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Cross EM, Akbari N, Ghassabian H, Hoad M, Pavan S, Ariawan D, Donnelly CM, Lavezzo E, Petersen GF, Forwood JK, Alvisi G. A functional and structural comparative analysis of large tumor antigens reveals evolution of different importin α-dependent nuclear localization signals. Protein Sci 2024; 33:e4876. [PMID: 38108201 PMCID: PMC10807245 DOI: 10.1002/pro.4876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2023] [Revised: 12/12/2023] [Accepted: 12/13/2023] [Indexed: 12/19/2023]
Abstract
Nucleocytoplasmic transport regulates the passage of proteins between the nucleus and cytoplasm. In the best characterized pathway, importin (IMP) α bridges cargoes bearing basic, classical nuclear localization signals (cNLSs) to IMPβ1, which mediates transport through the nuclear pore complex. IMPα recognizes three types of cNLSs via two binding sites: the major binding site accommodates monopartite cNLSs, the minor binding site recognizes atypical cNLSs, while bipartite cNLSs simultaneously interact with both major and minor sites. Despite the growing knowledge regarding IMPα-cNLS interactions, our understanding of the evolution of cNLSs is limited. We combined bioinformatic, biochemical, functional, and structural approaches to study this phenomenon, using polyomaviruses (PyVs) large tumor antigens (LTAs) as a model. We characterized functional cNLSs from all human (H)PyV LTAs, located between the LXCXE motif and origin binding domain. Surprisingly, the prototypical SV40 monopartite NLS is not well conserved; HPyV LTA NLSs are extremely heterogenous in terms of structural organization, IMPα isoform binding, and nuclear targeting abilities, thus influencing the nuclear accumulation properties of full-length proteins. While several LTAs possess bipartite cNLSs, merkel cell PyV contains a hybrid bipartite cNLS whose upstream stretch of basic amino acids can function as an atypical cNLS, specifically binding to the IMPα minor site upon deletion of the downstream amino acids after viral integration in the host genome. Therefore, duplication of a monopartite cNLS and subsequent accumulation of point mutations, optimizing interaction with distinct IMPα binding sites, led to the evolution of bipartite and atypical NLSs binding at the minor site.
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Affiliation(s)
- Emily M. Cross
- School of Dentistry and Medical SciencesCharles Sturt UniversityWagga WaggaAustralia
- Diamond Light SourceHarwell Science and Innovation CampusDidcotUnited Kingdom
| | - Nasim Akbari
- Department of Molecular MedicineUniversity of PadovaPadovaItaly
| | | | - Mikayla Hoad
- School of Dentistry and Medical SciencesCharles Sturt UniversityWagga WaggaAustralia
| | - Silvia Pavan
- Department of Molecular MedicineUniversity of PadovaPadovaItaly
| | - Daryl Ariawan
- Dementia Research CentreMacquarie UniversitySydneyAustralia
| | - Camilla M. Donnelly
- School of Dentistry and Medical SciencesCharles Sturt UniversityWagga WaggaAustralia
| | - Enrico Lavezzo
- Department of Molecular MedicineUniversity of PadovaPadovaItaly
| | | | - Jade K. Forwood
- School of Dentistry and Medical SciencesCharles Sturt UniversityWagga WaggaAustralia
- Gulbali InstituteCharles Sturt UniversityWagga WaggaAustralia
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Athukorala A, Donnelly CM, Pavan S, Nematollahzadeh S, Djossou VA, Nath B, Helbig KJ, Di Iorio E, McSharry BP, Alvisi G, Forwood JK, Sarker S. Structural and functional characterization of siadenovirus core protein VII nuclear localization demonstrates the existence of multiple nuclear transport pathways. J Gen Virol 2024; 105. [PMID: 38261399 DOI: 10.1099/jgv.0.001928] [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] [Indexed: 01/24/2024] Open
Abstract
Adenovirus protein VII (pVII) plays a crucial role in the nuclear localization of genomic DNA following viral infection and contains nuclear localization signal (NLS) sequences for the importin (IMP)-mediated nuclear import pathway. However, functional analysis of pVII in adenoviruses to date has failed to fully determine the underlying mechanisms responsible for nuclear import of pVII. Therefore, in the present study, we extended our analysis by examining the nuclear trafficking of adenovirus pVII from a non-human species, psittacine siadenovirus F (PsSiAdV). We identified a putative classical (c)NLS at pVII residues 120-128 (120PGGFKRRRL128). Fluorescence polarization and electrophoretic mobility shift assays demonstrated direct, high-affinity interaction with both IMPα2 and IMPα3 but not IMPβ. Structural analysis of the pVII-NLS/IMPα2 complex confirmed a classical interaction, with the major binding site of IMPα occupied by K124 of pVII-NLS. Quantitative confocal laser scanning microscopy showed that PsSiAdV pVII-NLS can confer IMPα/β-dependent nuclear localization to GFP. PsSiAdV pVII also localized in the nucleus when expressed in the absence of other viral proteins. Importantly, in contrast to what has been reported for HAdV pVII, PsSiAdV pVII does not localize to the nucleolus. In addition, our study demonstrated that inhibition of the IMPα/β nuclear import pathway did not prevent PsSiAdV pVII nuclear targeting, indicating the existence of alternative pathways for nuclear localization, similar to what has been previously shown for human adenovirus pVII. Further examination of other potential NLS signals, characterization of alternative nuclear import pathways, and investigation of pVII nuclear targeting across different adenovirus species is recommended to fully elucidate the role of varying nuclear import pathways in the nuclear localization of pVII.
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Affiliation(s)
- Ajani Athukorala
- Department of Microbiology, Anatomy, Physiology, and Pharmacology, School of Agriculture, Biomedicine and Environment, La Trobe University, Melbourne, VIC 3086, Australia
| | - Camilla M Donnelly
- School of Dentistry and Medical Sciences, Biomedical Sciences, Charles Sturt University, Wagga Wagga, NSW, Australia
| | - Silvia Pavan
- Department of Molecular Medicine, University of Padua, Via Gabelli 63, 35121 Padua, Italy
| | - Sepehr Nematollahzadeh
- Department of Molecular Medicine, University of Padua, Via Gabelli 63, 35121 Padua, Italy
| | | | - Babu Nath
- School of Dentistry and Medical Sciences, Biomedical Sciences, Charles Sturt University, Wagga Wagga, NSW, Australia
| | - Karla J Helbig
- Department of Microbiology, Anatomy, Physiology, and Pharmacology, School of Agriculture, Biomedicine and Environment, La Trobe University, Melbourne, VIC 3086, Australia
| | - Enzo Di Iorio
- Department of Molecular Medicine, University of Padua, Via Gabelli 63, 35121 Padua, Italy
| | - Brian P McSharry
- School of Dentistry and Medical Sciences, Biomedical Sciences, Charles Sturt University, Wagga Wagga, NSW, Australia
| | - Gualtiero Alvisi
- Department of Molecular Medicine, University of Padua, Via Gabelli 63, 35121 Padua, Italy
| | - Jade K Forwood
- School of Dentistry and Medical Sciences, Biomedical Sciences, Charles Sturt University, Wagga Wagga, NSW, Australia
| | - Subir Sarker
- Department of Microbiology, Anatomy, Physiology, and Pharmacology, School of Agriculture, Biomedicine and Environment, La Trobe University, Melbourne, VIC 3086, Australia
- Biomedical Sciences & Molecular Biology, College of Public Health Medical, and Veterinary Sciences, James Cook University, Townsville, QLD 4811, Australia
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Alvisi G, Manaresi E, Cross EM, Hoad M, Akbari N, Pavan S, Ariawan D, Bua G, Petersen GF, Forwood J, Gallinella G. Importin α/β-dependent nuclear transport of human parvovirus B19 nonstructural protein 1 is essential for viral replication. Antiviral Res 2023; 213:105588. [PMID: 36990397 DOI: 10.1016/j.antiviral.2023.105588] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Revised: 03/08/2023] [Accepted: 03/25/2023] [Indexed: 03/30/2023]
Abstract
Human parvovirus B19 (B19V) is a major human pathogen causing a variety of diseases, characterized by a selective tropism to human progenitor cells in bone marrow. In similar fashion to all Parvoviridae members, the B19V ssDNA genome is replicated within the nucleus of infected cells through a process which involves both cellular and viral proteins. Among the latter, a crucial role is played by non-structural protein (NS)1, a multifunctional protein involved in genome replication and transcription, as well as modulation of host gene expression and function. Despite the localization of NS1 within the host cell nucleus during infection, little is known regarding the mechanism of its nuclear transport pathway. In this study we undertake structural, biophysical, and cellular approaches to characterize this process. Quantitative confocal laser scanning microscopy (CLSM), gel mobility shift, fluorescence polarization and crystallographic analysis identified a short sequence of amino acids (GACHAKKPRIT-182) as the classical nuclear localization signal (cNLS) responsible for nuclear import, mediated in an energy and importin (IMP) α/β-dependent fashion. Structure-guided mutagenesis of key residue K177 strongly impaired IMPα binding, nuclear import, and viral gene expression in a minigenome system. Further, treatment with ivermectin, an antiparasitic drug interfering with the IMPα/β dependent nuclear import pathway, inhibited NS1 nuclear accumulation and viral replication in infected UT7/Epo-S1 cells. Thus, NS1 nuclear transport is a potential target of therapeutic intervention against B19V induced disease.
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Affiliation(s)
- Gualtiero Alvisi
- Department of Molecular Medicine, University of Padova, 35121, Padova, Italy.
| | - Elisabetta Manaresi
- Department of Pharmacy and Biotechnology, University of Bologna, 40138, Bologna, Italy
| | - Emily M Cross
- School of Dentistry and Medical Sciences, Charles Sturt University, Wagga Wagga, NSW, 2650, Australia
| | - Mikayla Hoad
- School of Dentistry and Medical Sciences, Charles Sturt University, Wagga Wagga, NSW, 2650, Australia
| | - Nasim Akbari
- Department of Molecular Medicine, University of Padova, 35121, Padova, Italy
| | - Silvia Pavan
- Department of Molecular Medicine, University of Padova, 35121, Padova, Italy
| | - Daryl Ariawan
- Dementia Research Centre, Macquarie University, Sydney, NSW, 2109, Australia
| | - Gloria Bua
- Department of Pharmacy and Biotechnology, University of Bologna, 40138, Bologna, Italy
| | - Gayle F Petersen
- School of Dentistry and Medical Sciences, Charles Sturt University, Wagga Wagga, NSW, 2650, Australia
| | - Jade Forwood
- School of Dentistry and Medical Sciences, Charles Sturt University, Wagga Wagga, NSW, 2650, Australia
| | - Giorgio Gallinella
- Department of Pharmacy and Biotechnology, University of Bologna, 40138, Bologna, Italy
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Ghassabian H, Falchi F, Timmoneri M, Mercorelli B, Loregian A, Palù G, Alvisi G. Divide et impera: An In Silico Screening Targeting HCMV ppUL44 Processivity Factor Homodimerization Identifies Small Molecules Inhibiting Viral Replication. Viruses 2021; 13:v13050941. [PMID: 34065234 PMCID: PMC8160850 DOI: 10.3390/v13050941] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2021] [Revised: 05/18/2021] [Accepted: 05/18/2021] [Indexed: 12/19/2022] Open
Abstract
Human cytomegalovirus (HCMV) is a leading cause of severe diseases in immunocompromised individuals, including AIDS patients and transplant recipients, and in congenitally infected newborns. The utility of available drugs is limited by poor bioavailability, toxicity, and emergence of resistant strains. Therefore, it is crucial to identify new targets for therapeutic intervention. Among the latter, viral protein–protein interactions are becoming increasingly attractive. Since dimerization of HCMV DNA polymerase processivity factor ppUL44 plays an essential role in the viral life cycle, being required for oriLyt-dependent DNA replication, it can be considered a potential therapeutic target. We therefore performed an in silico screening and selected 18 small molecules (SMs) potentially interfering with ppUL44 homodimerization. Antiviral assays using recombinant HCMV TB4-UL83-YFP in the presence of the selected SMs led to the identification of four active compounds. The most active one, B3, also efficiently inhibited HCMV AD169 strain in plaque reduction assays and impaired replication of an AD169-GFP reporter virus and its ganciclovir-resistant counterpart to a similar extent. As assessed by Western blotting experiments, B3 specifically reduced viral gene expression starting from 48 h post infection, consistent with the inhibition of viral DNA synthesis measured by qPCR starting from 72 h post infection. Therefore, our data suggest that inhibition of ppUL44 dimerization could represent a new class of HCMV inhibitors, complementary to those targeting the DNA polymerase catalytic subunit or the viral terminase complex.
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Affiliation(s)
- Hanieh Ghassabian
- Department of Molecular Medicine, University of Padova, 35121 Padova, Italy; (H.G.); (M.T.); (B.M.); (A.L.); (G.P.)
| | | | - Martina Timmoneri
- Department of Molecular Medicine, University of Padova, 35121 Padova, Italy; (H.G.); (M.T.); (B.M.); (A.L.); (G.P.)
| | - Beatrice Mercorelli
- Department of Molecular Medicine, University of Padova, 35121 Padova, Italy; (H.G.); (M.T.); (B.M.); (A.L.); (G.P.)
| | - Arianna Loregian
- Department of Molecular Medicine, University of Padova, 35121 Padova, Italy; (H.G.); (M.T.); (B.M.); (A.L.); (G.P.)
| | - Giorgio Palù
- Department of Molecular Medicine, University of Padova, 35121 Padova, Italy; (H.G.); (M.T.); (B.M.); (A.L.); (G.P.)
| | - Gualtiero Alvisi
- Department of Molecular Medicine, University of Padova, 35121 Padova, Italy; (H.G.); (M.T.); (B.M.); (A.L.); (G.P.)
- Correspondence:
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Di Antonio V, Palù G, Alvisi G. Live-Cell Analysis of Human Cytomegalovirus DNA Polymerase Holoenzyme Assembly by Resonance Energy Transfer Methods. Microorganisms 2021; 9:microorganisms9050928. [PMID: 33925913 PMCID: PMC8146696 DOI: 10.3390/microorganisms9050928] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 04/21/2021] [Accepted: 04/22/2021] [Indexed: 12/18/2022] Open
Abstract
Human cytomegalovirus (HCMV) genome replication is a complex and still not completely understood process mediated by the highly coordinated interaction of host and viral products. Among the latter, six different proteins form the viral replication complex: a single-stranded DNA binding protein, a trimeric primase/helicase complex and a two subunit DNA polymerase holoenzyme, which in turn contains a catalytic subunit, pUL54, and a dimeric processivity factor ppUL44. Being absolutely required for viral replication and representing potential therapeutic targets, both the ppUL44-pUL54 interaction and ppUL44 homodimerization have been largely characterized from structural, functional and biochemical points of view. We applied fluorescence and bioluminescence resonance energy transfer (FRET and BRET) assays to investigate such processes in living cells. Both interactions occur with similar affinities and can take place both in the nucleus and in the cytoplasm. Importantly, single amino acid substitutions in different ppUL44 domains selectively affect its dimerization or ability to interact with pUL54. Intriguingly, substitutions preventing DNA binding of ppUL44 influence the BRETmax of protein-protein interactions, implying that binding to dsDNA induces conformational changes both in the ppUL44 homodimer and in the DNA polymerase holoenzyme. We also compared transiently and stably ppUL44-expressing cells in BRET inhibition assays. Transient expression of the BRET donor allowed inhibition of both ppUL44 dimerization and formation of the DNA polymerase holoenzyme, upon overexpression of FLAG-tagged ppUL44 as a competitor. Our approach could be useful both to monitor the dynamics of assembly of the HCMV DNA polymerase holoenzyme and for antiviral drug discovery.
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Elbadawy HM, Mohammed Abdul MI, Aljuhani N, Vitiello A, Ciccarese F, Shaker MA, Eltahir HM, Palù G, Di Antonio V, Ghassabian H, Del Vecchio C, Salata C, Franchin E, Ponterio E, Bahashwan S, Thabet K, Abouzied MM, Shehata AM, Parolin C, Calistri A, Alvisi G. Generation of Combinatorial Lentiviral Vectors Expressing Multiple Anti-Hepatitis C Virus shRNAs and Their Validation on a Novel HCV Replicon Double Reporter Cell Line. Viruses 2020; 12:v12091044. [PMID: 32962117 PMCID: PMC7551853 DOI: 10.3390/v12091044] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2020] [Revised: 09/14/2020] [Accepted: 09/15/2020] [Indexed: 12/12/2022] Open
Abstract
Despite the introduction of directly acting antivirals (DAAs), for the treatment of hepatitis C virus (HCV) infection, their cost, patient compliance, and viral resistance are still important issues to be considered. Here, we describe the generation of a novel JFH1-based HCV subgenomic replicon double reporter cell line suitable for testing different antiviral drugs and therapeutic interventions. This cells line allowed a rapid and accurate quantification of cell growth/viability and HCV RNA replication, thus discriminating specific from unspecific antiviral effects caused by DAAs or cytotoxic compounds, respectively. By correlating cell number and virus replication, we could confirm the inhibitory effect on the latter of cell over confluency and characterize an array of lentiviral vectors expressing single, double, or triple cassettes containing different combinations of short hairpin (sh)RNAs, targeting both highly conserved viral genome sequences and cellular factors crucial for HCV replication. While all vectors were effective in reducing HCV replication, the ones targeting viral sequences displayed a stronger antiviral effect, without significant cytopathic effects. Such combinatorial platforms as well as the developed double reporter cell line might find application both in setting-up anti-HCV gene therapy approaches and in studies aimed at further dissecting the viral biology/pathogenesis of infection.
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Affiliation(s)
- Hossein M. Elbadawy
- Department of Pharmacology and Toxicology, College of Pharmacy, Taibah University, Almadinah Almunawwarah 41477, Saudi Arabia; (H.M.E.); (N.A.); (H.M.E.); (S.B.); (M.M.A.); (A.M.S.)
| | - Mohi I. Mohammed Abdul
- Department of Pharmacology and Toxicology, College of Pharmacy, Taibah University, Almadinah Almunawwarah 41477, Saudi Arabia; (H.M.E.); (N.A.); (H.M.E.); (S.B.); (M.M.A.); (A.M.S.)
- Correspondence: (M.I.M.A.); (A.C.); (G.A.)
| | - Naif Aljuhani
- Department of Pharmacology and Toxicology, College of Pharmacy, Taibah University, Almadinah Almunawwarah 41477, Saudi Arabia; (H.M.E.); (N.A.); (H.M.E.); (S.B.); (M.M.A.); (A.M.S.)
| | - Adriana Vitiello
- Department of Molecular Medicine, University of Padua, 35121 Padua, Italy; (A.V.); (F.C.); (G.P.); (V.D.A.); (H.G.); (C.D.V.); (C.S.); (E.F.); (E.P.); (C.P.)
| | - Francesco Ciccarese
- Department of Molecular Medicine, University of Padua, 35121 Padua, Italy; (A.V.); (F.C.); (G.P.); (V.D.A.); (H.G.); (C.D.V.); (C.S.); (E.F.); (E.P.); (C.P.)
- Immunology and Molecular Oncology Unit, Veneto Institute of Oncology IOV-IRCCS, 35128 Padua, Italy
| | - Mohamed A. Shaker
- Pharmaceutics and Pharmaceutical Technology Department, College of Pharmacy, Taibah University, Almadinah Almunawwarah 41477, Saudi Arabia;
- Pharmaceutics Department, Faculty of Pharmacy, Helwan University, Cairo 11795, Egypt
| | - Heba M. Eltahir
- Department of Pharmacology and Toxicology, College of Pharmacy, Taibah University, Almadinah Almunawwarah 41477, Saudi Arabia; (H.M.E.); (N.A.); (H.M.E.); (S.B.); (M.M.A.); (A.M.S.)
| | - Giorgio Palù
- Department of Molecular Medicine, University of Padua, 35121 Padua, Italy; (A.V.); (F.C.); (G.P.); (V.D.A.); (H.G.); (C.D.V.); (C.S.); (E.F.); (E.P.); (C.P.)
| | - Veronica Di Antonio
- Department of Molecular Medicine, University of Padua, 35121 Padua, Italy; (A.V.); (F.C.); (G.P.); (V.D.A.); (H.G.); (C.D.V.); (C.S.); (E.F.); (E.P.); (C.P.)
- Immunology and Molecular Oncology Unit, Veneto Institute of Oncology IOV-IRCCS, 35128 Padua, Italy
| | - Hanieh Ghassabian
- Department of Molecular Medicine, University of Padua, 35121 Padua, Italy; (A.V.); (F.C.); (G.P.); (V.D.A.); (H.G.); (C.D.V.); (C.S.); (E.F.); (E.P.); (C.P.)
| | - Claudia Del Vecchio
- Department of Molecular Medicine, University of Padua, 35121 Padua, Italy; (A.V.); (F.C.); (G.P.); (V.D.A.); (H.G.); (C.D.V.); (C.S.); (E.F.); (E.P.); (C.P.)
| | - Cristiano Salata
- Department of Molecular Medicine, University of Padua, 35121 Padua, Italy; (A.V.); (F.C.); (G.P.); (V.D.A.); (H.G.); (C.D.V.); (C.S.); (E.F.); (E.P.); (C.P.)
| | - Elisa Franchin
- Department of Molecular Medicine, University of Padua, 35121 Padua, Italy; (A.V.); (F.C.); (G.P.); (V.D.A.); (H.G.); (C.D.V.); (C.S.); (E.F.); (E.P.); (C.P.)
| | - Eleonora Ponterio
- Department of Molecular Medicine, University of Padua, 35121 Padua, Italy; (A.V.); (F.C.); (G.P.); (V.D.A.); (H.G.); (C.D.V.); (C.S.); (E.F.); (E.P.); (C.P.)
- Fondazione Policlinico Universitario "A. Gemelli"—I.R.C.C.S., 00168 Rome, Italy
| | - Saleh Bahashwan
- Department of Pharmacology and Toxicology, College of Pharmacy, Taibah University, Almadinah Almunawwarah 41477, Saudi Arabia; (H.M.E.); (N.A.); (H.M.E.); (S.B.); (M.M.A.); (A.M.S.)
| | - Khaled Thabet
- Department of Biochemistry, Faculty of Pharmacy, Minia University, Minia 61519, Egypt;
| | - Mekky M. Abouzied
- Department of Pharmacology and Toxicology, College of Pharmacy, Taibah University, Almadinah Almunawwarah 41477, Saudi Arabia; (H.M.E.); (N.A.); (H.M.E.); (S.B.); (M.M.A.); (A.M.S.)
- Department of Biochemistry, Faculty of Pharmacy, Minia University, Minia 61519, Egypt;
| | - Ahmed M. Shehata
- Department of Pharmacology and Toxicology, College of Pharmacy, Taibah University, Almadinah Almunawwarah 41477, Saudi Arabia; (H.M.E.); (N.A.); (H.M.E.); (S.B.); (M.M.A.); (A.M.S.)
- Department of Pharmacology and toxicology, Faculty of Pharmacy, Beni-Suef University, Beni-Suef 62511, Egypt
| | - Cristina Parolin
- Department of Molecular Medicine, University of Padua, 35121 Padua, Italy; (A.V.); (F.C.); (G.P.); (V.D.A.); (H.G.); (C.D.V.); (C.S.); (E.F.); (E.P.); (C.P.)
| | - Arianna Calistri
- Department of Molecular Medicine, University of Padua, 35121 Padua, Italy; (A.V.); (F.C.); (G.P.); (V.D.A.); (H.G.); (C.D.V.); (C.S.); (E.F.); (E.P.); (C.P.)
- Correspondence: (M.I.M.A.); (A.C.); (G.A.)
| | - Gualtiero Alvisi
- Department of Molecular Medicine, University of Padua, 35121 Padua, Italy; (A.V.); (F.C.); (G.P.); (V.D.A.); (H.G.); (C.D.V.); (C.S.); (E.F.); (E.P.); (C.P.)
- Correspondence: (M.I.M.A.); (A.C.); (G.A.)
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Human Cytomegalovirus DNA Polymerase Subunit UL44 Antagonizes Antiviral Immune Responses by Suppressing IRF3- and NF-κB-Mediated Transcription. J Virol 2019; 93:JVI.00181-19. [PMID: 30867312 DOI: 10.1128/jvi.00181-19] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Accepted: 03/02/2019] [Indexed: 01/09/2023] Open
Abstract
Innate immunity is the first line of host defense against viral invasion. The induction of type I interferons (IFNs) and inflammatory cytokines is essential to host antiviral immune responses, which are also key targets of viral immune evasion. Human cytomegalovirus (HCMV) can establish long-term latent infections, in which immune evasion is a pivotal step. In this study, we identified HCMV protein UL44, a DNA polymerase processivity factor, as an inhibitor of the interferon regulatory factor 3 (IRF3)- and NF-κB-dependent antiviral response. Ectopic expression of UL44 inhibited HCMV-triggered induction of downstream effector genes and enhanced viral replication. Conversely, knockdown of UL44 potentiated HCMV-triggered induction of downstream antiviral genes. UL44 interacted with IRF3 and p65, and it inhibited the binding of IRF3 and NF-κB to the promoters of their downstream antiviral genes. These findings reveal an important mechanism of immune evasion by HCMV at the transcriptional level.IMPORTANCE Induction of type I IFNs and inflammatory cytokines plays pivotal roles in host antiviral innate immune responses. Viruses have evolved various mechanisms to interfere with these processes. HCMV causes severe ailments in immunodeficient populations and is a major cause of birth defects. It has been shown that HCMV antagonizes host innate immune defenses, which is important for establishing immune evasion and latent infection. In this study, we identified the HCMV DNA polymerase subunit UL44 as a suppressor of antiviral innate immune responses. Overexpression of UL44 impaired HCMV-triggered induction of type I IFNs and other antiviral genes and thus potentiated viral replication, whereas UL44 deficiency showed opposite effects. Mechanistic studies indicated that UL44 acts by inhibiting the binding of IRF3 and NF-κB to the promoters of downstream antiviral genes. These findings defined an important mechanism of HCMV immune evasion at the transcriptional level, which may provide a therapeutic target for the treatment of HCMV infection.
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Fulcher AJ, Sivakumaran H, Jin H, Rawle DJ, Harrich D, Jans DA. The protein arginine methyltransferase PRMT6 inhibits HIV-1 Tat nucleolar retention. BIOCHIMICA ET BIOPHYSICA ACTA 2016; 1863:254-62. [PMID: 26611710 DOI: 10.1016/j.bbamcr.2015.11.019] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 10/30/2015] [Accepted: 11/18/2015] [Indexed: 10/22/2022]
Abstract
The human immunodeficiency virus (HIV)-1 transactivator protein Tat is known to play a key role in HIV infection, integrally related to its role in the host cell nucleus/nucleolus. Here we show for the first time that Tat localisation can be modulated by specific methylation, whereby overexpression of active but not catalytically inactive PRMT6 methyltransferase specifically leads to exclusion of Tat from the nucleolus. An R52/53A mutated Tat derivative does not show this redistribution, implying that R52/53, within Tat's nuclear/nucleolar localisation signal, are the targets of PRMT6 activity. Analysis using fluorescence recovery after photobleaching indicate that Tat nucleolar accumulation is largely through binding to nucleolar components, with methylation of Tat by PRMT6 preventing this. To our knowledge, this is the first report of specific protein methylation inhibiting nucleolar retention.
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Affiliation(s)
- Alex J Fulcher
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia; Monash Micro Imaging, Monash University, Clayton, Victoria 3800, Australia
| | - Haran Sivakumaran
- Department of Cell and Molecular Biology, QIMR Berghofer Medical Research Institute, Herston, Queensland 4029, Australia; The University of Queensland, School of Population Health, Herston, Queensland 4072, Australia
| | - Hongping Jin
- Department of Cell and Molecular Biology, QIMR Berghofer Medical Research Institute, Herston, Queensland 4029, Australia
| | - Daniel J Rawle
- Department of Cell and Molecular Biology, QIMR Berghofer Medical Research Institute, Herston, Queensland 4029, Australia; School of Chemistry and Molecular Biosciences, University of Queensland, St. Lucia, Queensland 4072, Australia
| | - David Harrich
- Department of Cell and Molecular Biology, QIMR Berghofer Medical Research Institute, Herston, Queensland 4029, Australia; Griffith Medical Research College, a joint program of Griffith University and the Queensland Institute of Medical Research, Queensland, Australia
| | - David A Jans
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia; ARC Centre of Excellence for Biotechnology and Development, Australia.
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9
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Wang YP, Huang LP, Du WJ, Wei YW, Xia DL, Wu HL, Feng L, Liu CM. The pseudorabies virus DNA polymerase processivity factor UL42 exists as a monomer in vitro and in vivo. Arch Virol 2016; 161:1027-31. [PMID: 26733297 DOI: 10.1007/s00705-015-2735-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Accepted: 12/20/2015] [Indexed: 10/22/2022]
Abstract
The processivity factors (PFs) of herpesviruses confer processivity to the DNA polymerase. Understanding whether the herpesvirus PFs function as monomers or multimers is important for clarifying the mechanism by which they provide the DNA polymerase with processivity. Herpes simplex virus type 1 UL42 is a monomer, whereas human cytomegalovirus UL44, Epstein-Barr virus BMRF1, and Kaposi's sarcoma-associated herpesvirus PF-8 exist as dimers. However, the oligomeric status of the pseudorabies virus (PRV) DNA polymerase PF UL42 has not been determined. Using fluorescence confocal microscopy and chemical crosslinking, we confirmed that UL42 is a monomer when expressed in vitro. Crosslinking of nuclear extracts from PRV-infected or uninfected PK-15 cells verified that UL42 exists as a monomer in vivo. Our demonstration that UL42 exists as a monomer in vitro and in vivo contributes to the further investigation of the mechanism used by UL42 to achieve processivity.
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Affiliation(s)
- Yi-Ping Wang
- Division of Swine Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, 427 Maduan Street, Nangang District, Harbin, 150001, People's Republic of China
| | - Li-Ping Huang
- Division of Swine Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, 427 Maduan Street, Nangang District, Harbin, 150001, People's Republic of China
| | - Wen-Juan Du
- Division of Swine Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, 427 Maduan Street, Nangang District, Harbin, 150001, People's Republic of China
| | - Yan-Wu Wei
- Division of Swine Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, 427 Maduan Street, Nangang District, Harbin, 150001, People's Republic of China
| | - De-Li Xia
- Division of Swine Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, 427 Maduan Street, Nangang District, Harbin, 150001, People's Republic of China
| | - Hong-Li Wu
- Division of Swine Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, 427 Maduan Street, Nangang District, Harbin, 150001, People's Republic of China
| | - Li Feng
- Division of Swine Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, 427 Maduan Street, Nangang District, Harbin, 150001, People's Republic of China
| | - Chang-Ming Liu
- Division of Swine Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, 427 Maduan Street, Nangang District, Harbin, 150001, People's Republic of China.
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Regulated transport into the nucleus of herpesviridae DNA replication core proteins. Viruses 2013; 5:2210-34. [PMID: 24064794 PMCID: PMC3798897 DOI: 10.3390/v5092210] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2013] [Revised: 09/03/2013] [Accepted: 09/04/2013] [Indexed: 12/11/2022] Open
Abstract
The Herpesvirdae family comprises several major human pathogens belonging to three distinct subfamilies. Their double stranded DNA genome is replicated in the nuclei of infected cells by a number of host and viral products. Among the latter the viral replication complex, whose activity is strictly required for viral replication, is composed of six different polypeptides, including a two-subunit DNA polymerase holoenzyme, a trimeric primase/helicase complex and a single stranded DNA binding protein. The study of herpesviral DNA replication machinery is extremely important, both because it provides an excellent model to understand processes related to eukaryotic DNA replication and it has important implications for the development of highly needed antiviral agents. Even though all known herpesviruses utilize very similar mechanisms for amplification of their genomes, the nuclear import of the replication complex components appears to be a heterogeneous and highly regulated process to ensure the correct spatiotemporal localization of each protein. The nuclear transport process of these enzymes is controlled by three mechanisms, typifying the main processes through which protein nuclear import is generally regulated in eukaryotic cells. These include cargo post-translational modification-based recognition by the intracellular transporters, piggy-back events allowing coordinated nuclear import of multimeric holoenzymes, and chaperone-assisted nuclear import of specific subunits. In this review we summarize these mechanisms and discuss potential implications for the development of antiviral compounds aimed at inhibiting the Herpesvirus life cycle by targeting nuclear import of the Herpesvirus DNA replicating enzymes.
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11
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Inhibition of herpesvirus and influenza virus replication by blocking polymerase subunit interactions. Antiviral Res 2013; 99:318-27. [DOI: 10.1016/j.antiviral.2013.05.014] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2013] [Revised: 05/24/2013] [Accepted: 05/29/2013] [Indexed: 11/18/2022]
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12
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The human cytomegalovirus DNA polymerase processivity factor UL44 is modified by SUMO in a DNA-dependent manner. PLoS One 2012; 7:e49630. [PMID: 23166733 PMCID: PMC3499415 DOI: 10.1371/journal.pone.0049630] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Accepted: 10/11/2012] [Indexed: 12/22/2022] Open
Abstract
During the replication of human cytomegalovirus (HCMV) genome, the viral DNA polymerase subunit UL44 plays a key role, as by binding both DNA and the polymerase catalytic subunit it confers processivity to the holoenzyme. However, several lines of evidence suggest that UL44 might have additional roles during virus life cycle. To shed light on this, we searched for cellular partners of UL44 by yeast two-hybrid screenings. Intriguingly, we discovered the interaction of UL44 with Ubc9, an enzyme involved in the covalent conjugation of SUMO (Small Ubiquitin-related MOdifier) to cellular and viral proteins. We found that UL44 can be extensively sumoylated not only in a cell-free system and in transfected cells, but also in HCMV-infected cells, in which about 50% of the protein resulted to be modified at late times post-infection, when viral genome replication is accomplished. Mass spectrometry studies revealed that UL44 possesses multiple SUMO target sites, located throughout the protein. Remarkably, we observed that binding of UL44 to DNA greatly stimulates its sumoylation both in vitro and in vivo. In addition, we showed that overexpression of SUMO alters the intranuclear distribution of UL44 in HCMV-infected cells, and enhances both virus production and DNA replication, arguing for an important role for sumoylation in HCMV life cycle and UL44 function(s). These data report for the first time the sumoylation of a viral processivity factor and show that there is a functional interplay between the HCMV UL44 protein and the cellular sumoylation system.
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13
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Alvisi G, Marin O, Pari G, Mancini M, Avanzi S, Loregian A, Jans DA, Ripalti A. Multiple phosphorylation sites at the C-terminus regulate nuclear import of HCMV DNA polymerase processivity factor ppUL44. Virology 2011; 417:259-67. [PMID: 21741668 DOI: 10.1016/j.virol.2011.06.015] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2011] [Revised: 06/13/2011] [Accepted: 06/14/2011] [Indexed: 12/31/2022]
Abstract
The processivity factor of human cytomegalovirus DNA polymerase, phosphoprotein ppUL44, is essential for viral replication. During viral infection ppUL44 is phosphorylated by the viral kinase pUL97, but neither the target residues on ppUL44 nor the effect of phosphorylation on ppUL44's activity are known. We report here that ppUL44 is phosphorylated when transiently expressed in mammalian cells and coimmunoprecipitates with cellular kinases. Of three potential phosphorylation sites (S413, S415, S418) located upstream of ppUL44's nuclear localization signal (NLS) and one (T427) within the NLS itself, protein kinase CK2 (CK2) specifically phosphorylates S413, to trigger a cascade of phosphorylation of S418 and S415 by CK1 and CK2, respectively. Negative charge at the CK2/CK1 target serine residues facilitates optimal nuclear accumulation of ppUL44, whereas negative charge on T427, a potential cyclin-dependent 1 phosphorylation site, strongly decreases nuclear accumulation. Thus, nuclear transport of ppUL44 is finely tuned during viral infection through complex phosphorylation events.
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Affiliation(s)
- Gualtiero Alvisi
- Department of Hematology and Oncology Lorenzo e Ariosto Seràgnoli, University of Bologna, Medical School, Bologna, Italy.
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14
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Regulation of nucleocytoplasmic trafficking of viral proteins: an integral role in pathogenesis? BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2011; 1813:2176-90. [PMID: 21530593 PMCID: PMC7114211 DOI: 10.1016/j.bbamcr.2011.03.019] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/16/2010] [Revised: 03/15/2011] [Accepted: 03/30/2011] [Indexed: 12/24/2022]
Abstract
Signal-dependent targeting of proteins into and out of the nucleus is mediated by members of the importin (IMP) family of transport receptors, which recognise targeting signals within a cargo protein and mediate passage through the nuclear envelope-embedded nuclear pore complexes. Regulation of this process is paramount to processes such as cell division and differentiation, but is also critically important for viral replication and pathogenesis; phosphorylation appears to play a major role in regulating viral protein nucleocytoplasmic trafficking, along with other posttranslational modifications. This review focuses on viral proteins that utilise the host cell IMP machinery in order to traffic into/out of the nucleus, and in particular those where trafficking is critical to viral replication and/or pathogenesis, such as simian virus SV40 large tumour antigen (T-ag), human papilloma virus E1 protein, human cytomegalovirus processivity factor ppUL44, and various gene products from RNA viruses such as Rabies. Understanding of the mechanisms regulating viral protein nucleocytoplasmic trafficking is paramount to the future development of urgently needed specific and effective anti-viral therapeutics. This article was originally intended for the special issue "Regulation of Signaling and Cellular Fate through Modulation of Nuclear Protein Import". The Publisher apologizes for any inconvenience caused.
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15
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Fulcher AJ, Dias MM, Jans DA. Binding of p110 retinoblastoma protein inhibits nuclear import of simian virus SV40 large tumor antigen. J Biol Chem 2010; 285:17744-53. [PMID: 20356831 PMCID: PMC2878538 DOI: 10.1074/jbc.m109.055491] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2009] [Revised: 03/29/2010] [Indexed: 01/19/2023] Open
Abstract
Nuclear import of the simian virus 40 large tumor antigen (T-ag) is dependent on its nuclear localization signal (NLS) within amino acids 126-132 that is recognized by the importin alpha/beta1 heterodimer, as well as a protein kinase CK2 site at serine 112 upstream of the NLS, which enhances the interaction approximately 50-fold. Here we show for the first time that T-ag nuclear import is negatively regulated by N-terminal sequences (amino acids 102-110), which represent the binding site (BS) for the retinoblastoma (Rb) tumor suppressor protein (p110(Rb)). Quantitative confocal laser scanning microscopic analysis of the transport properties of T-ag constructs with or without Rb binding site mutations in living transfected cells or in a reconstituted nuclear transport system indicates that the presence of the RbBS significantly reduces nuclear accumulation of T-ag. A number of approaches, including the analysis of T-ag nuclear import in an isogenic cell pair with and without functional p110(Rb) implicate p110(Rb) binding as being responsible for the reduced nuclear accumulation, with the Ser(106) phosphorylation site within the RbBS appearing to enhance the inhibitory effect. Immunoprecipitation experiments confirmed association of T-ag and p110(Rb) and dependence thereof on negative charge at Ser(106). The involvement of p110(Rb) in modulating T-ag nuclear transport has implications for the regulation of nuclear import of other proteins from viruses of medical significance that interact with p110(Rb), and how this may relate to transformation.
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Affiliation(s)
- Alex James Fulcher
- From the Nuclear Signaling Laboratory, Department of Biochemistry and Molecular Biology, Monash University, Victoria, Clayton 3800, Australia and
| | - Manisha M. Dias
- From the Nuclear Signaling Laboratory, Department of Biochemistry and Molecular Biology, Monash University, Victoria, Clayton 3800, Australia and
| | - David A. Jans
- From the Nuclear Signaling Laboratory, Department of Biochemistry and Molecular Biology, Monash University, Victoria, Clayton 3800, Australia and
- the ARC Centre of Excellence for Biotechnology and Development, Victoria, Melbourne 3000, Australia
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16
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Zhou X, Liao Q, Ricciardi RP, Peng C, Chen X. Kaposi's sarcoma-associated herpesvirus processivity factor-8 dimerizes in cytoplasm before being translocated to nucleus. Biochem Biophys Res Commun 2010; 397:520-5. [PMID: 20515658 DOI: 10.1016/j.bbrc.2010.05.147] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2010] [Accepted: 05/27/2010] [Indexed: 10/19/2022]
Abstract
The processivity factor-8 (PF-8) of Kaposi's sarcoma-associated herpesvirus (KSHV) plays an essential role in viral lytic replication. PF-8 forms homodimers in solution and is observed as a dimer on the DNA. Here, we show that PF-8 dimerizes in cells and that amino acid residues 1-21 and residues 277-304 of PF-8 (396R) are required for dimerization in vivo. Importantly, we demonstrate that PF-8 dimerizes in the cytoplasm before being translocated to the nucleus. The significance of PF-8 cytoplasmic dimerization as a possible first step in the formation of a prereplication complex is discussed.
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Affiliation(s)
- Xia Zhou
- State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430071, PR China
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17
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Fulcher AJ, Roth DM, Fatima S, Alvisi G, Jans DA. The BRCA‐1 binding protein BRAP2 is a novel, negative regulator of nuclear import of viral proteins, dependent on phosphorylation flanking the nuclear localization signal. FASEB J 2009; 24:1454-66. [DOI: 10.1096/fj.09-136564] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- Alex J. Fulcher
- Nuclear Signaling LaboratoryDepartment of Biochemistry and Molecular BiologyMonash UniversityClaytonVictoriaAustralia
| | - Daniela M. Roth
- Nuclear Signaling LaboratoryDepartment of Biochemistry and Molecular BiologyMonash UniversityClaytonVictoriaAustralia
| | - Shadma Fatima
- Nuclear Signaling LaboratoryDepartment of Biochemistry and Molecular BiologyMonash UniversityClaytonVictoriaAustralia
| | - Gualtiero Alvisi
- Nuclear Signaling LaboratoryDepartment of Biochemistry and Molecular BiologyMonash UniversityClaytonVictoriaAustralia
| | - David A. Jans
- Nuclear Signaling LaboratoryDepartment of Biochemistry and Molecular BiologyMonash UniversityClaytonVictoriaAustralia
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18
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The flexible loop of the human cytomegalovirus DNA polymerase processivity factor ppUL44 is required for efficient DNA binding and replication in cells. J Virol 2009; 83:9567-76. [PMID: 19570866 DOI: 10.1128/jvi.00669-09] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Phosphoprotein ppUL44 of the human cytomegalovirus (HCMV) DNA polymerase plays an essential role in viral replication, conferring processivity to the DNA polymerase catalytic subunit pUL54 by tethering it to the DNA. Here, for the first time, we examine in living cells the function of the highly flexible loop of ppUL44 (UL44-FL; residues 162 to 174 [PHTRVKRNVKKAP(174)]), which has been proposed to be directly involved in ppUL44's interaction with DNA. In particular, we use a variety of approaches in transfected cells to characterize in detail the behavior of ppUL44Deltaloop, a mutant derivative in which three of the five basic residues within UL44-FL are replaced by nonbasic amino acids. Our results indicate that ppUL44Deltaloop is functional in dimerization and binding to pUL54 but strongly impaired in binding nuclear structures within the nucleus, as shown by its inability to form nuclear speckles, reduced nuclear accumulation, and increased intranuclear mobility compared to wild-type ppUL44. Moreover, analysis of cellular fractions after detergent and DNase treatment indicates that ppUL44Deltaloop is strongly reduced in DNA-binding ability, in similar fashion to ppUL44-L86A/L87A, a point mutant derivative impaired in dimerization. Finally, ppUL44Deltaloop fails to transcomplement HCMV oriLyt-dependent DNA replication in cells and also inhibits replication in the presence of wild-type ppUL44, possibly via formation of heterodimers defective for double-stranded DNA binding. UL44-FL thus emerges for the first time as an important determinant for HCMV replication in cells, with potential implications for the development of novel antiviral approaches by targeting HCMV replication.
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19
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Dimerization and a novel Tax speckled structure localization signal are required for Tax nuclear localization. J Virol 2009; 83:5339-52. [PMID: 19321601 DOI: 10.1128/jvi.00232-09] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human T-cell leukemia virus type 1 oncoprotein Tax has pleiotropic activities, a subset of which likely leads to immortalization of T cells. Tax is expressed and known to function in both the cell nucleus and the cytoplasm. Tax has defined nuclear localization (NLS) and nuclear export signals that enable shuttling between the two compartments. In this study, we identified a novel region in Tax that targets the protein to discrete nuclear foci that we have previously termed Tax speckled structures (TSS). We demonstrated that the identified region is both necessary and sufficient for directing proteins to TSS. This novel TSS localization signal (TSLS), spanning amino acids 50 to 75, is separable from and adjacent to the NLS of Tax. Coexpression of a Tax NLS mutant and a Tax TSLS mutant rescued the nuclear entry and subnuclear TSS targeting of both proteins, demonstrating that these signals are independent domains. Our analysis also revealed that Tax proteins deficient for dimerization fail to localize to the nucleus. Consequently, when we restored dimerization via induction of a heterologous "dimerizer" domain, nuclear localization was rescued. Thus, we defined additional domains in Tax specific for nuclear localization and subnuclear targeting. Our results reveal a more complex network for regulation of Tax subcellular localization and subsequent function.
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20
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Alvisi G, Avanzi S, Musiani D, Camozzi D, Leoni V, Ly-Huynh JD, Ripalti A. Nuclear import of HSV-1 DNA polymerase processivity factor UL42 is mediated by a C-terminally located bipartite nuclear localization signal. Biochemistry 2009; 47:13764-77. [PMID: 19053255 DOI: 10.1021/bi800869y] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The polymerase accessory protein of the human herpes simplex virus type 1 (HSV-1) DNA polymerase UL42 plays an essential role in viral replication, conferring processivity to the catalytic subunit UL30. We show here that UL42 is imported to the nucleus of living cells in a Ran- and energy-dependent fashion, through a process that requires a C-terminally located bipartite nuclear localization signal (UL42-NLSbip; PTTKRGRSGGEDARADALKKPK(413)). Moreover cytoplasmic mutant derivatives of UL42 lacking UL42-NLSbip are partially relocalized into the cell nucleus upon HSV-1 infection or coexpression with UL30, implying that the HSV-1 DNA polymerase holoenzyme can assemble in the cytoplasm before nuclear translocation occurs, thus explaining why the UL42 C-terminal domain is not strictly required for viral replication in cultured cells. However, mutation of both UL30 and UL42 NLS results in retention of the DNA polymerase holoenzyme in the cytoplasm, suggesting that simultaneous inhibition of both NLSs could represent a viable strategy to hinder HSV-1 replication. Intriguingly, UL42-NLSbip is composed of two stretches of basic amino acids matching the consensus for classical monopartite NLSs (NLSA, PTTKRGR(397); NLSB, KKPK(413)), neither of which are capable of targeting GFP to the nucleus on their own, consistent with the hypothesis that P and G residues in position +3 of monopartite NLSs are not compatible with nuclear transport in the absence of additional basic sequences located in close proximity. Our results showing that substitution of G or P of the NLS with an A residue partially confers NLS function will help to redefine the consensus for monopartite NLSs.
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Affiliation(s)
- Gualtiero Alvisi
- Dipartimento di Ematologia e Scienze Oncologiche L.A. Seragnoli, Universita degli Studi di Bologna, Bologna, Italia.
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Role of homodimerization of human cytomegalovirus DNA polymerase accessory protein UL44 in origin-dependent DNA replication in cells. J Virol 2008; 82:12574-9. [PMID: 18842734 DOI: 10.1128/jvi.01193-08] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The presumed processivity subunit of human cytomegalovirus (HCMV) DNA polymerase, UL44, forms homodimers. The dimerization of UL44 is important for binding to DNA in vitro; however, whether it is also important for DNA replication in a cellular context is unknown. Here we show that UL44 point mutants that are impaired for dimerization, but not for nuclear localization or interaction with the C terminus of the polymerase catalytic subunit, are not capable of supporting HCMV oriLyt-dependent DNA replication in cells. These data suggest that the disruption of UL44 homodimers could represent a novel anti-HCMV strategy.
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22
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Regulated nucleocytoplasmic trafficking of viral gene products: a therapeutic target? BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2007; 1784:213-27. [PMID: 17933596 DOI: 10.1016/j.bbapap.2007.08.021] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2007] [Revised: 08/16/2007] [Accepted: 08/24/2007] [Indexed: 12/25/2022]
Abstract
The study of viral proteins and host cell factors that interact with them has represented an invaluable contribution to understanding of the physiology as well as associated pathology of key eukaryotic cell processes such as cell cycle regulation, signal transduction and transformation. Similarly, knowledge of nucleocytoplasmic transport is based largely on pioneering studies performed on viral proteins that enabled the first sequences responsible for the facilitated transport through the nuclear pore to be identified. The study of viral proteins has also enabled the discovery of several nucleocytoplasmic regulatory mechanisms, the best characterized being through phosphorylation. Recent delineation of the mechanisms whereby phosphorylation regulates nuclear import and export of key viral gene products encoded by important human pathogens such as human cytomegalovirus dengue virus and respiratory syncytial virus has implications for the development of antiviral therapeutics. In particular, the development of specific and effective kinase inhibitors makes the idea of blocking viral infection by inhibiting the phosphorylation-dependent regulation of viral gene product nuclear transport a real possibility. Additionally, examination of a chicken anemia virus (CAV) protein able to target selectively into the nucleus of tumor but not normal cells, as specifically regulated by phosphorylation, opens the exciting possibility of cancer cell-specific nuclear targeting. The study of nucleoplasmic transport may thus enable the development not only of new antiviral approaches, but also contribute to anti-cancer strategies.
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23
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Roth DM, Moseley GW, Glover D, Pouton CW, Jans DA. A microtubule-facilitated nuclear import pathway for cancer regulatory proteins. Traffic 2007; 8:673-86. [PMID: 17511743 DOI: 10.1111/j.1600-0854.2007.00564.x] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Nuclear protein import is dependent on specific targeting signals within cargo proteins recognized by importins (IMPs) that mediate translocation through the nuclear pore. Recent evidence, however, implicates a role for the microtubule (MT) network in facilitating nuclear import of the cancer regulatory proteins parathyroid hormone-related protein (PTHrP) and p53 tumor suppressor. Here we assess the extent to which MT and actin integrity may be generally required for nuclear protein import for the first time. We examine 10 nuclear-localizing proteins with diverse IMP-dependent nuclear import pathways, our results indicating that the cytoskeleton does not have a general mechanistic role in nuclear localization sequence-dependent nuclear protein import. Of the proteins examined, only the p110(Rb) tumor suppressor protein Rb, together with p53 and PTHrP, was found to require MT integrity for optimal nuclear import. Fluorescence recovery after photobleaching experiments indicated that the MT-dependent nuclear transport pathway increases both the rate and extent of Rb nuclear import but does not affect Rb nuclear export. Dynamitin overexpression experiments implicate the MT motor dynein in the import process. The results indicate that, additional to IMP/diffusion-dependent processes, certain cancer regulatory proteins utilize an MT-enhanced pathway for accelerated nuclear import that is presumably required for their nuclear functions.
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Affiliation(s)
- Daniela Martino Roth
- Nuclear Signalling Laboratory, Department of Biochemistry and Molecular Biology, Monash University, Monash, Victoria 3800, Australia
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24
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Alvisi G, Ripalti A, Ngankeu A, Giannandrea M, Caraffi SG, Dias MM, Jans DA. Human cytomegalovirus DNA polymerase catalytic subunit pUL54 possesses independently acting nuclear localization and ppUL44 binding motifs. Traffic 2006; 7:1322-32. [PMID: 16911590 DOI: 10.1111/j.1600-0854.2006.00477.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The catalytic subunit of human cytomegalovirus (HCMV) DNA polymerase pUL54 is a 1242-amino-acid protein, whose function, stimulated by the processivity factor, phosphoprotein UL44 (ppUL44), is essential for viral replication. The C-terminal residues (amino acids 1220-1242) of pUL54 have been reported to be sufficient for ppUL44 binding in vitro. Although believed to be important for functioning in the nuclei of infected cells, no data are available on either the interaction of pUL54 with ppUL44 in living mammalian cells or the mechanism of pUL54 nuclear transport and its relationship with that of ppUL44. The present study examines for the first time the nuclear import pathway of pUL54 and its interaction with ppUL44 using dual color, quantitative confocal laser scanning microscopy on live transfected cells and quantitative gel mobility shift assays. We showed that of two nuclear localization signals (NLSs) located at amino acids 1153-1159 (NLSA) and 1222-1227 (NLSB), NLSA is sufficient to confer nuclear localization on green fluorescent protein (GFP) by mediating interaction with importin alpha/beta. We also showed that pUL54 residues 1213-1242 are sufficient to confer ppUL44 binding abilities on GFP and that pUL54 and ppUL44 can be transported to the nucleus as a complex. Our work thus identified distinct sites within the HCMV DNA polymerase, which represent potential therapeutic targets and establishes the molecular basis of UL54 nuclear import.
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Affiliation(s)
- Gualtiero Alvisi
- Dipartimento di Medicina Clinica Specialistica e Sperimentale, Sezione di Microbiologia, Università degli Studi di Bologna, via Massarenti 9, 40138 Bologna, Italy.
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