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Lin HS, Li CH, Chen LW, Wang SS, Chen LY, Hung CH, Lin CL, Chang PJ. The varicella-zoster virus ORF16 protein promotes both the nuclear transport and the protein abundance of the viral DNA polymerase subunit ORF28. Virus Res 2024; 345:199379. [PMID: 38643859 PMCID: PMC11061344 DOI: 10.1016/j.virusres.2024.199379] [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: 02/05/2024] [Revised: 04/19/2024] [Accepted: 04/19/2024] [Indexed: 04/23/2024]
Abstract
Although all herpesviruses utilize a highly conserved replication machinery to amplify their viral genomes, different members may have unique strategies to modulate the assembly of their replication components. Herein, we characterize the subcellular localization of seven essential replication proteins of varicella-zoster virus (VZV) and show that several viral replication enzymes such as the DNA polymerase subunit ORF28, when expressed alone, are localized in the cytoplasm. The nuclear import of ORF28 can be mediated by the viral DNA polymerase processivity factor ORF16. Besides, ORF16 could markedly enhance the protein abundance of ORF28. Noteworthily, an ORF16 mutant that is defective in nuclear transport still retained the ability to enhance ORF28 abundance. The low abundance of ORF28 in transfected cells was due to its rapid degradation mediated by the ubiquitin-proteasome system. We additionally reveal that radicicol, an inhibitor of the chaperone Hsp90, could disrupt the interaction between ORF16 and ORF28, thereby affecting the nuclear entry and protein abundance of ORF28. Collectively, our findings imply that the cytoplasmic retention and rapid degradation of ORF28 may be a key regulatory mechanism for VZV to prevent untimely viral DNA replication, and suggest that Hsp90 is required for the interaction between ORF16 and ORF28.
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Affiliation(s)
- Huang-Shen Lin
- Department of Internal Medicine, Division of Infectious Diseases, Chang Gung Memorial Hospital, Chiayi 61363, Taiwan; Graduate Institute of Clinical Medical Sciences, College of Medicine, Chang Gung University, Taoyuan 33302, Taiwan
| | - Cheng-Han Li
- Graduate Institute of Clinical Medical Sciences, College of Medicine, Chang Gung University, Taoyuan 33302, Taiwan
| | - Lee-Wen Chen
- Department of Respiratory Care, Chang Gung University of Science and Technology, Chiayi 61363, Taiwan; Department of Pediatric Surgery, Chang Gung Memorial Hospital, Chiayi 61363, Taiwan
| | - Shie-Shan Wang
- Department of Pediatric Surgery, Chang Gung Memorial Hospital, Chiayi 61363, Taiwan; School of Medicine, Chang Gung University, Taoyuan 33302, Taiwan
| | - Li-Yu Chen
- Graduate Institute of Clinical Medical Sciences, College of Medicine, Chang Gung University, Taoyuan 33302, Taiwan
| | - Chien-Hui Hung
- Graduate Institute of Clinical Medical Sciences, College of Medicine, Chang Gung University, Taoyuan 33302, Taiwan
| | - Chun-Liang Lin
- Department of Nephrology, Chang Gung Memorial Hospital, Chiayi 61363, Taiwan
| | - Pey-Jium Chang
- Graduate Institute of Clinical Medical Sciences, College of Medicine, Chang Gung University, Taoyuan 33302, Taiwan; Department of Nephrology, Chang Gung Memorial Hospital, Chiayi 61363, Taiwan.
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Wang X, Ma L, Li N, Gao N. Structural insights into the assembly and mechanism of mpox virus DNA polymerase complex F8-A22-E4-H5. Mol Cell 2023; 83:4398-4412.e4. [PMID: 37995690 DOI: 10.1016/j.molcel.2023.10.038] [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: 02/14/2023] [Revised: 08/21/2023] [Accepted: 09/25/2023] [Indexed: 11/25/2023]
Abstract
The DNA replication of mpox virus is performed by the viral polymerase F8 and also requires other viral factors, including processivity factor A22, uracil DNA glycosylase E4, and phosphoprotein H5. However, the molecular roles of these viral factors remain unclear. Here, we characterize the structures of F8-A22-E4 and F8-A22-E4-H5 complexes in the presence of different primer-template DNA substrates. E4 is located upstream of F8 on the template single-stranded DNA (ssDNA) and is catalytically active, highlighting a functional coupling between DNA base-excision repair and DNA synthesis. Moreover, H5, in the form of tetramer, binds to the double-stranded DNA (dsDNA) region downstream of F8 in a similar position as PCNA (proliferating cell nuclear antigen) does in eukaryotic polymerase complexes. Omission of H5 or disruption of its DNA interaction showed a reduced synthesis of full-length DNA products. These structures provide snapshots for the working cycle of the polymerase and generate insights into the mechanisms of these essential factors in viral DNA replication.
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Affiliation(s)
- Xiaohan Wang
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Joint Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China
| | - Liangwen Ma
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Joint Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China; Changping Laboratory, Beijing 102206, China
| | - Ningning Li
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Joint Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China; Changping Laboratory, Beijing 102206, China.
| | - Ning Gao
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Joint Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China; Changping Laboratory, Beijing 102206, China; National Biomedical Imaging Center, Peking University, Beijing 100871, China.
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Xu Y, Hou G, Liu Q, Zhang Q, Li C, Hu L, Chen X, Chen R, Ding C, Li D, Li J. Helicase-independent function of RIG-I against murine gammaherpesvirus 68 via blocking the nuclear translocation of viral proteins. Int J Biol Macromol 2023; 250:126527. [PMID: 37633553 DOI: 10.1016/j.ijbiomac.2023.126527] [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: 07/15/2023] [Revised: 08/21/2023] [Accepted: 08/23/2023] [Indexed: 08/28/2023]
Abstract
Innate immunity is the first line of defense against viral pathogens. Retinoic Acid-Inducible Gene 1 (RIG-I) is a pattern recognition receptor that recognizes virus-associated double-stranded RNA and initiates the interferon responses. Besides signal transduction, RIG-I exerts direct antiviral functions to displace viral proteins on dsRNA via its Helicase activity. Nevertheless, this effector-like activity of RIG-I against herpesviruses remains largely unexplored. It has been previously reported that herpesviruses deamidate RIG-I, resulting in the abolishment of its Helicase activity and signal transduction. In this study, we discovered that RIG-I possessed signaling-independent antiviral activities against murine gamma herpesviruses 68 (γHV68, murid herpesvirus 4). Importantly, a Helicase-dead mutant of RIG-I (K270A) demonstrated comparable inhibition on herpesviruses lytic replication, indicating that this antiviral activity is Helicase-independent. Mechanistically, RIG-I bound the Replication and Transcription Activator (RTA) and diminished its nuclear localization to repress viral transcription. We further demonstrated that RIG-I blocked the nuclear translocation of ORF21 (Thymidine Kinase), ORF75c (vGAT), both of which form a nuclear complex with RTA and RNA polymerase II (Pol II) to facilitate viral transcription. Moreover, RIG-I retained ORF59 (DNA processivity factor) in the cytoplasm to repress viral DNA replication. Altogether, we illuminated a previously unidentified, Helicase-independent effector-like function of RIG-I against γHV68, representing an exquisite host strategy to counteract viral manipulations on innate immune signaling. IMPORTANCE: Retinoic acid-inducible gene I (RIG-I), a member of DExD/H box RNA helicase family, functions as a key pattern recognition receptor (PRR) responsible for the detection of intracellular double-stranded RNA (dsRNA) from virus-infected cells and induction of type I interferon (IFN) responses. Nevertheless, our understanding of the helicase-independent effector-like activity of RIG-I against virus infection, especially herpesvirus infection, remains largely unknown. Herein, by deploying murine gamma herpesviruses 68 (γHV68) as a model system, we demonstrated that RIG-I possessed an interferon and helicase-independent antiviral activity against γHV68 via blocking the nuclear trafficking of viral proteins, which concomitantly repressed the viral early transcription and genome replication thereof. Our work illuminates a previously unidentified antiviral strategy of RIG-I against herpesvirus infection.
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Affiliation(s)
- Yang Xu
- College of Animal Science and Technology, Hunan Agricultural University, Changsha 410128, China
| | - Guoli Hou
- College of Animal Science and Technology, Hunan Agricultural University, Changsha 410128, China
| | - Qizhi Liu
- Department of Surgery, Samuel Oschin Cancer Institute, Cedars-Sinai Medical Center, Los Angeles, CA 90048, USA
| | - Qiushi Zhang
- College of Animal Science and Technology, Hunan Agricultural University, Changsha 410128, China
| | - Chun Li
- College of Animal Science and Technology, Hunan Agricultural University, Changsha 410128, China
| | - Liang Hu
- College of Animal Science and Technology, Hunan Agricultural University, Changsha 410128, China
| | - Xiaoying Chen
- College of Animal Science and Technology, Hunan Agricultural University, Changsha 410128, China
| | - Rui Chen
- College of Animal Science and Technology, Hunan Agricultural University, Changsha 410128, China
| | - Chengming Ding
- The First Affiliated Hospital, Department of Hepatopancreatobiliary Surgery, Hengyang Medical School, University of South China, Hengyang, Hunan 421001, China
| | - Deliang Li
- College of Animal Science and Technology, Hunan Agricultural University, Changsha 410128, China.
| | - Junhua Li
- College of Animal Science and Technology, Hunan Agricultural University, Changsha 410128, China.
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G 1/S Cell Cycle Induction by Epstein-Barr Virus BORF2 Is Mediated by P53 and APOBEC3B. J Virol 2022; 96:e0066022. [PMID: 36069545 PMCID: PMC9517719 DOI: 10.1128/jvi.00660-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Herpesvirus lytic infection causes cells to arrest at the G1/S phase of the cell cycle by poorly defined mechanisms. In a prior study using fluorescent ubiquitination-based cell cycle indicator (FUCCI) cells that express fluorescently tagged proteins marking different stages of the cell cycle, we showed that the Epstein-Barr virus (EBV) protein BORF2 induces the accumulation of G1/S cells, and that BORF2 affects p53 levels without affecting the p53 target protein p21. We also found that BORF2 specifically interacted with APOBEC3B (A3B) and forms perinuclear bodies with A3B that prevent A3B from mutating replicating EBV genomes. We now show that BORF2 also interacts with p53 and that A3B interferes with the BORF2-p53 interaction, although A3B and p53 engage distinct surfaces on BORF2. Cell cycle analysis showed that G1/S induction by BORF2 is abrogated when either p53 or A3B is silenced or when an A3B-binding mutant of BORF2 is used. Furthermore, silencing A3B in EBV lytic infection increased cell proliferation, supporting a role for A3B in G1/S arrest. These data suggest that the p53 induced by BORF2 is inactive when it binds BORF2, but is released and induces G1/S arrest when A3B is present and sequesters BORF2 in perinuclear bodies. Interestingly, this mechanism is conserved in the BORF2 homologue in HSV-1, which also re-localizes A3B, induces and binds p53, and induces G1/S dependent on A3B and p53. In summary, we have identified a new mechanism by which G1/S arrest can be induced in herpesvirus lytic infection. IMPORTANCE In lytic infection, herpesviruses cause cells to arrest at the G1/S phase of the cell cycle in order to provide an optimal environment for viral replication; however, the mechanisms involved are not well understood. We have shown that the Epstein-Barr virus BORF2 protein and its homologue in herpes simplex virus 1 both induce G1/S, and do this by similar mechanisms which involve binding p53 and APOBEC3B and induction of p53. Our study identifies a new mechanism by which G1/S arrest can be induced in herpesvirus lytic infection and a new role of APOBEC3B in herpesvirus lytic infection.
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Abstract
Poxviruses, of which vaccinia virus is the prototype, are a large family of double-stranded DNA viruses that replicate exclusively in the cytoplasm of infected cells. This physical and genetic autonomy from the host cell nucleus necessitates that these viruses encode most, if not all, of the proteins required for replication in the cytoplasm. In this review, we follow the life of the viral genome through space and time to address some of the unique challenges that arise from replicating a 195-kb DNA genome in the cytoplasm. We focus on how the genome is released from the incoming virion and deposited into the cytoplasm; how the endoplasmic reticulum is reorganized to form a replication factory, thereby compartmentalizing and helping to protect the replicating genome from immune sensors; how the cellular milieu is tailored to support high-fidelity replication of the genome; and finally, how newly synthesized genomes are faithfully and specifically encapsidated into new virions. Expected final online publication date for the Annual Review of Virology, Volume 9 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Matthew D Greseth
- Department of Biochemistry and Molecular Biology, The Medical University of South Carolina, Charleston, South Carolina, USA;
| | - Paula Traktman
- Department of Biochemistry and Molecular Biology, The Medical University of South Carolina, Charleston, South Carolina, USA; .,Department of Microbiology and Immunology, The Medical University of South Carolina, Charleston, South Carolina, USA
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Abstract
Herpesviruses comprise a family of DNA viruses that cause a variety of human and veterinary diseases. During productive infection, mammalian, avian, and reptilian herpesviruses replicate their genomes using a set of conserved viral proteins that include a two subunit DNA polymerase. This enzyme is both a model system for family B DNA polymerases and a target for inhibition by antiviral drugs. This chapter reviews the structure, function, and mechanisms of the polymerase of herpes simplex viruses 1 and 2 (HSV), with only occasional mention of polymerases of other herpesviruses such as human cytomegalovirus (HCMV). Antiviral polymerase inhibitors have had the most success against HSV and HCMV. Detailed structural information regarding HSV DNA polymerase is available, as is much functional information regarding the activities of the catalytic subunit (Pol), which include a DNA polymerization activity that can utilize both DNA and RNA primers, a 3'-5' exonuclease activity, and other activities in DNA synthesis and repair and in pathogenesis, including some remaining to be biochemically defined. Similarly, much is known regarding the accessory subunit, which both resembles and differs from sliding clamp processivity factors such as PCNA, and the interactions of this subunit with Pol and DNA. Both subunits contribute to replication fidelity (or lack thereof). The availability of both pharmacologic and genetic tools not only enabled the initial identification of Pol and the pol gene, but has also helped dissect their functions. Nevertheless, important questions remain for this long-studied enzyme, which is still an attractive target for new drug discovery.
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