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Fan Y, Sanyal S, Bruzzone R. Breaking Bad: How Viruses Subvert the Cell Cycle. Front Cell Infect Microbiol 2018; 8:396. [PMID: 30510918 PMCID: PMC6252338 DOI: 10.3389/fcimb.2018.00396] [Citation(s) in RCA: 90] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2018] [Accepted: 10/22/2018] [Indexed: 01/10/2023] Open
Abstract
Interactions between the host and viruses during the course of their co-evolution have not only shaped cellular function and the immune system, but also the counter measures employed by viruses. Relatively small genomes and high replication rates allow viruses to accumulate mutations and continuously present the host with new challenges. It is therefore, no surprise that they either escape detection or modulate host physiology, often by redirecting normal cellular pathways to their own advantage. Viruses utilize a diverse array of strategies and molecular targets to subvert host cellular processes, while evading detection. These include cell-cycle regulation, major histocompatibility complex-restricted antigen presentation, intracellular protein transport, apoptosis, cytokine-mediated signaling, and humoral immune responses. Moreover, viruses routinely manipulate the host cell cycle to create a favorable environment for replication, largely by deregulating cell cycle checkpoints. This review focuses on our current understanding of the molecular aspects of cell cycle regulation that are often targeted by viruses. Further study of their interactions should provide fundamental insights into cell cycle regulation and improve our ability to exploit these viruses.
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Affiliation(s)
- Ying Fan
- HKU-Pasteur Research Pole, LKS Faculty of Medicine, School of Public Health, The University of Hong Kong, Hong Kong, Hong Kong.,MRC Protein Phosphorylation and Ubiquitylation Unit, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Sumana Sanyal
- HKU-Pasteur Research Pole, LKS Faculty of Medicine, School of Public Health, The University of Hong Kong, Hong Kong, Hong Kong.,LKS Faculty of Medicine, School of Biomedical Sciences, The University of Hong Kong, Hong Kong, Hong Kong
| | - Roberto Bruzzone
- HKU-Pasteur Research Pole, LKS Faculty of Medicine, School of Public Health, The University of Hong Kong, Hong Kong, Hong Kong.,Department of Cell Biology and Infection, Institut Pasteur, Paris, France
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Expression of the small T antigen of Lymphotropic Papovavirus is sufficient to transform primary mouse embryo fibroblasts. Virology 2015; 487:112-20. [PMID: 26517398 DOI: 10.1016/j.virol.2015.10.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Revised: 09/25/2015] [Accepted: 10/02/2015] [Indexed: 01/17/2023]
Abstract
Polyomaviruses induce cell proliferation and transformation through different oncoproteins encoded within the early region (ER): large T antigen (LT), small T antigen (sT) and, in some cases, additional components. Each virus utilizes different mechanisms to achieve transformation. For instance, the LTs of Simian virus 40 (SV40), BK and/or JC virus can induce transformation; but Merkel Cell Polyomavirus (MCPyV) requires expression of sT. Lymphotropic Papovavirus (LPV) is closely related to Human Polyomavirus 9 (HuPyV9) and, under similar conditions, mice expressing LPV.ER exhibit higher rates of tumor formation than mice expressing SV40.ER. We have investigated the contributions of individual LPV.ER components to cell transformation. In contrast to SV40, LPV.ER transforms mouse embryonic fibroblasts (MEFs), but expression of LPV LT is insufficient to transform MEFs. Furthermore, LPV sT induces immortalization and transformation of MEFs. Thus, in the case of LPV, sT is the main mediator of oncogenesis.
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Cellular transformation of mouse embryo fibroblasts in the absence of activator E2Fs. J Virol 2015; 89:5124-33. [PMID: 25717106 DOI: 10.1128/jvi.03578-14] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2014] [Accepted: 02/18/2015] [Indexed: 12/12/2022] Open
Abstract
UNLABELLED The E2F family of transcription factors, broadly divided into activator and repressor E2Fs, regulates cell cycle genes. Current models indicate that activator E2Fs are necessary for cell cycle progression and tumorigenesis and are also required to mediate transformation induced by DNA tumor viruses. E2Fs are negatively regulated by the retinoblastoma (RB) family of tumor suppressor proteins, and virus-encoded oncogenes disrupt the RB-E2F repressor complexes. This results in the release of activator E2Fs and induction of E2F-dependent genes. In agreement, expression of large tumor T antigens (TAg) encoded by polyomaviruses in mammalian cells results in increased transcriptional levels of E2F target genes. In addition, tumorigenesis induced by transgenic expression of simian virus 40 (SV40) TAg in choroid plexus or intestinal villi requires at least one activator E2F. In contrast, we show that SV40 TAg-induced transformation in mouse embryonic fibroblasts is independent of activator E2Fs. This work, coupled with recent studies showing that proliferation in stem and progenitor cells is independent of activator E2Fs, suggests the presence of parallel pathways governing cell proliferation and tumorigenesis. IMPORTANCE The RB-E2F pathway is altered in many cancers and is also targeted by DNA tumor viruses. Viral oncoprotein action on RBs results in the release of activator E2Fs and upregulation of E2F target genes; thus, activator E2Fs are considered essential for normal and tumorigenic cell proliferation. However, we have observed that SV40 large T antigen can induce cell proliferation and transformation in the absence of activator E2Fs. Our results also suggest that TAg action on pRBs regulates both E2F-dependent and -independent pathways that govern proliferation. Thus, specific cell proliferation pathways affected by RB alterations in cancer may be a factor in tumor behavior and response to therapy.
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Removal of a small C-terminal region of JCV and SV40 large T antigens has differential effects on transformation. Virology 2014; 468-470:47-56. [PMID: 25129438 DOI: 10.1016/j.virol.2014.07.038] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2014] [Revised: 06/23/2014] [Accepted: 07/21/2014] [Indexed: 01/12/2023]
Abstract
The large T antigen (LT) protein of JCV and SV40 polyomaviruses is required to induce tumors in rodents and transform cells in culture. When both LTs are compared side-by-side in cell culture assays, SV40 shows a more robust transformation phenotype even though the LT sequences are highly conserved. A complete understanding of SV40׳s enhanced transforming capabilities relative to JCV is lacking. When the least conserved region of the LT proteins, the variable linker and host range region (VHR), was removed, changes in T antigen expression and cellular p53 post-translational modifications occurred, but interaction with the pRB pathway was unaffected. Transformation assessed by growth in low serum was reduced after VHR truncation of the SV40, but not the JCV, T antigen. Conversely, anchorage independent transformation was enhanced only by truncation of the JCV VHR. This is the first report to link the SV40 or JCV VHR region to transformation potential.
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Holcakova J, Muller P, Tomasec P, Hrstka R, Nekulova M, Krystof V, Strnad M, Wilkinson GWG, Vojtesek B. Inhibition of post-transcriptional RNA processing by CDK inhibitors and its implication in anti-viral therapy. PLoS One 2014; 9:e89228. [PMID: 24586613 PMCID: PMC3931720 DOI: 10.1371/journal.pone.0089228] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2013] [Accepted: 01/17/2014] [Indexed: 01/31/2023] Open
Abstract
Cyclin-dependent kinases (CDKs) are key regulators of the cell cycle and RNA polymerase II mediated transcription. Several pharmacological CDK inhibitors are currently in clinical trials as potential cancer therapeutics and some of them also exhibit antiviral effects. Olomoucine II and roscovitine, purine-based inhibitors of CDKs, were described as effective antiviral agents that inhibit replication of a broad range of wild type human viruses. Olomoucine II and roscovitine show high selectivity for CDK7 and CDK9, with important functions in the regulation of RNA polymerase II transcription. RNA polymerase II is necessary for viral transcription and following replication in cells. We analyzed the effect of inhibition of CDKs by olomoucine II on gene expression from viral promoters and compared its effect to widely-used roscovitine. We found that both roscovitine and olomoucine II blocked the phosphorylation of RNA polymerase II C-terminal domain. However the repression of genes regulated by viral promoters was strongly dependent on gene localization. Both roscovitine and olomoucine II inhibited expression only when the viral promoter was not integrated into chromosomal DNA. In contrast, treatment of cells with genome-integrated viral promoters increased their expression even though there was decreased phosphorylation of the C-terminal domain of RNA polymerase II. To define the mechanism responsible for decreased gene expression after pharmacological CDK inhibitor treatment, the level of mRNA transcription from extrachromosomal DNA was determined. Interestingly, our results showed that inhibition of RNA polymerase II C-terminal domain phosphorylation increased the number of transcribed mRNAs. However, some of these mRNAs were truncated and lacked polyadenylation, which resulted in decreased translation. These results suggest that phosphorylation of RNA polymerase II C-terminal domain is critical for linking transcription and posttrancriptional processing of mRNA expressed from extrachromosomal DNA.
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Affiliation(s)
- Jitka Holcakova
- Regional Centre for Applied Molecular Oncology, Masaryk Memorial Cancer Institute, Brno, Czech Republic
| | - Petr Muller
- Regional Centre for Applied Molecular Oncology, Masaryk Memorial Cancer Institute, Brno, Czech Republic
| | - Peter Tomasec
- School of Medicine, Cardiff University, Cardiff, United Kingdom
| | - Roman Hrstka
- Regional Centre for Applied Molecular Oncology, Masaryk Memorial Cancer Institute, Brno, Czech Republic
| | - Marta Nekulova
- Regional Centre for Applied Molecular Oncology, Masaryk Memorial Cancer Institute, Brno, Czech Republic
| | - Vladimir Krystof
- Laboratory of Growth Regulators, Faculty of Science, Palacky University, Olomouc, Czech Republic
- Institute of Experimental Botany AS CR, Olomouc, Czech Republic
| | - Miroslav Strnad
- Laboratory of Growth Regulators, Faculty of Science, Palacky University, Olomouc, Czech Republic
- Institute of Experimental Botany AS CR, Olomouc, Czech Republic
| | | | - Borivoj Vojtesek
- Regional Centre for Applied Molecular Oncology, Masaryk Memorial Cancer Institute, Brno, Czech Republic
- * E-mail:
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Abstract
To replicate their genomes in cells and generate new progeny, viruses typically require factors provided by the cells that they have infected. Subversion of the cellular machinery that controls replication of the infected host cell is a common activity of many viruses. Viruses employ different strategies to deregulate cell cycle checkpoint controls and modulate cell proliferation pathways. A number of DNA and RNA viruses encode proteins that target critical cell cycle regulators to achieve cellular conditions that are beneficial for viral replication. Many DNA viruses induce quiescent cells to enter the cell cycle; this is thought to increase pools of deoxynucleotides and thus, facilitate viral replication. In contrast, some viruses can arrest cells in a particular phase of the cell cycle that is favorable for replication of the specific virus. Cell cycle arrest may inhibit early cell death of infected cells, allow the cells to evade immune defenses, or help promote virus assembly. Although beneficial for the viral life cycle, virus-mediated alterations in normal cell cycle control mechanisms could have detrimental effects on cellular physiology and may ultimately contribute to pathologies associated with the viral infection, including cell transformation and cancer progression and maintenance. In this chapter, we summarize various strategies employed by DNA and RNA viruses to modulate the replication cycle of the virus-infected cell. When known, we describe how these virus-associated effects influence replication of the virus and contribute to diseases associated with infection by that specific virus.
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Affiliation(s)
- Eishi Noguchi
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania USA
| | - Mariana C. Gadaleta
- Dept of Biochemistry & Molecular Biology, Drexel University College of Medicine, Philadelphia, USA
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Bellacchio E, Paggi MG. Understanding the targeting of the RB family proteins by viral oncoproteins to defeat their oncogenic machinery. J Cell Physiol 2013; 228:285-91. [PMID: 22718244 DOI: 10.1002/jcp.24137] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The retinoblastoma (RB) family consists of three genes, RB1, RBL1, and RBL2, that code for the pRb, p107, and pRb2/p130 proteins, respectively. All these factors have pivotal roles in controlling fundamental cellular mechanisms such as cell cycle, differentiation and apoptosis. The founder and the most investigated RB family protein is pRb, which is considered to be the paradigm of tumor suppressors. However, p107 and pRb2/p130 clearly display a high degree of structural and functional homology with pRb. Interestingly, these factors were first identified as physical targets of the Adenovirus E1A oncoprotein. Indeed, RB family proteins are the most important and widely investigated targets of small DNA virus oncoproteins, such as Adenovirus E1A, human papillomavirus E7 and Simian virus 40 large T antigen. By interacting with pRb and with other RB family members, these oncoproteins neutralize their growth suppressive properties, thus stimulating proliferation of the infected cells, de-differentiation, and resistance to apoptosis. All these acquired features strongly favor the rise and selection of immortalized and mutation-prone cells, leading to a higher propensity in undergoing transformation. Our present work aims to illustrate and delve into these protein-protein interactions. Considering that these viral oncoproteins are dispensable for normal cellular functions, they can create "oncogene addiction" in the infected/transformed cells. This makes the possibility to dismantle these interactions extremely attractive, thus promoting the development of highly specific smart molecules capable of targeting only the infected/transformed cells that express these viral factors.
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Hauser S, Ulrich T, Wurster S, Schmitt K, Reichert N, Gaubatz S. Loss of LIN9, a member of the DREAM complex, cooperates with SV40 large T antigen to induce genomic instability and anchorage-independent growth. Oncogene 2011; 31:1859-68. [PMID: 21860417 DOI: 10.1038/onc.2011.364] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The DREAM complex is an important regulator of mitotic gene expression during the cell cycle. Here we report that inactivation of LIN9, a subunit of DREAM, results in premature senescence, which can be overcome by the SV40 large T (LT) antigen. Together with the observation that p16(INK4a) and p21(Waf1) are upregulated upon loss of LIN9, these results indicate that senescence is triggered by the pRB and p53 tumor suppressor pathways. We also find that LIN9-null cells that escape senescence are chromosomally instable because of compromised mitotic fidelity. SV40 LT-expressing cells that adapt to the loss of LIN9 can grow anchorage-independently in soft agar, a hallmark of oncogenic transformation. Taken together, these results suggest an important role of mitotic gene regulation in the maintenance of genomic stability and tumor suppression.
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Affiliation(s)
- S Hauser
- Department of Physiological Chemistry I, Biocenter, University of Wuerzburg, Germany
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Abstract
Over 50 years of polyomavirus research has produced a wealth of insights into not only general biologic processes in mammalian cells, but also, how conditions can be altered and signaling systems tweaked to produce transformation phenotypes. In the past few years three new members (KIV, WUV, and MCV) have joined two previously known (JCV and BKV) human polyomaviruses. In this review, we present updated information on general virologic features of these polyomaviruses in their natural host, concentrating on the association of MCV with human Merkel cell carcinoma. We further present a discussion on advances made in SV40 as the prototypic model, which has and will continue to inform our understanding about viruses and cancer.
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Affiliation(s)
- Ole Gjoerup
- Cancer Virology Program, Hillman Cancer Research Pavilion, University of Pittsburgh Cancer Institute, Pittsburgh, PA, USA
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Nobre A, Kalve I, Cesnulevicius K, Ragancokova D, Rangancokova D, Ratzka A, Halfer N, Wesemann M, Krampfl K, Claus P, Grothe C. Characterization and differentiation potential of rat ventral mesencephalic neuronal progenitor cells immortalized with SV40 large T antigen. Cell Tissue Res 2010; 340:29-43. [PMID: 20177706 DOI: 10.1007/s00441-010-0933-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2009] [Accepted: 01/19/2010] [Indexed: 01/01/2023]
Abstract
Neuronal progenitor cells (NPCs) possess high potential for use in regenerative medicine. To overcome their limited mitotic competence, various immortalization strategies have been applied that allow their prolonged maintenance and expansion in vitro. Such immortalized cells can be used for the design and discovery of new cell-based therapies for neurodegenerative diseases, such as Parkinson's disease. We immortalized rat ventral mesencephalic NPCs by using SV40 large T antigen (SV40Tag). All cell clones displayed a two- to three-fold higher proliferation rate compared with the primary cells. In order to induce dopaminergic differentiation of generated cell clones, both glial-derived neurotrophic factor and di-butyryl cyclic adenosine monophosphate were applied. Treated cells were then characterized regarding the expression of dopaminergic lineage markers, differentiation of various cell populations, calcium imaging in the presence of kainate, and immunohistochemistry after intrastriatal transplantation. Treated cells displayed morphological maturation, and calcium imaging revealed neuronal properties in the presence of kainate. These cells also expressed low mRNA levels of the dopamine transporter and tyrosine hydroxylase (TH), although no TH-immunopositive neurons were found. Intrastriatal transplantation into the neurotoxin-lesioned rats did not induce further differentiation. As an alternative approach, we silenced SV40Tag with short interfering RNA, but this was not sufficient to trigger differentiation into dopaminergic neurons. Nevertheless, neuronal and glial cells were detected as shown by beta-tubulin type III and glial fibrillary acidic protein staining, respectively. SV40Tag cells are suitable for carrying out controlled genetic modifications as shown by overexpression of enhanced green fluorescence protein after efficient non-viral transfection.
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Affiliation(s)
- André Nobre
- Institute of Neuroanatomy, Hannover Medical School, 30625, Hannover, Germany
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Gualco E, Urbanska K, Perez-Liz G, Sweet T, Peruzzi F, Reiss K, Del Valle L. IGF-IR-dependent expression of Survivin is required for T-antigen-mediated protection from apoptosis and proliferation of neural progenitors. Cell Death Differ 2009; 17:439-51. [PMID: 19834489 PMCID: PMC2822053 DOI: 10.1038/cdd.2009.146] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The Insulin-like Growth Factor-1 Receptor (IGF-IR) and the human polyomavirus JCV protein, T-Antigen cooperate in the transformation of neuronal precursors in the cerebellum, which may be a contributing factor in the development of brain tumors. Since it is not clear why T-Antigen requires IGF-IR for transformation, we investigated this process in neural progenitors from IGF-IR knockout embryos (ko-IGF-IR) and from their wild type non-transgenic littermates (wt-IGF-IR). In contrast to wt-IGF-IR, the brain and dorsal root ganglia of ko-IGF-IR embryos showed low levels of the anti-apoptotic protein Survivin, accompanied by elevated numbers of apoptotic neurons and an earlier differentiation phenotype. In wt-IGF-IR neural progenitors in vitro, induction of T-Antigen expression tripled the expression of Survivin, and accelerated cell proliferation. In ko-IGF-IR progenitors induction of T-Antigen failed to increase Survivin, resulting in massive apoptosis. Importantly, ectopic expression of Survivin protected ko-IGF-IR progenitor cells from apoptosis and siRNA inhibition of Survivin activated apoptosis in wt-IGF-IR progenitors expressing T-Antigen. Our results indicate that reactivation of the anti-apoptotic Survivin may be a critical step in JCV T-Antigen induced transformation, which in neural progenitors requires IGF-IR.
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Affiliation(s)
- E Gualco
- Department of Neuroscience, Center for Neurovirology, Temple University School of Medicine, Philadelphia, PA, USA
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How the Rb tumor suppressor structure and function was revealed by the study of Adenovirus and SV40. Virology 2009; 384:274-84. [PMID: 19150725 DOI: 10.1016/j.virol.2008.12.010] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2008] [Accepted: 12/08/2008] [Indexed: 12/14/2022]
Abstract
The review recounts the history of how the study of the DNA tumor viruses including polyoma, SV40 and Adenovirus brought key insights into the structure and function of the Retinoblastoma protein (Rb). Knudsen's model of the two-hit hypothesis to explain patterns of hereditary and sporadic retinoblastoma provided the foundation for the tumor suppressor hypothesis that ultimately led to the cloning of the Rb gene. The discovery that SV40 and Adenovirus could cause tumors when inoculated into animals was startling not only because SV40 had contaminated the poliovirus vaccine and Adenovirus was a common cause of viral induced pneumonia but also because they provided an opportunity to study the genetics and biochemistry of cancer. Studies of mutant forms of these viruses led to the identification of the E1A and Large T antigen (LT) oncogenes and their small transforming elements including the Adenovirus Conserved Regions (CR), the SV40 J domain and the LxCxE motif. The immunoprecipitation studies that initially revealed the size and ultimately the identity of cellular proteins that could bind to these transforming elements were enabled by the widespread development of highly specific monoclonal antibodies against E1A and LT. The identification of Rb as an E1A and LT interacting protein quickly led to the cloning of p107, p130, p300, CBP, p400 and TRRAP and the concept that viral transformation was due, at least in part, to the perturbation of the function of normal cellular proteins. In addition, studies on the ability of E1A to transactivate the Adenovirus E2 promoter led to the cloning of the heterodimeric E2F and DP transcription factor and recognition that Rb repressed transcription of cellular genes required for cell cycle entry and progression. More recent studies have revealed how E1A and LT combine the activity of Rb and the other cellular associated proteins to perturb expression of many genes during viral infection and tumor formation.
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Hume AJ, Kalejta RF. Regulation of the retinoblastoma proteins by the human herpesviruses. Cell Div 2009; 4:1. [PMID: 19146698 PMCID: PMC2636798 DOI: 10.1186/1747-1028-4-1] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2009] [Accepted: 01/15/2009] [Indexed: 01/21/2023] Open
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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Vos MJ, Hageman J, Carra S, Kampinga HH. Structural and functional diversities between members of the human HSPB, HSPH, HSPA, and DNAJ chaperone families. Biochemistry 2008; 47:7001-11. [PMID: 18557634 DOI: 10.1021/bi800639z] [Citation(s) in RCA: 264] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Heat shock proteins (HSPs) were originally identified as stress-responsive proteins required to deal with proteotoxic stresses. Besides being stress-protective and possible targets for delaying progression of protein folding diseases, mutations in chaperones also have been shown to cause disease (chaperonopathies). The mechanism of action of the "classical", stress-inducible HSPs in serving as molecular chaperones preventing the irreversible aggregation of stress-unfolded or disease-related misfolded proteins is beginning to emerge. However, the human genome encodes several members for each of the various HSP families that are not stress-related but contain conserved domains. Here, we have reviewed the existing literature on the various members of the human HSPB (HSP27), HSPH (HSP110), HSPA (HSP70), and DNAJ (HSP40) families. Apart from structural and functional homologies, several diversities between members and families can be found that not only point to differences in client specificity but also seem to serve differential client handling and processing. How substrate specificity and client processing is determined is far from being understood.
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Affiliation(s)
- Michel J Vos
- Department of Cell Biology, Section of Radiation and Stress Cell Biology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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15
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Francis MA, Rainbow AJ. Role for Retinoblastoma Protein Family Members in UV-enhanced Expression from the Human Cytomegalovirus Immediate Early Promoter¶. Photochem Photobiol 2007. [DOI: 10.1562/0031-8655(2003)0770621rfrpfm2.0.co2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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16
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Guo HX, Cun W, Liu LD, Dong SZ, Wang LC, Dong CH, Li QH. Protein encoded by HSV-1 stimulation-related gene 1 (HSRG1) interacts with and inhibits SV40 large T antigen. Cell Prolif 2007; 39:507-18. [PMID: 17109635 PMCID: PMC6496204 DOI: 10.1111/j.1365-2184.2006.00408.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Herpes simplex virus (HSV)-1 stimulation-related gene 1 (HSRG1) protein expression is induced in HSV-1 infected cells. We found that HSRG1 interacts with SV40 large T antigen (LT) in yeast two-hybrid assay and bimolecular fluorescence complementation (BiFC) assay. This interaction alters LT's regulation of the SV40 promoter and its ability to influence the cell cycle. Choramphenicol acetyl-transferase (CAT) assays revealed that initiation of gene transcription by LT is changed by HSRG1 expression. HSRG1 inhibits the ability of LT to activate SV40 late gene transcription. Further data indicate that the ability of LT protein to stimulate S-phase entry is also inhibited by the expression of HSRG1. The results of a colony-forming assay suggested that expression of HSRG1 in cells transfected by LT gene decreased the rate of colony formation. Yeast two-hybrid beta-galactosidase assay revealed that amino acid residues 132-450 in LT bind HSRG1.
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Affiliation(s)
- H. X. Guo
- Institute of Medical Biology, Chinese Academy of Medical Sciences, Kunming, 650118, China
| | - W. Cun
- Institute of Medical Biology, Chinese Academy of Medical Sciences, Kunming, 650118, China
| | - L. D. Liu
- Institute of Medical Biology, Chinese Academy of Medical Sciences, Kunming, 650118, China
| | - S. Z. Dong
- Institute of Medical Biology, Chinese Academy of Medical Sciences, Kunming, 650118, China
| | - L. C. Wang
- Institute of Medical Biology, Chinese Academy of Medical Sciences, Kunming, 650118, China
| | - C. H. Dong
- Institute of Medical Biology, Chinese Academy of Medical Sciences, Kunming, 650118, China
| | - Q. H. Li
- Institute of Medical Biology, Chinese Academy of Medical Sciences, Kunming, 650118, China
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Bollag B, Kilpatrick LH, Tyagarajan SK, Tevethia MJ, Frisque RJ. JC virus T'135, T'136 and T'165 proteins interact with cellular p107 and p130 in vivo and influence viral transformation potential. J Neurovirol 2006; 12:428-42. [PMID: 17162659 DOI: 10.1080/13550280601009553] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The JC virus (JCV) regulatory proteins, large T antigen, small t antigen, T'135, T'136, and T'165, are encoded by five transcripts alternatively spliced from the viral early precursor mRNA. T antigen and the T' proteins share N-terminal amino acid sequences that include the L x CxE and J domains, motifs in SV40 T antigen known to mediate binding to the retinoblastoma (Rb) proteins and Hsc70, respectively. In this study, G418-resistant cell lines were created that express wild-type or mutant JCV T antigen and T' proteins individually or in combination. These cell lines were used to evaluate the ability of each viral protein to bind p107 and p130 in vivo, and to influence cellular growth characteristics. Differences were observed in the abilities of individual T' proteins to bind p107 and p130 and to alter their phosphorylation status. The T' proteins were also found to localize to the cell's nucleus and to be phosphorylated in a cell cycle-dependent manner. JCV T antigen and T' proteins expressed from a cytomegalovirus promoter failed to induce dense focus formation in Rat2 cells, but they did cooperate with a mutant Ras protein to overcome cellular senescence and immortalize rat embryo fibroblasts. These data indicate that, despite their sequence similarities, JCV early proteins exhibit unique activities that, in combination, effect the inactivation of cell cycle regulators, a requirement for polyomavirus-induced transformation.
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Affiliation(s)
- Brigitte Bollag
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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18
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Kasper JS, Arai T, DeCaprio JA. A novel p53-binding domain in CUL7. Biochem Biophys Res Commun 2006; 348:132-8. [PMID: 16875676 DOI: 10.1016/j.bbrc.2006.07.013] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2006] [Accepted: 07/01/2006] [Indexed: 11/21/2022]
Abstract
CUL7 is a member of the cullin RING ligase family and forms an SCF-like complex with SKP1 and FBXW8. CUL7 is required for normal mouse embryonic development and cellular proliferation, and is highly homologous to PARC, a p53-associated, parkin-like cytoplasmic protein. We determined that CUL7, in a manner similar to PARC, can bind directly to p53 but does not affect p53 expression. We identified a discrete, co-linear domain in CUL7 that is conserved in PARC and HERC2, and is necessary and sufficient for p53-binding. The presence of p53 stabilized expression of this domain and we demonstrate that this p53-binding domain of CUL7 contributes to the cytoplasmic localization of CUL7. The results support the model that p53 plays a role in regulation of CUL7 activity.
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Affiliation(s)
- Jocelyn S Kasper
- Department of Medical Oncology, Dana-Farber Cancer Institute, 44 Binney Street, Boston, MA 02115, USA
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19
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White MK, Khalili K. Interaction of retinoblastoma protein family members with large T-antigen of primate polyomaviruses. Oncogene 2006; 25:5286-93. [PMID: 16936749 DOI: 10.1038/sj.onc.1209618] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The retinoblastoma gene product pRb and other members of the Rb family of pocket proteins have a central role in the regulation of cell cycle progression. Soon after its discovery, pRb was found to interact with the transforming oncoproteins of DNA tumor viruses and this led to rapid advances in our understanding of the mechanisms of viral transformation and cell cycle progression. DNA viruses of the polyomavirus family have small, circular, double-stranded DNA genomes contained within non-enveloped icosahedral capsids and are highly tumorigenic in experimental animals. At least three types of polyomavirus infect humans: JC virus (JCV), BK virus (BKV) and Simian Vacuolating virus-40. The early region of these viruses encodes the transforming proteins large T-antigen and small t-antigen, which are involved in viral replication and also promote transformation of cells in culture and oncogenesis in vivo. Binding of T-antigen to pRb promotes the activation of the E2F family of transcription factors, which induce the expression of cellular genes required for S phase. In the context of lytic infection, this cell cycle progression is necessary for viral replication because polyomaviruses rely on S phase-specific host factors for their DNA synthesis. In the context of cellular transformation and tumorigenesis, T-antigen/pRB interaction is an indispensable event.
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Affiliation(s)
- M K White
- Center for Neurovirology, Department of Neuroscience, Temple University School of Medicine, Philadelphia, PA 19122, USA
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20
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Felsani A, Mileo AM, Paggi MG. Retinoblastoma family proteins as key targets of the small DNA virus oncoproteins. Oncogene 2006; 25:5277-85. [PMID: 16936748 DOI: 10.1038/sj.onc.1209621] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
RB, the most investigated tumor suppressor gene, is the founder of the RB family of growth/tumor suppressors, which comprises also p107 (RBL1) and Rb2/p130 (RBL2). The protein products of these genes, pRb, p107 and pRb2/p130, respectively, are also known as 'pocket proteins', because they share a 'pocket' domain responsible for most of the functional interactions characterizing the activity of this family of cellular factors. The interest in these genes and proteins springs essentially from their ability to regulate negatively cell cycle processes and for their ability to slow down or abrogate neoplastic growth. The pocket domain of the RB family proteins is dramatically hampered in its functions by the interference of a number of proteins produced by the small DNA viruses. In the last two decades, the 'viral hypothesis' of cancer has received a considerable renewed impulse from the notion that small DNA viruses, such as Adenovirus, Human papillomavirus (HPV) and Polyomavirus, produce factors that can physically interact with major cellular regulators and alter their function. These viral proteins (oncoproteins) act as multifaceted molecular devices that have evolved to perform very specific tasks. Owing to these features, viral oncoproteins have been widely employed as invaluable experimental tools for the identification of several key families of regulators, particularly of the cell cycle homeostasis. Adenovirus early-region 1A (E1A) is the most widely investigated small DNA tumor virus oncoprotein, but relevant interest in human oncology is raised by the E1A-related E7 protein from transforming HPV strains and by Polyomavirus oncoproteins, particularly large and small T antigens from Simian virus 40, JC virus and BK virus.
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Affiliation(s)
- A Felsani
- Istituto di Neurobiologia e Medicina Molecolare, CNR, Rome, Italy
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21
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Borger DR, DeCaprio JA. Targeting of p300/CREB binding protein coactivators by simian virus 40 is mediated through p53. J Virol 2006; 80:4292-303. [PMID: 16611888 PMCID: PMC1472010 DOI: 10.1128/jvi.80.9.4292-4303.2006] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The primary transforming functions of simian virus 40 large T antigen (SV40 LT) are conferred primarily through the binding and inactivation of p53 and the retinoblastoma family members. Normal p53 function requires an association with the CREB binding protein (CBP)/p300 coactivators, and a ternary complex containing SV40 LT, p53, and CBP/p300 has been identified previously. In this report, we have evaluated a secondary function of p53 bound to the SV40 LT complex in mediating the binding of human CBP/p300. We demonstrate that p53 associated with SV40 LT was posttranslationally modified in a manner consistent with the binding of CBP/p300. Furthermore, expression of SV40 LT induced the proportion of p53 phosphorylated on S15. An essential function for p53 in bridging the interaction between SV40 LT and CBP/p300 was identified through the reconstitution of the SV40 LT-CBP/p300 complex upon p53 reexpression in p53-null cells. In addition, the SV40 LT-CBP/p300 complex was disrupted through RNA interference-mediated depletion of endogenous p53. We also demonstrate that SV40 LT was acetylated in a p300- and p53-dependent manner, at least in part through the CH3 domain of p300. Therefore, the binding of p53 serves to modify SV40 LT by targeting CBP and p300 binding to direct the acetylation of SV40 LT.
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Affiliation(s)
- Darrell R Borger
- Dana-Farber Cancer Institute, Department of Medical Oncology, Harvard Medical School, Mayer Building 457, 44 Binney Street, Boston, Massachusetts 02115, USA
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22
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Kasper JS, Kuwabara H, Arai T, Ali SH, DeCaprio JA. Simian virus 40 large T antigen's association with the CUL7 SCF complex contributes to cellular transformation. J Virol 2005; 79:11685-92. [PMID: 16140746 PMCID: PMC1212609 DOI: 10.1128/jvi.79.18.11685-11692.2005] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Simian virus 40 large T antigen (T Ag) is capable of immortalizing and transforming rodent cells. The transforming activity of T Ag is due in large part to perturbation of the tumor suppressor proteins p53 and the retinoblastoma (pRB) family members. Inactivation of these tumor suppressors may not be sufficient for T Ag-mediated cellular transformation. It has been shown that T Ag associates with an SCF-like complex that contains a member of the cullin family of E3 ubiquitin ligases, CUL7, as well as SKP1, RBX1, and an F-box protein, FBXW8. We identified T Ag residues 69 to 83 as required for T Ag binding to the CUL7 complex. We demonstrate that delta69-83 T Ag, while it lost its ability to associate with CUL7, retained binding to p53 and pRB family members. In the presence of CUL7, wild-type (WT) T Ag but not delta69-83 T Ag was able to induce proliferation of mouse embryo fibroblasts, an indication of cellular transformation. In contrast, WT and delta69-83 T Ag enabled mouse embryo fibroblasts to proliferate to similarly high densities in the absence of CUL7. Our data suggest that, in addition to p53 and the pRB family members, T Ag serves to bind to and inactivate the growth-suppressing properties of CUL7. In addition, these results imply that, at least in the presence of T Ag, CUL7 may function as a tumor suppressor.
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Affiliation(s)
- Jocelyn S Kasper
- Dana-Farber Cancer Institute, Department of Medical Oncology and Harvard Medical School, Mayer Building 457, 44 Binney Street, Boston, MA 02115, USA
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23
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Skoczylas C, Henglein B, Rundell K. PP2A-dependent transactivation of the cyclin A promoter by SV40 ST is mediated by a cell cycle-regulated E2F site. Virology 2005; 332:596-601. [PMID: 15680424 DOI: 10.1016/j.virol.2004.12.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2004] [Revised: 09/10/2004] [Accepted: 12/16/2004] [Indexed: 11/17/2022]
Abstract
The Simian Virus 40 (SV40) small-t antigen (ST) plays an important role in driving cell proliferation, enhancing transformation by the large-T (LT) antigen. Potential targets of ST are the cyclin kinase inhibitor p27 and the cyclin A gene itself. Transactivation of the cyclin A promoter by ST depends on the interaction of ST with protein phosphatase 2A (PP2A) and occurs through a cell cycle-regulated E2F site near the transcription start site of the promoter. A third SV40 early protein, 17KT, also transactivates the cyclin A promoter but, in this case, transactivation depends on the dnaJ domain of the protein.
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Affiliation(s)
- Christine Skoczylas
- Department of Microbiology-Immunology, Northwestern University, 303 E. Chicago Avenue, Chicago, IL 60611, USA
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24
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Freed WJ, Zhang P, Sanchez JF, Dillon-Carter O, Coggiano M, Errico SL, Lewis BD, Truckenmiller ME. Truncated N-terminal mutants of SV40 large T antigen as minimal immortalizing agents for CNS cells. Exp Neurol 2005; 191 Suppl 1:S45-59. [PMID: 15629761 PMCID: PMC1925051 DOI: 10.1016/j.expneurol.2004.08.019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2004] [Indexed: 11/28/2022]
Abstract
Immortalized central nervous system (CNS) cell lines are useful as in vitro models for innumerable purposes such as elucidating biochemical pathways, studies of effects of drugs, and ultimately, such cells may also be useful for neural transplantation. The SV40 large T (LT) oncoprotein, commonly used for immortalization, interacts with several cell cycle regulatory factors, including binding and inactivating p53 and retinoblastoma family cell-cycle regulators. In an attempt to define the minimal requirements of SV40 T antigen for immortalizing cells of CNS origin, we constructed T155c, encoding the N-terminal 155 amino acids of LT. The p53 binding region is known to reside in the C-terminal region of LT. An additional series of mutants was produced to further narrow the molecular targets for immortalization, and plasmid vectors were constructed for each. In a p53 temperature sensitive cell line model, T64-7B, expression of T155c and all constructs having mutations outside of the first 82 amino acids were capable of overriding cell-cycle block at the non-permissive growth temperature. Several cell lines were produced from fetal rat mesencephalic and cerebral cortical cultures using the T155c construct. The E107K construct contained a mutation in the Rb binding region, but was nonetheless capable of overcoming cell cycle block in T64-7B cell and immortalizing primary cultured cells. Cells immortalized with T155c were often highly dependent on the presence of bFGF for growth. Telomerase activity, telomere length, growth rates, and integrity of the p53 gene in cells immortalized with T155c did not change over 100 population doublings in culture, indicating that cells immortalized with T155c were generally stable during long periods of continuous culture.
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Affiliation(s)
- William J Freed
- Cellular Neurobiology Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, MD 21224, USA.
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25
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Cinti C, Giordano A. The retinoblastoma gene family: its role in cancer onset and progression. ACTA ACUST UNITED AC 2005. [DOI: 10.1517/14728222.4.6.765] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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26
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Zhang YH, Kooistra K, Pietersen A, Rohn JL, Noteborn MHM. Activation of the tumor-specific death effector apoptin and its kinase by an N-terminal determinant of simian virus 40 large T antigen. J Virol 2004; 78:9965-76. [PMID: 15331730 PMCID: PMC515021 DOI: 10.1128/jvi.78.18.9965-9976.2004] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Apoptin, a viral death protein derived from chicken anemia virus, displays a number of tumor-specific behaviors. In particular, apoptin is phosphorylated, translocates to the nucleus, and induces apoptosis specifically in tumor or transformed cells, whereas it is nonphosphorylated and remains primarily inactive in the cytoplasm of nontransformed normal cells. Here, we show that in normal cells apoptin can also be activated by the transient transforming signals conferred by ectopically expressed simian virus 40 (SV40) large T antigen (LT), which rapidly induces apoptin's phosphorylation, nuclear accumulation, and the ability to induce apoptosis. Further analyses with mutants of LT showed that the minimum domain capable of inducing all three of apoptin's tumor-specific properties resided in the N-terminal J domain, a sequence which is largely shared by SV40 small t antigen (st). Interestingly, the J domain in st, which lacks its own nuclear localization signal (NLS), required nuclear localization to activate apoptin. These results reveal the existence of a cellular pathway shared by conditions of transient transformation and the stable cancerous or precancerous state, and they support a model whereby a transient transforming signal confers on apoptin both the upstream activity of phosphorylation and the downstream activity of nuclear accumulation and apoptosis induction. Such a pathway may reflect a general lesion contributing to human cancers.
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27
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Sullivan CS, Baker AE, Pipas JM. Simian virus 40 infection disrupts p130–E2F and p107–E2F complexes but does not perturb pRb–E2F complexes. Virology 2004; 320:218-28. [PMID: 15016545 DOI: 10.1016/j.virol.2003.10.035] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2003] [Revised: 10/23/2003] [Accepted: 10/27/2003] [Indexed: 11/30/2022]
Abstract
In its native host species, the Rhesus Macaque, simian virus 40 (SV40) forms a persistent infection in the kidneys with no apparent harmful side effects. We show that SV40 infection of growth-arrested monkey kidney epithelial cells results in the specific disruption of certain Rb-E2F family complexes. Throughout the course of infection, p130-E2F and p107-E2F complexes are disrupted, but surprisingly pRb-E2F complexes remain intact. This suggests that the presence of some pRb-E2F complexes is not inhibitory to productive infection. Additionally, while a decrease of p130 steady state levels is observed during the later time points of infection, early during infection, p130 is readily detectable. This suggests SV40 infection overrides p130-mediated growth arrest through a mechanism(s) in addition to the well-documented T antigen-mediated degradation of p130. Finally, infection induces a dramatic relocalization of E2F4 from the nucleus to the cytoplasm. The implications of these observations to the life cycle of the virus are addressed.
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Affiliation(s)
- C S Sullivan
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA
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28
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Ali SH, Kasper JS, Arai T, DeCaprio JA. Cul7/p185/p193 binding to simian virus 40 large T antigen has a role in cellular transformation. J Virol 2004; 78:2749-57. [PMID: 14990695 PMCID: PMC353757 DOI: 10.1128/jvi.78.6.2749-2757.2004] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2003] [Accepted: 11/10/2003] [Indexed: 01/19/2023] Open
Abstract
Simian virus 40 large T antigen (TAg) is a viral oncoprotein that can promote cellular transformation. TAg's transforming activity results in part by binding and inactivating key tumor suppressors, including p53 and the retinoblastoma protein (pRb). We have identified a TAg-associated 185-kDa protein that has significant homology to the cullin family of E3 ubiquitin ligases. TAg binds to an SCF-like complex that contains p185/Cul7, Rbx1, and the F box protein Fbw6. This SCF-like complex binds to an N-terminal region of TAg. Several p185/Cul7-binding-deficient mutants of TAg were generated that retained binding to pRb and p53 and were capable of overcoming Rb-mediated repression of E2F transcription. Despite binding to pRb and p53, these p185/Cul7-binding-defective mutants of TAg were unable to transform primary mouse embryo fibroblasts. Cells expressing p185/Cul7-binding-defective mutants of TAg were unable to grow to high density or grow in an anchorage-independent manner as determined by growth in soft agar. Considering the significance of other TAg-interacting proteins in regulation of the cell cycle, p185/Cul7 may also regulate an important growth control pathway.
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Affiliation(s)
- Syed Hamid Ali
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, USA
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29
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Abstract
SV40 large T antigen (Ag) binds to all members of the retinoblastoma (RB) tumor suppressor family including pRb, p107, and p130. Although the LXCXE motif of T Ag binds directly to the RB proteins, it is not sufficient to fully inactivate their function. The N-terminal DNA J domain of T Ag cooperates with the LXCXE motif to override RB-mediated repression of E2F-dependent transcription. In addition, T Ag can reduce the overall phosphorylation state of p107 and p130 that is dependent on an intact J domain and LXCXE motif. However, the mechanism of this activity has not been described. Here we describe the use of a cell-free system to characterize the effect of T Ag on p130 phosphorylation. When incubated in extracts prepared from S phase cells, p130 undergoes specific phosphorylation. Addition of T Ag to S phase extracts leads to a reduction of p130 phosphorylation in vitro. The ability of T Ag to reduce the phosphorylation of p130 in vitro is dependent on an intact DNA J domain and can be inhibited by okadaic acid and PP2A-specific inhibitors. These results suggest that T Ag recruits a phosphatase activity in a DNA J domain-dependent manner to reduce the phosphorylation of p130.
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Affiliation(s)
- Jennifer Y Lin
- Department of Medical Oncology, Dana-Farber Cancer Institute, 44 Binney Street, Boston, MA 02115, USA
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30
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Francis MA, Rainbow AJ. Role for retinoblastoma protein family members in UV-enhanced expression from the human cytomegalovirus immediate early promoters. Photochem Photobiol 2003; 77:621-7. [PMID: 12870848 DOI: 10.1562/0031-8655(2003)077<0621:rfrpfm>2.0.co;2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The expression from a reporter construct driven by a cytomegalovirus (CMV) immediate early (IE) promoter is strongly inducible by UV in human fibroblasts. This response is induced at lower UV fluences in transcription-coupled repair (TCR)-deficient fibroblasts compared with normal fibroblasts and is absent in their simian virus 40-transformed counterparts. In this study we demonstrate that expression of human papilloma virus (HPV) E7 (but not of HPV E6) can attenuate UV-induced expression from the human CMV-IE-driven reporter construct in human fibroblasts. Furthermore, UV-induced expression from the reporter construct appears impaired in murine fibroblasts harboring inactivating mutations in the retinoblastoma (Rb) gene family members p107 and pRb but not in fibroblasts harboring such mutations in the p53 gene. Taken together, these data suggest that one or more members of the pRb family (but not p53) play an essential role in mediating UV-induced expression from the CMV-IE promoter. In this study we report normal UV-upregulation of reporter expression in xeroderma pigmentosum (XP) group E fibroblasts, consistent with normal TCR. Because XP-E cells deficient in the p48 subunit of the damaged DNA-binding protein are impaired in E2F-1-activated transcription, these results also suggest that the (pRb-regulated) transcription factor E2F-1 does not play an essential role in UV-enhanced expression from the CMV-IE promoter.
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Affiliation(s)
- Murray A Francis
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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31
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Mitchell PJ, Perez-Nadales E, Malcolm DS, Lloyd AC. Dissecting the contribution of p16(INK4A) and the Rb family to the Ras transformed phenotype. Mol Cell Biol 2003; 23:2530-42. [PMID: 12640134 PMCID: PMC150721 DOI: 10.1128/mcb.23.7.2530-2542.2003] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2002] [Revised: 09/11/2002] [Accepted: 12/19/2002] [Indexed: 12/26/2022] Open
Abstract
Although oncogenic Ras commonly contributes to the development of cancer, in normal primary cells it induces cell cycle arrest rather than transformation. Here we analyze the additional genetic changes required for Ras to promote cell cycle progression rather than arrest. We show that loss of p53 is sufficient for oncogenic Ras to stimulate proliferation in the absence of extrinsic mitogens in attached cells. However, surprisingly, we find that p53 loss is not sufficient for Ras to overcome anchorage dependence or contact inhibition. In contrast, expression of simian virus 40 (SV40) large T antigen (LT) allows Ras to overcome these additional cell cycle controls. Mutational analysis of SV40 LT shows that this action of SV40 LT depends on its ability to inactivate the retinoblastoma (Rb) family of proteins, in concert with the loss of p53. Importantly, we show that inactivation of the Rb family of proteins can be mimicked by loss of the cyclin-dependent kinase inhibitor p16(INK4A). p16(INK4A) is commonly lost in human tumors, but its contribution to the transformed phenotype is unknown. We demonstrate here a role for p16(INK4A) in the loss of cell cycle controls required for tumorigenesis and show how accumulating genetic changes cooperate and contribute to the transformed phenotype.
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Affiliation(s)
- Philip J Mitchell
- MRC Laboratory for Molecular Cell Biology and Department of Biochemistry, University College London, London WC1E 6BT, United Kingdom
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32
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Bellan C, Lazzi S, De Falco G, Nyongo A, Giordano A, Leoncini L. Burkitt's lymphoma: new insights into molecular pathogenesis. J Clin Pathol 2003; 56:188-92. [PMID: 12610094 PMCID: PMC1769902 DOI: 10.1136/jcp.56.3.188] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The World Health Organisation classification reports three subcategories of Burkitt's lymphoma (BL)--endemic, non-endemic, and immunodeficiency associated--proposed to reflect the major clinical and genetic subtypes of this disease. These different types of BL have been reviewed and studied by immunohistochemistry and molecular methods. The results point out the heterogeneity of BL and suggest that AIDS related BL may have a different pathogenesis from that of classic BL.
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Affiliation(s)
- C Bellan
- Institute of Pathological Anatomy and Histology, University of Siena, Nuovo Policlinico Le Scotte, Via delle Scotte, 6, 53100 Siena, Italy.
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33
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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: 152] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [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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Tedesco D, Lukas J, Reed SI. The pRb-related protein p130 is regulated by phosphorylation-dependent proteolysis via the protein-ubiquitin ligase SCF(Skp2). Genes Dev 2002; 16:2946-57. [PMID: 12435635 PMCID: PMC187481 DOI: 10.1101/gad.1011202] [Citation(s) in RCA: 215] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
p130 is a tumor suppressor of the pocket protein family whose expression is posttranscriptionally regulated and largely G0 restricted. The mechanism of down-regulation of p130 expression in proliferating cells was investigated. Our results indicate that the decline of p130 expression as G0 cells reenter the cell cycle is due to a decrease in protein stability. The enhancement of p130 turnover in late G1 and S phase compared with G0 and early G1 phase was dependent on Cdk4/6-specific phosphorylation of p130 on Serine 672, and independent of Cdk2 activity. The activity of the ubiquitin ligase complex Skp1-Cul1/Cdc53-F-box protein Skp2 (SCF(Skp2)) and the proteasome were necessary for p130 degradation. In vitro, recombinant Skp2 was able to bind hyperphosphorylated but not dephosphorylated p130. Furthermore, in vitro polyubiquitination of p130 by SCF(Skp2) was specifically dependent on phosphorylation of p130 on Serine 672. Thus, like the Cdk inhibitor p27(Kip1), p130 turnover is regulated by Cdk-dependent G1 phosphorylation leading to ubiquitin-dependent proteolysis.
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Affiliation(s)
- Donato Tedesco
- Department of Molecular Biology, MB-7, The Scripps Research Institute, La Jolla, California 92037, USA
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35
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Cole SL, Tevethia MJ. Simian virus 40 large T antigen and two independent T-antigen segments sensitize cells to apoptosis following genotoxic damage. J Virol 2002; 76:8420-32. [PMID: 12134045 PMCID: PMC155145 DOI: 10.1128/jvi.76.16.8420-8432.2002] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The simian virus 40 (SV40) large tumor (T) antigen is sufficient to transform cells in cultures and induce tumors in experimental animals. Transformation of primary cells in cultures requires both overcoming growth arrest by stimulating the cell cycle and blocking cell death activities presumably activated by oncogene-mediated hyperproliferation signals. The study presented here examined the ability of specific regions and activities of T antigen to modulate apoptosis in cells treated with the genotoxic agent 5-fluorouracil (5-FU). The results showed that the expression of full-length T antigen rendered rat embryo fibroblasts (REF) sensitive to 5-FU-induced apoptosis. Thus, neither the p53-binding region nor the Bcl-2 homology region of T antigen was sufficient to prevent cell death induced by the DNA-damaging agent. T-antigen-mediated sensitization occurred independently of retinoblastoma protein or p53 and p300 binding. An N-terminal segment containing the first 127 T-antigen amino acids (T1-127) was sufficient to sensitize cells. A C-terminal segment consisting of T-antigen amino acids 251 to 708 (T251-708) also sensitized cells to 5-FU-induced apoptosis. This sensitization did not occur when T251-708 was targeted to the nucleus by inclusion of the SV40 nuclear localization signal. The introduction of mutations into the T-antigen J domain resulted in mutation-specific and variable inhibition of apoptosis. This result suggested that either the structural or the functional integrity of the J domain is required to sensitize cells to apoptosis. Treatment of REF or REF expressing full-length T antigen, an N-terminal segment, or T251-708 resulted in increased expression of the p53-responsive MDM2 gene; apoptosis occurred through a p53-dependent pathway, as p53-null cells expressing these T antigens were resistant to 5-FU-induced apoptosis. Possible mechanisms involved in sensitizing cells to a p53-dependent apoptosis pathway in spite of the ability of T antigen to bind and inactivate the transcriptional transactivating activity of p53 are discussed.
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Affiliation(s)
- Sara L Cole
- Department of Microbiology and Immunology, College of Medicine, Pennsylvania State University, Hershey 17033, USA
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36
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Lazzi S, Bellan C, De Falco G, Cinti C, Ferrari F, Nyongo A, Claudio PP, Tosi GM, Vatti R, Gloghini A, Carbone A, Giordano A, Leoncini L, Tosi P. Expression of RB2/p130 tumor-suppressor gene in AIDS-related non-Hodgkin's lymphomas: implications for disease pathogenesis. Hum Pathol 2002; 33:723-31. [PMID: 12196924 DOI: 10.1053/hupa.2002.125372] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In this study we examined 21 cases of AIDS-related lymphomas for genomic organization and expression of RB2/p130 oncosuppressor gene and compared the results with the proliferative features of these neoplasms. We found no mutations in the RB2/p130 gene and unusually high percentages of cells expressing nuclear pRb2/p130 in tumors with a high proliferative activity, such as AIDS-related lymphomas. These findings might suggest that a molecular mechanism usually observed in viral-linked oncogenesis could be involved. We performed in vitro and in vivo binding assays to investigate whether the human immunodeficiency virus (HIV) gene product Tat and Rb2/p130 could interact. The results of these assays revealed that the HIV-1 Tat protein binds specifically to pRb2/p130. This may result in the inactivation of its oncosuppressive properties and the induction of genes needed to proceed through the cell cycle including p107, cyclin A, and cyclin B. Using single-cell polymerase chain reaction (PCR) assay, we found HIV-1 DNA in the neoplastic cells of only 2 of the 21 cases examined, whereas PCR on whole tissue revealed HIV-1 DNA in all of the cases. Furthermore, a diffuse and nuclear stain was observed in tissue sections with anti-Tat monoclonal antibody. These findings are in accordance with the notion that soluble Tat protein could function as a biologically active extracellular protein released by infected cells and taken up readily by uninfected B cells. In conclusion, our results seem to suggest that pRb2/p130 oncosuppressor protein may be a target in the interaction between the HIV-1 gene products and host proteins.
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MESH Headings
- Adult
- Cell Line
- Child, Preschool
- DNA Mutational Analysis
- DNA Primers/chemistry
- DNA, Neoplasm/analysis
- DNA, Viral/analysis
- Embryo, Mammalian
- Female
- Gene Expression Regulation, Viral
- Gene Products, tat/immunology
- Gene Products, tat/metabolism
- HIV-1/genetics
- HIV-1/metabolism
- Humans
- In Situ Hybridization
- Kidney
- Lymphoma, AIDS-Related/genetics
- Lymphoma, AIDS-Related/metabolism
- Lymphoma, AIDS-Related/pathology
- Male
- Middle Aged
- Phosphoproteins/genetics
- Phosphoproteins/metabolism
- Protein Binding
- Proteins
- Retinoblastoma-Like Protein p130
- Transfection
- tat Gene Products, Human Immunodeficiency Virus
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Affiliation(s)
- Stefano Lazzi
- Institute of Pathological Anatomy and Histology, University of Siena, Siena, Italy
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37
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Truckenmiller ME, Vawter MP, Zhang P, Conejero-Goldberg C, Dillon-Carter O, Morales N, Cheadle C, Becker KG, Freed WJ. AF5, a CNS cell line immortalized with an N-terminal fragment of SV40 large T: growth, differentiation, genetic stability, and gene expression. Exp Neurol 2002; 175:318-37. [PMID: 12061863 DOI: 10.1006/exnr.2002.7898] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Central nervous system progenitor cells that are self-renewing in culture and also differentiate under controlled conditions are potentially useful for developmental studies and for cell-based therapies. We characterized growth and plasticity properties and gene expression in a rat mesencephalic cell line, AF5, that was immortalized with an N-terminal fragment of SV40 large T (T155g). For over 150 population doublings in culture, the growth rate of AF5 cells remained steady, the cells remained responsive to bFGF, and telomerase activity and telomere lengths were unchanged. While karyotype analyses revealed some chromosomal abnormalities, these were also unchanged over time; additionally, no mutations in p53 gene sequences were found, and wild-type p53 activation was normal. AF5 cells produced PDGF, TGFbeta1, TGFbeta2, and bFGF. Similar to primary progenitor cells, AF5 cells retained their plasticity in culture; they could be propagated in an undifferentiated state as "neurospheres" in serum-free media or as adherent cultures in serum-containing media, and they differentiated when allowed to become confluent. Adherent subconfluent actively growing cultures expressed a marker for immature neurons, nestin, while few cells expressed the mature neuronal cell marker betaIII-tubulin. Confluent cultures ceased growing, developed differentiated morphologies, contained few or no nestin-expressing cells, and acquired betaIII-tubulin expression. Global gene expression was examined using a 15,000 gene microarray, comparing exponential growth with and without bFGF stimulation, and the differentiated state. The AF5 cell line exhibited stable genetic and growth properties over extended periods of time, while retaining the ability to differentiate in vitro. These data suggest that the AF5 cell line may be useful as an in vitro model system for studies of neural differentiation.
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Affiliation(s)
- M E Truckenmiller
- Cellular Neurobiology Research Branch, National Institute on Drug Abuse, 5500 Nathan Shock Drive, Baltimore, Maryland 21224, USA
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38
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Sullivan CS, Pipas JM. T antigens of simian virus 40: molecular chaperones for viral replication and tumorigenesis. Microbiol Mol Biol Rev 2002; 66:179-202. [PMID: 12040123 PMCID: PMC120785 DOI: 10.1128/mmbr.66.2.179-202.2002] [Citation(s) in RCA: 182] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Simian virus 40 (SV40) is a small DNA tumor virus that has been extensively characterized due to its relatively simple genetic organization and the ease with which its genome is manipulated. The large and small tumor antigens (T antigens) are the major regulatory proteins encoded by SV40. Large T antigen is responsible for both viral and cellular transcriptional regulation, virion assembly, viral DNA replication, and alteration of the cell cycle. Deciphering how a single protein can perform such numerous and diverse functions has remained elusive. Recently it was established that the SV40 T antigens, including large T antigen, are molecular chaperones, each with a functioning DnaJ domain. The molecular chaperones were originally identified as bacterial genes essential for bacteriophage growth and have since been shown to be conserved in eukaryotes, participating in an array of both viral and cellular processes. This review discusses the mechanisms of DnaJ/Hsc70 interactions and how they are used by T antigen to control viral replication and tumorigenesis. The use of the DnaJ/Hsc70 system by SV40 and other viruses suggests an important role for these molecular chaperones in the regulation of the mammalian cell cycle and sheds light on the enigmatic SV40 T antigen-a most amazing molecule.
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Affiliation(s)
- Christopher S Sullivan
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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39
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Beachy TM, Cole SL, Cavender JF, Tevethia MJ. Regions and activities of simian virus 40 T antigen that cooperate with an activated ras oncogene in transforming primary rat embryo fibroblasts. J Virol 2002; 76:3145-57. [PMID: 11884539 PMCID: PMC136032 DOI: 10.1128/jvi.76.7.3145-3157.2002] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Prolonged expression of a ras oncogene in primary cells accelerates the natural process of senescence. This ras-induced permanent growth arrest is bypassed in cells expressing the simian virus 40 large T antigen. Previously we showed that two regions of T antigen, a region consisting of the N-terminal 147 amino acids and a region consisting of amino acids 251 to 708 (T251-708), independently overcome ras-induced senescence. Coexpression of either T-antigen fragment and Ras results in the appearance of dense foci of transformed cells. Using a series of mutants that produce shorter T-antigen fragments, we show that the C-terminal limit of the N-terminal T-antigen fragment that cooperates with Ras lies between amino acids 83 and 121. The N-terminal limit of the C-terminal T-antigen fragment lies between amino acids 252 and 271. In addition, we present evidence that cooperation between the N-terminal fragment and Ras depends upon an intact T-antigen J domain and the ability of the T antigen to bind and inactivate the growth-suppressive effect of the tumor suppressor Rb. Introduction of specific amino acid substitutions surrounding residue 400 into T251-708 prevented the fragment from cooperating with Ras. T251-708 proteins with these same substitutions inhibited the transcriptional transactivating potential of p53 as effectively as did the wild-type protein. Thus, at least one activity contained within T251-708, other than inactivating p53 as a transcriptional transactivator, is likely to be required to bypass Ras-induced senescence.
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Affiliation(s)
- Tina M Beachy
- Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA
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40
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Münger K, Basile JR, Duensing S, Eichten A, Gonzalez SL, Grace M, Zacny VL. Biological activities and molecular targets of the human papillomavirus E7 oncoprotein. Oncogene 2001; 20:7888-98. [PMID: 11753671 DOI: 10.1038/sj.onc.1204860] [Citation(s) in RCA: 414] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The human papillomavirus (HPV) E7 protein is one of only two viral proteins that remain expressed in HPV-associated human cancers. HPV E7 proteins share structural and functional similarities with oncoproteins encoded by other small DNA tumor viruses such as adenovirus E1A and SV40 large tumor antigen. The HPV E7 protein plays an important role in the viral life cycle by subverting the tight link between cellular differentiation and proliferation in normal epithelium, thus allowing the virus to replicate in differentiating epithelial cells that would have normally withdrawn from the cell division cycle. The transforming activities of E7 largely reflect this important function.
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Affiliation(s)
- K Münger
- Department of Pathology and Harvard Center for Cancer Biology, Harvard Medical School, Boston, MA 02115, USA.
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41
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Parreño M, Garriga J, Limón A, Albrecht JH, Graña X. E1A modulates phosphorylation of p130 and p107 by differentially regulating the activity of G1/S cyclin/CDK complexes. Oncogene 2001; 20:4793-806. [PMID: 11521191 DOI: 10.1038/sj.onc.1204644] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2001] [Revised: 05/10/2001] [Accepted: 05/17/2001] [Indexed: 11/08/2022]
Abstract
We have previously shown that the adenoviral 12S E1A protein modulates the phosphorylation status of p130 and p107 without apparent changes in the cell cycle dependent phosphorylation of the retinoblastoma protein. Here we report on the mechanisms by which E1A modifies differentially the phosphorylation status of pocket proteins. In human U-2 OS osteosarcoma cells transiently expressing E1A, ectopic expression of D-type cyclins alone or combined, but not cyclins E and/or A, fully rescues E1A-mediated block in hyperphosphorylation of p130 to form 3. However, cyclins E and A, individually or together, induce hyperphosphorylation of p130 to species with intermediate mobility. Phosphopeptide maps indicate that E1A inhibits phosphorylation of sites phosphorylatable by CDKs. One of these sites is Ser-1044. The effects of blocking the activities of endogenous and exogenous cyclins with p16 and dominant negative CDK2 in E1A expressing cells further indicate that p130 is phosphorylated by both D-type cyclin and cyclin E/CDK complexes and that E1A modulates the activity of these G1/S CDKs by independent mechanisms. Stable expression of E1A in MC3T3-E1 cells leads to downregulation of D-type cyclins, and upregulation of cyclins E and A. This is accompanied by increased CDK2 kinase activity. Downregulation of D-type cyclins in these cells correlates with a block on both p130 hyperphosphorylation to form 3 and hyperphosphorylation of p107. This is rescued by D-type cyclins but not by cyclin E. In addition, we show that the upregulation of cyclins E and A is at least partially dependent on an intact pocket protein/E2F pathway, but downregulation of D-type cyclins is not. Moreover, we provide evidence that while the lack of a functional pRB pathway also results in a block on hyperphosphorylation of p130 to form 3, this is not sufficient to induce constitutive expression of p130 form 2b.
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Affiliation(s)
- M Parreño
- Department of Biochemistry, Fels Institute for Cancer Research and Molecular Biology, Temple University School of Medicine, 3307 North Broad Street, Philadelphia, Pennsylvania, PA19140, USA
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42
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Affiliation(s)
- D T Simmons
- Department of Biological Sciences, University of Delaware, Newark 19716, USA
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43
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Rundell K, Parakati R. The role of the SV40 ST antigen in cell growth promotion and transformation. Semin Cancer Biol 2001; 11:5-13. [PMID: 11243894 DOI: 10.1006/scbi.2000.0341] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The simian virus 40 small-t (ST) antigen plays a key role in permissive and nonpermissive infections, increasing virus yields in lytic cycles of primate cells and enhancing the ability of large-T (LT) to transform rodent or even human cells. In the absence of ST, tumors in rodent model systems appear primarily in lymphoid and other proliferative tissues and transformation is reduced in several in vitro systems. The functions of ST largely reflect its binding and inhibition of protein phosphatase 2A, although a recently described dnaJ domain also contributes to its biology. The dnaJ domain is present in LT and a third early gene product, the 17kT protein, for which a potential role in transformation deserves further evaluation.
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Affiliation(s)
- K Rundell
- Department of Microbiology-Immunology, Northwestern University, and The Robert H. Lurie Comprehensive Cancer Center, Chicago, IL 60611, USA.
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44
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Ali SH, DeCaprio JA. Cellular transformation by SV40 large T antigen: interaction with host proteins. Semin Cancer Biol 2001; 11:15-23. [PMID: 11243895 DOI: 10.1006/scbi.2000.0342] [Citation(s) in RCA: 277] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
SV40 large T antigen (TAg) is a powerful oncoprotein capable of transforming a variety of cell types. The transforming activity of TAg is due in large part to its perturbation of the retinoblastoma (pRB) and p53 tumor suppressor proteins. In addition, TAg binds to several other cellular factors, including the transcriptional co-activators p300 and CBP, which may contribute to its transformation function. Several other features of TAg that appear to contribute to its full transformation potential are yet to be completely understood. Study of TAg therefore continues to provide new insights into the mechanism of cellular transformation.
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Affiliation(s)
- S H Ali
- Department of Adult Oncology, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA 02115, USA
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45
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Kim HY, Ahn BY, Cho Y. Structural basis for the inactivation of retinoblastoma tumor suppressor by SV40 large T antigen. EMBO J 2001; 20:295-304. [PMID: 11226179 PMCID: PMC140208 DOI: 10.1093/emboj/20.1.295] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Inactivation of the retinoblastoma (Rb) tumor suppressor by Simian virus 40 (SV40) large T antigen is one of the central features of tumorigenesis induced by SV40. Both the N-terminal J domain and the LxCxE motif of large T antigen are required for inactivation of Rb. The crystal structure of the N-terminal region (residues 7-117) of SV40 large T antigen bound to the pocket domain of Rb reveals that large T antigen contains a four-helix bundle, and residues from helices alpha2 and alpha4 and from a loop containing the LxCxE motif participate in the interactions with Rb. The two central helices and a connecting loop in large T antigen have structural similarities with the J domains of the molecular chaperones DnaJ and HDJ-1, suggesting that large T antigen may use a chaperone mechanism for its biological function. However, there are significant differences between large T antigen and the molecular chaperones in other regions and these differences are likely to provide the specificity needed for large T antigen to inactivate Rb.
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Affiliation(s)
- Hye-Yeon Kim
- Division of Molecular and Life Science, Pohang University of Science and Technology, Hyo-ja dong, San31, Pohang, KyungBook, Structural Biology Center, Korea Institute of Science and Technology, Seoul and Department of Biotechnology, Korea University, Seoul, South Korea Corresponding author e-mail:
| | - Byung-Yoon Ahn
- Division of Molecular and Life Science, Pohang University of Science and Technology, Hyo-ja dong, San31, Pohang, KyungBook, Structural Biology Center, Korea Institute of Science and Technology, Seoul and Department of Biotechnology, Korea University, Seoul, South Korea Corresponding author e-mail:
| | - Yunje Cho
- Division of Molecular and Life Science, Pohang University of Science and Technology, Hyo-ja dong, San31, Pohang, KyungBook, Structural Biology Center, Korea Institute of Science and Technology, Seoul and Department of Biotechnology, Korea University, Seoul, South Korea Corresponding author e-mail:
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46
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Ratineau C, Ronco A, Leiter AB. Role of the amino-terminal domain of simian virus 40 early region in inducing tumors in secretin-expressing cells in transgenic mice. Gastroenterology 2000; 119:1305-11. [PMID: 11054388 DOI: 10.1053/gast.2000.19278] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
BACKGROUND & AIMS The early region of simian virus 40 (SV40) encodes 2 transforming proteins, large T (Tag) and small t antigen, that produce neuroendocrine tumors in the intestine and the pancreas when expressed in secretin cells of transgenic mice. METHODS Two SV40 early-region transgenes containing a deletion that eliminated expression of the small t antigen were expressed in transgenic mice under control of the secretin gene. The 2 lines of mice, one expressing the native large T antigen and the other T antigen with a mutation in its N-terminal J domain, were examined to determine which biological activities of the SV40 early region were required for tumorigenesis. RESULTS Most animals expressing wild-type large T antigen developed pancreatic insulinomas and lymphomas and died between 3 and 6 months of age. However, small intestinal neoplasms were extremely rare in the absence of small t antigen expression. Transgenic lines expressing the J domain mutant failed to develop tumors. CONCLUSIONS Transformation of secretin-producing enteroendocrine cells by SV40 requires functional cooperation between intact large T and small t oncoproteins. In contrast, large T antigen alone is sufficient to induce tumors in the endocrine pancreas and thymus.
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Affiliation(s)
- C Ratineau
- Division of Gastroenterology and GRASP Digestive Disease Center, New England Medical Center, Tufts University School of Medicine, Boston, Massachusetts 02111, USA
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47
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Chao HH, Buchmann AM, DeCaprio JA. Loss of p19(ARF) eliminates the requirement for the pRB-binding motif in simian virus 40 large T antigen-mediated transformation. Mol Cell Biol 2000; 20:7624-33. [PMID: 11003658 PMCID: PMC86324 DOI: 10.1128/mcb.20.20.7624-7633.2000] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
At least three domains of simian virus 40 large T antigen (TAg) participate in cellular transformation. The LXCXE motif of TAg binds to all members of the retinoblastoma protein (pRB) family of tumor suppressors. The N-terminal 70 residues of TAg have significant homology to the J domain of Hsp40/DnaJ and cooperate with the LXCXE motif to inactivate the pRB family. A bipartite C-terminal domain of TAg binds to p53 and thereby disrupts the ability of p53 to act as a sequence-specific transcription factor. The contribution of these three domains of TAg to cellular transformation was evaluated in cells that contained inactivating mutations in the pRB and p53 pathways. Cells that stably expressed wild-type or selected mutant forms of TAg were generated in mouse embryo fibroblasts (MEFs) containing homozygous deletions in the RB, INK4a, and ARF loci. It was determined that the J domain, the LXCXE motif, and the p53-binding domain of TAg were required for full transformation of wild-type and RB(-/-) MEFs. In contrast, INK4a(-/-) MEFs that lacked expression of p16(INK4a) and p19(ARF) and ARF(-/-) MEFs that lacked p19(ARF) but expressed p16(INK4a) acquired anchorage-independent growth when expressing wild-type TAg or mutant derivatives that disrupted either the pRB-binding or p53-binding domain. The expression and function of the pRB family members were not overly disrupted in ARF(-/-) MEFs expressing LXCXE mutants of TAg. These results suggest that inactivating mutations of p19(ARF) can relieve the requirement for the LXCXE motif in TAg-mediated transformation and that TAg may have additional functions in transformation.
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MESH Headings
- Amino Acid Motifs
- Animals
- Antigens, Viral, Tumor/chemistry
- Antigens, Viral, Tumor/genetics
- Antigens, Viral, Tumor/metabolism
- Blotting, Western
- Carrier Proteins/genetics
- Carrier Proteins/metabolism
- Cell Count
- Cell Cycle Proteins
- Cell Division
- Cell Line, Transformed
- Cell Transformation, Neoplastic/genetics
- Contact Inhibition
- Cyclin-Dependent Kinase Inhibitor p16
- DNA-Binding Proteins
- E2F Transcription Factors
- Fibroblasts
- Gene Deletion
- Gene Expression Regulation, Neoplastic
- Genes, Reporter
- Mice
- Promoter Regions, Genetic
- Protein Binding
- Proteins/genetics
- Proteins/metabolism
- Retinoblastoma Protein/genetics
- Retinoblastoma Protein/metabolism
- Retinoblastoma-Binding Protein 1
- Transcription Factor DP1
- Transcription Factors/metabolism
- Tumor Suppressor Protein p14ARF
- Tumor Suppressor Protein p53/metabolism
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Affiliation(s)
- H H Chao
- Dana-Farber Cancer Institute and Harvard Medical School, Boston, Massachusetts 02115, USA
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48
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Sheng Q, Love TM, Schaffhausen B. J domain-independent regulation of the Rb family by polyomavirus large T antigen. J Virol 2000; 74:5280-90. [PMID: 10799605 PMCID: PMC110883 DOI: 10.1128/jvi.74.11.5280-5290.2000] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The ability of polyomavirus large T antigen (LT) to promote cell cycling, to immortalize primary cells, and to block differentiation has been linked to its effects on tumor suppressors of the retinoblastoma susceptibility (Rb) gene family. Our previous studies have shown that LT requires an intact N-terminal DnaJ domain, in addition to an Rb binding site, for activation of simple E2F-containing promoters and stimulation of cell cycle progression. Here we show that some LT effects dependent on interaction with the Rb family are largely DnaJ independent. In differentiating C2C12 myoblasts, overexpression of LT caused apoptosis. Although this activity of LT completely depended on Rb binding, LTs with mutations in the J domain remained able to kill. Comparisons of Rb(-) and J(-) LTs revealed additional differences. Wild-type but not Rb(-) LT activated the cyclin A promoter under serum starvation conditions. Genetic analysis of the promoter linked the Rb requirement to an E2F site in the promoter. LTs with mutations in the J domain were still able to activate the promoter. Finally, J mutant LTs caused changes in phosphorylation of both pRb and p130. In the case of p130, Thr-986 was shown to be a site that is regulated by J mutant LT. Taken together, these observations reveal that LT regulation of Rb function can be separated into both DnaJ-dependent and DnaJ-independent pathways.
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Affiliation(s)
- Q Sheng
- Department of Biochemistry, Tufts University School of Medicine, Boston, Massachusetts, USA
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49
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Parreño M, Garriga J, Limón A, Mayol X, Beck GR, Moran E, Graña X. E1A blocks hyperphosphorylation of p130 and p107 without affecting the phosphorylation status of the retinoblastoma protein. J Virol 2000; 74:3166-76. [PMID: 10708433 PMCID: PMC111817 DOI: 10.1128/jvi.74.7.3166-3176.2000] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The phosphorylation status of the pRB family of growth suppressor proteins is regulated in a cell cycle entry-, progression-, and exit-dependent manner in normal cells. We have shown previously that p130, a member of this family, exhibits patterns of phosphorylated forms associated with various cell growth and differentiation stages. However, human 293 cells, which are transformed cells that express the adenoviral oncoproteins E1A and E1B, exhibit an abnormal pattern of p130 phosphorylated forms. Here we report that, unlike pRB, the phosphorylation status of both p130 and p107 is not modulated during the cell cycle in 293 cells as it is in other cells. Conditional overexpression of individual G(1)/S cyclins in 293 cells does not alter the phosphorylation status of p130, suggesting that the expression of E1A and/or E1B blocks hyperphosphorylation of p130. In agreement with these observations, transient cotransfection of vectors expressing E1A 12S, but not E1B, in combination with pocket proteins into U-2 OS cells blocks hyperphosphorylation of both p130 and p107. However, the phosphorylation status of pRB is not altered by cotransfection of E1A 12S vectors. Moreover, MC3T3-E1 preosteoblasts stably expressing E1A 12S also exhibit a block in hyperphosphorylation of endogenous p130 and p107. Direct binding of E1A to p130 and p107 is not required for the phosphorylation block since E1A 12S mutants defective in binding to the pRB family also block hyperphosphorylation of p130 and p107. Our data reported here identify a novel function of E1A, which affects p130 and p107 but does not affect pRB. Since E1A does not bind the hyperphosphorylated forms of p130, this function of E1A might prevent the existence of "free" hyperphosphorylated p130, which could act as a CDK inhibitor.
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Affiliation(s)
- M Parreño
- Fels Institute for Cancer Research and Molecular Biology and Department of Biochemistry, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA
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Gjoerup O, Chao H, DeCaprio JA, Roberts TM. pRB-dependent, J domain-independent function of simian virus 40 large T antigen in override of p53 growth suppression. J Virol 2000; 74:864-74. [PMID: 10623749 PMCID: PMC111607 DOI: 10.1128/jvi.74.2.864-874.2000] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/1999] [Accepted: 10/20/1999] [Indexed: 01/05/2023] Open
Abstract
Simian virus 40 (SV40) large T antigen (LT) can immortalize and transform many cell types. These activities are attributed in large part to the binding and functional inactivation by LT of two major tumor suppressors: p53 and the retinoblastoma protein, pRB. Most effects of LT on pRB have been shown to additionally require an intact J domain, which mediates binding to Hsc70. We show here that the J domain is not required for p53 override in full-length LT. Although LT binds p53, it was shown previously that overcoming a p53-induced cell cycle arrest requires binding to pRB family members (R. S. Quartin et al., J. Virol. 68:1334-1341). We demonstrate that an LT mutant defective for pRB family member binding (K1) can be complemented for efficient override of p53 arrest by a construct encoding the first 135 amino acids of LT with a J domain-inactivating mutation, H42Q. Hence, complementation does not require the J domain, and pRB binding by LT is important for more than dissociating pRB-E2F complexes, which is J dependent. In accordance with this notion, LT alleviates pRB small-pocket-mediated transcriptional repression independently of the J domain. The LT K1 mutant can also be complemented for p53 override by small t antigen (st) in a manner independent of its J domain. Our observations underscore the importance of multiple SV40 functions, two in LT and one in st, that act cooperatively to counteract p53 growth suppression.
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Affiliation(s)
- O Gjoerup
- Department of Cancer Biology, Dana-Farber Cancer Institute and Harvard Medical School, Boston, Massachusetts 02115, USA
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