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Baydoun HH, Cherian MA, Green P, Ratner L. Inducible nitric oxide synthase mediates DNA double strand breaks in Human T-Cell Leukemia Virus Type 1-induced leukemia/lymphoma. Retrovirology 2015; 12:71. [PMID: 26265053 PMCID: PMC4534112 DOI: 10.1186/s12977-015-0196-y] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2015] [Accepted: 07/30/2015] [Indexed: 01/23/2023] Open
Abstract
Background Adult T-cell leukemia/lymphoma (ATLL) is an aggressive and fatal malignancy of CD4+ T-lymphocytes infected by the Human T-Cell Virus Type 1 (HTLV-1). The molecular mechanisms of transformation in ATLL have not been fully elucidated. However, genomic instability and cumulative DNA damage during the long period of latency is believed to be essential for HTLV-1 induced leukemogenesis. In addition, constitutive activation of the NF-κB pathway was found to be a critical determinant for transformation. Whether a connection exists between NF-κB activation and accumulation of DNA damage is not clear. We recently found that the HTLV-1 viral oncoprotein, Tax, the activator of the NF-κB pathway, induces DNA double strand breaks (DSBs). Results Here, we investigated whether any of the NF-κB target genes are critical in inducing DSBs. Of note, we found that inducible nitric oxide synthase (iNOS) that catalyzes the production of nitric oxide (NO) in macrophages, neutrophils and T-cells is over expressed in HTLV-1 infected and Tax-expressing cells. Interestingly, we show that in HTLV-1 infected cells, iNOS expression is Tax-dependent and specifically requires the activation of the classical NF-κB and JAK/STAT pathways. A dramatic reduction of DSBs was observed when NO production was inhibited, indicating that Tax induces DSBs through the activation of NO synthesis. Conclusions Determination of the impact of NO on HTLV-1-induced leukemogenesis opens a new area for treatment or prevention of ATLL and perhaps other cancers in which NO is produced.
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Affiliation(s)
- Hicham H Baydoun
- Division of Molecular Oncology, Department of Medicine Campus, Washington University School of Medicine, 660 South Euclid Avenue, St Louis, MO, 63110, USA.
| | - Mathew A Cherian
- Division of Molecular Oncology, Department of Medicine Campus, Washington University School of Medicine, 660 South Euclid Avenue, St Louis, MO, 63110, USA.
| | - Patrick Green
- Department of Veterinary Biosciences, The Ohio State University, Columbus, OH, USA.
| | - Lee Ratner
- Division of Molecular Oncology, Department of Medicine Campus, Washington University School of Medicine, 660 South Euclid Avenue, St Louis, MO, 63110, USA. .,Department of Molecular Microbiology, Washington University School of Medicine, St Louis, MO, USA.
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2
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Weitzman MD, Weitzman JB. What's the damage? The impact of pathogens on pathways that maintain host genome integrity. Cell Host Microbe 2014; 15:283-94. [PMID: 24629335 DOI: 10.1016/j.chom.2014.02.010] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Maintaining genome integrity and transmission of intact genomes is critical for cellular, organismal, and species survival. Cells can detect damaged DNA, activate checkpoints, and either enable DNA repair or trigger apoptosis to eliminate the damaged cell. Aberrations in these mechanisms lead to somatic mutations and genetic instability, which are hallmarks of cancer. Considering the long history of host-microbe coevolution, an impact of microbial infection on host genome integrity is not unexpected, and emerging links between microbial infections and oncogenesis further reinforce this idea. In this review, we compare strategies employed by viruses, bacteria, and parasites to alter, subvert, or otherwise manipulate host DNA damage and repair pathways. We highlight how microbes contribute to tumorigenesis by directly inducing DNA damage, inactivating checkpoint controls, or manipulating repair processes. We also discuss indirect effects resulting from inflammatory responses, changes in cellular metabolism, nuclear architecture, and epigenome integrity, and the associated evolutionary tradeoffs.
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Affiliation(s)
- Matthew D Weitzman
- Division of Cancer Pathobiology, Department of Pathology and Laboratory Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA; The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA.
| | - Jonathan B Weitzman
- University Paris Diderot, Sorbonne Paris Cité, Epigenetics and Cell Fate, UMR 7216 CNRS, 75013 Paris, France.
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Currer R, Van Duyne R, Jaworski E, Guendel I, Sampey G, Das R, Narayanan A, Kashanchi F. HTLV tax: a fascinating multifunctional co-regulator of viral and cellular pathways. Front Microbiol 2012; 3:406. [PMID: 23226145 PMCID: PMC3510432 DOI: 10.3389/fmicb.2012.00406] [Citation(s) in RCA: 103] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2012] [Accepted: 11/12/2012] [Indexed: 12/18/2022] Open
Abstract
Human T-cell lymphotropic virus type 1 (HTLV-1) has been identified as the causative agent of adult T-cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The virus infects between 15 and 20 million people worldwide of which approximately 2-5% develop ATL. The past 35 years of research have yielded significant insight into the pathogenesis of HTLV-1, including the molecular characterization of Tax, the viral transactivator, and oncoprotein. In spite of these efforts, the mechanisms of oncogenesis of this pleiotropic protein remain to be fully elucidated. In this review, we illustrate the multiple oncogenic roles of Tax by summarizing a recent body of literature that refines our understanding of cellular transformation. A focused range of topics are discussed in this review including Tax-mediated regulation of the viral promoter and other cellular pathways, particularly the connection of the NF-κB pathway to both post-translational modifications (PTMs) of Tax and subcellular localization. Specifically, recent research on polyubiquitination of Tax as it relates to the activation of the IkappaB kinase (IKK) complex is highlighted. Regulation of the cell cycle and DNA damage responses due to Tax are also discussed, including Tax interaction with minichromosome maintenance proteins and the role of Tax in chromatin remodeling. The recent identification of HTLV-3 has amplified the importance of the characterization of emerging viral pathogens. The challenge of the molecular determination of pathogenicity and malignant disease of this virus lies in the comparison of the viral transactivators of HTLV-1, -2, and -3 in terms of transformation and immortalization. Consequently, differences between the three proteins are currently being studied to determine what factors are required for the differences in tumorogenesis.
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Affiliation(s)
- Robert Currer
- National Center for Biodefense and Infectious Diseases, George Mason University Manassas, VA, USA
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4
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The cellular autophagy pathway modulates human T-cell leukemia virus type 1 replication. J Virol 2012; 87:1699-707. [PMID: 23175371 DOI: 10.1128/jvi.02147-12] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Autophagy, a general homeostatic process for degradation of cytosolic proteins or organelles, has been reported to modulate the replication of many viruses. The role of autophagy in human T-cell leukemia virus type 1 (HTLV-1) replication has, however, been uncharacterized. Here, we report that HTLV-1 infection increases the accumulation of autophagosomes and that this accumulation increases HTLV-1 production. We found that the HTLV-1 Tax protein increases cellular autophagosome accumulation by acting to block the fusion of autophagosomes to lysosomes, preventing the degradation of the former by the latter. Interestingly, the inhibition of cellular autophagosome-lysosome fusion using bafilomycin A increased the stability of the Tax protein, suggesting that cellular degradation of Tax occurs in part through autophagy. Our current findings indicate that by interrupting the cell's autophagic process, Tax exerts a positive feedback on its own stability.
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5
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Human T-cell leukemia virus type 1 (HTLV-1) and leukemic transformation: viral infectivity, Tax, HBZ and therapy. Oncogene 2010; 30:1379-89. [PMID: 21119600 DOI: 10.1038/onc.2010.537] [Citation(s) in RCA: 201] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The human T-cell leukemia virus type 1 (HTLV-1) was the first retrovirus discovered to be causative of a human cancer, adult T-cell leukemia. The transforming entity of HTLV-1 has been attributed to the virally-encoded oncoprotein, Tax. Unlike the v-onc proteins encoded by other oncogenic animal retroviruses that transform cells, Tax does not originate from a c-onc counterpart. In this article, we review progress in our understanding of HTLV-1 infectivity, cellular transformation, anti-sense transcription and therapy, 30 years after the original discovery of this virus.
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6
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Chlichlia K, Khazaie K. HTLV-1 Tax: Linking transformation, DNA damage and apoptotic T-cell death. Chem Biol Interact 2010; 188:359-65. [PMID: 20558150 DOI: 10.1016/j.cbi.2010.06.005] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2010] [Revised: 06/01/2010] [Accepted: 06/06/2010] [Indexed: 11/20/2022]
Abstract
The human T-cell leukemia virus type I (HTLV-1) is the causative agent of adult T-cell leukemia (ATL), an aggressive CD4-positive T-cell neoplasia. The HTLV-1 proto-oncogene Tax, a potent transcriptional activator of cellular and viral genes, is thought to play a pivotal role in the transforming properties of the virus by deregulating intracellular signaling pathways. During the course of HTLV-1 infection, the dysregulation of cell-cycle checkpoints and the suppression of DNA damage repair is tightly linked to the activity of the viral oncoprotein Tax. Tax activity is associated with production of reactive oxygen intermediates (ROS), chromosomal instability and DNA damage, apoptotic cell death and cellular transformation. Changes in the intracellular redox status induced by Tax promote DNA damage. Tax-mediated DNA damage is believed to be essential in initiating the transformation process by subjecting infected T cells to genetic changes that eventually promote the neoplastic state. Apoptosis and immune surveillance would then exert the necessary selection pressure for eliminating the majority of virally infected cells, while escape variants acquiring a mutator phenotype would constitute a subpopulation of genetically altered cells prone to neoplasia. While the potency of Tax-activity seems to be a determining factor for the observed effects, the cooperation of Tax with other viral proteins determines the fate and progression of HTLV-1-infected cells through DNA damage, apoptosis, survival and transformation.
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Affiliation(s)
- Katerina Chlichlia
- Department of Molecular Biology and Genetics, Democritus University of Thrace, Alexandroupolis, Greece.
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Kinjo T, Ham-Terhune J, Peloponese JM, Jeang KT. Induction of reactive oxygen species by human T-cell leukemia virus type 1 tax correlates with DNA damage and expression of cellular senescence marker. J Virol 2010; 84:5431-7. [PMID: 20219913 PMCID: PMC2863840 DOI: 10.1128/jvi.02460-09] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2009] [Accepted: 02/27/2010] [Indexed: 01/29/2023] Open
Abstract
Human T-cell leukemia virus type 1 (HTLV-1) Tax affects cellular genomic stability and senescence. As yet, the mechanism(s) for these events caused by Tax is incompletely understood. Here, we show that Tax expression in primary human cells induces reactive oxygen species (ROS), which elicits DNA damage and the expression of senescence marker. Treatment with a ROS scavenger or knockdown of Tax expression by small interfering RNA (siRNA) abrogated Tax-induced DNA damage and the expression of senescence marker. Our data suggest that ROS induction explains Tax-induced cellular DNA damage and cellular senescence.
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Affiliation(s)
- Takao Kinjo
- Molecular Virology Section, Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, Division of Pathology and Cell Biology, Graduate School and Faculty of Medicine, University of the Ryukyus, Okinawa 903-0215, Japan, Division of Morphological Pathology, Department of Basic Laboratory Sciences, School of Health Sciences, University of the Ryukyus, Okinawa 903-0215, Japan, CNRS and Université Montpellier 1, UM5236, Centre d'Études d'Agents Pathogènes et Biotechnologies pour la Santé (CPBS), Montpellier F-34965, France, CPBS, Université Montpellier 2, Montpellier F-34095, France
| | - Julia Ham-Terhune
- Molecular Virology Section, Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, Division of Pathology and Cell Biology, Graduate School and Faculty of Medicine, University of the Ryukyus, Okinawa 903-0215, Japan, Division of Morphological Pathology, Department of Basic Laboratory Sciences, School of Health Sciences, University of the Ryukyus, Okinawa 903-0215, Japan, CNRS and Université Montpellier 1, UM5236, Centre d'Études d'Agents Pathogènes et Biotechnologies pour la Santé (CPBS), Montpellier F-34965, France, CPBS, Université Montpellier 2, Montpellier F-34095, France
| | - Jean-Marie Peloponese
- Molecular Virology Section, Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, Division of Pathology and Cell Biology, Graduate School and Faculty of Medicine, University of the Ryukyus, Okinawa 903-0215, Japan, Division of Morphological Pathology, Department of Basic Laboratory Sciences, School of Health Sciences, University of the Ryukyus, Okinawa 903-0215, Japan, CNRS and Université Montpellier 1, UM5236, Centre d'Études d'Agents Pathogènes et Biotechnologies pour la Santé (CPBS), Montpellier F-34965, France, CPBS, Université Montpellier 2, Montpellier F-34095, France
| | - Kuan-Teh Jeang
- Molecular Virology Section, Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, Division of Pathology and Cell Biology, Graduate School and Faculty of Medicine, University of the Ryukyus, Okinawa 903-0215, Japan, Division of Morphological Pathology, Department of Basic Laboratory Sciences, School of Health Sciences, University of the Ryukyus, Okinawa 903-0215, Japan, CNRS and Université Montpellier 1, UM5236, Centre d'Études d'Agents Pathogènes et Biotechnologies pour la Santé (CPBS), Montpellier F-34965, France, CPBS, Université Montpellier 2, Montpellier F-34095, France
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Kesic M, Doueiri R, Ward M, Semmes OJ, Green PL. Phosphorylation regulates human T-cell leukemia virus type 1 Rex function. Retrovirology 2009; 6:105. [PMID: 19919707 PMCID: PMC2780990 DOI: 10.1186/1742-4690-6-105] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2009] [Accepted: 11/17/2009] [Indexed: 11/10/2022] Open
Abstract
Background Human T-cell leukemia virus type 1 (HTLV-1) is a pathogenic complex deltaretrovirus, which is the causative agent of adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis. In addition to the structural and enzymatic viral gene products, HTLV-1 encodes the positive regulatory proteins Tax and Rex along with viral accessory proteins. Tax and Rex proteins orchestrate the timely expression of viral genes important in viral replication and cellular transformation. Rex is a nucleolar-localizing shuttling protein that acts post-transcriptionally by binding and facilitating the export of the unspliced and incompletely spliced viral mRNAs from the nucleus to the cytoplasm. HTLV-1 Rex (Rex-1) is a phosphoprotein and general protein kinase inhibition correlates with reduced function. Therefore, it has been proposed that Rex-1 function may be regulated through site-specific phosphorylation. Results We conducted a phosphoryl mapping of Rex-1 over-expressed in transfected 293 T cells using a combination of affinity purification and liquid chromatography tandem mass spectrometry. We achieved 100% physical coverage of the Rex-1 polypeptide and identified five novel phosphorylation sites at Thr-22, Ser-36, Thr-37, Ser-97, and Ser-106. We also confirmed evidence of two previously identified residues, Ser-70 and Thr-174, but found no evidence of phosphorylation at Ser-177. The functional significance of these phosphorylation events was evaluated using a Rex reporter assay and site-directed mutational analysis. Our results indicate that phosphorylation at Ser-97 and Thr-174 is critical for Rex-1 function. Conclusion We have mapped completely the site-specific phosphorylation of Rex-1 identifying a total of seven residues; Thr-22, Ser-36, Thr-37, Ser-70, Ser-97, Ser-106, and Thr-174. Overall, this work is the first to completely map the phosphorylation sites in Rex-1 and provides important insight into the regulation of Rex-1 function.
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Affiliation(s)
- Matthew Kesic
- Center for Retrovirus Research, The Ohio State University, Columbus, OH 43210, USA.
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9
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Yasunaga J, Jeang KT. Viral transformation and aneuploidy. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2009; 50:733-740. [PMID: 19326462 PMCID: PMC2760603 DOI: 10.1002/em.20480] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Human tumor viruses are associated with a variety of human malignancies, and it is estimated that 15% of all human cancers have a viral etiology. An abnormality in chromosomal ploidy or aneuploidy is a hallmark of cancers. In normal cells, euploidy is governed by several factors including an intact spindle assembly checkpoint, accurate centrosome duplication, and proper cytokinesis. Viral oncoproteins are suggested to perturb the cellular machineries for chromosomal segregation creating aneuploidy which can lead to the malignant transformation of infected cells. Here, we review in brief some of the mechanisms used by viruses that can cause cellular aneuploidy.
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Affiliation(s)
- Junichiro Yasunaga
- Molecular Virology Section, Laboratory of Molecular Microbiology, The National Institute of Allergy and Infectious Diseases/NIH, 9000 Rockville Pike, Bethesda, MD 20892, USA
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10
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Shoji T, Higuchi M, Kondo R, Takahashi M, Oie M, Tanaka Y, Aoyagi Y, Fujii M. Identification of a novel motif responsible for the distinctive transforming activity of human T-cell leukemia virus (HTLV) type 1 Tax1 protein from HTLV-2 Tax2. Retrovirology 2009; 6:83. [PMID: 19761585 PMCID: PMC2754985 DOI: 10.1186/1742-4690-6-83] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2009] [Accepted: 09/17/2009] [Indexed: 01/09/2023] Open
Abstract
Background Human T-cell leukemia virus type 1 (HTLV-1) is a causative agent of adult T-cell leukemia (ATL), whereas its relative HTLV-2 is not associated with any malignancies including ATL. HTLV-1 Tax1 transformed a T-cell line from interleukin (IL)-2-dependent growth to IL-2-independent growth, with an activity that was much more potent in comparison to HTLV-2 Tax2. This distinction was mediated by at least two Tax1 specific functions, an interaction with host cellular factors through the PDZ domain binding motif (PBM) and the activation of NF-kappaB2 (NF-κB2)/p100. Results Using a series of Tax1 chimeric proteins with Tax2, we found that amino acids 225-232 of Tax1, the Tax1(225-232) region, was essential for the activation of NF-κB2 as well as for the high transforming activity. The strict amino acid conservation of Tax1(225-232) among HTLV-1 and simian T-cell leukemia virus type 1 (STLV-1), but not HTLV-2 and STLV-2, indicates that function(s) through the Tax1(225-232) region are biologically significant. Interestingly, another HTLV-1 relative, HTLV-3, has a PBM, but does not conserve the Tax1(225-232) motif in Tax3, thus indicating that these two motifs classify the three HTLVs into the separate groups. Conclusion These results suggest that the combinatory functions through Tax1(225-232) and PBM play crucial roles in the distinct biological properties of the three HTLVs, perhaps also including their pathogenesis.
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Affiliation(s)
- Toshiyuki Shoji
- Division of Virology, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachi-Dori, Niigata 951-8510, Japan.
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11
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Site-specific phosphorylation regulates human T-cell leukemia virus type 2 Rex function in vivo. J Virol 2009; 83:8859-68. [PMID: 19553333 DOI: 10.1128/jvi.00908-09] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human T-cell leukemia virus type 2 (HTLV-2) Rex is a transacting regulatory protein required for efficient cytoplasmic expression of the unspliced and incompletely spliced viral mRNA transcripts encoding the structural and enzymatic proteins. Previously, it was demonstrated that phosphorylation of Rex-2, predominantly on serine residues, is correlated with an altered conformation, as observed by a gel mobility shift and the detection of two related protein species (p24(Rex) and p26(Rex)). Rex-2 phosphorylation is required for specific binding to its viral-mRNA target sequence and inhibition of mRNA splicing and may be linked to subcellular compartmentalization. Thus, the phosphorylation-induced structural state of Rex in the infected cell may be a switch that determines whether HTLV exists in a latent or productive state. We conducted a phosphoryl and functional mapping of both structural forms of mammalian-cell-expressed Rex 2 using affinity purification, liquid chromatography-tandem mass spectrometry, and site-directed substitutional mutational analysis. We identified two phosphorylation sites in p24(Rex) at Ser-117 and Thr-164. We also identified six phosphorylation sites in p26(Rex) at Thr-19, Ser-117, Ser-125, Ser-151, Ser-153, and Thr-164. We evaluated the functional significance of these phosphorylation events and found that phosphorylation on Thr-164, Ser-151, and Ser-153 is critical for Rex-2 function in vivo and that phosphorylation of Ser-151 is correlated with nuclear/nucleolar subcellular localization. Overall, this work is the first to completely map the phosphorylation sites in Rex-2 and provides important insight into the phosphorylation continuum that tightly regulates Rex-2 structure, cellular localization, and function.
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Zhang L, Zhi H, Liu M, Kuo YL, Giam CZ. Induction of p21(CIP1/WAF1) expression by human T-lymphotropic virus type 1 Tax requires transcriptional activation and mRNA stabilization. Retrovirology 2009; 6:35. [PMID: 19356250 PMCID: PMC2676247 DOI: 10.1186/1742-4690-6-35] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2008] [Accepted: 04/08/2009] [Indexed: 11/25/2022] Open
Abstract
HTLV-1 Tax can induce senescence by up-regulating the levels of cyclin-dependent kinase inhibitors p21CIP1/WAF1 and p27KIP1. Tax increases p27KIP1 protein stability by activating the anaphase promoting complex/cyclosome (APC/C) precociously, causing degradation of Skp2 and inactivation of SCFSkp2, the E3 ligase that targets p27KIP1. The rate of p21CIP1/WAF1 protein turnover, however, is unaffected by Tax. Rather, the mRNA of p21CIP1/WAF1 is greatly up-regulated. Here we show that Tax increases p21 mRNA expression by transcriptional activation and mRNA stabilization. Transcriptional activation of p21CIP1/WAF1 by Tax occurs in a p53-independent manner and requires two tumor growth factor-β-inducible Sp1 binding sites in the -84 to -60 region of the p21CIP1/WAF1 promoter. Tax binds Sp1 directly, and the CBP/p300-binding activity of Tax is required for p21CIP1/WAF1 trans-activation. Tax also increases the stability of p21CIP1/WAF1 transcript. Several Tax mutants trans-activated the p21 promoter, but were attenuated in stabilizing p21CIP1/WAF1 mRNA, and were less proficient in increasing p21CIP1/WAF1 expression. The possible involvement of Tax-mediated APC/C activation in p21CIP1/WAF1 mRNA stabilization is discussed.
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Affiliation(s)
- Ling Zhang
- Department of Microbiology and Immunology, Uniformed Services University, Bethesda, MD 20814, USA.
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Human T-cell leukemia virus type 2 Rex carboxy terminus is an inhibitory/stability domain that regulates Rex functional activity and viral replication. J Virol 2009; 83:5232-43. [PMID: 19279097 DOI: 10.1128/jvi.02271-08] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human T-cell leukemia virus (HTLV) regulatory protein, Rex, functions to increase the expression of the viral structural and enzymatic gene products. The phosphorylation of two serine residues (S151 and S153) at the C terminus is important for the function of HTLV-2 Rex (Rex-2). The Rex-2 phosphomimetic double mutant (S151D, S153D) is locked in a functionally active conformation. Since rex and tax genes overlap, Rex S151D and S153D mutants were found to alter the Tax oncoprotein coding sequence and transactivation activities. Therefore, additional Rex-2 mutants including P152D, A157D, S151Term, and S158Term were generated and characterized ("Term" indicates termination codon). All Rex-2 mutants and wild-type (wt) Rex-2 localized predominantly to the nucleus/nucleolus, but in contrast to the detection of phosphorylated and unphosphorylated forms of wt Rex-2 (p26 and p24), mutant proteins were detected as a single phosphoprotein species. We found that Rex P152D, A157D, and S158Term mutants are more functionally active than wt Rex-2 and that the Rex-2 C terminus and its specific phosphorylation state are required for stability and optimal expression. In the context of the provirus, the more active Rex mutants (A157D or S158Term) promoted increased viral protein production, increased viral infectious spread, and enhanced HTLV-2-mediated cellular proliferation. Moreover, these Rex mutant viruses replicated and persisted in inoculated rabbits despite higher antiviral antibody responses. Thus, we identified in Rex-2 a novel C-terminal inhibitory domain that regulates functional activity and is positively regulated through phosphorylation. The ability of this domain to modulate viral replication likely plays a key role in the infectious spread of the virus and in virus-induced cellular proliferation.
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14
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Kinetic analysis of human T-cell leukemia virus type 1 gene expression in cell culture and infected animals. J Virol 2009; 83:3788-97. [PMID: 19193802 DOI: 10.1128/jvi.02315-08] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human T-cell leukemia virus type 1 (HTLV-1) infection causes adult T-cell leukemia and is associated with a variety of lymphocyte-mediated disorders. It has been hypothesized that a highly regulated pattern of HTLV-1 gene expression is critical for virus survival and disease pathogenesis. In this study, real-time reverse transcriptase PCR was used to determine the kinetics of viral gene expression in cells transiently transfected with an HTLV-1 proviral plasmid, in newly infected human peripheral blood mononuclear cells (PBMCs), and in PBMCs from newly infected rabbits. The HTLV-1 gene expression profiles in transiently transfected and infected cells were similar; over time, all transcripts increased and then maintained stable levels. gag/pol, tax/rex, and env mRNA were detected first and at the highest levels, whereas the expression levels of the accessory genes, including the antisense Hbz, were significantly lower than the tax/rex levels (ranging from 1 to 4 logs depending on the specific mRNA). In infected rabbits, tax/rex and gag/pol mRNA levels peaked early after inoculation and progressively decreased, which correlated inversely with the proviral load and host antibody response against viral proteins. Interestingly, Hbz mRNA was detectable at 1 week postinfection and increased and stabilized. The expression levels of all other HTLV-1 genes in infected rabbit PBMCs were at or below our limit of detection. This analysis provides insight into viral gene expression under various in vitro and in vivo experimental conditions. Our in vivo data indicate that in infected rabbits, Hbz mRNA expression over time directly correlates with the proviral load, which provides the first evidence linking Hbz expression to proviral load and the survival of the virus-infected cell in the host.
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