Role of SV40 Small t in Cell Lysis, Transformation, and Signaling

Montano, Ximena; Rundell, Kathy

doi:10.1385/1-59259-117-5:229

Cited by 3 publications

(3 citation statements)

References 31 publications

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“…The highly multifunctional large T antigen (LT) is the key early protein essential for both driving viral replication as well as inducing cellular transformation. Two other early proteins, small t antigen and 17k T antigen (17k) may perform auxiliary functions during the viral life cycle (39,69). LT has served as a powerful model system for understanding fundamental cellular processes such as nuclear translocation, transcriptional regulation, eukaryotic DNA replication, immortalization, and malignant transformation (reviewed in references 26 and 37).…”

mentioning

confidence: 99%

Simian Virus 40 Large T Antigen Disrupts Genome Integrity and Activates a DNA Damage Response via Bub1 Binding

Hein

Boichuk

et al. 2009

J Virol

119

132

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Simian virus 40 (SV40) large T antigen (LT) is a multifunctional protein that is important for viral replication and oncogenic transformation. Previously, infection of monkey or human cells with SV40 was shownto lead to the induction of DNA damage response signaling, which is required for efficient viral replication. However, it was not clear if LT is sufficient to induce the damage response and, if so, what the genetic requirements and functional consequences might be. Here, we show that the expression of LT alone, without a replication origin, can induce key DNA damage response markers including the accumulation of ␥-H2AX and 53BP1 in nuclear foci. Other DNA damage-signaling components downstream of ATM/ATR kinases were induced, including chk1 and chk2. LT also bound the Claspin mediator protein, which normally facilitates the ATR activation of chk1 and monitors cellular replication origins. Stimulation of the damage response by LT depends mainly on binding to Bub1 rather than to the retinoblastoma protein. LT has long been known to stabilize p53 despite functionally inactivating it. We show that the activation of a DNA damage response by LT via Bub1 appears to play a major role in p53 stabilization by promoting the phosphorylation of p53 at Ser15. Accompanying the DNA damage response, LT induces tetraploidy, which is also dependent on Bub1 binding. Taken together, our data suggest that LT, via Bub1 binding, breaches genome integrity mechanisms, leading to DNA damage responses, p53 stabilization, and tetraploidy.Simian virus 40 (SV40) is a small DNA tumor virus, belonging to the polyomavirus family, that induces a productive infection in its natural host, the rhesus macaque, but yields oncogenic transformation in nonpermissive hosts such as rodent cells. The highly multifunctional large T antigen (LT) is the key early protein essential for both driving viral replication as well as inducing cellular transformation. Two other early proteins, small t antigen and 17k T antigen (17k) may perform auxiliary functions during the viral life cycle (39, 69). LT has served as a powerful model system for understanding fundamental cellular processes such as nuclear translocation, transcriptional regulation, eukaryotic DNA replication, immortalization, and malignant transformation (reviewed in references 26 and 37).LT overrides cellular control mechanisms and reprograms the host cell to create a permissive environment for viral replication. The deregulation of cellular proliferation is dependent on LT's interaction with specific host proteins, among which the tumor suppressors p53 and the retinoblastoma protein (pRB) are the best characterized (reviewed in reference 37). Transformation in vitro and tumor induction in vivo frequently depend on LT binding and functionally inactivating these key tumor suppressors (37).

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mentioning

confidence: 99%

Simian Virus 40 Large T Antigen Disrupts Genome Integrity and Activates a DNA Damage Response via Bub1 Binding

Hein

Boichuk

et al. 2009

J Virol

119

132

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“…To confirm that smt acted as a cochaperone, we analyzed the ability of purified smt to stimulate the ATPase activity of DnaK in vitro. Smt was purified as described previously (22) and used in a steady-state ATPase assay (8). The results are shown in Fig.…”

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confidence: 99%

Simian Virus 40 T Antigens and J Domains: Analysis of Hsp40 Cochaperone Functions in Escherichia coli

Genevaux

Lang

Schwager

et al. 2003

J Virol

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The N-terminal exon of DNA tumor virus T antigens represents a J domain that can direct interaction with the host-encoded Hsp70 chaperones. We have taken advantage of rapid Hsp40 cochaperone assays with Escherichia coli to assess simian virus 40 (SV40)-encoded J-domain loss of function. We found a strong correlation between loss of cochaperone function in E. coli and defective SV40 growth, suggesting that the major role of the J domain in DNA tumor viruses is to provide cochaperone function. We also report the expression of native SV40 virus T antigens in E. coli. Our results show that small t antigen, but not large T antigen (LT) or LT truncation TN125 or TN136, can functionally replace under limited growth conditions DnaJ (Hsp40) function in vivo. In addition, purified small t antigen can efficiently stimulate E. coli DnaK's (Hsp70) ATPase in vitro, thus behaving like a bona fide cochaperone. Furthermore, small t amino acids 83 to 174, which are adjacent to the viral J domain, can replace the E. coli DnaJ J-domain glycine-phenylalanine-rich domain, immediately adjacent to the J-domain sequences, even in the absence of significant amino acid similarity to their DnaJ counterpart. Taken together, our studies demonstrate that functionally related Hsp40 proteins from mammalian viral systems can be rapidly studied in bacteria and exploited to probe the universally conserved Hsp70 chaperone machine mechanism.The ability of simian virus 40 (SV40) to regulate many aspects of the cell cycle has made it an invaluable tool for probing fundamental biological questions and the molecular origins of human cancer (13). Viral early gene products that include large T antigen (LT), small t antigen (smt), and 17k antigen are coordinately affected by N-terminal exon mutations because this exon is common to all mature spliced early genes (27, 39). Mutations in the N-terminal region of SV40 T antigens have been described that alter viral DNA replication, capsid morphogenesis, cellular transformation, immortalization, transcriptional activation, sensitization to apoptosis, and modulation of growth control signaling pathways (2,5,18,32,39). The multifunctional viral T antigens and their interactions with host proteins have been the subject of extensive recent reviews (1, 29, 39).Of particular importance to viral replication is advancing the cell cycle. Viral infection of nonpermissive cells may lead to cellular transformation because of the targeting and sustained inactivation of key regulatory proteins, including the tumor suppressor retinoblastoma (RB) family and p53. SV40 LT specifically interacts with p53, and the retinoblastoma family members pRB, p130, and p107 (39). smt enhances transformation in many cell types, particularly those that are growth arrested (39). smt specifically interacts with protein phosphatase 2A and attenuates its activity, thereby aiding the progression of S phase (43). smt alone can also transactivate the cyclin A and adenovirus E2 promoters independent of smt-dependent inactivation of protein phosphatase ...

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“…Since polyomavirus Sm t-Ags cooperate with LT-Ag in transformation of cells in tissue culture and animal model systems [ 40 , 46 , 125 , 126 , 127 , 128 ], we reasoned that some of the new Sm t-Ag targets have an apparent relevance to the cell transformation pathways. As such, the chromatin-remodeling proteins (Smarca1 and 5) could be, for example, categorized into this category.…”

Section: Resultsmentioning

confidence: 99%

A Comprehensive Proteomics Analysis of the JC Virus (JCV) Large and Small Tumor Antigen Interacting Proteins: Large T Primarily Targets the Host Protein Complexes with V-ATPase and Ubiquitin Ligase Activities While Small t Mostly Associates with Those Having Phosphatase and Chromatin-Remodeling Functions

Saribas

Safak

2020

Viruses

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The oncogenic potential of both the polyomavirus large (LT-Ag) and small (Sm t-Ag) tumor antigens has been previously demonstrated in both tissue culture and animal models. Even the contribution of the MCPyV tumor antigens to the development of an aggressive human skin cancer, Merkel cell carcinoma, has been recently established. To date, the known primary targets of these tumor antigens include several tumor suppressors such as pRb, p53, and PP2A. However, a comprehensive list of the host proteins targeted by these proteins remains largely unknown. Here, we report the first interactome of JCV LT-Ag and Sm t-Ag by employing two independent “affinity purification/mass spectroscopy” (AP/MS) assays. The proteomics data identified novel targets for both tumor antigens while confirming some of the previously reported interactions. LT-Ag was found to primarily target the protein complexes with ATPase (v-ATPase and Smc5/6 complex), phosphatase (PP4 and PP1), and ligase (E3-ubiquitin) activities. In contrast, the major targets of Sm t-Ag were identified as Smarca1/6, AIFM1, SdhA/B, PP2A, and p53. The interactions between “LT-Ag and SdhB”, “Sm t-Ag and Smarca5”, and “Sm t-Ag and SDH” were further validated by biochemical assays. Interestingly, perturbations in some of the LT-Ag and Sm t-Ag targets identified in this study were previously shown to be associated with oncogenesis, suggesting new roles for both tumor antigens in novel oncogenic pathways. This comprehensive data establishes new foundations to further unravel the new roles for JCV tumor antigens in oncogenesis and the viral life cycle.

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Role of SV40 Small t in Cell Lysis, Transformation, and Signaling

Cited by 3 publications

References 31 publications

Simian Virus 40 Large T Antigen Disrupts Genome Integrity and Activates a DNA Damage Response via Bub1 Binding

Simian Virus 40 Large T Antigen Disrupts Genome Integrity and Activates a DNA Damage Response via Bub1 Binding

Simian Virus 40 T Antigens and J Domains: Analysis of Hsp40 Cochaperone Functions in Escherichia coli

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