Cytokine regulation of env gene expression of human endogenous retrovirus-R in human vascular endothelial cells

Lamivudine, Doravirine, and Cabotegravir Downregulate the Expression of Human Endogenous Retroviruses (HERVs), Inhibit Cell Growth, and Reduce Invasive Capability in Melanoma Cell Lines

This study explores the impact of antiretroviral administration on the expression of human endogenous retroviruses (HERVs), cell growth, and invasive capability of human melanoma cell lines in culture. We investigated three antiretrovirals-lamivudine, doravirine, and cabotegravir-in A375, FO-1, and SK-Mel-28, BRAF-mutated, and in MeWo, P53-mutated, melanoma cell lines. The findings indicate a general capability of these drugs to downregulate the expression of HERV-K Pol and Env genes and hinder cell viability, mobility, and colony formation capacity of melanoma cells. The antiretroviral drugs also demonstrate selectivity against malignant cells, sparing normal human epithelial melanocytes. The study reveals that the integrase inhibitor cabotegravir is particularly effective in inhibiting cell growth and invasion across different cell lines in comparison with lamivudine and doravirine, which are inhibitors of the viral reverse transcriptase enzyme. The investigation further delves into the molecular mechanisms underlying the observed effects, highlighting the potential induction of ferroptosis, apoptosis, and alterations in cell cycle regulatory proteins. Our findings showed cytostatic effects principally revealed in A375, and SK-Mel-28 cell lines through a downregulation of retinoblastoma protein phosphorylation and/or cyclin D1 expression. Signs of ferroptosis were detected in both A375 cells and FO-1 cells by a decrease in glutathione peroxidase 4 and ferritin expression, as well as by an increase in transferrin protein levels. Apoptosis was also detected in FO-1 and SK-Mel-28, but only with cabotegravir treatment. Moreover, we explored the expression and activity of the stimulator of interferon genes (STING) protein and its correlation with programmed death-ligand 1 (PD-L1) expression. Both the STING activity and PD-L1 expression were decreased, suggesting that the antiretroviral treatments may counteract the detrimental effects of PD-L1 expression activation through the STING/interferon pathway triggered by HERV-K. Finally, this study underscores the potential therapeutic significance of cabotegravir in melanoma treatment. The findings also raise the prospect of using antiretroviral drugs to downregulate PD-L1 expression, potentially enhancing the therapeutic responses of immune checkpoint inhibitors.

Human Endogenous Retrovirus, SARS-CoV-2, and HIV Promote PAH via Inflammation and Growth Stimulation

Pulmonary arterial hypertension (PAH) is a pulmonary vascular disease characterized by the progressive elevation of pulmonary arterial pressures. It is becoming increasingly apparent that inflammation contributes to the pathogenesis and progression of PAH. Several viruses are known to cause PAH, such as severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), human endogenous retrovirus K(HERV-K), and human immunodeficiency virus (HIV), in part due to acute and chronic inflammation. In this review, we discuss the connections between HERV-K, HIV, SARS-CoV-2, and PAH, to stimulate research regarding new therapeutic options and provide new targets for the treatment of the disease.

Bisphenols induce human genomic damage and modulate HERVs/env expression

Bisphenol A (BPA), a recognized endocrine-disrupting chemical, is used in the production of epoxy and polycarbonate resins. Since human exposure to BPA has been associated with increased cancer susceptibility, the market has shifted to products often labeled as "BPA free" containing BPA analogs such as bisphenol F (BPF) and bisphenol S (BPS). However, the European legislation on BPF and BPS is still unclear. This study analyzed the effects of BPA, BPF, and BPS exposure on human peripheral blood mononuclear cells by using in vitro micronucleus assay. Furthermore, it investigated the impact of bisphenols exposure on human endogenous retroviruses (HERVs) expression, which is implicated with the pathogenesis of several human diseases. The micronucleus assay revealed a significant genotoxic effect in peripheral blood cells after exposure to BPA and BPF at concentrations of 0.1, 0.05, and 0.025 μg/ml, and to BPS at 0.1 and 0.05 μg/ml. In addition, BPA exposure seems to upregulate the expression of HERVs, while a downregulation was observed after BPF and BPS treatments. Overall, our data showed the toxic effect of BPA and its analogs on circulating cells in the blood and demonstrated that they could modulate the HERVs expression.

Human Endogenous Retroviruses as Gene Expression Regulators: Insights from Animal Models into Human Diseases

The human genome contains many retroviral elements called human endogenous retroviruses (HERVs), resulting from the integration of retroviruses throughout evolution. HERVs once were considered inactive junk because they are not replication-competent, primarily localized in the heterochromatin, and silenced by methylation. But HERVs are now clearly shown to actively regulate gene expression in various physiological and pathological conditions such as developmental processes, immune regulation, cancers, autoimmune diseases, and neurological disorders. Recent studies report that HERVs are activated in patients suffering from coronavirus disease 2019 (COVID-19), the current pandemic caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) infection. In this review, we describe internal and external factors that influence HERV activities. We also present evidence showing the gene regulatory activity of HERV LTRs (long terminal repeats) in model organisms such as mice, rats, zebrafish, and invertebrate models of worms and flies. Finally, we discuss several molecular and cellular pathways involving various transcription factors and receptors, through which HERVs affect downstream cellular and physiological events such as epigenetic modifications, calcium influx, protein phosphorylation, and cytokine release. Understanding how HERVs participate in various physiological and pathological processes will help develop a strategy to generate effective therapeutic approaches targeting HERVs.

The role of endogenous retroviruses-K in human cancer

It is known that human endogenous retroviruses (HERVs) constitute almost 8% of the human genome. Although the expression of HERVs from the human genome is tightly regulated, different exogenous and endogenous factors could trigger HERV activation. Aberrant expression of different HERVs may potentially cause a variety of diseases such as neurological and autoimmune diseases as well as cancer. It is suggested that HERV-K can induce cancer through different mechanisms that are discussed. The interplay between some tumor viruses and HERV-K seems to be a key player in progression of viral-associated cancers because elevated levels of Rec and Np9 proteins are observed in several cancers. The frequent over expression of HERV proteins and some specific antibodies in cancer cells could be considered as suitable prognostic and therapeutic biomarkers in diagnosis and treatment of cancers. The expression of HERV proteins in cancers and development of immune responses against them may also be used as targets for cancer immunotherapy. Further studies are warranted to evaluate the role of HERVs in cancer formation and use of different HERV proteins in developing new diagnostic and therapeutic approaches for cancer treatments.

The contribution of HERV-E clone 4-1 and other HERV-E members to the pathogenesis of rheumatic autoimmune diseases

Human endogenous retroviruses (HERV)-E consist of a family of more than 1300 elements, stably integrated in the human genome. Some of them are full-length proviruses able to synthesize the viral proteins gag, pol and env. The reactivation of HERV-E elements has been associated to placentation, cancer and autoimmunity. In this narrative review, we aimed to report the status of the art concerning the involvement of HERV-E in rheumatic autoimmune diseases. Following a research on PubMed database, a total of 87 articles were selected. The highest amount of evidence derives from studies on systemic lupus erythematosus (SLE), whereas a few to no data are available on other immune-mediated diseases. In SLE, the hyper-expression of HERV-E clone 4-1 in peripheral blood mononuclear cells or differentiated lymphocytes has been associated with disease activity and autoantibody production. It is likely that HERV-E take part to the pathogenesis of rheumatic autoimmune diseases but additional research is needed.

Endogenous Retroviruses Activity as a Molecular Signature of Neurodevelopmental Disorders

Human endogenous retroviruses (HERVs) are genetic elements resulting from relics of ancestral infection of germline cells, now recognized as cofactors in the etiology of several complex diseases. Here we present a review of findings supporting the role of the abnormal HERVs activity in neurodevelopmental disorders. The derailment of brain development underlies numerous neuropsychiatric conditions, likely starting during prenatal life and carrying on during subsequent maturation of the brain. Autism spectrum disorders, attention deficit hyperactivity disorders, and schizophrenia are neurodevelopmental disorders that arise clinically during early childhood or adolescence, currently attributed to the interplay among genetic vulnerability, environmental risk factors, and maternal immune activation. The role of HERVs in human embryogenesis, their intrinsic responsiveness to external stimuli, and the interaction with the immune system support the involvement of HERVs in the derailed neurodevelopmental process. Although definitive proofs that HERVs are involved in neurobehavioral alterations are still lacking, both preclinical models and human studies indicate that the abnormal expression of ERVs could represent a neurodevelopmental disorders-associated biological trait in affected individuals and their parents.

Expressional activation and functional roles of human endogenous retroviruses in cancers

Human endogenous retroviruses (HERVs) are widely believed to be remnants of ancestral germ line infections by exogenous retroviruses. Although HERVs are deemed as “nonfunctional DNAs” due to loss of most of their viral protein coding capacity during evolution as part of the human genome, cumulative evidences are showing the expressional activation and potential roles of HERVs in diseases especially cancers. Work by other researchers and us has observed the dysregulation of HERVs in cancers, identified new HERV‐related genes, and revealed their potential importance in cancer development. Here, we summarized the current knowledge on the mechanisms of the expressional activation and functional roles of HERVs, with a focus on the H family HERV (HERV‐H), in carcinogenesis. HERV expression is regulated by external chemical or physical substances and exogenous virus infection, as well as host factors such as epigenetic DNA methylation, transcription factors, cytokines, and small RNAs. Diverse roles of HERVs have been proposed by acting in the forms of noncoding RNAs, proteins, and transcriptional regulators during carcinogenesis. However, much remains to be learnt about the contributions of HERVs to human cancers. More investigation is warranted to elucidate the functions of these “fossil remnants” yet important viral DNAs in the human genome.

Human endogenous retroviruses role in cancer cell stemness

Cancer incidence and mortality, metastasis, drug resistance and recurrence are still the critical issues of oncological diseases. In this scenario, increasing scientific evidences demonstrate that the activation of human endogenous retroviruses (HERVs) is involved in the aggressiveness of tumors such as melanoma, breast, germ cell, renal, ovarian, liver and haematological cancers. In their dynamic regulation, HERVs have also proved to be important determinants of pluripotency in human embryonic stem cells (ESC) and of the reprogramming process of induced pluripotent stem cells (iPSCs). In many types of tumors, essential characteristics of aggressiveness have been associated with the achievement of stemness features, often accompanied with the identification of defined subpopulations, termed cancer stem cells (CSCs), which possess stem cell-like properties and sustain tumorigenesis. Indeed, CSCs show high self-renewal capacity with a peculiar potential in tumor initiation, progression, metastasis, heterogeneity, recurrence, radiotherapy and drug resistance. However, HERVs role in CSCs biology is still not fully elucidated. In this regard, CD133 is a widely recognized marker of CSCs, and our group demonstrated, for the first time, the requirement of HERV-K activation to expand and maintain a CD133+ melanoma cell subpopulation with stemness features in response to microenvironmental modifications. The review will discuss HERVs expression as cancer hallmark, with particular focus on their role in the regulation of cancer stemness features and the potential involvement as targets for therapy.

Endogenous Retrovirus 3 - History, Physiology, and Pathology

Endogenous viral elements (EVE) seem to be present in all eukaryotic genomes. The composition of EVE varies between different species. The endogenous retrovirus 3 (ERV3) is one of these elements that is present only in humans and other Catarrhini. Conservation of ERV3 in most of the investigated Catarrhini and the expression pattern in normal tissues suggest a putative physiological role of ERV3. On the other hand, ERV3 has been implicated in the pathogenesis of auto-immunity and cancer. In the present review we summarize knowledge about this interesting EVE. We propose the model that expression of ERV3 (and probably other EVE loci) under pathological conditions might be part of a metazoan SOS response.

Regulation of the human endogenous retrovirus K (HML-2) transcriptome by the HIV-1 Tat protein

Approximately 8% of the human genome is made up of endogenous retroviral sequences. As the HIV-1 Tat protein activates the overall expression of the human endogenous retrovirus type K (HERV-K) (HML-2), we used next-generation sequencing to determine which of the 91 currently annotated HERV-K (HML-2) proviruses are regulated by Tat. Transcriptome sequencing of total RNA isolated from Tat- and vehicle-treated peripheral blood lymphocytes from a healthy donor showed that Tat significantly activates expression of 26 unique HERV-K (HML-2) proviruses, silences 12, and does not significantly alter the expression of the remaining proviruses. Quantitative reverse transcription-PCR validation of the sequencing data was performed on Tat-treated PBLs of seven donors using provirus-specific primers and corroborated the results with a substantial degree of quantitative similarity.

IMPORTANCE

The expression of HERV-K (HML-2) is tightly regulated but becomes markedly increased following infection with HIV-1, in part due to the HIV-1 Tat protein. The findings reported here demonstrate the complexity of the genome-wide regulation of HERV-K (HML-2) expression by Tat. This work also demonstrates that although HERV-K (HML-2) proviruses in the human genome are highly similar in terms of DNA sequence, modulation of the expression of specific proviruses in a given biological situation can be ascertained using next-generation sequencing and bioinformatics analysis.

Microarray analysis reveals global modulation of endogenous retroelement transcription by microbes

BACKGROUND

A substantial proportion of both the mouse and human genomes comprise of endogenous retroelements (REs), which include endogenous retroviruses. Over evolutionary time, REs accumulate inactivating mutations or deletions and thus lose the ability to replicate. Additionally, REs can be transcriptionally repressed by dedicated mechanisms of the host. Nevertheless, many of them still possess and express intact open reading frames, and their transcriptional activity has been associated with many physiological and pathological processes of the host. However, this association remains tenuous due to incomplete understanding of the mechanism by which RE transcription is regulated. Here, we use a bioinformatics tool to examine RE transcriptional activity, measured by microarrays, in murine and human immune cells responding to microbial stimulation.

RESULTS

Immune cell activation by microbial signals in vitro caused extensive changes in the transcription not only of the host genes involved in the immune response, but also of numerous REs. Modulated REs were frequently found near or embedded within similarly-modulated host genes. Focusing on probes reporting single-integration, intergenic REs, revealed extensive transcriptional responsiveness of these elements to microbial signals. Microbial stimulation modulated RE expression in a cell-intrinsic manner. In line with these results, the transcriptional activity of numerous REs followed characteristics in different tissues according to exposure to environmental microbes and was further heavily altered during viral infection or imbalances with intestinal microbiota, both in mice and humans.

CONCLUSIONS

Together, these results highlight the utility of improved methodologies in assessing RE transcription profiles in both archived and new microarray data sets. More importantly, application of this methodology suggests that immune activation, as a result of infection with pathogens or dysbiosis with commensal microbes, causes global modulation of RE transcription. RE responsiveness to external stimuli should, therefore, be considered in any association between RE transcription and disease.

Expression of human endogenous retrovirus-w including syncytin-1 in cutaneous T-cell lymphoma

The pathomechanism of mycosis fungoides (MF), the most common type of primary cutaneous T-cell lymphomas (CTCLs) and a malignancy of non-recirculating, skin-resident T-cells, is unknown albeit underlying viral infections have been sought for. Human endogenous retroviruses (HERVs) are ancient retroviral sequences in the human genome and their transcription is often deregulated in cancers. We explored the transcriptional activity of HERV sequences in a total of 34 samples comprising MF and psoriasis skin lesions, as well as corresponding non-malignant skin using a retrovirus-specific microarray and quantitative RT-PCR. To identify active HERV-W loci, we cloned the HERV-W specific RT-PCR products, sequenced the cDNA clones and assigned the sequences to HERV-W loci. Finally, we used immunohistochemistry on MF patient and non-malignant inflammatory skin samples to confirm specific HERV-encoded protein expression. Firstly, a distinct, skin-specific transcription profile consisting of five constitutively active HERV groups was established. Although individual variability was common, HERV-W showed significantly increased transcription in MF lesions compared to clinically intact skin from the same patient. Predominantly transcribed HERV-W loci were found to be located in chromosomes 6q21 and 7q21.2, chromosomal regions typically altered in CTCL. Surprisingly, we also found the expression of 7q21.2/ERVWE1-encoded Syncytin-1 (Env) protein in MF biopsies and expression of Syncytin-1 was seen in malignant lymphocytes, especially in the epidermotropic ones, in 15 of 30 cases studied. Most importantly, no Syncytin-1 expression was detected in inflammatory dermatosis (Lichen ruber planus) with skin-homing, non-malignant T lymphocytes. The expression of ERVWE1 mRNA was further confirmed in 3/7 MF lesions analyzed. Our observations strengthen the association between activated HERVs and cancer. The study offers a new perspective into the pathogenesis of CTCL since we demonstrate that differences in HERV-W transcription levels between lesional MF and non-malignant skin are significant, and that ERVWE1-encoded Syncytin-1 is expressed in MF lymphoma cells.

The role of human endogenous retroviral long terminal repeat sequences in human cancer (Review)

Human endogenous retrovirus (HERV) and solitary long terminal repeats (LTRs) constitute 8% of the human genome. Although most HERV genes are partially deleted and not intact, HERV LTRs comprise features including promoters, enhancers, selective splicer sites and polyadenylation sites in order to regulate the expression of neighboring genes. Owing to the genetic instability of LTRs, their wide distributions along human chromosomes are not only non-random, but are also correlated with gene density. Considerable evidence indicates that HERV LTRs regulate the expression of their adjacent viral and cellular genes in placental development and tumorigenesis. However, the regulatory mechanism of HERV LTRs on the expression of its neighboring cancer-associated genes in human cancers remains to be elucidated. Insertional mutagenesis, recombination and polymorphism are three principal factors of LTR that contribute to its genetic instability. Moreover, genetic instability, hypomethylation, transactivation and the antisense transcript of LTRs enhance the activity of LTRs and regulate the expression of their adjacent genes in human cancers. Therefore, in the present review, we examined the mechanism of HERV LTRs in tumorigenesis in combination with the structure and function of LTRs.

Human endogenous retroviruses and cancer prevention: evidence and prospects

Background

Cancer is a significant and growing problem worldwide. While this increase may, in part, be attributed to increasing longevity, improved case notifications and risk-enhancing lifestyle (such as smoking, diet and obesity), hygiene-related factors resulting in immuno-regulatory failure may also play a major role and call for a revision of vaccination strategies to protect against a range of cancers in addition to infections.

Discussion

Human endogenous retroviruses (HERVs) are a significant component of a wider family of retroelements that constitutes part of the human genome. They were originated by the integration of exogenous retroviruses into the human genome millions of years ago. HERVs are estimated to comprise about 8% of human DNA and are ubiquitous in somatic and germinal tissues.

Physiologic and pathologic processes are influenced by some biologically active HERV families. HERV antigens are only expressed at low levels by the host, but in circumstances of inappropriate control their genes may initiate or maintain pathological processes. Although the precise mechanism leading to abnormal HERVs gene expression has yet to be clearly elucidated, environmental factors seem to be involved by influencing the human immune system.

HERV-K expression has been detected in different types of tumors.

Among the various human endogenous retroviral families, the K series was the latest acquired by the human species. Probably because of its relatively recent origin, the HERV-K is the most complete and biologically active family.

The abnormal expression of HERV-K seemingly triggers pathological processes leading to melanoma onset, but also contributes to the morphological and functional cellular modifications implicated in melanoma maintenance and progression.

The HERV-K-MEL antigen is encoded by a pseudo-gene incorporated in the HERV-K env-gene. HERV-K-MEL is significantly expressed in the majority of dysplastic and normal naevi, as well as other tumors like sarcoma, lymphoma, bladder and breast cancer. An amino acid sequence similar to HERV-K-MEL, recognized to cause a significant protective effect against melanoma, is shared by the antigenic determinants expressed by some vaccines such as BCG, vaccinia virus and the yellow fever virus.

HERV-K are also reactivated in the majority of human breast cancers. Monoclonal and single-chain antibodies against the HERV-K Env protein recently proved capable of blocking the proliferation of human breast cancer cells in vitro, inhibiting tumor growth in mice bearing xenograft tumors.

Summary

A recent epidemiological study provided provisional evidence of how melanoma risk could possibly be reduced if the yellow fever virus vaccine (YFV) were received at least 10 years before, possibly preventing tumor initiation rather than culling melanoma cells already compromised. Further research is recommended to confirm the temporal pattern of this protection and eliminate/attenuate the potential role of relevant confounders as socio-economic status and other vaccinations.

It appears also appropriate to examine the potential protective effect of YFV against other malignancies expressing high levels of HERV-K antigens, namely breast cancer, sarcoma, lymphoma and bladder cancer.

Tumor immune-therapy, as described for the monoclonal antibodies against breast cancer, is indeed considered more complex and less advantageous than immune-prevention. Cellular immunity possibly triggered by vaccines as for YFV might also be involved in anti-cancer response, in addition to humoral immunity.

Anti-inflammatory and vasoprotective activity of a retroviral-derived peptide, homologous to human endogenous retroviruses: endothelial cell effects

Malignant and inflammatory tissues sometimes express endogenous retroviruses or their proteins. A highly-conserved sequence from retroviral transmembrane (TM) proteins, termed the “immunosuppressive domain (ID)”, is associated with inhibition of immune and inflammatory functions. An octadecapeptide (MN10021) from the ID of retroviral TM protein p15E inhibits in vitro release of pro-inflammatory cytokines and increases synthesis of anti-inflammatory IL-10. We sought to determine if MN10021 has significant in vivo effects. MN10021, prepared by solid-phase synthesis, was dimerized through a naturally-occurring, carboxy-terminal cysteine. In vivo anti-inflammatory activity was determined using a murine model of sodium periodate (NaIO₄)-induced peritonitis. In vivo vasoprotective effects were determined using: (1) a carrageenan-induced model of disseminated intravascular coagulation (DIC) in mice; (2) a reverse passive Arthus model in guinea pigs; and (3) vasoregulatory effects in spontaneously hypertensive rats (SHR). In vitro studies included: (1) binding/uptake of MN10021 using human monocytes, cultured fibroblasts, and vascular endothelial cells (VEC); (2) gene expression by RT-PCR of MN10021-treated VEC; and (3) apoptosis of MN10021-treated VEC exposed to staurosporine or TNF-α. One-tenth nmol MN10021 inhibits 50 percent of the inflammatory response in the mouse peritonitis model. Furthermore, 73 nmol MN10021 completely protects mice in a lethal model of carrageenan-induced DIC and inhibits vascular leak in both the mouse DIC model and a guinea pig reverse passive Arthus reaction. MN10021 binds to and is taken up in a specific manner by both human monocytes and VEC but not by cultured human fibroblasts. Surprisingly, orally-administered MN10021 lowers blood pressure in SHR rats by 10–15% within 1 h suggesting a direct or indirect effect on the vascular endothelium. MN10021 and derived octapeptides induce iNOS (inducible nitric oxide synthase) mRNA in VEC and nitrate in VEC cell culture supernatants and protect VEC from induced apoptosis or necrosis. However, pretreatment of VEC with nitro-L-arginine methyl ester (L-NAME), while inhibiting the release of nitrate, does not block the anti-apoptotic effect of MN10021 and derived octapeptides suggesting that their potent vasoprotective and anti-inflammatory activity is not nitric oxide dependent.

Radiation-induced human endogenous retrovirus (HERV)-R env gene expression by epigenetic control

It is commonly accepted that ionizing radiation induces genomic instability by changes in genomic structure, epigenetic regulation and gene expression. Human endogenous retroviruses (HERV)-R also are often differentially expressed between normal and disease tissues under unstable genomic conditions and are implicated in the pathogenesis of several human diseases. To understand the influence of ionizing radiation on HERV-R expression, we performed quantitative reverse transcription-polymerase chain reaction (RT-PCR) analyses using γ-irradiated normal human cells. Compared to nonirradiated cells, HERV-R expression was up-regulated in γ-irradiated cells. The regulatory mechanism of HERV-R expression in irradiated cells was investigated by methylation analyses of HERV-R 5'LTRs and treatment with garcinol. These data indicated that the up-regulated transcription of HERV-R may be regulated by radiation-induced epigenetic changes induced by histone modification, and thus could be of great importance for understanding the relationship between radiation-induced biological effects and transposable elements.

Expression of human endogenous retrovirus type K (HML-2) is activated by the Tat protein of HIV-1

Human endogenous retroviruses (HERVs) make up 8% of the human genome. The expression of HERV-K (HML-2), the family of HERVs that most recently entered the genome, is tightly regulated but becomes markedly increased after infection with HIV-1. To better understand the mechanisms involved in this activation, we explored the role of the HIV-1 Tat protein in inducing the expression of these endogenous retroviral genes. Administration of recombinant HIV-1 Tat protein caused a 13-fold increase in HERV-K (HML-2) gag RNA transcripts in Jurkat T cells and a 10-fold increase in primary lymphocytes, and the expression of the HERV-K (HML-2) rec and np9 oncogenes was also markedly increased. This activation was seen especially in lymphocytes and monocytic cells, the natural hosts for HIV-1 infection. Luciferase reporter gene assays demonstrated that the effect of Tat on HERV-K (HML-2) expression occurred at the level of the transcriptional promoter. The transcription factors NF-κB and NF-AT contribute to the Tat-induced activation of the promoter, as shown by chromatin immunoprecipitation assays, mutational analysis of the HERV-K (HML-2) long terminal repeat, and treatments with agents that inhibit NF-κB or NF-AT activation. These studies demonstrate that HIV-1 Tat plays an important role in activating expression of HERV-K (HML-2) in the setting of HIV-1 infection.

Benefits of random-priming: exhaustive survey of a cDNA library from lung tissue of a SARS patient

The severe acute respiratory syndrome (SARS) leads to severe injury in the lungs with multiple factors, though the pathogenesis is still largely unclear. This paper describes the particular analyses of the transcriptome of human lung tissue that was infected by SARS‐associated coronavirus (SARS‐CoV). Random primers were used to produce ESTs from total RNA samples of the lung tissue. The result showed a high diversity of the transcripts, covering much of the human genome, including loci which do not contain protein coding sequences. 10,801 ESTs were generated and assembled into 267 contigs plus 7,659 singletons. Sequences matching to SARS‐CoV RNAs and other pneumonia‐related microbes were found. The transcripts were well classified by functional annotation. Among the 7,872 assembled sequences that were identified as from human genome, 578 non‐coding genes were revealed by BLAST search. The transcripts were mapped to the human genome with the restriction of identity = 100%, which found a candidate pool of 448 novel transcriptional loci where EST transcriptional signal was never found before. Among these, 13 loci were never reported to be transcriptional by other detection methods such as gene chips, tiling arrays, and paired‐end ditags (PETs). The result showed that random‐priming cDNA library is valid for the investigation of transcript diversity in the virus‐infected tissue. The EST data could be a useful supplemental source for SARS pathology researches. J. Med. Virol. 83:574–586, 2011. © 2011 Wiley‐Liss, Inc.

Endogenous retroviral pathogenesis in lupus

PURPOSE OF REVIEW

Genetic and environmental factors influence the development of systemic lupus erythematosus (SLE). Endogenous retroviruses (ERVs) are proposed as a molecular link between the human genome and environmental factors, such as viruses, in lupus pathogenesis.

RECENT FINDINGS

The HRES-1 human ERV encodes a 28-kD nuclear autoantigen and a 24-kD small GTP-ase, termed HRES-1/Rab4. HRES-1/p28 is a target of cross-reactive antiviral antibodies, whereas HRES-1/Rab4 regulates the surface expression of CD4 via endosome recycling. The tat gene of HIV-1 induces the expression of HRES-1/Rab4, which in turn downregulates expression of CD4 and susceptibility to reinfection by HIV-1. HRES-1/Rab4 is overexpressed in lupus T cells where it correlates with increased recycling of CD4 and CD3 and contributes to downregulation of CD3/TCRzeta via lysosomal degradation. Chilblain lupus has been linked to the deficiency of 3'-5' repair exonuclease Trex1 that metabolizes DNA reverse-transcribed from ERV. Trex1 deficiency or blocked integration of ERV-encoded DNA also promotes lupus in murine models.

SUMMARY

ERV proteins may trigger lupus through structural and functional molecular mimicry, whereas the accumulation of ERV-derived nucleic acids stimulates interferon and anti-DNA antibody production in SLE.

Human endogenous retroviruses and multiple sclerosis: innocent bystanders or disease determinants?

Human endogenous retroviruses (HERVs) constitute 5–8% of human genomic DNA and are replication incompetent despite expression of individual HERV genes from different chromosomal loci depending on the specific tissue. Several HERV genes have been detected as transcripts and proteins in the central nervous system, frequently in the context of neuroinflammation. The HERV-W family has received substantial attention in large part because of associations with diverse syndromes including multiple sclerosis (MS) and several psychiatric disorders. A HERV-W-related retroelement, multiple sclerosis retrovirus (MSRV), has been reported in MS patients to be both a biomarker as well as an effector of aberrant immune responses. HERV-H and HERV-K have also been implicated in MS and other neurological diseases but await delineation of their contributions to disease. The HERV-W envelope-encoded glycosylated protein, syncytin-1, is encoded by chromosome 7q21 and exhibits increased glial expression within MS lesions. Overexpression of syncytin-1 in glia induces endoplasmic reticulum stress leading to neuroinflammation and the induction of free radicals, which damage proximate cells. Syncytin-1's receptor, ASCT1 is a neutral amino acid transporter expressed on glia and is suppressed in white matter of MS patients. Of interest, antioxidants ameliorate syncytin-1's neuropathogenic effects raising the possibility of using these agents as therapeutics for neuroinflammatory diseases. Given the multiple insertion sites of HERV genes as complete and incomplete open reading frames, together with their differing capacity to be expressed and the complexities of individual HERVs as both disease markers and bioactive effectors, HERV biology is a compelling area for understanding neuropathogenic mechanisms and developing new therapeutic strategies.

Infection: a hypothesis on active susceptibility and species immunity with implications for AIDS prevention

There is no fundamental difference in contagiousness or pathogenicity between the normal and pathogenic microfloras: both are contagious, and both may either cause illness or persist in the body of a healthy carrier. The contagiousness of the normal microflora is determined by its positive function in the host. In addition to the normal microflora, endogenous retrovirus genes are also useful for a macroorganism: they have been found to be integral elements of many animal and plant genomes and participate in vital functions, such as genome activity control, antiviral defense, and formation of the placenta; dysfunction of some endogenous retrovirus genes causes pathology. Components of bacterial cells cause protective effects with respect to noninfectious somatic diseases. Therefore, it is reasonable to assume that natural susceptibility to both "normal" and "pathogenic" microfloras results from vital necessity for a macroorganism to interact with them. The necessity to interact with specific microorganisms and, hence, susceptibility to them is the cause of their infectivity. In this connection, studies on the positive functions of specific "pathogenic" microflora in a macroorganism with the use of SPF animals would be of interest. Even more interesting would be experiments with transfer of specific microbial genes into the genomes of susceptible species, which may help to understand the causes and mechanisms of susceptibility/insusceptibility as a basis of species immunity and develop fundamentally new and more natural methods for preventing and treating infectious diseases.

Human endogenous retrovirus-R Env glycoprotein as possible autoantigen in autoimmune disease

It has long been discussed whether endogenous retroviruses (ERVs) are involved in the pathogenesis of autoimmune diseases. Among various human endogenous retroviruses (HERVs), we have focused on HERV-R. To investigate the biological roles of HERV-R, we earlier established transgenic rats carrying the full sequence of the viral genome. In these HERV-R rats, however, no disease occurred. Another trigger that induces autoimmunity may be essential for the recognition of HERV-R products by the immune system. Thus, in this study, we mated HERV-R rats with env-pX rats (transgenic rats carrying the env-pX gene of human T cell leukemia virus type I) that develop autoimmune diseases, and generated double transgenic (DTG) rats. In DTG rats, autoimmune diseases occurred similarly in env-pX rats. Interestingly, deposition of rat IgM but not IgG was observed on the glomerular endothelial cells. Such IgM deposition was never seen in the parental HERV-R or env-pX rats. We considered that in situ formation of immune complexes consisted of the HERV-R env glycoprotein and anti-HERV-R env IgM antibodies (Abs) in DTG rats, according to the following evidence: (1) No dense deposit, representing deposition of circulating immune complexes, was seen on glomerular endothelial cells. (2) IgM Abs reactive with HERV-R env glycoprotein were generated in the serum. (3) HERV-R env glycoprotein was expressed in the kidney, specifically on glomerular endothelial cells. (4) IgM deposition was partly colocalized with the HERV-R env glycoprotein on the glomeruli. These findings strongly suggest that the HERV-R env glycoprotein is recognized as an autoantigen in the host with autoimmune diseases.

The activation of human endogenous retrovirus K (HERV-K) is implicated in melanoma cell malignant transformation

Melanoma development is a multi-step process arising from a series of genetic and epigenetic events. Although the sequential stages involved in progression from melanocytes to malignant melanoma are clearly defined, our current understanding of the mechanisms leading to melanoma onset is still incomplete. Growing evidence show that the activation of endogenous retroviral sequences might be involved in transformation of melanocytes as well as in the increased ability of melanoma cells to escape immune surveillance. Here we show that human melanoma cells in vitro undergo a transition from adherent to a more malignant, non-adherent phenotype when exposed to stress conditions. Melanoma-derived non-adherent cells are characterized by an increased proliferative potential and a decreased expression of both HLA class I molecules and Melan-A/MART-1 antigen, similarly to highly malignant cells. These phenotypic and functional modifications are accompanied by the activation of human endogenous retrovirus K expression (HERV-K) and massive production of viral-like particles. Down-regulation of HERV-K expression by RNA interference prevents the transition from the adherent to the non-adherent growth phenotype in low serum. These results implicate HERV-K in at least some critical steps of melanoma progression.

Molecular mimicry and immunomodulation by the HRES-1 endogenous retrovirus in SLE

Genetic and environmental factors are believed to influence development of systemic lupus erythematosus (SLE). Endogenous retroviruses (ERV) correspond to the integrated proviral form of infectious retroviruses, which are trapped within the genome due to mutations. ERV represent a key molecular link between the host genome and infectious viral particles. ERV-encoded proteins are recognized by antiviral immune responses and become targets of autoreactivity. Alternatively, ERV protein may influence cellular processes and the life cycle of infectious viruses. As examples, the HRES-1 human ERV encodes a 28-kDa nuclear autoantigen and a 24-kDa small GTP-ase, termed HRES-1/Rab4. HRES-1/p28 is a nuclear autoantigen recognized by cross-reactive antiviral antibodies, while HRES-1/Rab4 regulates surface expression of CD4 and the transferrin receptor (TFR) through endosome recycling. Expression of HRES-1/Rab4 is induced by the tat gene of HIV-1, which in turn down-regulates expression of CD4 and susceptibility to re-infection by HIV-1. CD4 and the TFR play essential roles in formation of the immunological synapse (IS) during normal T-cell activation by a cognate MHC class II peptide complex. The key intracellular transducer of T-cell activation, Lck, is brought to the IS via binding to CD4. T-cell receptorzeta (TCRzeta) chain binds to the TFR. Abnormal T-cell responses in SLE have been associated with reduced lck and TCRzeta chain levels. HRES-1 is centrally located on chromosome 1 at q42 relative to lupus-linked microsatellite markers and polymorphic HRES-1 alleles have been linked to the development of SLE. 1q42 is one of the three most common fragile sites in the human genome, and is inducible by DNA demethylation, a known mechanism of retroviral gene activation. Molecular mimicry and immunomodulation by a ERV, such as HRES-1, may contribute to self-reactivity and abnormal T and B-cell functions in SLE.

Endogenous retroviruses: suspects in the disease world

Endogenous retroviruses (ERVs) integrated into human genome after cross-species infectious events millions of years ago. Few of the ERVs retain the basic structure of the integrated proviral form of infectious retroviruses. Human endogenous retroviruses (HERVs) represent a key molecular link between the host genome and infectious viral particles. They constitute a large reservoir of viral genes that could be activated by various factors such as mutations or carcinogenic chemical exposures and so forth. Endogenous retroviruses are transmitted genetically in a Mendelian fashion through the germline as proviral DNA. Expression pattern of HERVs can influence the outcome of their presence in many forms, which can be either beneficial or detrimental to the host. ERVs have been reported to play a role in both human physiology and human pathology. Along with their expression in many disease conditions, they have also been reported to be expressed on normal peripheral blood lymphocytes, salivary glands and keratinocytes.

The human endogenous retrovirus envelope glycoprotein, syncytin-1, regulates neuroinflammation and its receptor expression in multiple sclerosis: a role for endoplasmic reticulum chaperones in astrocytes

Retroviral envelopes are pathogenic glycoproteins which cause neuroinflammation, neurodegeneration, and endoplasmic reticulum stress responses. The human endogenous retrovirus (HERV-W) envelope protein, Syncytin-1, is highly expressed in CNS glia of individuals with multiple sclerosis (MS). In this study, we investigated the mechanisms by which Syncytin-1 mediated neuroimmune activation and oligodendrocytes damage. In brain tissue from individuals with MS, ASCT1, a receptor for Syncytin-1 and a neutral amino acid transporter, was selectively suppressed in astrocytes (p < 0.05). Syncytin-1 induced the expression of the endoplasmic reticulum stress sensor, old astrocyte specifically induced substance (OASIS), in cultured astrocytes, similar to findings in MS brains. Overexpression of OASIS in astrocytes increased inducible NO synthase expression but concurrently down-regulated ASCT1 (p < 0.01). Treatment of astrocytes with a NO donor enhanced expression of early growth response 1, with an ensuing reduction in ASCT1 expression (p < 0.05). Small-interfering RNA molecules targeting Syncytin-1 selectively down-regulated its expression, preventing the suppression of ASCT1 and the release of oligodendrocyte cytotoxins by astrocytes. A Syncytin-1-transgenic mouse expressing Syncytin-1 under the glial fibrillary acidic protein promoter demonstrated neuroinflammation, ASCT1 suppression, and diminished levels of myelin proteins in the corpus callosum, consistent with observations in CNS tissues from MS patients together with neurobehavioral abnormalities compared with wild-type littermates (p < 0.05). Thus, Syncytin-1 initiated an OASIS-mediated suppression of ASCT1 in astrocytes through the induction of inducible NO synthase with ensuing oligodendrocyte injury. These studies provide new insights into the role of HERV-mediated neuroinflammation and its contribution to an autoimmune disease.

Expression of multiple human endogenous retrovirus surface envelope proteins in ovarian cancer

Individual classes of human endogenous retrovirus (HERV) genes and proteins are expressed in cancer, but expression of more than one type of HERV is rare. We report here the expression of multiple HERV genes and proteins in ovarian cell lines and tissues. Expression of HERV-K env mRNA was greater in ovarian epithelial tumors than in normal ovarian tissues (N = 254). The expression of this protein on the surface and in the cytoplasm of ovarian cancer cells was confirmed using anti-HERV-K specific antibody by flow cytometric analysis. The frequency of expression of HERV-K env protein in multitissue microarrays (N = 641) was determined by immunohistochemistry and a significant correlation with tumor histotype was found. A significantly increased expression of HERV-K was observed in tumors with low malignant potential and low grade, relative to expression in normal ovarian tissues. The increase in expression of HERV-K env protein took place in a stepwise fashion in serous papillary adenocarcinoma. Interestingly, we found that other classes of HERV env mRNAs, including ERV3 and HERV-E, are expressed in the same ovarian cancer tissues that expressed HERV-K. Furthermore, anti-HERV antibodies including anti-ERV3 (30%), anti-HERV-E (40%) and anti-HERV-K (55%) were detected in patients with ovarian cancer, but not in normal female controls. HERV env proteins are frequently transcribed and translated in ovarian epithelial tumors, and multiple HERV families are detectable in ovarian cancer. HERV env proteins, and especially those expressed on the cell surface, may serve as novel tumor targets for detection, diagnosis and immunotherapy of ovarian cancer.

Quantitative analysis of human endogenous retrovirus-W env in neuroinflammatory diseases

Although human endogenous retroviruses (HERVs) constitute 8% of the human genome, their role(s) in health and disease remain uncertain. Nonetheless, increased HERV gene activity has been reported in neuroinflammatory diseases such as multiple sclerosis (MS). The human endogenous retrovirus (HERV)-W7q envelope gene encodes a glycosylated envelope protein, syncytin-1, which is expressed in many tissues. Analysis of HERV envelopes (env) revealed a selectively increased abundance of syncytin-1 encoding RNA in brains from patients with MS (p<0.01) relative to non-MS patients. However, HERV env expression from blood-derived leukocytes did not differ between groups. A quantitative PCR-based assay for syncytin-1 RNA showed that median viral RNA levels were higher in brains of MS patients (5.0 log10 copies/microg RNA) relative to non-MS patients (4.6 log10 copies/microg RNA) (p<0.05). Median syncytin-1 DNA levels in MS brains (9.8 log10/microg DNA) were higher than non-MS brain tissue (7.9 log10/microg DNA) (p<0.001) without evidence of new integration events. In contrast, there were no differences in syncytin-1 RNA copy numbers between groups in both CSF (non-MS: 5.0 log10/ml versus MS: 3.8 log10/ml) and plasma (non-MS: 5.033 log10/ml versus MS: 2.9 log10/ml). These observations emphasize the selective induction of syncytin-1 in brain tissue of MS patients but also illustrate the complex dynamics of this retroelement in neuroinflammatory processes.

Short communication: expression of human endogenous retrovirus-R gene links to differentiation of squamous cells

To investigate the biological roles of human endogenous retrovirus-R (HERV-R) in vivo, we established transgenic rats carrying the full sequence of the viral genome with control of its own long terminal repeat promoter. The Env protein was expressed on the surface of the epidermis of fetal HERV-R transgenic rats on day 10 of gestation. The epidermal Env expression disappeared by day 18 of gestation. After day 18 of gestation, the Env protein was detected in the prickle layer of the esophageal epithelium of transgenic rats. Interestingly, it was not detected in the basal layer of the epithelium, and the expression in the granular layer was weaker than in the prickle layer. These findings suggest that expression of HERV-R is linked not only to the development but also to the differentiation of squamous cells. Next, we examined alterations in the expression of the HERV-R env gene in cultured human squamous cells after exposure to all-trans retinoic acids (ATRA). The env expression was increased by ATRA in a dose-dependent manner, while the expression of transglutaminase 1 (TGM1), a terminal marker for squamous differentiation, was decreased. TGM1 is expressed in the granular layer of the squamous epithelium, and ATRA suppresses the differentiation of cultured squamous cells. Thus, these in vitro data also suggest that HERV-R expression is regulated by a mechanism closely related to the differentiation of squamous cells. This study is the first to demonstrate the association of HERV-R expression and differentiation of squamous cells.

Factors regulating endogenous retroviral sequences in human and mouse

Endogenous retroviruses (ERVs) are stably integrated in the genome of vertebrates and inherited as Mendelian genes. The several human ERV (HERV) families and related elements represent up to 5-8% of the DNA of our species. ERVs may be involved in the regulation of adjacent genomic loci, especially promoting the tissue-specific expression of genes; some HERVs may have functional roles, e.g., coding for the placental fusogenic protein, syncytin. This paper reviews the growing evidence about factors that may modulate ERVs, including: cell and tissue types (with special attention to placenta and germ cells), processes related to differentiation and aging, cytokines, agents that disrupt cell functions (e.g., DNA hypomethylating agents) and steroids. Special attention is given to HERVs, due to their possible involvement in autoimmunity and reproduction, as well as altered expression in some cancer types; moreover, different HERV families may deserve specific attention, due to remarkable differences concerning, e.g., expression in tissues. A comparison with factors interacting with murine ERV-related sequences indicates that the mouse may be a useful model for studying some patterns of HERV regulation. Overall, the available evidence identifies the diverse, potential interactions with endogenous or exogenous factors as a promising field for investigating the roles of ERVs in physiology and disease.

Retroelements and the human genome: new perspectives on an old relation

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.

Provirus expansion and deregulation of apoptosis-related genes in the spinal cord of a rat model for human T-lymphocyte virus type I-associated myeloneuropathy

Apoptosis of the spinal oligodendrocytes is the main factor linked to the pathogenesis of human T-lymphocyte virus type I (HTLV-I)-induced myeloneuropathy in rats (HAM rat). To clarify apoptosis-related mechanisms, expression of apoptosis-related genes in the spinal cord of these rats was chronologically examined by means of a semiquantitative reverse transcriptase-polymerase chain reaction. Provirus expansion and increment of HTLV-I pX mRNA were evident at 7 months after the induced infection. Tumor necrosis factor-alpha increased gradually soon after pX expression. The expression of a major apoptosis-resistant gene, bcl-2, was markedly suppressed at a period of the provirus expansion and bax was also down-regulated. p53 was consistently expressed at high levels. These findings were never observed in spinal cords of HAM-resistant strains with HTLV-I infection even throughout their entire life. Collective evidence suggests that the local provirus expansion and deregulation of apoptosis-related genes, especially down-regulation of bcl-2, may lead to apoptosis of oligodendrocytes, thus being a major pathogenetic pathway in the HTLV-I-induced myeloneuropathy.

Provirus expansion and deregulation of apoptosis-related genes in the spinal cord of a rat model for human T-lymphocyte virus type I-associated myeloneuropathy

Apoptosis of the spinal oligodendrocytes is the main factor linked to the pathogenesis of human T-lymphocyte virus type I (HTLV-I)-induced myeloneuropathy in rats (HAM rat). To clarify apoptosis-related mechanisms, expression of apoptosis-related genes in the spinal cord of these rats was chronologically examined by means of a semiquantitative reverse transcriptase-polymerase chain reaction. Provirus expansion and increment of HTLV-I pX mRNA were evident at 7 months after the induced infection. Tumor necrosis factor-alpha increased gradually soon after pX expression. The expression of a major apoptosis-resistant gene, bcl-2, was markedly suppressed at a period of the provirus expansion and bax was also down-regulated. p53 was consistently expressed at high levels. These findings were never observed in spinal cords of HAM-resistant strains with HTLV-I infection even throughout their entire life. Collective evidence suggests that the local provirus expansion and deregulation of apoptosis-related genes, especially down-regulation of bcl-2, may lead to apoptosis of oligodendrocytes, thus being a major pathogenetic pathway in the HTLV-I-induced myeloneuropathy.

Detecting the expression of human endogenous retrovirus E envelope transcripts in human prostate adenocarcinoma

BACKGROUND

The expression of human endogenous retrovirus (HERV) mRNA and proteins was associated recently with diseases that include human malignancies. The authors report that, in the current study, transcripts encoding the envelope region of an HERV family, HERV-E, were expressed in human prostate carcinoma.

METHODS

RNA was isolated from various prostate tissues and was tested for the expression of various HERV envelope (env) genes by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, RNA in situ hybridization (ISH), and Northern blot analysis. Variants of HERV that appeared in prostate carcinoma tissues were sequenced, and HERV-E was expressed in prokaryotic and eukaryotic systems.

RESULTS

In the current study, the authors found that the mRNA of the env gene of one particular family of HERVs, HERV-E, was expressed in some prostate carcinoma tissues (38.8% positive; n = 49 specimens) but not in normal prostate tissues using RT-PCR, RNA ISH, and Northern blot assays. The expression of HERV-E transcripts in prostate tumor epithelial cells was confirmed further by ISH using an HERV-E specific antisense probe. Approximately 50% of the cDNA of HERV-E obtained from prostate carcinoma specimens contained no stop codon and expressed proteins in prokaryotic or eukaryotic expression systems. Furthermore, the expression of both HERV-E and ERV3 (another class of HERV) was detected in the same prostate carcinoma tissues.

CONCLUSIONS

The expression and distribution of multiple HERV-E endogenous retroviral elements in prostate carcinoma, but not in normal control specimens, suggests that they may serve as novel tumor markers for the early diagnosis and immunotherapy of patients with prostate carcinoma.

Tissue specific high level expression of a full length human endogenous retrovirus genome transgene, HERV-R, under control of its own promoter in rats

Human endogenous retrovirus-R (HERV-R) is one of a full length HERV with a long open reading frame in the env region. The env transcripts are expressed in various human tissues. To investigate the biological role of HERV-R in vivo, we established two lines of transgenic rats carrying a full sequence of HERV-R under control of its own long terminal repeat (LTR) promoter. One line with tandem integration of multiple copies of the transgene expressed HERV-R mRNA in various organs with different expression levels and relatively higher in Harderian and submandibular salivary glands. In another line, the transgene was integrated as a single copy in a haploid and the expression was detected only in Harderian and submandibular salivary glands. In the placenta, one of the tissues with high levels of the HERV-R expression in humans, the transcription was evident starting the 12th day after gestation. A rabbit antiserum against synthetic peptides corresponding with the HERV-R env gene sequence led to detection of an 85 kDa product as a glycoprotein in the Harderian glands. While no pathological significance was observed in either line, the transgenic rat may prove to be a suitable model for analyzing the role of HERV-R function in vivo.

Role of endogenous retroviruses in autoimmune diseases

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.

Demystified. Human endogenous retroviruses

Human endogenous retroviruses (HERVs) are a family of viruses within our genome with similarities to present day exogenous retroviruses. HERVs have been inherited by successive generations and it is possible that some have conferred biological benefits. However, several HERVs have been implicated in certain cancers and autoimmune diseases. This article demystifies these retroviruses by providing an insight into HERVs, their means of classification, and a synopsis of HERVs implicated in cancer and autoimmunity. Furthermore, the biological roles of HERVs are explored.

Analysis of the expression of endogenous murine leukemia viruses in the brains of senescence-accelerated mice (SAMP8) and the relationship between expression and brain histopathology

Many studies have explored the premature aging of accelerated senescence-prone (SAMP8) mice. However, the cause of premature aging in this strain remains unknown. We analyzed the expression of ecotropic, xenotropic, and polytropic murine leukemia viruses (MuLVs) in the brains of accelerated senescence-resistant (SAMR1) and SAMP8 mice. No ecotropic mRNA was detected in SAMR1 mice, and only Akv-type ecotropic MuLV mRNA was detected in SAMP8 mice. Restriction mapping of the full-length infectious E-MuLV genome from SAMP8 confirmed its identity as Akv. mRNAs corresponding to a prototypical polytropic MuLV and to an unusual xenotropic MuLV were detected at equal levels in SAMP8 and SAMR1 mice, but no infectious virus of either host range type was detected. In order to determine the cellular localization of Akv expression in SAMP8 mice, we used immunohistochemistry and electron microscopy to detect expression of the E-MuLV capsid gag (CAgag) gene in striatum, brainstem, hippocampus, and cerebellum of 12-month-old SAMR1 and SAMP8 mice. The CAgag antigen was seen in the neurons, oligodendroglia, and vascular endothelium of these brain regions of SAMP8 mice, but not in SAMR1 mice. To evaluate the correlation between activation of astrocytes and expression of Akv, we performed double-immunohistochemical staining for both glial fibrillary acidic protein (GFAP) and CAgag in SAMR1 and SAMP8 mice. Strong astrocytic activation and extensive vacuolation were observed around CAgag-positive neurons in SAMP8 mice, whereas in SAMR1 mice neither astrocytosis nor vacuolation were present. CAgag antigen was also localized in astrocytes of the hippocampus region of SAMP8 mice. Electron micrography showed that a number of vacuoles were found in the cytoplasm of MuLV-positive neurons and the extracellular space surrounding these neurons showed lytic changes. These results suggest that endogenous Akv provirus is expressed in neurons, astrocytes, vascular endothelium, and oligodendroglia in the brains of SAMP8 and that this virus could play an important role in the brain aging processes in this mouse strain.

A novel animal model of thymic tumour: development of epithelial thymoma in transgenic rats carrying human T lymphocyte virus type I pX gene

The pX region encodes a major product of human T lymphocyte virus type I (HTLV-I) that has been implicated previously in tumour formation. To investigate the pathogenesis of pX gene in lymphoid tissues, we established a series of novel transgenic rats carrying the pX gene under the control of a rat lymphocyte-specific protein tyrosine kinase (p56lck) proximal promoter. The transgene was constructed with the -269 to +26 region of a rat p56lck proximal promoter and the pX cDNA, and was microinjected into fertilized ova of Fischer 344/jcl female rats. Six transgenic lines from 114 pups were established. Integration and expression of the transgene were detected by polymerase chain reaction (PCR) and Southern hybridization or by reverse transcriptase-PCR, northern hybridization, and immunostaining. Thymic tumours with lethal expansion occurred in 4 of 6 transgenic lines. The tumour consisted of spindle shaped cells. Immunohistochemical and ultra-structural analysis characterized the tumour cells to as epithelial cell type, and in the tumour arose in the medulla. Therefore, the tumour is classified into predominantly epithelial and spindle cell of medullary thymoma (type A of the new World Health Organization classification), as based on the human classification. Tumor occurrence increased in proportion to levels of the pX transcription in the thymus, for each line, and sex distinction was evident regarding rates related to tumour expansion. The transgenic rat model described here is suitable as a model for analysing tumorigenesis in epithelial thymoma occurring in humans.

Monocyte activation and differentiation augment human endogenous retrovirus expression: implications for inflammatory brain diseases

Human endogenous retroviruses (HERVs) have been implicated as causative agents in diseases characterized by inflammation and macrophage activation, such as multiple sclerosis. Because monocyte activation and differentiation influence retroviral transcription and replication, we investigated the contribution of these processes to the expression of four HERV families (HERV-W, HERV-K, HERV-E, and HERV-H) in human monocytes, and autopsied brain tissue from patients with brain diseases associated with increased macrophage activity. Reverse transcriptase-polymerase chain reaction analysis of primary macrophages and U937 monocytoid cells stimulated with phorbol-12-myristate-13-acetate or lipopolysaccharide revealed three- to ninefold increases in HERV-W, HERV-K, and HERV-H RNA levels. In addition, elevated reverse transcriptase activity and HERV RNA were detectable in supernatants from PMA-stimulated U937 cultures, properties that could be attenuated with the inhibitor of monocyte differentiation threonine-lysine-proline. In contrast, stimulation of monocytes decreased or had no effect on HERV-E expression. Compared with controls, HERV-W and HERV-K expression was increased in brain tissue from patients with multiple sclerosis or human immunodeficiency virus infection or AIDS, with concomitant elevated tumor necrosis factor-alpha levels. Similarly, elevated HERV-W levels were detected in patients with Alzheimer's dementia only when tumor necrosis factor-alpha expression was also evident (2 of 6 cases). The detection of several HERVs in inflammatory brain diseases and the capacity to augment HERV expression in monocytes with compounds that influence cellular activity suggest that increased expression of these viruses is a consequence of increased immune activity rather than causative of distinct diseases.