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Chameettachal A, Mustafa F, Rizvi TA. Understanding Retroviral Life Cycle and its Genomic RNA Packaging. J Mol Biol 2023; 435:167924. [PMID: 36535429 DOI: 10.1016/j.jmb.2022.167924] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Revised: 12/12/2022] [Accepted: 12/12/2022] [Indexed: 12/23/2022]
Abstract
Members of the family Retroviridae are important animal and human pathogens. Being obligate parasites, their replication involves a series of steps during which the virus hijacks the cellular machinery. Additionally, many of the steps of retrovirus replication are unique among viruses, including reverse transcription, integration, and specific packaging of their genomic RNA (gRNA) as a dimer. Progress in retrovirology has helped identify several molecular mechanisms involved in each of these steps, but many are still unknown or remain controversial. This review summarizes our present understanding of the molecular mechanisms involved in various stages of retrovirus replication. Furthermore, it provides a comprehensive analysis of our current understanding of how different retroviruses package their gRNA into the assembling virions. RNA packaging in retroviruses holds a special interest because of the uniqueness of packaging a dimeric genome. Dimerization and packaging are highly regulated and interlinked events, critical for the virus to decide whether its unspliced RNA will be packaged as a "genome" or translated into proteins. Finally, some of the outstanding areas of exploration in the field of RNA packaging are highlighted, such as the role of epitranscriptomics, heterogeneity of transcript start sites, and the necessity of functional polyA sequences. An in-depth knowledge of mechanisms that interplay between viral and cellular factors during virus replication is critical in understanding not only the virus life cycle, but also its pathogenesis, and development of new antiretroviral compounds, vaccines, as well as retroviral-based vectors for human gene therapy.
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Affiliation(s)
- Akhil Chameettachal
- Department of Microbiology & Immunology, College of Medicine and Health Sciences (CMHS), United Arab Emirates University, Al Ain, United Arab Emirates. https://twitter.com/chameettachal
| | - Farah Mustafa
- Department of Biochemistry, College of Medicine and Health Sciences (CMHS), United Arab Emirates University, Al Ain, United Arab Emirates; Zayed bin Sultan Center for Health Sciences (ZCHS), United Arab Emirates University, Al Ain, United Arab Emirates.
| | - Tahir A Rizvi
- Department of Microbiology & Immunology, College of Medicine and Health Sciences (CMHS), United Arab Emirates University, Al Ain, United Arab Emirates; Zayed bin Sultan Center for Health Sciences (ZCHS), United Arab Emirates University, Al Ain, United Arab Emirates.
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2
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Bral CM, Steinke JW, Kang CJ, Peterson DO. RNA polymerase II transcription complex assembly in nuclear extracts. Gene Expr 2018; 7:191-204. [PMID: 9840811 PMCID: PMC6151951] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
In vitro transcription systems based on nuclear extracts of eukaryotic cells continue to be valuable experimental systems for assessing function of promoter sequences and defining new activities involved in transcription complex assembly and activity, but many aspects of such systems have not been experimentally examined. Here, transcription complex assembly on the promoter from the long terminal repeat of mouse mammary tumor virus was assessed in vitro with a transcription system derived from nuclear extracts of cultured HeLa cells. The extent of preinitiation complex assembly on the promoter was limited by the availability of template, even though only a small fraction of the template present in the assays participated in transcription. These results support a model for transcription complex assembly in which template DNA has two alternative fates, one leading to assembly of a functional transcription complex, and another that leads to irreversible template inactivation. The observed kinetics of assembly reflects loss of template by both pathways and is dominated by a relatively rapid rate of template inactivation. Supplementing nuclear extracts with purified TATA binding protein increased the extent as well as the apparent rate of assembly. Both effects can be explained by a TATA binding protein-dependent increase in the rate of assembly that leads to altered partitioning of template between competing pathways.
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Affiliation(s)
- Christopher M. Bral
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128
| | - John W. Steinke
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128
| | - Chang-Joong Kang
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128
| | - David O. Peterson
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128
- Address correspondence to David O. Peterson. Tel: (409) 845-0953; Fax: (409) 845-9274; E-mail:
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3
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Kopytek SJ, Peterson DO. ATP-mediated activation of RNA polymerase II transcription complexes. Gene Expr 2018; 7:75-86. [PMID: 9699480 PMCID: PMC6190198] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Transcription initiation by RNA polymerase II is a complex, multistep process that minimally involves transcription complex assembly, open complex formation, and promoter clearance. Hydrolysis of the beta--gamma phosphoanhydride bond of ATP has previously been shown to be required for open complex formation, as well as for the phosphorylation of the carboxy-terminal domain of the largest subunit of RNA polymerase II. The observation that ATP-dependent activation of transcription complexes can be blocked by ATP analogues that contain nonhydrolyzable beta--gamma phosphoanhydride bonds (such as ATPgammaS) was exploited to develop a functional kinetic assay for ATP-activated transcription complexes. Activated complexes on the promoter present in the long terminal repeat of the proviral DNA of mouse mammary tumor virus were defined as those that could productively initiate transcription in the presence of excess ATPgammaS. Activation is dependent on treatment of assembled preinitiation complexes with ATP (or dATP) prior to addition of ATPgammaS. At least 15-35% of the total number of preinitiation complexes present become activated within 2 min in the presence of (d)ATP, and activation appears to be rapidly reversible. The time course of formation of activated complexes in the presence of dATP is characterized by two kinetic phases: a rapid formation followed by a relatively slow decay. Activated complexes were estimated to form with a half-time of less than 1 min.
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Affiliation(s)
- Stephan J. Kopytek
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128
| | - David O. Peterson
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128
- Address correspondence to David O. Peterson. Tel: (409) 845-0953; Fax: (409) 845-9274; E-mail:
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4
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Akhlaq S, Panicker NG, Philip PS, Ali LM, Dudley JP, Rizvi TA, Mustafa F. A cis-Acting Element Downstream of the Mouse Mammary Tumor Virus Major Splice Donor Critical for RNA Elongation and Stability. J Mol Biol 2018; 430:4307-4324. [PMID: 30179605 DOI: 10.1016/j.jmb.2018.08.025] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2018] [Revised: 08/28/2018] [Accepted: 08/28/2018] [Indexed: 12/11/2022]
Abstract
BACKGROUND The mouse mammary tumor virus (MMTV) encodes a functional signal peptide, a cleavage product of envelope and Rem proteins. Signal peptide interacts with a 3' cis-acting RNA element, the Rem-responsive element (RmRE), to facilitate expression of both unspliced genomic (gRNA) and spliced mRNAs. An additional RmRE has been proposed at the 5' end of the genome, facilitating nuclear export of the unspliced gRNA, whereas the 3' RmRE could facilitate translation of all other mRNAs, including gRNA. RESULTS To address this hypothesis, a series of mutations were introduced into a 24-nt region found exclusively in the unspliced gRNA. Mutant clones using MMTV or human cytomegalovirus promoters were tested in both transient and stable transfections to determine their effect on gRNA nuclear export, stability, and translation. Nuclear export of the gRNA was affected only in a small mutant subset in stably transfected Jurkat T cells. Quantitative real-time RT-PCR of actinomycin D-treated cells expressing MMTV revealed that multiple mutants were severely compromised for RNA expression and stability. Both genomic and spliced nuclear RNAs were reduced, leading to abrogation of Gag and Env protein expressed from unspliced and spliced mRNAs, respectively. RT-PCRs with multiple primer pairs indicated failure to elongate genomic MMTV transcripts beyond ~500 nt compared to the wild type in a cell line-dependent manner. CONCLUSIONS MMTV contains a novel cis-acting element downstream of the major splice donor critical for facilitating MMTV gRNA elongation and stability. Presence of a mirror repeat within the element may represent important viral/host factor binding site(s) within MMTV gRNA.
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Affiliation(s)
- Shaima Akhlaq
- Department of Biochemistry, College of Medicine and Health Sciences, UAE University, Tawam Hospital Complex, P.O. Box 17666, Al Ain, United Arab Emirates.
| | - Neena G Panicker
- Department of Biochemistry, College of Medicine and Health Sciences, UAE University, Tawam Hospital Complex, P.O. Box 17666, Al Ain, United Arab Emirates.
| | - Pretty S Philip
- Department of Microbiology & Immunology, College of Medicine and Health Sciences, UAE University, Tawam Hospital Complex, P.O. Box 17666, Al Ain, United Arab Emirates.
| | - Lizna M Ali
- Department of Microbiology & Immunology, College of Medicine and Health Sciences, UAE University, Tawam Hospital Complex, P.O. Box 17666, Al Ain, United Arab Emirates.
| | - Jaquelin P Dudley
- LaMontagne Center for Infectious Diseases, The University of Texas at Austin, 100 East 24th Street, NHB 2.616, Austin, TX 78712, USA.
| | - Tahir A Rizvi
- Department of Microbiology & Immunology, College of Medicine and Health Sciences, UAE University, Tawam Hospital Complex, P.O. Box 17666, Al Ain, United Arab Emirates.
| | - Farah Mustafa
- Department of Biochemistry, College of Medicine and Health Sciences, UAE University, Tawam Hospital Complex, P.O. Box 17666, Al Ain, United Arab Emirates.
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Castillo-Lluva S, Hontecillas-Prieto L, Blanco-Gómez A, Del Mar Sáez-Freire M, García-Cenador B, García-Criado J, Pérez-Andrés M, Orfao A, Cañamero M, Mao JH, Gridley T, Castellanos-Martín A, Pérez-Losada J. A new role of SNAI2 in postlactational involution of the mammary gland links it to luminal breast cancer development. Oncogene 2015; 34:4777-90. [PMID: 26096931 PMCID: PMC4560637 DOI: 10.1038/onc.2015.224] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Revised: 04/25/2015] [Accepted: 05/16/2015] [Indexed: 12/30/2022]
Abstract
Breast cancer is a major cause of mortality in women. The transcription factor SNAI2 has been implicated in the pathogenesis of several types of cancer, including breast cancer of basal origin. Here we show that SNAI2 is also important in the development of breast cancer of luminal origin in MMTV-ErbB2 mice. SNAI2 deficiency leads to longer latency and fewer luminal tumors, both of these being characteristics of pretumoral origin. These effects were associated with reduced proliferation and a decreased ability to generate mammospheres in normal mammary glands. However, the capacity to metastasize was not modified. Under conditions of increased ERBB2 oncogenic activity after pregnancy plus SNAI2 deficiency, both pretumoral defects-latency and tumor load-were compensated. However, the incidence of lung metastases was dramatically reduced. Furthermore, SNAI2 was required for proper postlactational involution of the breast. At 3 days post lactational involution, the mammary glands of Snai2-deficient mice exhibited lower levels of pSTAT3 and higher levels of pAKT1, resulting in decreased apoptosis. Abundant noninvoluted ducts were still present at 30 days post lactation, with a greater number of residual ERBB2+ cells. These results suggest that this defect in involution leads to an increase in the number of susceptible target cells for transformation, to the recovery of the capacity to generate mammospheres and to an increase in the number of tumors. Our work demonstrates the participation of SNAI2 in the pathogenesis of luminal breast cancer, and reveals an unexpected connection between the processes of postlactational involution and breast tumorigenesis in Snai2-null mutant mice.
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Affiliation(s)
- S Castillo-Lluva
- Instituto de Biología Molecular y Celular del Cáncer (IBMCC), Universidad de Salamanca/CSIC, Salamanca, Spain
- Instituto de Investigación Biomédica de Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
| | - L Hontecillas-Prieto
- Instituto de Biología Molecular y Celular del Cáncer (IBMCC), Universidad de Salamanca/CSIC, Salamanca, Spain
- Instituto de Investigación Biomédica de Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
| | - A Blanco-Gómez
- Instituto de Biología Molecular y Celular del Cáncer (IBMCC), Universidad de Salamanca/CSIC, Salamanca, Spain
- Instituto de Investigación Biomédica de Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
| | - M Del Mar Sáez-Freire
- Instituto de Biología Molecular y Celular del Cáncer (IBMCC), Universidad de Salamanca/CSIC, Salamanca, Spain
- Instituto de Investigación Biomédica de Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
| | - B García-Cenador
- Instituto de Investigación Biomédica de Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
- Departamento de Cirugía, Universidad de Salamanca, Salamanca, Spain
| | - J García-Criado
- Instituto de Investigación Biomédica de Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
- Departamento de Cirugía, Universidad de Salamanca, Salamanca, Spain
| | - M Pérez-Andrés
- Instituto de Biología Molecular y Celular del Cáncer (IBMCC), Universidad de Salamanca/CSIC, Salamanca, Spain
- Instituto de Investigación Biomédica de Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
- Unidad de Citometría de flujo, Universidad de Salamanca, IBSAL, Salamanca, Spain
| | - A Orfao
- Instituto de Biología Molecular y Celular del Cáncer (IBMCC), Universidad de Salamanca/CSIC, Salamanca, Spain
- Instituto de Investigación Biomédica de Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
- Unidad de Citometría de flujo, Universidad de Salamanca, IBSAL, Salamanca, Spain
| | - M Cañamero
- Centro Nacional de Investigaciones Oncológicas (CNIO), Madrid, Spain
| | - J H Mao
- Life Sciences Division, Lawrence Berkeley National Laboratory (LBNL), University of California, Berkeley, Berkeley, CA, USA
| | - T Gridley
- Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough, ME, USA
| | - A Castellanos-Martín
- Instituto de Biología Molecular y Celular del Cáncer (IBMCC), Universidad de Salamanca/CSIC, Salamanca, Spain
- Instituto de Investigación Biomédica de Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
| | - J Pérez-Losada
- Instituto de Biología Molecular y Celular del Cáncer (IBMCC), Universidad de Salamanca/CSIC, Salamanca, Spain
- Instituto de Investigación Biomédica de Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
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6
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Determination of immunity T-cell link state and content of cancer stem cells as criterion to estimate efficiency of preventive breast cancer therapy with cryopreserved fetal liver cells. ACTA ACUST UNITED AC 2014. [DOI: 10.15407/cryo24.03.238] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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7
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Abstract
The ability to externally regulate the expression or function of a gene product has proven to be a powerful tool in the study of proteins and disease in vitro, and more recently in transgenic animal models. The transfer of these technologies to regulate a therapeutic, adoptively transferred gene product in a clinical setting may provide a means to exert additional control over a large variety of therapies for many diseases, leading to increased safety and effectiveness. This could be applied to any biological therapy, including gene therapy, viral therapies, cellular therapies (such as immune cell therapies, stem cell therapies and bone marrow transplant), some vaccines and even organ transplant. A variety of systems have been used in a basic research setting to conditionally regulate the function of a protein, including control of transcription and mRNA stability, and the use of protein inhibitors. However, most of these have disadvantages for medical use, where a simple, specific, tunable, reversible and broadly applicable means to regulate protein function is needed. Recent advances in controlling the stability or function of proteins through the interaction of small-molecule effectors and fusion domains on the protein have raised the possibility that direct and highly specific external control of therapeutic protein function in humans will be feasible.
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Morabito JE, Trott JF, Korz DM, Fairfield HE, Buck SH, Hovey RC. A 5' distal palindrome within the mouse mammary tumor virus-long terminal repeat recruits a mammary gland-specific complex and is required for a synergistic response to progesterone plus prolactin. J Mol Endocrinol 2008; 41:75-90. [PMID: 18524869 PMCID: PMC8959018 DOI: 10.1677/jme-08-0027] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Progesterone (P) and prolactin (PRL) fulfill crucial roles during growth and differentiation of the mammary epithelium, and each has been implicated in the pathogenesis of mammary cancer. We previously identified that these hormones synergistically stimulate the proliferation of mouse mammary epithelial cells in vivo, although the mechanism(s) underlying their cooperative effect are unknown. We now report a novel pathway by which P and PRL synergize to activate transcription from the long terminal repeat (LTR) of the mouse mammary tumor virus-LTR (MMTV-LTR) in T47D breast cancer cells. Using serial 5' and 3' deletions of the MMTV-LTR, in addition to selective mutations, we identified that a previously uncharacterized inverted palindrome on the distal enhancer (-941/-930), in addition to a signal transducer and activator of transcription 5 site, was essential for the synergistic activation of transcription by P and PRL. Notably, hormone synergy occurred via a mechanism that was independent of the P receptor DNA-binding elements found in the proximal MMTV-LTR hormone-response element. The palindrome specifically recruited a protein complex (herein termed mammary gland-specific complex) that was almost exclusive to normal and cancerous mammary cells. The synergy between P and PRL occurred via a Janus kinase 2 and c-Src/Fyn-dependent signaling cascade downstream of P and PRL receptors. Combined, our data outline a novel pathway in T47D cells that may facilitate the action(s) of P and PRL during mammary development and breast cancer.
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Affiliation(s)
- Joseph E Morabito
- Lactation and Mammary Gland Biology Group College of Medicine, The University of Vermont, Burlington, Vermont 05405, USA
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9
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Abstract
There are well-established risk factors for breast cancer, most of which relate to estrogens and growth hormones in females. These include early-age menarche, late-age menopause, postmenopausal obesity and use of hormone therapy. However, these factors do not account for the sixfold difference in breast cancer incidence and mortality between countries and the fact that these differences dramatically lessen after migration; nor do they account for male breast cancer. Accordingly, hormone-responsive viruses have become major suspects as etiological agents for human breast cancer. Human papillomaviruses, mouse mammary tumor virus and Epstein-Barr virus are the prime candidate viruses as causes of human breast cancer. Human papillomaviruses and the mouse mammary tumor virus have hormone responsive elements that appear to be associated with enhanced replication of these viruses in the presence of corticosteroid and other hormones. This biological phenomenon is particularly relevant because of the hormone dependence of breast cancer. Viral genetic material for each of these candidate viruses has been identified by polymerase chain reaction in breast tumors but rarely in normal breast tissue controls. Pooled data from controlled studies show substantial odds ratios for the presence of viral genetic material in breast tumors compared with normal controls. These and additional data provide substantial, but not conclusive, evidence that human papillomavirus, the mouse mammary tumor virus and Epstein-Barr virus may have a role in the etiology of human breast cancer. If conclusive evidence for a role of these viruses in breast carcinogenesis can be developed, there is a practical possibility of primary prevention.
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Affiliation(s)
- James S Lawson
- School of Public Health, University of New South Wales, Sydney, Australia.
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Agu CA, Klein R, Schwab S, König-Schuster M, Kodajova P, Ausserlechner M, Binishofer B, Bläsi U, Salmons B, Günzburg WH, Hohenadl C. The cytotoxic activity of the bacteriophage lambda-holin protein reduces tumour growth rates in mammary cancer cell xenograft models. J Gene Med 2006; 8:229-41. [PMID: 16170834 DOI: 10.1002/jgm.833] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The potential use of gene therapy for cancer treatment is being intensively studied. One approach utilises the expression of genes encoding cytotoxic proteins. Such proteins can affect cellular viability, for example by inhibiting the translation machinery or disturbing membrane integrity. The bacteriophage Lambda (lambda)-holin protein is known to form a lesion in the cytoplasmic membrane of E. coli, triggering bacterial cell lysis and thereby enabling the release of new bacteriophage particles. The aim of this study was to evaluate whether the lambda-holin protein has a cytotoxic impact on eukaryotic cells and whether it holds potential as a new therapeutic protein for cancer gene therapy. METHODS To explore this possibility, stably transfected human cell lines were established that harbour a tetracycline (Tet)-inducible system for controlled expression of the lambda-holin gene. The effect of the lambda-holin protein on eukaryotic cells was studied in vitro by applying several viability assays. We also investigated the effect of lambda-holin gene expression in vivo using a human breast cancer cell tumour xenograft as well as a syngeneic mammary adenocarcinoma mouse model. RESULTS The lambda-holin-encoding gene was inducibly expressed in eukaryotic cells in vitro. Expression led to a substantial reduction of cell viability of more than 98%. In mouse models, lambda-holin-expressing tumour cell xenografts revealed significantly reduced growth rates in comparison to xenografts not expressing the lambda-holin gene. CONCLUSIONS The lambda-holin protein is cytotoxic for eukaryotic cells in vitro and inhibits tumour growth in vivo suggesting potential therapeutic use in cancer gene therapy.
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Affiliation(s)
- Chukwuma A Agu
- Research Institute of Virology and Biomedicine, University of Veterinary Medicine Vienna, Veterinärplatz 1, A-1210 Vienna, Austria
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Metzner C, Salmons B, Gunzburg WH, Gemeiner M, Miller I, Gesslbauer B, Kungl A, Dangerfield JA. MMTV accessory factor Naf affects cellular gene expression. Virology 2006; 346:139-50. [PMID: 16310820 DOI: 10.1016/j.virol.2005.10.029] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2005] [Revised: 08/23/2005] [Accepted: 10/21/2005] [Indexed: 11/25/2022]
Abstract
Mouse mammary tumour virus (MMTV) encodes a viral superantigen (Sag) and a negative acting factor (Naf) which share parts of their coding sequence. Using 2-dimensional gel electrophoresis (2D-DIGE), we could show that at least 10 different cellular proteins were differentially expressed in Naf positive cells. Also, luciferase reporter expression was down-regulated in Naf expressing cells independent of the promoter used and further experiments suggested that this effect was due in part to a decrease in cellular growth rates. Although in Naf positive cells expression of the major sag containing transcript was strongly induced by the synthetic glucocorticoid dexamethasone, the hormone analogue neither influenced luciferase expression nor mRNA expression of selected cellular proteins identified by 2D-DIGE. Taken together, these data support the previous finding that Naf and Sag have separable activities and suggest that Naf may play a role in modulating host cell gene expression during MMTV infection.
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Affiliation(s)
- Christoph Metzner
- Research Institute of Virology and Biomedicine, University of Veterinary Medicine, A-1210 Vienna, Austria.
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12
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Landis MD, Seachrist DD, Abdul-Karim FW, Keri RA. Sustained trophism of the mammary gland is sufficient to accelerate and synchronize development of ErbB2/Neu-induced tumors. Oncogene 2006; 25:3325-34. [PMID: 16434967 PMCID: PMC1602057 DOI: 10.1038/sj.onc.1209365] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Epidemiological studies indicate that parity enhances HER2/ErbB2/Neu-induced breast tumorigenesis. Furthermore, recent studies using multiparous, ErbB2/Neu-overexpressing mouse mammary tumor virus (MMTV-Neu) mice have shown that parity induces a population of cells that are targeted for ErbB2/Neu-induced transformation. Although parity accelerates mammary tumorigenesis, the pattern of tumor development in multiparous MMTV-Neu mice remains stochastic, suggesting that additional events are required for ErbB2/Neu to cause mammary tumors. Whether such events are genetic in nature or reflective of the dynamic hormonal control of the gland that occurs with pregnancy remains unclear. We postulated that young age at pregnancy initiation or chronic trophic maintenance of mammary epithelial cells might provide a cellular environment that significantly increases susceptibility to ErbB2/Neu-induced tumorigenesis. MMTV-Neu mice that were maintained pregnant or lactating beginning at 3 weeks of age demonstrated accelerated tumorigenesis, but this process was still stochastic, indicating that early pregnancy does not provide the requisite events of tumorigenesis. However, bitransgenic mice that were generated by breeding MMTV-Neu mice with a luteinizing hormone-overexpressing mouse model of ovarian hyperstimulation developed multifocal mammary tumors in an accelerated, synchronous manner compared to virgin MMTV-Neu animals. This synchrony of tumor development in the bitransgenic mice suggests that trophic maintenance of the mammary gland provides the additional events required for tumor formation and maintains the population of cells that are targeted by ErbB2/Neu for transformation. Both the synchrony of tumor appearance and the ability to characterize a window of commitment by ovariectomy/palpation studies permitted microarray analysis to evaluate changes in gene expression over a defined timeline that spans the progression from normal to preneoplastic mammary tissue. These approaches led to identification of several candidate genes whose expression changes in the mammary gland with commitment to ErbB2/Neu-induced tumorigenesis, suggesting that they may either be regulated by ErbB2/Neu and/or contribute to tumor formation.
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MESH Headings
- Animals
- Cell Transformation, Neoplastic/genetics
- Cell Transformation, Neoplastic/metabolism
- Cell Transformation, Neoplastic/pathology
- Female
- Male
- Mammary Glands, Animal/metabolism
- Mammary Glands, Animal/pathology
- Mammary Neoplasms, Experimental/genetics
- Mammary Neoplasms, Experimental/metabolism
- Mammary Neoplasms, Experimental/pathology
- Mice
- Mice, Transgenic
- Pregnancy
- Pregnancy Complications, Neoplastic/genetics
- Pregnancy Complications, Neoplastic/metabolism
- Pregnancy Complications, Neoplastic/pathology
- Receptor, ErbB-2/genetics
- Receptor, ErbB-2/physiology
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Affiliation(s)
- MD Landis
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
| | - DD Seachrist
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
| | - FW Abdul-Karim
- Department of Pathology, School of Medicine, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, OH, USA and
| | - RA Keri
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
- Division of General Medical Sciences-Oncology, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
- Correspondence: RA Keri, Department of Pharmacology, CASE School of Medicine, 2109 Adelbert Road RT300, Cleveland, OH 44106-4965, USA. E-mail:
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13
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Belikov S, Holmqvist PH, Astrand C, Wrange O. Nuclear Factor 1 and Octamer Transcription Factor 1 Binding Preset the Chromatin Structure of the Mouse Mammary Tumor Virus Promoter for Hormone Induction. J Biol Chem 2004; 279:49857-67. [PMID: 15381691 DOI: 10.1074/jbc.m409713200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
When the mouse mammary tumor virus (MMTV) is integrated into the genome of a mammalian cell, its long terminal repeat (LTR) harbors six specifically positioned nucleosomes. Transcription from the MMTV promoter is regulated by the glucocorticoid hormone via the glucocorticoid receptor (GR). The mechanism of the apparently constitutive nucleosome arrangement has remained unclear. Previous in vitro reconstitution of nucleosome(s) on small segments of the MMTV LTR suggested that the DNA sequence was decisive for the nucleosome arrangement. However, microinjection of MMTV LTR DNA in Xenopus oocytes rendered randomly distributed nucleosomes. This indicated that oocytes lack factor(s) that induces nucleosome positioning at the MMTV LTR in other cells. Here we demonstrate that specific and concomitant binding of nuclear factor 1 (NF1) and octamer factor 1 (Oct1) to their cognate sites within the MMTV promoter induce a partial nucleosome positioning that is an intermediary state between the randomly organized inactive promoter and the hormone and GR-activated promoter containing distinctly positioned nucleosomes. Oct1 and NF1 reciprocally facilitate each other's binding to the MMTV LTR in vivo. The NF1 and Oct1 binding also facilitate hormone-dependent GR-DNA interaction and result in a faster and stronger hormone response. Since NF1 and Oct1 generate an intermediary state of nucleosome positioning and enhance the hormone-induced response, we refer to this as a preset chromatin structure. We propose that this state of NF1 and Oct1-induced chromatin presetting mimics the early step(s) of chromatin remodeling involved in tissue-specific gene expression.
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Affiliation(s)
- Sergey Belikov
- Department of Cell and Molecular Biology, The Medical Nobel Institute, P. O. Box 285, Karolinska Institutet, Stockholm SE-17177, Sweden
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14
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Torres-Arzayus MI, Font de Mora J, Yuan J, Vazquez F, Bronson R, Rue M, Sellers WR, Brown M. High tumor incidence and activation of the PI3K/AKT pathway in transgenic mice define AIB1 as an oncogene. Cancer Cell 2004; 6:263-74. [PMID: 15380517 DOI: 10.1016/j.ccr.2004.06.027] [Citation(s) in RCA: 304] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2004] [Revised: 06/09/2004] [Accepted: 06/29/2004] [Indexed: 01/12/2023]
Abstract
The gene encoding AIB1, an estrogen receptor coactivator, is amplified in a subset of human breast cancers. Here we show that overexpression of AIB1 in transgenic mice (AIB1-tg) leads to mammary hypertrophy, hyperplasia, abnormal postweaning involution, and the development of malignant mammary tumors. Tumors are also increased in other organs, including the pituitary and uterus. AIB1 overexpression increases mammary IGF-I mRNA and serum IGF-I protein levels. In addition, IGF-I receptor and downstream signaling molecules are activated in primary mammary epithelial cells and mammary tumor cells derived from AIB1-tg mice. Knockdown of AIB1 expression in cultured AIB1-tg mammary tumor cells leads to reduced IGF-I mRNA levels and increased apoptosis, suggesting that an autocrine IGF-I loop underlies the mechanism of AIB1-induced oncogenesis.
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Affiliation(s)
- Maria I Torres-Arzayus
- Division of Molecular and Cellular Oncology, Department of Medical Oncology, Dana-Farber Cancer Institute and Harvard Medical School, 44 Binney Street, Boston, MA 02115, USA
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15
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Guth SE, Böhm S, Mussler BH, Eisenbrand G. Sensitivein vitro test systems to determine androgenic/antiandrogenic activity. Mol Nutr Food Res 2004; 48:282-91. [PMID: 15497179 DOI: 10.1002/mnfr.200400023] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We report on the establishment of one transgenic and two endogenous reporter gene assays to determine androgenic/antiandrogenic activity. A transient transactivation assay was developed in COS-7 African green monkey kidney cells. Three plasmids were co-transfected by electroporation: the human androgen receptor expression vector pSG5AR, the reporter gene vector pMamneoLuc, expressing luciferase under the control of the mouse mammary tumor virus (MMTV) promotor containing 4 hormone responsive elements (HREs), and the control plasmid pSVbeta. Transcriptional activation was measured by luciferase-mediated chemoluminescence. In T47D human breast cancer cells two endogenous reporter gene systems were established: one based on the androgen-induced expression of prostate-specific antigen (PSA), the other based on the androgen-repressed expression of testosterone repressed message 2 (TRPM-2). PSA protein was measured by enzyme-linked immunosorbent assay (ELISA), TRPM-2 m-RNA by reverse transcriptase polymerase chain reaction (RT-PCR). All three test systems were validated using the physiological androgen dihydrotestosterone (DHT) as agonist and the established antiandrogens hydroxyflutamide and p,p'-dichlorodiphenylethene (p,p'-DDE) as antagonists. The PSA assay was the most sensitive test system with an EC50 of 0.7 nM for DHT-induced response. The transient transactivation assay in COS-7 cells was less sensitive with an EC50 of 9.7 nM DHT. In the PSA assay hydroxyflutamide was a more potent antagonist (IC30 = 0.02 microM) than p,p'-DDE (IC30 = 0.9 microM). In the transient transactivation assay in COS-7 cells, both compounds elicited about 30% of the agonistic response induced by 100 nM DHT, thus showing partial agonistic properties. In summary, three highly sensitive and complementary in vitro test systems, together achieving enhanced specificity for detection and assessment of androgenic/antiandrogenic activity have been established and validated.
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Affiliation(s)
- Sabine E Guth
- Department of Chemistry, Division of Food Chemistry and Environmental Toxicology, University of Kaiserslautern, Kaiserslautem, Germany
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16
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Abstract
The field of cancer gene therapy is in continuous expansion, and technology is quickly moving ahead as far as gene targeting and regulation of gene expression are concerned. This review focuses on the endocrine aspects of gene therapy, including the possibility to exploit hormone and hormone receptor functions for regulating therapeutic gene expression, the use of endocrine-specific genes as new therapeutic tools, the effects of viral vector delivery and transgene expression on the endocrine system, and the endocrine response to viral vector delivery. Present ethical concerns of gene therapy and the risk of germ cell transduction are also discussed, along with potential lines of innovation to improve cell and gene targeting.
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Affiliation(s)
- Luisa Barzon
- Department of Histology, Microbiology, and Medical Biotechnologies, University of Padova, I-35121 Padua, Italy
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17
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Fee BE, Steinke JW, Pierce J, Peterson DO. Initiation site binding protein and the initiator-like promoter element of mouse mammary tumor virus. Virology 2002; 302:185-94. [PMID: 12429527 DOI: 10.1006/viro.2002.1603] [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
The mouse mammary tumor virus (MMTV) promoter contains an element near its transcription initiation site that is recognized by a protein termed initiation site binding protein (ISBP). Spacing between the TATA box and the ISBP site is important for MMTV promoter function, as altered spacing results in heterogeneity in start site selection in vitro and in vivo. The sequence of the ISBP site is related to initiator elements common in many RNA polymerase II promoters. However, binding of partially purified ISBP to several promoters that contain well-characterized initiator elements was not detected; these promoters included binding sites for a number of previously identified initiator-binding proteins. Partially purified ISBP did, however, bind with high affinity to sequences near the initiation sites of the SV40 major late and adenovirus 2 E1B promoters.
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Affiliation(s)
- Brian E Fee
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128, USA
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18
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He B, Lee LW, Minges JT, Wilson EM. Dependence of selective gene activation on the androgen receptor NH2- and COOH-terminal interaction. J Biol Chem 2002; 277:25631-9. [PMID: 12000757 DOI: 10.1074/jbc.m202809200] [Citation(s) in RCA: 124] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The agonist-induced androgen receptor NH(2)- and COOH-terminal (N/C) interaction is mediated by the FXXLF and WXXLF NH(2)-terminal motifs. Here we demonstrate that agonist-dependent transactivation of prostate-specific antigen (PSA) and probasin enhancer/promoter regions requires the N/C interaction, whereas the sex-limited protein gene and mouse mammary tumor virus long terminal repeat do not. Transactivation of PSA and probasin response regions also depends on activation function 1 (AF1) in the NH(2)-terminal region but can be increased by binding an overexpressed p160 coactivator to activation function 2 (AF2) in the ligand binding domain. The dependence of the PSA and probasin enhancer/promoters on the N/C interaction for transactivation allowed us to demonstrate that in the presence of androgen, the WXXLF motif with the sequence (433)WHTLF(437) contributes as an inhibitor to AR transactivation. We further show that like the FXXLF and LXXLL motifs, the WXXLF motif interacts in the presence of androgen with AF2 in the ligand binding domain. Sequence comparisons among species indicate greater conservation of the FXXLF motif compared with the WXXLF motif, paralleling the functional significance of these binding motifs. The data provide evidence for promoter-specific differences in the requirement for the androgen receptor N/C interaction and in the contributions of AF1 and AF2 in androgen-induced gene regulation.
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Affiliation(s)
- Bin He
- Laboratories for Reproductive Biology, University of North Carolina, Chapel Hill 27599-7500, USA
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19
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Chua SS, Ma ZQ, Gong L, Lin SH, DeMayo FJ, Tsai SY. Ectopic expression of FGF-3 results in abnormal prostate and Wolffian duct development. Oncogene 2002; 21:1899-908. [PMID: 11896623 DOI: 10.1038/sj.onc.1205096] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2001] [Revised: 09/27/2001] [Accepted: 10/12/2001] [Indexed: 11/09/2022]
Abstract
To evaluate the effects of FGF-3 expression in the prostate and male reproductive tract, we employed a bitransgenic system to target FGF-3 to these organs. We present a first study that ectopic FGF-3 expression resulted in exuberant hyperplasia of all bigenic prostatic lobes typified by epithelial stratification, cribiform structures and papillary tufts. These cells displayed increased nuclear-to-cytoplasmic ratios and bromodeoxyuridine (BrdU) proliferative index but retained relatively uniform nuclear androgen receptor (AR) and the tumor suppressor C-CAM1 staining. Furthermore, the dysmorphogenic prostatic cells also resembled PIN (prostatic intraepithelial neoplasia)-like lesions but did not appear to have invaded the basal lamina. In addition to these phenotypes, profound disorders of the bigenic Wolffian duct derivatives were observed. The bigenic ampullary glands and vas deferens were extremely cystic, hypertrophic and hyperplastic; the enlarged epididymi showed a reduction of spermatozoa and the seminal vesicles exhibited a dramatic reduction of seminal secretions. Because of these severe abnormalities, these infertile males presented with diaphragmatic hernias, hemoperitoneum and many secondary abnormalities at sacrifice. Taken together, we show that ectopic FGF-3 expression severely perturbs normal prostate development and our system should be useful for the analyses of early changes in prostatic hyperplasia.
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Affiliation(s)
- Steven S Chua
- Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, Texas, TX 77030, USA
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20
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Abstract
Current treatment of solid tumors is limited by severe adverse effects, resulting in a narrow therapeutic index. Therefore, cancer gene therapy has emerged as a targeted approach that would significantly reduce undesired side effects in normal tissues. This approach requires a clear understanding of the molecular biology of both the malignant clone and the biological vectors that serve as vehicles to target cancer cells. In this review we discuss novel approaches for conditional gene expression in cancer cells. Targeting transgene expression to malignant tissues requires the use of specific regulatory elements including promoters based on tumor biology, tissue-specific promoters and inducible regulatory elements. We also discuss the regulation of both replication and transgene expression by conditionally-replicative viruses. These approaches have the potential to restrict the expression of transgenes exclusively to tissues of interest and thereby to increase the therapeutic index of future vectors for cancer gene therapy.
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Affiliation(s)
- Y S Haviv
- Division of Human Gene Therapy, Departments of Medicine, Surgery and Pathology, University of Alabama at Birmingham, 1824 6th Avenue South, Birmingham, AL 35294, USA
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21
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Valve EM, Ruohola JK, Tasanen MJ, Glover JF, Darbre PD, Härkönen PL. Expression of the androgen-dependent MMTV-specific orf gene in Shionogi 115 mouse mammary tumor cells. J Steroid Biochem Mol Biol 2001; 78:389-400. [PMID: 11738549 DOI: 10.1016/s0960-0760(01)00116-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The Shionogi 115 (S115) mouse mammary tumor cells express the MMTV-specific 1.7 kb mRNA (orf) at a high level in the presence of androgens. In lymphoid cells the orf-gene encodes a superantigen which has an important role in establishing self-tolerance but in mammary and breast cancer cells the function of the orf gene is unclear. In the present work we studied the expression of the S115 mammary tumor cell orf sequence and its role in the androgen regulated growth of S115 cells. The cloning and sequencing of the cDNA specific for the 1.7 kb mRNA from the S115 mouse mammary tumor cells revealed a 990 bp DNA sequence with a 99.8% homology to the Mtv-17 proviral strain. There was a difference of only one amino acid (isoleu-tyr) in the coding region. A peptide was synthesized according to the hypervariable C-terminal part of the predicted protein and used to raise a rabbit antiserum. The anti-S115-orf antiserum immunoprecipitated an approximately 45 kDa protein from the metabolically labeled S115 cell lysates. In order to analyze the putative functions of the protein, the orf-sequence was linked to MoMLV-LTR and to the human ss-actin promoter in the mammalian expression vectors pLTRpoly and pHssAPr-1-neo, respectively, and transfected into NIH3T3 and S115 cells. NIH3T3 transfectants expressing orf mRNA did not show a transformed phenotype in vitro. The S115 orf transfectants proliferated somewhat more slowly than the vector transfected control cells in cell culture, both in the presence or absence of androgen, but there was no obvious change in the phenotype of S115 cells or in expression of the fibroblast growth factor 8 (FGF-8). This factor is activated by Mtv-6 integration and mediates androgen effects in these cells. Unexpectedly, however, the formation of tumors by S115 orf cells in nude mice was considerably prolonged and tumor growth retarded when compared with vector transfected control or parent S115 cells. The results suggest that MMTV-orf can be functional in breast cancer cells but the mechanism of the growth repressive effect in mammary tumor remains to be analyzed.
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MESH Headings
- 3T3 Cells
- Amino Acid Sequence
- Androgens/pharmacology
- Animals
- Base Sequence
- Cell Division/drug effects
- Cloning, Molecular
- DNA, Complementary/genetics
- DNA, Viral/genetics
- Female
- Gene Expression
- Genes, Viral
- Male
- Mammary Neoplasms, Experimental/genetics
- Mammary Neoplasms, Experimental/metabolism
- Mammary Neoplasms, Experimental/virology
- Mammary Tumor Virus, Mouse/genetics
- Mice
- Mice, Nude
- Molecular Sequence Data
- Neoplasms, Hormone-Dependent/genetics
- Neoplasms, Hormone-Dependent/metabolism
- Neoplasms, Hormone-Dependent/virology
- Open Reading Frames
- Promoter Regions, Genetic
- RNA, Messenger/genetics
- RNA, Viral/genetics
- Sequence Homology, Amino Acid
- Transfection
- Tumor Cells, Cultured
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Affiliation(s)
- E M Valve
- Department of Anatomy and MediCity Research Laboratory, Institute of Biomedicine, University of Turku, Tykistökatu 6A, FIN-20520, Turku, Finland
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22
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Kang CJ, Peterson DO. In vitro analysis of transcriptional repression of the mouse mammary tumor virus promoter. Biochem Biophys Res Commun 2001; 287:402-10. [PMID: 11554742 DOI: 10.1006/bbrc.2001.5601] [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
Transcription of the proviral DNA of mouse mammary tumor virus (MMTV) is induced by several classes of hormone-activated steroid receptor proteins. Basal promoter activity in the absence of receptor-mediated activation is selectively repressed by a distal negative regulatory element (dNRE) centered approximately 400 bp upstream of the transcription initiation site. An in vitro transcription system based on synthetic T-free cassette templates was developed to assess MMTV promoter activity, and dNRE-mediated repression was partially reconstituted with this system. Repression was observed with templates in which the dNRE was present in several sequence contexts. The activity of transcription preinitiation complexes formed in vitro in the presence of the dNRE could not be distinguished from that of complexes formed in its absence as assessed by the kinetics of transcript accumulation after addition of nucleoside triphosphates to preformed preinitiation complexes. dNRE-mediated repression in vitro appeared to be the result of decreased efficiency of assembly of functional transcription complexes on the MMTV promoter. However, repression could not be explained by inhibition of assembly of TATA-binding protein or transcription factor IIB into transcription complexes, as neither protein decreased the extent of repression when supplied in excess as a purified recombinant protein.
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Affiliation(s)
- C J Kang
- School of Life Science and Biotechnology, Kyung Hee University, Yongin, Kyunggido 449-701, Korea.
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23
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Tabotta W, Klein D, Hohenadl C, Salmons B, Günzburg WH. Genetic reshuffling reconstitutes functional expression cassettes in retroviral vectors. J Gene Med 2001; 3:418-26. [PMID: 11601755 DOI: 10.1002/jgm.209] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
BACKGROUND A major prerequisite for the design of retroviral vectors encoding cell toxic or harmful genes is the possibility to tightly control gene expression, thus limiting activity to the relevant target cells and protecting the packaging cell used for production of recombinant viral particles. METHODS In the present study a system was developed in which genetic reshuffling during the retroviral life cycle is exploited, allowing reconstitution of functional expression cassettes from separate elements exclusively in transduced target cells. For construction of these murine leukaemia virus (MLV)-based reconstituting viral vectors (ReCon), a promoterless inverted enhanced green fluorescent protein (EGFP) reporter gene cassette was inserted in place of the U3 region of the 3' LTR. Subsequently, the human ubiquitin promoter was inserted in the inverse orientation into the R/U5 border of the 5' LTR of the vector. RESULTS PA317 packaging cells stably transfected with ReCon vectors were established and EGFP expression was analysed by fluorescence-activated cell sorting (FACS). After detection of low-level background expression, an additional polyadenylation signal was introduced in antisense orientation into the 3' LTR at the R/U5 border to prevent accidental read-through transcription from neighbouring cellular promoters. Virus-containing cell culture supernatants were then used to infect NIH3T3 target cells. EGFP expression, recloning and sequencing of integrated proviruses demonstrated the correct reassembly of the transduced ubiquitin/EGFP transcription unit in these infected cells. CONCLUSIONS This facile and convenient system should allow production of retroviral vectors encoding potentially toxic proteins, cell cycle inhibitors or inducers of apoptosis, all of which would interfere with vector production if expressed in the retroviral packaging cell.
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Affiliation(s)
- W Tabotta
- Institute of Virology, University of Veterinary Sciences, Vienna, Austria
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24
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Biola A, Lefebvre P, Perrin-Wolff M, Sturm M, Bertoglio J, Pallardy M. Interleukin-2 inhibits glucocorticoid receptor transcriptional activity through a mechanism involving STAT5 (signal transducer and activator of transcription 5) but not AP-1. Mol Endocrinol 2001; 15:1062-76. [PMID: 11435608 DOI: 10.1210/mend.15.7.0657] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Cytokines and glucocorticoids (GCs) signaling pathways interfere with each other in the regulation of apoptosis and gene expression in the immune system. Interleukin-2 (IL-2), through the Janus kinase/signal transducers and activators of transcription (Jak/STAT) and mitogen-activated protein kinase (MAPK) pathways, activates STAT5 and activated protein-1 (AP-1) transcription factors, respectively, which are known to repress glucocorticoid receptor (GR) activity, at least in part, through protein-protein interactions. In this work, we have analyzed the mechanisms whereby IL-2 down-regulates the GC-induced transactivation of the mouse mammary tumor virus long terminal repeat (MMTV-LTR) in murine CTLL-2 T lymphocytes. Mutagenesis studies revealed that the MMTV-LTR STAT5 binding site (-923/-914) was not required for IL-2-mediated inhibition but identified both glucocorticoid response elements (GREs) and the -104/+1 region as critical elements for this negative response. The DNA binding activities of transcription factors required for GC-mediated activation of the MMTV-LTR promoter and that bind to the -104/+1 region (nuclear factor-1, Oct-1) were not affected by IL-2 treatment. Overexpression of wild-type STAT5B enhanced the effect of IL-2 on MMTV-LTR activity, and a dominant negative form of STAT5B (Y699F) abolished the IL-2-mediated MMTV-LTR inhibition, whereas AP-1 activation had no effect in this system. Direct interaction between liganded GR and STAT5 was observed in CTLL-2 cells in a STAT5 phosphorylation-independent manner. Overexpression of nuclear coactivators CBP (CREB-binding protein) or SRC-1a (steroid receptor coactivator 1a) did not blunt IL-2 inhibitory effects. We suggest that the STAT5-repressive activity on the GC-dependent transcription may involve direct interaction of STAT5 with GR, is dependent on the promoter context and STAT5 activation level, and occurs independently of coactivators levels in T cells.
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Affiliation(s)
- A Biola
- INSERM U461 Faculté de Pharmacie Paris-Sud 92296 Châtenay-Malabry, France
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25
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Steinke JW, Kopytek SJ, Peterson DO. Discrete promoter elements affect specific properties of RNA polymerase II transcription complexes. Nucleic Acids Res 2000; 28:2726-35. [PMID: 10908329 PMCID: PMC102648 DOI: 10.1093/nar/28.14.2726] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The frequency of transcription initiation at specific RNA polymerase II promoters is, in many cases, related to the ability of the promoter to recruit the transcription machinery to a specific site. However, there may also be functional differences in the properties of assembled transcription complexes that are promoter-specific or regulator-dependent and affect their activity. Transcription complexes formed on variants of the adenovirus major late (AdML) promoter were found to differ in several ways. Mutations in the initiator element increased the sarkosyl sensitivity of the rate of elongation and decreased the rate of early steps in initiation as revealed by a sarkosyl challenge assay that exploited the resistance of RNA synthesis to high concentrations of sarkosyl after formation of one or two phospho-diester bonds. Similar, but clearly distinct, effects were also observed after deletion of the binding site for upstream stimulatory factor from the AdML promoter. In contrast, deletion of binding sites for nuclear factor 1 and Oct-1, as well as mutations in the recognition sequence for initiation site binding protein, were without apparent effect on transcription complexes on templates containing the mouse mammary tumor virus promoter.
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Affiliation(s)
- J W Steinke
- Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, TX 77843-2128, USA
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26
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Aurrekoetxea-Hernández K, Buetti E. Synergistic action of GA-binding protein and glucocorticoid receptor in transcription from the mouse mammary tumor virus promoter. J Virol 2000; 74:4988-98. [PMID: 10799572 PMCID: PMC110850 DOI: 10.1128/jvi.74.11.4988-4998.2000] [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: 11/20/2022] Open
Abstract
B lymphocytes are among the first cells to be infected by mouse mammary tumor virus (MMTV), and they play a crucial role in its life cycle. To study transcriptional regulation of MMTV in B cells, we have analyzed two areas of the long terminal repeat (LTR) next to the glucocorticoid receptor binding site, fp1 (at position -139 to -146 from the cap site) and fp2 (at -157 to -164). Both showed B-cell-specific protection in DNase I in vitro footprinting assays and contain binding sites for Ets transcription factors, a large family of proteins involved in cell proliferation and differentiation and oncogenic transformation. In gel retardation assays, fp1 and fp2 bound the heterodimeric Ets factor GA-binding protein (GABP) present in B-cell nuclear extracts, which was identified by various criteria: formation of dimers and tetramers, sensitivity to pro-oxidant conditions, inhibition of binding by specific antisera, and comigration of complexes with those formed by recombinant GABP. Mutations which prevented complex formation in vitro abolished glucocorticoid-stimulated transcription from an MMTV LTR linked to a reporter gene in transiently transfected B-cell lines, whereas they did not affect the basal level. Exogenously expressed GABP resulted in an increased level of hormone response of the LTR reporter plasmid and produced a synergistic effect with the coexpressed glucocorticoid receptor, indicating cooperation between the two. This is the first example of GABP cooperation with a steroid receptor, providing the opportunity for studying the integration of their intracellular signaling pathways.
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27
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Kang CJ, Peterson DO. Identification of a protein that recognizes a distal negative regulatory element within the mouse mammary tumor virus long terminal repeat. Virology 1999; 264:211-9. [PMID: 10544147 DOI: 10.1006/viro.1999.9969] [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] [Indexed: 11/22/2022]
Abstract
The mouse mammary tumor virus (MMTV) long terminal repeat contains a distal negative regulatory element (dNRE) that selectively represses activity of the proviral promoter in the absence of steroid hormone receptor-mediated activation. A protein, termed MMTV NRE-binding protein 1 (MNBP-1), that recognizes long terminal repeat sequences between -433 and -418 was identified by gel electrophoresis mobility shift assays and methylation interference footprinting in nuclear extracts of HeLa and Ltk(-) cells. Mutations within the defined binding site affect dNRE-mediated promoter repression in vivo. MNBP-1 has an apparent molecular mass of approximately 100 kDa as determined by gel filtration chromatography.
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Affiliation(s)
- C J Kang
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128, USA
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28
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Ma ZQ, Chua SS, DeMayo FJ, Tsai SY. Induction of mammary gland hyperplasia in transgenic mice over-expressing human Cdc25B. Oncogene 1999; 18:4564-76. [PMID: 10467401 DOI: 10.1038/sj.onc.1202809] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Cdc25 A and B are dual-specificity phosphatases which have been implicated in neoplastic transformation. Although Cdc25A and Cdc25B have been found to be over-expressed in many cancer cell lines and primary tumors, the physiological roles of Cdc25A and B in vivo are largely undefined. To investigate the roles of these proteins in the oncogenic transformation of the mammary gland we used the mouse mammary tumor virus (MMTV) promoter to target over-expression of the Cdc25B transgene in the mammary glands of transgenic mouse lines. Here we report that the over-expression of Cdc25B enhances the proliferation of mammary epithelial cells resulting in the formation of precocious alveolar hyperplasia. At the molecular level, marked increases in cyclin D1 protein have been found in transgenic mammary epithelial cells. The accelerated growth rate of the mammary epithelial cells could also be attributed to the increased levels of cyclin E/cdk2 activity. In addition, a pronounced decrease in apoptosis was also observed during the involution of mammary gland. The reduction of apoptosis during involution correlated well with the reduced expression of c-myc and p53, both of which have been implicated in apoptosis. Taken together, our results clearly indicate that the deregulated expression of Cdc25B generates mammary gland hyperplasia.
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Affiliation(s)
- Z Q Ma
- Department of Cell Biology, Baylor College of Medicine, One Baylor Plaza, Houston, Texas, TX 77030, USA
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29
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Grimm SL, Nordeen SK. A composite enhancer element directing tissue-specific expression of mouse mammary tumor virus requires both ubiquitous and tissue-restricted factors. J Biol Chem 1999; 274:12790-6. [PMID: 10212264 DOI: 10.1074/jbc.274.18.12790] [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: 11/06/2022] Open
Abstract
Mouse mammary tumor virus (MMTV) expression is restricted primarily to mammary epithelial cells. Sequences responsible for both the mammary-specific expression of MMTV and the activation of cellular oncogenes are located within two enhancer elements at the 5'-end of the long terminal repeat. Whereas the Ban2 enhancer (-1075 to -978) has been well characterized, the mammary-specific enhancer of MMTV from -956 to -862 has only recently been recognized as a key determinant of mammary-specific oncogene activation by MMTV. The present study identifies and characterizes three binding sites located within this element. Transient transfection of deletion and mutation constructs shows that all three sites contribute to the basal expression of MMTV in mammary cells. One of the binding activities (footprint I) is restricted to mammary cells, whereas the other two sites bind factors found in both mammary and nonmammary cells. The multimerized mammary-specific enhancer of MMTV on its own can enhance a minimal promoter in a mammary-specific fashion. However, the FpI binding site alone cannot mediate this effect. Thus, it is the binding of multiple factors in a combinatorial fashion that mediates the mammary-restricted expression of MMTV.
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Affiliation(s)
- S L Grimm
- Program in Molecular Biology, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA
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30
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Ardavín C, Martín P, Ferrero I, Azcoitia I, Anjuère F, Diggelmann H, Luthi F, Luther S, Acha-Orbea H. B Cell Response After MMTV Infection: Extrafollicular Plasmablasts Represent the Main Infected Population and Can Transmit Viral Infection. THE JOURNAL OF IMMUNOLOGY 1999. [DOI: 10.4049/jimmunol.162.5.2538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Abstract
The immune response to mouse mammary tumor virus (MMTV) relies on the presentation of an MMTV-encoded superantigen by infected B cells to superantigen-specific T cells. The initial extrafollicular B cell differentiation involved the generation of B cells expressing low levels of B220. These B220low B cells corresponded to plasmablasts that expressed high levels of CD43 and syndecan-1 and were CD62 ligand− and IgD−. Viral DNA was detected nearly exclusively in these B220low B cells by PCR, and retroviral type-A particles were observed in their cytoplasm by electron microscopy. An MMTV transmission to the offspring was also achieved after transfer of B220low CD62 ligand− CD43+ plasmablasts into noninfected females. These data suggest that B220low plasmablasts, representing the bulk of infected B cells, are capable of sustaining viral replication and may be involved in the transmission of MMTV.
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Affiliation(s)
- Carlos Ardavín
- *Ludwig Institute for Cancer Research, Lausanne Branch, and
- ‡Department of Cell Biology, Faculty of Biology, Complutense University, Madrid, Spain; and
| | - Pilar Martín
- ‡Department of Cell Biology, Faculty of Biology, Complutense University, Madrid, Spain; and
| | - Isabel Ferrero
- ‡Department of Cell Biology, Faculty of Biology, Complutense University, Madrid, Spain; and
| | - Iñigo Azcoitia
- ‡Department of Cell Biology, Faculty of Biology, Complutense University, Madrid, Spain; and
| | - Fabienne Anjuère
- ‡Department of Cell Biology, Faculty of Biology, Complutense University, Madrid, Spain; and
| | - Heidi Diggelmann
- §Institute of Microbiology, University of Lausanne, Lausanne, Switzerland
| | - Frédéric Luthi
- §Institute of Microbiology, University of Lausanne, Lausanne, Switzerland
| | - Sanjiv Luther
- *Ludwig Institute for Cancer Research, Lausanne Branch, and
- †Institute for Biochemistry, University of Lausanne, Epalinges, Switzerland
| | - Hans Acha-Orbea
- *Ludwig Institute for Cancer Research, Lausanne Branch, and
- †Institute for Biochemistry, University of Lausanne, Epalinges, Switzerland
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31
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Korpelainen EI, Karkkainen MJ, Tenhunen A, Lakso M, Rauvala H, Vierula M, Parvinen M, Alitalo K. Overexpression of VEGF in testis and epididymis causes infertility in transgenic mice: evidence for nonendothelial targets for VEGF. J Cell Biol 1998; 143:1705-12. [PMID: 9852161 PMCID: PMC2132976 DOI: 10.1083/jcb.143.6.1705] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Vascular endothelial growth factor (VEGF) is a key regulator of endothelial growth and permeability. However, VEGF may also target nonendothelial cells, as VEGF receptors and responsiveness have been detected for example in monocytes, and high concentrations of VEGF have been reported in human semen. In this work we present evidence that overexpression of VEGF in the testis and epididymis of transgenic mice under the mouse mammary tumor virus (MMTV) LTR promoter causes infertility. The testes of the transgenic mice exhibited spermatogenic arrest and increased capillary density. The ductus epididymidis was dilated, containing areas of epithelial hyperplasia. The number of subepithelial capillaries in the epididymis was also increased and these vessels were highly permeable as judged by the detection of extravasated fibrinogen products. Intriguingly, the expression of VEGF receptor-1 (VEGFR-1) was detected in certain spermatogenic cells in addition to vascular endothelium, and both VEGFR-1 and VEGFR-2 were also found in the Leydig cells of the testis. The infertility of the MMTV-VEGF male mice could thus result from VEGF acting on both endothelial and nonendothelial cells of the male genital tract. Taken together, these findings suggest that the VEGF transgene has nonendothelial target cells in the testis and that VEGF may regulate male fertility.
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MESH Headings
- Animals
- Endothelial Growth Factors/biosynthesis
- Endothelial Growth Factors/genetics
- Endothelium, Vascular/metabolism
- Endothelium, Vascular/pathology
- Epididymis/blood supply
- Epididymis/metabolism
- Epididymis/pathology
- Gene Expression Regulation
- Genetic Vectors
- Humans
- Hyperplasia
- Infertility, Male/genetics
- Infertility, Male/metabolism
- Infertility, Male/pathology
- Lymphokines/biosynthesis
- Lymphokines/genetics
- Male
- Mammary Tumor Virus, Mouse/genetics
- Mice
- Mice, Transgenic
- Proto-Oncogene Proteins/genetics
- Receptor Protein-Tyrosine Kinases/genetics
- Receptors, Growth Factor/genetics
- Receptors, Mitogen/genetics
- Receptors, Vascular Endothelial Growth Factor
- Seminiferous Tubules/pathology
- Spermatogenesis
- Terminal Repeat Sequences
- Testis/blood supply
- Testis/metabolism
- Testis/pathology
- Vascular Endothelial Growth Factor A
- Vascular Endothelial Growth Factor Receptor-1
- Vascular Endothelial Growth Factors
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Affiliation(s)
- E I Korpelainen
- Molecular/Cancer Biology Laboratory, Haartman Institute, Helsinki, Finland
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32
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Abstract
Integration of mouse mammary tumor virus (MMTV) near the int genes results in the inappropriate expression of these proto-oncogenes and initiates events that lead to the formation of mammary adenocarcinomas. In most cases, the MMTV provirus integrates in a transcriptional orientation opposite that of the int genes. We have used a novel, vector-based system designed to recapitulate the integration of MMTV upstream of the int-2 promoter. Compared to a cellular promoter or another retroviral promoter, the MMTV long terminal repeat (LTR) in this configuration is particularly efficacious at activating the int-2 promoter. The sequences responsible for enhancing the activity of the int-2 promoter map to two domains in the 5' end of the MMTV LTR. One domain is a previously defined element; the second is an element delineated by these studies that acts synergistically with the first. Both of these elements display mammary cell-specific activity. Thus, even though the MMTV promoter itself is weak without hormonal stimulation, viral integration can position the 5' LTR elements to efficiently activate transcription from cellular proto-oncogenes. Other functional elements in the LTR have little effect on the activation of the int-2 promoter. Even stimulation of the MMTV promoter with steroid hormones only modestly activates transcription from the int-2 promoter, suggesting that the 5' elements of the LTR are the predominant determinants of the tissue- and orientation-specific activation of cellular promoters by MMTV.
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Affiliation(s)
- S L Grimm
- Program in Molecular Biology, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA
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33
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Reuss FU, Coffin JM. Mouse mammary tumor virus superantigen expression in B cells is regulated by a central enhancer within the pol gene. J Virol 1998; 72:6073-82. [PMID: 9621071 PMCID: PMC110413 DOI: 10.1128/jvi.72.7.6073-6082.1998] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Expression of mouse mammary tumor virus (MMTV)-encoded superantigens in B lymphocytes is required for viral transmission and pathogenesis. The mechanism of superantigen expression from the viral sag gene in B cells is largely unknown, due to problems with detection and quantification of these low-abundance proteins. We have established a sensitive superantigen-luciferase reporter assay to study the expression and regulation of the MMTV sag gene in B-cell lymphomas. The regulatory elements for retroviral gene expression are generally located in the 5' long terminal repeat (LTR) of the provirus. However, we found that neither promoters nor enhancers in the MMTV 5' LTR play a significant role in superantigen expression in these cells. Instead, the essential regulatory regions are located in the pol and env genes of MMTV. We report here that maximal sag expression in B-cell lines depends on an enhancer within the viral pol gene which can be localized to a minimal 183-bp region. Regulation of sag gene expression differs between B-cell lymphomas and pro-B cells, where an enhancer within the viral LTRs is involved. Thus, MMTV sag expression during B-cell development is achieved through the use of two separate enhancer elements.
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Affiliation(s)
- F U Reuss
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA
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34
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Saller RM, Oztürk F, Salmons B, Günzburg WH. Construction and characterization of a hybrid mouse mammary tumor virus/murine leukemia virus-based retroviral vector. J Virol 1998; 72:1699-703. [PMID: 9445081 PMCID: PMC124659 DOI: 10.1128/jvi.72.2.1699-1703.1998] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Mouse mammary tumor virus (MMTV)-based vectors are characterized by low titers. In an effort to transfer MMTV-specific regulation of gene expression to a more efficient murine leukemia virus (MLV) vector, we have replaced the complete 3' U3 region of MLV with the complete U3 region of MMTV. Virus titers were not significantly affected by this modification, there was no impairment of reverse transcription and integration, and after infection of cells, the MMTV promoter is duplicated and translocated to the 5' long terminal repeat, resulting in glucocorticoid-regulatable RNA expression.
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Affiliation(s)
- R M Saller
- Institut für Molekulare Virologie, GSF-Forschungszentrum für Umwelt und Gesundheit, Oberschleissheim, Germany
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35
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Rudolph-Owen LA, Cannon P, Matrisian LM. Overexpression of the matrix metalloproteinase matrilysin results in premature mammary gland differentiation and male infertility. Mol Biol Cell 1998; 9:421-35. [PMID: 9450965 PMCID: PMC25271 DOI: 10.1091/mbc.9.2.421] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/1997] [Accepted: 11/14/1997] [Indexed: 02/06/2023] Open
Abstract
To examine the role of matrilysin (MAT), an epithelial cell-specific matrix metalloproteinase, in the normal development and function of reproductive tissues, we generated transgenic animals that overexpress MAT in several reproductive organs. Three distinct forms of human MAT (wild-type, active, and inactive) were placed under the control of the murine mammary tumor virus promoter/enhancer. Although wild-type, active, and inactive forms of the human MAT protein could be produced in an in vitro culture system, mutations of the MAT cDNA significantly decreased the efficiency with which the MAT protein was produced in vivo. Therefore, animals carrying the wild-type MAT transgene that expressed high levels of human MAT in vivo were further examined. Mammary glands from female transgenic animals were morphologically normal throughout mammary development, but displayed an increased ability to produce beta-casein protein in virgin animals. In addition, beginning at approximately 8 mo of age, the testes of male transgenic animals became disorganized with apparent disintegration of interstitial tissue that normally surrounds the seminiferous tubules. The disruption of testis morphology was concurrent with the onset of infertility. These results suggest that overexpression of the matrix-degrading enzyme MAT alters the integrity of the extracellular matrix and thereby induces cellular differentiation and cellular destruction in a tissue-specific manner.
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Affiliation(s)
- L A Rudolph-Owen
- Department of Cell Biology, Vanderbilt University, Nashville, Tennessee 37232, USA
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36
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Günzburg WH, Karle P, Mrochen S, Sparmann G, Saller R, Klein D, Uckert W, Salmons B. Regulated gene expression after retroviral vector-mediated delivery of cancer-relevant therapeutic genes. Recent Results Cancer Res 1997; 144:116-26. [PMID: 9304713 DOI: 10.1007/978-3-642-46836-0_13] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- W H Günzburg
- Institute for Molecular Virology, GSF Centre for Environmental and Health Research, Oberschleissheim, Germany
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37
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Fernandes AO, Banerji AP. Long-term feeding of field bean protein containing protease inhibitors suppresses virus-induced mammary tumors in mice. Cancer Lett 1997; 116:1-7. [PMID: 9177450 DOI: 10.1016/s0304-3835(97)04721-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Protease inhibitors (PIs) of synthetic, bacterial or soybean origin have been shown to suppress carcinogen or radiation-induced rat mammary carcinogenesis. We report, for the first time, the effect of year-long feeding of Field bean meal, a rich source of PIs with a 24% protein content, at different protein levels in the diet, on mouse mammary tumor virus (MMTV)-induced mammary tumorigenesis in C3H/Jax mice. Weanling female mice were randomized and divided into groups and fed chow or chow with 2%, 4%, 8% FB protein (FBP) or autoclaved 2% FBP (AFBP) until 49 weeks and the incidence of mammary tumors was recorded until 58 weeks when they were sacrificed. Mice fed 2% FBP showed significant (P < 0.001) reduction (68%) in tumor incidence and delay (P < 0.02) in tumor appearance compared to controls. This suppressive effect on mammary tumorigenesis increased with increased FBP intake with values of tumor suppression being 75% and 81% in mice groups fed 4% and 8% FBP, respectively. Incidentally, the tumors appeared earlier (P < 0.05) in the 8% FBP-treated mice compared to other groups. Moreover, this suppressive effect on mammary tumorigenesis was related to the PI activity of the FB meal, since mice fed 2% AFBP showed no reduction in tumor incidence. Heat treatment, which had destroyed the PI activity, apparently did not affect other chemopreventive agents known to be present in plant material. This possibility is supported by our observation that prolonged feeding of 2% FBP or 2% AFBP increased the liver glutathione content of mice, suggesting the presence of a highly heat-stable factor, other than PIs, in the FBP, which brought about this elevation. Further, while 2% or 4% FBP- and 2% AFBP- treated mice showed no adverse growth effects, only the 8% FBP-fed group showed a significant lower growth curve compared to control mice, with some of them showing pancreatic lesions.
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Affiliation(s)
- A O Fernandes
- Biological Chemistry Division, Cancer Research Institute, Parel, Bombay, India
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38
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Wiren KM, Zhang X, Chang C, Keenan E, Orwoll ES. Transcriptional up-regulation of the human androgen receptor by androgen in bone cells. Endocrinology 1997; 138:2291-300. [PMID: 9165014 DOI: 10.1210/endo.138.6.5163] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Androgen regulation of androgen receptor (AR) expression has been observed in a variety of tissues, generally as inhibition, and is thought to attenuate cellular responses to androgen. AR is expressed in osteoblasts, the bone-forming cell, suggesting direct actions of androgens on bone. Here we characterized the effect of androgen exposure on AR gene expression in human osteoblastic SaOS-2 and U-2 OS cells. Treatment of osteoblastic cells with the nonaromatizable androgen 5alpha-dihydrotestosterone increased AR steady state messenger RNA levels in a time- and dose-dependent fashion. Reporter assays with 2.3 kilobases of the proximal 5'-flanking region of the human AR promoter linked to the chloramphenicol acetyltransferase gene in transfected cultures showed that up-regulation of AR promoter activity by androgen was time and dose dependent. Treatment with other steroid hormones, including progesterone, 17beta-estradiol, and dexamethasone, was without effect. The antiandrogen hydroxyflutamide completely antagonized androgen up-regulation. Thus, in contrast to many other androgen target tissues, androgen exposure increases steady state AR messenger RNA levels in osteoblasts. This regulation occurs at least partially at the level of transcription, is mediated by the 5'-promoter region of the AR gene, and is dependent on functional AR. These results suggest that physiological concentrations of androgens have significant effects on AR expression in skeletal tissue.
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Affiliation(s)
- K M Wiren
- Bone and Mineral Research Unit, Veterans Affairs Medical Center, Portland, Oregon 97201, USA.
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39
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Haraguchi S, Good RA, Engelman RW, Greene S, Day NK. Prolactin, epidermal growth factor or transforming growth factor-alpha activate a mammary cell-specific enhancer in mouse mammary tumor virus-long terminal repeat. Mol Cell Endocrinol 1997; 129:145-55. [PMID: 9202398 DOI: 10.1016/s0303-7207(97)04053-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Mammary specific expression of elevated levels of mouse mammary tumor virus (MMTV) contributes to mammary carcinogenesis. Mechanisms which regulate provirus expression have not been completely defined. Using a MMTV-long repeat terminal (MMTV-LRT) directed chloramphenicol-acetyltransferase (CAT) reporter gene system and a human breast cancer cell line T47D, we demonstrate that prolactin (PRL), epidermal growth factor (EGF), or transforming growth factor-alpha (TGF-alpha) act on a mammary cell-specific enhancer at the extreme 5' end of the MMTV-LTR involving sequences -1094 through -858. PRL and either EGF or TGF-alpha exert concerted roles in this activation of these sequences. In contrast, using a plasmid construct lacking this mammary cell-specific enhancer, EGF or TGF-alpha, but not PRL, act synergistically with progesterone to induce CAT activity, indicating that the action of PRL on regulatory elements of the MMTV-LTR is restricted to this mammary cell-specific enhancer involving sequences -1094 through -858. A mobility shift assay was used to demonstrate that PRL, EGF or TGF-alpha induce nuclear factors (MP4, MAF, and MGF) which bind directly to this mammary cell-specific enhancer element.
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Affiliation(s)
- S Haraguchi
- Department of Pediatrics, All Children's Hospital, University of South Florida College of Medicine, St. Petersburg 33701, USA
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40
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Arroyo J, Winchester E, McLellan BS, Huber BT. Shared promoter elements between a viral superantigen and the major histocompatibility complex class II-associated invariant chain. J Virol 1997; 71:1237-45. [PMID: 8995647 PMCID: PMC191178 DOI: 10.1128/jvi.71.2.1237-1245.1997] [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: 02/03/2023] Open
Abstract
Superantigens have the ability to stimulate subsets of T lymphocytes bearing particular T-cell receptor Vbeta chains. The best-known viral superantigen is Mls, a product of the murine mammary tumor virus (MMTV) sag gene. The MMTV superantigen is not displayed by the virus itself; however, after infection of B lymphocytes, the superantigen is expressed. The resulting immune stimulation is essential for viral transmission. We have analyzed the transcriptional elements which control Mls-1 expression. Here we present evidence that a region at the 3' end of Mtv-7 env, Penv2, controls B-cell-specific expression of sag. Penv2 has elements homologous with promoters of immunoglobulin H chain, the invariant chain, and major histocompatibility complex class II, suggesting a coordinate regulation of expression of these various B-cell-specific genes and indicating a possible eukaryotic origin of MMTV sag. We have determined that both an IgH heptamer element and a Y box are essential for Penv2 promoter activity and that tandem octamer motifs in the U3 region of the 3' MMTV long terminal repeat function as enhancers. We propose that Penv2 controls constitutive Mls expression in B lymphocytes.
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Affiliation(s)
- J Arroyo
- Immunology Program, Department of Pathology, Tufts University, Boston, Massachusetts 02111, USA
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41
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Mouse Mammary Tumor Virus: Immunological Interplays between Virus and Host **This article was accepted for publication on 1 October 1996. Adv Immunol 1997. [DOI: 10.1016/s0065-2776(08)60743-9] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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42
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Kusk P, John S, Fragoso G, Michelotti J, Hager GL. Characterization of an NF-1/CTF family member as a functional activator of the mouse mammary tumor virus long terminal repeat 5' enhancer. J Biol Chem 1996; 271:31269-76. [PMID: 8940131 DOI: 10.1074/jbc.271.49.31269] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The long terminal repeat of the mouse mammary tumor virus restricts virus expression primarily to the mammary epithelium. The extreme 5' end of the long terminal repeat contains an enhancer that has been associated with tissue-specific expression of the virus. A total of six functional cis-acting elements have been identified in the enhancer. Although proteins binding to these elements have been reported, only one has been identified; this factor, mp5, is identical or closely related to the transcription factor AP-2 (Mellentin-Michelotti, J., John, S., Pennie, W. D., Williams, T., and Hager, G. L. (1994) J. Biol. Chem. 269, 31983-31990). The other factors are hitherto unidentified and poorly described. We report here the characterization of another of the six elements, previously referred to as the F3 site (Mink, S., Hartig, E., Jennewein, P., Doppler, W., and Cato, A. C. (1992) Mol. Cell Biol. 12, 4906-4918). We show that the F3 binding activity and AP-2 act synergistically to enhance mouse mammary tumor virus-directed transcription, but only in the presence of glucocorticoid hormone. The F3 element has an NF-1-like half-site, but the activity recognizing this element has binding characteristics distinct from the NF-1/CTF family as well as the rest of the CCAAT-binding proteins. We conclude that the F3 activity represents a new member of the NF-1/CTF family.
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Affiliation(s)
- P Kusk
- Laboratory of Receptor Biology and Gene Expression, NCI, National Institutes of Health, Bethesda, Maryland 20892-5055, USA.
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43
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Walther W, Stein U. Targeted vectors for gene therapy of cancer and retroviral infections. Mol Biotechnol 1996; 6:267-86. [PMID: 9067974 DOI: 10.1007/bf02761707] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Gene therapy has developed to a technology which rapidly moved from the laboratory bench to the bedside in the clinic. This implies safe, efficient and targeted gene transfer systems for suitable application to the patient. Beside the development of such gene transfer vectors of viral or nonviral origin, improvement of cell type specific and inducible gene expression is pivotal for successful gene therapy leading to targeted gene action. Numerous gene therapy approaches for treatment of cancer and retroviral infections utilize cell type specific and/or regulatable promoter and enhancer sequences for the selective expression of therapeutic genes in the desired cell populations and tissues. In this article the recent developments and the potential of expression targeting are reviewed for gene therapy approaches of cancer and retroviral infections.
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Affiliation(s)
- W Walther
- Max-Delbrück-Center for Molecular Medicine, Berlin
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44
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Walther W, Stein U. Cell type specific and inducible promoters for vectors in gene therapy as an approach for cell targeting. J Mol Med (Berl) 1996; 74:379-92. [PMID: 8841950 DOI: 10.1007/bf00210632] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Gene therapy is used to correct genetic defects or to deliver new therapeutic functions to the target cells. Viral vectors are employed mainly as a gene delivery system. A great variety of viral expression systems have been developed and assessed for their ability to transfer genes into somatic cells. In particular, retroviral and adenoviral mediated gene transfer have been extensively studied and improved. Preclinical and clinical studies covering a large range of genetic disorders are currently underway to solve basic issues dealing with gene transfer efficiencies, regulation of gene expression, and potential risks of the use of viral vectors. The majority of clinical gene therapy trials that employ viral vectors perform exvivo gene transfer into target cells. The main issue in potential clinical application of gene therapy is the need for increased gene transfer efficiency and target specificity associated with regulated gene expression at therapeutically relevant levels in vivo. Gene regulatory elements, such as promoters and enhancers, possess cell type specific activities and can be activated by certain induction factors (e.g., hormones, growth factors, cytokines, cytostatics, irradiation, heat shock) via responsive elements. A controlled and restricted expression of these genes can be achieved using such regulatory elements as internal promoters to drive the expression of therapeutic genes in viral vector constructs. In addition to high level and efficient gene expression, minimizing or excluding inappropriate gene expression in surrounding nontarget cells is of great importance for numerous gene therapeutic approaches. This contribution furnishes insight into the field of cell type specific promoter and enhancer systems which have been used for targeted and inducible expression of therapeutic genes in certain genetic disorders, viral infections, and malignancies. We also discuss promoters that represent attractive candidates for the construction of viral vectors.
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Affiliation(s)
- W Walther
- Max Delbrück Center for Molecular Medicine, Berlin, Germany
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45
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Le Ricousse S, Gouilleux F, Fortin D, Joulin V, Richard-Foy H. Glucocorticoid and progestin receptors are differently involved in the cooperation with a structural element of the mouse mammary tumor virus promoter. Proc Natl Acad Sci U S A 1996; 93:5072-7. [PMID: 8643531 PMCID: PMC39408 DOI: 10.1073/pnas.93.10.5072] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
We have previously characterized a regulatory element located between -294 and -200 within the mouse mammary tumor virus (MMTV) long terminal repeat (LTR). This element termed AA element cooperates with the glucocorticoid response elements (GREs) for glucocorticoid activation. Here we show that in a MMTV LTR wild type context, the deletion of this element significantly reduces both glucocorticoid and progestin activation of the promoter. Deletion of the two most distal GREs forces the glucocorticoid receptor (GR) and the progestin receptor (PR) to bind the same response elements and results in a dramatic decrease in the inducibility of the MMTV promoter by the two hormones. The simultaneous deletion of the two distal GREs and of the AA element abolishes completely the glucocorticoid-induced activation of the promoter. In contrast it restores a significant level of progestin-induced activation. This different effect of the double deletion on glucocorticoid- and progestin-induced MMTV promoter activation is not cell specific because it is also observed, and is even stronger, when either GR or PR is expressed in the same cell line (NIH 3T3). This is the first description of a mutated MMTV promoter that, although retaining GREs, is activated by progestins and not by glucocorticoids. This suggests a different functional cooperation between protein(s) interacting with the AA element and GR or PR. Cotransfections with constructs containing wild-type or mutated MMTV LTR with either PR lacking its C-terminal domain or GR/PR chimeras in which the N-terminal domains have been exchanged demonstrate that the N-terminal domains of the receptors specify the different behavior of GR and PR regarding the AA element.
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MESH Headings
- 3T3 Cells
- Amino Acid Sequence
- Animals
- Base Sequence
- Chimera/genetics
- DNA Primers/genetics
- Female
- Gene Deletion
- Genes, Viral
- Mammary Tumor Virus, Mouse/genetics
- Mammary Tumor Virus, Mouse/metabolism
- Mice
- Models, Genetic
- Molecular Sequence Data
- Plasmids/genetics
- Polymerase Chain Reaction
- Promoter Regions, Genetic
- Receptors, Glucocorticoid/genetics
- Receptors, Glucocorticoid/metabolism
- Receptors, Progesterone/genetics
- Receptors, Progesterone/metabolism
- Repetitive Sequences, Nucleic Acid
- Transfection
- Tumor Cells, Cultured
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Affiliation(s)
- S Le Ricousse
- Unité de Recherche sur les Communication Hormonales de I'Institut National de la Santé et de la Recherche Médicale, Bicêtre, France
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46
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Ritzi EM. Quantitative flow cytometry reveals a hierarchy of glucocorticoid effect on cell surface mouse mammary tumor virus gp52. J Steroid Biochem Mol Biol 1996; 57:33-42. [PMID: 8645615 DOI: 10.1016/0960-0760(95)00241-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
A flow cytometry protocol with CM mouse mammary tumor cells (Mm5mt/C1) was utilized to provide a fluorescence measurement of hormone-mediated changes in mouse mammary tumor virus (MMTV) cell surface envelope glycoprotein (gp52 CSA). Standards permitted gp52-specific fluorescence intensity to be measured as molecules of equivalent soluble fluorescein (MESF). The feasibility of using MESF determinations to reflect hormone-modulated changes in continuously infected cells was tested. A panel of five glucocorticoids having differing affinity for the glucocorticoid receptor were tested in 60 h treatments at dosages ranging from 10(-6) M to 10(-8) M. Determinations of MESF, as a measure of gp52 CSA, were highest with 10(-6) M treatments (36.7-44.5 x 10(-6) MESF). At lower dosages, MESF determinations were lower but showed a clear hierarchy of glucocorticoid effect. At 10(-8) M treatments, determinations of MESF x 10(-6) demonstrated the following glucocorticoid hierarchy: triamcinolone acetonide (TA) (33.7 +/- 1.6) > dexamethasone (DEX) (26.1 +/- 1.7) > prednisolone (8.0 +/- 0.3) > triamcinolone (6.6 +/- 0.4) > hydrocortisone (6.4 +/- 0.4) > control (2.4 +/- 0.1). The MESF-derived respective fold increases over control for this hierarchy were: 13.87, 10.74, 3.31, 2.71, and 2.65. The ability of TA to enhance gp52 CSA was 1.3-fold greater than DEX. 10-fold higher levels of steroid controls did not significantly elevate MESF levels. Findings argue that dosage, duration of treatment and relative affinity of glucocorticoids for receptor are reflected in MESF determinations of changing gp52 levels. Therefore, this new measure of effect may be useful in studying hormonal influence on viral and cellular regulatory systems in chronically infected cells.
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MESH Headings
- Administration, Topical
- Animals
- Anti-Inflammatory Agents/pharmacology
- Antigens, Viral, Tumor/analysis
- Antigens, Viral, Tumor/drug effects
- Dexamethasone/pharmacology
- Dose-Response Relationship, Drug
- Flow Cytometry/methods
- Fluorescein
- Fluoresceins/analysis
- Fluoresceins/chemistry
- Fluoresceins/metabolism
- Glucocorticoids/analysis
- Glucocorticoids/pharmacology
- Hydrocortisone/metabolism
- Hydrocortisone/pharmacology
- Mammary Neoplasms, Experimental/pathology
- Mice
- Mice, Inbred C3H
- Receptors, Glucocorticoid/metabolism
- Time Factors
- Tumor Cells, Cultured
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Affiliation(s)
- E M Ritzi
- Department of Microbiology and Immunology School of Medicine, Texas Tech University Health Sciences Center, Lubbock 79430, USA
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47
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Giffin W, Haché RJ. Nuclear factor binding to a DNA sequence element that represses MMTV transcription induces a structural transition and leads to the contact of single-stranded binding proteins with DNA. DNA Cell Biol 1995; 14:1025-35. [PMID: 8534369 DOI: 10.1089/dna.1995.14.1025] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
NRE1 is a DNA sequence element in the long terminal repeat of mouse mammary tumor virus through which viral transcription is repressed. In addition to double-stranded DNA binding, both upper- and lower-stranded NRE1 binding activities occur in nuclear extracts. All three binding activities appear to be important for transcriptional effects. We report that occupancy of NRE1 within linear double-stranded NRE1 induces a structural transition in upstream flanking DNA that is facilitated by Mg2+. This transition was reflected by the striking DNase I sensitivity of the DNA. As Mg2+ concentration was increased, discrete DNase I hypersensitivity on one face of the DNA progressed to complete degradation of template. On the DNA face opposite the DNase I hypersensitivity, Mg2+ promoted regularly spaced cleavage by the single-strand-specific cleavage agents KMnO4 and S1 nuclease. Induction of degradation by DNase I occurred independently of MMTV sequences flanking NRE1, because nuclear extract-dependent DNase I sensitivity was conferred to an unrelated DNA fragment by introduction of a 23-bp NRE1-containing oligonucleotide. UV protein-DNA cross-linking revealed that addition of Mg2+ to a double-stranded NRE1 DNA binding assay induced conversion from a double- to a single-stranded protein-DNA cross-linking pattern. Thus, nuclear factor binding to NRE1 induces changes in DNA topology that promote the direct contact of single-stranded NRE1 binding factors with DNA.
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Affiliation(s)
- W Giffin
- Department of Medicine, University of Ottawa, Loeb Institute for Medical Research, Ottawa Civic Hospital, Ontario, Canada
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48
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Kim MH, Peterson DO. Oct-1 Protein Promotes Functional Transcription Complex Assembly on the Mouse Mammary Tumor Virus Promoter. J Biol Chem 1995. [DOI: 10.1074/jbc.270.46.27823] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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49
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Mangues R, Schwartz S, Seidman I, Pellicer A. Promoter demethylation in MMTV/N-rasN transgenic mice required for transgene expression and tumorigenesis. Mol Carcinog 1995; 14:94-102. [PMID: 7576104 DOI: 10.1002/mc.2940140205] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We studied demethylation within the transgene promoter in transgenic mice carrying the N-ras proto-oncogene driven by the mouse mammary tumor long terminal repeat (MMTV/N-rasN) and the relationship of demethylation to transgene overexpression and tumorigenesis. Demethylation at Fspl or Clal sites correlated with age of the animal and transgene expression in nontumorous mammary gland. Demethylation preceded expression in this tissue. In lymphomas and mammary tumors, the promoter Fspl and Clal sites were significantly more demethylated than in nontumorous control tissues. The Aval, Cfol, and Hpall sites were also found to be undermethylated in older animals and showed differences between tumor and control tissues. Two additional sites (Eagl and Narl) remained fully methylated in all tissues. In contrast with normal tissue, demethylation at the Fspl and Clal sites and expression were not correlated in tumor tissue. An increase in expression in normal tissue initially occurred and was correlated with the level of promoter demethylation; this increase was followed by a further increment in transgene expression when tumors developed. Thus, promoter demethylation leading to transgene overexpression was associated with long-latency tumorigenesis in MMTV/N-rasN transgenic mice. Demethylation of proto-oncogene promoters may therefore be a mechanism of carcinogenesis that requires further investigation in human tumors.
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Affiliation(s)
- R Mangues
- Department of Pathology, New York University Medical Center, New York 10016, USA
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50
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Roberts MS, Fragoso G, Hager GL. Nucleosomes reconstituted in vitro on mouse mammary tumor virus B region DNA occupy multiple translational and rotational frames. Biochemistry 1995; 34:12470-80. [PMID: 7547993 DOI: 10.1021/bi00038a046] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The mouse mammary tumor virus acquires a highly reproducible chromatin structure when integrated into cellular DNA. Previous studies have suggested that the LTR is arranged as a series of six phased nucleosomes, that occupy specific positions on the LTR. On the basis of nucleosome reconstitution studies using DNA from the B region of the LTR, it has been argued that this sequence directs a uniquely positioned nucleosome. Here we demonstrate in vitro that reconstituted B region nucleosomes adopt at least five distinct translational positions in two rotational frames on a 206 bp fragment of DNA. We have resolved an initial reconstitute into its component species using nondenaturing gel electrophoresis, and precisely mapped the positions of each species using a hydroxyl radical footprinting assay. To confirm the nucleosome positions determined with the hydroxyl radical assay, nucleosome boundaries were mapped using exonuclease III. Comparison of the results from the hydroxyl radical footprinting and exonuclease III assays revealed a symmetrical pattern of overdigestion by exonuclease III which made unequivocal determination of nucleosome boundaries dubious. We conclude that the general use of exonuclease III to map the positions of nucleosomes may lead to incorrect assignment of position, and that assignment of position through the determination of the nucleosome pseudo-dyad from hydroxyl radical footprinting data represents a superior method of analysis.
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Affiliation(s)
- M S Roberts
- Laboratory of Molecular Virology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-5055, USA
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