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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. Viruses 2020; 12:v12101192. [PMID: 33092197 PMCID: PMC7594058 DOI: 10.3390/v12101192] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Revised: 10/13/2020] [Accepted: 10/15/2020] [Indexed: 02/06/2023] Open
Abstract
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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Rotondo JC, Mazzoni E, Bononi I, Tognon M, Martini F. Association Between Simian Virus 40 and Human Tumors. Front Oncol 2019; 9:670. [PMID: 31403031 PMCID: PMC6669359 DOI: 10.3389/fonc.2019.00670] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Accepted: 07/09/2019] [Indexed: 12/17/2022] Open
Abstract
Simian virus 40 (SV40) is a small DNA tumor virus of monkey origin. This polyomavirus was administered to human populations mainly through contaminated polio vaccines, which were produced in naturally infected SV40 monkey cells. Previous molecular biology and recent immunological assays have indicated that SV40 is spreading in human populations, independently from earlier SV40-contaminated vaccines. SV40 DNA sequences have been detected at a higher prevalence in specific human cancer specimens, such as the brain and bone tumors, malignant pleural mesotheliomas, and lymphoproliferative disorders, compared to the corresponding normal tissues/specimens. However, other investigations, which reported negative data, did not confirm an association between SV40 and human tumors. To circumvent the controversies, which have arisen because of these molecular biology studies, immunological researches with newly developed indirect ELISA tests were carried out in serum samples from patients affected by the same kind of tumors as mentioned above. These innovative indirect ELISAs employ synthetic peptides as mimotopes/specific SV40 antigens. SV40 mimotopes do not cross-react with the homologous human polyomaviruses, BKPyV, and JCPyV. Immunological data obtained from indirect ELISAs, using SV40 mimotopes, employed to analyze serum samples from oncological patients, have indicated that these sera had a higher prevalence of antibodies against SV40 compared to healthy subjects. The main data on (i) the biology and genetics of SV40; (ii) the epidemiology of SV40 in the general population, (iii) the mechanisms of SV40 transformation; (iv) the putative role of SV40 in the onset/progression of specific human tumors, and (v) its association with other human diseases are reported in this review.
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Affiliation(s)
- John Charles Rotondo
- Section of Pathology, Oncology and Experimental Biology, Department of Morphology, Surgery and Experimental Medicine, University of Ferrara, Ferrara, Italy
| | - Elisa Mazzoni
- Section of Pathology, Oncology and Experimental Biology, Department of Morphology, Surgery and Experimental Medicine, University of Ferrara, Ferrara, Italy
| | - Ilaria Bononi
- Section of Pathology, Oncology and Experimental Biology, Department of Morphology, Surgery and Experimental Medicine, University of Ferrara, Ferrara, Italy
| | - Mauro Tognon
- Section of Pathology, Oncology and Experimental Biology, Department of Morphology, Surgery and Experimental Medicine, University of Ferrara, Ferrara, Italy
| | - Fernanda Martini
- Section of Pathology, Oncology and Experimental Biology, Department of Morphology, Surgery and Experimental Medicine, University of Ferrara, Ferrara, Italy
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Baez CF, Brandão Varella R, Villani S, Delbue S. Human Polyomaviruses: The Battle of Large and Small Tumor Antigens. Virology (Auckl) 2017; 8:1178122X17744785. [PMID: 29238174 PMCID: PMC5721967 DOI: 10.1177/1178122x17744785] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Accepted: 10/30/2017] [Indexed: 12/17/2022] Open
Abstract
About 40 years ago, the large and small tumor antigens (LT-Ag and sT-Ag) of the polyomavirus (PyVs) simian vacuolating virus 40 have been identified and characterized. To date, it is well known that all the discovered human PyVs (HPyVs) encode these 2 multifunctional and tumorigenic proteins, expressed at viral replication early stage. The 2 T-Ags are able to transform cells both in vitro and in vivo and seem to play a distinct role in the pathogenesis of some tumors in humans. In addition, they are involved in viral DNA replication, transcription, and virion assembly. This short review focuses on the structural and functional features of the HPyVs’ LT-Ag and sT-Ag, with special attention to their transforming properties.
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Affiliation(s)
- Camila Freze Baez
- Department of Preventive Medicine, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | | | - Sonia Villani
- Department of Biomedical, Surgical and Dental Sciences, University of Milano, Milano, Italy
| | - Serena Delbue
- Department of Biomedical, Surgical and Dental Sciences, University of Milano, Milano, Italy
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Wang L, Zhang J, Zhang Y, Nkhata K, Quealy E, Liao JD, Cleary MP, Lü J. Lobe-specific lineages of carcinogenesis in the transgenic adenocarcinoma of mouse prostate and their responses to chemopreventive selenium. Prostate 2011; 71:1429-40. [PMID: 21360561 DOI: 10.1002/pros.21360] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/23/2010] [Accepted: 01/19/2011] [Indexed: 11/09/2022]
Abstract
BACKGROUND The transgenic adenocarcinoma of mouse prostate (TRAMP) model is by far the most practical transgenic model for preclinical prostate cancer chemoprevention studies. It is critical to characterize the prostate lobe-specificity of lesion lineages to consolidate the advantages of this model and minimize its limitations for chemoprevention studies. METHODS We dissected dorsolateral (DLP), ventral (VP), and anterior prostate (AP) lobes, and macroscopic tumors from 90 male C57BL/6J TRAMP mice at 22-24 weeks of age (WOA) and analyzed lesions by histological, biochemical and proteomic approaches. To determine whether methylseleninic acid (MSeA) led to a deletion of initiated cells, we gave oral MSeA to TRAMP mice from 5 to 23 WOA or from 5 to 15 WOA and analyzed lesions at 23 WOA. RESULTS All tumors (n = 18) were T-antigen(+), synaptophysin (SYP)(+), androgen-receptor(-), and E-cadherin(-) poorly differentiated neuroendocrine carcinomas (NE-Ca). They were traceable most frequently to VP (66.7%) and rarely to DLP (11.1%) and AP (5.6%) with an estimated life-time incidence of 1 out of 3 mice. In DLP, epithelial lesions ranged from mild-to-severe atypical hyperplasia, with T-antigen(+), SYP(-), androgen-receptor(+), and E-cadherin(+). Proteomic profiling revealed many molecular differences between VP and DLP. In MSeA experiment, 6 out of 19 (31.5%) mice developed NE-Ca in the control group, only 2 in each MSeA group of 17-18 mice (11.1-11.8%) bore a detectable NE-Ca. CONCLUSION The C57BL/6J TRAMP mouse represents at least two lineages of prostate carcinogenesis. Chemoprevention studies should incorporate this knowledge for efficacy assessment and molecular target validations.
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Affiliation(s)
- Lei Wang
- Hormel Institute, University of Minnesota, Austin, Minnesota, USA
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Knox C, Luke GA, Blatch GL, Pesce ER. Heat shock protein 40 (Hsp40) plays a key role in the virus life cycle. Virus Res 2011; 160:15-24. [DOI: 10.1016/j.virusres.2011.06.013] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2011] [Revised: 06/17/2011] [Accepted: 06/21/2011] [Indexed: 01/04/2023]
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Gharbi-Ayachi A, Labbé JC, Burgess A, Vigneron S, Strub JM, Brioudes E, Van-Dorsselaer A, Castro A, Lorca T. The substrate of Greatwall kinase, Arpp19, controls mitosis by inhibiting protein phosphatase 2A. Science 2010; 330:1673-1677. [PMID: 21164014 DOI: 10.1016/b978-0-12-374145-5.00168-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Initiation and maintenance of mitosis require the activation of protein kinase cyclin B-Cdc2 and the inhibition of protein phosphatase 2A (PP2A), which, respectively, phosphorylate and dephosphorylate mitotic substrates. The protein kinase Greatwall (Gwl) is required to maintain mitosis through PP2A inhibition. We describe how Gwl activation results in PP2A inhibition. We identified cyclic adenosine monophosphate-regulated phosphoprotein 19 (Arpp19) and α-Endosulfine as two substrates of Gwl that, when phosphorylated by this kinase, associate with and inhibit PP2A, thus promoting mitotic entry. Conversely, in the absence of Gwl activity, Arpp19 and α-Endosulfine are dephosphorylated and lose their capacity to bind and inhibit PP2A. Although both proteins can inhibit PP2A, endogenous Arpp19, but not α-Endosulfine, is responsible for PP2A inhibition at mitotic entry in Xenopus egg extracts.
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Affiliation(s)
- Aicha Gharbi-Ayachi
- Universités Montpellier 2 et 1, Centre de Recherche de Biochimie Macromoléculaire, CNRS UMR 5237, IFR 122, 1919 Route de Mende, 34293 Montpellier cedex 5, France
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Kotadia S, Kao LR, Comerford SA, Jones RT, Hammer RE, Megraw TL. PP2A-dependent disruption of centrosome replication and cytoskeleton organization in Drosophila by SV40 small tumor antigen. Oncogene 2008; 27:6334-46. [PMID: 18663356 DOI: 10.1038/onc.2008.254] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Viruses of the DNA tumor virus family share the ability to transform vertebrate cells through the action of virus-encoded tumor antigens that interfere with normal cell physiology. They accomplish this very efficiently by inhibiting endogenous tumor suppressor proteins that control cell proliferation and apoptosis. Simian virus 40 (SV40) encodes two oncoproteins, large tumor antigen, which directly inhibits the tumor suppressors p53 and Rb, and small tumor antigen (ST), which interferes with serine/threonine protein phosphatase 2A (PP2A). We have constructed a Drosophila model for SV40 ST expression and show that ST induces supernumerary centrosomes, an activity we also demonstrate in human cells. In early Drosophila embryos, ST also caused increased microtubule stability, chromosome segregation errors, defective assembly of actin into cleavage furrows, cleavage failure, a rise in cyclin E levels and embryonic lethality. Using ST mutants and genetic interaction experiments between ST and PP2A subunit mutations, we show that all of these phenotypes are dependent on ST's interaction with PP2A. These analyses demonstrate the validity and utility of Drosophila as a model for viral oncoprotein function in vivo.
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Affiliation(s)
- S Kotadia
- Department of Pharmacology, The Cecil and Ida Green Center for Reproductive Biology Sciences, The University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390-9051, USA
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Sablina AA, Hahn WC. SV40 small T antigen and PP2A phosphatase in cell transformation. Cancer Metastasis Rev 2008; 27:137-46. [PMID: 18214640 DOI: 10.1007/s10555-008-9116-0] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The SV40 early region protein, SV40 small t antigen, promotes cell transformation through negative regulation of the protein phosphatase 2A (PP2A) family of serine-threonine phosphatases. More recently, reduced levels of PP2A activity have been found in different types of human cancer. This occurs either through inactivating mutations of PP2A structural subunits, or by upregulation of the cellular PP2A inhibitors, CIP2A and SET. Several distinct PP2A complexes have been identified that contribute directly to tumor suppression by regulating specific phosphorylation events. These studies provide us with new insights into the role of protein phosphatases in cancer initiation and maintenance.
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Affiliation(s)
- Anna A Sablina
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA
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Fan F, Feng L, He J, Wang X, Jiang X, Zhang Y, Wang Z, Chen Y. RKTG sequesters B-Raf to the Golgi apparatus and inhibits the proliferation and tumorigenicity of human malignant melanoma cells. Carcinogenesis 2008; 29:1157-63. [PMID: 18515281 DOI: 10.1093/carcin/bgn119] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Raf kinase trapping to Golgi (RKTG) is a newly characterized negative regulator of the Ras-Raf-mitogen-activated and extracellular signal-regulated kinase kinase (MEK)-extracellular signal-regulated kinase (ERK)-signaling pathway via sequestrating Raf-1 to the Golgi apparatus. Among Raf kinase family members, B-Raf is the most frequently mutated gene in human cancers and an activated B-Raf mutation V600E is associated with >60% of human melanomas. Here, we show that RKTG can also bind and translocate B-Raf to the Golgi apparatus. When overexpressed in A375, a human malignant melanoma cell line with B-Raf(V600E), RKTG inhibits ERK activation, cell proliferation and transformation of A375 cells. In addition, the tumorigenicity of the RKTG-expressing A375 cells is suppressed in nude mice. Consistently, cell proliferation rate was reduced in the tumor xenografts in which RKTG was overexpressed. Collectively, our results suggest that RKTG may play a suppressive role in human melanoma that harbors an oncogenic B-Raf mutation via its antagonistic action on B-Raf.
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Affiliation(s)
- Fengjuan Fan
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Graduate School of the Chinese Academy of Sciences, Shanghai 200031, China
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Khalili K, Sariyer IK, Safak M. Small tumor antigen of polyomaviruses: role in viral life cycle and cell transformation. J Cell Physiol 2008; 215:309-19. [PMID: 18022798 PMCID: PMC2716072 DOI: 10.1002/jcp.21326] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The regulatory proteins of polyomaviruses, including small and large T antigens, play important roles, not only in the viral life cycle but also in virus-induced cell transformation. Unlike many other tumor viruses, the transforming proteins of polyomaviruses have no cellular homologs but rather exert their effects mostly by interacting with cellular proteins that control fundamental processes in the regulation of cell proliferation and the cell cycle. Thus, they have proven to be valuable tools to identify specific signaling pathways involved in tumor progression. Elucidation of these pathways using polyomavirus transforming proteins as tools is critically important in understanding fundamental regulatory mechanisms and hence to develop effective therapeutic strategies against cancer. In this short review, we will focus on the structural and functional features of one polyomavirus transforming protein, that is, the small t-antigen of the human neurotropic JC virus (JCV) and the simian virus, SV40.
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Affiliation(s)
- Kamel Khalili
- Department of Neuroscience and Center for Neurovirology, Temple University School of Medicine, Philadelphia, Pennsylvania
| | - Ilker Kudret Sariyer
- Department of Neuroscience and Center for Neurovirology, Temple University School of Medicine, Philadelphia, Pennsylvania
| | - Mahmut Safak
- Department of Neuroscience and Center for Neurovirology, Temple University School of Medicine, Philadelphia, Pennsylvania
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Klucky B, Wintersberger E. Polyomavirus small T antigen transactivates genes by its ability to provoke the synthesis and the stabilization of MYC. Oncogene 2007; 26:6356-60. [PMID: 17438527 DOI: 10.1038/sj.onc.1210458] [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: 01/16/2023]
Abstract
DNA tumor viruses are capable of driving quiescent cells into the cell cycle. In case of polyomaviridae, two viral proteins, the large and the small (ST) T antigens are responsible for this outcome. ST interacts with the protein phosphatase PP2A and with chaperons of the dnaK type and leads to the transactivation of several genes, which play a role in S-phase induction. One of these is the transcription factor myelocytomatosis (MYC), which by itself is an important regulator of growth. Microarray analysis has revealed several ST-induced genes, which are also targets of MYC; hence, ST may induce these genes via MYC. Experiments shown here are in line with this assumption. MYC-regulated genes are induced by ST at later times than MYC and a MYC responsive promoter is stimulated by ST. Regulation of MYC occurs through signal transduction pathways, which are co-ordinated by PP2A suggesting that they may be targets of ST. Here, we show that this is the case as important kinases involved in these pathways appear in the active phosphorylated form in the presence of ST. Inhibition of these kinases interferes with MYC induction and inhibition of MYC activity blocks ST-mediated transactivation.
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Affiliation(s)
- B Klucky
- Division of Molecular Biology, Department of Medical Biochemistry, MFPL, Medical University of Vienna, Vienna, Austria
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Robinson C, van Bruggen I, Segal A, Dunham M, Sherwood A, Koentgen F, Robinson BWS, Lake RA. A novel SV40 TAg transgenic model of asbestos-induced mesothelioma: malignant transformation is dose dependent. Cancer Res 2006; 66:10786-94. [PMID: 17108115 DOI: 10.1158/0008-5472.can-05-4668] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Although it has been clear for >40 years that mesothelioma can be caused by asbestos, not all patients with this disease have a history of asbestos exposure. Other factors, including non-asbestos fibers and ionizing radiation, are known to cause malignant transformation of mesothelial cells. In addition, it is likely that genetics will play some role in susceptibility. Recently, it has been suggested that SV40 viral oncogenes could contribute to the carcinogenicity of asbestos. To better understand the role of SV40, we used the mesothelin promoter to construct MexTAg mice that express SV40 large T antigen (TAg) in the mesothelial compartment. We generated four MexTAg lines that carry high, intermediate, and low copy numbers of the transgene. All of these mice show a relatively low level of spontaneous tumor development. High-copy, 299h mice rapidly developed mesotheliomas when exposed to asbestos, and these tumors were faster growing and more invasive than those developing in wild-type and single-copy (266s) mice. In addition, we found a direct relationship between transgene copy number and survival after exposure to asbestos. A single copy of TAg was sufficient to immortalize mesothelial cells in vitro, but these cells did not show evidence of malignant transformation. In contrast, cell lines developed from mesothelial cells of animals carrying multiple copies of TAg were growth factor independent and could be cloned at limiting dilution in soft agar. These data provide the first in vivo demonstration of co-carcinogenicity between SV40 and asbestos.
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Affiliation(s)
- Cleo Robinson
- School of Medicine and Pharmacology and Western Australian Institute for Medical Research, University of Western Australia, Perth, Australia
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Abstract
Malignant mesothelioma (MM) is an uncommon tumor with high mortality and morbidity rates. It arises from mesothelial cells that line the pleural, pericardial, peritoneal, and testicular cavities. This is a disease with an indolent course because tumors arise 20 to 40 years after exposure to an inciting agent. Extensive research has shown that mesothelial cells are transformed into MM cells through various chromosomal and cellular pathway defects. These changes alter the normal cells' ability to survive, proliferate, and metastasize. This article discusses the alterations that occur in transforming normal mesothelial cells into MM. It also details some of the signal transduction pathways that seem to be important in MM with the potential for novel targeted therapeutics.
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Affiliation(s)
- Evan Pisick
- Department of Medicine, Section of Hematology/Oncology, Tufts-New England Medical Center, Boston, MA, USA
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Hui L, Rodrik V, Pielak RM, Knirr S, Zheng Y, Foster DA. mTOR-dependent Suppression of Protein Phosphatase 2A Is Critical for Phospholipase D Survival Signals in Human Breast Cancer Cells. J Biol Chem 2005; 280:35829-35. [PMID: 16109716 DOI: 10.1074/jbc.m504192200] [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: 11/06/2022] Open
Abstract
A critical aspect of tumor progression is the generation of survival signals that overcome default apoptotic programs. Recent studies have revealed that elevated phospholipase D activity generates survival signals in breast and perhaps other human cancers. We report here that the elevated phospholipase D activity in the human breast cancer cell line MDA-MB-231 suppresses the activity of the putative tumor suppressor protein phosphatase 2A in a mammalian target of rapamycin (mTOR)-dependent manner. Increasing the phospholipase D activity in MCF7 cells also suppressed protein phosphatase 2A activity. Elevated phospholipase D activity suppressed association of protein phosphatase 2A with both ribosomal subunit S6-kinase and eukaryotic initiation factor 4E-binding protein 1. Suppression of protein phosphatase 2A by SV40 small t-antigen has been reported to be critical for the transformation of human cells with SV40 early region genes. Consistent with a critical role for protein phosphatase 2A in phospholipase D survival signals, either SV40 small t-antigen or pharmacological suppression of protein phosphatase 2A restored survival signals lost by the suppression of either phospholipase D or mTOR. Blocking phospholipase D signals also led to reduced phosphorylation of the pro-apoptotic protein BAD at the protein phosphatase 2A dephosphorylation site at Ser-112. The ability of phospholipase D to suppress protein phosphatase 2A identifies a critical target of an emerging phospholipase D/mTOR survival pathway in the transformation of human cells.
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Affiliation(s)
- Li Hui
- Department of Biological Sciences, Hunter College of the City University of New York, New York, New York 10021, USA
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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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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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Wikström P, Lindahl C, Bergh A. Characterization of the autochthonous transgenic adenocarcinoma of the mouse prostate (TRAMP) as a model to study effects of castration therapy. Prostate 2005; 62:148-64. [PMID: 15389804 DOI: 10.1002/pros.20123] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
BACKGROUND In order to learn more about short- and long-term effects of castration therapy, relevant model systems for prostate cancer are required. In this study, we examined whether the transgenic adenocarcinoma of the mouse prostate (TRAMP) tumor response to castration in C57BL/6 mice mimics that seen in patients. METHODS Transgenic animals were examined before and 3 days after castration, at the ages of 17, 24, and 36 weeks. Moreover, 24-weeks old animals were castrated and followed for 6 months. Immunohistochemistry (IHC) and stereology were used to evaluate epithelial cell proliferation and death, blood vessel volume, androgen receptor (AR) expression, and transgenic expression of SV40 large T. RESULTS Cancer developed preferentially in the dorso-lateral prostate lobe. Tumor burden and incidence of metastases increased with age. The majority of tumors were well differentiated, while poorly differentiated, large tumors and macroscopic metastases developed in 8% of the animals. Well and moderately differentiated tumors responded to castration with cessation of proliferation and induction of apoptosis. Poorly differentiated tumors and metastases did not respond. Castration prevented local tumor growth for at least 6 months in 82% of the cases. Although, 45% of the treated animals developed wide-spread metastatic disease suggesting that castration may enhance growth of distant metastases. CONCLUSIONS The C57Bl/6 TRAMP tumor in several ways mimics how prostate cancer in patients responds to castration both in the short and long term, but some differences may also exist. This model can preferably be used to elucidate how this treatment works, and to test how it can be improved by additional therapies.
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Affiliation(s)
- Pernilla Wikström
- Department of Medical Bioscience, Pathology, Umeå University, 091 85 Umeå, Sweden.
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18
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Klucky B, Koch B, Radolf M, Steinlein P, Wintersberger E. Polyomavirus tumorantigens have a profound effect on gene expression in mouse fibroblasts. Oncogene 2004; 23:4707-21. [PMID: 15122341 DOI: 10.1038/sj.onc.1207640] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Polyomavirus (Py) large and small tumorantigens together are competent to induce S phase in growth-arrested mouse fibroblasts. The capacity of the large tumorantigen to bind the pocket proteins, pRB, p130 and p107, is important for the transactivation of DNA synthesis enzymes and the cyclins E and A, while the interference of small tumorantigen with protein phosphatase PP2A causes a destabilization of the cdk2 inhibitor p27, and thus leads to strong cyclin E- and cyclin A-dependent cdk2 activity. Py small tumorantigen, in addition, is able to transactivate cyclin A. Hence, this protein might have a much wider effect on gene expression in arrested mouse fibroblasts than hitherto suspected. This may have a profound part in the known capacity of Py to form tumors in mice. Therefore, it was interesting to gain an insight into the spectrum of transcriptional deregulation by Py tumorantigens. Accordingly, we performed microarray analysis of quiescent mouse fibroblasts in the absence and presence of small or large tumorantigen. We found that the viral proteins can induce or repress a great variety of genes beyond those involved in the S phase induction and DNA synthesis. The results of the microarray analysis were confirmed for selected genes by several methods, including real-time PCR. Interestingly, a mutation of the binding site for pocket proteins in case of LT and for PP2A in case of ST has a variable effect on the deregulation of genes by the viral proteins depending on the gene in question. In fact, some genes are transactivated by LT as well as ST completely independent of an interaction with their major cellular targets, pocket proteins and PP2A, respectively.
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Affiliation(s)
- Britta Klucky
- Institute of Medical Biochemistry, Division of Molecular Biology, Medical University of Vienna, Dr. Bohrgasse 9, A-1030 Vienna, Austria
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19
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Frijhoff AFW, Conti CJ, Senderowicz AM. Advances in molecular carcinogenesis: current and future use of mouse models to screen and validate molecularly targeted anticancer drugs. Mol Carcinog 2004; 39:183-94. [PMID: 15057870 DOI: 10.1002/mc.20013] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Survival of patients with advanced solid tumors has not significantly improved over the past 30 years. Although molecularly targeted anticancer drugs offer promise, few drugs make it through the end of the Food and Drug Administration approval process. Animal models that more closely resemble human carcinogenesis may bridge the gap between preclinical success and benefits for patients. We discuss pros and cons of several mouse models, including genetically engineered mice that each represent different aspects of human cancer, and the screening of targeted drugs in these models.
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Affiliation(s)
- Anita F W Frijhoff
- The University of Texas M. D. Anderson Cancer Center, Science Park-Research Division, Smithville, Texas, USA
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20
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Ory S, Zhou M, Conrads TP, Veenstra TD, Morrison DK. Protein phosphatase 2A positively regulates Ras signaling by dephosphorylating KSR1 and Raf-1 on critical 14-3-3 binding sites. Curr Biol 2003; 13:1356-64. [PMID: 12932319 DOI: 10.1016/s0960-9822(03)00535-9] [Citation(s) in RCA: 234] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
BACKGROUND Kinase Suppressor of Ras (KSR) is a conserved component of the Ras pathway that acts as a molecular scaffold to facilitate signal transmission through the MAPK cascade. Although recruitment of KSR1 from the cytosol to the plasma membrane is required for its scaffolding function, the precise mechanism(s) regulating the translocation of KSR1 have not been fully elucidated. RESULTS Using mass spectrometry to analyze the KSR1-scaffolding complex, we identify the serine/threonine protein phosphatase PP2A as a KSR1-associated protein and show that PP2A is a critical regulator of KSR1 activity. We find that the enzymatic core subunits of PP2A (PR65A and catalytic C) constitutively associate with the N-terminal domain of KSR1, whereas binding of the regulatory PR55B subunit is induced by growth factor treatment. Specific inhibition of PP2A activity prevents the growth factor-induced dephosphorylation event involved in the membrane recruitment of KSR1 and blocks the activation of KSR1-associated MEK and ERK. Moreover, we find that PP2A activity is required for activation of the Raf-1 kinase and that both Raf and KSR1 must be dephosphorylated by PP2A on critical regulatory 14-3-3 binding sites for KSR1 to promote MAPK pathway activation. CONCLUSIONS These findings identify KSR1 as novel substrate of PP2A and demonstrate the inducible dephosphorylation of KSR1 in response to Ras pathway activation. Further, these results elucidate a common regulatory mechanism for KSR1 and Raf-1 whereby their localization and activity are modulated by the PP2A-mediated dephosphorylation of critical 14-3-3 binding sites.
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Affiliation(s)
- Stéphane Ory
- Regulation of Cell Growth Laboratory, NCI-Frederick, Frederick, MD 21702, USA
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21
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Johannessen M, Olsen PA, Sørensen R, Johansen B, Seternes OM, Moens U. A role of the TATA box and the general co-activator hTAF(II)130/135 in promoter-specific trans-activation by simian virus 40 small t antigen. J Gen Virol 2003; 84:1887-1897. [PMID: 12810884 DOI: 10.1099/vir.0.19057-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The small t antigen (st-ag) of simian virus 40 can exert pleiotropic effects on biological processes such as DNA replication, cell cycle progression and gene expression. One possible mode of achieving these effects is through stimulation of NFkappaB-responsive genes encoding growth factors, cytokines, transcription factors and cell cycle regulatory proteins. Indeed, a previous study has shown that st-ag enhanced NFkappaB-mediated transcription. This study demonstrates that promoters possessing a consensus TATA box (i.e. TATAAAAG) in the context of either NFkappaB- or Sp1-binding sites are trans-activated by st-ag. Overexpressing the general transcription factor hTAF(II)130/135, but not hTAF(II)28 or hTAF(II)80, stimulated the activity of promoters in a consensus TATA box-dependent mode. Converting the consensus TATA motif into a non-consensus TATA box strongly impaired activation by st-ag and hTAF(II)130/135. Conversely, mutating a non-consensus TATA motif into the consensus TATA box rendered the mutated promoter inducible by st-ag and hTAF(II)130/135. Mutation of the TATA box had no effect on TNFalpha- or RelA/p65-mediated induction of NFkappaB-responsive promoters, indicating a specific st-ag effect on hTAF(II)130/135. St-ag stimulated the intrinsic transcriptional activity of hTAF(II)130/135. Substitutions in the conserved HPDKGG motif in the N-terminal region or a mutation that impaired the interaction with protein phosphatase 2A abrogated the ability of st-ag to activate hTAF(II)130/135-mediated transcription. These results indicate that trans-activation of promoters by st-ag may depend on a consensus TATA motif and suggest that such promoters recruit the general transcription factor hTAF(II)130/135.
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Affiliation(s)
- Mona Johannessen
- Department of Biochemistry, Section for Molecular Genetics, Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway
| | - Petter Angell Olsen
- Department of Biochemistry, Section for Molecular Genetics, Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway
| | - Rita Sørensen
- Department of Biochemistry, Section for Molecular Genetics, Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway
| | - Bjarne Johansen
- Department of Biochemistry, Section for Molecular Genetics, Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway
| | - Ole Morten Seternes
- Department of Biochemistry, Section for Molecular Genetics, Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway
| | - Ugo Moens
- Department of Biochemistry, Section for Molecular Genetics, Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway
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22
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Pernasetti F, Spady TJ, Hall SB, Rosenberg SB, Givens ML, Anderson S, Paulus M, Miller WL, Mellon PL. Pituitary tumorigenesis targeted by the ovine follicle-stimulating hormone beta-subunit gene regulatory region in transgenic mice. Mol Cell Endocrinol 2003; 203:169-83. [PMID: 12782413 DOI: 10.1016/s0303-7207(02)00430-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Targeted tumorigenesis in transgenic mice has been a powerful tool for the study of gene expression and oncogenesis, as well as for the production of differentiated immortal cell lines from rare cell types. Follicle-stimulating hormone (FSH) is secreted by the gonadotrope cells of the anterior pituitary gland and plays a pivotal role in mammalian reproduction. Here we have used the regulatory region of the ovine FSH beta gene to direct expression of the SV40 T antigen oncogene to gonadotrope cells in the pituitary of transgenic mice. Two of five transgenic mouse lines bearing this fusion gene rapidly developed pituitary tumors, with appearance of adenomatous foci as early as 6 weeks of age, resulting in death by 12 weeks of age in both genders. Histologic examination of tumor development over time revealed that increases in cell proliferation and dysplasia were accompanied by decreases in synthesis of pituitary hormones, indicating dedifferentiation of the pituitary cells. Histological features observed in these tumors were in agreement with this rapid transformation of cell phenotype. Tumors were multifocal in origin, and the most highly transformed cell types observed consisted of giant pale basophilic cells with enormous hyperploid nuclei associated with infiltrating neuronal-like cells, which were very abundant at later stages of tumor development. Mitotic indices were much higher in transgenic than wild-type pituitaries, as expected. Morphologic analysis of the gonads of these transgenic mice showed no major developmental differences, as compared to wild-type littermates, however the length of the seminiferous tubules in transgenic males was greater than age-matched wild-type animals. Despite this phenotype difference, both genders were fertile, with normal sperm development observed in males and normal estrous cycle stages in females. Moreover, while 8 -- 10-week-old transgenic males had much lower blood levels of FSH than littermates, transgenic female FSH levels were the same as those of wild-type females. These animals offer a unique and potentially useful model of organ-specific tumorigenesis, where a multistage pathway of tumor development is evident, both histologically and temporally. Study of such models will advance our knowledge on the physiological and molecular mechanisms involved in gene expression as well as tumor formation.
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Affiliation(s)
- Flavia Pernasetti
- Departments of Reproductive Medicine and Neuroscience, University of California, 2057 Cellular and Molecular Medicine, East 9500 Gilman Drive, San Diego, La Jolla, CA 2093-0674, USA
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23
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Johannessen M, Olsen PA, Johansen B, Seternes OM, Moens U. Activation of the coactivator four-and-a-half-LIM-only protein FHL2 and the c-fos promoter through inhibition of protein phosphatase 2A. Biochem Pharmacol 2003; 65:1317-28. [PMID: 12694872 DOI: 10.1016/s0006-2952(03)00071-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Previous studies have demonstrated that the serine/threonine protein phosphatase 2A (PP2A) can modulate the transcriptional activity of several sequence-specific DNA-binding proteins. However, less is known about the effect of PP2A on the activities of general transcription factors and transcriptional coregulators. Here we describe that the activity of a general coactivator, the four-and-a-half-LIM-only protein 2 (FHL2), is regulated in a PP2A-dependent manner. Specific inhibition of PP2A by simian virus 40 (SV40) small t-antigen (st-ag) stimulated the intrinsic transcriptional activity of FHL2 more than 10-fold, while a st-ag mutant unable to bind PP2A had no effect. Overexpression of the B56 subunits alpha, beta, and gamma1 of PP2A impaired the induction of FHL2 by st-ag. FHL2 functioned as a coactivator for CREB-mediated transcription, and inactivation of PP2A further increased FHL2-induced CREB-directed transcription. Overexpression of FHL2 readily enhanced the transcription of the luciferase reporter gene driven by the c-fos promoter, and inhibition of PP2A further stimulated FHL2-induced transactivation of this promoter. These results suggest that dephosphorylation of the general coactivator FHL2 may represent a novel mechanism by which PP2A modulates the transcription of FHL2-responsive genes.
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Affiliation(s)
- Mona Johannessen
- Department of Biochemistry, Section for Molecular Genetics, Institute of Medical Biology, University of Tromsø, Norway
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24
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Mitsuhashi S, Shima H, Tanuma N, Matsuura N, Takekawa M, Urano T, Kataoka T, Ubukata M, Kikuchi K. Usage of tautomycetin, a novel inhibitor of protein phosphatase 1 (PP1), reveals that PP1 is a positive regulator of Raf-1 in vivo. J Biol Chem 2003; 278:82-8. [PMID: 12374792 DOI: 10.1074/jbc.m208888200] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein phosphatase type 1 (PP1), together with protein phosphatase 2A (PP2A), is a major eukaryotic serine/threonine protein phosphatase involved in regulation of numerous cell functions. Although the roles of PP2A have been studied extensively using okadaic acid, a well known inhibitor of PP2A, biological analysis of PP1 has remained restricted because of lack of a specific inhibitor. Recently we reported that tautomycetin (TC) is a highly specific inhibitor of PP1. To elucidate the biological effects of TC, we demonstrated in preliminary experiments that treatment of COS-7 cells with 5 microm TC for 5 h inhibits endogenous PP1 by more than 90% without affecting PP2A activity. Therefore, using TC as a specific PP1 inhibitor, the biological effect of PP1 on MAPK signaling was examined. First, we found that inhibition of PP1 in COS-7 cells by TC specifically suppresses activation of ERK, among three MAPK kinases (ERK, JNK, and p38). TC-mediated inhibition of PP1 also suppressed activation of Raf-1, resulting in the inactivation of the MEK-ERK pathway. To examine the role of PP1 in regulation of Raf-1, we overexpressed the PP1 catalytic subunit (PP1C) in COS-7 cells and found that PP1C enhanced activation of Raf-1 activity, whereas phosphatase-dead PP1C blocked Raf-1 activation. Furthermore, a physical interaction between PP1C and Raf-1 was also observed. These data strongly suggest that PP1 positively regulates Raf-1 in vivo.
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Affiliation(s)
- Shinya Mitsuhashi
- Division of Biochemical Oncology and Immunology, Institute for Genetic Medicine, Hokkaido University, Kita-15, Nishi-7, Kita-ku, Sapporo 060-0815, Japan
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25
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Zhou B, Wang ZX, Zhao Y, Brautigan DL, Zhang ZY. The specificity of extracellular signal-regulated kinase 2 dephosphorylation by protein phosphatases. J Biol Chem 2002; 277:31818-25. [PMID: 12082107 DOI: 10.1074/jbc.m203969200] [Citation(s) in RCA: 170] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The extracellular signal-regulated protein kinase 2 (ERK2) is the founding member of a family of mitogen-activated protein kinases (MAPKs) that are central components of signal transduction pathways for cell proliferation, stress responses, and differentiation. The MAPKs are unique among the Ser/Thr protein kinases in that they require both Thr and Tyr phosphorylation for full activation. The dual phosphorylation of Thr-183 and Tyr-185 in ERK2 is catalyzed by MAPK/ERK kinase 1 (MEK1). However, the identity and relative activity of protein phosphatases that inactivate ERK2 are less well established. In this study, we performed a kinetic analysis of ERK2 dephosphorylation by protein phosphatases using a continuous spectrophotometric enzyme-coupled assay that measures the inorganic phosphate produced in the reaction. Eleven different protein phosphatases, many previously suggested to be involved in ERK2 regulation, were compared, including tyrosine-specific phosphatases (PTP1B, CD45, and HePTP), dual specificity MAPK phosphatases (VHR, MKP3, and MKP5), and Ser/Thr protein phosphatases (PP1, PP2A, PP2B, PP2C alpha, and lambda PP). The results provide biochemical evidence that protein phosphatases display exquisite specificity in their substrate recognition and implicate HePTP, MKP3, and PP2A as ERK2 phosphatases. The fact that ERK2 inactivation could be carried out by multiple specific phosphatases shows that signals can be integrated into the pathway at the phosphatase level to determine the cellular response to external stimuli. Important insights into the roles of various protein phosphatases in ERK2 kinase signaling are obtained, and further analysis of the mechanism by which different protein phosphatases recognize and inactivate MAPKs will increase our understanding of how this kinase family is regulated.
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Affiliation(s)
- Bo Zhou
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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26
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Branton PE, Roopchand DE. The role of adenovirus E4orf4 protein in viral replication and cell killing. Oncogene 2001; 20:7855-65. [PMID: 11753668 DOI: 10.1038/sj.onc.1204862] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
It has only been within the last few years that insights have been gained into the remarkable diversity of functions of the adenovirus early transcription region 4 (E4) products. The polypeptide encoded by E4 open reading frame 4 (E4orf4) has emerged as an enigmatic product. Although it accomplishes certain functions that propel viral replication, it has also been shown to be highly toxic, an effect that could dampen the infectious cycle, but that also might serve to facilitate release of viral progeny. When expressed alone, E4orf4 induces a novel form of p53-independent apoptosis in cancer cells but not in normal human cells, thus making it of potential use in cancer gene therapy. In addition, knowledge of its mechanism of action, especially with regard to its interaction with protein phosphatase 2A (PP2A), could provide insights to develop new small molecule anti-cancer drugs. Thus future studies on E4orf4 should be both informative and potentially valuable therapeutically. In this study we review the current status of knowledge on E4orf4.
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Affiliation(s)
- P E Branton
- Department of Biochemistry, McGill University, McIntyre Medical Building, 3655 Promenade Sir William Osler, Montreal, Quebec, H3G 1Y6, Canada.
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27
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Carter AB, Tephly LA, Hunninghake GW. The absence of activator protein 1-dependent gene expression in THP-1 macrophages stimulated with phorbol esters is due to lack of p38 mitogen-activated protein kinase activation. J Biol Chem 2001; 276:33826-32. [PMID: 11454854 DOI: 10.1074/jbc.m100209200] [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: 11/06/2022] Open
Abstract
Activator protein 1 (AP-1) binds to the promoters of many genes involved in immune and inflammatory responses. We have previously shown that the p38 mitogen-activated protein (MAP) kinase regulates NF-kappa B-dependent gene expression by modulating the phosphorylation and subsequent activation of TATA-binding protein (TBP). In this study, we asked whether the p38 MAP kinase regulated the transcriptional activity of AP-1. We found that phorbol 12-myristate 13-acetate (PMA) was unable to drive the AP-1-dependent reporter gene in THP-1 cells. PMA activated both the extracellular signal-regulated kinase and c-Jun NH(2)-terminal kinase MAP kinases, but it did not activate the p38 MAP kinase. We found that cells expressing MAP kinase kinase 6(Glu), which is the upstream kinase that activates the p38 MAP kinase, had significantly increased AP-1-dependent gene expression alone and when stimulated with PMA. These cells also had increased phosphorylation of native c-Jun, suggesting that both c-Jun NH(2)-terminal kinase and p38 MAP kinases phosphorylate c-Jun. More importantly, expression of a constitutive active MAP kinase kinase 6(Glu) resulted in the phosphorylation of a His-TBP fusion protein and increased direct interaction of TBP with c-Jun. These findings suggest that in macrophages, the p38 MAP kinase regulates AP-1-driven transcription by modulating the activation of TBP.
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Affiliation(s)
- A B Carter
- University of Iowa College of Medicine and the Iowa City Veterans Affairs Medical Center, Iowa City, Iowa 52242, USA.
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28
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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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29
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Abstract
Although epidemiological findings have established that exposure to asbestos fibers is the major cause of malignant mesothelioma (MM), recent studies have implicated simian virus 40 (SV40) in the etiology of some of these tumors. Cytogenetic and molecular genetic evidence suggests that multiple somatic genetic events are required for tumorigenic conversion of a mesothelial cell. As with many other types of cancer, in MM critical oncogenic events exert their action via perturbations of the cell cycle. Interactions between the retinoblastoma (Rb) family of proteins and oncoproteins encoded by SV40 lead to cell cycle alterations. Likewise, inhibition of the p53 tumor suppressor by SV40 can inactivate a crucial cell cycle checkpoint, thereby permitting cells to undergo mitosis regardless of the presence of DNA damage. Many MMs exhibit loss and/or inactivation of the tumor suppressors p16(INK4a)and p14(ARF), components of the pRb and p53 cell cycle regulatory pathways, respectively. Recent investigations have demonstrated that SV40 large T antigen, isolated from frozen biopsies of human MM specimens, binds to and inactivates various tumor suppressor gene products such as pRb and p53. In this review, we discuss how SV40-oncosuppressor interactions can lead to functional alterations of the pRb- and p53-dependent cell cycle regulatory pathways and thereby contribute to neoplastic transformation of human mesothelial cells.
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Affiliation(s)
- J R Testa
- Human Genetics Program, Fox Chase Cancer Center, Philadelphia, PA 19111, USA.
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30
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Abstract
Dynamic phosphorylation and dephosphorylation of proteins are fundamental mechanisms utilized by cells to transduce signals. Whereas transduction by protein kinases has been a major focus of studies in the last decade, protein phosphatase 2A (PP2A) enzymes emerge in this millenium as the most fashionable players in cellular signaling. Viral proteins target specific PP2A enzymes in order to deregulate chosen cellular pathways in the host and promote viral progeny. The observation that a variety of viruses utilize PP2A to alienate cellular behavior emphasizes the fundamental importance of PP2A in signal transduction. This review will primarily focus on discussing the uniqueness of PP2A regulation and uncovering the critical role played by protein-protein interactions in the modulation of PP2A signaling. Moreover, the place of PP2A in signaling pathways and its functional significance for human diseases will be discussed.
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Affiliation(s)
- E Sontag
- Department of Pathology/Neuropathology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9073, USA.
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31
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Polyoma virus middle t-antigen: growth factor receptor mimic. ACTA ACUST UNITED AC 2001. [DOI: 10.1016/s0168-7069(01)05004-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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32
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Carter AB, Hunninghake GW. A constitutive active MEK --> ERK pathway negatively regulates NF-kappa B-dependent gene expression by modulating TATA-binding protein phosphorylation. J Biol Chem 2000; 275:27858-64. [PMID: 10878013 DOI: 10.1074/jbc.m003599200] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Endotoxin-induced cytokine gene expression is regulated, in part, by NF-kappaB. We have shown that both the ERK and p38 mitogen-activated protein (MAP) kinases are necessary for cytokine gene transcription and that the p38 MAP kinase is required for NF-kappaB-driven transcription, so we hypothesized that the MEK --> ERK pathway regulated NF-kappaB-driven transcription as well. We found that a constitutive active MEK --> ERK pathway inhibited NF-kappaB-driven transcription. In addition, both PD 98059 and a dominant negative ERK2 augmented NF-kappaB-driven transcription; however, neither PD 98059 nor MEK1 altered NF-kappaB activation at any level. The constitutive active MEK --> ERK pathway inhibited the phosphorylation of TBP, which is necessary for both interaction with RelA and binding to the TATA box. Due to the fact that we have shown that the p38 MAP kinase modulates TBP activation, we evaluated the effect of the constitutive active MEK --> ERK pathway on p38 MAP kinase activity. We found that the MEK --> ERK pathway negatively regulates NF-kappaB-driven transcription, in part, by inhibiting p38 MAP kinase activity. Thus, the ERK and p38 MAP kinases have differential effects on NF-kappaB-driven transcription.
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Affiliation(s)
- A B Carter
- University of Iowa College of Medicine and the Iowa City Veterans Administration Medical Center, Iowa City, Iowa 52242, USA.
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33
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Gamberi G, Benassi MS, Pompetti F, Ferrari C, Ragazzini P, Sollazzo MR, Molendini L, Merli M, Magagnoli G, Chiesa F, Gobbi AG, Powers A, Picci P. Presence and expression of the simian virus-40 genome in human giant cell tumors of bone. Genes Chromosomes Cancer 2000; 28:23-30. [PMID: 10738299 DOI: 10.1002/(sici)1098-2264(200005)28:1<23::aid-gcc3>3.0.co;2-w] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
SV40 DNA sequences have been found in human tumors, such as mesotheliomas, ependymomas, and bone tumors, suggesting that SV40 may be involved in their etiology. The FOS oncogene could play an important role in bone development because SV40 is able to induce FOS in cell culture. In this study, the presence of SV40 sequences, large T antigen (Tag), and FOS protein expression were investigated in 120 giant cell tumors (GCTs), moderately benign bone tumors that in some cases can progress to a malignant phenotype. Polymerase chain reaction (PCR), using primers that amplify the RB1 pocket binding domain and the intron of Tag, was used to analyze GCT for the presence of SV40 DNA. Tag and FOS protein expression was evaluated by immunohistochemistry. SV40 sequences were found in 30/107 GCTs, and of these, 22/30 samples expressed Tag protein (73%) and 15/30 overexpressed the FOS oncogene (50%). FOS was undetectable in 77 SV40-negative GCTs. Sequence analysis of the amplified DNAs confirmed that the amplified sequences corresponded to SV40 DNA. The correlation between FOS overexpression and SV40-positive GCTs was highly statistically significant (P < 0.001). These results show that SV40 DNA sequences and SV40 Tag are present in GCTs and might induce FOS activity. These data suggest that SV40 might play a role in the development and progression of some GCTs.
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Affiliation(s)
- G Gamberi
- Laboratory of Oncologic Research, Rizzoli Institute, Bologna, Italy.
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34
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Garcia A, Cayla X, Sontag E. Protein phosphatase 2A: a definite player in viral and parasitic regulation. Microbes Infect 2000; 2:401-7. [PMID: 10817642 DOI: 10.1016/s1286-4579(00)00327-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Cells use phosphorylation/dephosphorylation mechanisms to regulate the activity of several proteins required to transmit information from the cell surface to the nucleus. Recent studies have significantly increased our knowledge regarding the structure/function of one major regulator of cell phosphorylation: protein phosphatase 2A (PP2A). This review will discuss the role of PP2A in virology and parasitology.
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Affiliation(s)
- A Garcia
- Laboratoire de signalisation immuno-parasitaire, département d'immunologie, Institut Pasteur, Paris, France
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Garcia A, Cereghini S, Sontag E. Protein phosphatase 2A and phosphatidylinositol 3-kinase regulate the activity of Sp1-responsive promoters. J Biol Chem 2000; 275:9385-9. [PMID: 10734082 DOI: 10.1074/jbc.275.13.9385] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The transcription factor Sp1 regulates the activity of a large number of eukaryotic gene promoters, including early SV40 and human immunodeficiency virus type 1 (HIV-1). Here, we report that expression of SV40 small tumor antigen (small t) in quiescent CV-1 cells transactivates two Sp1-responsive promoters, including a deletion mutant of HIV-1 LTR, through specific inhibition of endogenous AC and ABalphaC forms of protein phosphatase 2A (PP2A). Expression of a small t mutant, lacking the PP2A-binding domain, failed to transactivate Sp1. Overexpression of the B56alpha, B56beta, and B56gamma1 regulatory PP2A subunits strongly inhibited the ability of small t, but not the phosphatase inhibitor, okadaic acid, to enhance Sp1-driven gene expression. Using inhibitors and co-expression of kinase-deficient mutants, we also show that functional phosphatidylinositol 3-kinase (PI 3-kinase) and atypical protein kinase C zeta are required for small t-induced Sp1-dependent promoter transcriptional activation. Moreover, two inhibitors of PI 3-kinase, wortmannin and LY294002, inhibit the initiation of SV40 DNA replication in quiescent CV-1 cells. Taken together, these results suggest that PP2A and PI 3-kinase contribute to the ability of small t to regulate Sp1 activity, stimulate early SV40 DNA replication, and enhance the transformation of resting cells during SV40 infection.
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Affiliation(s)
- A Garcia
- Laboratoire de Signalisation Immuno-Parasitaire, URA CNRS 1960, Département d'Immunologie, Institut Pasteur, 75015 Paris, France
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36
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Marti A, Ballmer-Hofer K. Polyomavirus large- and small-T relieve middle-T-induced cell cycle arrest in normal fibroblasts. J Gen Virol 1999; 80 ( Pt 11):2917-2921. [PMID: 10580053 DOI: 10.1099/0022-1317-80-11-2917] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Papovavirus tumour antigens have been widely used to study cell growth regulation in cultured cells. We investigated the role of mouse polyomavirus T antigens, small-, middle- and large-T, in stimulating growth-arrested REF52 fibroblasts to enter the S phase. Microinjecting cells with cDNAs encoding the various T antigens showed: first, that middle-T expression blocked cell cycle stimulation by serum; second, that middle-T-arrested cells were released into the S phase upon coexpression of small-T; third, that expression of middle-T together with large-T committed resting cells to enter the cell cycle even in the absence of serum. Our data indicate that extensive cooperation among polyomavirus T antigens is essential for T antigen-mediated cell cycle stimulation in growth-arrested cells. In addition, the data suggest a new role for small-T in signalling to mitogenic pathways.
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Affiliation(s)
- Alain Marti
- Institute of Medical Radiobiology at the Paul Scherrer Institute and of the University of Zürich, 5232- Villigen-PSI, Switzerland1
| | - Kurt Ballmer-Hofer
- Institute of Medical Radiobiology at the Paul Scherrer Institute and of the University of Zürich, 5232- Villigen-PSI, Switzerland1
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37
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Whalen B, Laffin J, Friedrich TD, Lehman JM. SV40 small T antigen enhances progression to >G2 during lytic infection. Exp Cell Res 1999; 251:121-7. [PMID: 10438577 DOI: 10.1006/excr.1999.4572] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The infection of monkey kidney (CV-1) cells with simian virus 40 (SV40) stimulates the cells into successive rounds of DNA synthesis without an intervening mitosis, leading to the acquisition of a >G2 DNA content. To elucidate the role of small t antigen in cell cycle progression and in viral replication during infection, studies were performed using an SV40 mutant (dl888) that lacks the ability to produce small t. Initially dl888-infected cells move through the first S phase at roughly the same rate as wild-type infected cells. Upon reaching G2, however, the dl888-infected cells progressed to >G2 at a reduced rate relative to wild-type. The slower rate of entry into >G2 of dl888-infected cells is associated with a decrease in total pRb and an increase in the ratio of hypophosphorylated to hyperphosphorylated pRb. The expression of cyclin D1 and p27(kip1) were elevated in dl888-infected cells compared to wild-type-infected CV-1 cells. Taken together, these results indicate that small t antigen plays a role in stimulating entry into >G2 in SV40-infected CV-1 cells, possibly by affecting the regulation of key cell cycle proteins.
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Affiliation(s)
- B Whalen
- Department of Microbiology, Immunology, and Molecular Genetics, Albany Medical College, 47 New Scotland Avenue, Albany, New York 12208, USA
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38
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Toivola D, Eriksson J. Toxins Affecting Cell Signalling and Alteration of Cytoskeletal Structure. Toxicol In Vitro 1999; 13:521-30. [DOI: 10.1016/s0887-2333(99)00024-7] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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39
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Chung H, Brautigan DL. Protein phosphatase 2A suppresses MAP kinase signalling and ectopic protein expression. Cell Signal 1999; 11:575-80. [PMID: 10433518 DOI: 10.1016/s0898-6568(99)00033-9] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Signalling by MAP kinase was examined in COS-7 cells by transiently expressing a transcription reporter system plus epitope-tagged protein phosphatase 2A catalytic subunit [(HA)3-PP2Ac]. Transactivation of a luciferase gene by GAL4-Elk-1 in serum-stimulated cells was reduced 20-fold by co-expression of wild type (HA)3-PP2Ac. This reduction of MAP kinase signalling required specific type-2A phosphatase activity, because the effects were not mimicked by co-expression of either a mutated, inactive (HA)3-PP2Ac or wild-type PP1Cdelta. Expression of (HA)3-PP2Ac was severely restricted by its own activity because 3-fold more inactive (HA)3-PP2Ac was produced. In a different assay the kinase activity of FLAG-ERK2 was 4-fold lower when co-transfected with (HA)3-PP2Ac, compared to controls. Unexpectedly, mRNA of the reporter constructs were nearly eliminated by even low level expression of (HA)3-PP2Ac in either COS7 or HEK293 cells. The results show that PP2A activity is strictly regulated and can be a limiting factor in ectopic expression of various proteins.
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Affiliation(s)
- H Chung
- Center for Cell Signalling, University of Virginia, Charlottesville 22908, USA
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40
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Al-Murrani SW, Woodgett JR, Damuni Z. Expression of I2PP2A, an inhibitor of protein phosphatase 2A, induces c-Jun and AP-1 activity. Biochem J 1999; 341 ( Pt 2):293-8. [PMID: 10393085 PMCID: PMC1220359] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
Transient expression of I2PP2A, a potent inhibitor of protein phosphatase 2A (PP2A), in HEK-293 cells increased the concentration and DNA binding of the proto-oncogene c-Jun. In contrast, expression of the catalytic subunit of PP2A (PP2AC) markedly decreased the concentration and DNA binding of c-Jun. Expression of I2PP2A also increased the transcriptional activity of activator protein-1, and this effect was diminished in a dose-dependent manner by expression of PP2AC. Densitometric analysis following Western blotting of extracts with antibodies specific for phospho-Ser63 and Ser73 suggests that the effects of I2PP2A and PP2AC expression might be mediated, in part, by changes in the phosphorylation of c-Jun at Ser63. The results indicate that I2PP2A elicits effects that are consistent with it acting as an inhibitor of PP2A in intact cells, and suggest that PP2A might exhibit site selectivity with respect to c-Jun phosphorylation.
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Affiliation(s)
- S W Al-Murrani
- Department of Cellular and Molecular Physiology H166, The Pennsylvania State University College of Medicine, Milton S. Hershey Medical Centre, P.O. Box 850, Hershey, PA 17033, USA
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41
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Yen A, Cherington V, Schaffhausen B, Marks K, Varvayanis S. Transformation-defective polyoma middle T antigen mutants defective in PLCgamma, PI-3, or src kinase activation enhance ERK2 activation and promote retinoic acid-induced, cell differentiation like wild-type middle T. Exp Cell Res 1999; 248:538-51. [PMID: 10222145 DOI: 10.1006/excr.1999.4423] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In HL-60 human myeloblastic leukemia cells, retinoic acid is known to cause cFMS, RAF, MEK, and ERK2 dependent myeloid cell differentiation and G0 arrest associated with RB tumor suppressor protein hypophosphorylation, implicating receptor tyrosine kinase signal transduction in propelling these retinoic acid-induced cellular effects. Furthermore, ectopic expression of polyoma middle T antigen, which activates similar early signal transduction molecules as PDGF class receptors such as cFMS, accelerates these retinoic acid-induced effects. To determine if this depends on middle T's ability to activate PLCgamma, PI-3 kinase, and src-like kinases, stable transfectants of HL-60 cells expressing either the polyoma middle T dl23 mutant, which is defective for PLCgamma and PI-3 kinase activation, or the Delta205 mutant, which in addition has greatly attenuated src-like kinase activation ability, were created and compared to wild-type middle T-transfected HL-60. The transgenes were under control of the retinoic acid (or 1, 25-dihydroxy vitamin D3) inducible Moloney murine leukemia virus LTRs. Expression of the dl23 or Delta205 mutant accelerated retinoic acid-induced cell differentiation. The effects of the mutants were comparable to those of the wild-type middle T. Likewise, retinoic acid-induced G0 arrest of mutant transfected cells and wild-type middle T transfected cells was similar. The same was true for 1, 25-dihydroxy vitamin D3-induced monocytic differentiation as for retinoic acid-induced myeloid differentiation. The mutants did not cause the same slight shortening of the cell cycle as wild-type middle T. Both the mutants and the wild-type middle T caused a similar increase in the cellular basal level of activated ERK2 MAPK. Since retinoic acid increases ERK2 activation, which is necessary for differentiation, the data suggest that mutant and wild-type middle T enhanced the retinoic acid effects by increasing basal levels of ERK2 activation. Consistent with this, the polyoma-induced foreshortening of the time for differentiation coincided with the time for retinoic acid to significantly increase ERK2 activation. As in wild-type HL-60, retinoic acid induced the early down-regulation of RXRalpha in mutant transfectants similar to wild-type middle T transfectants, consistent with no loss or gain of relevant functions due to the mutations. In contrast, vitamin D3 did not down-regulate RXRalpha in HL-60 or transfectants. Polyoma middle T and these transformation-defective mutants thus enhanced ERK2 activation to have an early effect in promoting retinoic acid-induced differentiation without a strong dependence on activating PLCgamma, PI-3 kinase, or src-like kinase.
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Affiliation(s)
- A Yen
- Department of Pathology, Cornell University, Ithaca, New York, 14853, USA
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42
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Carter AB, Monick MM, Hunninghake GW. Both Erk and p38 kinases are necessary for cytokine gene transcription. Am J Respir Cell Mol Biol 1999; 20:751-8. [PMID: 10101008 DOI: 10.1165/ajrcmb.20.4.3420] [Citation(s) in RCA: 256] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
A critical feature of sepsis-induced acute lung injury is the release of cytokines from endotoxin (LPS)- stimulated alveolar macrophages (AM). LPS is also known to activate various members of the mitogen- activated protein kinase (MAPK) family in other types of cells. In this study, we evaluated whether multiple members of the MAPK family regulate cytokine gene expression in LPS-stimulated AM. We found that LPS activates both the extracellular signal-regulated kinase (Erk) and p38 kinases, and that this activation is augmented when the cells are cultured in serum. Inhibition of either the Erk (with PD98059) or p38 (with SB203580) kinase pathway resulted in only a partial reduction in cytokine (interleukin-6 and tumor necrosis factor) messenger RNA accumulation and cytokine release, whereas inhibition of both pathways simultaneously resulted in a decrease in cytokine gene expression to near-control levels. Nuclear run-on assays showed that the effect of these MAPK pathways on LPS-induced expression of the cytokine genes was attributable, at least in part, to regulation of gene transcription. These findings suggest that activation of both the Erk and p38 kinase pathways is necessary for optimal cytokine gene expression in LPS-stimulated human AM, and that the MAPK pathways play a critical role in the inflammatory response that occurs in sepsis-induced acute lung injury.
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Affiliation(s)
- A B Carter
- University of Iowa College of Medicine and the Iowa City Veterans Administration Medical Center, Iowa City, Iowa, USA.
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43
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Andersson MB, Ketterman AJ, Bogoyevitch MA. Differential regulation of parallel mitogen-activated protein kinases in cardiac myocytes revealed by phosphatase inhibition. Biochem Biophys Res Commun 1998; 251:328-33. [PMID: 9790955 DOI: 10.1006/bbrc.1998.9476] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Previous studies have suggested that the contribution of inducible phosphatases to ERK MAPK deactivation is both cell-type- and agonist-specific. The aim of this study was to define the role of inducible phosphatases in ERK MAPK regulation in cardiac myocytes. We examined the kinetics of activation/deactivation of ERK MAPKs following the exposure of cardiac myocytes to endothelin-1 or phorbol ester. Deactivation was prevented by inhibition of protein synthesis indicating a contribution of inducible phosphatases. In contrast, okadaic acid failed to prolong ERK MAPK activation, but activated three myelin basic protein kinases (MBPKs, 55, 62, and 87 kDa) and two c-Jun kinases (46 and 55 kDa). Although the identity of the MBPKs is unknown, the c-Jun kinases corresponded to JNK MAPKs. Simultaneous exposure of cardiac myocytes to okadaic acid and osmotic shock potentiated JNK MAPK activation. Thus, inducible phosphatases regulate ERK MAPK deactivation, whereas okadaic acid-sensitive phosphatases regulate JNK MAPKs and three novel MBPKs.
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Affiliation(s)
- M B Andersson
- William Harvey Research Institute, Charterhouse Square, London, EC1M 6BQ, England
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44
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Ruediger R, Brewis N, Ohst K, Walter G. Increasing the ratio of PP2A core enzyme to holoenzyme inhibits Tat-stimulated HIV-1 transcription and virus production. Virology 1997; 238:432-43. [PMID: 9400615 DOI: 10.1006/viro.1997.8873] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We demonstrated previously that PP2A exists in many cell types as two abundant forms: (1) holoenzyme composed of two regulatory subunits, A and B, and a catalytic subunit C; and (2) core enzyme consisting of the A and C subunits. These two forms have different substrate specificities. Since published data suggested that HIV-1 transcription may be regulated by a cellular protein phosphatase, it was of interest to determine whether changing the ratio between PP2A core and holoenzyme affects HIV-1 gene expression. This question was addressed by expression in COS cells of an N-terminal mutant of the A subunit, A delta 5, which binds the C but not the B subunit. This resulted in an increase in the amount of core enzyme and a decrease in the amount of holoenzyme concomitant with the expected change in phosphatase activity. Tat-stimulated transcription from the HIV-1 LTR was inhibited 5-fold by mutant A delta 5, whereas mRNA synthesis directed by the actin promoter was not affected. Furthermore, virus production in COS, HeLa, and Jurkat T cells was inhibited 45-, 5-, and 3-fold, respectively, by mutant A delta 5. These results demonstrate that the balance between PP2A holoenzyme and core enzyme is important for HIV-1 gene expression and virus production.
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Affiliation(s)
- R Ruediger
- Department of Pathology, University of California at San Diego, La Jolla 92093-0612, USA
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45
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Carbone M, Rizzo P, Grimley PM, Procopio A, Mew DJ, Shridhar V, de Bartolomeis A, Esposito V, Giuliano MT, Steinberg SM, Levine AS, Giordano A, Pass HI. Simian virus-40 large-T antigen binds p53 in human mesotheliomas. Nat Med 1997; 3:908-12. [PMID: 9256284 DOI: 10.1038/nm0897-908] [Citation(s) in RCA: 200] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We found that simian virus 40 (SV40) induces mesotheliomas in hamsters and that 60% of human mesotheliomas contain and express SV40 sequences, results now confirmed by others [ref. 3-5, and presentations by D. Griffiths & R. Weiss, F. Galateau-SallE, and H.I.P. at "Simian virus 40: A possible human polyoma virus," NIH workshop, 27-28 January 1997, Bethesda, MD (transcript available through SAG Corp., Washington, DC 20008)]. Mesothelioma, an aggressive malignancy resistant to therapy, originates from the serosal lining of the pleural, pericardial and peritoneal cavities. The incidence of mesothelioma continues to increase worldwide because of exposure to crocidolite asbestos. However, at least 20% of mesotheliomas in the United States are not associated with asbestos exposure, and only a minority of people exposed to high concentrations of asbestos develop mesothelioma. Thus, other carcinogens may induce mesothelioma in individuals not exposed to asbestos, and/or may render particular individuals more susceptible to the carcinogenic effect of asbestos. We investigated whether the expression of the SV40 large T-antigen (Tag) interferes with the normal expression of the tumor suppressor gene p53 in human mesotheliomas. We found that SV40 Tag retains its ability to bind and to inactivate p53, a cellular protein that when normally expressed plays an important role in suppressing tumor growth and in inducing sensitivity to therapy. Our findings do not establish a cause-and-effect relation, but indicate that the possibility that SV40 contributes to the development of human mesotheliomas should be carefully investigated.
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Affiliation(s)
- M Carbone
- Cardinal Bernardin Cancer Center, Department of Pathology, Loyola University Chicago, Maywood, Illinois 60153, USA
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Pompetti F, Rizzo P, Simon RM, Freidlin B, Mew DJ, Pass HI, Picci P, Levine AS, Carbone M. Oncogene alterations in primary, recurrent, and metastatic human bone tumors. J Cell Biochem 1996; 63:37-50. [PMID: 8891902 DOI: 10.1002/(sici)1097-4644(199610)63:1%3c37::aid-jcb3%3e3.0.co;2-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
We investigated the structure and the expression of various oncogenes in three of the most common human bone tumors-osteosarcoma (36 samples from 34 patients), giant cell tumor (10 patients), and chondrosarcoma (18 patients)-in an attempt to identify the genetic alterations associated with these malignancies. Alterations of RB and p53 were detected only in osteosarcomas. Alterations of c-myc, N-myc, and c-fos were detected in osteosarcomas and giant cell tumors. Ras alterations (H-ras, Ki-ras, N-ras) were rare. Chondrosarcomas did not contain any detectable genetic alterations. Our results suggest that alterations of c-myc, N-myc, and c-fos oncogenes occur in osteosarcomas, in addition to those previously described for the tumor suppressor genes RB and p53. Moreover, statistical analyses indicate that c-fos alterations occur more frequently in osteosarcoma patients with recurrent or metastatic disease.
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Affiliation(s)
- F Pompetti
- Department of Pathology, University of Chicago, Illinois 60637, USA
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47
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Pompetti F, Rizzo P, Simon RM, Freidlin B, Mew DJ, Pass HI, Picci P, Levine AS, Carbone M. Oncogene alterations in primary, recurrent, and metastatic human bone tumors. J Cell Biochem 1996. [DOI: 10.1002/(sici)1097-4644(199610)63:1<37::aid-jcb3>3.0.co;2-0] [Citation(s) in RCA: 77] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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48
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Abstract
The simian virus 40 (SV40) early gene product large T antigen promiscuously activates simple promoters containing a TATA box or initiator element and at least one upstream transcription factor-binding site. Previous studies have suggested that promoter activation requires that large T antigen interacts with both the basal transcription complex and the upstream-bound factor. This mechanism of activation is similar to that proposed for TBP-associated factors (TAFs). We report genetic and biochemical evidence suggesting that large T antigen performs a TAF-like function. In the ts13 cell line, large T antigen can rescue the temperature-sensitive (ts) defect in TAF(II)250. In contrast, neither E1a, small t antigen, nor mutants of large T antigen defective in transcriptional activation were able to rescue the ts defect. These data suggest that transcriptional activation by large T antigen is attributable, at least in part, to an ability to augment or replace a function of TAF(II)250. In addition, we show that large T antigen interacts in vitro with the Drosophila TAFs (dTAFs) dTAF(II)150, dTAF(II)110, and dTAF(II)40, as well as TBP. The relevance of these in vitro results was established in coimmunoprecipitation experiments using extracts of SV40-infected alpha3 cells that express an epitope-tagged TBP. Large T antigen was coimmunoprecipitated by antibodies to epitope-tagged TBP, endogenous TBP, hTAF(II)100, hTAF(II)130, and hTAF(II)250, under conditions where holo-TFIID would be precipitated. In addition, large T antigen copurified and coimmunoprecipitated with phosphocellulose-purified TFIID from SV40-infected alpha3 cells. Large T antigen also coprecipitated with anti-TBP antibody from extracts of ts13 cells expressing wild-type large T antigen under conditions where the ts defect in TAF(II)250 was rescued. In contrast, a transactivation mutant of large T antigen, which was unable to rescue the ts defect, failed to coprecipitate. We conclude from these data that transcriptional activation of many promoters by large T antigen results from its performing a TAF-like function in a complex with TFIID.
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Affiliation(s)
- B Damania
- Department of Microbiology, School of Medicine, University of Pennsylvania, Philadelphia, 19104-6142, USA
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49
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Chapter 29. The MAP Kinase Family: New “MAPs” for Signal Transduction Pathways and Novel Targets for Drug Discovery. ANNUAL REPORTS IN MEDICINAL CHEMISTRY 1996. [DOI: 10.1016/s0065-7743(08)60468-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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50
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Wang JL, Nistér M, Bongcam-Rudloff E, Pontén J, Westermark B. Suppression of platelet-derived growth factor alpha- and beta-receptor mRNA levels in human fibroblasts by SV40 T/t antigen. J Cell Physiol 1996; 166:12-21. [PMID: 8557760 DOI: 10.1002/(sici)1097-4652(199601)166:1<12::aid-jcp2>3.0.co;2-j] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
It is known that down-regulation of cell surface platelet-derived growth factor (PDGF) receptors accompanies transformation by SV40. In this work human embryonic lung fibroblasts were used as a model system to study the effects of SV 40 on PDGF receptor expression. It is shown that transformation by SV 40 early region leads to a total loss of PDGF alpha-receptor and partial loss of beta-receptor mRNA. Microinjection experiments revealed that receptor down-regulation was a primary effect, and not only secondary to transformation and clonal selection. Total loss of PDGF alpha-receptor expression requires both large T and small t, and down-regulation of the PDGF alpha-receptor occurs independently of p53 and Rb binding to large T.
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Affiliation(s)
- J L Wang
- Department of Pathology, University Hospital, Uppsala, Sweden
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