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Gao Y, Yu XF, Chen T. Human endogenous retroviruses in cancer: Expression, regulation and function. Oncol Lett 2020; 21:121. [PMID: 33552242 PMCID: PMC7798031 DOI: 10.3892/ol.2020.12382] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Accepted: 11/27/2020] [Indexed: 12/16/2022] Open
Abstract
Human endogenous retroviruses (HERVs) are the remnants of ancient retroviruses that infected human germline cells and became integrated into the human genome millions of years ago. Although most of these sequences are incomplete and silent, several potential pathological roles of HERVs have been observed in numerous diseases, such as multiple sclerosis and rheumatoid arthritis, and especially cancer, including breast cancer and pancreatic carcinoma. The present review investigates the expression signatures and complex regulatory mechanisms of HERVs in cancer. The long terminal repeats-driven transcriptional initiation of HERVs are regulated by transcription factors (such as Sp3) and epigenetic modifications (such as DNA methylation), and are influenced by environmental factors (such as ultraviolet radiation). In addition, this review focuses on the dual opposing effects of HERVs in cancer. HERVs can suppress cancer via immune activation; however, they can also promote cancer. HERV env gene serves a prime role in promoting carcinogenesis in certain malignant tumors, including breast cancer, pancreatic cancer, germ cell tumors, leukemia and Kaposi's sarcoma. Also, HERV ENV proteins can promote cancer via immune suppression. Targeting ENV proteins is a potential future antitumor treatment modality.
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Affiliation(s)
- Yuan Gao
- Cancer Institute, Key Laboratory of Cancer Prevention and Intervention, Ministry of Education, Second Affiliated Hospital of Zhejiang University School of Medicine, Hangzhou, Zheijang 310009, P.R. China
| | - Xiao-Fang Yu
- Cancer Institute, Key Laboratory of Cancer Prevention and Intervention, Ministry of Education, Second Affiliated Hospital of Zhejiang University School of Medicine, Hangzhou, Zheijang 310009, P.R. China
| | - Ting Chen
- Cancer Institute, Key Laboratory of Cancer Prevention and Intervention, Ministry of Education, Second Affiliated Hospital of Zhejiang University School of Medicine, Hangzhou, Zheijang 310009, P.R. China
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Rigogliuso G, Biniossek ML, Goodier JL, Mayer B, Pereira GC, Schilling O, Meese E, Mayer J. A human endogenous retrovirus encoded protease potentially cleaves numerous cellular proteins. Mob DNA 2019; 10:36. [PMID: 31462935 PMCID: PMC6707001 DOI: 10.1186/s13100-019-0178-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2019] [Accepted: 08/13/2019] [Indexed: 11/21/2022] Open
Abstract
Background A considerable portion of the human genome derives from retroviruses inherited over millions of years. Human endogenous retroviruses (HERVs) are usually severely mutated, yet some coding-competent HERVs exist. The HERV-K(HML-2) group includes evolutionarily young proviruses that encode typical retroviral proteins. HERV-K(HML-2) has been implicated in various human diseases because transcription is often upregulated and some of its encoded proteins are known to affect cell biology. HERV-K(HML-2) Protease (Pro) has received little attention so far, although it is expressed in some disease contexts and other retroviral proteases are known to process cellular proteins. Results We set out to identify human cellular proteins that are substrates of HERV-K(HML-2) Pro employing a modified Terminal Amine Isotopic Labeling of Substrates (TAILS) procedure. Thousands of human proteins were identified by this assay as significantly processed by HERV-K(HML-2) Pro at both acidic and neutral pH. We confirmed cleavage of a majority of selected human proteins in vitro and in co-expression experiments in vivo. Sizes of processing products observed for some of the tested proteins coincided with product sizes predicted by TAILS. Processed proteins locate to various cellular compartments and participate in diverse, often disease-relevant cellular processes. A limited number of HERV-K(HML-2) reference and non-reference loci appears capable of encoding active Pro. Conclusions Our findings from an approach combining TAILS with experimental verification of candidate proteins in vitro and in cultured cells suggest that hundreds of cellular proteins are potential substrates of HERV-K(HML-2) Pro. It is therefore conceivable that even low-level expression of HERV-K(HML-2) Pro affects levels of a diverse array of proteins and thus has a functional impact on cell biology and possible relevance for human diseases. Further studies are indicated to elucidate effects of HERV-K(HML-2) Pro expression regarding human substrate proteins, cell biology, and disease. The latter also calls for studies on expression of specific HERV-K(HML-2) loci capable of encoding active Pro. Endogenous retrovirus-encoded Pro activity may also be relevant for disease development in species other than human. Electronic supplementary material The online version of this article (10.1186/s13100-019-0178-z) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Giuseppe Rigogliuso
- 1Department of Human Genetics, Medical Faculty, University of Saarland, Homburg, Germany
| | - Martin L Biniossek
- 2Institute of Molecular Medicine and Cell Research, University of Freiburg, Freiburg, Germany
| | - John L Goodier
- 3McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD USA
| | - Bettina Mayer
- 2Institute of Molecular Medicine and Cell Research, University of Freiburg, Freiburg, Germany
| | - Gavin C Pereira
- 3McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD USA
| | - Oliver Schilling
- 4Institute of Surgical Pathology, Medical Center, University of Freiburg, Freiburg, Germany.,5German Cancer Consortium (DKTK) and German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Eckart Meese
- 1Department of Human Genetics, Medical Faculty, University of Saarland, Homburg, Germany
| | - Jens Mayer
- 1Department of Human Genetics, Medical Faculty, University of Saarland, Homburg, Germany
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Garcia-Montojo M, Doucet-O'Hare T, Henderson L, Nath A. Human endogenous retrovirus-K (HML-2): a comprehensive review. Crit Rev Microbiol 2018; 44:715-738. [PMID: 30318978 DOI: 10.1080/1040841x.2018.1501345] [Citation(s) in RCA: 110] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The human genome contains a large number of retroviral elements acquired over the process of evolution, some of which are specific to primates. However, as many of these are defective or silenced through epigenetic changes, they were historically considered "junk DNA" and their potential role in human physiology or pathological circumstances have been poorly studied. The most recently acquired, human endogenous retrovirus-K (HERV-K), has multiple copies in the human genome and some of them have complete open reading frames that are transcribed and translated, especially in early embryogenesis. Phylogenetically, HERV-K is considered a supergroup of viruses. One of the subtypes, termed HML-2, seems to be the most active and hence, it is the best studied. Aberrant expression of HML-2 in adult tissues has been associated with certain types of cancer and with neurodegenerative diseases. This review discusses the discovery of these viruses, their classification, structure, regulation and potential for replication, physiological roles, and their involvement in disease pathogenesis. Finally, it presents different therapeutic approaches being considered to target these viruses.
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Affiliation(s)
- Marta Garcia-Montojo
- a Section of Infections of the Nervous System , National Institute of Neurological Disorders and Stroke, National Institutes of Health , Bethesda , MD , USA
| | - Tara Doucet-O'Hare
- a Section of Infections of the Nervous System , National Institute of Neurological Disorders and Stroke, National Institutes of Health , Bethesda , MD , USA
| | - Lisa Henderson
- a Section of Infections of the Nervous System , National Institute of Neurological Disorders and Stroke, National Institutes of Health , Bethesda , MD , USA
| | - Avindra Nath
- a Section of Infections of the Nervous System , National Institute of Neurological Disorders and Stroke, National Institutes of Health , Bethesda , MD , USA
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Biniossek ML, Niemer M, Maksimchuk K, Mayer B, Fuchs J, Huesgen PF, McCafferty DG, Turk B, Fritz G, Mayer J, Haecker G, Mach L, Schilling O. Identification of Protease Specificity by Combining Proteome-Derived Peptide Libraries and Quantitative Proteomics. Mol Cell Proteomics 2016; 15:2515-24. [PMID: 27122596 DOI: 10.1074/mcp.o115.056671] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2015] [Indexed: 01/17/2023] Open
Abstract
We present protease specificity profiling based on quantitative proteomics in combination with proteome-derived peptide libraries. Peptide libraries are generated by endoproteolytic digestion of proteomes without chemical modification of primary amines before exposure to a protease under investigation. After incubation with a test protease, treated and control libraries are differentially isotope-labeled using cost-effective reductive dimethylation. Upon analysis by liquid chromatography-tandem mass spectrometry, cleavage products of the test protease appear as semi-specific peptides that are enriched for the corresponding isotope label. We validate our workflow with two proteases with well-characterized specificity profiles: trypsin and caspase-3. We provide the first specificity profile of a protease encoded by a human endogenous retrovirus and for chlamydial protease-like activity factor (CPAF). For CPAF, we also highlight the structural basis of negative subsite cooperativity between subsites S1 and S2'. For A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) -4, -5, and -15, we show a canonical preference profile, including glutamate in P1 and glycine in P3'. In total, we report nearly 4000 cleavage sites for seven proteases. Our protocol is fast, avoids enrichment or synthesis steps, and enables probing for lysine selectivity as well as subsite cooperativity. Due to its simplicity, we anticipate usability by most proteomic laboratories.
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Affiliation(s)
| | - Melanie Niemer
- §Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, Vienna, Austria
| | | | - Bettina Mayer
- From the ‡Institute of Molecular Medicine and Cell Research
| | | | - Pitter F Huesgen
- **Central Institute for Engineering, Electronics and Analytics, ZEA-3 Analytics, Forschungszentrum Jülich, 52425 Jülich, Germany
| | | | - Boris Turk
- ‡‡Department of Chemistry, Duke University, Medical Center, Durham, NC 27708, USA; Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innsbruck, Austria
| | - Guenther Fritz
- §§Department of Biochemistry and Molecular and Structural Biology, Jozef Stefan Institute, Ljubljana, Slovenia; Department of Human Genetics and Center of Human and Molecular Biology, Medical Faculty, University of Saarland Homburg, Germany
| | | | | | - Lukas Mach
- §Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, Vienna, Austria
| | - Oliver Schilling
- From the ‡Institute of Molecular Medicine and Cell Research, ‡‡‡BIOSS Centre for Biological Signaling Studies, University of Freiburg, Freiburg, Germany; §§§German Cancer Consortium (DKTK), German Cancer Research Center (DKFZ), Heidelberg, Germany
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Heyne K, Kölsch K, Bruand M, Kremmer E, Grässer FA, Mayer J, Roemer K. Np9, a cellular protein of retroviral ancestry restricted to human, chimpanzee and gorilla, binds and regulates ubiquitin ligase MDM2. Cell Cycle 2015; 14:2619-33. [PMID: 26103464 DOI: 10.1080/15384101.2015.1064565] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Humans and primates are long-lived animals with long reproductive phases. One factor that appears to contribute to longevity and fertility in humans, as well as to cancer-free survival, is the transcription factor and tumor suppressor p53, controlled by its main negative regulator MDM2. However, p53 and MDM2 homologs are found throughout the metazoan kingdom from Trichoplacidae to Hominidae. Therefore the question arises, if p53/MDM2 contributes to the shaping of primate features, then through which mechanisms. Previous findings have indicated that the appearances of novel p53-regulated genes and wild-type p53 variants during primate evolution are important in this context. Here, we report on another mechanism of potential relevance. Human endogenous retrovirus K subgroup HML-2 (HERV-K(HML-2)) type 1 proviral sequences were formed in the genomes of the predecessors of contemporary Hominoidea and can be identified in the genomes of Nomascus leucogenys (gibbon) up to Homo sapiens. We previously reported on an alternative splicing event in HERV-K(HML-2) type 1 proviruses that can give rise to nuclear protein of 9 kDa (Np9). We document here the evolution of Np9-coding capacity in human, chimpanzee and gorilla, and show that the C-terminal half of Np9 binds directly to MDM2, through a domain of MDM2 that is known to be contacted by various cellular proteins in response to stress. Np9 can inhibit the MDM2 ubiquitin ligase activity toward p53 in the cell nucleus, and can support the transactivation of genes by p53. Our findings point to the possibility that endogenous retrovirus protein Np9 contributes to the regulation of the p53-MDM2 pathway specifically in humans, chimpanzees and gorillas.
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Affiliation(s)
- Kristina Heyne
- a José Carreras Center and Internal Medicine I; University of Saarland Medical Center ; Homburg , Germany
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Schmitt K, Reichrath J, Roesch A, Meese E, Mayer J. Transcriptional profiling of human endogenous retrovirus group HERV-K(HML-2) loci in melanoma. Genome Biol Evol 2013; 5:307-28. [PMID: 23338945 PMCID: PMC3590776 DOI: 10.1093/gbe/evt010] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Recent studies suggested a role for the human endogenous retrovirus (HERV) group HERV-K(HML-2) in melanoma because of upregulated transcription and expression of HERV-K(HML-2)-encoded proteins. Very little is known about which HML-2 loci are transcribed in melanoma. We assigned >1,400 HML-2 cDNA sequences generated from various melanoma and related samples to genomic HML-2 loci, identifying a total of 23 loci as transcribed. Transcription profiles of loci differed significantly between samples. One locus was found transcribed only in melanoma-derived samples but not in melanocytes and might represent a marker for melanoma. Several of the transcribed loci harbor ORFs for retroviral Gag and/or Env proteins. Env-encoding loci were transcribed only in melanoma. Specific investigation of rec and np9 transcripts indicated transcription of protein encoding loci in melanoma and melanocytes hinting at the relevance of Rec and Np9 in melanoma. UVB irradiation changed transcription profiles of loci and overall transcript levels decreased in melanoma and melanocytes. We further identified transcribed HML-2 loci formed by reverse transcription of spliced HML-2 transcripts by L1 machinery or in a retroviral fashion, with loci potentially encoding HML-2-like proteins. We reveal complex, sample-specific transcription of HML-2 loci in melanoma and related samples. Identified HML-2 loci and proteins encoded by those loci are particularly relevant for further studying the role of HML-2 in melanoma. Transcription of HERVs appears as a complex mechanism requiring specific studies to elucidate which HERV loci are transcribed and how transcribed HERVs may be involved in disease.
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Affiliation(s)
- Katja Schmitt
- Institute of Human Genetics, Medical Faculty, University of Saarland, Homburg/Saar, Germany
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George M, Schwecke T, Beimforde N, Hohn O, Chudak C, Zimmermann A, Kurth R, Naumann D, Bannert N. Identification of the protease cleavage sites in a reconstituted Gag polyprotein of an HERV-K(HML-2) element. Retrovirology 2011; 8:30. [PMID: 21554716 PMCID: PMC3114732 DOI: 10.1186/1742-4690-8-30] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2011] [Accepted: 05/09/2011] [Indexed: 12/27/2022] Open
Abstract
BACKGROUND The human genome harbors several largely preserved HERV-K(HML-2) elements. Although this retroviral family comes closest of all known HERVs to producing replication competent virions, mutations acquired during their chromosomal residence have rendered them incapable of expressing infectious particles. This also holds true for the HERV-K113 element that has conserved open reading frames (ORFs) for all its proteins in addition to a functional LTR promoter. Uncertainty concerning the localization and impact of post-insertional mutations has greatly hampered the functional characterization of these ancient retroviruses and their proteins. However, analogous to other betaretroviruses, it is known that HERV-K(HML-2) virions undergo a maturation process during or shortly after release from the host cell. During this process, the subdomains of the Gag polyproteins are released by proteolytic cleavage, although the nature of the mature HERV-K(HML-2) Gag proteins and the exact position of the cleavage sites have until now remained unknown. RESULTS By aligning the amino acid sequences encoded by the gag-pro-pol ORFs of HERV-K113 with the corresponding segments from 10 other well-preserved human specific elements we identified non-synonymous post-insertional mutations that have occurred in this region of the provirus. Reversion of these mutations and a partial codon optimization facilitated the large-scale production of maturation-competent HERV-K113 virus-like particles (VLPs). The Gag subdomains of purified mature VLPs were separated by reversed-phase high-pressure liquid chromatography and initially characterized using specific antibodies. Cleavage sites were identified by mass spectrometry and N-terminal sequencing and confirmed by mutagenesis. Our results indicate that the gag gene product Pr74Gag of HERV-K(HML-2) is processed to yield p15-MA (matrix), SP1 (spacer peptide of 14 amino acids), p15, p27-CA (capsid), p10-NC (nucleocapsid) and two C-terminally encoded glutamine- and proline-rich peptides, QP1 and QP2, spanning 23 and 19 amino acids, respectively. CONCLUSIONS Expression of reconstituted sequences of original HERV elements is an important tool for studying fundamental aspects of the biology of these ancient viruses. The analysis of HERV-K(HML-2) Gag processing and the nature of the mature Gag proteins presented here will facilitate further studies of the discrete functions of these proteins and of their potential impact on the human host.
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Affiliation(s)
- Maja George
- Center for HIV and Retrovirology, Robert Koch Institute, Nordufer 20, 13353 Berlin, Germany
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Kraus B, Boller K, Reuter A, Schnierle BS. Characterization of the human endogenous retrovirus K Gag protein: identification of protease cleavage sites. Retrovirology 2011; 8:21. [PMID: 21429186 PMCID: PMC3073897 DOI: 10.1186/1742-4690-8-21] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Accepted: 03/23/2011] [Indexed: 11/16/2022] Open
Abstract
Background Viral genomes of the human endogenous retrovirus K (HERV-K) family are integrated into the human chromosome and are transmitted vertically as Mendelian genes. Although viral particles are released by some transformed cells, they have never been shown to be infectious. In general, gammaretroviruses are produced as immature viral particles by accumulation of the Gag polyproteins at the plasma membrane, which subsequently bud from the cell surface. After release from the cell, Gag is further processed by proteolytic cleavage by the viral protease (PR), which results in morphologically mature particles with condensed cores. The HERV-K Gag polyprotein processing and function has not yet been precisely determined. Results We generated a recombinant poxvirus, encoding the human endogenous retrovirus K consensus gag-pro-pol genes (MVA-HERV-Kcon) and obtained high levels of HERV-K Gag expression. The resulting retroviral particle assembled at the plasma membrane, as is typical for gammaretroviruses; and immature as well as mature retrovirus-like particles (VLPs) were observed around the infected cells. VLPs were purified, concentrated and separated by two-dimensional gel electrophoresis. The HERV-K Gag fragments were identified by mass spectroscopy and N-terminal sequencing which revealed that HERV-K Gag is processed into MA, a short spacer peptide, p15, CA and NC. Conclusion The cleavage sites of HERV-K Gag were mapped and found to be highly conserved among HERV-K genomes. The consensus HERV-K gag gene used in this study is known to support viral, infectivity [1], and thus the cleavage sites that were mapped in this study for all the Gag components are relevant for HERV-K infectivity.
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Affiliation(s)
- Benjamin Kraus
- Paul-Ehrlich-Institut, Paul-Ehrlich-Strasse 51-59, 63225 Langen, Germany
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Boller K, Schönfeld K, Lischer S, Fischer N, Hoffmann A, Kurth R, Tönjes RR. Human endogenous retrovirus HERV-K113 is capable of producing intact viral particles. J Gen Virol 2008; 89:567-572. [PMID: 18198388 DOI: 10.1099/vir.0.83534-0] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Of all human endogenous retroviruses known today, HERV-K is the only one that has been shown to produce viral particles. While the first of the approximately 30 HERV-K sequences integrated into the human genome more than 40 million years ago, evidence is accumulating that HERV-K was active more recently, provirus HERV-K113 being the youngest sequence found. However, it is unclear which HERV-K sequences code for the viral particles that are produced by human germ-cell tumours or melanomas. Here, we show that the provirus HERV-K113, cloned into a baculovirus expression vector, is capable of producing intact particles of retroviral morphology, exhibiting the typical structure of those particles that were characterized in cell lines derived from human germ-cell tumours. Thus, the HERV-K113 sequence is a candidate for particle production in vivo and for an active human endogenous retrovirus of today.
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Affiliation(s)
- Klaus Boller
- Paul-Ehrlich-Institut, Paul-Ehrlich-Straße 51-59, D-63225 Langen, Germany
| | - Kurt Schönfeld
- Paul-Ehrlich-Institut, Paul-Ehrlich-Straße 51-59, D-63225 Langen, Germany
| | - Stefanie Lischer
- Paul-Ehrlich-Institut, Paul-Ehrlich-Straße 51-59, D-63225 Langen, Germany
| | - Nicole Fischer
- Paul-Ehrlich-Institut, Paul-Ehrlich-Straße 51-59, D-63225 Langen, Germany
| | - Andreas Hoffmann
- Paul-Ehrlich-Institut, Paul-Ehrlich-Straße 51-59, D-63225 Langen, Germany
| | - Reinhard Kurth
- Robert Koch-Institut, Nordufer 20, D-13353 Berlin, Germany
| | - Ralf R Tönjes
- Paul-Ehrlich-Institut, Paul-Ehrlich-Straße 51-59, D-63225 Langen, Germany
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Mayer J, Meese E. Human endogenous retroviruses in the primate lineage and their influence on host genomes. Cytogenet Genome Res 2005; 110:448-56. [PMID: 16093697 DOI: 10.1159/000084977] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2003] [Accepted: 01/30/2004] [Indexed: 10/25/2022] Open
Abstract
Primates emerged about 60 million years ago. Since that time various primate-targeting retroviruses have integrated in the germ line of primate species, and some drifted to fixation. After germ line fixation, continued activity of proviruses resulted in intragenomic spread of so-called endogenous retroviruses (ERVs). Variant ERVs emerged, amplified in the genome and profoundly altered genome structures and potentially functionality. Importantly, ERVs are genome modifiers of exogenous origin. The human genome contains about 8% of sequences of retroviral origin. The human ERVs (HERVs) comprise many distinct families that amplified to copy numbers of up to several thousand. We review here the evolution of several well-characterized HERV families in the human lineage since initial germ line fixation. It is apparent that endogenous retroviruses profoundly affected the genomes of species in the evolutionary lineage leading to Homo sapiens.
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Affiliation(s)
- J Mayer
- Department of Human Genetics, Medical Faculty, University of Saarland, Homburg/Saar, Germany.
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Seifarth W, Frank O, Zeilfelder U, Spiess B, Greenwood AD, Hehlmann R, Leib-Mösch C. Comprehensive analysis of human endogenous retrovirus transcriptional activity in human tissues with a retrovirus-specific microarray. J Virol 2005; 79:341-52. [PMID: 15596828 PMCID: PMC538696 DOI: 10.1128/jvi.79.1.341-352.2005] [Citation(s) in RCA: 165] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Retrovirus-like sequences account for 8 to 9% of the human genome. Among these sequences, about 8,000 pol-containing proviral elements have been identified to date. As part of our ongoing search for active and possibly disease-relevant human endogenous retroviruses (HERVs), we have recently developed an oligonucleotide-based microarray. The assay allows for both the detection and the identification of most known retroviral reverse transcriptase (RT)-related nucleic acids in biological samples. In the present study, we have investigated the transcriptional activity of representative members of 20 HERV families in 19 different normal human tissues. Qualitative evaluation of chip hybridization signals and quantitative analysis by real-time RT-PCR revealed distinct HERV activity in the human tissues under investigation, suggesting that HERV elements are active in human cells in a tissue-specific manner. Most active members of HERV families were found in mRNA prepared from skin, thyroid gland, placenta, and tissues of reproductive organs. In contrast, only few active HERVs were detectable in muscle cells. Human tissues that lack HERV transcription could not be found, confirming that human endogenous retroviruses are permanent components of the human transcriptome. Distinct activity patterns may reflect the characteristics of the regulatory machinery in these cells, e.g., cell type-dependent occurrence of transcriptional regulatory factors.
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Affiliation(s)
- Wolfgang Seifarth
- Medical Clinic III, Faculty of Clinical Medicine Mannheim, University of Heidelberg, Mannheim, Germany.
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Bannert N, Kurth R. Retroelements and the human genome: new perspectives on an old relation. Proc Natl Acad Sci U S A 2004; 101 Suppl 2:14572-9. [PMID: 15310846 PMCID: PMC521986 DOI: 10.1073/pnas.0404838101] [Citation(s) in RCA: 365] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Retroelements constitute a large portion of our genomes. One class of these elements, the human endogenous retroviruses (HERVs), is comprised of remnants of ancient exogenous retroviruses that have gained access to the germ line. After integration, most proviruses have been the subject of numerous amplifications and have suffered extensive deletions and mutations. Nevertheless, HERV-derived transcripts and proteins have been detected in healthy and diseased human tissues, and HERV-K, the youngest, most conserved family, is able to form virus-like particles. Although it is generally accepted that the integration of retroelements can cause significant harm by disrupting or disregulating essential genes, the role of HERV expression in the etiology of malignancies and autoimmune and neurologic diseases remains controversial. In recent years, striking evidence has accumulated indicating that some proviral sequences and HERV proteins might even serve the needs of the host and are therefore under positive selection. The remarkable progress in the analysis of host genomes has brought to light the significant impact of HERVs and other retroelements on genetic variation, genome evolution, and gene regulation.
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Abstract
Endogenous retroviruses (ERVs) correspond to the integrated proviral form of infectious retroviruses that are trapped within the genome by mutations. Endogenous retroviruses represent a key molecular link between the host genome and infectious viral particles. Proteins encoded by ERVs are recognized by antiviral immune responses and become targets of autoreactivity. Activation of ERVs, such as human ERV-K or a human T-cell lymphotropic virus-related endogenous sequence, may also mediate pathogenicity of Epstein-Barr virus. Endogenous retrovirus peptides can directly regulate immune responses. Thus, molecular mimicry and immunomodulation by ERVs may account for self-reactivity and abnormal T- and B-cell functions in autoimmune disorders.
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Affiliation(s)
- Andras Perl
- Departments of Medicine and Microbiology and Immunology, College of Medicine, State University of New York Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210, USA.
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Kuhelj R, Rizzo CJ, Chang CH, Jadhav PK, Towler EM, Korant BD. Inhibition of human endogenous retrovirus-K10 protease in cell-free and cell-based assays. J Biol Chem 2001; 276:16674-82. [PMID: 11278433 DOI: 10.1074/jbc.m008763200] [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] [Indexed: 11/06/2022] Open
Abstract
A full-length and C-terminally truncated version of human endogenous retrovirus (HERV)-K10 protease were expressed in Escherichia coli and purified to homogeneity. Both versions of the protease efficiently processed HERV-K10 Gag polyprotein substrate. HERV-K10 Gag was also cleaved by human immunodeficiency virus, type 1 (HIV-1) protease, although at different sites. To identify compounds that could inhibit protein processing dependent on the HERV-K10 protease, a series of cyclic ureas that had previously been shown to inhibit HIV-1 protease was tested. Several symmetric bisamides acted as very potent inhibitors of both the truncated and full-length form of HERV-K10 protease, in subnanomolar or nanomolar range, respectively. One of the cyclic ureas, SD146, can inhibit the processing of in vitro translated HERV-K10 Gag polyprotein substrate by HERV-K10 protease. In addition, in virus-like particles isolated from the teratocarcinoma cell line NCCIT, there is significant accumulation of Gag and Gag-Pol precursors upon treatment with SD146, suggesting the compound efficiently blocks HERV-K Gag processing in cells. This is the first report of an inhibitor able to block cell-associated processing of Gag polypeptides of an endogenous retrovirus.
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Affiliation(s)
- R Kuhelj
- Department of Virology, Experimental Station, DuPont Pharmaceuticals, Wilmington, Delaware 19880, USA
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15
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Boese A, Galli U, Geyer M, Sauter M, Mueller-Lantzsch N. The Rev/Rex homolog HERV-K cORF multimerizes via a C-terminal domain. FEBS Lett 2001; 493:117-21. [PMID: 11287007 DOI: 10.1016/s0014-5793(01)02280-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Expression of human endogenous retrovirus K (HERV-K) is associated with germ-cell neoplasia. HERV-K encodes a protein of the Rev/Rex family, cORF, that supports cellular transformation and binds the promyelocytic leukemia zinc finger (PLZF) protein implicated in spermatogenesis. Rev/Rex function invariably depends on multimerization. Here we show that cORF likewise self-associates to form higher-order oligomers. Amino acids (aa) 47-87 in cORF are sufficient, aa 75-87 essential for self-association. Consistently, this domain is predicted to form a hydrophobic alpha-helix that may represent an oligomerization interface. The existence of a dimerization-competent cORF mutant lacking PLZF-binding activity (cORF47-87) suggests a way of dominant negative inhibition of the proposed tumor susceptibility factor cORF.
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Affiliation(s)
- A Boese
- Institut für Medizinische Mikrobiologie und Hygiene, Abteilung, Virologie, Haus 47, 66421 Hamburg, Germany
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16
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Bieda K, Hoffmann A, Boller K. Phenotypic heterogeneity of human endogenous retrovirus particles produced by teratocarcinoma cell lines. J Gen Virol 2001; 82:591-596. [PMID: 11172100 DOI: 10.1099/0022-1317-82-3-591] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Human endogenous retrovirus (HERV) sequences represent about 0.5% of the human genome. The only HERV known to express virus particles is human teratocarcinoma-derived virus (HTDV), which is now termed HTDV/HERV-K. Between 25 and 50 different copies of HERV-K are present in the human genome, three of which contain full-length genes for viral structural proteins. To determine whether genes of different HERV-K proviruses can be expressed, the morphologies and protein expression patterns of HTDV/HERV-K produced by various human teratocarcinoma cell lines were compared. Three different types of retrovirus-like particles were observed, showing differences in the presence of viral surface proteins and the existence of free mature virions. These distinct morphological features between virion types were in accordance with the results of immunoblotting analyses that revealed differences in the cleavage of a viral Gag protein precursor and the presence of a putative Env protein. These data suggest that different HERV-K proviruses are transcribed in human teratocarcinoma cell lines.
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Affiliation(s)
- Katrin Bieda
- Paul-Ehrlich-Institut, Paul-Ehrlich-Straße 51-59, D-63225 Langen, Germany1
| | - Andreas Hoffmann
- Paul-Ehrlich-Institut, Paul-Ehrlich-Straße 51-59, D-63225 Langen, Germany1
| | - Klaus Boller
- Paul-Ehrlich-Institut, Paul-Ehrlich-Straße 51-59, D-63225 Langen, Germany1
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17
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Ericsson T, Oldmixon B, Blomberg J, Rosa M, Patience C, Andersson G. Identification of novel porcine endogenous betaretrovirus sequences in miniature swine. J Virol 2001; 75:2765-70. [PMID: 11222699 PMCID: PMC115900 DOI: 10.1128/jvi.75.6.2765-2770.2001] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
PCR amplification of genomic DNA from miniature swine peripheral blood lymphocytes, using primers corresponding to highly conserved regions of the polymerase (pol) gene, allowed the identification of two novel porcine endogenous retrovirus (PERV) sequences, PMSN-1 and PMSN-4. Phylogenetic analyses of the nucleotide sequences of PMSN-1 and PMSN-4 revealed them to be most closely related to betaretroviruses. The identification of PERVs belonging to the Betaretrovirus genus shows that endogenous retroviruses of this family are more broadly represented in mammalian species than previously appreciated. Both sequences contained inactivating mutations, implying that these particular loci are defective. However, Southern blot analysis showed additional copies of closely related proviruses in the miniature swine genome. Analyses of fetal and adult miniature swine tissues revealed a broad mRNA expression pattern of both PMSN-1 and PMSN-4. The most abundant expression was detected in whole bone marrow c-kit(+) (CD117(+)) progenitor bone marrow cells, fetal liver, salivary gland, and thymus. It appears unlikely that functional loci encoding these novel PERV sequences exist, but this remains to be established. The betaretrovirus sequences described in this report will allow such investigations to be actively pursued.
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MESH Headings
- Animals
- Blotting, Southern
- DNA, Viral/genetics
- Endogenous Retroviruses/classification
- Endogenous Retroviruses/genetics
- Gene Products, pol/genetics
- Genes, pol
- Genome
- Genome, Viral
- Humans
- Leukocytes, Mononuclear/virology
- Mice
- Molecular Sequence Data
- Phylogeny
- Polymerase Chain Reaction
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Sequence Analysis, DNA
- Swine, Miniature/virology
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Affiliation(s)
- T Ericsson
- BioTransplant, Inc., Charlestown, Massachusetts 02129, USA
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18
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Padow M, Lai L, Fisher RJ, Zhou YC, Wu X, Kappes JC, Towler EM. Analysis of human immunodeficiency virus type 1 containing HERV-K protease. AIDS Res Hum Retroviruses 2000; 16:1973-80. [PMID: 11153080 DOI: 10.1089/088922200750054701] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The human endogenous retrovirus, type K (HERV-K) represents the most biologically active form of known retroelements present in the human genome. Several HERV-K genomes have transcriptionally active open reading frames and encode their own protease (PR). The HERV-K PR has been shown to authentically cleave human immunodeficiency virus type 1 (HIV-1) matrix-capsid peptide in the presence of HIV-1 PR inhibitors. This raised the possibility that HERV-K PR could complement HIV-1 PR function in HIV-1-infected individuals. To investigate this possibility, we fused the HIV-1 vpr gene to the HERV-K PR gene (vpr-PR). The vpr-PR expression plasmid and a PR-defective HIV-1 clone were cotransfected into 293T cells. Progeny virions were assayed for processing of the HIV-1 polyproteins by Western blot and for changes in infectivity. HERV-K PR fused to Vpr was incorporated into HIV-1 virions at a high concentration and cleaved the Gag and Pol precursor proteins. However, neither Gag nor Pol polyproteins were correctly processed. Moreover, the HERV-K PR did not restore virus infectivity. While these results do not exclude the possibility that the HERV-K PR could complement an HIV-1 PR whose function is impaired due to drugs or drug-resistant mutations, they clearly demonstrate that the HERV-K PR cannot substitute for the function of the wild-type HIV-1 PR.
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Affiliation(s)
- M Padow
- Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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19
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Lapatschek M, Dürr S, Löwer R, Magin C, Wagner H, Miethke T. Functional analysis of the env open reading frame in human endogenous retrovirus IDDMK(1,2)22 encoding superantigen activity. J Virol 2000; 74:6386-93. [PMID: 10864649 PMCID: PMC112145 DOI: 10.1128/jvi.74.14.6386-6393.2000] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mice harbor a family of endogenous retroviruses, the mouse mammary tumor viruses (MMTV), which encode superantigens. These superantigens are responsible for the deletion of T cells expressing certain Vbeta chains of the T-cell receptor in the thymus. Human T cells are able to recognize MMTV-encoded superantigens presented by human major histocompatibility complex class II-positive cells. Owing to this and to the similarity of the human and murine immune systems, it was speculated that human endogenous retroviruses might also code for superantigens. Recently, it was reported that a proviral clone (IDDMK(1,2)22) of the human endogenous retrovirus family HTDV/HERV-K encodes a superantigen. The putative superantigen gene was located within the env region of the virus. Stimulated by these findings, we amplified by PCR and cloned into eucaryotic expression vectors open reading frames (ORFs) which were identical or very similar to IDDMK(1,2)22. When we transfected these vectors into A20 cells, a murine B-cell lymphoma, we were able to demonstrate mRNA expression and protein production. However, we did not find any evidence that the ORF stimulated human or murine T cells in a Vbeta-specific fashion, the most prominent feature of superantigens.
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Affiliation(s)
- M Lapatschek
- Institute of Medical Microbiology, Immunology and Hygiene, Technical University of Munich, 81675 Munich, Germany
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20
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Tönjes RR, Czauderna F, Kurth R. Genome-wide screening, cloning, chromosomal assignment, and expression of full-length human endogenous retrovirus type K. J Virol 1999; 73:9187-95. [PMID: 10516026 PMCID: PMC112952 DOI: 10.1128/jvi.73.11.9187-9195.1999] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human genome harbors 25 to 50 proviral copies of the endogenous retrovirus type K (HERV-K), some of which code for the characteristic retroviral proteins Gag, Pol, and Env. For a genome-wide cloning approach of full-length and intact HERV-K proviruses, a human P1 gene library was screened with a gag-specific probe. Both HERV-K type 1 and 2 clones were isolated. Sixteen HERV-K type 2 proviral genomes were characterized by direct coupled in vitro transcription-in vitro translation assays to analyze the coding potential of isolated gag, pol, and env amplicons from individual P1 clones. After determination of long terminal repeat (LTR) sequences and adjacent chromosomal integration sites by inverse PCR techniques, two HERV-K type 2 proviruses displaying long retroviral open reading frames (ORFs) were assigned to chromosomes 7 (C7) and 19 (C19) by using a human-rodent monochromosomal cell hybrid mapping panel. HERV-K(C7) shows an altered (YIDD-to-CIDD) motif in the reverse transcriptase domain. HERV-K(C19) is truncated in the 5' LTR and harbors a defective protease gene due to a point mutation. Direct amplification of proviral structures from single chromosomes by using chromosomal flanking primers was performed by long PCR for HERV-K(C7) and HERV-K(C19) and for type 1 proviruses HERV-K10 and HERV-K18 from chromosomes 5 and 1, respectively. HERV-K18, in contrast to HERV-K10, bears no intact gag ORF and shows close homology to HERV-K/IDDMK(1,2)22. In transfection experiments, HERV-K(C7) and HERV-K cDNA-based expression vectors yielded the proteins Gag and cORF whereas HERV-K10 vectors yielded Gag alone. The data suggest that the human genome does not contain an entire, intact proviral copy of HERV-K.
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Affiliation(s)
- R R Tönjes
- Paul-Ehrlich-Institut, D-63225 Langen, Germany
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21
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Berkhout B, Jebbink M, Zsíros J. Identification of an active reverse transcriptase enzyme encoded by a human endogenous HERV-K retrovirus. J Virol 1999; 73:2365-75. [PMID: 9971820 PMCID: PMC104482 DOI: 10.1128/jvi.73.3.2365-2375.1999] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Of the numerous endogenous retroviral elements that are present in the human genome, the abundant HERV-K family is distinct because several members are transcriptionally active and coding for biologically active proteins. A detailed phylogeny of the HERV-K family based on the partial sequence of the reverse transcriptase (RT) gene revealed a high incidence of an intact RT open reading frame within the HML-2 subgroup of HERV-K elements. In this study, we report the cloning of six full-length HML-2 RT genes, of which five contain an uninterrupted open reading frame. The RT enzymes were expressed as glutathione S-transferase fusion proteins in Escherichia coli, and several HERV-K RT enzymes demonstrated polymerase as well as RNase H activity. Several biochemical properties of the RT polymerase were analyzed, including the template requirements and optimal reaction conditions (temperature, type of divalent cation). Inspection of the nucleotide sequence of the HERV-K RT genes demonstrated a mosaic structure, suggesting that a high level of genetic recombination has occurred in this virus family, which is a hallmark of replication by means of reverse transcription. The selective pressure to maintain the RT coding potential is illustrated by the sequence of a particular HERV-K isolate that contains three 1-nucleotide deletions within a small RT segment, thus maintaining the open reading frame. These combined results may suggest that these endogenous RT enzymes still have a biological function. It is possible that the RT activity was involved in the spread of this major class of retroelements by retrotransposition, and in fact it cannot be excluded that this retrovirus group is still mobile. The endogenous RT activity may also have been involved in the shaping of the human genome, e.g., by formation of pseudogenes.
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Affiliation(s)
- B Berkhout
- Department of Human Retrovirology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
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22
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Towler EM, Gulnik SV, Bhat TN, Xie D, Gustschina E, Sumpter TR, Robertson N, Jones C, Sauter M, Mueller-Lantzsch N, Debouck C, Erickson JW. Functional characterization of the protease of human endogenous retrovirus, K10: can it complement HIV-1 protease? Biochemistry 1998; 37:17137-44. [PMID: 9860826 DOI: 10.1021/bi9818927] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To investigate the biochemical properties of the protease encoded by the human endogenous retrovirus, K10 (HERV-K), 213 amino acids of the 3'-end of the HERV-K protease (PR) open reading frame were expressed in Escherichia coli. Autocatalytic cleavage of the expressed polypeptide resulted in an 18.2 kDa protein which was shown to be proteolytically active against a fluorogenic peptide used as a substrate for HIV-1 protease. On the basis of sequence homology and molecular modeling, the 106 N-terminal amino acids of HERV-K PR were predicted to comprise a retroviral protease core domain. An 11.6 kDa protein corresponding to this region was expressed and shown to be a fully functional enzyme. The 11.6 kDa domain of HERV-K PR is unusually stable over a wide pH range, exhibits optimal catalytic activity between pH 4.0 and 5.0, and exists as a dimer at pH 7.0 with a Kd of 50 microM. Like HIV-1 PR, the HERV-K PR core domain is activated by high salt concentrations and processes HIV-1 matrix-capsid polyprotein at the authentic HIV-1 PR recognition site. However, both the 18.2 and 11.6 kDa forms of HERV-K PR were highly resistant to a number of clinically useful HIV-1 PR inhibitors, including ritonavir, indinavir, and saquinavir. This raises the possibility that HERV-K PR may complement HIV-1 PR during infection, and could have implications for protease inhibitor therapy and drug resistance.
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Affiliation(s)
- E M Towler
- Protein Chemistry Laboratory, Structural Biochemistry Program, SAIC Frederick, Maryland 21702, USA.
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23
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Roelofs H, van Gurp RJ, Oosterhuis JW, Looijenga LH. Detection of human endogenous retrovirus type K-specific transcripts in testicular parenchyma and testicular germ cell tumors of adolescents and adults: clinical and biological implications. THE AMERICAN JOURNAL OF PATHOLOGY 1998; 153:1277-82. [PMID: 9777959 PMCID: PMC1853062 DOI: 10.1016/s0002-9440(10)65672-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Testicular germ cell tumors (TGCTs) of adolescents and adults have been shown to contain proteins of the human endogenous retrovirus type K family. In a recent study, expression of these retroviral sequences was confirmed using in situ hybridization, which also showed expression in carcinoma in situ, the precursor of all TGCTs. Because of the clinical significance of a test for early diagnosis of TGCTs, we studied whether expression of human endogenous retrovirus type K genes could be an informative parameter. Therefore, we investigated TGCTs of various histologies and testicular parenchyma with and without carcinoma in situ using reverse transcription-polymerase chain reaction for expression of the gag, env, and prt genes. The gag and prt genes were expressed in all samples tested. The env transcripts were not found in TGCTs showing somatic differentiation only but could be detected in most normal testicular parenchyma samples. Therefore, detection of human endogenous retrovirus type K transcripts cannot be used for early diagnosis of TGCTs. Simultaneous expression of multiple gag sequences was found both in normal parenchyma and TGCTs, and we demonstrated that expression of gag sequences with an extra G, necessary to generate a functional protein, was not limited to TGCTs.
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Affiliation(s)
- H Roelofs
- Laboratory for Experimental Patho-Oncology, Daniel den Hoed Cancer Center, University Hospital Rotterdam, The Netherlands
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24
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Evidence for Copurification of HERV-K–Related Transcripts and a Reverse Transcriptase Activity in Human Platelets From Patients With Essential Thrombocythemia. Blood 1997. [DOI: 10.1182/blood.v90.10.4022] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
AbstractWe have previously reported that particles resembling retroviral particles and possessing an RNA-directed DNA polymerase activity can be prepared from platelets. Furthermore, we and others have shown that these particles are present at higher levels in patients with essential thrombocythemia and polycythemia vera. We show here that these particles package RNA molecules that encode HERV-K–related pol genes. A subset of the RNA molecules that are packaged are likely to encode the RNA directed DNA polymerase activity and, because these RNAs possess long/full-length open reading frames for the reverse transcriptase and RNaseH (also for part of the integrase domains in genomic clones) of HERV-K, we propose that these transcripts are indeed strong candidates for encoding the enzyme activity found in these particles. Moreover, by using a modification of the polymerase chain reaction-based reverse transcriptase assay in which activated DNA is added during cDNA synthesis to suppress DNA polymerase-mediated RNA-directed DNA synthesis, we have found that the particle-associated enzyme behaves like a retroviral reverse transcriptase, further supporting the conclusion that retrovirus-like, perhaps HERV-K sequences, encode this enzyme activity.
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25
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Boller K, Janssen O, Schuldes H, Tönjes RR, Kurth R. Characterization of the antibody response specific for the human endogenous retrovirus HTDV/HERV-K. J Virol 1997; 71:4581-8. [PMID: 9151852 PMCID: PMC191680 DOI: 10.1128/jvi.71.6.4581-4588.1997] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Differentiated human teratocarcinoma cell lines produce the human teratocarcinoma-derived virus (HTDV) particles encoded by the human endogenous retrovirus sequence HERV-K. We screened almost 2,000 human sera for antibodies against this endogenous human retrovirus, HTDV/HERV-K. Specificity of the immunofluorescence reactions using particle producing teratocarcinoma cells was confirmed by immunoelectron microscopy of ultrathin frozen sections. Immunoblot analyses using lysates of HTDV-producing cells revealed a 80-kDa HERV-K Gag precursor and a 90-kDa putative viral Env protein after incubation with positive sera. No processed Gag protein could be observed. Virus-specific bands were not detected in lysates of nonproducing cells. High antibody titers were found in about 60% of male patients with germ cell tumors. Antibody reactivity declined after tumor removal. In healthy blood donors, anti-HTDV reactivity was found only at low titers in a small percentage (3.9%) of individuals. A slightly elevated but statistically significant percentage of HTDV positivity was also observed for sera of pregnant women, whereas human immunodeficiency virus-positive individuals exhibited no peculiarity compared to normal blood donors. Our results provide evidence that HTDV particles are expressed in vivo and that the immune reaction against HTDV/HERV-K is specific for defined viral proteins.
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Affiliation(s)
- K Boller
- Paul-Ehrlich-Institut, Langen, Germany.
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26
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Tönjes RR, Löwer R, Boller K, Denner J, Hasenmaier B, Kirsch H, König H, Korbmacher C, Limbach C, Lugert R, Phelps RC, Scherer J, Thelen K, Löwer J, Kurth R. HERV-K: the biologically most active human endogenous retrovirus family. JOURNAL OF ACQUIRED IMMUNE DEFICIENCY SYNDROMES AND HUMAN RETROVIROLOGY : OFFICIAL PUBLICATION OF THE INTERNATIONAL RETROVIROLOGY ASSOCIATION 1996; 13 Suppl 1:S261-7. [PMID: 8797733 DOI: 10.1097/00042560-199600001-00039] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The human genome contains a wide variety of endogenous retrovirus-like sequences. The human endogenous retrovirus type K (HERV-K) family comprises 30-50 members per haploid genome in humans and is highly conserved in Old World monkeys and apes. Some proviruses are displaying open reading frames (ORF) with coding capacity for viral particles. HERV-K sequences most likely code for the previously described human teratocarcinoma-derived virus (HTDV) and correlated expression of HERV-K Gag has been demonstrated by immunoelectron microscopy studies. Protease, but not yet reverse transcriptase (RT), enzymatic activity was demonstrated for recombinant HERV-K proteins. However, an ultrasensitive RT assay revealed specific polymerase activity associated with the HTDV particles. HERV-K transcription is specifically regulated by viral long terminal repeats and RNA is expressed at low steady-state levels in a variety of human tissues and tumours. In teratocarcinoma cell lines, HERV-K is highly expressed in a complex pattern showing full-length as well as subgenomic envelope (env) and two alternatively spliced small transcripts. The doubly spliced 1.8-kb mRNA codes for cORF protein which resembles Rev of HIV-1 and is located in the nucleolus. In addition, the cORF sequence acts as a leader and is essential for effective expression of glycosylated HERV-K Env protein. Although HERV-K sequences code for all necessary retroviral proteins, infectious particles could not yet be demonstrated. The putative implication of HERV sequences in pathophysiological processes, for example, testicular malignancies, remains to be elucidated.
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