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Liu Z, Zhang Z, Yang L, Zhang Y, Li D, Zhang Q, Niu C, Zhang B, Zhai Y, Wang Z. Effect and mechanism of C-terminal cysteine on the properties of HEV p222 protein. Virology 2024; 595:110091. [PMID: 38718446 DOI: 10.1016/j.virol.2024.110091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2024] [Revised: 04/07/2024] [Accepted: 04/18/2024] [Indexed: 05/18/2024]
Abstract
Preliminary investigations have demonstrated that the cysteines located at the C-terminus of HEV ORF2 protein exhibits disulfide bonding capability during virus-like particles (VLPs) assembly. However, the effect and mechanism underlying the pairing of disulfide bonds formed by C627, C630, and C638 remains unclear. The p222 protein encompasses C-terminus and serves as a representative of HEV ORF2 to investigate the specific impacts of C627, C630, and C638. The three cysteines were subjected to site-directed mutagenesis and expressed in prokaryotes; Both the mutated proteins and p222 underwent polymerization except for p222A; Surprisingly, only p222 was observed as abundant spherical particles under transmission electron microscope (TEM); Stability and immunogenicity of the p222 exhibited higher than other mutated proteins; LC/MS/MS analysis identified four disulfide bonds in the p222. The novel findings suggest that the three cysteines contribute to structural and functional properties of ORF2 protein, highlighting the indispensability of each cysteine.
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Affiliation(s)
- Zhenzhen Liu
- College of Medicine, Henan Polytechnic University, Jiaozuo, 454000, Henan, China
| | - Zhenzhen Zhang
- College of Medicine, Henan Polytechnic University, Jiaozuo, 454000, Henan, China
| | - Lanping Yang
- College of Medicine, Henan Polytechnic University, Jiaozuo, 454000, Henan, China
| | - Yongwen Zhang
- College of Medicine, Henan Polytechnic University, Jiaozuo, 454000, Henan, China
| | - Dong Li
- College of Medicine, Henan Polytechnic University, Jiaozuo, 454000, Henan, China
| | - Qingling Zhang
- College of Medicine, Henan Polytechnic University, Jiaozuo, 454000, Henan, China
| | - Chao Niu
- College of Medicine, Henan Polytechnic University, Jiaozuo, 454000, Henan, China
| | - Baobao Zhang
- College of Medicine, Henan Polytechnic University, Jiaozuo, 454000, Henan, China
| | - Yangyang Zhai
- College of Medicine, Henan Polytechnic University, Jiaozuo, 454000, Henan, China
| | - Zhenhui Wang
- College of Medicine, Henan Polytechnic University, Jiaozuo, 454000, Henan, China.
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2
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Panny L, Akrhymuk I, Bracci N, Woodson C, Flor R, Elliott I, Zhou W, Narayanan A, Campbell C, Kehn-Hall K. Venezuelan equine encephalitis virus E1 protein interacts with PDIA6 and PDI inhibition reduces alphavirus production. Antiviral Res 2023; 212:105560. [PMID: 36822370 DOI: 10.1016/j.antiviral.2023.105560] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Revised: 02/13/2023] [Accepted: 02/19/2023] [Indexed: 02/25/2023]
Abstract
Venezuelan equine encephalitis virus (VEEV) is an alphavirus transmitted by mosquitos that can cause a febrile illness and induce severe neurological complications in humans and equine populations. Currently there are no FDA approved vaccines or antiviral treatments to combat VEEV. Proteomic techniques were utilized to create an interactome of the E1 fusion glycoprotein of VEEV. VEEV E1 interacted with a number of cellular chaperone proteins including protein disulfide isomerase family A member 6 (PDIA6). PDI inhibition through LOC14 and/or nitazoxanide treatment effectively decreased production of VEEV and other alphaviruses in vitro, including eastern equine encephalitis virus, Sindbis virus, and chikungunya virus. Decreased oxidoreductive capabilities of PDIs through LOC14 or nitazoxanide treatment impacted both early and late events in viral replication, including the production of non-infectious virions and decreased VEEV E1 disulfide bond formation. Results from this study identified PDIs as critical regulators of alphavirus replication and potential therapeutic targets.
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Affiliation(s)
- Lauren Panny
- Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24060, USA; Center for Emerging, Zoonotic, and Arthropod-borne Pathogens, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24060, USA
| | - Ivan Akrhymuk
- Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24060, USA
| | - Nicole Bracci
- Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24060, USA
| | - Caitlin Woodson
- Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24060, USA
| | - Rafaela Flor
- Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24060, USA; Center for Emerging, Zoonotic, and Arthropod-borne Pathogens, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24060, USA
| | - Isaac Elliott
- Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24060, USA
| | - Weidong Zhou
- Center for Applied Proteomics and Molecular Medicine, School of Systems Biology, George Mason University, Manassas, VA, 20110, USA
| | - Aarthi Narayanan
- Department of Biology, George Mason University, Fairfax, VA, 22030, USA
| | | | - Kylene Kehn-Hall
- Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24060, USA; Center for Emerging, Zoonotic, and Arthropod-borne Pathogens, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24060, USA.
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3
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Langton M, Pandelia ME. Hepatitis B Virus Oncoprotein HBx Is Not an ATPase. ACS OMEGA 2020; 5:16772-16778. [PMID: 32685845 PMCID: PMC7364715 DOI: 10.1021/acsomega.0c01762] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Accepted: 06/12/2020] [Indexed: 06/11/2023]
Abstract
HBx is the smallest gene product of the Hepatitis B virus (HBV) and an oncogenic stimulus in chronic infections leading to liver disease. HBx interacts and interferes with numerous cellular processes, but its modes of action remain poorly understood. It has been invoked that HBx employs nucleotide hydrolysis to regulate molecular pathways or protein-protein interactions. In the present study, we reinvestigate the (d)NTP hydrolysis of recombinant HBx to explore its potential as a biochemical probe for antiviral studies. For our investigations, we employed existing soluble constructs (i.e., GST-HBx, MBP-HBx) and engineered new fusion proteins (i.e., DsbC-HBx, NusA-HBx), which are shown to serve as better systems for in vitro research. We performed mutational scanning of the computationally predicted NTP-binding domain, which includes residues associated with clinical cases. Steady-state and end-point activity assays, in tandem with mass-spectrometric analyses, reveal that the observed hydrolysis of all alleged HBx substrates, ATP, dATP, and GTP, is contingent on the presence of the GroEL chaperone, which preferentially copurifies as a contaminant with GST-HBx and MBP-HBx. Collectively, our findings provide new technical standards for recombinant HBx studies and reveal that nucleotide hydrolysis is not an operant mechanism by which HBx contributes to viral HBV carcinogenesis.
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Liu Z, Behloul N, Baha S, Wei W, Tao W, Zhang T, Li W, Shi R, Meng J. Role of the C-terminal cysteines in virus-like particle formation and oligomerization of the hepatitis E virus ORF2 truncated proteins. Virology 2020; 544:1-11. [DOI: 10.1016/j.virol.2020.01.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2019] [Revised: 01/26/2020] [Accepted: 01/26/2020] [Indexed: 12/12/2022]
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Prescott NA, Bram Y, Schwartz RE, David Y. Targeting Hepatitis B Virus Covalently Closed Circular DNA and Hepatitis B Virus X Protein: Recent Advances and New Approaches. ACS Infect Dis 2019; 5:1657-1667. [PMID: 31525994 DOI: 10.1021/acsinfecdis.9b00249] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Chronic Hepatitis B virus (HBV) infection remains a worldwide concern and public health problem. Two key aspects of the HBV life cycle are essential for viral replication and thus the development of chronic infections: the establishment of the viral minichromosome, covalently closed circular (ccc) DNA, within the nucleus of infected hepatocytes and the expression of the regulatory Hepatitis B virus X protein (HBx). Interestingly, nuclear HBx redirects host epigenetic machinery to activate cccDNA transcription. In this Perspective, we provide an overview of recent advances in understanding the regulation of cccDNA and the mechanistic and functional roles of HBx. We also describe the progress toward targeting both cccDNA and HBx for therapeutic purposes. Finally, we outline standing questions in the field and propose complementary chemical biology approaches to address them.
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Affiliation(s)
- Nicholas A. Prescott
- Chemical Biology Program, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, United States
- Tri-Institutional PhD Program in Chemical Biology, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, United States
| | - Yaron Bram
- Division of Gastroenterology and Hepatology, Department of Medicine, Weill Cornell Medicine, 1300 York Avenue, New York, New York 10065, United States
| | - Robert E. Schwartz
- Division of Gastroenterology and Hepatology, Department of Medicine, Weill Cornell Medicine, 1300 York Avenue, New York, New York 10065, United States
- Department of Physiology, Biophysics and Systems Biology, Weill Cornell Medicine, 1300 York Avenue, New York, New York 10065, United States
| | - Yael David
- Chemical Biology Program, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, United States
- Tri-Institutional PhD Program in Chemical Biology, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, United States
- Department of Physiology, Biophysics and Systems Biology, Weill Cornell Medicine, 1300 York Avenue, New York, New York 10065, United States
- Department of Pharmacology, Weill Cornell Medicine, 1300 York Avenue, New York, New York 10065, United States
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Hepatitis B Virus X Protein Function Requires Zinc Binding. J Virol 2019; 93:JVI.00250-19. [PMID: 31167910 PMCID: PMC6675892 DOI: 10.1128/jvi.00250-19] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Accepted: 05/28/2019] [Indexed: 12/18/2022] Open
Abstract
The host structural maintenance of chromosomes 5/6 complex (Smc5/6) suppresses hepatitis B virus (HBV) transcription. HBV counters this restriction by expressing the X protein (HBx), which redirects the cellular DNA damage-binding protein 1 (DDB1)-containing E3 ubiquitin ligase to target Smc5/6 for degradation. However, the details of how HBx modulates the interaction between DDB1 and Smc5/6 remain to be determined. In this study, we performed biophysical analyses of recombinant HBx and functional analysis of HBx mutants in HBV-infected primary human hepatocytes (PHH) to identify key regions and residues that are required for HBx function. We determined that recombinant HBx is soluble and exhibits stoichiometric zinc binding when expressed in the presence of DDB1. Mass spectrometry-based hydrogen-deuterium exchange and cysteine-specific chemical footprinting of the HBx:DDB1 complex identified several HBx cysteine residues (located between amino acids 61 and 137) that are likely involved in zinc binding. These cysteine residues did not form disulfide bonds in HBx expressed in human cells. In line with the biophysical data, functional analysis demonstrated that HBx amino acids 45 to 140 are required for Smc6 degradation and HBV transcription in PHH. Furthermore, site-directed mutagenesis determined that C61, C69, C137, and H139 are necessary for HBx function, although they are likely not essential for DDB1 binding. This CCCH motif is highly conserved in HBV as well as in the X proteins from various mammalian hepadnaviruses. Collectively, our data indicate that the essential HBx cysteine and histidine residues form a zinc-binding motif that is required for HBx function.IMPORTANCE The structural maintenance of chromosomes 5/6 complex (Smc5/6) is a host restriction factor that suppresses HBV transcription. HBV counters this restriction by expressing HBV X protein (HBx), which redirects a host ubiquitin ligase to target Smc5/6 for degradation. Despite this recent advance in understanding HBx function, the key regions and residues of HBx required for Smc5/6 degradation have not been determined. In the present study, we performed biochemical, biophysical, and cell-based analyses of HBx. By doing so, we mapped the minimal functional region of HBx and identified a highly conserved CCCH motif in HBx that is likely responsible for coordinating zinc and is essential for HBx function. We also developed a method to produce soluble recombinant HBx protein that likely adopts a physiologically relevant conformation. Collectively, this study provides new insights into the HBx structure-function relationship and suggests a new approach for structural studies of this enigmatic viral regulatory protein.
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Kapoor NR, Chadha R, Kumar S, Choedon T, Reddy VS, Kumar V. The HBx gene of hepatitis B virus can influence hepatic microenvironment via exosomes by transferring its mRNA and protein. Virus Res 2017; 240:166-174. [PMID: 28847700 DOI: 10.1016/j.virusres.2017.08.009] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2017] [Revised: 08/02/2017] [Accepted: 08/21/2017] [Indexed: 12/13/2022]
Abstract
The cellular secretory vesicles known as 'exosomes' have emerged as key player in intercellular transport and communication between different eukaryotic in order to maintain body homeostasis. Many pathogenic viruses utilize exosome pathway to efficiently transfer bioactive components from infected cells to naïve cells. Here, we show that HBx can tweak the exosome biogenesis machinery both by enhancing neutral sphingomyelinase2 activity as well as by interacting with exosomal biomarkers such as neutral sphingomyelinase2, CD9 and CD81. The nano particle tracking analysis revealed enhanced secretion of exosomes by the HBx-expressing cells while confocal studies confirmed the co-localization of HBx with CD9 and CD63. Importantly, we observed the encapsulation of HBx mRNA and protein in these exosomes besides some other qualitative changes. The exosomal cargo secreted by HBx-expressing cells had a profound effect on the recipient hepatic cells including creation of a milieu conducive for cellular-transformation. Thus, the present study unfolds a novel role of HBx in intercellular communication by facilitating horizontal transfer of viral gene products and other host factors via exosomes in order to support viral spread and pathogenesis.
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Affiliation(s)
- Neetu Rohit Kapoor
- Virology Group, International Centre for Genetic Engineering and Biotechnology, New Delhi, India
| | - Radhika Chadha
- Virology Group, International Centre for Genetic Engineering and Biotechnology, New Delhi, India
| | - Saravanan Kumar
- Plant Transformation Group, International Centre for Genetic Engineering and Biotechnology, New Delhi, India
| | - Tenzin Choedon
- Virology Group, International Centre for Genetic Engineering and Biotechnology, New Delhi, India
| | - Vanga Siva Reddy
- Plant Transformation Group, International Centre for Genetic Engineering and Biotechnology, New Delhi, India
| | - Vijay Kumar
- Virology Group, International Centre for Genetic Engineering and Biotechnology, New Delhi, India.
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Cho MY, Cheong JY, Lim W, Jo S, Lee Y, Wang HJ, Han KH, Cho H. Prognostic significance of catalase expression and its regulatory effects on hepatitis B virus X protein (HBx) in HBV-related advanced hepatocellular carcinomas. Oncotarget 2015; 5:12233-46. [PMID: 25361011 PMCID: PMC4322996 DOI: 10.18632/oncotarget.2625] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2014] [Accepted: 10/23/2014] [Indexed: 02/06/2023] Open
Abstract
Hepatitis B virus X protein (HBx) plays a role in liver cancer development. We previously showed that ROS increased HBx levels and here, we investigated the role of antioxidants in the regulation of HBx expression and their clinical relevance. We found that overexpression of catalase induced a significant loss in HBx levels. The cysteine null mutant of HBx (Cys-) showed a dramatic reduction in its protein stability. In clonogenic proliferation assays, Huh7-X cells produced a significant number of colonies whereas Huh7-Cys- cells failed to generate them. The Cys at position 69 of HBx was crucial to maintain its protein stability and transactivation function in response to ROS. Among 50 HBV-related hepatocellular carcinoma (HCC) specimens, 72% of HCCs showed lower catalase levels than those of surrounding non-tumor tissues. In advanced stage IV, catalase levels in non-tumor tissues were increased whereas those in tumors were further reduced. Accordingly, patients with a high T/N ratio for catalase showed significantly longer survival than those with a low T/N ratio. Together, catalase expression in HCC patients can be clinically useful for prediction of patient survival, and restoration of catalase expression in HCCs could be an important strategy for intervention in HBV-induced liver diseases.
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Affiliation(s)
- Mi-Young Cho
- Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, The Graduate School, Ajou University, Suwon, Korea. Department of Biomedical Sciences, The Graduate School, Ajou University, Suwon, Korea
| | - Jae Youn Cheong
- Department of Gastroenterology, Ajou University Hospital, Ajou University School of Medicine, Suwon, Korea
| | - Wonchung Lim
- Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, The Graduate School, Ajou University, Suwon, Korea. Current address: Department of Sports Medicine, Cheongju University, Cheongju, Korea
| | - Sujin Jo
- Genomic Instability Research Center, Ajou University School of Medicine, Suwon, Korea
| | - Youngsoo Lee
- Genomic Instability Research Center, Ajou University School of Medicine, Suwon, Korea
| | - Hee-Jung Wang
- Department of Surgery, Ajou University Hospital, Ajou University School of Medicine, Suwon, Korea
| | - Kyou-Hoon Han
- Biomedical Translational Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Korea
| | - Hyeseong Cho
- Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, The Graduate School, Ajou University, Suwon, Korea. Department of Biomedical Sciences, The Graduate School, Ajou University, Suwon, Korea. Genomic Instability Research Center, Ajou University School of Medicine, Suwon, Korea
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Ahuja R, Kapoor NR, Kumar V. The HBx oncoprotein of hepatitis B virus engages nucleophosmin to promote rDNA transcription and cellular proliferation. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2015; 1853:1783-95. [PMID: 25918010 DOI: 10.1016/j.bbamcr.2015.04.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 10/14/2014] [Revised: 04/10/2015] [Accepted: 04/14/2015] [Indexed: 12/31/2022]
Abstract
The pleiotropic HBx oncoprotein of hepatitis B virus is well known to promote the expression of ribosomal RNAs and several host proteins that are known to support the development and progression of hepatocellular carcinoma (HCC). While overexpression of the nucleolar phosphoprotein, nucleophosmin (NPM), correlates with HCC progression, its upregulation by viral HBx and the resulting impact on perturbed nucleolar functions remain enigmatic. The present study shows that HBx up-regulates NPM levels and hijacks its functions to promote cellular proliferation. We found that HBx expression stabilizes NPM through post-translational modifications. Enhanced CDK2-mediated phosphorylation of NPM at Thr199 upon HBx expression prevented its proteolytic cleavage and provided resistance to apoptosis. Further, HBx directly interacted with the C-terminal domain of NPM and got translocated into the nucleolus where it facilitated the recruitment of RNA polymerase I transcriptional machinery onto the rDNA promoter. Our results indicate that HBx enhances rDNA transcription via a novel regulatory mechanism involving acetylation of NPM and the subsequent depletion of histones from the rDNA promoter. Enhanced production of ribosomal RNA resulting from co-expression of HBx and NPM promoted ribosome biogenesis, cellular proliferation and transformation. Taken together, our study strongly suggests an important role of NPM in mediating the oncogenic effects of HBx and the corresponding nucleolar perturbations induced by this viral oncoprotein.
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Affiliation(s)
- Richa Ahuja
- Virology Group, International Centre for Genetic Engineering and Biotechnology (ICGEB), Aruna Asaf Ali Marg, New Delhi 110067, India
| | - Neetu Rohit Kapoor
- Virology Group, International Centre for Genetic Engineering and Biotechnology (ICGEB), Aruna Asaf Ali Marg, New Delhi 110067, India
| | - Vijay Kumar
- Virology Group, International Centre for Genetic Engineering and Biotechnology (ICGEB), Aruna Asaf Ali Marg, New Delhi 110067, India.
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Hepatitis B virus HBx protein interactions with the ubiquitin proteasome system. Viruses 2014; 6:4683-702. [PMID: 25421893 PMCID: PMC4246244 DOI: 10.3390/v6114683] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Revised: 11/16/2014] [Accepted: 11/20/2014] [Indexed: 01/04/2023] Open
Abstract
The hepatitis B virus (HBV) causes acute and chronic hepatitis, and the latter is a major risk factor for the development of hepatocellular carcinoma (HCC). HBV encodes a 17-kDa regulatory protein, HBx, which is required for virus replication. Although the precise contribution(s) of HBx to virus replication is unknown, many viruses target cellular pathways to create an environment favorable for virus replication. The ubiquitin proteasome system (UPS) is a major conserved cellular pathway that controls several critical processes in the cell by regulating the levels of proteins involved in cell cycle, DNA repair, innate immunity, and other processes. We summarize here the interactions of HBx with components of the UPS, including the CUL4 adaptor DDB1, the cullin regulatory complex CSN, and the 26S proteasome. Understanding how these protein interactions benefit virus replication remains a challenge due to limited models in which to study HBV replication. However, studies from other viral systems that similarly target the UPS provide insight into possible strategies used by HBV.
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Saxena N, Kumar V. The HBx oncoprotein of hepatitis B virus deregulates the cell cycle by promoting the intracellular accumulation and re-compartmentalization of the cellular deubiquitinase USP37. PLoS One 2014; 9:e111256. [PMID: 25347529 PMCID: PMC4210131 DOI: 10.1371/journal.pone.0111256] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2014] [Accepted: 09/16/2014] [Indexed: 01/25/2023] Open
Abstract
The HBx oncoprotein of hepatitis B Virus has been accredited as one of the protagonists in driving hepatocarcinogenesis. HBx exerts its influence over the cell cycle progression by potentiating the activity of cyclin A/E-CDK2 complex, the Cyclin A partner of which is a well-known target of cellular deubiquitinase USP37. In the present study, we observed the intracellular accumulation of cyclin A and USP37 proteins under the HBx microenvironment. Flow cytometry analysis of the HBx-expressing cells showed deregulation of cell cycle apparently due to the enhanced gene expression and stabilization of USP37 protein and deubiquitination of Cyclin A by USP37. Our co-immunoprecipitation and confocal microscopic studies suggested a direct interaction between USP37 and HBx. This interaction promoted the translocation of USP37 outside the nucleus and prevented its association and ubiquitination by E3 ubiquitin ligases - APC/CDH1 and SCF/β-TrCP. Thus, HBx seems to control the cell cycle progression via the cyclin A-CDK2 complex by regulating the intracellular distribution and stability of deubiquitinase USP37.
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Affiliation(s)
- Nehul Saxena
- Virology Group, International Center for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi, India
| | - Vijay Kumar
- Virology Group, International Center for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi, India
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