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Relevance of HBx for Hepatitis B Virus-Associated Pathogenesis. Int J Mol Sci 2023; 24:ijms24054964. [PMID: 36902395 PMCID: PMC10003785 DOI: 10.3390/ijms24054964] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2023] [Revised: 02/20/2023] [Accepted: 03/02/2023] [Indexed: 03/08/2023] Open
Abstract
The hepatitis B virus (HBV) counts as a major global health problem, as it presents a significant causative factor for liver-related morbidity and mortality. The development of hepatocellular carcinomas (HCC) as a characteristic of a persistent, chronic infection could be caused, among others, by the pleiotropic function of the viral regulatory protein HBx. The latter is known to modulate an onset of cellular and viral signaling processes with emerging influence in liver pathogenesis. However, the flexible and multifunctional nature of HBx impedes the fundamental understanding of related mechanisms and the development of associated diseases, and has even led to partial controversial results in the past. Based on the cellular distribution of HBx-nuclear-, cytoplasmic- or mitochondria-associated-this review encompasses the current knowledge and previous investigations of HBx in context of cellular signaling pathways and HBV-associated pathogenesis. In addition, particular focus is set on the clinical relevance and potential novel therapeutic applications in the context of HBx.
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Xu QG, Yuan SX, Tao QF, Yu J, Cai J, Yang Y, Guo XG, Lin KY, Ma JZ, Dai DS, Wang ZG, Gu FM, Zhao LH, Li LQ, Liu JF, Sun SH, Zang YJ, Liu H, Yang F, Zhou WP. A novel HBx genotype serves as a preoperative predictor and fails to activate the JAK1/STATs pathway in hepatocellular carcinoma. J Hepatol 2019; 70:904-917. [PMID: 30654066 DOI: 10.1016/j.jhep.2019.01.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Revised: 11/29/2018] [Accepted: 01/04/2019] [Indexed: 12/19/2022]
Abstract
BACKGROUND & AIMS Genetic variability in the hepatitis B virus X gene (HBx) is frequently observed and is associated with hepatocellular carcinoma (HCC) progression. However, a genotype classification based on the full-length HBx sequence and the impact of genotypes on hepatitis B virus (HBV)-related HCC prognosis remain unclear. We therefore aimed to perform this genotype classification and assess its clinical impact. METHODS We classified the genotypes of the full-length HBx gene through sequencing and a cluster analysis of HBx DNA from a cohort of patients with HBV-related HCC, which served as the primary cohort (n = 284). Two independent HBV-related HCC cohorts, a validation cohort (n = 171) and a serum cohort (n = 168), were used to verify the results. Protein microarray assay analysis was performed to explore the underlying mechanism. RESULTS In the primary cohort, the HBx DNA was classified into 3 genotypes: HBx-EHBH1, HBx-EHBH2, and HBx-EHBH3. HBx-EHBH2 (HBx-E2) indicated better recurrence-free survival and overall survival for patients with HCC. HBx-E2 was significantly correlated with the absence of liver cirrhosis, a small tumor size, a solitary tumor, complete encapsulation and Barcelona Clinic Liver Cancer (BCLC) stage A-0 tumors. Additionally, HBx-E2 served as a significant prognostic factor for patients with BCLC stage B HCC after hepatectomy. Mechanistically, HBx-E2 is unable to promote proliferation in HCC cells and normal hepatocytes. It also fails to activate the Janus kinase 1 (JAK1)/signal transducer and activator of transcription 3 (STAT3)/STAT5 pathway. CONCLUSION Our study identifies a novel HBx genotype that is unable to promote the proliferation of HCC cells and suggests a potential marker to preoperatively predict the prognosis of patients with BCLC stage B, HBV-associated, HCC. LAY SUMMARY We classified a novel genotype of the full-length hepatitis B virus X gene (HBx), HBx-E2. This genotype was identified in tumor and nontumor tissues from patients with hepatitis B virus-related hepatocellular carcinoma. HBx-E2 could preoperatively predict the prognosis of patients with intermediate stage hepatocellular carcinoma, after resection.
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Affiliation(s)
- Qing-Guo Xu
- The Third Department of Hepatic Surgery, Shanghai Eastern Hepatobiliary Surgery Hospital, Shanghai, China; Organ Transplantation Center, Affiliated Hospital of Qingdao University, Qingdao, China
| | - Sheng-Xian Yuan
- The Third Department of Hepatic Surgery, Shanghai Eastern Hepatobiliary Surgery Hospital, Shanghai, China
| | - Qi-Fei Tao
- The Third Department of Hepatic Surgery, Shanghai Eastern Hepatobiliary Surgery Hospital, Shanghai, China
| | - Jian Yu
- The Third Department of Hepatic Surgery, Shanghai Eastern Hepatobiliary Surgery Hospital, Shanghai, China
| | - Jie Cai
- The Third Department of Hepatic Surgery, Shanghai Eastern Hepatobiliary Surgery Hospital, Shanghai, China
| | - Yuan Yang
- The Third Department of Hepatic Surgery, Shanghai Eastern Hepatobiliary Surgery Hospital, Shanghai, China
| | - Xing-Gang Guo
- The Third Department of Hepatic Surgery, Shanghai Eastern Hepatobiliary Surgery Hospital, Shanghai, China
| | - Kong-Ying Lin
- The Third Department of Hepatic Surgery, Shanghai Eastern Hepatobiliary Surgery Hospital, Shanghai, China; Mengchao Hepatobiliary Hospital of Fujian Medical University, Fujian, China
| | - Jin-Zhao Ma
- The Department of Medical Genetics, Second Military Medical University, Shanghai, China
| | - De-Shu Dai
- The Third Department of Hepatic Surgery, Shanghai Eastern Hepatobiliary Surgery Hospital, Shanghai, China
| | - Zhen-Guang Wang
- The Third Department of Hepatic Surgery, Shanghai Eastern Hepatobiliary Surgery Hospital, Shanghai, China
| | - Fang-Ming Gu
- The Third Department of Hepatic Surgery, Shanghai Eastern Hepatobiliary Surgery Hospital, Shanghai, China
| | - Ling-Hao Zhao
- The Third Department of Hepatic Surgery, Shanghai Eastern Hepatobiliary Surgery Hospital, Shanghai, China
| | - Le-Qun Li
- Department of Hepatobiliary Surgery, Affiliated Tumor Hospital of Guangxi Medical University, Guangxi, China
| | - Jing-Feng Liu
- Mengchao Hepatobiliary Hospital of Fujian Medical University, Fujian, China
| | - Shu-Han Sun
- The Department of Medical Genetics, Second Military Medical University, Shanghai, China
| | - Yun-Jin Zang
- Organ Transplantation Center, Affiliated Hospital of Qingdao University, Qingdao, China
| | - Hui Liu
- The Third Department of Hepatic Surgery, Shanghai Eastern Hepatobiliary Surgery Hospital, Shanghai, China.
| | - Fu Yang
- The Department of Medical Genetics, Second Military Medical University, Shanghai, China.
| | - Wei-Ping Zhou
- The Third Department of Hepatic Surgery, Shanghai Eastern Hepatobiliary Surgery Hospital, Shanghai, China; Key Laboratory of Signaling Regulation and Targeting Therapy of Liver Cancer (SMMU), Ministry of Education, Shanghai, China; Shanghai Key Laboratory of Hepatobiliary Tumor Biology (EHBH), Shanghai, China.
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Li W, Goto K, Matsubara Y, Ito S, Muroyama R, Li Q, Kato N. The characteristic changes in hepatitis B virus x region for hepatocellular carcinoma: a comprehensive analysis based on global data. PLoS One 2015; 10:e0125555. [PMID: 25942596 PMCID: PMC4420286 DOI: 10.1371/journal.pone.0125555] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2014] [Accepted: 03/25/2015] [Indexed: 12/12/2022] Open
Abstract
OBJECTIVES Mutations in hepatitis B virus (HBV) X region (HBx) play important roles in hepatocarcinogenesis while the results remain controversial. We sought to clarify potential hepatocellular carcinoma (HCC)-characteristic mutations in HBx from HBV genotype C-infected patients and the distribution of those mutations in different disease phases and genotypes. METHODS HBx sequences downloaded from an online global HBV database were screened and then classified into Non-HCC or HCC group by diagnosis information. Patients' data of patient age, gender, country or area, and viral genotype were also extracted. Logistic regression was performed to evaluate the effects of mutations on HCC risk. RESULTS 1) Full length HBx sequences (HCC: 161; Non-HCC: 954) originated from 1115 human sera across 29 countries/areas were extracted from the downloaded 5956 HBx sequences. Genotype C occupied 40.6% of Non-HCC (387/954) and 89.4% of HCC (144/161). 2) Sixteen nucleotide positions showed significantly different distributions between genotype C HCC and Non-HCC groups. 3) Logistic regression showed that mutations A1383C (OR: 2.32, 95% CI: 1.34-4.01), R1479C/T (OR: 1.96, 95% CI: 1.05-3.64; OR: 5.15, 95% CI: 2.53-10.48), C1485T (OR: 2.40, 95% CI: 1.41-4.08), C1631T (OR: 4.09, 95% CI: 1.41-11.85), C1653T (OR: 2.58, 95% CI: 1.59-4.19), G1719T (OR: 2.11, 95% CI: 1.19-3.73), and T1800C (OR: 23.59, 95% CI: 2.25-247.65) were independent risk factors for genotype C HBV-related HCC, presenting different trends among individual disease phases. 4) Several genotype C HCC risk mutations pre-existed, even as major types, in early disease phases with other genotypes. CONCLUSIONS Mutations associated with HCC risk were mainly located in HBx transactivation domain, viral promoter, protein/miRNA binding sites, and the area for immune epitopes. Furthermore, the signatures of these mutations were unique to disease phases leading to HCC, suggesting molecular counteractions between the virus and host during hepatocarcinogenesis.
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Affiliation(s)
- Wenwen Li
- Division of advanced genome medicine, Advanced clinical research center, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan
| | - Kaku Goto
- Division of advanced genome medicine, Advanced clinical research center, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan
| | - Yasuo Matsubara
- Division of advanced genome medicine, Advanced clinical research center, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan
| | - Sayaka Ito
- Division of advanced genome medicine, Advanced clinical research center, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan
| | - Ryosuke Muroyama
- Division of advanced genome medicine, Advanced clinical research center, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan
| | - Qiang Li
- Affiliated Infectious Disease Hospital of Shandong University, Jinan, Shandong, China
| | - Naoya Kato
- Division of advanced genome medicine, Advanced clinical research center, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan
- * E-mail:
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Abstract
The hepatitis B virus (HBV) is a small enveloped DNA virus that causes acute and chronic hepatitis. HBV infection is a world health problem, with 350 million chronically infected people at increased risk of developing liver disease and hepatocellular carcinoma (HCC). HBV has been classified among human tumor viruses by virtue of a robust epidemiologic association between chronic HBV carriage and HCC occurrence. In the absence of cytopathic effect in infected hepatocytes, the oncogenic role of HBV might involve a combination of direct and indirect effects of the virus during the multistep process of liver carcinogenesis. Liver inflammation and hepatocyte proliferation driven by host immune responses are recognized driving forces of liver cell transformation. Genetic and epigenetic alterations can also result from viral DNA integration into host chromosomes and from prolonged expression of viral gene products. Notably, the transcriptional regulatory protein HBx encoded by the X gene is endowed with tumor promoter activity. HBx has pleiotropic activities and plays a major role in HBV pathogenesis and in liver carcinogenesis. Because hepatic tumors carry a dismal prognosis, there is urgent need to develop early diagnostic markers of HCC and effective therapies against chronic hepatitis B. Deciphering the oncogenic mechanisms that underlie HBV-related tumorigenesis might help developing adapted therapeutic strategies.
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Affiliation(s)
- Lise Rivière
- Institut Pasteur, Hepacivirus and Innate Immunity Unit, 28 rue du Dr Roux, 75015, Paris, France,
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Liu LP, Hu BG, Ye C, Ho RLK, Chen GG, Lai PBS. HBx mutants differentially affect the activation of hypoxia-inducible factor-1α in hepatocellular carcinoma. Br J Cancer 2013; 110:1066-73. [PMID: 24346287 PMCID: PMC3929872 DOI: 10.1038/bjc.2013.787] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2013] [Revised: 11/19/2013] [Accepted: 11/27/2013] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Mutations in HBx gene are frequently found in HBV-associated hepatocellular carcinoma (HCC). Activation of hypoxia-inducible factor-1α (HIF-1α) contributes to HCC development and progression. Wild-type HBx has been demonstrated to activate HIF-1α, but the effect of HBx mutations on HIF-1α has not been elucidated. METHODS HBx mutations were identified by gene sequencing in 101 HCC tissues. Representative HBx mutants were cloned and transfected into HCC cells. Expression and activation of HIF-1α were analysed by western blot and luciferase assays, respectively. The relationship between HBx mutants and HIF-1α expression in HCC tissues was also evaluated. RESULTS The dual mutations K130M/V131I enhanced the functionality of HBx as they upregulated the expression and transcriptional activity of HIF-1α. The C-terminal truncations and deletion mutations, however, weakened the ability of HBx to upregulate HIF-1α. Meanwhile, the C-terminus was further found to be essential for the stability and transactivation of HBx. In the HCC tissues, there was a positive association between the HBx mutants and HIF-1α expression. CONCLUSION Different mutations of HBx exert differentiated effects on the functionality of HIF-1α, however, the overall activity of HBx mutants appears to increase the expression and transcriptional activity of HIF-1α.
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Affiliation(s)
- L-P Liu
- 1] Department of Surgery, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong SAR, China [2] Department of Hepatobiliary and Pancreas Surgery, the Second Clinical Medical College of Jinan University (Shenzhen People's Hospital), Shenzhen, Guangdong Province, China
| | - B-G Hu
- Department of Surgery, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong SAR, China
| | - C Ye
- Department of Surgery, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong SAR, China
| | - R L K Ho
- Department of Surgery, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong SAR, China
| | - G G Chen
- Department of Surgery, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong SAR, China
| | - P B S Lai
- Department of Surgery, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong SAR, China
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Martín-Vílchez S, Moreno-Otero R, Sanz-Cameno P. [Effects of hepatitis B virus X protein on chronic hepatitis B pathophysiology]. Med Clin (Barc) 2013; 140:508-13. [PMID: 23245531 DOI: 10.1016/j.medcli.2012.09.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2012] [Revised: 08/07/2012] [Accepted: 09/06/2012] [Indexed: 02/07/2023]
Abstract
The infection by hepatitis B virus often promotes chronic liver inflammation which progresses to cirrhosis and hepatocellular carcinoma in a high percentage of patients. The persistent activation of the immune system causes an incessant liver damage, which fosters a disorganized stimulation of tissue repair and remodelling phenomena. In turn, the viral protein X (HBx) is essential for virus replication and therefore for the maintenance of chronic infection. However, the important oncogenic potential of HBx seems to reside, on one hand, in its ability to integrate into cellular DNA and, additionally, in the transactivation of different cellular signaling pathways involved in cell growth regulation, apoptosis and DNA repair. HBx also interacts with proteasome subunits and notably affects mitochondrial electric potential, thus altering cellular calcium homeostasis. Finally, this review discusses the pathogenic role of HBx in the progression of chronic hepatitis B through its effects on angiogenic, fibrogenic and oncogenic processes.
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Affiliation(s)
- Samuel Martín-Vílchez
- Servicio de Aparato Digestivo, Hospital Universitario La Princesa, Universidad Autónoma de Madrid, Madrid, España
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Lee SH, Cha EJ, Lim JE, Kwon SH, Kim DH, Cho H, Han KH. Structural characterization of an intrinsically unfolded mini-HBX protein from hepatitis B virus. Mol Cells 2012; 34:165-9. [PMID: 22820921 PMCID: PMC3887815 DOI: 10.1007/s10059-012-0060-z] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2012] [Revised: 05/24/2012] [Accepted: 05/25/2012] [Indexed: 12/19/2022] Open
Abstract
The hepatitis B virus x protein (HBX) is expressed in HBV-infected liver cells and can interact with a wide range of cellular proteins. In order to understand such promiscuous behavior of HBX we expressed a truncated mini-HBX protein (named Tr-HBX) (residues 18-142) with 5 Cys → Ser mutations and characterized its structural features using circular dichroism (CD) spectropolarimetry, NMR spectroscopy as well as bioinformatics tools for predicting disorder in intrinsically unstructured proteins (IUPs). The secondary structural content of Tr-HBX from CD data suggests that Tr-HBX is only partially folded. The protein disorder prediction by IUPred reveals that the unstructured region encompasses its N-terminal ~30 residues of Tr-HBX. A two-dimensional (1)H-(15)N HSQC NMR spectrum exhibits fewer number of resonances than expected, suggesting that Tr-HBX is a hybrid type IUP where its folded C-terminal half coexists with a disordered N-terminal region. Many IUPs are known to be capable of having promiscuous interactions with a multitude of target proteins. Therefore the intrinsically disordered nature of Tr-HBX revealed in this study provides a partial structural basis for the promiscuous structure-function behavior of HBX.
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Affiliation(s)
- Si-Hyung Lee
- Biomedical Translational Research Center, Division of Convergent Biomedical Research, Korea Research Institute of Bioscience and Biotechnology, Daejeon 305-806,
Korea
| | - Eun-Ji Cha
- Biomedical Translational Research Center, Division of Convergent Biomedical Research, Korea Research Institute of Bioscience and Biotechnology, Daejeon 305-806,
Korea
| | - Ji-Eun Lim
- Biomedical Translational Research Center, Division of Convergent Biomedical Research, Korea Research Institute of Bioscience and Biotechnology, Daejeon 305-806,
Korea
| | - Soon-Hwan Kwon
- Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, Suwon 443-721,
Korea
| | - Do-Hyoung Kim
- Biomedical Translational Research Center, Division of Convergent Biomedical Research, Korea Research Institute of Bioscience and Biotechnology, Daejeon 305-806,
Korea
| | - Hyeseong Cho
- Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, Suwon 443-721,
Korea
| | - Kyou-Hoon Han
- Biomedical Translational Research Center, Division of Convergent Biomedical Research, Korea Research Institute of Bioscience and Biotechnology, Daejeon 305-806,
Korea
- Department of Bioinformatics, University of Science and Technology, Daejeon 305-333,
Korea
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Basu A, Leong SSJ. Development of an enzyme-linked immunosorbent assay analytical platform for refolding yield determination of recombinant hepatitis B virus X (HBx) protein. Anal Biochem 2011; 418:155-7. [DOI: 10.1016/j.ab.2011.07.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Revised: 07/11/2011] [Accepted: 07/13/2011] [Indexed: 10/17/2022]
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Martin-Vilchez S, Lara-Pezzi E, Trapero-Marugán M, Moreno-Otero R, Sanz-Cameno P. The molecular and pathophysiological implications of hepatitis B X antigen in chronic hepatitis B virus infection. Rev Med Virol 2011; 21:315-29. [PMID: 21755567 DOI: 10.1002/rmv.699] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2011] [Revised: 05/23/2011] [Accepted: 05/26/2011] [Indexed: 12/16/2022]
Abstract
Hepatitis B virus is considered one of the most significant environmental carcinogens in humans. Because the mechanisms of HBV replication and the development of hepatocellular carcinoma (HCC) are partially known, HBV-associated pathogenesis remains a challenge to increase its understanding. Evidence suggests that the regulatory protein hepatitis B virus X (HBx) mediates the establishment and maintenance of the chronic carrier state. HBx is a multifunctional and potentially oncogenic protein that is conserved among mammalian hepadnaviruses; it is produced very early after infection and throughout the chronic phase. HBx exerts its effects by interacting with cellular proteins and activating various signaling pathways. HBx stimulates the transcription of genes that regulate cell growth, apoptosis, and DNA repair. It also interacts with proteasome subunits and affects mitochondrial stability. Moreover, HBx participates in processes that are associated with the progression of chronic liver disease, including angiogenesis and fibrosis. This review discusses the function of HBx in the life cycle of HBV and its contribution to the pathogenesis of HCC.
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Affiliation(s)
- Samuel Martin-Vilchez
- CIBERehd, ISCIII, Madrid, Spain; Servicio Digestivo, Hospital Universitario "La Princesa" and Instituto de Investigación Biomédica "La Princesa", Madrid, Spain
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Overlapping genes produce proteins with unusual sequence properties and offer insight into de novo protein creation. J Virol 2009; 83:10719-36. [PMID: 19640978 DOI: 10.1128/jvi.00595-09] [Citation(s) in RCA: 141] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
It is widely assumed that new proteins are created by duplication, fusion, or fission of existing coding sequences. Another mechanism of protein birth is provided by overlapping genes. They are created de novo by mutations within a coding sequence that lead to the expression of a novel protein in another reading frame, a process called "overprinting." To investigate this mechanism, we have analyzed the sequences of the protein products of manually curated overlapping genes from 43 genera of unspliced RNA viruses infecting eukaryotes. Overlapping proteins have a sequence composition globally biased toward disorder-promoting amino acids and are predicted to contain significantly more structural disorder than nonoverlapping proteins. By analyzing the phylogenetic distribution of overlapping proteins, we were able to confirm that 17 of these had been created de novo and to study them individually. Most proteins created de novo are orphans (i.e., restricted to one species or genus). Almost all are accessory proteins that play a role in viral pathogenicity or spread, rather than proteins central to viral replication or structure. Most proteins created de novo are predicted to be fully disordered and have a highly unusual sequence composition. This suggests that some viral overlapping reading frames encoding hypothetical proteins with highly biased composition, often discarded as noncoding, might in fact encode proteins. Some proteins created de novo are predicted to be ordered, however, and whenever a three-dimensional structure of such a protein has been solved, it corresponds to a fold previously unobserved, suggesting that the study of these proteins could enhance our knowledge of protein space.
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Li SK, Ho SF, Tsui KW, Fung KP, Waye MYM. Identification of functionally important amino acid residues in the mitochondria targeting sequence of hepatitis B virus X protein. Virology 2008; 381:81-8. [PMID: 18805561 DOI: 10.1016/j.virol.2008.07.037] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2008] [Revised: 07/07/2008] [Accepted: 07/28/2008] [Indexed: 01/26/2023]
Abstract
Chronic hepatitis B virus (HBV) infection has been strongly associated with hepatocellular carcinoma (HCC) and the X protein (HBx) is thought to mediate the cellular changes associated with carcinogenesis. Recently, isolation of the hepatitis B virus integrants from HCC tissue by others have established the fact that the X gene is often truncated at its C-terminus. Expression of the GFP fusion proteins of HBx and its truncation mutants with a GFP tag in human liver cell-lines in this study revealed that the C-terminus of HBx is indispensable for its specific localization in the mitochondria. A crucial region of seven amino acids at the C-terminus has been mapped out in which the cysteine residue at position 115 serves as the most important residue for the subcellular localization. When cysteine 115 of HBx is mutated to alanine the mitochondria targeting property of HBx is abrogated.
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Affiliation(s)
- Sai Kam Li
- Croucher Laboratory for Human Genomics, Chinese University of Hong Kong, Shatin, N.T., Hong Kong, S.A.R., China
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Rui E, Moura PR, Gonçalves KA, Rooney RJ, Kobarg J. Interaction of the hepatitis B virus protein HBx with the human transcription regulatory protein p120E4F in vitro. Virus Res 2005; 115:31-42. [PMID: 16112766 DOI: 10.1016/j.virusres.2005.07.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2005] [Revised: 07/08/2005] [Accepted: 07/11/2005] [Indexed: 11/24/2022]
Abstract
Infection with the hepatitis B virus has been identified as one of the major causes of liver cancer. A large body of experimental work points to a central role for the virally encoded protein HBx in this form of carcinogenesis. HBx is expressed in HBV-infected liver cells and interacts with a wide range of cellular proteins, thereby interfering in cellular processes including cell signaling, cycle regulation and apoptosis. In order to identify possible new targets of the HBx protein, we performed a yeast two-hybrid screen using a truncated protein mini-HBx(18-142) as the bait. In addition to known interacting partners, such as RXR and UVDDB1, we identified several new candidates including the human transcriptional regulatory protein p120E4F, which has been implicated in the regulation of mitosis and the cell cycle. In vitro pull down experiments confirmed the interaction and transcription activation assays in the yeast demonstrated that HBx protein was able to repress GAL4AD-p120E4F-dependent activation of a reporter gene under the control of E4F binding sites found in the adenovirus E4 promoter and the HBV enhancer II region. We also showed that the cysteine residues in HBx are necessary for its interaction with UVDDB1 but not for the interaction with RXR or p120E4F. The possible functional relevance of the interaction between HBx and E4F proteins is discussed in the contexts of cellular transformation and host-virus co-evolution.
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Affiliation(s)
- Edmilson Rui
- Centro de Biologia Molecular Estrutural, Laboratório Nacional de Luz Síncrotron, Rua Giuseppe Máximo Scolfaro 10.000, C.P. 6192, 13084-971 Campinas, SP, Brazil
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