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Rawson JMO, Mansky LM. Retroviral vectors for analysis of viral mutagenesis and recombination. Viruses 2014; 6:3612-42. [PMID: 25254386 PMCID: PMC4189041 DOI: 10.3390/v6093612] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Revised: 09/15/2014] [Accepted: 09/17/2014] [Indexed: 12/29/2022] Open
Abstract
Retrovirus population diversity within infected hosts is commonly high due in part to elevated rates of replication, mutation, and recombination. This high genetic diversity often complicates the development of effective diagnostics, vaccines, and antiviral drugs. This review highlights the diverse vectors and approaches that have been used to examine mutation and recombination in retroviruses. Retroviral vectors for these purposes can broadly be divided into two categories: those that utilize reporter genes as mutation or recombination targets and those that utilize viral genes as targets of mutation or recombination. Reporter gene vectors greatly facilitate the detection, quantification, and characterization of mutants and/or recombinants, but may not fully recapitulate the patterns of mutagenesis or recombination observed in native viral gene sequences. In contrast, the detection of mutations or recombination events directly in viral genes is more biologically relevant but also typically more challenging and inefficient. We will highlight the advantages and disadvantages of the various vectors and approaches used as well as propose ways in which they could be improved.
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Affiliation(s)
- Jonathan M O Rawson
- Institute for Molecular Virology, University of Minnesota, Moos Tower 18-242, 515 Delaware St SE, Minneapolis, MN 55455, USA.
| | - Louis M Mansky
- Institute for Molecular Virology, University of Minnesota, Moos Tower 18-242, 515 Delaware St SE, Minneapolis, MN 55455, USA.
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Delviks-Frankenberry K, Galli A, Nikolaitchik O, Mens H, Pathak VK, Hu WS. Mechanisms and factors that influence high frequency retroviral recombination. Viruses 2011; 3:1650-1680. [PMID: 21994801 PMCID: PMC3187697 DOI: 10.3390/v3091650] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2011] [Revised: 08/18/2011] [Accepted: 08/25/2011] [Indexed: 01/25/2023] Open
Abstract
With constantly changing environmental selection pressures, retroviruses rely upon recombination to reassort polymorphisms in their genomes and increase genetic diversity, which improves the chances for the survival of their population. Recombination occurs during DNA synthesis, whereby reverse transcriptase undergoes template switching events between the two copackaged RNAs, resulting in a viral recombinant with portions of the genetic information from each parental RNA. This review summarizes our current understanding of the factors and mechanisms influencing retroviral recombination, fidelity of the recombination process, and evaluates the subsequent viral diversity and fitness of the progeny recombinant. Specifically, the high mutation rates and high recombination frequencies of HIV-1 will be analyzed for their roles in influencing HIV-1 global diversity, as well as HIV-1 diagnosis, drug treatment, and vaccine development.
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Affiliation(s)
- Krista Delviks-Frankenberry
- Viral Mutation Section, HIV Drug Resistance Program, National Cancer Institute at Frederick, Frederick, MD 21702, USA; E-Mails: (K.D.-F.); (V.K.P.)
| | - Andrea Galli
- Viral Recombination Section, HIV Drug Resistance Program, National Cancer Institute at Frederick, Frederick, MD 21702, USA; E-Mails: (A.G.); (O.N.)
- Copenhagen Hepatitis C Program, Department of Infectious Diseases, Copenhagen University Hospital, Hvidovre 2650, Denmark
| | - Olga Nikolaitchik
- Viral Recombination Section, HIV Drug Resistance Program, National Cancer Institute at Frederick, Frederick, MD 21702, USA; E-Mails: (A.G.); (O.N.)
| | - Helene Mens
- Department of Epidemic Diseases, Rigshospitalet, København 2100, Denmark; E-Mail:
| | - Vinay K. Pathak
- Viral Mutation Section, HIV Drug Resistance Program, National Cancer Institute at Frederick, Frederick, MD 21702, USA; E-Mails: (K.D.-F.); (V.K.P.)
| | - Wei-Shau Hu
- Viral Recombination Section, HIV Drug Resistance Program, National Cancer Institute at Frederick, Frederick, MD 21702, USA; E-Mails: (A.G.); (O.N.)
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +1-301-846-1250; Fax: +1-301-846-6013
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Liu J, Sørensen AB, Wang B, Wabl M, Nielsen AL, Pedersen FS. Identification of novel Bach2 transcripts and protein isoforms through tagging analysis of retroviral integrations in B-cell lymphomas. BMC Mol Biol 2009; 10:2. [PMID: 19159451 PMCID: PMC2635362 DOI: 10.1186/1471-2199-10-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2008] [Accepted: 01/21/2009] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The Bach2 gene functions as a transcriptional repressor in B-cells, showing high expression level only before the plasma cell stage. Several lines of evidence indicate that Bach2 is a B-cell specific tumor suppressor. We here address patterns of insertional mutagenesis and expression of Bach2 is a murine retroviral model of B-cell lymphoma induction. RESULTS We report that the Bach2 gene is a target of proviral integrations in B-cell lymphomas induced by murine leukemia virus. An alternative Bach2 promoter was identified within intron 2 and this promoter was activated in one of the tumors harboring proviral integration. The alternative promoter was active in both normal and tumor tissue and the tissue specificity of the two Bach2 promoters was similar. Three different alternatively used Bach2 terminal exons were identified to be located in intron 4. The inclusion of these exons resulted in the generation of Bach2 mRNA with open reading frames lacking the bZIP DNA binding domain present in the normal Bach2 protein, but retaining a partial BTB protein dimerization domain. Such Bach2 protein was excluded from the cell nucleus. CONCLUSION We have identified an alternative promoter and new protein isoforms of Bach2. Our data imply that activation of an alternative promoter by proviral integration serves as a possible mechanism of up-regulation of the Bach2 gene with a potential role in B-cell lymphomagenesis. The finding of novel Bach2 transcripts and protein isoforms will facilitate a better insight into the normal and pathophysiological regulation of the Bach2 gene.
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Affiliation(s)
- Jinghua Liu
- Department of Molecular Biology, C.F. Møllers Allé 1.130, University of Aarhus, Aarhus C, Denmark.
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Ma SL, Sørensen AB, Kunder S, Sørensen KD, Quintanilla-Martinez L, Morris DW, Schmidt J, Pedersen FS. The Icsbp locus is a common proviral insertion site in mature B-cell lymphomas/plasmacytomas induced by exogenous murine leukemia virus. Virology 2006; 352:306-18. [PMID: 16780917 DOI: 10.1016/j.virol.2006.05.006] [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] [Received: 01/20/2006] [Revised: 02/16/2006] [Accepted: 05/03/2006] [Indexed: 10/24/2022]
Abstract
ICSBP (interferon consensus sequence binding protein)/IRF8 (interferon regulatory factor 8) is an interferon gamma-inducible transcription factor expressed predominantly in hematopoietic cells, and down-regulation of this factor has been observed in chronic myelogenous leukemia and acute myeloid leukemia in man. By screening about 1200 murine leukemia virus (MLV)-induced lymphomas, we found proviral insertions at the Icsbp locus in 14 tumors, 13 of which were mature B-cell lymphomas or plasmacytomas. Only one was a T-cell lymphoma, although such tumors constituted about half of the samples screened. This indicates that the Icsbp locus can play a specific role in the development of mature B-lineage malignancies. Two proviral insertions in the last Icsbp exon were found to act by a poly(A)-insertion mechanism. The remaining insertions were found within or outside Icsbp. Since our results showed expression of Icsbp RNA and protein in all end-stage tumor samples, a simple tumor suppressor function of ICSBP is not likely. Interestingly, proviral insertions at Icsbp have not been reported from previous extensive screenings of mature B-cell lymphomas induced by endogenous MLVs. We propose that ICSBP might be involved in an early modulation of an immune response to exogenous MLVs that might also play a role in proliferation of the mature B-cell lymphomas.
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MESH Headings
- Animals
- Base Sequence
- Interferon Regulatory Factors/genetics
- Leukemia Virus, Murine/genetics
- Leukemia Virus, Murine/pathogenicity
- Lymphoma, B-Cell/etiology
- Lymphoma, B-Cell/genetics
- Lymphoma, B-Cell/pathology
- Lymphoma, B-Cell/virology
- Mice
- Plasmacytoma/etiology
- Plasmacytoma/genetics
- Plasmacytoma/pathology
- Plasmacytoma/virology
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Neoplasm/genetics
- RNA, Neoplasm/metabolism
- Virus Integration/genetics
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Affiliation(s)
- Shi Liang Ma
- Department of Molecular Biology, University of Aarhus, C.F. Møllers Alle, Bldg. 130, DK-8000 Aarhus C, Denmark
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Sørensen KD, Sørensen AB, Quintanilla-Martinez L, Kunder S, Schmidt J, Pedersen FS. Distinct roles of enhancer nuclear factor 1 (NF1) sites in plasmacytoma and osteopetrosis induction by Akv1-99 murine leukemia virus. Virology 2005; 334:234-44. [PMID: 15780873 DOI: 10.1016/j.virol.2005.01.039] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2004] [Revised: 12/30/2004] [Accepted: 01/31/2005] [Indexed: 10/25/2022]
Abstract
Murine leukemia viruses (MLVs) can be lymphomagenic and bone pathogenic. In this work, the possible roles of two distinct proviral enhancer nuclear factor 1 (NF1) binding sites in osteopetrosis and tumor induction by B-lymphomagenic Akv1-99 MLV were investigated. Akv1-99 and mutants either with NF1 site 1, NF1 site 2 or both sites disrupted induced tumors (plasma cell proliferations by histopathology) with remarkably similar incidence and mean latency in inbred NMRI mice. Clonal immunoglobulin gene rearrangement detection, by Southern analysis, confirmed approximately half of the tumors induced by each virus to be plasmacytomas while the remaining lacked detectable clonally rearranged Ig genes and were considered polyclonal; a demonstration that enhancer NF1 sites are dispensable for plasmacytoma induction by Akv1-99. In contrast, X-ray analysis revealed significant differences in osteopetrosis induction by the four viruses strongly indicating that NF1 site 2 is critical for viral bone pathogenicity, whereas NF1 site 1 is neutral or moderately inhibitory. In conclusion, enhancer NF1 sites are major determinants of osteopetrosis induction by Akv1-99 without significant influence on viral oncogenicity.
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Affiliation(s)
- Karina Dalsgaard Sørensen
- Department of Molecular Biology, University of Aarhus, C.F. Møllers Allé, Building 130, DK-8000 Aarhus C, Denmark
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Wang CL, Hodgson JG, Malek T, Pedersen FS, Wabl M. A murine leukemia virus with Cre-LoxP excisible coding sequences allowing superinfection, transgene delivery, and generation of host genomic deletions. Retrovirology 2004; 1:5. [PMID: 15169571 PMCID: PMC419723 DOI: 10.1186/1742-4690-1-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2004] [Accepted: 04/05/2004] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND To generate a replication-competent retrovirus that could be conditionally inactivated, we flanked the viral genes of the Akv murine leukemia virus with LoxP sites. This provirus can delete its envelope gene by LoxP/Cre mediated recombination and thereby allow superinfection of Cre recombinase expressing cells. RESULTS In our studies, the virus repeatedly infected the cell and delivered multiple copies of the viral genome to the host genome; the superinfected cells expressed a viral transgene on average twenty times more than non-superinfected cells. The insertion of multiple LoxP sites into the cellular genome also led to genomic deletions, as demonstrated by comparative genome hybridization. CONCLUSION We envision that this technology may be particularly valuable for delivering transgenes and/or causing deletions.
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Affiliation(s)
- Clifford L Wang
- Department of Microbiology and Immunology, University of California, San Francisco, CA, USA, 94143-0414
| | - J Graeme Hodgson
- Department of Laboratory Medicine, University of California, San Francisco, CA, USA, 94143-0808
| | - Tiffany Malek
- Fred Hutchinson Cancer Research Centre, Department of Human Biology, Seattle, WA 98109, USA
| | - Finn Skou Pedersen
- Department of Molecular Biology and Department of Medical Microbiology and Immunology, University of Aarhus, Denmark, DK-8000
| | - Matthias Wabl
- Department of Microbiology and Immunology, University of California, San Francisco, CA, USA, 94143-0414
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DiFronzo NL, Frieder M, Loiler SA, Pham QN, Holland CA. Duplication of U3 sequences in the long terminal repeat of mink cell focus-inducing viruses generates redundancies of transcription factor binding sites important for the induction of thymomas. J Virol 2003; 77:3326-33. [PMID: 12584358 PMCID: PMC149780 DOI: 10.1128/jvi.77.5.3326-3333.2003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The ability of mink cell focus-inducing (MCF) viruses to induce thymomas is determined, in part, by transcriptional enhancers in the U3 region of their long terminal repeats (LTRs). To elucidate sequence motifs important for enhancer function in vivo, we injected newborn mice with MCF 1dr (supF), a weakly pathogenic, molecularly tagged (supF) MCF virus containing only one copy of a sequence that is present as two copies (known as the directly repeated [DR] sequence) in the U3 region of MCF 247 and analyzed LTRs from supF-tagged proviruses in two resulting thymomas. Tagged proviruses integrated upstream and in the reverse transcriptional orientation relative to c-myc provided the focus of our studies. These proviruses are thought to contribute to thymoma induction by enhancer-mediated deregulation of c-myc expression. The U3 region in a tagged LTR in one thymoma was cloned and sequenced. Relative to MCF 1dr (supF), the cloned U3 region contained an insertion of 140 bp derived predominantly from the DR sequence of the injected virus. The inserted sequence contains predicted binding sites for transcription factors known to regulate the U3 regions of various murine leukemia viruses. Similar constellations of binding sites were duplicated in two proviral LTRs integrated upstream from c-myc in a second thymoma. We replaced the U3 sequences in an infectious molecular clone of MCF 247 with the cloned proviral U3 sequences from the first thymoma and generated an infectious chimeric virus, MCF ProEn. When injected into neonatal AKR mice, MCF ProEn was more pathogenic than the parental virus, MCF 1dr (supF), as evidenced by the more rapid onset and higher incidence of thymomas. Molecular analyses of the resultant thymomas indicated that the U3 region of MCF ProEn was genetically stable. These data suggest that the arrangement and/or redundancy of transcription factor binding sites generated by specific U3 sequence duplications are important to the biological events mediated by MCF proviruses integrated near c-myc that contribute to transformation.
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Affiliation(s)
- Nancy L DiFronzo
- Center for Virology and Immunology Research, Children's Research Institute, George Washington University School of Medical and Health Sciences, Washington, DC 20010, USA
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8
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Lovmand J, Sorensen AB, Schmidt J, Ostergaard M, Luz A, Pedersen FS. B-Cell lymphoma induction by akv murine leukemia viruses harboring one or both copies of the tandem repeat in the U3 enhancer. J Virol 1998; 72:5745-56. [PMID: 9621033 PMCID: PMC110375 DOI: 10.1128/jvi.72.7.5745-5756.1998] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Akv is an endogenous, ecotropic murine leukemia virus (MuLV) of the AKR strain. It has served as a prototype nonpathogenic or weakly pathogenic reference virus for studies of closely related potent lymphomagenic viruses such as the T-lymphomagenic SL3-3. We here report that Akv and an Akv mutant (Akv1-99) with only one copy of the 99-bp transcriptional enhancer induce malignant lymphomas with nearly 100% incidence and mean latency periods of 12 months after injection into newborn NMRI mice. Molecular analysis of tumor DNA showed that the majority of the tumors were of the B-cell type. Sequence analysis of proviral transcriptional enhancers in DNA of B-cell lymphomas revealed conservation of the enhancer sequence, as well as a lack of sequence duplications of the Akv1-99 variant, while the repeat copy number in Akv was subject to fluctuations. In support of a B-cell specificity of the Akv enhancer, a murine plasmacytoma cell line was found to sustain three- to fivefold-higher transient transcriptional activity upon the Akv and Akv1-99 enhancers than upon the enhancer of the T-lymphomagenic SL3-3 MuLV. Thus, the overall picture is that Akv MuLV possesses a B- lymphomagenic potential and that the second copy of the 99-bp sequence seems to be of minor importance for this potential. However, in one animal the lymphomas induced by Akv1-99 were of the T-cell type. Among the 24 tumors analyzed only this one harbored a clonal proviral integration in the c-myc locus. This provirus had undergone a duplication of a 113-bp sequence of the enhancer region, partly overlapping with the 99-bp repeat of Akv, as well as a few single nucleotide alterations within and outside the repeats. Taken together with previous studies, our results suggest that T- versus B-lymphomagenic specificity of the enhancer is governed by more than one nucleotide difference and that alterations in binding sites for transcription factors of the AML1 and nuclear-factor-1 families may contribute to this specificity.
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Affiliation(s)
- J Lovmand
- Department of Molecular and Structural Biology, University of Aarhus, DK-8000 Aarhus C, Denmark
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9
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Kim V, Green WR. The role of proximal and distal sequence variations in the presentation of an immunodominant CTL epitope encoded by the ecotropic AK7 MuLV. Virology 1997; 236:221-33. [PMID: 9325230 DOI: 10.1006/viro.1997.8747] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
An emv-14-derived, replication-competent ecotropic murine leukemia virus [MuLV], designated AK7, was previously cloned from the AKXL-5 recombinant inbred mouse strain and partially characterized. While genetically encoding for an envelope-derived immunodominant CTL epitope [KSPWFTTL] located in the transmembrane region of p15TM, this virus, unlike the emv-11-derived virus AKR623, fails to be efficiently recognized by AKR/Gross MuLV-specific cytotoxic T lymphocytes [CTL]. AK7 thus provides the opportunity to study the role of retroviral sequence variations that are located outside of the immunodominant epitope as a mechanism of escape from CTL-mediated immune surveillance. In an attempt to identify which region[s] of the AK7 genome could account for its ability to evade efficient recognition by AKR/Gross MuLV-specific CTL, we have constructed recombinant murine retroviruses. The direct influence of a sequence variation twelve amino acids N-terminal to KSPWFTTL was explored with the use of chimeric viruses and determined not to significantly impair the presentation of KSPWFTTL to AKR/Gross MuLV-specific CTL. The long terminal repeat [LTR] derived from the AK7 virus, which possesses only one copy of the 99-base pair transcriptional enhancer in the U3 region, in contrast to AKR623 that possesses two copies of the tandem direct repeat enhancers, was also analyzed for its influence on the presentation of KSPWFTTL. Interestingly, our data indicate that the enhancer region derived from AK7 negatively influences the presentation of KSPWFTTL in the context of a recombinant AKR623 virus.
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Affiliation(s)
- V Kim
- Department of Microbiology, Dartmouth Medical School, Lebanon, New Hampshire, USA
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10
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Ethelberg S, Hallberg B, Lovmand J, Schmidt J, Luz A, Grundström T, Pedersen FS. Second-site proviral enhancer alterations in lymphomas induced by enhancer mutants of SL3-3 murine leukemia virus: negative effect of nuclear factor 1 binding site. J Virol 1997; 71:1196-206. [PMID: 8995642 PMCID: PMC191173 DOI: 10.1128/jvi.71.2.1196-1206.1997] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
SL3-3 is a highly T-lymphomagenic murine retrovirus. Previously, mutation of binding sites in the U3 repeat region for the AML1 transcription factor family (also known as core binding factor [CBF], polyomavirus enhancer binding protein 2 [PEBP2], and SL3-3 enhancer factor 1 [SEF1]) were found to strongly reduce the pathogenicity of SL3-3 (B. Hallberg, J. Schmidt, A. Luz, F. S. Pedersen, and T. Grundström, J. Virol. 65:4177-4181, 1991). We have now examined the few cases in which tumors developed harboring proviruses that besides the AML1 (core) site mutations carried second-site alterations in their U3 repeat structures. In three distinct cases we observed the same type of alteration which involved deletions of regions known to contain binding sites for nuclear factor 1 (NF1) and the addition of extra enhancer repeat elements. In transient-expression experiments in T-lymphoid cells, these new U3 regions acted as stronger enhancers than the U3 regions of the original viruses. This suggests that the altered proviruses represent more-pathogenic variants selected for in the process of tumor formation. To analyze the proviral alterations, we generated a series of different enhancer-promoter reporter constructs. These constructs showed that the additional repeat elements are not critical for enhancer strength, whereas the NF1 sites down-regulate the level of transcription in T-lymphoid cells whether or not the AML1 (core) sites are functional. We therefore also tested SL3-3 viruses with mutated NF1 sites. These viruses have unimpaired pathogenic properties and thereby distinguish SL3-3 from Moloney murine leukemia virus.
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Affiliation(s)
- S Ethelberg
- Department of Molecular and Structural Biology, University of Aarhus, Denmark
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11
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Ostergaard M, Pedersen L, Schmidt J, Luz A, Lovmand J, Erfle V, Pedersen FS, Strauss PG. Mapping of a major osteomagenic determinant of murine leukemia virus RFB-14 to non-long terminal repeat sequences. J Virol 1997; 71:645-9. [PMID: 8985395 PMCID: PMC191096 DOI: 10.1128/jvi.71.1.645-649.1997] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Certain isolates of murine leukemia viruses (MuLVs) have, apart from a leukemogenic potential, the capability of inducing diseases of nonhematopoietic tissues in susceptible strains of mice. We have reported on the molecular cloning of a bone-tumorigenic virus, RFB-14 MuLV, which was found to induce benign bone tumors, osteomas, with 100% incidence in mice of the CBA/Ca strain (L. Pedersen, W. Behnisch, J. Schmidt, A. Luz, F. S. Pedersen, V. Erfle, and P. G. Strauss, J. Virol. 66:6186-6190, 1992). In order to analyze the bone tumor-inducing phenotype of RFB-14 MuLV, we have studied the pathogenic potential of recombinant viruses between RFB-14 and the nonosteomagenic, highly leukemogenic SL3-3 MuLV. The recombinants were constructed so as to reveal whether a major determinant of osteomagenicity maps to sequences within or outside the long terminal repeats (LTR). Our data show that a major determinant of the osteoma-inducing potential of RFB-14 MuLV maps to the non-LTR region of the genome. Furthermore, we demonstrate that a strong determinant of leukemogenicity is harbored by the non-LTR region of SL3-3 MuLV.
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Affiliation(s)
- M Ostergaard
- Department of Molecular and Structural Biology, University of Aarhus, Denmark
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12
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Fourel G, Ringeisen F, Flajolet M, Tronche F, Pontoglio M, Tiollais P, Buendia MA. The HNF1/HNF4-dependent We2 element of woodchuck hepatitis virus controls viral replication and can activate the N-myc2 promoter. J Virol 1996; 70:8571-83. [PMID: 8970982 PMCID: PMC190950 DOI: 10.1128/jvi.70.12.8571-8583.1996] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Transcriptional activation of myc family proto-oncogenes through the insertion of viral sequences is the predominant mechanism by which woodchuck hepatitis virus (WHV) induces liver tumors in chronically infected animals. The main target is N-myc2, a functional retroposon of the N-myc gene, but c-myc and N-myc are also marginally involved. Here we identify a major, liver-specific regulatory element in the WHV genome (We2) which efficiently activates the N-myc2 promoter in cultured hepatoma cells. In the context of the episomal viral genome, We2 governs the production of pregenomic RNA and thus plays a central role in the control of viral replication. We2 activity is primarily controlled by the liver-enriched HNF1 and HNF4 transcription factors, although NF1 and Oct proteins were also shown to bind in a central region. The expression of HNF1 and HNF4 appears to be maintained in woodchuck tumors. Thus, We2 is a prime candidate for controlling myc gene cis activation during WHV-induced hepatocarcinogenesis.
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Affiliation(s)
- G Fourel
- Unité de Recombinaison et Expression Génétique, INSERM U163, Institut Pasteur, Paris, France
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13
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Nielsen AL, Nørby PL, Pedersen FS, Jørgensen P. Various modes of basic helix-loop-helix protein-mediated regulation of murine leukemia virus transcription in lymphoid cell lines. J Virol 1996; 70:5893-901. [PMID: 8709209 PMCID: PMC190607 DOI: 10.1128/jvi.70.9.5893-5901.1996] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The transcriptionally regulatory regions of the lymphomagenic Akv and SL3-3 murine leukemia retroviruses (MLVs) contain two types of E-box consensus motifs, CAGATG. One type, EA/S, is located in the upstream promoter region, and the other, E(gre), is located in a tandem repeat with enhancer properties. We have examined the requirements of the individual E-boxes in MLV transcriptional regulation. In lymphoid cell lines only, the E(gre)-binding protein complexes included ALF1 or HEB and E2A basic helix-loop-helix proteins. Ectopic ALF1 and E2A proteins required intact E(gre) motifs for mediating transcriptional activation. ALF1 transactivated transcription of Akv MLV through the two E(gre) motifs equally, whereas E2A protein required the promoter-proximal E(gre) motif. In T- and B-cell lines, the E(gre) motifs were of major importance for Akv MLV transcriptional activity, while the EA/S motif had some effect. In contrast, neither E(gre) nor EA/S motifs contributed pronouncedly to Akv MLV transcription in NIH 3T3 cells lacking DNA-binding ALF1 or HEB and E2A proteins. The Id1 protein was found to repress ALF1 activity in vitro and in vivo. Moreover, ectopic Id1 repressed E(gre)-directed but not EA/S-directed MLV transcription in lymphoid cell lines. In conclusion, E(gre) motifs and interacting basic helix-loop-helix proteins are important determinants for MLV transcriptional activity in lymphocytic cell lines.
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Affiliation(s)
- A L Nielsen
- Department of Molecular and Structural Biology, University of Aarhus, Denmark
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14
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Julias JG, Hash D, Pathak VK. E- vectors: development of novel self-inactivating and self-activating retroviral vectors for safer gene therapy. J Virol 1995; 69:6839-46. [PMID: 7474097 PMCID: PMC189597 DOI: 10.1128/jvi.69.11.6839-6846.1995] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
We have developed novel self-inactivating and self-activating retroviral vectors based on the previously observed high-frequency deletion of direct repeats. We constructed spleen necrosis virus (SNV)-based viral vectors that contained large direct repeats flanking the viral encapsidation sequence (E). A large proportion of the proviruses in the target cells had E and one copy of the direct repeat deleted. Direct repeats of 1,333 and 788 bp were deleted at frequencies of 93 and 85%, respectively. To achieve a 100% deletion efficiency in target cells after ex vivo infection and drug selection, we constructed a self-activating vector that simultaneously deleted E and reconstituted the neomycin phosphotransferase gene. Selection of the target cells for resistance to G418 (a neomycin analog) ensured that all integrated proviruses had E deleted. The proviruses with E deleted were mobilized by a replication-competent virus 267,000-fold less efficiently than proviruses with E. We named these self-inactivating vectors E- (E-minus) vectors. These vectors should increase the safety of retroviral vector-mediated gene therapy by preventing the spread of vector sequences to nontarget cells in the event of coinfection with helper virus. We propose that direct-repeat deletions occur during RNA-dependent DNA synthesis and suggest that template switches occur without a requirement for RNA breaks. The minimum template dissociation frequency was estimated as 8%/100 bp per replication cycle. These vectors demonstrate that large direct repeats and template-switching properties of reverse transcriptase can be utilized to delete any sequence or reconstitute genes during retroviral replication.
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Affiliation(s)
- J G Julias
- Department of Biochemistry, West Virginia University, Morgantown 26506, USA
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15
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Athas GB, Lobelle-Rich P, Levy LS. Function of a unique sequence motif in the long terminal repeat of feline leukemia virus isolated from an unusual set of naturally occurring tumors. J Virol 1995; 69:3324-32. [PMID: 7745680 PMCID: PMC189044 DOI: 10.1128/jvi.69.6.3324-3332.1995] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Feline leukemia virus (FeLV) proviruses have been characterized from naturally occurring non-B-cell, non-T-cell tumors occurring in the spleens of infected cats. These proviruses exhibit a unique sequence motif in the long terminal repeat (LTR), namely, a 21-bp tandem triplication beginning 25 bp downstream of the enhancer. The repeated finding of the triplication-containing LTR in non-B-cell, non-T-cell lymphomas of the spleen suggests that the unique LTR is an essential participant in the development of tumors of this particular phenotype. The nucleotide sequence of the triplication-containing LTR most closely resembles that of FeLV subgroup C. Studies performed to measure the ability of the triplication-containing LTR to modulate gene expression indicate that the 21-bp triplication provides transcriptional enhancer function to the LTR that contains it and that it substitutes at least in part for the duplication of the enhancer. The 21-bp triplication confers a bona fide enhancer function upon LTR-directed reporter gene expression; however, the possibility of a spacer function was not eliminated. The studies demonstrate further that the triplication-containing LTR acts preferentially in a cell-type-specific manner, i.e., it is 12-fold more active in K-562 cells than is an LTR lacking the triplication. A recombinant, infectious FeLV bearing the 21-bp triplication in U3 was constructed. Cells infected with the recombinant were shown to accumulate higher levels of viral RNA transcripts and virus particles in culture supernatants than did cells infected with the parental type. The triplication-containing LTR is implicated in the induction of tumors of a particular phenotype, perhaps through transcriptional regulation of the virus and/or adjacent cellular genes, in the appropriate target cell.
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Affiliation(s)
- G B Athas
- Department of Microbiology and Immunology, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA
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16
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Nielsen AL, Pallisgaard N, Pedersen FS, Jørgensen P. Basic helix-loop-helix proteins in murine type C retrovirus transcriptional regulation. J Virol 1994; 68:5638-47. [PMID: 8057444 PMCID: PMC236965 DOI: 10.1128/jvi.68.9.5638-5647.1994] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
E boxes, recognition sequences for basic helix-loop-helix (bHLH) transcription factors, are detected in the enhancer and promoter regions of several murine type C retroviruses. Here we show that ALF1, a member of bHLH protein family of transcription factors, in vitro binds with differing affinities to distinct E-box sequences found in the U3 regulatory regions of Friend, Moloney, SL3-3, and Akv murine leukemia viruses (MLVs) as well as Friend spleen focus-forming virus (SFFV). In NIH 3T3 fibroblasts, ALF1 overexpression elevated transcription from the U3 region of Moloney MLV and the complete long terminal repeat regions of Friend SFFV, Akv MLV, and SL3-3 MLV but neither from the U3 region nor from the complete long terminal repeat of Friend MLV. Introduction of mutations in the Akv MLV E boxes showed the E-box cis elements to be required for the function of ALF1 as a transcription factor. ALF1 and the glucocorticoid receptor, with overlapping DNA binding sequences, did not act synergistically with respect to transcriptional trans activation of expression from the Akv MLV promoter-enhancer region. We conclude that ALF1 in vivo may be an important transcription regulator for Akv, SL3-3, and Moloney MLVs as well as for Friend SFFV.
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Affiliation(s)
- A L Nielsen
- Department of Molecular Biology, Aarhus University, Denmark
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17
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Duch M, Paludan K, Lovmand J, Pedersen L, Jørgensen P, Pedersen FS. A correlation between dexamethasone inducibility and basal expression levels of retroviral vector proviruses. Nucleic Acids Res 1993; 21:4777-82. [PMID: 8233826 PMCID: PMC331505 DOI: 10.1093/nar/21.20.4777] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Identical transcription units inserted at different positions of mammalian chromosomes may vary widely in transcriptional activity. We have used a set of ten cell clones with random unselected single integrations of retroviral vectors to study such position effects. The vector used carries a neo gene driven by the Akv murine leukemia virus long terminal repeat that has only a weak promoter-enhancer activity in the target cell, the lymphoid cell line L691. Under transient expression conditions, the strength of the Akv promoter-enhancer in the L691 cells is increased by dexamethasone. In cell clones with single vector integrations, a correlation is observed between the non-induced expression levels and the degree of dexamethasone induction. The strongest relative induction is found for the integrated vectors with the lowest non-induced expression levels and approaches the inducibility under transient expression. These results indicate that expression levels are composed of distinct contributions from the integrated vector and from the site of integration and are best explained in terms of a model in which the sites of chromosomal integration exert variable positive enhancer effects upon vector transcription.
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Affiliation(s)
- M Duch
- Department of Molecular Biology, University of Aarhus, Denmark
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18
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Tupper JC, Chen H, Hays EF, Bristol GC, Yoshimura FK. Contributions to transcriptional activity and to viral leukemogenicity made by sequences within and downstream of the MCF13 murine leukemia virus enhancer. J Virol 1992; 66:7080-8. [PMID: 1331510 PMCID: PMC240380 DOI: 10.1128/jvi.66.12.7080-7088.1992] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
We have identified nucleotide sequences that regulate transcription in both a cell-type-specific and general manner in the long terminal repeat of the MCF13 murine leukemia virus. Besides the enhancer element, we have observed that the region between the enhancer and promoter (DEN) has a profound effect on transcription in different cell types. This effect, however, was dependent on the copy number of enhancer repeats and was detectable in the presence of a single repeat. When two enhancer repeats were present, the effect of DEN on transcription was abrogated except in T cells. DEN also makes a significant contribution to the leukemogenic property of the MCF13 retrovirus. Its deletion from the MCF13 virus dramatically reduced the incidence of thymic lymphoma and increased the latency of disease in comparison with the wild-type virus. This effect was most marked when one rather than two enhancer repeats was present in the mutant viruses. We also observed that the removal of one repeat alone remarkably reduced leukemogenicity by the MCF13 virus. A newly identified protein-binding site (MLPal) located within DEN affects transcription only in T cells, and its deletion attenuates the ability of an MCF13 virus with a single enhancer repeat to induce thymic lymphoma. This observation suggests that the MLPal protein-binding site contributes to the effect of the DEN region on T-cell-specific transcription and viral leukemogenicity. This study identifies the importance of nonenhancer sequences in the long terminal repeat for the oncogenesis of the MCF13 retrovirus.
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MESH Headings
- 3T3 Cells
- Animals
- Animals, Newborn
- Base Sequence
- Binding Sites
- Cell Line
- Chloramphenicol O-Acetyltransferase/genetics
- Chloramphenicol O-Acetyltransferase/metabolism
- DNA, Viral/genetics
- DNA-Binding Proteins/metabolism
- Enhancer Elements, Genetic
- Leukemia Virus, Murine/genetics
- Leukemia Virus, Murine/pathogenicity
- Leukemia, Experimental/microbiology
- Lymphoma/microbiology
- Mice
- Mice, Inbred AKR
- Molecular Sequence Data
- Muridae
- Mutagenesis, Site-Directed
- Oligodeoxyribonucleotides
- Recombinant Proteins/metabolism
- Repetitive Sequences, Nucleic Acid
- Restriction Mapping
- Sequence Deletion
- Thymus Neoplasms/microbiology
- Transcription, Genetic
- Transfection
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Affiliation(s)
- J C Tupper
- Department of Biological Structure, University of Washington, Seattle 98195
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19
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Murine helix-loop-helix transcriptional activator proteins binding to the E-box motif of the Akv murine leukemia virus enhancer identified by cDNA cloning. Mol Cell Biol 1992. [PMID: 1321336 DOI: 10.1128/mcb.12.8.3449] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The enhancer region of Akv murine leukemia virus contains the sequence motif ACAGATGG. This sequence is homologous to the E-box motif originally defined as a regulatory element in the enhancers of immunoglobulin mu and kappa genes. We have used double-stranded oligonucleotide probes, corresponding to the E box of the murine leukemia virus Akv, to screen a randomly primed lambda gt11 cDNA expression library made from mouse NIH 3T3 fibroblast RNA. We have identified seven lambda clones expressing DNA-binding proteins representing two different genes termed ALF1 and ALF2. The results of sequencing ALF2 cDNA suggests that we have recovered the gene for the basic-helix-loop-helix transcription factor A1, the murine analog of the human transcription factor E47. The cDNA sequence of ALF1 codes for a new member of the basic-helix-loop-helix protein family. Two splice variants of ALF1 cDNA have been found, differing by a 72-bp insertion, coding for putative proteins of 682 and 706 amino acids. The two ALF1 mRNAs are expressed at various levels in mouse tissues. In vitro DNA binding assays, using prokaryotically expressed ALF1 proteins, demonstrated specific binding of the ALF1 proteins to the Akv murine leukemia virus E-box motif ACAGATGG. Expression in NIH 3T3 fibroblasts of GAL4-ALF1 chimeric protein stimulated expression from a minimal promoter linked to a GAL4 binding site, indicating the existence of a transcriptional activator domain in ALF1.
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20
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Nielsen AL, Pallisgaard N, Pedersen FS, Jørgensen P. Murine helix-loop-helix transcriptional activator proteins binding to the E-box motif of the Akv murine leukemia virus enhancer identified by cDNA cloning. Mol Cell Biol 1992; 12:3449-59. [PMID: 1321336 PMCID: PMC364594 DOI: 10.1128/mcb.12.8.3449-3459.1992] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The enhancer region of Akv murine leukemia virus contains the sequence motif ACAGATGG. This sequence is homologous to the E-box motif originally defined as a regulatory element in the enhancers of immunoglobulin mu and kappa genes. We have used double-stranded oligonucleotide probes, corresponding to the E box of the murine leukemia virus Akv, to screen a randomly primed lambda gt11 cDNA expression library made from mouse NIH 3T3 fibroblast RNA. We have identified seven lambda clones expressing DNA-binding proteins representing two different genes termed ALF1 and ALF2. The results of sequencing ALF2 cDNA suggests that we have recovered the gene for the basic-helix-loop-helix transcription factor A1, the murine analog of the human transcription factor E47. The cDNA sequence of ALF1 codes for a new member of the basic-helix-loop-helix protein family. Two splice variants of ALF1 cDNA have been found, differing by a 72-bp insertion, coding for putative proteins of 682 and 706 amino acids. The two ALF1 mRNAs are expressed at various levels in mouse tissues. In vitro DNA binding assays, using prokaryotically expressed ALF1 proteins, demonstrated specific binding of the ALF1 proteins to the Akv murine leukemia virus E-box motif ACAGATGG. Expression in NIH 3T3 fibroblasts of GAL4-ALF1 chimeric protein stimulated expression from a minimal promoter linked to a GAL4 binding site, indicating the existence of a transcriptional activator domain in ALF1.
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MESH Headings
- 3T3 Cells
- Amino Acid Sequence
- Animals
- Bacteriophage lambda/genetics
- Base Sequence
- Basic Helix-Loop-Helix Transcription Factors
- Binding Sites
- Blotting, Southern
- Cloning, Molecular
- DNA, Viral/genetics
- DNA, Viral/isolation & purification
- DNA-Binding Proteins/genetics
- DNA-Binding Proteins/metabolism
- Enhancer Elements, Genetic
- Gene Library
- Genes, Viral
- Humans
- Leukemia Virus, Murine/genetics
- Mice
- Molecular Sequence Data
- Oligodeoxyribonucleotides
- Protein Binding
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Sequence Homology, Nucleic Acid
- TCF Transcription Factors
- Trans-Activators/genetics
- Transcription Factor 7-Like 1 Protein
- Transcription Factors/genetics
- Transcription Factors/metabolism
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Affiliation(s)
- A L Nielsen
- Department of Molecular Biology, Aarhus University, Denmark
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21
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Pedersen K, Lovmand S, Jørgensen EC, Pedersen FS, Jørgensen P. Efficient replication and expression of murine leukemia virus with major deletions in the enhancer region of U3. Virology 1992; 187:821-4. [PMID: 1372141 DOI: 10.1016/0042-6822(92)90486-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The effect of deletions within the enhancer region in the U3 part of the LTR derived from the murine retrovirus Akv was studied. The deletions were stably transmitted through normal virus replication as shown by sequence analysis of cloned polymerase chain reaction product of the cDNA copy of the viral RNA. Genetic tagging of the retrovirus with lacO facilitated the analysis. Among the individual mutated LTRs an over 100-fold difference in a transient expression assay was previously detected. This difference was not revealed in studies of viral replication in cell culture, where the expression level of virus with the deleted LTRs all reached the level of virus with the intact LTR. We propose that stimulatory cis-acting sequences either adjacent to the site of proviral integration or in the coding regions of the provirus may compensate for deletions in the LTR.
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Affiliation(s)
- K Pedersen
- Department of Molecular Biology, Aarhus University, Denmark
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22
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Chang KC, Hansen E, Jaenicke T, Goldspink G, Butterworth P. Transformation of a novel direct-repeat repressor element into a promoter and enhancer by multimerisation. Nucleic Acids Res 1992; 20:1669-74. [PMID: 1374558 PMCID: PMC312254 DOI: 10.1093/nar/20.7.1669] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Studies on the regulation of interferon (IFN) responsive genes have mainly been centred on the highly conserved IFN stimulated responsive elements (ISREs) which can mediate type I and II IFN inducibility. To date little is known about other functional cis-acting regulatory motifs in IFN responsive genes. We report here on the identification of a repressor element in the human MxA gene defined to a 19 base pair (bp) region which houses a 9 bp direct repeat. DNA-specific protein binding on this element is not affected by IFN treatment and is distinct from ISRE binding proteins. Remarkably, contrary to expectations, when the repressor element is multimerised and spliced, in either orientation, to a reporter gene it behaves like a functional, constitutive promoter. Positioning the multimerised element in front of the SV40 enhancerless promoter also led to enhanced expression. The same protein(s) seem to bind to both the single repressor element and its multimerised form. This discovery of phenotypic reversal on a repressor element via multimerisation may have important implications in vivo.
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Affiliation(s)
- K C Chang
- Unit of Veterinary Molecular and Cellular Biology, Royal Veterinary College, University of London, UK
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23
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Jørgensen P, Mikkelsen T, Pedersen K, Pedersen FS, Kjeldgaard NO. Tagging the genome of the murine leukemia retrovirus SL3-3 by a bacterial lac operator sequence. Gene 1991; 109:243-7. [PMID: 1722473 DOI: 10.1016/0378-1119(91)90615-i] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The bacterial lactose operator (lacO) was introduced into the PstI site of the long terminal repeat of the SL3-3 murine leukemia virus, generating a virus, SL3-3lacO, that can replicate in NIH3T3 cell cultures. DNA sequences harboring the lacO sequence might be recovered by molecular cloning in Escherichia coli lac+ lacZ+ using bacteriophage lambda or plasmid vectors. The high copy numbers of the lacO sequence titrate out the lac repressor, leading to the induction of the lac operon in the host. We show here that the lacO and the proviral sequences are carried stably together in the genomes of SL3-3lacO-infected cell cultures and in viral particles. This system is designed to facilitate studies on the provirus and the site of viral integration.
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Affiliation(s)
- P Jørgensen
- Institute of Molecular Biology, Aarhus University, Denmark
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24
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Morrison HL, Dai HY, Pedersen FS, Lenz J. Analysis of the significance of two single-base-pair differences in the SL3-3 and Akv virus long terminal repeats. J Virol 1991; 65:1019-22. [PMID: 1846181 PMCID: PMC239851 DOI: 10.1128/jvi.65.2.1019-1022.1991] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Two single-base-pair differences between the long terminal repeats (LTRs) of the T-lymphomagenic murine retrovirus SL3-3 and nonleukemogenic Akv virus were tested for effects on activity of the LTRs. Evidence was obtained from electrophoretic mobility shift assays for the presence of at least one factor in both T and non-T cells that bound to the region of the viral enhancers that contained the differences. However, no significant differences in activity in expression assays were detected when the two base-pair differences were exchanged between the two LTRs. Therefore, they do not contribute to the higher activity of the SL3-3 LTR in T-lymphoma cell lines.
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Affiliation(s)
- H L Morrison
- Department of Molecular Genetics, Albert Einstein College of Medicine, Bronx, New York 10461
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25
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Olsen HS, Lovmand S, Lovmand J, Jørgensen P, Kjeldgaard NO, Pedersen FS. Involvement of nuclear factor I-binding sites in control of Akv virus gene expression. J Virol 1990; 64:4152-61. [PMID: 2166811 PMCID: PMC247879 DOI: 10.1128/jvi.64.9.4152-4161.1990] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The U3 region of Akv murine leukemia virus carries a 99-base-pair repeat that is associated with transcriptional enhancement in murine NIH 3T3 cells. Deletion analysis points to a critical function of a region within the repeat unit related to the recognition sequences for nuclear factor I proteins but distinct from the sites previously analyzed in related viruses. Nuclear proteins binding to the critical site were detected in NIH 3T3 cells and in mouse livers. A protein fraction binding to this site was purified from mouse livers by ion-exchange and DNA affinity chromatography and shown to have nuclear factor I properties. Mutations that caused a partial or complete reduction of the in vitro binding were introduced into an Akv long terminal repeat with one 99-base-pair repeat copy driving a reporter gene, and the expression activities of the mutants in NIH 3T3 cells were found to correspond to their in vitro binding activities. This correlation strongly supports the role of nuclear factor I proteins in Akv expression. Residual expression activity was, however, detected in mutants devoid of in vitro binding. This residual activity may relate to the presence of additional sequences with homology to nuclear factor I binding sites both within and outside the repeat region. The ability of these sites to bind crude and purified protein fractions with nuclear factor I activity was analyzed, and the role of the sites within and outside the repeat region for control of gene expression of Akv and related viruses is discussed.
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Affiliation(s)
- H S Olsen
- Department of Molecular Biology and Plant Physiology, University of Aarhus, Denmark
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