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The Structure of Protein Phosphatase 2A and Its Inhibition of Tumorigenesis. PROG BIOCHEM BIOPHYS 2009. [DOI: 10.3724/sp.j.1206.2008.00420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Cheng J, DeCaprio JA, Fluck MM, Schaffhausen BS. Cellular transformation by Simian Virus 40 and Murine Polyoma Virus T antigens. Semin Cancer Biol 2009; 19:218-28. [PMID: 19505649 PMCID: PMC2694755 DOI: 10.1016/j.semcancer.2009.03.002] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2009] [Revised: 03/19/2009] [Accepted: 03/20/2009] [Indexed: 01/09/2023]
Abstract
Simian Virus 40 (SV40) and Mouse Polyoma Virus (PY) are small DNA tumor viruses that have been used extensively to study cellular transformation. The SV40 early region encodes three tumor antigens, large T (LT), small T (ST) and 17KT that contribute to cellular transformation. While PY also encodes LT and ST, the unique middle T (MT) generates most of the transforming activity. SV40 LT mediated transformation requires binding to the tumor suppressor proteins Rb and p53 in the nucleus and ST binding to the protein phosphatase PP2A in the cytoplasm. SV40 LT also binds to several additional cellular proteins including p300, CBP, Cul7, IRS1, Bub1, Nbs1 and Fbxw7 that contribute to viral transformation. PY MT transformation is dependent on binding to PP2A and the Src family protein tyrosine kinases (PTK) and assembly of a signaling complex on cell membranes that leads to transformation in a manner similar to Her2/neu. Phosphorylation of MT tyrosine residues activates key signaling molecules including Shc/Grb2, PI3K and PLCgamma1. The unique contributions of SV40 LT and ST and PY MT to cellular transformation have provided significant insights into our understanding of tumor suppressors, oncogenes and the process of oncogenesis.
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Affiliation(s)
- Jingwei Cheng
- Department of Medical Oncology, Dana-Farber Cancer Institute; Department of Medicine, Brigham and Women’s Hospital; and Harvard Medical School, Boston, MA 02115
| | - James A. DeCaprio
- Department of Medical Oncology, Dana-Farber Cancer Institute; Department of Medicine, Brigham and Women’s Hospital; and Harvard Medical School, Boston, MA 02115
- Center for Applied Cancer Science, Dana-Farber Cancer Institute, Boston, MA 02115
| | - Michele M. Fluck
- Department of Microbiology and Molecular Genetics, Interdepartmental Program in Cell and Molecular Biology, Michigan State University, East Lansing, MI 48824
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Cantalupo PG, Sáenz-Robles MT, Rathi AV, Beerman RW, Patterson WH, Whitehead RH, Pipas JM. Cell-type specific regulation of gene expression by simian virus 40 T antigens. Virology 2009; 386:183-91. [PMID: 19201438 DOI: 10.1016/j.virol.2008.12.038] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2008] [Revised: 12/02/2008] [Accepted: 12/26/2008] [Indexed: 10/21/2022]
Abstract
SV40 transforms cells through the action of two oncoproteins, large T antigen and small t antigen. Small t antigen targets phosphatase PP2A, while large T antigen stimulates cell proliferation and survival by action on multiple proteins, including the tumor suppressors Rb and p53. Large T antigen also binds components of the transcription initiation complex and several transcription factors. We examined global gene expression in SV40-transformed mouse embryo fibroblasts, and in enterocytes obtained from transgenic mice. SV40 transformation alters the expression of approximately 800 cellular genes in both systems. Much of this regulation is observed in both MEFs and enterocytes and is consistent with T antigen action on the Rb-E2F pathway. However, the regulation of many genes is cell-type specific, suggesting that unique signaling pathways are activated in different cell types upon transformation, and that the consequences of SV40 transformation depends on the type of cell targeted.
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Affiliation(s)
- Paul G Cantalupo
- Department of Biological Sciences, 559 Crawford Hall, University of Pittsburgh Pittsburgh, Pennsylvania 15260, USA
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Kiely PA, Baillie GS, Lynch MJ, Houslay MD, O'Connor R. Tyrosine 302 in RACK1 is essential for insulin-like growth factor-I-mediated competitive binding of PP2A and beta1 integrin and for tumor cell proliferation and migration. J Biol Chem 2008; 283:22952-61. [PMID: 18567578 DOI: 10.1074/jbc.m800802200] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Insulin-like growth factor (IGF)-I regulates a mutually exclusive interaction of PP2A and beta1 integrin with the WD repeat scaffolding protein RACK1. This interaction is required for the integration of IGF-I receptor (IGF-IR) and adhesion signaling. Here we investigated the nature of the binding site for PP2A and beta1 integrin in RACK1. A WD7 deletion mutant of RACK1 did not associate with PP2A but retained some interaction with beta1 integrin, whereas a WD6/WD7 mutant lost the ability to bind to both PP2A and beta1 integrin. Using immobilized peptide arrays representing the entire RACK1 protein, we identified a common cluster of amino acids (FAGY) at positions 299-302 within WD7 of RACK1 which were essential for binding of both PP2A and beta1 integrin to RACK1. PP2A showed a higher level of association with a peptide in which Tyr-302 was phosphorylated compared with an unphosphorylated peptide, whereas beta1 integrin binding was not affected by phosphorylation. RACK1 mutants in which either the FAGY cluster or Tyr-302 were mutated to AAAF, or Phe, respectively, did not interact with either PP2A or beta1 integrin. These mutants were unable to rescue the decrease in PP2A activity caused by suppression of RACK1 in MCF-7 cells with small interfering RNA. MCF-7 cells and R+ (IGF-IR-overexpressing fibroblasts) expressing these mutants exhibited decreased proliferation and migration, whereas R- cells (IGF-IR null fibroblasts) were unaffected. Taken together, the data demonstrate that Tyr-302 in RACK1 is required for interaction with PP2A and beta1 integrin, for regulation of PP2A activity, and for IGF-I-mediated cell migration and proliferation.
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Affiliation(s)
- Patrick A Kiely
- Department of Biochemistry, BioSciences Institute, University College Cork, Ireland
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Eichhorn PJA, Creyghton MP, Bernards R. Protein phosphatase 2A regulatory subunits and cancer. Biochim Biophys Acta Rev Cancer 2008; 1795:1-15. [PMID: 18588945 DOI: 10.1016/j.bbcan.2008.05.005] [Citation(s) in RCA: 273] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2008] [Revised: 05/20/2008] [Accepted: 05/21/2008] [Indexed: 01/06/2023]
Abstract
The serine/threonine protein phosphatase (PP2A) is a trimeric holoenzyme that plays an integral role in the regulation of a number of major signaling pathways whose deregulation can contribute to cancer. The specificity and activity of PP2A are highly regulated through the interaction of a family of regulatory B subunits with the substrates. Accumulating evidence indicates that PP2A acts as a tumor suppressor. In this review we summarize the known effects of specific PP2A holoenzymes and their roles in cancer relevant pathways. In particular we highlight PP2A function in the regulation of MAPK and Wnt signaling.
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Affiliation(s)
- Pieter J A Eichhorn
- Division of Molecular Carcinogenesis, Center for Cancer Genomics and Center for Biomedical Genetics, The Netherlands Cancer Institute, Amsterdam, The Netherlands
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Chandramouli S, Yu CY, Yusoff P, Lao DH, Leong HF, Mizuno K, Guy GR. Tesk1 interacts with Spry2 to abrogate its inhibition of ERK phosphorylation downstream of receptor tyrosine kinase signaling. J Biol Chem 2007; 283:1679-1691. [PMID: 17974561 DOI: 10.1074/jbc.m705457200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The Sprouty (Spry) proteins function as inhibitors of the Ras-ERK pathway downstream of various receptor tyrosine kinases. In this study, we have identified Tesk1 (testicular protein kinase 1) as a novel regulator of Spry2 function. Endogenous Tesk1 and Spry2 exist in a complex in cell lines and mouse tissues. Tesk1 coexpression relocalizes Spry2 to vesicles including endosomes, inhibiting its translocation to membrane ruffles upon growth factor stimulation. Independent of its kinase activity, Tesk1 binding leads to a loss of Spry2 function as an inhibitor of ERK phosphorylation and reverses inhibition of basic fibroblast growth factor (bFGF)- and nerve growth factor-induced neurite outgrowth in PC12 cells by Spry2. Furthermore, depletion of endogenous Tesk1 in PC12 cells leads to a reduction in neurite outgrowth induced by bFGF. Tesk1 nullifies the inhibitory effect of Spry2 by abrogating its interaction with the adaptor protein Grb2 and interfering with its serine dephosphorylation upon bFGF and FGF receptor 1 stimulation by impeding its binding to the catalytic subunit of protein phosphatase 2A. A construct of Tesk1 that binds to Spry2 but does not localize to the vesicles does not interfere with its function, highlighting the importance of subcellular localization of Tesk1 in this context. Conversely, Tesk1 does not affect interaction of Spry2 with the E3 ubiquitin ligase, c-Cbl, and consequently, does not affect its inhibition of Cbl-mediated ubiquitination of the epidermal growth factor receptor. By selectively modulating the downstream effects of Spry2, Tesk1 may thus serve as a molecular determinant of the signaling outcome.
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Affiliation(s)
- Sumana Chandramouli
- Institute of Molecular and Cell Biology, 61 Biopolis Drive, Proteos, Singapore 138673
| | - Chye Yun Yu
- Institute of Molecular and Cell Biology, 61 Biopolis Drive, Proteos, Singapore 138673
| | - Permeen Yusoff
- Institute of Molecular and Cell Biology, 61 Biopolis Drive, Proteos, Singapore 138673
| | - Dieu-Hung Lao
- Institute of Molecular and Cell Biology, 61 Biopolis Drive, Proteos, Singapore 138673
| | - Hwei Fen Leong
- Institute of Molecular and Cell Biology, 61 Biopolis Drive, Proteos, Singapore 138673
| | - Kensaku Mizuno
- Department of Biomolecular Sciences, Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi 980-8578, Japan
| | - Graeme R Guy
- Institute of Molecular and Cell Biology, 61 Biopolis Drive, Proteos, Singapore 138673.
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Sáenz-Robles MT, Markovics JA, Chong JL, Opavsky R, Whitehead RH, Leone G, Pipas JM. Intestinal hyperplasia induced by simian virus 40 large tumor antigen requires E2F2. J Virol 2007; 81:13191-9. [PMID: 17855529 PMCID: PMC2169091 DOI: 10.1128/jvi.01658-07] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The simian virus 40 large T antigen contributes to neoplastic transformation, in part, by targeting the Rb family of tumor suppressors. There are three known Rb proteins, pRb, p130, and p107, all of which block the cell cycle by preventing the transcription of genes regulated by the E2F family of transcription factors. T antigen interacts directly with Rb proteins and disrupts Rb-E2F complexes both in vitro and in cultured cells. Consequently, T antigen is thought to inhibit transcriptional repression by the Rb family proteins by disrupting their interaction with E2F proteins, thus allowing E2F-dependent transcription and the expression of cellular genes needed for entry into S phase. This model predicts that active E2F-dependent transcription is required for T-antigen-induced transformation. To test this hypothesis, we have examined the status of Rb-E2F complexes in murine enterocytes. Previous studies have shown that T antigen drives enterocytes into S phase, resulting in intestinal hyperplasia, and that the induction of enterocyte proliferation requires T-antigen binding to Rb proteins. In this paper, we show that normal growth-arrested enterocytes contain p130-E2F4 complexes and that T-antigen expression destroys these complexes, most likely by stimulating p130 degradation. Furthermore, unlike their normal counterparts, enterocytes expressing T antigen contain abundant levels of E2F2 and E2F3a. Concomitantly, T-antigen-induced intestinal proliferation is reduced in mice lacking either E2F2 alone or both E2F2 and E2F3a, but not in mice lacking E2F1. These studies support a model in which T antigen eliminates Rb-E2F repressive complexes so that specific activator E2Fs can drive S-phase entry.
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Affiliation(s)
- M Teresa Sáenz-Robles
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA
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Dahl J, Chen HI, George M, Benjamin TL. Polyomavirus small T antigen controls viral chromatin modifications through effects on kinetics of virus growth and cell cycle progression. J Virol 2007; 81:10064-71. [PMID: 17626093 PMCID: PMC2045420 DOI: 10.1128/jvi.00821-07] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Minichromosomes of wild-type polyomavirus were previously shown to be highly acetylated on histones H3 and H4 compared either to bulk cell chromatin or to viral chromatin of nontransforming hr-t mutants, which are defective in both the small T and middle T antigens. A series of site-directed virus mutants have been used along with antibodies to sites of histone modifications to further investigate the state of viral chromatin and its dependence on the T antigens. Small T but not middle T was important in hyperacetylation at major sites in H3 and H4. Mutants blocked in middle T signaling pathways but encoding normal small T showed a hyperacetylated pattern similar to that of wild-type virus. The hyperacetylation defect of hr-t mutant NG59 was partially complemented by growth of the mutant in cells expressing wild-type small T. In contrast to the hypoacetylated state of NG59, NG59 minichromosomes were hypermethylated at specific lysines in H3 and also showed a higher level of phosphorylation at H3ser10, a modification associated with the late G(2) and M phases of the cell cycle. Comparisons of virus growth kinetics and cell cycle progression in wild-type- and NG59-infected cells showed a correlation between the phase of the cell cycle at which virus assembly occurred and histone modifications in the progeny virus. Replication and assembly of wild-type virus were completed largely during S phase. Growth of NG59 was delayed by about 12 h with assembly occurring predominantly in G(2). These results suggest that small T affects modifications of viral chromatin by altering the temporal coordination of virus growth and the cell cycle.
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Affiliation(s)
- Jean Dahl
- Department of Pathology, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
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