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Thevenin KR, Tieche IS, Di Benedetto CE, Schrager M, Dye KN. The small tumor antigen of Merkel cell polyomavirus accomplishes cellular transformation by uniquely localizing to the nucleus despite the absence of a known nuclear localization signal. Virol J 2024; 21:125. [PMID: 38831469 PMCID: PMC11149282 DOI: 10.1186/s12985-024-02395-x] [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: 01/19/2024] [Accepted: 05/22/2024] [Indexed: 06/05/2024] Open
Abstract
BACKGROUND Merkel Cell Carcinoma (MCC) is an aggressive skin cancer that is three times deadlier than melanoma. In 2008, it was found that 80% of MCC cases are caused by the genomic integration of a novel polyomavirus, Merkel Cell Polyomavirus (MCPyV), and the expression of its small and truncated large tumor antigens (ST and LT-t, respectively). MCPyV belongs to a family of human polyomaviruses; however, it is the only one with a clear association to cancer. METHODS To investigate the role and mechanisms of various polyomavirus tumor antigens in cellular transformation, Rat-2 and 293A cells were transduced with pLENTI MCPyV LT-t, MCPyV ST, TSPyV ST, HPyV7 ST, or empty pLENTI and assessed through multiple transformation assays, and subcellular fractionations. One-way ANOVA tests were used to assess statistical significance. RESULTS Soft agar, proliferation, doubling time, glucose uptake, and serum dependence assays confirmed ST to be the dominant transforming protein of MCPyV. Furthermore, it was found that MCPyV ST is uniquely transforming, as the ST antigens of other non-oncogenic human polyomaviruses such as Trichodysplasia Spinulosa-Associated Polyomavirus (TSPyV) and Human Polyomavirus 7 (HPyV7) were not transforming when similarly assessed. Identification of structural dissimilarities between transforming and non-transforming tumor antigens revealed that the uniquely transforming domain(s) of MCPyV ST are likely located within the structurally dissimilar loops of the MCPyV ST unique region. Of all known MCPyV ST cellular interactors, 62% are exclusively or transiently nuclear, suggesting that MCPyV ST localizes to the nucleus despite the absence of a canonical nuclear localization signal. Indeed, subcellular fractionations confirmed that MCPyV ST could achieve nuclear localization through a currently unknown, regulated mechanism independent of its small size, as HPyV7 and TSPyV ST proteins were incapable of nuclear translocation. Although nuclear localization was found to be important for several transforming properties of MCPyV ST, some properties were also performed by a cytoplasmic sequestered MCPyV ST, suggesting that MCPyV ST may perform different transforming functions in individual subcellular compartments. CONCLUSIONS Together, these data further elucidate the unique differences between MCPyV ST and other polyomavirus ST proteins necessary to understand MCPyV as the only known human oncogenic polyomavirus.
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Affiliation(s)
- Kaira R Thevenin
- Department of Health Sciences, Stetson University, 421 N Woodland Blvd, DeLand, FL, 32723, USA
| | - Isabella S Tieche
- Department of Health Sciences, Stetson University, 421 N Woodland Blvd, DeLand, FL, 32723, USA
| | - Cody E Di Benedetto
- Department of Health Sciences, Stetson University, 421 N Woodland Blvd, DeLand, FL, 32723, USA
| | - Matt Schrager
- Department of Health Sciences, Stetson University, 421 N Woodland Blvd, DeLand, FL, 32723, USA
| | - Kristine N Dye
- Department of Health Sciences, Stetson University, 421 N Woodland Blvd, DeLand, FL, 32723, USA.
- Department of Biology, Stetson University, DeLand, FL, 32723, USA.
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Peters DK, Erickson KD, Garcea RL. Live Cell Microscopy of Murine Polyomavirus Subnuclear Replication Centers. Viruses 2020; 12:v12101123. [PMID: 33023278 PMCID: PMC7650712 DOI: 10.3390/v12101123] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2020] [Revised: 09/22/2020] [Accepted: 09/30/2020] [Indexed: 01/24/2023] Open
Abstract
During polyomavirus (PyV) infection, host proteins localize to subnuclear domains, termed viral replication centers (VRCs), to mediate viral genome replication. Although the protein composition and spatial organization of VRCs have been described using high-resolution immunofluorescence microscopy, little is known about the temporal dynamics of VRC formation over the course of infection. We used live cell fluorescence microscopy to analyze VRC formation during murine PyV (MuPyV) infection of a mouse fibroblast cell line that constitutively expresses a GFP-tagged replication protein A complex subunit (GFP-RPA32). The RPA complex forms a heterotrimer (RPA70/32/14) that regulates cellular DNA replication and repair and is a known VRC component. We validated previous observations that GFP-RPA32 relocalized to sites of cellular DNA damage in uninfected cells and to VRCs in MuPyV-infected cells. We then used GFP-RPA32 as a marker of VRC formation and expansion during live cell microscopy of infected cells. VRC formation occurred at variable times post-infection, but the rate of VRC expansion was similar between cells. Additionally, we found that the early viral protein, small TAg (ST), was required for VRC expansion but not VRC formation, consistent with the role of ST in promoting efficient vDNA replication. These results demonstrate the dynamic nature of VRCs over the course of infection and establish an approach for analyzing viral replication in live cells.
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Affiliation(s)
- Douglas K. Peters
- BioFrontiers Institute, University of Colorado Boulder, Boulder, CO 80309, USA; (D.K.P.); (K.D.E.)
| | - Kimberly D. Erickson
- BioFrontiers Institute, University of Colorado Boulder, Boulder, CO 80309, USA; (D.K.P.); (K.D.E.)
| | - Robert L. Garcea
- BioFrontiers Institute, University of Colorado Boulder, Boulder, CO 80309, USA; (D.K.P.); (K.D.E.)
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado Boulder, Boulder, CO 80309, USA
- Correspondence:
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3
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Hashida Y, Higuchi T, Nakajima S, Nakajima K, Ujihara T, Kabashima K, Sano S, Daibata M. Human Polyomavirus 6 Detected in Cases of Eosinophilic Pustular Folliculitis. J Infect Dis 2020; 223:1724-1732. [PMID: 32989462 DOI: 10.1093/infdis/jiaa607] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2020] [Accepted: 09/24/2020] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Human polyomaviruses (HPyVs) have been associated with several cutaneous inflammatory conditions. More investigation is needed to identify further presentations of cutaneous pathology associated with HPyVs. Our aim was to investigate the possible association of skin-tropic HPyVs with folliculitis, particularly eosinophilic pustular folliculitis (EPF). METHODS This study included 55 Japanese patients, comprising 13 patients with EPF and 42 patients with suppurative folliculitis. HPyV DNAs were detected by quantitative polymerase chain reaction. Expression of viral antigen and geographically related viral genotypes were also assessed. RESULTS Human polyomavirus 6 (HPyV6) DNA was found in 9 of 13 (69%) patients with EPF, a rate significantly higher than that found in suppurative folliculitis (1/42; 2%). Of the 7 HPyV6 DNA-positive EPF specimens analyzed, 4 were positive for HPyV6 small tumor antigen. All the HPyV6 strains detected in this study were of the Asian/Japanese genotype. CONCLUSIONS The predominant detection of HPyV6 DNA and the expression of viral antigen suggest a possible association between HPyV6 infection and EPF in a subset of patients. Worldwide studies are warranted to determine whether Asian/Japanese genotype HPyV6 is associated preferentially with the incidence and pathogenesis of this eosinophil-related skin disease that has an ethnic predilection for the East Asian population.
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Affiliation(s)
- Yumiko Hashida
- Department of Microbiology and Infection, Kochi Medical School, Kochi University, Kochi, Japan
| | - Tomonori Higuchi
- Department of Microbiology and Infection, Kochi Medical School, Kochi University, Kochi, Japan
| | - Saeko Nakajima
- Department of Dermatology, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Kimiko Nakajima
- Department of Dermatology, Kochi Medical School, Kochi University, Kochi, Japan
| | - Takako Ujihara
- Department of Microbiology and Infection, Kochi Medical School, Kochi University, Kochi, Japan.,Science Research Center, Kochi Medical School, Kochi University, Kochi, Japan
| | - Kenji Kabashima
- Department of Dermatology, Kyoto University Graduate School of Medicine, Kyoto, Japan.,Singapore Immunology Network and Skin Research Institute of Singapore, Agency for Science, Technology and Research, Singapore
| | - Shigetoshi Sano
- Department of Dermatology, Kochi Medical School, Kochi University, Kochi, Japan
| | - Masanori Daibata
- Department of Microbiology and Infection, Kochi Medical School, Kochi University, Kochi, Japan
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4
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Hashida Y, Higuchi T, Nakajima K, Ujihara T, Murakami I, Fujieda M, Sano S, Daibata M. Human Polyomavirus 6 with the Asian-Japanese Genotype in Cases of Kimura Disease and Angiolymphoid Hyperplasia with Eosinophilia. J Invest Dermatol 2020; 140:1650-1653.e4. [PMID: 31981580 DOI: 10.1016/j.jid.2019.12.027] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2019] [Revised: 11/06/2019] [Accepted: 12/09/2019] [Indexed: 01/10/2023]
Affiliation(s)
- Yumiko Hashida
- Department of Microbiology and Infection, Kochi Medical School, Kochi University, Kochi, Japan
| | - Tomonori Higuchi
- Department of Microbiology and Infection, Kochi Medical School, Kochi University, Kochi, Japan
| | - Kimiko Nakajima
- Department of Dermatology Kochi Medical School, Kochi University, Kochi, Japan
| | - Takako Ujihara
- Department of Microbiology and Infection, Kochi Medical School, Kochi University, Kochi, Japan; Science Research Center, Kochi Medical School, Kochi University, Kochi, Japan
| | - Ichiro Murakami
- Department of Pathology, Kochi Medical School, Kochi University, Kochi, Japan
| | - Mikiya Fujieda
- Department of Pediatrics, Kochi Medical School, Kochi University, Kochi, Japan
| | - Shigetoshi Sano
- Department of Dermatology Kochi Medical School, Kochi University, Kochi, Japan
| | - Masanori Daibata
- Department of Microbiology and Infection, Kochi Medical School, Kochi University, Kochi, Japan.
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5
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White MK, Khalili K. Expression of JC virus regulatory proteins in human cancer: potential mechanisms for tumourigenesis. Eur J Cancer 2005; 41:2537-48. [PMID: 16219459 DOI: 10.1016/j.ejca.2005.08.019] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
JC virus (JCV) is a human polyomavirus that is the etiologic agent of the fatal demyelinating disease of the central nervous system known as progressive multifocal leukoencephalopathy (PML). JCV is also linked to some tumours of the brain and other organs as evidenced by the presence of JCV DNA sequences and the expression of viral proteins in clinical samples. Since JCV is highly oncogenic in experimental animals and transforms cells in culture, it is possible that JCV contributes to the malignant phenotype of human tumours with which it is associated. JCV encodes three non-capsid regulatory proteins: large T-antigen, small t-antigen and agnoprotein that interact with a number of cellular target proteins and interfere with certain normal cellular functions. In this review, we discuss how JCV proteins deregulate signalling pathways especially ones pertaining to transcriptional regulation and cell cycle control. These effects may be involved in the progression of JCV-associated tumours and may represent potential therapeutic targets.
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Affiliation(s)
- Martyn K White
- Center for Neurovirology, Department of Neuroscience, Temple University School of Medicine, 1900 North 12th Street, MS 015-96, Room 203, Philadelphia, PA 19122, USA
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White MK, Gordon J, Reiss K, Del Valle L, Croul S, Giordano A, Darbinyan A, Khalili K. Human polyomaviruses and brain tumors. ACTA ACUST UNITED AC 2005; 50:69-85. [PMID: 15982744 DOI: 10.1016/j.brainresrev.2005.04.007] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2004] [Revised: 04/12/2005] [Accepted: 04/21/2005] [Indexed: 12/25/2022]
Abstract
Polyomaviruses are DNA tumor viruses with small circular genomes. Three polyomaviruses have captured attention with regard to their potential role in the development of human brain tumors: JC virus (JCV), BK virus (BKV), and simian vacuolating virus 40 (SV40). JCV is a neurotropic polyomavirus that is the etiologic agent of progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease of the central nervous system occurring mainly in AIDS patients. BKV is the causative agent of polyomavirus-associated nephropathy (PVN) which occurs after renal transplantation when BKV reactivates from a latent state during immunosuppressive therapy to cause allograft failure. SV40, originating in rhesus monkeys, gained notoriety when it entered the human population via contaminated polio vaccines. All three viruses are highly oncogenic when injected into the brain of experimental animals. Reports indicate that these viruses, especially JCV, are associated with brain tumors and other cancers in humans as evidenced from the analysis of clinical samples for the presence of viral DNA sequences and expression of viral proteins. Human polyomaviruses encode three non-capsid regulatory proteins: large T-antigen, small t-antigen, and agnoprotein. These proteins interact with a number of cellular target proteins to exert effects that dysregulate pathways involved in the control of various host cell functions including the cell cycle, DNA repair, and others. In this review, we describe the three polyomaviruses, their abilities to cause brain and other tumors in experimental animals, the evidence for an association with human brain tumors, and the latest findings on the molecular mechanisms of their actions.
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Affiliation(s)
- Martyn K White
- Center for Neurovirology and Cancer Biology, College of Science and Technology, Temple University, 1900 North 12th Street, 015-96, Room 203, Philadelphia, PA 19122, USA
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Nunbhakdi-Craig V, Craig L, Machleidt T, Sontag E. Simian virus 40 small tumor antigen induces deregulation of the actin cytoskeleton and tight junctions in kidney epithelial cells. J Virol 2003; 77:2807-18. [PMID: 12584304 PMCID: PMC149746 DOI: 10.1128/jvi.77.5.2807-2818.2003] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
There is increasing evidence that the transforming DNA tumor virus simian virus 40 (SV40) is associated with human malignancies. SV40 small tumor antigen (small t) interacts with endogenous serine/threonine protein phosphatase 2A (PP2A) and is required for the transforming activity of SV40 in epithelial cells of the lung and kidney. Here, we show that expression of SV40 small t in epithelial MDCK cells induces acute morphological changes and multilayering. Significantly, it also causes severe defects in the biogenesis and barrier properties of tight junctions (TJs) but does not prevent formation of adherens junctions. Small t-induced TJ defects are associated with a loss of PP2A from areas of cell-cell contact; altered distribution and reduced amounts of the TJ proteins ZO-1, occludin, and claudin-1; and marked disorganization of the actin cytoskeleton. Small t-mediated F-actin rearrangements encompass increased Rac-induced membrane ruffling and lamellipodia, Cdc42-initiated filopodia, and loss of Rho-dependent stress fibers. Indeed, these F-actin changes coincide with elevated levels of Rac1 and Cdc42 and decreased amounts of RhoA in small t-expressing cells. Notably, these cellular effects of small t are dependent on its interaction with endogenous PP2A. Thus, our findings provide the first evidence that, in polarized epithelial cells, expression of small t alone is sufficient to induce deregulation of Rho GTPases, F-actin, and intercellular adhesion, through interaction with endogenous PP2A. Because defects in the actin cytoskeleton and TJ disruption have been linked to loss of cell polarity and tumor invasiveness, their deregulation by PP2A and small t likely contributes to the role of SV40 in epithelial cell transformation.
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Affiliation(s)
- Viyada Nunbhakdi-Craig
- Department of Pathology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9073, USA
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8
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Simsir A, Fetsch P, Bedrossian CW, Ioffe OB, Abati A. Absence of SV-40 large T antigen (Tag) in malignant mesothelioma effusions: an immunocytochemical study. Diagn Cytopathol 2001; 25:203-7. [PMID: 11599101 DOI: 10.1002/dc.2039] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Simian Virus 40 (SV 40) was recently implicated in the pathogenesis of malignant mesothelioma. The oncogenic capacity of SV-40 is a function of a nuclear protein, the large T antigen (Tag). SV-40 Tag DNA sequences are detected by the polymerase chain reaction in 40-80% of malignant mesothelial proliferations. However, the role of immunohistochemistry (IHC) in demonstrating the nuclear localization of Tag is controversial. We sought to determine the clinical utility of SV-40 Tag IHC in pleural effusion cytology as an ancillary tool in the cytologic diagnosis of malignant mesothelioma (MM). Formalin-fixed, paraffin-embedded cell block sections from 100 pleural effusions (32 MMs, 25 benign reactive, 43 metastatic adenocarcinomas) were immunostained for the SV-40 anti-Tag, using two primary monoclonal SV-40 Tag antibodies: clone Pab 416 and clone Pab 101. Despite strong and consistent immunoreactivity in positive controls, no nuclear immunostaining was observed in any case. We believe the small sample size in cytology cell block sections, the low viral copy number in infected cells, and the effect of formalin fixation may have resulted in absence of immunoreactivity. The role of SV-40 Tag IHC in diagnostic cytopathology remains unclear unless further studies reliably show its detection.
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Affiliation(s)
- A Simsir
- Department of Pathology, New York University Medical Center, New York, New York 10016, USA.
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9
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Wang WB, Bikel I, Marsilio E, Newsome D, Livingston DM. Transrepression of RNA polymerase II promoters by the simian virus 40 small t antigen. J Virol 1994; 68:6180-7. [PMID: 8083958 PMCID: PMC237037 DOI: 10.1128/jvi.68.10.6180-6187.1994] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Simian virus 40 (SV40) small t antigen (t) can activate transcription from certain RNA polymerase II and III promoters (M. Loeken, I. Bikel, D. M. Livingston, and J. Brady, Cell 55:1171-1177, 1988). Here we report a new function of t, its ability to repress human c-fos promoter and AP-1 transcriptional activity in CV-1P cells. This function is the product of a discrete N-terminal domain of t, because the large T antigen (T)/t-common polypeptide, which contains only the first 82 amino acids common to both T and t of SV40, was, like the intact protein, an active repressor. The data further suggest that the t- and T/t-common-mediated repression of c-fos expression was most likely manifest at the level of transcription. In keeping with the possibility that t affects the expression of the genomic c-fos promoter, it also led to repression of AP-1 formation. Thus, SV40 is both an activator and a repressor of transcription. Its ability to inhibit c-fos expression should be considered in light of the natural history of SV40 in its natural host.
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Affiliation(s)
- W B Wang
- Dana-Farber Cancer Institute, Boston, Massachusetts 02115
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10
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Cicala C, Avantaggiati ML, Graessmann A, Rundell K, Levine AS, Carbone M. Simian virus 40 small-t antigen stimulates viral DNA replication in permissive monkey cells. J Virol 1994; 68:3138-44. [PMID: 8151779 PMCID: PMC236804 DOI: 10.1128/jvi.68.5.3138-3144.1994] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The simian virus 40 (SV40) large-T antigen is essential for SV40 DNA replication and for late viral gene expression, but the role of the SV40 small-t antigen in these processes is still unclear. We have previously demonstrated that small t inhibits SV40 DNA replication in vitro. In this study, we investigated the effect of small t on SV40 replication in cultured cells. CV1 monkey cell infection experiments indicated that mutant viruses that lack small t replicate less efficiently than the wild-type virus. We next microinjected CV1 cells with SV40 DNA with and without purified small-t protein and analyzed viral DNA replication efficiency by Southern blotting. Replication of either wild-type SV40 or small-t deletion mutant DNA was increased three- to fivefold in cells coinjected with purified small t. Thus, in contrast to our in vitro observation, small t stimulated viral DNA replication in vivo. This result suggests that small t has cellular effects that are not detectable in a reconstituted in vitro replication system. We also found that small t stimulated progression of permissive monkey cells--but not of nonpermissive rodent cells--from G0-G1 to the S phase of the cell cycle, possibly leading to an optimal intracellular environment for viral replication.
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Affiliation(s)
- C Cicala
- Section on DNA Replication, Repair, and Mutagenesis, National Institute of Child Health and Human Development, Bethesda, Maryland 20892
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11
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Sontag E, Fedorov S, Kamibayashi C, Robbins D, Cobb M, Mumby M. The interaction of SV40 small tumor antigen with protein phosphatase 2A stimulates the map kinase pathway and induces cell proliferation. Cell 1993; 75:887-97. [PMID: 8252625 DOI: 10.1016/0092-8674(93)90533-v] [Citation(s) in RCA: 434] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Interaction with SV40 small tumor antigen (small t) compromised the ability of multimeric protein phosphatase 2A to inactivate the mitogen-activated protein kinase ERK1 and the mitogen-activated protein kinase kinase MEK1. Transient expression of small t in CV-1 cells activated MEK and ERK but did not affect Raf activity. Small t stimulated the growth of quiescent CV-1 cells almost as effectively as did serum. Coexpression of kinase-deficient ERK2 blocked most, but not all, of the proliferation caused by small t. Activation of the mitogen-activated protein kinase pathway and stimulation of cell growth were dependent on the interaction of small t with protein phosphatase 2A. These findings indicate that SV40 small t is capable of inducing cell growth through blockade of protein phosphatase and deregulation of the mitogen-activated protein kinase cascade.
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Affiliation(s)
- E Sontag
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75235-9041
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12
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Pryciak PM, Varmus HE. Fv-1 restriction and its effects on murine leukemia virus integration in vivo and in vitro. J Virol 1992; 66:5959-66. [PMID: 1326652 PMCID: PMC241473 DOI: 10.1128/jvi.66.10.5959-5966.1992] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
We have investigated the mechanisms by which alleles at the mouse Fv-1 locus restrict replication of murine leukemia viruses. Inhibition of productive infection is closely paralleled by reduced accumulation of integrated proviral DNA as well as by reduced levels of linear viral DNA in a cytoplasmic fraction. Nevertheless, viral DNA is present at nearly normal levels in a nuclear fraction, and total amounts of viral DNA are only mildly affected in restrictive infections, suggesting a block in integration to account for reduced levels of proviral DNA. However, integrase (IN)-dependent trimming of 3' ends of viral DNA occurs normally in vivo during restrictive infections, demonstrating that not all IN-mediated events are prevented in vivo. Furthermore, viral integration complexes present in nuclear extracts of infected restrictive cells are fully competent to integrate their DNA into a heterologous target in vitro. Thus, the Fv-1-dependent activity that restricts integration in vivo may be lost in vitro; alternatively, Fv-1 restriction may prevent a step required for integration in vivo that is bypassed in vitro.
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Affiliation(s)
- P M Pryciak
- Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0502
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Abstract
One objective of this review is to sort through and collate the recent data that suggest that human cellular oncogenes, which have been implicated as the etiologic agents in both animal and human malignancies, have also the potential to be employed as clinical tools in the struggle against cancer. For nearly 10 years, reports have been suggesting that advantage can be taken of cellular oncogenes as to their use as diagnostic and prognostic indicators of cancer and eventually as therapeutic cancer agents. It is also the purpose of this review to give an objective evaluation of these predictions. Moreover, this review will try to highlight some of the significant advances in this most rapidly evolving field of biology. Although the enormity of what has been learned about cellular oncogenes is nothing less than impressive, it is the view here that the routine implementation of oncogenes into the clinical setting will not become evident as early as the many predictions had purported.
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Affiliation(s)
- S Demczuk
- Karolinska Institute, NOVUM, Huddinge, Sweden
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14
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Mumby MC, Walter G. Protein phosphatases and DNA tumor viruses: transformation through the back door? CELL REGULATION 1991; 2:589-98. [PMID: 1663787 PMCID: PMC361850 DOI: 10.1091/mbc.2.8.589] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Cellular transformation by many oncogenic viruses is mediated by alterations in signal transduction pathways that control normal growth and proliferation. Common targets for many transforming viruses are pathways regulated by protein phosphorylation. The biochemical control of proteins in these pathways is a dynamic process that is regulated by the relative activities of protein kinases and phosphatases. Although there are numerous examples of viral oncogenes that encode protein kinases (Hunter, 1991), until recently there has been no evidence linking altered phosphatase activity to transformation. In this review we describe a novel mechanism, utilized by small DNA tumor viruses, in which viral oncogenes bind to and regulate a cellular protein serine/threonine phosphatase. The currently available evidence indicates that alteration of phosphatase activity and subsequent changes in phosphorylation levels is an important step in transformation by these viruses.
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Affiliation(s)
- M C Mumby
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75235-9041
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15
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Jog P, Joshi B, Dhamankar V, Imperiale MJ, Rutila J, Rundell K. Mutational analysis of simian virus 40 small-t antigen. J Virol 1990; 64:2895-900. [PMID: 2159550 PMCID: PMC249472 DOI: 10.1128/jvi.64.6.2895-2900.1990] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Several point mutations in the simian virus 40 (SV40) small-t antigen have been analyzed for their effects on protein stability, transformation, transactivation, and binding of two cellular proteins. All mutations which affected cysteine residues in two cysteine clusters produced highly unstable small-t antigens. Four point mutations outside these clusters and one in-frame deletion mutant, dl890, produced stable proteins but reduced transformation efficiency. These were able to transactivate the EII promoter and bind the cellular proteins, suggesting that these activities are not sufficient for small-t-mediated enhancement of transformation.
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Affiliation(s)
- P Jog
- Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, Illinois 60611-3008
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16
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Montano X, Lane DP. Monoclonal antibody analysis of simian virus 40 small t-antigen expression in infected and transformed cells. J Virol 1989; 63:3128-34. [PMID: 2542620 PMCID: PMC250870 DOI: 10.1128/jvi.63.7.3128-3134.1989] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The monoclonal antibody PAb280 binds to small t antigen but not to large T antigen. Its binding site within the unique region of small t antigen was localized by studying its reaction with simian virus 40 mutants, other papovaviruses, and bacterial expression vectors coding for fragments of small t antigen. The antibody was used to define the cellular location of small t antigen by immunocytochemistry and by immunoprecipitation of subcellular extracts of infected cells. PAb280 reacts strongly with a cytoplasmic form of small t antigen that appears to be associated with the cytoskeleton and is not detected by antibodies directed to the common N terminus of small t and large T antigens. Immunoperoxidase staining of cells infected by the simian virus 40 defective strain SV402 with PAb280 and other anti-T antibodies demonstrated that this virus produced an N-terminal fragment of large T antigen as well as small t antigen. In cells infected by the virus, this fragment was located in the cell nucleus but was very unstable. These results suggest that the activity of the SV402 virus in transformation assays may not be entirely due to the action of small t antigen alone.
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Affiliation(s)
- X Montano
- Department of Biochemistry, Imperial College London, United Kingdom
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Bikel I, Montano X, Agha ME, Brown M, McCormack M, Boltax J, Livingston DM. SV40 small t antigen enhances the transformation activity of limiting concentrations of SV40 large T antigen. Cell 1987; 48:321-30. [PMID: 3026642 DOI: 10.1016/0092-8674(87)90435-1] [Citation(s) in RCA: 113] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
A murine recombinant Neo(r) retrovirus encoding the SV40 small t antigen was used to infect Balb/c 3T3 CIA31 cells. From analyses of G418-resistant clones containing at least as much intact t as Cos-1 cells, we found that t, alone, had no detectable A31 transforming activity. In contrast, we noted that SV40 large T promoted A31 agar colony formation when present over a 5- to 7.5-fold concentration range. However, at the low end of the spectrum, its transforming effect was manifest inefficiently except in the presence of t. Thus a major role for t in the SV40 transforming mechanism is to enhance directly or indirectly the transforming function of T.
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The t-unique coding domain is important to the transformation maintenance function of the simian virus 40 small t antigen. Mol Cell Biol 1987. [PMID: 3023875 DOI: 10.1128/mcb.6.4.1172] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The small t antigen (t) of simian virus 40, a 174-amino-acid-containing protein, when present together with the other early viral protein, large T antigen (T), plays an important role in the maintenance of simian virus 40-induced neoplastic phenotype in certain cells. Indeed, each protein functions in a complementary manner in this process. The t coding unit is composed of two segments, a 5' region of 246 nucleotides which is identical to that of the corresponding 5' region of the T coding unit and a 3' segment of 276 nucleotides which is unique. Two mutant, t-encoding genomes, one bearing a missense and the other a nonsense mutation at the same point in the t-unique coding region were constructed in vitro and found to be defective in their ability to dissolve the actin cytoskeleton of rat fibroblasts and to complement T in the growth of mouse fibroblasts in soft agar. Therefore, the unique segment of the t gene encodes a portion of the t molecule which is essential to its transformation maintenance function.
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Berger H, Wintersberger E. Polyomavirus small T antigen enhances replication of viral genomes in 3T6 mouse fibroblasts. J Virol 1986; 60:768-70. [PMID: 3022009 PMCID: PMC288954 DOI: 10.1128/jvi.60.2.768-770.1986] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Transfection of 3T6 cells with a cloned polyomavirus genome encoding only large T antigen resulted in DNA replication with only about 1/10 the efficiency of wild-type viral DNA coding for all three T antigens. This replication defect was at least in part overcome by the simultaneous transfections of polyomavirus genomes which allowed the expression of small T antigen. We conclude that polyomavirus small T antigen has a (probably indirect) role in replication.
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Noda T, Satake M, Robins T, Ito Y. Isolation and characterization of NIH 3T3 cells expressing polyomavirus small T antigen. J Virol 1986; 60:105-13. [PMID: 3018277 PMCID: PMC253907 DOI: 10.1128/jvi.60.1.105-113.1986] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The polyomavirus small T-antigen gene, together with the polyomavirus promoter, was inserted into a retrovirus vector pGV16 which contains the Moloney sarcoma virus long terminal repeat and neomycin resistance gene driven by the simian virus 40 promoter. This expression vector, pGVST, was packaged into retrovirus particles by transfection of psi 2 cells which harbor packaging-defective murine retrovirus genome. NIH 3T3 cells were infected by this replication-defective retrovirus containing pGVST. Of the 15 G418-resistant cell clones, 8 express small T antigen at various levels as revealed by immunoprecipitation. A cellular protein with an apparent molecular weight of about 32,000 coprecipitates with small T antigen. Immunofluorescent staining shows that small T antigen is mainly present in the nuclei. Morphologically, cells expressing small T antigen are indistinguishable from parental NIH 3T3 cells and have a microfilament pattern similar to that in parental NIH 3T3 cells. Cells expressing small T antigen form a flat monolayer but continue to grow beyond the saturation density observed for parental NIH 3T3 cells and eventually come off the culture plate as a result of overconfluency. There is some correlation between the level of expression of small T antigen and the growth rate of the cells. Small T-antigen-expressing cells form small colonies in soft agar. However, the proportion of cells which form these small colonies is rather small. A clone of these cells tested did not form tumors in nude mice within 3 months after inoculation of 10(6) cells per animal. Thus, present studies establish that the small T antigen of polyomavirus is a second nucleus-localized transforming gene product of the virus (the first one being large T antigen) and by itself has a function which is to stimulate the growth of NIH 3T3 cells beyond their saturation density in monolayer culture.
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MESH Headings
- Animals
- Antigens, Polyomavirus Transforming
- Antigens, Viral, Tumor/analysis
- Antigens, Viral, Tumor/biosynthesis
- Antigens, Viral, Tumor/physiology
- Cell Line
- DNA, Recombinant
- DNA, Viral/genetics
- Fibroblasts/metabolism
- Fibroblasts/ultrastructure
- Genes, Synthetic
- Genetic Vectors
- Mice
- Oncogene Proteins, Viral/biosynthesis
- Oncogene Proteins, Viral/physiology
- Polyomavirus/immunology
- Polyomavirus/physiology
- Recombinant Proteins/biosynthesis
- Recombinant Proteins/physiology
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Murphy CI, Bikel I, Livingston DM. Cellular proteins which can specifically associate with simian virus 40 small t antigen. J Virol 1986; 59:692-702. [PMID: 3016331 PMCID: PMC253242 DOI: 10.1128/jvi.59.3.692-702.1986] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
When crude, radiolabeled extracts of various cells were applied to homogeneous simian virus 40 small t antigen-Sepharose adsorbents, three cell proteins (57, 32, and 20 kilodaltons [kDa]) bound specifically. Each also bound to an insoluble, truncated t derivative composed of the COOH-terminal 123 residues of the protein. The binding of these proteins was greatly inhibited after reduction and alkylation of the t ligand. Therefore, some element of native conformation, but not all of the primary structure of t, is necessary for this binding property, which may constitute a discrete, in vitro biochemical function of this protein. Results of cell fractionation experiments suggested that the 57- and 32-kDa proteins are nonnuclear cell constituents, whereas the 20-kDa protein was closely associated with a detergent-washed nuclear fraction. Specific immunoblotting and comparative partial proteolytic digestion analyses indicated that the 57-kDa protein is tubulin, a major component of the cytoskeleton. In this regard, t and tubulin were observed to coimmunoprecipitate from crude cell extracts after incubation with monospecific anti-t antibody. Therefore, it is possible that t and tubulin interact in vivo.
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Bikel I, Mamon H, Brown EL, Boltax J, Agha M, Livingston DM. The t-unique coding domain is important to the transformation maintenance function of the simian virus 40 small t antigen. Mol Cell Biol 1986; 6:1172-8. [PMID: 3023875 PMCID: PMC367629 DOI: 10.1128/mcb.6.4.1172-1178.1986] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The small t antigen (t) of simian virus 40, a 174-amino-acid-containing protein, when present together with the other early viral protein, large T antigen (T), plays an important role in the maintenance of simian virus 40-induced neoplastic phenotype in certain cells. Indeed, each protein functions in a complementary manner in this process. The t coding unit is composed of two segments, a 5' region of 246 nucleotides which is identical to that of the corresponding 5' region of the T coding unit and a 3' segment of 276 nucleotides which is unique. Two mutant, t-encoding genomes, one bearing a missense and the other a nonsense mutation at the same point in the t-unique coding region were constructed in vitro and found to be defective in their ability to dissolve the actin cytoskeleton of rat fibroblasts and to complement T in the growth of mouse fibroblasts in soft agar. Therefore, the unique segment of the t gene encodes a portion of the t molecule which is essential to its transformation maintenance function.
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