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Albright ER, Walter RM, Saffert RT, Kalejta RF. NFκB and Cyclic AMP Response Element Sites Mediate the Valproic Acid and UL138 Responsiveness of the Human Cytomegalovirus Major Immediate Early Enhancer and Promoter. J Virol 2023; 97:e0002923. [PMID: 36856444 PMCID: PMC10062163 DOI: 10.1128/jvi.00029-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2023] [Accepted: 02/08/2023] [Indexed: 03/02/2023] Open
Abstract
The major immediate early enhancer and promoter (MIEP) of human cytomegalovirus (HCMV) drives the transcription of the immediate early one (IE1) and IE2 genes, whose encoded proteins stimulate productive, lytic replication. The MIEP is activated by the virally encoded and tegument-delivered pp71 protein at the start of de novo lytic infections of fully differentiated cells. Conversely, the MIEP is silenced at the start of de novo latent infections within incompletely differentiated myeloid cells in part because tegument-delivered pp71 is sequestered in the cytoplasm in these cells, but also by viral factors that repress transcription from this locus, including the UL138 protein. During both modes of infection, MIEP activity can be increased by the histone deacetylase inhibitor valproic acid (VPA); however, UL138 inhibits the VPA-responsiveness of the MIEP. Here, we show that two families of cellular transcription factors, NF-κB and cAMP response element-binding protein (CREB), together control the VPA-mediated activation and UL138-mediated repression of the HCMV MIEP. IMPORTANCE Artificial regulation of the HCMV MIEP, either activation or repression, is an attractive potential means to target the latent reservoirs of virus for which there is currently no available intervention. The MIEP could be repressed to prevent latency reactivation or induced to drive the virus into the lytic stage that is visible to the immune system and inhibited by multiple small-molecule antiviral drugs. Understanding how the MIEP is regulated is a critical part of designing and implementing either strategy. Our revelation here that NF-κB and CREB control the responsiveness of the MIEP to the viral UL138 protein and the FDA-approved drug VPA could help in the formulation and execution of promoter regulatory strategies against latent HCMV.
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Affiliation(s)
- Emily R. Albright
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Ryan M. Walter
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Ryan T. Saffert
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Robert F. Kalejta
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin, USA
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2
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Iwahori S, Umaña AC, Kalejta RF, Murata T. Serine 13 of the human cytomegalovirus viral cyclin-dependent kinase UL97 is required for regulatory protein 14-3-3 binding and UL97 stability. J Biol Chem 2022; 298:102513. [PMID: 36150501 PMCID: PMC9587022 DOI: 10.1016/j.jbc.2022.102513] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Revised: 09/08/2022] [Accepted: 09/13/2022] [Indexed: 11/14/2022] Open
Abstract
The human cytomegalovirus (HCMV) UL97 protein is a conserved herpesvirus protein kinase (CHPK) and a viral cyclin-dependent kinase (v-CDK). However, mechanisms regulating its activity in the context of infection are unknown. Here, we identified several cellular regulatory 14-3-3 proteins as UL97-interacting partners that promote UL97 stability. Humans are known to encode seven isoforms of 14-3-3 proteins (β, ε, η, γ, σ, θ, and ζ) that bind phosphoserines or phosphothreonines to impact protein structure, stability, activity, and localization. Our proteomic analysis of UL97 identified 49 interacting partners, including 14-3-3 isoforms β, η, and γ. Furthermore, coimmunoprecipitation with Western blotting assays demonstrated that UL97 interaction with 14-3-3 isoforms β, ε, η, γ, and θ occurs in a kinase activity-dependent manner. Using mutational analysis, we determined the serine residue at amino acid 13 of UL97 is crucial for 14-3-3 interaction. We demonstrate UL97 S13A (serine to alanine substitution at residue 13) retains kinase activity but the mutant protein accumulated at lower levels than WT UL97. Finally, we show both laboratory (AD169) and clinical (TB40/E) strains of HCMV encoding UL97 S13A replicated with WT kinetics in fibroblasts but showed decreased UL97 accumulation. Taken together, we conclude that 14-3-3 proteins interact with and stabilize UL97 during HCMV infection.
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Affiliation(s)
- Satoko Iwahori
- Department of Virology and Parasitology, Fujita Health University School of Medicine, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi 470-1192, Japan; Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, WI, USA
| | - Angie C Umaña
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, WI, USA
| | - Robert F Kalejta
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, WI, USA.
| | - Takayuki Murata
- Department of Virology and Parasitology, Fujita Health University School of Medicine, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi 470-1192, Japan.
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3
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Albright ER, Mickelson CK, Kalejta RF. Human Cytomegalovirus UL138 Protein Inhibits the STING Pathway and Reduces Interferon Beta mRNA Accumulation during Lytic and Latent Infections. mBio 2021; 12:e0226721. [PMID: 34903048 PMCID: PMC8669494 DOI: 10.1128/mbio.02267-21] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Accepted: 11/05/2021] [Indexed: 11/20/2022] Open
Abstract
The cGAS/STING/TBK1 (cyclic guanine monophosphate-AMP synthase/stimulator of interferon genes/Tank-binding kinase 1) innate immunity pathway is activated during human cytomegalovirus (HCMV) productive (lytic) replication in fully differentiated cells and during latency within incompletely differentiated myeloid cells. While multiple lytic-phase HCMV proteins neutralize steps along this pathway, none of them are expressed during latency. Here, we show that the latency-associated protein UL138 inhibits the cGAS/STING/TBK1 innate immunity pathway during transfections and infections, in fully differentiated cells and incompletely differentiated myeloid cells, and with loss of function and restoration of function approaches. UL138 inhibits the pathway downstream of STING but upstream of interferon regulatory factor 3 (IRF3) phosphorylation and NF-κB function and reduces the accumulation of interferon beta mRNA during both lytic and latent infections. IMPORTANCE While a cellular restriction versus viral countermeasure arms race between innate immunity and viral latency is expected, few examples have been documented. Our identification of the first HCMV latency protein that inactivates the cGAS/STING/TBK1 innate immune pathway opens the door to understanding how innate immunity, or its neutralization, impacts long-term persistence by HCMV and other latent viruses.
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Affiliation(s)
- Emily R. Albright
- Institute for Molecular Virology, University of Wisconsin—Madison, Madison, Wisconsin, USA
- McArdle Laboratory for Cancer Research, University of Wisconsin—Madison, Madison, Wisconsin, USA
| | - Clayton K. Mickelson
- Institute for Molecular Virology, University of Wisconsin—Madison, Madison, Wisconsin, USA
- McArdle Laboratory for Cancer Research, University of Wisconsin—Madison, Madison, Wisconsin, USA
| | - Robert F. Kalejta
- Institute for Molecular Virology, University of Wisconsin—Madison, Madison, Wisconsin, USA
- McArdle Laboratory for Cancer Research, University of Wisconsin—Madison, Madison, Wisconsin, USA
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4
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Lyon SM, Yetming KD, Paulus C, Nevels M, Kalejta RF. Human Cytomegalovirus Genomes Survive Mitosis via the IE19 Chromatin-Tethering Domain. mBio 2020; 11:e02410-20. [PMID: 32994332 PMCID: PMC7527735 DOI: 10.1128/mbio.02410-20] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Accepted: 08/26/2020] [Indexed: 12/12/2022] Open
Abstract
The genomes of DNA tumor viruses regain nuclear localization after nuclear envelope breakdown during mitosis through the action of a viral protein with a chromatin-tethering domain (CTD). Here, we report that the human cytomegalovirus (HCMV) genome is maintained during mitosis by the CTD of the viral IE19 protein. Deletion of the IE19 CTD or disruption of the IE19 splice acceptor site reduced viral genome maintenance and progeny virion formation during infection of dividing fibroblasts, both of which were rescued by IE19 ectopic expression. The discovery of a viral genome maintenance factor during productive infection provides new insight into the mode of HCMV infection implicated in birth defects, organ transplant failure, and cancer.IMPORTANCE Human cytomegalovirus (HCMV) is the leading infectious cause of birth defects, represents a serious complication for immunocompromised HIV/AIDS and organ transplant patients, and contributes to both immunosenescence and cardiovascular diseases. HCMV is also implicated in cancers such as glioblastoma multiforme (GBM) and infects ex vivo-cultured GBM tumor cells. In dividing tumor cells, the genomes of DNA tumor viruses regain nuclear localization after nuclear envelope breakdown during mitosis. This mitotic survival is mediated by a viral protein with a chromatin-tethering domain (CTD). Here, we report that the HCMV genome is maintained in dividing fibroblasts by the CTD of the viral IE19 protein. The discovery of a viral genome maintenance factor during productive infection could help explain viral genome dynamics within HCMV-positive tumors as well as during latency.
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Affiliation(s)
- Shelby M Lyon
- Institute for Molecular Virology, University of Wisconsin-Madison, Madison, Wisconsin, USA
- McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Kristen D Yetming
- Institute for Molecular Virology, University of Wisconsin-Madison, Madison, Wisconsin, USA
- McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Christina Paulus
- Biomedical Sciences Research Complex, University of St. Andrews, St. Andrews, United Kingdom
| | - Michael Nevels
- Biomedical Sciences Research Complex, University of St. Andrews, St. Andrews, United Kingdom
| | - Robert F Kalejta
- Institute for Molecular Virology, University of Wisconsin-Madison, Madison, Wisconsin, USA
- McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin, USA
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5
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Kalejta RF, Albright ER. Expanding the Known Functional Repertoire of the Human Cytomegalovirus pp71 Protein. Front Cell Infect Microbiol 2020; 10:95. [PMID: 32226778 PMCID: PMC7080695 DOI: 10.3389/fcimb.2020.00095] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Accepted: 02/25/2020] [Indexed: 12/11/2022] Open
Abstract
The human cytomegalovirus pp71 protein is packaged within the tegument of infectious virions and performs multiple functions in host cells to prime them for productive, lytic replication. Here we review the known and hypothesized functions of pp71 in regulating proteolysis, infection outcome (lytic or latent), histone deposition, transcription, translation, immune evasion, cell cycle progression, and pathogenesis. We also highlight recent advances in CMV-based vaccine candidates informed by an improved understanding of pp71 function.
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Affiliation(s)
| | - Emily R. Albright
- McArdle Laboratory for Cancer Research, Institute for Molecular Virology, University of Wisconsin – Madison, Madison, WI, United States
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6
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Lee JH, Pasquarella JR, Kalejta RF. Cell Line Models for Human Cytomegalovirus Latency Faithfully Mimic Viral Entry by Macropinocytosis and Endocytosis. J Virol 2019; 93:e01021-19. [PMID: 31391271 PMCID: PMC6803280 DOI: 10.1128/jvi.01021-19] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2019] [Accepted: 08/05/2019] [Indexed: 02/06/2023] Open
Abstract
Human cytomegalovirus (HCMV) enters primary CD34+ hematopoietic progenitor cells by macropinocytosis, where it establishes latency in part because its tegument-transactivating protein, pp71, remains associated with endosomes and is therefore unable to initiate productive, lytic replication. Here we show that multiple HCMV strains also enter cell line models used to study latency by macropinocytosis and endocytosis. In all latency models tested, tegument-delivered pp71 was found to be colocalized with endosomal markers and was not associated with the seven other cytoplasmic localization markers tested. Like the capsid-associated pp150 tegument protein, we initially detected capsid proteins in association with endosomes but later detected them in the nucleus. Inhibitors of macropinocytosis and endocytosis reduced latent viral gene expression and precluded reactivation. Importantly, we utilized electron microscopy to observe entry by macropinocytosis and endocytosis, providing additional visual corroboration of the findings of our functional studies. Our demonstration that HCMV enters cell line models for latency in a manner indistinguishable from that of its entry into primary cells illustrates the utility of these cell lines for probing the mechanisms, host genetics, and small-molecule-mediated inhibition of HCMV entry into the cell types where it establishes latency.IMPORTANCE Primary cells cultured in vitro currently provide the highest available relevance for examining molecular and genetic requirements for the establishment, maintenance, and reactivation of HCMV latency. However, their expense, heterogeneity, and intransigence to both long-term culture and molecular or genetic modification create rigor and reproducibility challenges for HCMV latency studies. There are several cell line models for latency not obstructed by deficiencies inherent in primary cells. However, many researchers view cell line studies of latency to be physiologically irrelevant because of the perception that these models display numerous and significant differences from primary cells. Here, we show that the very first step in a latent HCMV infection, entry of the virus into cells, occurs in cell line models in a manner indistinguishable from that in which it occurs in primary CD34+ hematopoietic progenitor cells. Our data argue that experimental HCMV latency is much more similar than it is different in cell lines and primary cells.
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Affiliation(s)
- Jeong-Hee Lee
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Joseph R Pasquarella
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Robert F Kalejta
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin, USA
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7
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Gelbmann CB, Kalejta RF. The Golgi sorting motifs of human cytomegalovirus UL138 are not required for latency maintenance. Virus Res 2019; 270:197646. [PMID: 31260705 PMCID: PMC6697590 DOI: 10.1016/j.virusres.2019.197646] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2019] [Revised: 06/26/2019] [Accepted: 06/27/2019] [Indexed: 02/07/2023]
Abstract
Human cytomegalovirus (HCMV) establishes latency within incompletely differentiated cells of the myeloid lineage. The viral protein UL138 participates in establishing and maintaining this latent state. UL138 has multiple functions during latency that include silencing productive phase viral gene transcription and modulating intracellular protein trafficking. Trafficking and subsequent downregulation of the multidrug resistance-associated protein 1 (MRP1) by UL138 is mediated by one of four Golgi sorting motifs within UL138. Here we investigate whether any of the Golgi sorting motifs of UL138 are required for the establishment and/or maintenance of HCMV latency in model cell systems in vitro. We determined that a mutant UL138 protein lacking an acidic cluster dileucine sorting motif unable to downregulate MRP1, as well as another mutant lacking all four Golgi sorting motifs still silenced viral immediate early (IE) gene expression and prevented progeny virion formation during latency. We conclude that the Golgi sorting motifs are not required for latency establishment or maintenance in model cell systems in vitro.
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Affiliation(s)
- Christopher B Gelbmann
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research University of Wisconsin-Madison, 1525 Linden Drive, Madison, WI, 53706, USA
| | - Robert F Kalejta
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research University of Wisconsin-Madison, 1525 Linden Drive, Madison, WI, 53706, USA.
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8
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Bristol JA, Djavadian R, Albright ER, Coleman CB, Ohashi M, Hayes M, Romero-Masters JC, Barlow EA, Farrell PJ, Rochford R, Kalejta RF, Johannsen EC, Kenney SC. A cancer-associated Epstein-Barr virus BZLF1 promoter variant enhances lytic infection. PLoS Pathog 2018; 14:e1007179. [PMID: 30052684 PMCID: PMC6082571 DOI: 10.1371/journal.ppat.1007179] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Revised: 08/08/2018] [Accepted: 06/25/2018] [Indexed: 12/29/2022] Open
Abstract
Latent Epstein-Barr virus (EBV) infection contributes to both B-cell and epithelial-cell malignancies. However, whether lytic EBV infection also contributes to tumors is unclear, although the association between malaria infection and Burkitt lymphomas (BLs) may involve excessive lytic EBV replication. A particular variant of the viral promoter (Zp) that controls lytic EBV reactivation is over-represented, relative to its frequency in non-malignant tissue, in EBV-positive nasopharyngeal carcinomas and AIDS-related lymphomas. To date, no functional differences between the prototype Zp (Zp-P) and the cancer-associated variant (Zp-V3) have been identified. Here we show that a single nucleotide difference between the Zp-V3 and Zp-P promoters creates a binding site for the cellular transcription factor, NFATc1, in the Zp-V3 (but not Zp-P) variant, and greatly enhances Zp activity and lytic viral reactivation in response to NFATc1-inducing stimuli such as B-cell receptor activation and ionomycin. Furthermore, we demonstrate that restoring this NFATc1-motif to the Zp-P variant in the context of the intact EBV B95.8 strain genome greatly enhances lytic viral reactivation in response to the NFATc1-activating agent, ionomycin, and this effect is blocked by the NFAT inhibitory agent, cyclosporine, as well as NFATc1 siRNA. We also show that the Zp-V3 variant is over-represented in EBV-positive BLs and gastric cancers, and in EBV-transformed B-cell lines derived from EBV-infected breast milk of Kenyan mothers that had malaria during pregnancy. These results demonstrate that the Zp-V3 enhances EBV lytic reactivation to physiologically-relevant stimuli, and suggest that increased lytic infection may contribute to the increased prevalence of this variant in EBV-associated malignancies. Whether excessive lytic EBV infection increases the risk of EBV-induced cancers is not clear. A particular variant (Zp-V3) of the viral promoter driving expression of the EBV immediate-early BZLF1 (Z) protein that mediates lytic viral reactivation has been reported to be over-represented (relative to the prototype Zp-P form of the promoter) in certain EBV-positive malignancies, but no functional difference between the two promoter variants has been reported. Here we show that the malignancy-associated Zp-V3 variant (but not the Zp-P variant) contains a binding site for the cellular NFATc1 (nuclear factor of activated T cells c1) transcription factor that allows it to be activated by NFATc1-inducing stimuli such as B-cell receptor stimulation. Furthermore, we demonstrate that restoring this NFATc1-motif to the Zp-P variant in the context of the intact EBV genome greatly enhances lytic viral reactivation in response to the NFATc1-inducing stimuli. We also find that the Zp-V3 variant is over-represented in EBV-positive Burkitt lymphomas and gastric carcinomas, and in lymphoblastoid cell lines transformed by EBV-infected breast milk of Kenyan mothers that had malaria during pregnancy. These findings suggest that the Zp-V3 version of the EBV BZLF1 promoter increases the likelihood of EBV-induced malignancies by increasing lytic EBV infection.
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Affiliation(s)
- Jillian A. Bristol
- Department of Oncology in Wisconsin Institutes for Medical Research, McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
| | - Reza Djavadian
- Department of Oncology in Wisconsin Institutes for Medical Research, McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
| | - Emily R. Albright
- Department of Molecular Virology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
| | - Carrie B. Coleman
- Department of Immunology & Microbiology, University of Colorado School of Medicine, Denver, Colorado, United States of America
| | - Makoto Ohashi
- Department of Oncology in Wisconsin Institutes for Medical Research, McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
| | - Mitchell Hayes
- Department of Oncology in Wisconsin Institutes for Medical Research, McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
| | - James C. Romero-Masters
- Department of Oncology in Wisconsin Institutes for Medical Research, McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
- Department of Pathology and Laboratory Medicine, McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
| | - Elizabeth A. Barlow
- Department of Oncology in Wisconsin Institutes for Medical Research, McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
| | - Paul J. Farrell
- Molecular Virology, Department of Medicine, Imperial College London, London, United Kingdom
| | - Rosemary Rochford
- Department of Immunology & Microbiology, University of Colorado School of Medicine, Denver, Colorado, United States of America
- Department of Immunology and Microbiology, University of Colorado, Aurora, Colorado United States of America
| | - Robert F. Kalejta
- Department of Molecular Virology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
| | - Eric C. Johannsen
- Department of Oncology in Wisconsin Institutes for Medical Research, McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
- Department of Medicine, McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
| | - Shannon C. Kenney
- Department of Oncology in Wisconsin Institutes for Medical Research, McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
- Department of Medicine, McArdle Laboratory for Cancer Research, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
- * E-mail:
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9
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Lyon SM, Kalejta RF. HCMV Assembly Is Totally Tubular. Dev Cell 2018; 45:1-2. [PMID: 29634930 DOI: 10.1016/j.devcel.2018.03.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Microtubules are normally organized at centrosomes, but other sites can also serve as microtubule organizing centers (MTOCs). In this issue of Developmental Cell, Procter et al. (2018) show that the human cytomegalovirus virion assembly compartment acts as a dynamic Golgi-derived MTOC where EB3 nucleates microtubules and regulates infectious virion production.
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Affiliation(s)
- Shelby M Lyon
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, WI 53706, USA.
| | - Robert F Kalejta
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, WI 53706, USA.
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10
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Abstract
Viral cyclin-dependent kinases (v-Cdks) functionally emulate their cellular Cdk counterparts. Such viral mimicry is an established phenomenon that we extend here through chemical genetics. Kinases contain gatekeeper residues that limit the size of molecules that can be accommodated within the enzyme active site. Mutating gatekeeper residues to smaller amino acids allows larger molecules access to the active site. Such mutants can utilize bio-orthoganol ATPs for phosphate transfer and are inhibited by compounds ineffective against the wild type protein, and thus are referred to as analog-sensitive (AS) kinases. We identified the gatekeeper residues of the v-Cdks encoded by Epstein-Barr virus (EBV) and human cytomegalovirus (HCMV) and mutated them to generate AS kinases. The AS-v-Cdks are functional and utilize different ATP derivatives with a specificity closely matching their cellular ortholog, AS-Cdk2. The AS derivative of the EBV v-Cdk was used to transfer a thiolated phosphate group to targeted proteins which were then purified through covalent capture and identified by mass spectrometry. Pathway analysis of these newly identified direct substrates of the EBV v-Cdk extends the potential influence of this kinase into all stages of gene expression (transcription, splicing, mRNA export, and translation). Our work demonstrates the biochemical similarity of the cellular and viral Cdks, as well as the utility of AS v-Cdks for substrate identification to increase our understanding of both viral infections and Cdk biology.
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Affiliation(s)
- Angie C. Umaña
- Institute for Molecular Virology
and McArdle Laboratory for Cancer Research, University of Wisconsin—Madison, Madison, Wisconsin 53706, United States
| | - Satoko Iwahori
- Institute for Molecular Virology
and McArdle Laboratory for Cancer Research, University of Wisconsin—Madison, Madison, Wisconsin 53706, United States
| | - Robert F. Kalejta
- Institute for Molecular Virology
and McArdle Laboratory for Cancer Research, University of Wisconsin—Madison, Madison, Wisconsin 53706, United States
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11
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Iwahori S, Kalejta RF. Phosphorylation of transcriptional regulators in the retinoblastoma protein pathway by UL97, the viral cyclin-dependent kinase encoded by human cytomegalovirus. Virology 2017; 512:95-103. [PMID: 28946006 DOI: 10.1016/j.virol.2017.09.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2017] [Revised: 09/08/2017] [Accepted: 09/11/2017] [Indexed: 01/11/2023]
Abstract
Human cytomegalovirus (HCMV) encodes a viral cyclin-dependent kinase (v-CDK), the UL97 protein. UL97 phosphorylates Rb, p107 and p130, thereby inactivating all three retinoblastoma (Rb) family members. Rb proteins function through regulating the activity of transcription factors to which they bind. Therefore, we examined whether the UL97-mediated regulation of the Rb tumor suppressors also extended to their binding partners. We observed that UL97 phosphorylates LIN52, a component of p107- and p130-assembled transcriptionally repressive DREAM complexes that control transcription during the G0/G1 phases, and the Rb-associated E2F3 protein that activates transcription through G1 and S phases. Intriguingly, we also identified FoxM1B, a transcriptional regulator during the S and G2 phases, as a UL97 substrate. This survey extends the influence of UL97 beyond simply the Rb proteins themselves to their binding partners, as well as past the G1/S transition into later stages of the cell cycle.
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Affiliation(s)
- Satoko Iwahori
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, 1525 Linden Drive, Madison, WI 53706, United States
| | - Robert F Kalejta
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, 1525 Linden Drive, Madison, WI 53706, United States.
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12
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Iwahori S, Umaña AC, VanDeusen HR, Kalejta RF. Human cytomegalovirus-encoded viral cyclin-dependent kinase (v-CDK) UL97 phosphorylates and inactivates the retinoblastoma protein-related p107 and p130 proteins. J Biol Chem 2017; 292:6583-6599. [PMID: 28289097 DOI: 10.1074/jbc.m116.773150] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 03/09/2017] [Indexed: 01/19/2023] Open
Abstract
The human cytomegalovirus (HCMV)-encoded viral cyclin-dependent kinase (v-CDK) UL97 phosphorylates the retinoblastoma (Rb) tumor suppressor. Here, we identify the other Rb family members p107 and p130 as novel targets of UL97. UL97 phosphorylates p107 and p130 thereby inhibiting their ability to repress the E2F-responsive E2F1 promoter. As with Rb, this phosphorylation, and the rescue of E2F-responsive transcription, is dependent on the L1 LXCXE motif in UL97 and its interacting clefts on p107 and p130. Interestingly, UL97 does not induce the disruption of all p107-E2F or p130-E2F complexes, as it does to Rb-E2F complexes. UL97 strongly interacts with p107 but not Rb or p130. Thus the inhibitory mechanisms of UL97 for Rb family protein-mediated repression of E2F-responsive transcription appear to differ for each of the Rb family proteins. The immediate early 1 (IE1) protein of HCMV also rescues p107- and p130-mediated repression of E2F-responsive gene expression, but it does not induce their phosphorylation and does not disrupt p107-E2F or p130-E2F complexes. The unique regulation of Rb family proteins by HCMV UL97 and IE1 attests to the importance of modulating Rb family protein function in HCMV-infected cells.
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Affiliation(s)
- Satoko Iwahori
- From the Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Angie C Umaña
- From the Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Halena R VanDeusen
- From the Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Robert F Kalejta
- From the Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin 53706
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13
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Lee WH, Higuchi H, Ikeda S, Macke EL, Takimoto T, Pattnaik BR, Liu C, Chu LF, Siepka SM, Krentz KJ, Rubinstein CD, Kalejta RF, Thomson JA, Mullins RF, Takahashi JS, Pinto LH, Ikeda A. Mouse Tmem135 mutation reveals a mechanism involving mitochondrial dynamics that leads to age-dependent retinal pathologies. eLife 2016; 5:e19264. [PMID: 27863209 PMCID: PMC5117855 DOI: 10.7554/elife.19264] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Accepted: 10/25/2016] [Indexed: 12/21/2022] Open
Abstract
While the aging process is central to the pathogenesis of age-dependent diseases, it is poorly understood at the molecular level. We identified a mouse mutant with accelerated aging in the retina as well as pathologies observed in age-dependent retinal diseases, suggesting that the responsible gene regulates retinal aging, and its impairment results in age-dependent disease. We determined that a mutation in the transmembrane 135 (Tmem135) is responsible for these phenotypes. We observed localization of TMEM135 on mitochondria, and imbalance of mitochondrial fission and fusion in mutant Tmem135 as well as Tmem135 overexpressing cells, indicating that TMEM135 is involved in the regulation of mitochondrial dynamics. Additionally, mutant retina showed higher sensitivity to oxidative stress. These results suggest that the regulation of mitochondrial dynamics through TMEM135 is critical for protection from environmental stress and controlling the progression of retinal aging. Our study identified TMEM135 as a critical link between aging and age-dependent diseases.
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Affiliation(s)
- Wei-Hua Lee
- Department of Medical Genetics, University of Wisconsin-Madison, Madison, United States
| | - Hitoshi Higuchi
- Department of Medical Genetics, University of Wisconsin-Madison, Madison, United States
| | - Sakae Ikeda
- Department of Medical Genetics, University of Wisconsin-Madison, Madison, United States
- McPherson Eye Research Institute, University of Wisconsin-Madison, Madison, United States
| | - Erica L Macke
- Department of Medical Genetics, University of Wisconsin-Madison, Madison, United States
| | - Tetsuya Takimoto
- Department of Medical Genetics, University of Wisconsin-Madison, Madison, United States
| | - Bikash R Pattnaik
- McPherson Eye Research Institute, University of Wisconsin-Madison, Madison, United States
- Department of Pediatrics, University of Wisconsin-Madison, Madison, United States
| | - Che Liu
- Institute for Molecular Virology, University of Wisconsin-Madison, Madison, United States
- McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, United States
| | - Li-Fang Chu
- Morgridge Institute for Research, Madison, United States
| | - Sandra M Siepka
- Department of Neurobiology, Northwestern University, Evanston, United States
| | - Kathleen J Krentz
- Transgenic Mouse Facility, Biotechnology Center, University of Wisconsin-Madison, Madison, United States
| | - C Dustin Rubinstein
- Translational Genomics Facility, Biotechnology Center, University of Wisconsin-Madison, Madison, United States
| | - Robert F Kalejta
- Institute for Molecular Virology, University of Wisconsin-Madison, Madison, United States
- McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, United States
| | | | - Robert F Mullins
- Department of Ophthalmology and Visual, University of Iowa, Iowa City, United States
| | - Joseph S Takahashi
- Department of Neuroscience, Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, United States
| | - Lawrence H Pinto
- Department of Neurobiology, Northwestern University, Evanston, United States
| | - Akihiro Ikeda
- Department of Medical Genetics, University of Wisconsin-Madison, Madison, United States
- McPherson Eye Research Institute, University of Wisconsin-Madison, Madison, United States
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14
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Kalejta RF. Sifting and Winnowing through Human Cytomegalovirus Lytic Replication and Latency. PLoS Pathog 2016; 12:e1005607. [PMID: 27657905 PMCID: PMC5033567 DOI: 10.1371/journal.ppat.1005607] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022] Open
Affiliation(s)
- Robert F. Kalejta
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research,University of Wisconsin-Madison, Madison, Wisconsin
- * E-mail:
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15
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Lee SH, Albright ER, Lee JH, Jacobs D, Kalejta RF. Cellular defense against latent colonization foiled by human cytomegalovirus UL138 protein. Sci Adv 2015; 1:e1501164. [PMID: 26702450 PMCID: PMC4681346 DOI: 10.1126/sciadv.1501164] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2015] [Accepted: 10/08/2015] [Indexed: 05/10/2023]
Abstract
Intrinsic immune defenses mediated by restriction factors inhibit productive viral infections. Select viruses rapidly establish latent infections and, with gene expression profiles that imply cell-autonomous intrinsic defenses, may be the most effective immune control measure against latent reservoirs. We illustrate that lysine-specific demethylases (KDMs) are restriction factors that prevent human cytomegalovirus from establishing latency by removing repressive epigenetic modifications from histones associated with the viral major immediate early promoter (MIEP), stimulating the expression of a viral lytic phase target of cell-mediated adaptive immunity. The viral UL138 protein negates this defense by preventing KDM association with the MIEP. The presence of an intrinsic defense against latency and the emergence of a cognate neutralizing viral factor indicate that "arms races" between hosts and viruses over lifelong colonization exist at the cellular level.
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16
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Iwahori S, Hakki M, Chou S, Kalejta RF. Molecular Determinants for the Inactivation of the Retinoblastoma Tumor Suppressor by the Viral Cyclin-dependent Kinase UL97. J Biol Chem 2015; 290:19666-80. [PMID: 26100623 DOI: 10.1074/jbc.m115.660043] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2015] [Indexed: 01/10/2023] Open
Abstract
The retinoblastoma (Rb) tumor suppressor restricts cell cycle progression by repressing E2F-responsive transcription. Cellular cyclin-dependent kinase (CDK)-mediated Rb inactivation through phosphorylation disrupts Rb-E2F complexes, stimulating transcription. The human cytomegalovirus (HCMV) UL97 protein is a viral CDK (v-CDK) that phosphorylates Rb. Here we show that UL97 phosphorylates 11 of the 16 consensus CDK sites in Rb. A cleft within Rb accommodates peptides with the amino acid sequence LXCXE. UL97 contains three such motifs. We determined that the first LXCXE motif (L1) of UL97 and the Rb cleft enhance UL97-mediated Rb phosphorylation. A UL97 mutant with a non-functional L1 motif (UL97-L1m) displayed significantly reduced Rb phosphorylation at multiple sites. Curiously, however, it efficiently disrupted Rb-E2F complexes but failed to relieve Rb-mediated repression of E2F reporter constructs. The HCMV immediate early 1 protein cooperated with UL97-L1m to inactivate Rb in transfection assays, likely indicating that cells infected with a UL97-L1m mutant virus show no defects in growth or E2F-responsive gene expression because of redundant viral mechanisms to inactivate Rb. Our data suggest that UL97 possesses a mechanism to elicit E2F-dependent gene expression distinct from disruption of Rb-E2F complexes and dependent upon both the L1 motif of UL97 and the cleft region of Rb.
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Affiliation(s)
- Satoko Iwahori
- From the Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin 53706 and
| | - Morgan Hakki
- the Division of Infectious Diseases, Oregon Health and Science University and
| | - Sunwen Chou
- the Division of Infectious Diseases, Oregon Health and Science University and Veterans Affairs Portland Health Care System, Portland, Oregon 97239
| | - Robert F Kalejta
- From the Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin 53706 and
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17
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Qin Q, Lee SH, Liang R, Kalejta RF. Insertion of myeloid-active elements into the human cytomegalovirus major immediate early promoter is not sufficient to drive its activation upon infection of undifferentiated myeloid cells. Virology 2013; 448:125-32. [PMID: 24314643 DOI: 10.1016/j.virol.2013.10.011] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Revised: 07/29/2013] [Accepted: 10/07/2013] [Indexed: 12/13/2022]
Abstract
The Major Immediate Early Promoter (MIEP) of human cytomegalovirus (HCMV) controls viral Immediate Early (IE) gene expression, which must be activated to initiate productive infection and repressed to establish latency. Regulation of the MIEP is critical for both viral spread and persistence. In addition to the Daxx-mediated intrinsic cellular defense that regulates the MIEP, the cell-type specific balance between cellular activators and repressors of the promoter may help dictate whether viral IE genes will be expressed or silenced. For example, in undifferentiated myeloid cells, transcriptional repressors of the MIEP may outnumber transcriptional activators, leading to promoter silencing and latency establishment. We created a recombinant viral genome in which a myeloid-active promoter replaced part of the MIEP. The viable virus generated failed to express the viral IE genes in an undifferentiated myeloid cell line. These observations have mechanistic implications regarding how viral IE gene expression is regulated during latency.
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Affiliation(s)
- Qingsong Qin
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, WI 53706, USA
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18
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Abstract
Herpesviruses assemble large virions capable of delivering to a newly infected cell not only the viral genome, but also viral proteins packaged within the tegument layer between the DNA-containing capsid and the lipid envelope. In this review, we describe the tegument transactivator of the β-herpesvirus human CMV, the pp71 protein. We present the known mechanistic features through which it activates viral gene expression during a lytic infection but fails to do so when the virus establishes latency, and describe how pp71 stimulates the cell cycle and may help infected cells avoid detection by the adaptive immune system. A historical overview of pp71 is extended with current perceptions of its roles during human CMV infections and suggestions for future avenues of experimentation.
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Affiliation(s)
- Rhiannon R Penkert
- Institute for Molecular Virology & McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, 1525 Linden Drive, Madison, WI 53706, USA
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19
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Dziurzynski K, Chang SM, Heimberger AB, Kalejta RF, McGregor Dallas SR, Smit M, Soroceanu L, Cobbs CS. Consensus on the role of human cytomegalovirus in glioblastoma. Neuro Oncol 2012; 14:246-55. [PMID: 22319219 DOI: 10.1093/neuonc/nor227] [Citation(s) in RCA: 216] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The human cytomegalovirus (HCMV) and glioma symposium was convened on April 17, 2011 in Washington, DC, and was attended by oncologists and virologists involved in studying the relationship between HCMV and gliomas. The purpose of the meeting was to reach a consensus on the role of HCMV in the pathology of gliomas and to clarify directions for future research. First, the group summarized data that describe how HCMV biology overlaps with the key pathways of cancer. Then, on the basis of published data and ongoing research, a consensus was reached that there is sufficient evidence to conclude that HCMV sequences and viral gene expression exist in most, if not all, malignant gliomas, that HCMV could modulate the malignant phenotype in glioblastomas by interacting with key signaling pathways; and that HCMV could serve as a novel target for a variety of therapeutic strategies. In summary, existing evidence supports an oncomodulatory role for HCMV in malignant gliomas, but future studies need to focus on determining the role of HCMV as a glioma-initiating event.
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Affiliation(s)
- Kristine Dziurzynski
- Department of Neurosurgery, The University of Texas MD Anderson Cancer Center, 1400 Holcombe Blvd., Unit 442, Houston, TX 77030, USA.
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20
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Hwang J, Kalejta RF. In vivo analysis of protein sumoylation induced by a viral protein: Detection of HCMV pp71-induced Daxx sumoylation. Methods 2011; 55:160-5. [PMID: 21816224 DOI: 10.1016/j.ymeth.2011.07.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2011] [Revised: 07/13/2011] [Accepted: 07/14/2011] [Indexed: 10/18/2022] Open
Abstract
Small ubiquitin-like modifiers (SUMOs) are covalently conjugated to target proteins to regulate numerous biological processes, including subcellular localization, protein-protein interactions, and transactivational activities. While the majority of identified SUMO targets are cellular proteins, SUMO modified viral proteins have also been identified. In addition, there are a growing number of examples where viruses alter the sumoylation status of host cell proteins. Work from our laboratory has previously demonstrated that the human cytomegalovirus (HCMV) virion tegument protein pp71 binds to Daxx, a cellular transcriptional co-repressor, and promotes its sumoylation. Here we describe the in vivo techniques used to detect pp71-induced sumoylation of Daxx in a cotransfection system as well as the endogenous SUMO modified form of Daxx in HCMV-infected cells. The approaches we describe can be easily adapted to infections with other viruses and for the detection of sumoylation of other proteins.
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Affiliation(s)
- Jiwon Hwang
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, WI 53706, USA
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21
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Penkert RR, Kalejta RF. Tegument protein control of latent herpesvirus establishment and animation. Herpesviridae 2011; 2:3. [PMID: 21429246 PMCID: PMC3063196 DOI: 10.1186/2042-4280-2-3] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/29/2010] [Accepted: 02/08/2011] [Indexed: 12/18/2022]
Abstract
Herpesviruses are successful pathogens that infect most vertebrates as well as at least one invertebrate species. Six of the eight human herpesviruses are widely distributed in the population. Herpesviral infections persist for the life of the infected host due in large part to the ability of these viruses to enter a non-productive, latent state in which viral gene expression is limited and immune detection and clearance is avoided. Periodically, the virus will reactivate and enter the lytic cycle, producing progeny virus that can spread within or to new hosts. Latency has been classically divided into establishment, maintenance, and reactivation phases. Here we focus on demonstrated and postulated molecular mechanisms leading to the establishment of latency for representative members of each human herpesvirus family. Maintenance and reactivation are also briefly discussed. In particular, the roles that tegument proteins may play during latency are highlighted. Finally, we introduce the term animation to describe the initiation of lytic phase gene expression from a latent herpesvirus genome, and discuss why this step should be separated, both molecularly and theoretically, from reactivation.
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Affiliation(s)
- Rhiannon R Penkert
- Institute for Molecular Virology, McArdle Laboratory for Cancer Research, and Cell and Molecular Biology Training Program, University of Wisconsin-Madison, Madison, WI, 53706, USA.
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22
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Abstract
Viruses are obligate intracellular parasites that alter the environment of infected cells in order to replicate more efficiently. One way viruses achieve this is by modulating cell cycle progression. The main regulators of progression out of G0, through G1, and into S phase are the members of the retinoblastoma (Rb) family of tumor suppressors. Rb proteins repress the transcription of genes controlled by the E2F transcription factors. Because the expression of E2F-responsive genes is required for cell cycle progression into the S phase, Rb arrests the cell cycle in G0/G1. A number of viral proteins directly target Rb family members for inactivation, presumably to create an environment more hospitable for viral replication. Such viral proteins include the extensively studied oncoproteins E7 (from human papillomavirus), E1A (from adenovirus), and the large T (tumor) antigen (from simian virus 40). Elucidating how these three viral proteins target and inactivate Rb has proven to be an invaluable approach to augment our understanding of both normal cell cycle progression and carcinogenesis. In addition to these proteins, a number of other virally-encoded inactivators of the Rb family have subsequently been identified including a surprising number encoded by human herpesviruses. Here we review how the human herpesviruses modulate Rb function during infection, introduce the individual viral proteins that directly or indirectly target Rb, and speculate about what roles Rb modulation by these proteins may play in viral replication, pathogenesis, and oncogenesis.
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Affiliation(s)
- Adam J Hume
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, WI 53706-1596, USA.
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23
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Abstract
Flow cytometric analysis of fluorescent protein expressing cells is of particular interest to researchers in many areas. The detection of fluorescent proteins in cells allows one to monitor gene expression, determine intracellular protein localization, and identify transfected cells. Wild-type green fluorescent protein has limited utility as its spectral properties are not suitable for standard cytometers. Site-directed mutations have produced enhanced variants with improved extinction coefficient and quantum yield with standard 488-nm excitation. Other variants have been constructed with shifted excitation and emission maxima and high quantum yield. It is now possible to monitor multiple processes in a single cell and detect enhanced green, yellow, and cyan fluorescent proteins using a single excitation beam at 458 nm. The authors carefully describe the custom filter setup required to accomplish this and the Boolean gating logic for analysis of the various subpopulations expressing any given combination of fluorescent proteins.
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Affiliation(s)
- A J Beavis
- Princeton University, Princeton, New Jersey, USA
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24
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Hume AJ, Finkel JS, Kamil JP, Coen DM, Culbertson MR, Kalejta RF. Phosphorylation of retinoblastoma protein by viral protein with cyclin-dependent kinase function. Science 2008; 320:797-9. [PMID: 18467589 DOI: 10.1126/science.1152095] [Citation(s) in RCA: 172] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
As obligate intracellular parasites, viruses expertly modify cellular processes to facilitate their replication and spread, often by encoding genes that mimic the functions of cellular proteins while lacking regulatory features that modify their activity. We show that the human cytomegalovirus UL97 protein has activities similar to cellular cyclin-cyclin-dependent kinase (CDK) complexes. UL97 phosphorylated and inactivated the retinoblastoma tumor suppressor, stimulated cell cycle progression in mammalian cells, and rescued proliferation of Saccharomyces cerevisiae lacking CDK activity. UL97 is not inhibited by the CDK inhibitor p21 and lacks amino acid residues conserved in the CDKs that permit the attenuation of kinase activity. Thus, UL97 represents a functional ortholog of cellular CDKs that is immune from normal CDK control mechanisms.
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Affiliation(s)
- Adam J Hume
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, WI 53706, USA
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25
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Abstract
The promyelocytic leukemia (PML) protein gathers other cellular proteins, such as Daxx and Sp100, to form subnuclear structures termed PML-nuclear bodies (PML-NBs) or ND10 domains. Many infecting viral genomes localize to PML-NBs, leading to speculation that these structures may represent the most efficient subnuclear location for viral replication. Conversely, many viral proteins modify or disrupt PML-NBs, suggesting that viral replication may be more efficient in the absence of these structures. Thus, a debate remains as to whether PML-NBs inhibit or enhance viral replication. Here we review and discuss recent data indicating that for herpesviruses, PML-NB proteins inhibit viral replication in cell types where productive, lytic replication occurs, while at the same time may enhance the establishment of lifelong latent infections in other cell types.
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Affiliation(s)
- Ryan T Saffert
- University of Wisconsin-Madison, Institute for Molecular Virology & McArdle Laboratory for Cancer Research, Madison, WI, USA Tel.: +1 608 265 5546; ;
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26
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Abstract
Proteins within the tegument layer of herpesviruses such as human cytomegalovirus (HCMV) are released into the cell upon entry when the viral envelope fuses with the cell membrane. These proteins are fully formed and active, and they mediate key events at the very start of the lytic infectious cycle, including the delivery of the viral genome to the nucleus and the initiation of viral gene expression. This review examines what is known about tegument protein function prior to the immediate early (IE) phase of the viral lytic replication cycle and identifies key questions that need to be answered to better understand how these proteins promote HCMV infection so that antiviral treatments that target these important viral regulators can be developed.
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Affiliation(s)
- R F Kalejta
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, WI 53706-1596, USA.
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27
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Hwang J, Kalejta RF. Proteasome-dependent, ubiquitin-independent degradation of Daxx by the viral pp71 protein in human cytomegalovirus-infected cells. Virology 2007; 367:334-8. [PMID: 17590404 DOI: 10.1016/j.virol.2007.05.037] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2007] [Revised: 04/18/2007] [Accepted: 05/31/2007] [Indexed: 10/23/2022]
Abstract
The cellular Daxx protein represses human cytomegalovirus (HCMV) gene expression from the major immediate early promoter. HCMV prevents Daxx-mediated silencing during lytic infection by delivering the viral pp71 tegument protein to the nucleus, where pp71 binds to and induces the proteasomal degradation of Daxx. In this study, we show that a functional ubiquitin pathway is not required for the proteasomal degradation of the endogenous Daxx protein by tegument-delivered pp71 in HCMV-infected cells, demonstrating that the pp71-mediated degradation of Daxx occurs through a proteasome-dependent, ubiquitin-independent pathway.
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Affiliation(s)
- Jiwon Hwang
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, WI 53706, USA
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28
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Saffert RT, Kalejta RF. Human cytomegalovirus gene expression is silenced by Daxx-mediated intrinsic immune defense in model latent infections established in vitro. J Virol 2007; 81:9109-20. [PMID: 17596307 PMCID: PMC1951389 DOI: 10.1128/jvi.00827-07] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
In addition to productive lytic infections, herpesviruses such as human cytomegalovirus (HCMV) establish a reservoir of latently infected cells that permit lifelong colonization of the host. When latency is established, the viral immediate-early (IE) genes that initiate the lytic replication cycle are not expressed. HCMV IE gene expression at the start of a lytic infection is facilitated by the viral pp71 protein, which is delivered to cells by infectious viral particles. pp71 neutralizes the Daxx-mediated cellular intrinsic immune defense that silences IE gene expression by generating a repressive chromatin structure on the viral major IE promoter (MIEP). In naturally latently infected cells and in cells latently infected in vitro, the MIEP also adopts a similar silenced chromatin structure. Here we analyze the role of Daxx in quiescent HCMV infections in vitro that mimic some, but not all, of the characteristics of natural latency. We show that in these "latent-like" infections, the Daxx-mediated defense that represses viral gene expression is not disabled because pp71 and Daxx localize to different cellular compartments. We demonstrate that Daxx is required to establish quiescent HCMV infections in vitro because in cells that would normally foster the establishment of these latent-like infections, the loss of Daxx causes the lytic replication cycle to be initiated. Importantly, the lytic cycle is inefficiently completed, which results in an abortive infection. Our work demonstrates that, in certain cell types, HCMV must silence its own gene expression to establish quiescence and prevent abortive infection and that the virus usurps a Daxx-mediated cellular intrinsic immune defense mechanism to do so. This identifies Daxx as one of the likely multiple viral and cellular determinants in the pathway of HCMV quiescence in vitro, and perhaps in natural latent infections as well.
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Affiliation(s)
- Ryan T Saffert
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, WI 53706, USA
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29
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Saffert RT, Kalejta RF. Inactivating a cellular intrinsic immune defense mediated by Daxx is the mechanism through which the human cytomegalovirus pp71 protein stimulates viral immediate-early gene expression. J Virol 2006; 80:3863-71. [PMID: 16571803 PMCID: PMC1440479 DOI: 10.1128/jvi.80.8.3863-3871.2006] [Citation(s) in RCA: 232] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Human cytomegalovirus (HCMV) masterfully evades adaptive and innate immune responses, allowing infection to be maintained and periodically reactivated for the life of the host. Here we show that cells also possess an intrinsic immune defense against HCMV that is disarmed by the virus. In HCMV-infected cells, the promyelocytic leukemia nuclear body (PML-NB) protein Daxx silences viral immediate-early gene expression through the action of a histone deacetylase. However, this antiviral tactic is efficiently neutralized by the viral pp71 protein, which is incorporated into virions, delivered to cells upon infection, and mediates the proteasomal degradation of Daxx. This work demonstrates the mechanism through which pp71 activates viral immediate-early gene expression in HCMV-infected cells. Furthermore, it provides insight into how a PML-NB protein institutes an intrinsic immune defense against a DNA virus and how HCMV pp71 inactivates this defense.
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Affiliation(s)
- Ryan T Saffert
- Institute for Molecular Virology, and McArdle Laboratory for Cancer Research, University of Wisconsin--Madison, 1525 Linden Drive, Madison, Wisconsin 53706, USA
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Kalejta RF. Human cytomegalovirus pp71: a new viral tool to probe the mechanisms of cell cycle progression and oncogenesis controlled by the retinoblastoma family of tumor suppressors. J Cell Biochem 2005; 93:37-45. [PMID: 15352160 DOI: 10.1002/jcb.20177] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The DNA tumor virus oncogenes (adenovirus E1A, simian virus 40 (SV40) large T antigen, and papillomavirus E7) have been instrumental in illuminating the molecules and mechanisms of cell cycle progression and carcinogenesis. However, since these multifunctional proteins target so many important cellular regulators, it is sometimes difficult to establish the functional importance of any individual interaction. Perhaps a herpesvirus protein, newly defined as a cell cycle regulator, can help address these issues. Like the DNA tumor virus proteins, the human cytomegalovirus (HCMV) pp71 protein contains a retinoblastoma protein (Rb) binding motif (LxCxD), and stimulates DNA synthesis in quiescent cells. Unlike E1A, T antigen, and E7, pp71 expression does not induce apoptosis, nor does it cooperate to transform primary cells. Determining how pp71 induces cell cycle progression without invoking apoptosis or leading to cellular transformation may help in defining the signals that ultimately lead to these processes.
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Affiliation(s)
- Robert F Kalejta
- Institute for Molecular Virology and McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin, USA.
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Kalejta RF, Shenk T. Proteasome-dependent, ubiquitin-independent degradation of the Rb family of tumor suppressors by the human cytomegalovirus pp71 protein. Proc Natl Acad Sci U S A 2003; 100:3263-8. [PMID: 12626766 PMCID: PMC152280 DOI: 10.1073/pnas.0538058100] [Citation(s) in RCA: 154] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/31/2002] [Indexed: 12/24/2022] Open
Abstract
Most of the substrates degraded by the proteasome are marked with polyubiquitin chains. However, there are a limited number of examples of nonubiquitinated proteins that are degraded by the proteasome. Here, we describe the degradation of the retinoblastoma family of tumor suppressor proteins by the proteasome in the absence of polyubiquitination. The retinoblastoma protein (p105), p107, and p130 are each targeted for degradation by the pp71 protein, which is encoded by the UL82 gene of human cytomegalovirus. It functions to direct their degradation in the absence of other viral proteins. While the pp71-mediated degradation of the retinoblastoma family of proteins requires proteasome function, it occurs without the attachment of ubiquitin to the substrates and in the absence of a functioning ubiquitin-conjugation system.
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Affiliation(s)
- Robert F Kalejta
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
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Abstract
As viruses are reliant upon their host cell to serve as proper environments for their replication, many have evolved mechanisms to alter intracellular conditions to suit their own needs. For example, human cytomegalovirus induces quiescent cells to enter the cell cycle and then arrests them in late G(1), before they enter the S phase, a cell cycle compartment that is presumably favorable for viral replication. Here we show that the protein product of the human cytomegalovirus UL82 gene, pp71, can accelerate the movement of cells through the G(1) phase of the cell cycle. This activity would help infected cells reach the late G(1) arrest point sooner and thus may stimulate the infectious cycle. pp71 also induces DNA synthesis in quiescent cells, but a pp71 mutant protein that is unable to induce quiescent cells to enter the cell cycle still retains the ability to accelerate the G(1) phase. Thus, the mechanism through which pp71 accelerates G(1) cell cycle progression appears to be distinct from the one that it employs to induce quiescent cells to exit G(0) and subsequently enter the S phase.
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Affiliation(s)
- Robert F Kalejta
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544-1014, USA
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Kalejta RF, Bechtel JT, Shenk T. Human cytomegalovirus pp71 stimulates cell cycle progression by inducing the proteasome-dependent degradation of the retinoblastoma family of tumor suppressors. Mol Cell Biol 2003; 23:1885-95. [PMID: 12612064 PMCID: PMC149485 DOI: 10.1128/mcb.23.6.1885-1895.2003] [Citation(s) in RCA: 147] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The oncoproteins of the DNA tumor viruses, adenovirus E1A, simian virus 40 T antigen, and papillomavirus E7, each interact with the retinoblastoma family of tumor suppressors, leading to cell cycle stimulation, apoptosis induction, and cellular transformation. These proteins utilize a conserved LXCXE motif, which is also found in cellular proteins, to target the retinoblastoma family. Here, we describe a herpesvirus protein that shares a subset of the properties of the DNA tumor virus oncoproteins but maintains important differences as well. The human cytomegalovirus pp71 protein employs an LXCXD motif to attack the retinoblastoma family members and induce DNA synthesis in quiescent cells. pp71 binds to and induces the degradation of the hypophosphorylated forms of the retinoblastoma protein and its family members p107 and p130 in a proteasome-dependent manner. However, pp71 does not induce apoptosis and fails to transform cells. Thus, the similarities and differences in comparison to E1A, T antigen, and E7 make pp71 an interesting new tool with which to further dissect the role of the retinoblastoma/E2F pathway in cellular growth control and carcinogenesis.
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Affiliation(s)
- Robert F Kalejta
- Molecular Biology Department, Princeton University, Princeton, NJ 08544-1014, USA
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34
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Abstract
The human cytomegalovirus-induced changes to the transcriptome and proteome of infected cells in many ways resemble an abortive mitogenic response. The virus induces quiescent cells to re-enter the cell cycle, but they are prevented from entering the S phase, where the synthesis of the cellular genome would compete with that of the virus for the available precursors for DNA replication. The mechanisms of these cell cycle alterations include transcriptional induction and repression, post-translational modifications and changes in protein stability. Essentially every class of cell cycle regulators is affected, and some of the key proteins are targeted by multiple different mechanisms. While the effects on cell cycle progression of viral infection, and of individual viral genes outside the context of viral infection have been described, it is now important to synthesize these two experimental approaches to gain a more complete understanding of how and why human cytomegalovirus infection affects cell cycle progression.
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Affiliation(s)
- Robert F Kalejta
- Department of Molecular Biology, Princeton University, Princeton NJ 08544-1014, USA
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Tao W, Pennica D, Xu L, Kalejta RF, Levine AJ. Wrch-1, a novel member of the Rho gene family that is regulated by Wnt-1. Genes Dev 2001; 15:1796-807. [PMID: 11459829 PMCID: PMC312736 DOI: 10.1101/gad.894301] [Citation(s) in RCA: 165] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2001] [Accepted: 05/22/2001] [Indexed: 11/25/2022]
Abstract
We report the isolation and cloning of the Wrch-1 (Wnt-1 responsive Cdc42 homolog) cDNA. Wrch-1 is a novel gene whose mRNA level increases in response to Wnt-1 signaling in Wnt-1 transformed cells, Wnt-1 transgene induced mouse mammary tumors, and Wnt-1 retrovirus infected cells. Wrch-1 encodes a homolog of the Rho family of GTPases. It shares 57% amino acid sequence identity with Cdc42, but possesses a unique N-terminal domain that contains several putative PXXP SH3-binding motifs. Like Cdc42, Wrch-1 can activate PAK-1 and JNK-1, and induce filopodium formation and stress fiber dissolution. Active Wrch-1 stimulates quiescent cells to reenter the cell cycle. Moreover, overexpression of Wrch-1 phenocopies Wnt-1 in morphological transformation of mouse mammary epithelial cells. Taken together, Wrch-1 could mediate the effects of Wnt-1 signaling in the regulation of cell morphology, cytoskeletal organization, and cell proliferation.
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Affiliation(s)
- W Tao
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA
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36
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Abstract
BACKGROUND Development of spectrally distinct green fluorescent protein (GFP) variants has allowed for simultaneous flow cytometric detection of two different colored mutants expressed in a single cell. However, the dual-laser methods employed in such experiments are not widely applicable since they require a specific, expensive laser, and single-laser analysis at 488 nm exhibits considerable spectral overlap. The purpose of this work was to evaluate detection of enhanced cyan fluorescent protein (ECFP) in combination with the enhanced green (EGFP) and enhanced yellow (EYFP) fluorescent proteins by flow cytometry. METHODS Cells transfected with expression constructs for EGFP, EYFP, or ECFP were analyzed by flow cytometry using excitation wavelengths at 458, 488, or 514 nm. Fluorescence signals were separated with a custom optical filter configuration: 525 nm shortpass and 500 nm longpass dichroics; 480/30 (ECFP), 510/20 (EGFP) and 550/30 (EYFP) bandpasses; 458 nm laser blocking filters. RESULTS All three fluorescent proteins when expressed individually or in combination in living cells were excited by the 458 nm laser line and their corresponding signals could be electronically compensated in real time. CONCLUSIONS This method demonstrates the detection of three fluorescent proteins expressed simultaneously in living cells using single laser excitation and is applicable for use on flow cytometers equipped with a tunable argon ion laser.
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Affiliation(s)
- A J Beavis
- Flow Cytometry Core Facility, Princeton University, Princeton, New Jersey 08544-1014, USA.
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Kalejta RF, Brideau AD, Banfield BW, Beavis AJ. An integral membrane green fluorescent protein marker, Us9-GFP, is quantitatively retained in cells during propidium iodide-based cell cycle analysis by flow cytometry. Exp Cell Res 1999; 248:322-8. [PMID: 10094838 DOI: 10.1006/excr.1999.4427] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Previously, we described GFP-spectrin, a membrane-localized derivative of the green fluorescent protein that can be employed as a marker during the simultaneous identification of transfected cells and cell cycle analysis by flow cytometry (Kalejta et al., Cytometry 29: 286-291, 1997). A membrane-anchored GFP fusion protein is necessary because the ethanol permeabilization step required to achieve efficient propidium iodide staining allows cytoplasmic GFP to leach out of the cell. However, viable cells expressing GFP-spectrin are not as bright as cells expressing cytoplasmic GFP and their fluorescence intensity is further diminished after ethanol treatment. Here, we demonstrate that the fluorescence intensity of cells expressing an integral membrane GFP fusion protein (Us9-GFP) is similar to that of cells expressing cytoplasmic GFP and is quantitatively maintained in cells after ethanol treatment. By allowing an accurate assessment of the expression level of GFP, Us9-GFP allows a more precise analysis of the effects of a cotransfected plasmid on the cell cycle and thus represents an improvement upon the original membrane-associated GFP fusion proteins employed in this assay.
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Affiliation(s)
- R F Kalejta
- Molecular Biology Department, Princeton University, Princeton, New Jersey, 08544, USA
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Kalejta RF, Li X, Mesner LD, Dijkwel PA, Lin HB, Hamlin JL. Distal sequences, but not ori-beta/OBR-1, are essential for initiation of DNA replication in the Chinese hamster DHFR origin. Mol Cell 1998; 2:797-806. [PMID: 9885567 DOI: 10.1016/s1097-2765(00)80294-4] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In the Chinese hamster dihydrofolate reductase replication initiation zone, the ori-beta locus is preferred over other start sites. To test the hypothesis that ori-beta contains a genetic replicator, we restored a deletion in the 3' end of the DHFR gene with a cosmid that provides the missing sequence and simultaneously knocks out the downstream ori-beta locus. Replication initiates normally in ori-beta knockout cell lines, and the DHFR domain is still synthesized in early S phase. However, initiation is completely suppressed in the starting deletion variant lacking the 3' end of the gene. We conclude that ori-beta does not contain an essential replicator, but that distant sequence elements have profound effects on origin activity in this locus.
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Affiliation(s)
- R F Kalejta
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville 22908, USA
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Kalejta RF, Shenk T, Beavis AJ. Use of a membrane-localized green fluorescent protein allows simultaneous identification of transfected cells and cell cycle analysis by flow cytometry. Cytometry 1997; 29:286-91. [PMID: 9415410 DOI: 10.1002/(sici)1097-0320(19971201)29:4<286::aid-cyto4>3.0.co;2-8] [Citation(s) in RCA: 104] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The simultaneous detection of the green fluorescent protein (GFP) and DNA content using propidium iodide (PI) by flow cytometry is made difficult because of the unique nature of these 2 fluorogenic reagents. For PI to enter cells efficiently and to stain DNA quantitatively, the cells must first be permeabilized; ethanol treatment is a routine method to achieve this. However, this permeabilization step causes GFP, which is normally found in the cytoplasm, to leach out of the cells. Although the use of paraformaldehyde-based fixatives allows GFP to be maintained in cells and retain its fluorescence even after ethanol permeabilization, the protocol we commonly employ results in inefficient PI staining and poor quality DNA histograms. To circumvent these difficulties, we have employed a GFP-fusion protein which localizes to the cellular membrane and as such is retained in cells upon ethanol permeabilization without prior fixation. This allows the GFP signal to be detected in cells treated with ethanol in preparation for PI staining and cell cycle analysis. This property facilitates the use of GFP as a marker for transfected cells in experiments designed to characterize the effects of ectopic expression of cellular or viral genes on cell cycle progression.
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Affiliation(s)
- R F Kalejta
- Department of Molecular Biology, Princeton University, New Jersey 08544-1014, USA
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40
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Abstract
The plant amino acid, mimosine, is an extremely effective inhibitor of DNA replication in mammalian cells, but the mechanism by which this inhibition is achieved is unknown. The drug has been proposed either to inhibit initiation at origins of replication or to inhibit chain elongation by lowering nucleotide pool levels. In an attempt to determine which mode of action is correct, we have analyzed its effects on SV40 DNA replication. Using a two-dimensional gel replicon mapping technique, we show that mimosine completely inhibits incorporation of [3H]thymidine into viral DNA, but only after approximately 4 h. Qualitative analysis of replication intermediates during this interval suggests that the drug partially inhibits both initiation and elongation, and pulse-chase experiments support this contention. The drug has no effect when added directly to an SV40 in vitro replication extract. However, extracts prepared from cells pretreated with mimosine are compromised in their ability to support replication in vitro in the presence of a full complement of nucleotides. Thus, although mimosine may alter nucleotide pool levels in vivo, it also appears to affect one or more essential replication proteins.
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Affiliation(s)
- R F Kalejta
- Department of Biochemistry and Cell and Molecular Biology Program, University of Virginia School of Medicine, Charlottesville, Virginia, 22908, USA
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41
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Abstract
The neutral/neutral two-dimensional (2-D) gel replicon mapping technique has been used to great advantage to localize and characterize origins of replication. Interestingly, many yeast origins display a composite pattern consisting of both a bubble arc and a single-fork arc. Moreover, in every instance in which neutral/neutral 2-D gels have been used to analyze origins in higher eukaryotic cells, two or more adjacent fragments display these composite patterns. We believe that composite patterns signal inefficient origin usage in yeast cells because the replicators in question are not active in every cell cycle and in higher eukaryotic replicons because initiation sites are chosen from among many potential sites lying within a zone. However, others have suggested that the single-fork arcs in these composite gel patterns arise from nicking activity that converts replication bubbles to branched structures that comigrate with bona fide single forks. Here, we have used three different replicon mapping strategies to show that broken simian virus 40 replication bubbles trace unique arcs that are clearly distinguishable from classic, intact single forks. Thus, it is likely that composite 2-D gel patterns represent origins that are inefficiently utilized.
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Affiliation(s)
- R F Kalejta
- Department of Biochemistry, University of Virginia School of Medicine, Charlottesvile 22098, USA
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Kalejta RF, Lin HB, Dijkwel PA, Hamlin JL. Characterizing replication intermediates in the amplified CHO dihydrofolate reductase domain by two novel gel electrophoretic techniques. Mol Cell Biol 1996; 16:4923-31. [PMID: 8756651 PMCID: PMC231494 DOI: 10.1128/mcb.16.9.4923] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Using neutral/neutral and neutral/alkaline two-dimensional (2-D) gel techniques, we previously obtained evidence that initiation can occur at any of a large number of sites distributed throughout a broad initiation zone in the dihydrofolate reductase (DHFR) domain of Chinese hamster ovary (CHO) cells. However, other techniques have suggested a much more circumscribed mode of initiation in this locus. This dichotomy has raised the issue whether the patterns of replicating DNA on 2-D gels have been misinterpreted and, in some cases, may represent such noncanonical replication intermediates as broken bubbles or microbubbles. In an accompanying study (R. F. Kalejta and J. L. Hamlin, Mol. Cell. Biol. 16:4915-4922, 1996), we have shown that broken bubbles migrate to unique positions in three different gel systems and therefore are not likely to be confused with classic replication intermediates. Here, we have applied a broken bubble assay developed from that study to an analysis of the amplified DHFR locus in CHO cells. This assay gives information about the number and positions of initiation sites within a fragment. In addition, we have analyzed the DHFR locus by a novel stop-and-go-alkaline gel technique that measures the size of nascent strands at all positions along each arc in a neutral/neutral 2-D gel. Results of these analyses support the view that the 2-D gel patterns previously assigned to classic, intact replication bubbles and single-forked structures indeed correspond to these entities. Furthermore, potential nascent-strand start sites appear to be distributed at very frequent intervals along the template in the intergenic region in the DHFR domain.
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Affiliation(s)
- R F Kalejta
- Department of Biochemistry, University of Virginia School of Medicine, Charlottesville 22908, USA
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