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An N-terminally truncated envelope protein encoded by a human endogenous retrovirus W locus on chromosome Xq22.3.

ABSTRACT: BACKGROUND: We previously showed that the envelope (env) sequence of a human endogenous retrovirus (HERV)-W locus on chromosome Xq22.3 is transcribed in human peripheral blood mononuclear cells. The env open reading frame (ORF) of this locus is interrupted by a premature stop at codon 39, but otherwise harbors a long ORF for an N-terminally truncated 475 amino acid Env protein, starting at an in-frame ATG at codon 68. We set out to characterize the protein encoded by that ORF. RESULTS: Transient expression of the 475 amino acid Xq22.3 HERV-W env ORF produced an N-terminally truncated HERV-W Env protein, as detected by the monoclonal anti-HERV-W Env antibodies 6A2B2 and 13H5A5. Remarkably, reversion of the stop at codon 39 in Xq22.3 HERV-W env reconstituted a full-length HERV-W Xq22.3 Env protein. Similar to the full-length HERV-W Env protein Syncytin-1, reconstituted full-length Xq22.3 HERV-W Env is glycosylated, forms oligomers, and is expressed at the cell surface. In contrast, Xq22.3 HERV-W Env is unglycosylated, does not form oligomers, and is located intracellularly, probably due to lack of a signal peptide. Finally, we reconfirm by immunohistochemistry that monoclonal antibody 6A2B2 detects an antigen expressed in placenta and multiple sclerosis brain lesions. CONCLUSIONS: A partially defective HERV-W env gene located on chromosome Xq22.3, which we propose to designate ERVWE2, has retained coding capacity and can produce ex vivo an N-terminally truncated Env protein, named N-Trenv. Detection of an antigen by 6A2B2 in placenta and multiple sclerosis lesions opens the possibility that N-Trenv could be expressed in vivo. More generally, our findings are compatible with the idea that defective HERV elements may be capable of producing incomplete HERV proteins that, speculatively, may exert functions in human physiology or pathology.

SUBMITTER: Roebke C

PROVIDER: S-EPMC2936387 | biostudies-literature | 2010

REPOSITORIES: biostudies-literature

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An N-terminally truncated envelope protein encoded by a human endogenous retrovirus W locus on chromosome Xq22.3.

Roebke Christina C Wahl Silke S Laufer Georg G Stadelmann Christine C Sauter Marlies M Mueller-Lantzsch Nikolaus N Mayer Jens J Ruprecht Klemens K

Retrovirology 20100824

<h4>Background</h4>We previously showed that the envelope (env) sequence of a human endogenous retrovirus (HERV)-W locus on chromosome Xq22.3 is transcribed in human peripheral blood mononuclear cells. The env open reading frame (ORF) of this locus is interrupted by a premature stop at codon 39, but otherwise harbors a long ORF for an N-terminally truncated 475 amino acid Env protein, starting at an in-frame ATG at codon 68. We set out to characterize the protein encoded by that ORF.<h4>Results< ...[more]

PMID: 20735848

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Project description:Endogenous retroviruses are the remnants of past retroviral infections that are scattered within mammalian genomes. In humans, most of these elements are old degenerate sequences that have lost their coding properties. The HERV-K(HML2) family is an exception: it recently amplified in the human genome and corresponds to the most active proviruses, with some intact open reading frames and the potential to encode viral particles. Here, using a reconstructed consensus element, we show that HERV-K(HML2) proviruses are able to inhibit Tetherin, a cellular restriction factor that is active against most enveloped viruses and acts by keeping the viral particles attached to the cell surface. More precisely, we identify the Envelope protein (Env) as the viral effector active against Tetherin. Through immunoprecipitation experiments, we show that the recognition of Tetherin is mediated by the surface subunit of Env. Similar to Ebola glycoprotein, HERV-K(HML2) Env does not mediate Tetherin degradation or cell surface removal; therefore, it uses a yet-undescribed mechanism to inactivate Tetherin. We also assessed all natural complete alleles of endogenous HERV-K(HML2) Env described to date for their ability to inhibit Tetherin and found that two of them (out of six) can block Tetherin restriction. However, due to their recent amplification, HERV-K(HML2) elements are extremely polymorphic in the human population, and it is likely that individuals will not all possess the same anti-Tetherin potential. Because of Tetherin's role as a restriction factor capable of inducing innate immune responses, this could have functional consequences for individual responses to infection.Tetherin, a cellular protein initially characterized for its role against HIV-1, has been proven to counteract numerous enveloped viruses. It blocks the release of viral particles from producer cells, keeping them tethered to the cell surface. Several viruses have developed strategies to inhibit Tetherin activity, allowing them to efficiently infect and replicate in their host. Here, we show that human HERV-K(HML2) elements, the remnants of an ancient retroviral infection, possess an anti-Tetherin activity which is mediated by the envelope protein. It is likely that this activity was an important factor that contributed to the recent, human-specific amplification of this family of elements. Also, due to their recent amplification, HERV-K(HML2) elements are highly polymorphic in the human population. Since Tetherin is a mediator of innate immunity, interindividual variations among HERV-K(HML2) Env genes may result in differences in immune responses to infection.

Project description:The envelope (env) protein of the human endogenous retrovirus type K (HERV-K) family is commonly expressed on the surface of breast cancer cells. We assessed whether HERV-K env is a potential target for antibody-based immunotherapy of breast cancer.We examined the expression of HERV-K env protein in various malignant (MDA-MB-231, MCF-7, SKBR3, MDA-MB-453, T47D, and ZR-75-1) and nonmalignant (MCF-10A and MCF-10AT) human breast cell lines by immunoblot, enzyme-linked immunosorbent assay, immunofluorescence staining, and flow cytometry. Anti-HERV-K env monoclonal antibodies (mAbs; 6H5, 4D1, 4E11, 6E11, and 4E6) were used to target expression of HERV-K, and antitumor effects were assessed by quantifying growth and apoptosis of breast cancer cells in vitro, and tumor growth in vivo in mice (n = 5 per group) bearing xenograft tumors. The mechanisms responsible for 6H5 mAb-mediated effects were investigated by microarray assays, flow cytometry, immunoblot, and immunofluorescence staining. The expression of HERV-K env protein was assessed in primary breast tumors (n = 223) by immunohistochemistry. All statistical tests were two-sided.The expression of HERV-K env protein in malignant breast cancer cell lines was substantially higher than nonmalignant breast cells. Anti-HERV-K-specific mAbs inhibited growth and induced apoptosis of breast cancer cells in vitro. Mice treated with 6H5 mAb showed statistically significantly reduced growth of xenograft tumors compared with mice treated with control immunoglobulin (control [mIgG] vs 6H5 mAb, for tumors originating from MDA-MB-231 cells, mean size = 1448.33 vs 475.44 mm(3); difference = 972.89 mm(3), 95% CI = 470.17 to 1475.61 mm(3); P < .001). Several proteins involved in the apoptotic signaling pathways were overexpressed in vitro in 6H5 mAb-treated malignant breast cells compared with mIgG-treated control. HERV-K expression was detected in 148 (66%) of 223 primary breast tumors, and a higher rate of lymph node metastasis was associated with HERV-K-positive compared with HERV-K-negative tumors (43% vs 23%, P = .003).Monoclonal antibodies against HERV-K env protein show potential as novel immunotherapeutic agents for breast cancer therapy.

Project description:OBJECTIVES:There is growing evidence to suggest that human endogenous retroviruses (HERVs) have contributed to human evolution, being expressed in development, normal physiology and disease. A key difficulty in the scientific evaluation of this potential viral contribution is the accurate demonstration of virally expressed protein in specific human cells and tissues. In this study, we have adopted the endogenous retrovirus, ERV3, as our test model in developing a reliable high-capacity methodology for the expression of such endogenous retrovirus-coded protein. DESIGN:Two affinity-purified polyclonal antibodies to ERV3 Env-encoded protein were generated to detect the corresponding protein expression pattern in specific human cells, tissues and organs. PARTICIPANTS:Sampling included normal tissues from 144 individuals ranging from childhood to old age. This included more than forty different tissues and organs and some 216 different cancer tissues representing the twenty commonest forms of human cancer. SETTING:The Rudbeck Laboratory, Uppsala University and Uppsala University Hospital, Uppsala, Sweden. MAIN OUTCOME MEASURES:The potential expression at likely physiological level of the ERV3Env encoded protein in a wide range of human cells, tissues and organs. RESULTS:We found that ERV3 encoded Env protein is expressed at substantive levels in placenta, testis, adrenal gland, corpus luteum, Fallopian tubes, sebaceous glands, astrocytes, bronchial epithelium and the ducts of the salivary glands. Substantive expression was also seen in a variety of epithelial cells as well as cells known to undergo fusion in inflammation and in normal physiology, including fused macrophages, myocardium and striated muscle. This contrasted strongly with the low levels expressed in other tissues types. These findings suggest that this virus plays a significant role in human physiology and may also play a possible role in disease. CONCLUSION:This technique can now be extended to the study of other HERV genomes within the human chromosomes that may have contributed to human evolution, physiology and disease.

Project description:BackgroundA 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.ResultsWe 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.ConclusionsOur 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.

Project description:Human endogenous retroviruses (HERVs) are differentially expressed depending on the cell type and physiological circumstances. HERV-K has been implicated in the pathogenesis of several diseases although the functional consequences of its expression remain unknown. Human immunodeficiency virus (HIV) infection causes neuroinflammation with neuronal damage and death. Herein, we investigated HERV-K(II)/(HML-2) envelope (Env) expression and its actions in the brain during HIV/AIDS. HERV-K(II) Env expression was assessed in healthy brain tissues, autopsied HIV HIV- infected (HIV+) and uninfected (HIV-) brains and in neural cell cultures by real time RT-PCR, massively parallel (deep) sequencing, immunoblotting and immunohistochemistry. Neuronal and neural stem cells expressing HERV-K(II) Env were analyzed in assays of host responses including cellular viability, immune responses and neurobehavioral outcomes. Deep sequencing of human brain transcriptomes disclosed that RNA sequences encoded by HERV-K were among the most abundant HERV sequences detected in human brain. Comparison of different cell types revealed that HERV-K(II) env RNA abundance was highest in cultured human neurons but was suppressed by epidermal growth factor exposure. HERV-K(II) Env immunoreactivity was increased in the cerebral cortex from persons with HIV/AIDS, principally localized in neurons. Human neuronal cells transfected with HERV-K(II) Env exhibited increased NGF and BDNF expression. Expression of HERV-K(II) Env in neuronal cells increased cellular viability and prevented neurotoxicity mediated by HIV-1 Vpr. Intracerebral delivery of HERV-K(II) Env expressed by neural stem cells suppressed TNF-α expression and microglial activation while also improving neurobehavioral deficits in vpr/RAG1-/- mice. HERV-K(II) Env was highly expressed in human neurons, especially during HIV/AIDS, but in addition exerted neuroprotective effects. These findings imply that HERV gene products might exert adaptive effects in circumstances of pathophysiological stress, perhaps underlying the conservation of HERVs within the human genome.

Dataset Information

An N-terminally truncated envelope protein encoded by a human endogenous retrovirus W locus on chromosome Xq22.3.

Publications

An N-terminally truncated envelope protein encoded by a human endogenous retrovirus W locus on chromosome Xq22.3.

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