins; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; D000072000:NF-KappaB Inhibitor alpha; D002118:Calcium