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Westbroek W, Nguyen M, Siebert M, Lindstrom T, Burnett RA, Aflaki E, Jung O, Tamargo R, Rodriguez-Gil JL, Acosta W, Hendrix A, Behre B, Tayebi N, Fujiwara H, Sidhu R, Renvoise B, Ginns EI, Dutra A, Pak E, Cramer C, Ory DS, Pavan WJ, Sidransky E. A new glucocerebrosidase-deficient neuronal cell model provides a tool to probe pathophysiology and therapeutics for Gaucher disease. Dis Model Mech 2016; 9:769-78. [PMID: 27482815 PMCID: PMC4958308 DOI: 10.1242/dmm.024588] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 05/12/2016] [Indexed: 12/30/2022] Open
Abstract
Glucocerebrosidase is a lysosomal hydrolase involved in the breakdown of glucosylceramide. Gaucher disease, a recessive lysosomal storage disorder, is caused by mutations in the gene GBA1. Dysfunctional glucocerebrosidase leads to accumulation of glucosylceramide and glycosylsphingosine in various cell types and organs. Mutations in GBA1 are also a common genetic risk factor for Parkinson disease and related synucleinopathies. In recent years, research on the pathophysiology of Gaucher disease, the molecular link between Gaucher and Parkinson disease, and novel therapeutics, have accelerated the need for relevant cell models with GBA1 mutations. Although induced pluripotent stem cells, primary rodent neurons, and transfected neuroblastoma cell lines have been used to study the effect of glucocerebrosidase deficiency on neuronal function, these models have limitations because of challenges in culturing and propagating the cells, low yield, and the introduction of exogenous mutant GBA1. To address some of these difficulties, we established a high yield, easy-to-culture mouse neuronal cell model with nearly complete glucocerebrosidase deficiency representative of Gaucher disease. We successfully immortalized cortical neurons from embryonic null allele gba−/− mice and the control littermate (gba+/+) by infecting differentiated primary cortical neurons in culture with an EF1α-SV40T lentivirus. Immortalized gba−/− neurons lack glucocerebrosidase protein and enzyme activity, and exhibit a dramatic increase in glucosylceramide and glucosylsphingosine accumulation, enlarged lysosomes, and an impaired ATP-dependent calcium-influx response; these phenotypical characteristics were absent in gba+/+ neurons. This null allele gba−/− mouse neuronal model provides a much-needed tool to study the pathophysiology of Gaucher disease and to evaluate new therapies. Summary: This work describes the generation of a novel immortalized glucocerebrosidase-deficient neuronal cell model with utility for pathophysiology research and therapeutic development in Gaucher disease.
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Affiliation(s)
- Wendy Westbroek
- Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Matthew Nguyen
- Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Marina Siebert
- Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA Postgraduate Program in Cellular and Molecular Biology, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 91501-970, Brazil
| | - Taylor Lindstrom
- Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Robert A Burnett
- Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Elma Aflaki
- Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Olive Jung
- Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Rafael Tamargo
- Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Jorge L Rodriguez-Gil
- Genomics, Development, and Disease Section, Genetic Disease Research Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | | | - An Hendrix
- Laboratory of Experimental Cancer Research, Department of Radiation Oncology and Experimental Cancer Research, Ghent University Hospital, Ghent 9000, Belgium
| | - Bahafta Behre
- Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Nahid Tayebi
- Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Hideji Fujiwara
- Washington University School of Medicine, St. Louis, MO 63110-1093, USA
| | - Rohini Sidhu
- Washington University School of Medicine, St. Louis, MO 63110-1093, USA
| | - Benoit Renvoise
- Cell Biology Section, Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Edward I Ginns
- Lysosomal Disorders Treatment and Research Program, Clinical Labs, University of Massachusetts Medical School, Worcester, MA 01655, USA
| | - Amalia Dutra
- Cytogenetics Core, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Evgenia Pak
- Cytogenetics Core, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | | | - Daniel S Ory
- Washington University School of Medicine, St. Louis, MO 63110-1093, USA
| | - William J Pavan
- Genomics, Development, and Disease Section, Genetic Disease Research Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Ellen Sidransky
- Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
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2
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LRPPRC mutation suppresses cytochrome oxidase activity by altering mitochondrial RNA transcript stability in a mouse model. Biochem J 2012; 441:275-83. [PMID: 21880015 DOI: 10.1042/bj20110985] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
LRPPRC (leucine-rich pentatricopeptide repeat-containing) has been shown to be essential for the maturation of COX (cytochrome c oxidase), possibly by stabilizing RNA transcripts of COXI, COXII and COXIII genes encoded in mtDNA (mitochondrial DNA). We established a mouse 'gene-trap' model using ES cells (embryonic stem cells) in which the C-terminus of LRPPRC has been replaced with a β-geo construct. Mice homozygous for this modification were found to be subject to embryonic lethality, with death before 12.5 dpc (days post-coitum). Biochemical analysis of MEFs (mouse embryonic fibroblasts) isolated from homozygous mutants showed a major decrease in COX activity, with slight reductions in other respiratory chain complexes with mtDNA encoded components. Constructs of LRPPRC containing different numbers of PPRs (pentatricopeptide repeats) were expressed as recombinant proteins and tested for their ability to bind to the COXI mRNA transcript. Full binding required the first 19 PPR motifs. A specific segment of COXI mRNA was identified as the binding target for LRPPRC, encoded by mouse mtDNA nucleotides 5961-6020. These data strongly suggest that LRPPRC is involved in the maturation of COX, and is involved in stabilizing of mitochondrial mRNAs encoding COX transcripts.
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3
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Maj MC, Tkachyova I, Patel P, Addis JB, Mackay N, Levandovskiy V, Lee J, Lang AE, Cameron JM, Robinson BH. Oxidative stress alters the regulatory control of p66Shc and Akt in PINK1 deficient cells. Biochem Biophys Res Commun 2010; 399:331-5. [PMID: 20637729 DOI: 10.1016/j.bbrc.2010.07.033] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2010] [Accepted: 07/12/2010] [Indexed: 02/08/2023]
Abstract
Mitochondrial dysfunction is involved in the underlying pathology of Parkinson's Disease (PD). PINK1 deficiency, which gives rise to familial early-onset PD, is associated with this dysfunction as well as increased oxidative stress. We have established primary fibroblast cell lines from two patients with PD who carry mutations in the PINK1 gene. The phosphorylation of Akt is abrogated in the presence of oxidative stressors in the complete absence of PINK1 suggesting enhanced apoptotic signalling. We have found an imbalance between the production of reactive oxygen species where the capacity of the cell to remove these toxins by anti-oxidative enzymes is greatly reduced. The expression levels of the anti-oxidant enzymes glutathione peroxidase-1, MnSOD, peroxiredoxin-3 and thioredoxin-2 were diminished. The p66(Shc) adaptor protein has recently been identified to become activated by oxidative stress by phosphorylation at residue Ser36 which then translocates to the mitochondrial inner membrane space. The phosphorylation of p66(Shc) at Ser36 is significantly increased in PINK1 deficient cell lines under normal tissue culture conditions, further still in the presence of compounds which elicit oxidative stress. The stable transfection of PINK1 in the fibroblasts which display the null phenotype ameliorates the hyper-phosphorylation of p66(Shc).
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Affiliation(s)
- Mary C Maj
- Metabolism Research Programme, Research Institute, The Hospital for Sick Children, 555 University Avenue, Toronto, ON, Canada M5G 1X8
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4
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A structure-guided mutational analysis of simian virus 40 large T antigen: identification of surface residues required for viral replication and transformation. J Virol 2009; 83:8781-8. [PMID: 19553311 DOI: 10.1128/jvi.00621-09] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Simian virus 40 large T antigen (TAg) transforms cells in culture and induces tumors in rodents. Genetic studies suggest that TAg interaction with the chaperone hsp70 and tumor suppressors pRb and p53 may not be sufficient to elicit complete transformation of cells. In order to identify additional cellular factors important for transformation, we designed mutations on the solvent-exposed surface of TAg. We hypothesized that surface residues would interact directly with cellular targets and that the mutation of these residues might disrupt this interaction without perturbing TAg's global structure. Using structural data, we identified 61 amino acids on the surface of TAg. Each surface amino acid was changed to an alanine. Furthermore, five patches containing clusters of charged amino acids on the surface of TAg were identified. Within these patches, we selectively mutated three to four charged amino acids and thus generated five mutants (patch mutants 1 to 5). We observed that while patch mutants 3 and 4 induced foci in REF52 cells, patch mutants 1 and 2 were deficient in focus formation. We determined that the patch 1 mutant is defective in p53 binding, thus explaining its defect in transformation. The patch 2 mutant can interact with the Rb family members and p53 like wild-type TAg but is unable to transform cells, suggesting that it is defective for action on an unknown cellular target essential for transformation. Our results suggest that the histone acetyltransferase CBP/p300 is one of the potential targets affected by the mutations in patch 2.
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5
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Ahuja D, Sáenz-Robles MT, Pipas JM. SV40 large T antigen targets multiple cellular pathways to elicit cellular transformation. Oncogene 2005; 24:7729-45. [PMID: 16299533 DOI: 10.1038/sj.onc.1209046] [Citation(s) in RCA: 399] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
DNA tumor viruses such as simian virus 40 (SV40) express dominant acting oncoproteins that exert their effects by associating with key cellular targets and altering the signaling pathways they govern. Thus, tumor viruses have proved to be invaluable aids in identifying proteins that participate in tumorigenesis, and in understanding the molecular basis for the transformed phenotype. The roles played by the SV40-encoded 708 amino-acid large T antigen (T antigen), and 174 amino acid small T antigen (t antigen), in transformation have been examined extensively. These studies have firmly established that large T antigen's inhibition of the p53 and Rb-family of tumor suppressors and small T antigen's action on the pp2A phosphatase, are important for SV40-induced transformation. It is not yet clear if the Rb, p53 and pp2A proteins are the only targets through which SV40 transforms cells, or whether additional targets await discovery. Finally, expression of SV40 oncoproteins in transgenic mice results in effects ranging from hyperplasia to invasive carcinoma accompanied by metastasis, depending on the tissue in which they are expressed. Thus, the consequences of SV40 action on these targets depend on the cell type being studied. The identification of additional cellular targets important for transformation, and understanding the molecular basis for the cell type-specific action of the viral T antigens are two important areas through which SV40 will continue to contribute to our understanding of cancer.
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Affiliation(s)
- Deepika Ahuja
- Department of Biological Sciences, University of Pittsburgh, PA 15260, USA
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6
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Zhang YH, Kooistra K, Pietersen A, Rohn JL, Noteborn MHM. Activation of the tumor-specific death effector apoptin and its kinase by an N-terminal determinant of simian virus 40 large T antigen. J Virol 2004; 78:9965-76. [PMID: 15331730 PMCID: PMC515021 DOI: 10.1128/jvi.78.18.9965-9976.2004] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Apoptin, a viral death protein derived from chicken anemia virus, displays a number of tumor-specific behaviors. In particular, apoptin is phosphorylated, translocates to the nucleus, and induces apoptosis specifically in tumor or transformed cells, whereas it is nonphosphorylated and remains primarily inactive in the cytoplasm of nontransformed normal cells. Here, we show that in normal cells apoptin can also be activated by the transient transforming signals conferred by ectopically expressed simian virus 40 (SV40) large T antigen (LT), which rapidly induces apoptin's phosphorylation, nuclear accumulation, and the ability to induce apoptosis. Further analyses with mutants of LT showed that the minimum domain capable of inducing all three of apoptin's tumor-specific properties resided in the N-terminal J domain, a sequence which is largely shared by SV40 small t antigen (st). Interestingly, the J domain in st, which lacks its own nuclear localization signal (NLS), required nuclear localization to activate apoptin. These results reveal the existence of a cellular pathway shared by conditions of transient transformation and the stable cancerous or precancerous state, and they support a model whereby a transient transforming signal confers on apoptin both the upstream activity of phosphorylation and the downstream activity of nuclear accumulation and apoptosis induction. Such a pathway may reflect a general lesion contributing to human cancers.
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7
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Soloff RS, Katayama C, Lin MY, Feramisco JR, Hedrick SM. Targeted deletion of protein kinase C lambda reveals a distribution of functions between the two atypical protein kinase C isoforms. THE JOURNAL OF IMMUNOLOGY 2004; 173:3250-60. [PMID: 15322187 DOI: 10.4049/jimmunol.173.5.3250] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Protein kinase C lambda (PKClambda) is an atypical member of the PKC family of serine/threonine kinases with high similarity to the other atypical family member, PKCzeta. This similarity has made it difficult to determine specific roles for the individual atypical isoforms. Both PKClambda and PKCzeta have been implicated in the signal transduction, initiated by mediators of innate immunity, that culminates in the activation of MAPKs and NF-kappaB. In addition, work from invertebrates shows that atypical PKC molecules play a role in embryo development and cell polarity. To determine the unique functions of PKClambda, mice deficient for PKClambda were generated by gene targeting. The ablation of PKClambda results in abnormalities early in gestation with lethality occurring by embryonic day 9. The role of PKClambda in cytokine-mediated cellular activation was studied by making mouse chimeras from PKClambda-deficient embryonic stem cells and C57BL/6 or Rag2-deficient blastocysts. Cell lines derived from these chimeric animals were then used to dissect the role of PKClambda in cytokine responses. Although the mutant cells exhibited alterations in actin stress fibers and focal adhesions, no other phenotypic differences were noted. Contrary to experiments using dominant interfering forms of PKClambda, mutant cells responded normally to TNF, serum, epidermal growth factor, IL-1, and LPS. In addition, no abnormalities were found in T cell development or T cell activation. These data establish that, in vertebrates, the two disparate functions of atypical PKC molecules have been segregated such that PKCzeta mediates signal transduction of the innate immune system and PKClambda is essential for early embryogenesis.
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Affiliation(s)
- Rachel S Soloff
- Division of Biological Sciences, Moores University of California at San Diego Cancer Center, La Jolla 92093, USA
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8
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Ali SH, Kasper JS, Arai T, DeCaprio JA. Cul7/p185/p193 binding to simian virus 40 large T antigen has a role in cellular transformation. J Virol 2004; 78:2749-57. [PMID: 14990695 PMCID: PMC353757 DOI: 10.1128/jvi.78.6.2749-2757.2004] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2003] [Accepted: 11/10/2003] [Indexed: 01/19/2023] Open
Abstract
Simian virus 40 large T antigen (TAg) is a viral oncoprotein that can promote cellular transformation. TAg's transforming activity results in part by binding and inactivating key tumor suppressors, including p53 and the retinoblastoma protein (pRb). We have identified a TAg-associated 185-kDa protein that has significant homology to the cullin family of E3 ubiquitin ligases. TAg binds to an SCF-like complex that contains p185/Cul7, Rbx1, and the F box protein Fbw6. This SCF-like complex binds to an N-terminal region of TAg. Several p185/Cul7-binding-deficient mutants of TAg were generated that retained binding to pRb and p53 and were capable of overcoming Rb-mediated repression of E2F transcription. Despite binding to pRb and p53, these p185/Cul7-binding-defective mutants of TAg were unable to transform primary mouse embryo fibroblasts. Cells expressing p185/Cul7-binding-defective mutants of TAg were unable to grow to high density or grow in an anchorage-independent manner as determined by growth in soft agar. Considering the significance of other TAg-interacting proteins in regulation of the cell cycle, p185/Cul7 may also regulate an important growth control pathway.
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Affiliation(s)
- Syed Hamid Ali
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, USA
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9
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Cole SL, Tevethia MJ. Simian virus 40 large T antigen and two independent T-antigen segments sensitize cells to apoptosis following genotoxic damage. J Virol 2002; 76:8420-32. [PMID: 12134045 PMCID: PMC155145 DOI: 10.1128/jvi.76.16.8420-8432.2002] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The simian virus 40 (SV40) large tumor (T) antigen is sufficient to transform cells in cultures and induce tumors in experimental animals. Transformation of primary cells in cultures requires both overcoming growth arrest by stimulating the cell cycle and blocking cell death activities presumably activated by oncogene-mediated hyperproliferation signals. The study presented here examined the ability of specific regions and activities of T antigen to modulate apoptosis in cells treated with the genotoxic agent 5-fluorouracil (5-FU). The results showed that the expression of full-length T antigen rendered rat embryo fibroblasts (REF) sensitive to 5-FU-induced apoptosis. Thus, neither the p53-binding region nor the Bcl-2 homology region of T antigen was sufficient to prevent cell death induced by the DNA-damaging agent. T-antigen-mediated sensitization occurred independently of retinoblastoma protein or p53 and p300 binding. An N-terminal segment containing the first 127 T-antigen amino acids (T1-127) was sufficient to sensitize cells. A C-terminal segment consisting of T-antigen amino acids 251 to 708 (T251-708) also sensitized cells to 5-FU-induced apoptosis. This sensitization did not occur when T251-708 was targeted to the nucleus by inclusion of the SV40 nuclear localization signal. The introduction of mutations into the T-antigen J domain resulted in mutation-specific and variable inhibition of apoptosis. This result suggested that either the structural or the functional integrity of the J domain is required to sensitize cells to apoptosis. Treatment of REF or REF expressing full-length T antigen, an N-terminal segment, or T251-708 resulted in increased expression of the p53-responsive MDM2 gene; apoptosis occurred through a p53-dependent pathway, as p53-null cells expressing these T antigens were resistant to 5-FU-induced apoptosis. Possible mechanisms involved in sensitizing cells to a p53-dependent apoptosis pathway in spite of the ability of T antigen to bind and inactivate the transcriptional transactivating activity of p53 are discussed.
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Affiliation(s)
- Sara L Cole
- Department of Microbiology and Immunology, College of Medicine, Pennsylvania State University, Hershey 17033, USA
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10
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Köksoy S, Phipps AJ, Hayes KA, Mathes LE. SV40 Immortalization of feline fibroblasts as targets for MHC-restricted cytotoxic T-cell assays. Vet Immunol Immunopathol 2001; 79:285-95. [PMID: 11389962 DOI: 10.1016/s0165-2427(01)00272-0] [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: 11/16/2022]
Abstract
CTL assays in outbred cats have been difficult to perform because of a lack of a good source of syngeneic target cell. Primary fibroblasts from cats are widely used as target cells for MHC-restricted cytotoxic T-cell (CTL) assays, but their limited life-spans of 8-10 culture passages can be problematic for longitudinal studies. To circumvent the life-span limitations of primary fibroblast cultures, we developed a procedure for immortalizing feline primary fibroblast cells by transfection with a molecular clone of simian virus 40 (SV40). Fibroblast cultures from skin biopsies of 28 cats were immortalized using this procedure and have been passaged for longer than 6 months without showing any phenotypic difference from the original primary cells. Non-SV40 transfected feline fibroblasts from a selection of animals in the same group survived for only 6-8 weeks before reaching senescence. The immortalized fibroblasts expressed SV40 T-antigen and Class I MHC protein, and were successfully used as target cells in 51Cr release CTL assays in feline immunodeficiency virus (FIV)-infected cats and in vitro stimulated allogeneic T-cell cultures.
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MESH Headings
- Animals
- Antigens, Polyomavirus Transforming/biosynthesis
- Antigens, Polyomavirus Transforming/genetics
- Antigens, Polyomavirus Transforming/immunology
- Cats/immunology
- Cell Transformation, Viral/genetics
- Cell Transformation, Viral/immunology
- Cellular Senescence/physiology
- Chromium Radioisotopes
- Cytotoxicity Tests, Immunologic/methods
- Cytotoxicity Tests, Immunologic/veterinary
- Epitopes, T-Lymphocyte/immunology
- Fibroblasts/cytology
- Fibroblasts/immunology
- Fluorescent Antibody Technique/veterinary
- Histocompatibility Antigens Class I/biosynthesis
- Histocompatibility Antigens Class I/genetics
- Histocompatibility Antigens Class II/biosynthesis
- Histocompatibility Antigens Class II/genetics
- Immunodeficiency Virus, Feline/isolation & purification
- Isoantigens/immunology
- Simian virus 40/immunology
- Specific Pathogen-Free Organisms
- T-Lymphocytes, Cytotoxic/immunology
- Transfection/veterinary
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Affiliation(s)
- S Köksoy
- Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, 1925 Coffey Rd., Columbus, OH 43210,USA
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11
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Abstract
The SV40 large T-antigen (TAg) has proven useful in studying pathways involved with cell division and tissue homeostasis. TAg disrupts the normal action of tumor suppressors pRb and p53. It is unclear whether T-antigen inhibition of p53 and pRb is sufficient for oncogenic transformation or if additional T-antigen activities are required. To pursue this question, cell lines were generated that coexpress an amino-terminal fragment of T-antigen (TAgN136), which has been shown to be sufficient to block pRb function, together with a dominant-negative p53. Neither focus formation nor saturation density was enhanced by coexpression of the dominant-negative p53 molecule, p53DD, along with TAgN136. Furthermore, a full-length TAg mutant incapable of binding p53 was capable of relieving contact inhibition, a hallmark of transformation. These results suggest the presence of a novel transforming activity in addition to the binding and inactivation of p53, requiring TAg amino acids 137 to 708.
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Affiliation(s)
- K F Sachsenmeier
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA
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12
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Ford KG, Darling D, Souberbielle B, Farzaneh F. Protein transduction: a new tool for the study of cellular ageing and senescence. Mech Ageing Dev 2000; 121:113-21. [PMID: 11164465 DOI: 10.1016/s0047-6374(00)00202-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Protein transduction can be described as the direct uptake by the cell of exogenous proteins/peptides or protein/peptide:chemical complexes, as a result of a specific property of the protein/peptide component. In this review, the three most widely studied protein transducing activities are described, with particular emphasis on the TAT protein transduction domain. Current progress in protein transduction technology suggests the potential development of a variety of molecular and cell biology tools that will enable researchers to by-pass conventional genetic routes for modulating the cells' biological activity, thus negating many of the problems associated with genetic intervention. The potential application of this class of molecule in the development of tools for the study of senescent populations is discussed.
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Affiliation(s)
- K G Ford
- Department of Molecular Medicine, Guy's, King's and St. Thomas' School of Medicine and Dentistry, The Rayne Institute, 123 Coldharbour Lane, London SE5 9NU, UK.
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13
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Gjoerup O, Chao H, DeCaprio JA, Roberts TM. pRB-dependent, J domain-independent function of simian virus 40 large T antigen in override of p53 growth suppression. J Virol 2000; 74:864-74. [PMID: 10623749 PMCID: PMC111607 DOI: 10.1128/jvi.74.2.864-874.2000] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/1999] [Accepted: 10/20/1999] [Indexed: 01/05/2023] Open
Abstract
Simian virus 40 (SV40) large T antigen (LT) can immortalize and transform many cell types. These activities are attributed in large part to the binding and functional inactivation by LT of two major tumor suppressors: p53 and the retinoblastoma protein, pRB. Most effects of LT on pRB have been shown to additionally require an intact J domain, which mediates binding to Hsc70. We show here that the J domain is not required for p53 override in full-length LT. Although LT binds p53, it was shown previously that overcoming a p53-induced cell cycle arrest requires binding to pRB family members (R. S. Quartin et al., J. Virol. 68:1334-1341). We demonstrate that an LT mutant defective for pRB family member binding (K1) can be complemented for efficient override of p53 arrest by a construct encoding the first 135 amino acids of LT with a J domain-inactivating mutation, H42Q. Hence, complementation does not require the J domain, and pRB binding by LT is important for more than dissociating pRB-E2F complexes, which is J dependent. In accordance with this notion, LT alleviates pRB small-pocket-mediated transcriptional repression independently of the J domain. The LT K1 mutant can also be complemented for p53 override by small t antigen (st) in a manner independent of its J domain. Our observations underscore the importance of multiple SV40 functions, two in LT and one in st, that act cooperatively to counteract p53 growth suppression.
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Affiliation(s)
- O Gjoerup
- Department of Cancer Biology, Dana-Farber Cancer Institute and Harvard Medical School, Boston, Massachusetts 02115, USA
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14
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Powell AJ, Darmon AJ, Gonos ES, Lam EW, Peden KW, Jat PS. Different functions are required for initiation and maintenance of immortalization of rat embryo fibroblasts by SV40 large T antigen. Oncogene 1999; 18:7343-50. [PMID: 10602490 DOI: 10.1038/sj.onc.1203154] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We have used two different, but complementary assays to characterize functions of SV40 T antigen that are necessary for its ability to immortalize rat embryo fibroblasts. In accordance with previous work, we found that several functions were required. These include activities that map to the p53 binding domain and the amino terminal 176 amino acids which contain the J domain as well as the CR1 and CR2 domain required for binding and sequestering the RB family of pocket proteins. Moreover, we found that even though activities dependent only upon the amino terminus were sufficient for immortalization they were unable to maintain it. This suggests that immortalization by these amino terminal functions requires either additional events or immortalization of a subset of cells within the heterogeneous rat embryo fibroblast population. We further found that an activity dependent upon amino acids 17 - 27 which remove a portion of the CR1 domain and the predicted alpha-1 helix of the J domain was not necessary to maintain growth but was required for direct immortalization suggesting that at least one of the functions required initially was not required to maintain the immortal state. This represents the first demonstration that some of the functions required for maintenance of the immortal state differ from those required for initiation of immortalization.
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Affiliation(s)
- A J Powell
- Ludwig Institute for Cancer Research, Royal Free and University College School of Medicine, Courtauld Building, 91 Riding House Street, London W1P 8BT, UK
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15
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Affiliation(s)
- H L Ozer
- Department of Microbiology and Molecular Genetics UMD-New Jersey Medical School 07103-2714, USA
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Cavender JF, Mummert C, Tevethia MJ. Transactivation of a ribosomal gene by simian virus 40 large-T antigen requires at least three activities of the protein. J Virol 1999; 73:214-24. [PMID: 9847324 PMCID: PMC103825 DOI: 10.1128/jvi.73.1.214-224.1999] [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: 11/20/2022] Open
Abstract
Simian virus 40 large-T antigen transactivates the ribosomal genes which are transcribed by RNA polymerase (pol I), as well as genes that are dependent on either pol II or pol III. This report identifies regions and activities of T antigen that are required to transactivate a pol I-dependent rat ribosomal gene promoter. By using the rat ribosomal gene (rDNA) promoter linked to a chloramphenicol acetyltransferase gene, we show that at least three separable T-antigen regions are necessary to achieve wild-type levels of transactivation of rDNA in transiently transfected monkey cells. One activity depends on the region of T antigen shared with small-t antigen (T/t common region). A second activity maps to amino acids 109 to 626 and is highly sensitive to mutational inactivation. Complementation analyses suggest that at least one activity in this region is independent of and must be in cis with the activity within the T/t common region. In addition, a functional nuclear localization signal is required for maximal T-antigen-mediated transactivation of rat rDNA. The three activities work in concert to override cellular species-specific controls and transactivate the rat ribosomal gene promoter. Finally, we provide evidence that although the tumor suppressor protein Rb has been shown to repress a pol I-dependent promoter, transactivation of the rat rDNA promoter does not depend on T antigen's ability to bind the tumor suppressor product Rb.
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Affiliation(s)
- J F Cavender
- Department of Biology, Elizabethtown College, Elizabethtown, Pennsylvania 17022, USA.
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17
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Abstract
Human diploid cells have a limited life span, ending in replicative senescence, in contrast to cell lines derived from tumors, which show an indefinite life span and are immortal, suggesting that replicative senescence is a tumor suppression mechanism. We have utilized introduction of SV40 sequences to develop matched sets of nonimmortal and immortal cell lines to help dissect the mechanism of immortalization and have found that it has multiple facets, involving both SV40-dependent and -independent aspects. These studies have led to the identification of a novel growth suppressor gene (SEN6) as well as providing a model system for the study of cellular aging, apoptosis, and telomere stabilization among other things. It is anticipated that SV40-transformed cells will continue to provide a very useful experimental system leading to insights into the behavior of cells with altered expression of oncogenes and growth suppressor gene products.
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Affiliation(s)
- K K Jha
- Department of Microbiology and Molecular Genetics, UMDNJ-New Jersey Medical School, Newark, New Jersey, 07103-2714, USA
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18
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Sedivy JM. Can ends justify the means?: telomeres and the mechanisms of replicative senescence and immortalization in mammalian cells. Proc Natl Acad Sci U S A 1998; 95:9078-81. [PMID: 9689036 PMCID: PMC33878 DOI: 10.1073/pnas.95.16.9078] [Citation(s) in RCA: 141] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Finite replicative lifespan, or senescence, of mammalian cells in culture is a phenomenon that has generated much curiosity since its description. The obvious significance of senescence to organismal aging and the development of cancer has engendered a long-lasting and lively debate about its mechanisms. Recent discoveries concerning the phenotypes of telomerase knockout mice, the consequences of telomerase reexpression in somatic cells, and genes that regulate senescence have provided striking molecular insights but also have uncovered important new questions. The objective of this review is to reconcile old observations with new molecular details and to focus attention on the key remaining puzzles.
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Affiliation(s)
- J M Sedivy
- Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, RI 02912, USA.
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