Exogenous Retroviral Infections Research Articles

The Oncoprotein Fra-2 Drives the Activation of Human Endogenous Retrovirus Env Expression in Adult T-Cell Leukemia/Lymphoma (ATLL) Patients.

Human endogenous retroviruses (HERVs) are retroviral sequences integrated into 8% of the human genome resulting from ancient exogenous retroviral infections. Unlike endogenous retroviruses of other mammalian species, HERVs are mostly replication and retro-transposition defective, and their transcription is strictly regulated by epigenetic mechanisms in normal cells. A significant addition to the growing body of research reveals that HERVs' aberrant activation is often associated with offsetting diseases like autoimmunity, neurodegenerative diseases, cancers, and chemoresistance. Adult T-cell leukemia/lymphoma (ATLL) is a very aggressive and chemoresistant leukemia caused by the human T-cell leukemia virus type 1 (HTLV-1). The prognosis of ATLL remains poor despite several new agents being approved in the last few years. In the present study, we compare the expression of HERV genes in CD8+-depleted PBMCs from HTLV-1 asymptomatic carriers and patients with acute ATLL. Herein, we show that HERVs are highly upregulated in acute ATLL. Our results further demonstrate that the oncoprotein Fra-2 binds the LTR region and activates the transcription of several HERV families, including HERV-H and HERV-K families. This raises the exciting possibility that upregulated HERV expression could be a key factor in ATLL development and the observed chemoresistance, potentially leading to new therapeutic strategies and significantly impacting the field of oncology and virology.

Exploring the role of endogenous retroviruses in seasonal reproductive cycles: a case study of the ERV-V envelope gene in mink.

Endogenous retroviruses (ERVs), which originated from exogenous retroviral infections of germline cells millions of years ago and were inherited by subsequent generations as per Mendelian inheritance patterns, predominantly comprise non-protein-coding sequences due to the accumulation of mutations, insertions, deletions, and truncations. Nevertheless, recent studies have revealed that ERVs play a crucial role in diverse biological processes by encoding various proteins. In this study, we successfully identified an ERV envelope (env) gene in a mink species. A phylogenetic tree of mink ERV-V env and reference sequences was constructed using Bayesian methods and maximum-likelihood inference. Phylogenetic analyses indicated a significant degree of sequence conservation and positive selection within the env-surface open reading frame. Additionally, qRT-PCR revealed diverse patterns of mink ERV-V env expression in various tissues. The expression of mink ERV-V env gene in testicular tissue strongly correlated with the seasonal reproductive cycles of minks. Our study suggests that the ERV-V env gene in mink may have been repurposed for host functions.

Human endogenous retroviruses and the inflammatory response: A vicious circle associated with health and illness.

Human Endogenous Retroviruses (HERVs) are derived from ancient exogenous retroviral infections that have infected our ancestors' germline cells, underwent endogenization process, and were passed throughout the generations by retrotransposition and hereditary transmission. HERVs comprise 8% of the human genome and are critical for several physiological activities. Yet, HERVs reactivation is involved in pathological process as cancer and autoimmune diseases. In this review, we summarize the multiple aspects of HERVs' role within the human genome, as well as virological and molecular aspects, and their fusogenic property. We also discuss possibilities of how the HERVs are possibly transactivated and participate in modulating the inflammatory response in health conditions. An update on their role in several autoimmune, inflammatory, and aging-related diseases is also presented.

Transcriptional Regulation of Endogenous Retroviruses and Their Misregulation in Human Diseases

Endogenous retroviruses (ERVs), deriving from exogenous retroviral infections of germ line cells occurred millions of years ago, represent ~8% of human genome. Most ERVs are highly inactivated because of the accumulation of mutations, insertions, deletions, and/or truncations. However, it is becoming increasingly apparent that ERVs influence host biology through genetic and epigenetic mechanisms under particular physiological and pathological conditions, which provide both beneficial and deleterious effects for the host. For instance, certain ERVs expression is essential for human embryonic development. Whereas abnormal activation of ERVs was found to be involved in numbers of human diseases, such as cancer and neurodegenerative diseases. Therefore, understanding the mechanisms of regulation of ERVs would provide insights into the role of ERVs in health and diseases. Here, we provide an overview of mechanisms of transcriptional regulation of ERVs and their dysregulation in human diseases.

Effects of prolonged exposure to ELF-EMF on HERVs expression in human melanoma cells.

The Human endogenous retroviruses (HERVs) are ancient remnants of exogenous retroviral infections. Their abnormal activation is associated with several diseases, such as cancer and autoimmunity. Epigenetic and environmental factors are probably playing essential roles in the expression of these elements. This study aimed to examine the 96-hour effects of ELF-EMF on HERV-H, K, and W expression in human melanoma cells. SK-MEL-37 cells (the human skin malignant melanoma) were continuously exposed to ELF-EMF (50 Hz) at 1.5 and 3 mT intensity for 96 hours. Following mRNA extraction, the expression level of HERV-H, K, and W was assessed by qPCR. According to our results, exposure to ELF-EMF intensities for 96 hours could significantly downregulate HERV-H, K, and W env gene expression (P<0.001). Our obtained data suggest that low intensity and long-term exposure to ELF-EMF may pave using this type of radiation as a novel therapeutic approach by neutralizing the HERVs upregulated expression in melanoma cells.

Implication of human endogenous retrovirus W family envelope in hepatocellular carcinoma promotes MEK/ERK-mediated metastatic invasiveness and doxorubicin resistance

Human endogenous retrovirus (HERVs), originating from exogenous retroviral infections of germ cells millions of years ago, have the potential for human diseases. Syncytin-1, an envelope protein encoded by the HERV W family, participates in the contexts of schizophrenia, multiple sclerosis, diabetes, and several types of cancers. Nevertheless, there is no report on the expression pattern and potential mechanism of Syncytin-1 in HCC. Here we found Syncytin-1 expression was up-regulated in HCC compared to adjacent non-tumorous tissues, especially in advanced HCC. Syncytin-1 was an independent risk factor to predict vascular invasion, metastasis, larger tumor size, and poor prognosis in HCC patients. Further analysis discovered that Syncytin-1 overexpression positively associated with HCC patients with serum HBsAg positive. Functional experiments in vitro and in vivo demonstrated that Syncytin-1 enhanced cell proliferation, metastasis, and tumorigenicity in HCC. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis suggested that the mitogen-activated protein kinase (MEK)/extracellular signal-regulated protein kinase (ERK) pathway was involved in HCC. Our clinical data indicated that the levels of phosphorylation MEK1/2 and ERK1/2 were increased in HCC comparing with adjacent non-tumorous tissues. It showed the linear correlation between Syncytin-1 expression and upregulated MEK1/2 and ERK1/2 phosphorylation levels in HCC. Furthermore, Syncytin-1 activated MEK/ERK pathway in HCC cells. In-depth research showed that the inflammation-activated MEK/ERK pathway was essential in Syncytin-1 promoted hepatocarcinogenesis. Syncytin-1 suppressed doxorubicin-induced apoptosis via MEK/ERK cascade. In conclusion, Syncytin-1 promoted HCC progression and doxorubicin resistance via the inflammation-activated MEK/ERK pathway. Our findings revealed that Syncytin-1 was a potential prognostic biomarker and therapeutic target for HCC.

Human endogenous retroviruses env gene expression and long terminal repeat methylation in colorectal cancer patients

Human endogenous retroviruses (HERV) are remnants of exogenous retroviral infections, representing 8% of the human genome. Their regulation is based on the DNA methylation of promoters, the long terminal repeats (LTRs). Transcripts from HERV have been associated with cancers, but reports concerning HERV expression in colorectal cancer remain sporadic. Sixty-three patients with advanced stages of colorectal cancer were enrolled in this study. The expressions of HERV env gene, and HERV-H, -K, -R and -P LTRs and Alu, LINE-1 methylation levels, were investigated in the tumor, normal adjacent tissues, and, where possible, blood and plasmatic extracellular vesicles (EVs). Associations among HERV env expression, methylation status and clinical characteristics were evaluated. No differences were observed in HERV env gene expression levels among the clinical specimens, while Alu, LINE-1, HERV-H and -K LTRs were demethylated in the tumor compared to the normal adjacent tissues (p < 0.05).The HERV env gene was expressed in the EVs at of 54% (-H), 38% (-K), 31% (-R) patients. Association was not found between HERV env expression and LTR methylation, but significant higher expression of HERV-P and -R env was found in tumor tissues arising from the right colon. Our findings do not demonstrate significant overexpression of the studied HERV in colorectal cancer, but their association with tumor localization and specificity of the changes in DNA methylation of retroelements are shown. HERV sequences were packaged in the EVs and might be transferred from one cell to another.

Endogenous retroviruses of sheep: a model system for understanding physiological adaptation to an evolving ruminant genome

Endogenous retroviruses (ERVs) are present in the genome of all vertebrates and are remnants of ancient exogenous retroviral infections of the host germline transmitted vertically from generation to generation. Sheep betaretroviruses offer a unique model system to study the complex interaction between retroviruses and their host. The sheep genome contains 27 endogenous betaretroviruses (enJSRVs) related to the exogenous and pathogenic Jaagsiekte sheep retrovirus (JSRV), the causative agent of a transmissible lung cancer in sheep. The enJSRVs can protect their host against JSRV infection by blocking early and late steps of the JSRV replication cycle. In the female reproductive tract, enJSRVs are specifically expressed in the uterine luminal and glandular epithelia as well as in the conceptus (embryo and associated extraembryonic membranes) trophectoderm and in utero loss-of-function experiments found the enJSRVs envelope (env) to be essential for conceptus elongation and trophectoderm growth and development. Collectively, available evidence in sheep and other mammals indicate that ERVs coevolved with their hosts for millions of years and were positively selected for biological roles in genome plasticity and evolution, protection of the host against infection of related pathogenic and exogenous retroviruses, and placental development.

Feline Leukemia Virus (FeLV) Disease Outcomes in a Domestic Cat Breeding Colony: Relationship to Endogenous FeLV and Other Chronic Viral Infections.

Exogenous feline leukemia virus (FeLV) is a feline gammaretrovirus that results in a variety of disease outcomes. Endogenous FeLV (enFeLV) is a replication-defective provirus found in species belonging to the Felis genus, which includes the domestic cat (Felis catus). There have been few studies examining interaction between enFeLV genotype and FeLV progression. We examined point-in-time enFeLV and FeLV viral loads, as well as occurrence of FeLV/enFeLV recombinants (FeLV-B), to determine factors relating to clinical disease in a closed breeding colony of cats during a natural infection of FeLV. Coinfections with feline foamy virus (FFV), feline gammaherpesvirus 1 (FcaGHV-1), and feline coronavirus (FCoV) were also documented and analyzed for impact on cat health and FeLV disease. Correlation analysis and structural equation modeling techniques were used to measure interactions among disease parameters. Progressive FeLV disease and FeLV-B presence were associated with higher FeLV proviral and plasma viral loads. Female cats were more likely to have progressive disease and FeLV-B. Conversely, enFeLV copy number was higher in male cats and negatively associated with progressive FeLV disease. Males were more likely to have abortive FeLV disease. FFV proviral load was found to correlate positively with higher FeLV proviral and plasma viral load, detection of FeLV-B, and FCoV status. Male cats were much more likely to be infected with FcaGHV-1 than female cats. This analysis provides insights into the interplay between endogenous and exogenous FeLV during naturally occurring disease and reveals striking variation in the infection patterns among four chronic viral infections of domestic cats.IMPORTANCE Endogenous retroviruses are harbored by many animals, and their interactions with exogenous retroviral infections have not been widely studied. Feline leukemia virus (FeLV) is a relevant model system to examine this question, as endogenous and exogenous forms of the virus exist. In this analysis of a large domestic cat breeding colony naturally infected with FeLV, we documented that enFeLV copy number was higher in males and inversely related to FeLV viral load and associated with better FeLV disease outcomes. Females had lower enFeLV copy numbers and were more likely to have progressive FeLV disease and FeLV-B subtypes. FFV viral load was correlated with FeLV progression. FFV, FcaGHV-1, and FeLV displayed markedly different patterns of infection with respect to host demographics. This investigation revealed complex coinfection outcomes and viral ecology of chronic infections in a closed population.

Related Endogenous Retrovirus-K Elements Harbor Distinct Protease Active Site Motifs

Background: Endogenous retrovirus-K is a group of related genomic elements descending from retroviral infections in human ancestors. HML2 is the clade of these viruses which contains the most intact provirus copies. These elements can be transcribed and translated in healthy and diseased tissues, and some of them produce active retroviral enzymes, such as protease. Retroviral gene products, including protease, contribute to illness in exogenous retroviral infections. There are ongoing efforts to test anti-retroviral regimens against endogenous retroviruses. Herein, we examine the potential activity and diversity of human endogenous retrovirus-K proteases, and their potential for impact on immunity and human disease.Results: Sequences similar to the endogenous retrovirus-K HML2 protease and reverse transcriptase were identified in the human genome, classified by phylogenetic inference and compared to Repbase reference sequences. The topologies of trees inferred from protease and reverse transcriptase sequences were similar and agreed with the classification using reference sequences. Surprisingly, only 62/480 protease sequences identified by BLAST were classified as HML2; the remainder were classified as other HML groups, with the majority (216) classified as HML3. Variation in functionally significant protease motifs was explored, and two major active site variants were identified – the DTGAD variant is common in all groups, but the DTGVD motif appears limited to HML3, HML5, and HML6. Furthermore, distinct RNA expression patterns of protease variants are seen in disease states, such as amyotrophic lateral sclerosis, breast cancer, and prostate cancer.Conclusion: Transcribed ERVK proteases exhibit a diversity which could impact immunity and inhibitor-based treatments, and these facets should be considered when designing therapeutic regimens.

Hypomethylation and presence of human endogenous retroviruses –h and –k in the extracellular microvescicles of colon cancer patients.

e24071Background: Human Endogenous Retroviruses (HERVs) are remnants of ancient exogenous retroviral infections of the humans, representing 8% of the human genome. Their regulation is based on epig...

Cytotoxic stress induces transfer of mitochondria-associated human endogenous retroviral RNA and proteins between cancer cells.

About 8 % of the human genome consists of human endogenous retroviruses (HERVs), which are relicts of ancient exogenous retroviral infections incurred during evolution. Although the majority of HERVs have functional gene defects or epigenetic modifications, many of them are still able to produce retroviral proteins that have been proposed to be involved in cellular transformation and cancer development.We found that, in chemo-resistant U87RETO glioblastoma cells, cytotoxic stress induced by etoposide promotes accumulation and large-scale fission of mitochondria, associated with the detection of HERV-WE1 (syncytin-1) and HERV-FRD1 (syncytin-2) in these organelles. In addition, mitochondrial preparations also contained the corresponding receptors, i.e. ASCT2 and MFSD2. We clearly demonstrated that mitochondria associated with HERV-proteins were shuttled between adjacent cancer cells not only via tunneling tubes, but also by direct cellular uptake across the cell membrane. Furthermore, anti-syncytin-1 and anti-syncytin-2 antibodies were able to specifically block this direct cellular uptake of mitochondria even more than antibodies targeting the cognate receptors.Here, we suggest that the association of mitochondria with syncytin-1/syncytin-2 together with their respective receptors could represent a novel mechanism of cell-to-cell transfer. In chemotherapy-refractory cancer cells, this might open up attractive avenues to novel mitochondria-targeting therapies.

Abstract IA02: Functional role of endogenous retroviruses in cancer immunity

Abstract Endogenous retroviruses (ERVs) are derived from past exogenous retroviral infections of germ cells, which integrated into the genome of mammals and are inherited in a Mendelian manner. ERVs belong to the class of retro-elements possessing three main viral genes: group-specific antigen (gag), polymerase (pol) and envelope (env) flanked by two long terminal repeats (LTR). More than 8% of the human genome is considered of retroviral origin. Most ERV genes are protein non-functional due to recombination, mutations and deletions; however some ERV gag, pol and env genes produce functional proteins. Although largely gene defective, the LTRs of ERVs retained their regulatory activities resulting in high transcriptional levels; and in addition represent most of the ~10,000 annotated long non-coding (lnc) RNAs. In somatic cells ERVs are generally silent; however we and others demonstrated ERVs become activated during tumorigenesis. Recently we showed that induction of immune responses in human cancer cells by DNA methyltransferase inhibitors (DNMTi), like 5-azacytidine (Aza) and 2'-deoxy-5-azacytidine (Dac) is primarily due to the activation of (hyper)-methylated ERVs (Chiappinelli et al. 2015, Cell 162: 974-86). Furthermore, the unique genomic architecture of ERVs with 5 and 3 LTRs induced sense and antisense RNAs leading to formation of cytosolic dsRNA, which activated the cellular viral RNA sensing and defense pathway (like TLR3 and MAVS) triggering the type I interferon (IFN) response. This kind of response following ERV activation is called viral mimicry or endogenous viremia. Using ovarian carcinoma (OVCA) cell lines as a model, we showed that Aza significantly induced multiple ERV families and IFN stimulated genes (ISG). The induction was due to the formation of dsRNA, which was abolished with RNAse III (hydrolyzing dsRNA) and TLR3 or MAVS specific inhibition. ISGs were also directly induced by transfected ERV genes. Subsequently, a cohort of primary human serous OVCA tissues was analyzed and a significant positive correlation between ERV and ISG expression could be demonstrated. We and others previously showed that treatment with the DNMTi Aza positively contributed to immune checkpoint blockade therapy in a mouse model and in human cancers. Like exogenous retroviruses, which upregulate immune checkpoint genes (ICG), we also evaluated for a possible connection between ERV induction and ICG expression in primary tumors. Presently, we demonstrate that human serous OVCA tissues express significantly higher ICGs than control ovarian tissues, with VTCN-1 (B7-H4) as the highest expressed ICG. Using serous OVCA cell lines transfected with different ERV genes we could show an early induction of ICGs, primarily LGALS9 and PD-L1. Further analysis of tumor infiltrating immune cells using the same serous OVCA cohort and multiplex immunohistochemistry (IHC), we detect in some tumors high levels of tumor-associated CD79a, CD3+/CD8- and CD3+/CD8+ cells. Moreover, we find a direct link between ISG, ICG and infiltrating immune cells in OVCA. Analyzing other human tumors, e.g. brain tumors, like glioblastoma multiforme (GBM) and giant cell GBM (gcGBM) also demonstrate a significant correlation between high ERV induction and ISG as well as ICG expression. In contrast to serous OVCA, PD1 and VTCN-1 were the highest expressed ICG in GBM and gcGBM, which could also be shown with ERV transfected GBM cell lines. Using IHC gcGBM shows a high level of immune cell infiltration, which associated with giant cells and ICG expression, like PD-L1. Interestingly, the highest ERV expression was found in gcGBM, which correlated with endomitosis and cell fusion leading to giant nuclei and multinucleated cells as also shown with a stable ERV transfected GBM cell line. In summary, DNMTi mediated loss of methylation induced ERVs forming dsRNA in tumor cells and stimulated the innate immune system via ISGs. ERV RNA per se induced ISGs, but also ICGs similar to exogenous retroviruses in order to escape the immune system. Different upregulated ERVs, ISGs and ICGs were found in different cancers, like serous OVCA, GBM and gcGBM indicating diverse tumor and tumor microenvironment signatures. Thus ERVs have an ambivalent role in tumorigenesis, where tumor microenvironmental factors tip the balance being detrimental by generating immune evasion or beneficial for cancer therapy by stimulating the innate immune system. Citation Format: Reiner Strick. Functional role of endogenous retroviruses in cancer immunity. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr IA02.

PML/TRIM19-Dependent Inhibition of Retroviral Reverse-Transcription by Daxx.

PML (Promyelocytic Leukemia protein), also known as TRIM19, belongs to the family of tripartite motif (TRIM) proteins. PML is mainly expressed in the nucleus, where it forms dynamic structures known as PML nuclear bodies that recruit many other proteins, such as Sp100 and Daxx. While the role of PML/TRIM19 in antiviral defense is well documented, its effect on HIV-1 infection remains unclear. Here we show that infection by HIV-1 and other retroviruses triggers the formation of PML cytoplasmic bodies, as early as 30 minutes post-infection. Quantification of the number and size of PML cytoplasmic bodies revealed that they last approximately 8 h, with a peak at 2 h post-infection. PML re-localization is blocked by reverse-transcription inhibitors and is not observed following infection with unrelated viruses, suggesting it is specifically triggered by retroviral reverse-transcription. Furthermore, we show that PML interferes with an early step of retroviral infection since PML knockdown dramatically increases reverse-transcription efficiency. We demonstrate that PML does not inhibit directly retroviral infection but acts through the stabilization of one of its well-characterized partners, Daxx. In the presence of PML, cytoplasmic Daxx is found in the vicinity of incoming HIV-1 capsids and inhibits reverse-transcription. Interestingly, Daxx not only interferes with exogenous retroviral infections but can also inhibit retrotransposition of endogenous retroviruses, thus identifying Daxx as a broad cellular inhibitor of reverse-transcription. Altogether, these findings unravel a novel antiviral function for PML and PML nuclear body-associated protein Daxx.

Activation and regulation of endogenous retroviral genes in the human pituitary gland and related endocrine tumours

Adenohypophysis (AH) hormone-producing cells represent the origin of diverse groups of pituitary adenomas (PA). Deregulation of hypothalamic hormone receptors, growth factors and cAMP signalling have been implicated in the aetiology of PA. Endogenous retroviruses (ERVs) are derived from past exogenous retroviral infections and represent more than 8% of the human genome. Some ERV genes encode open reading frames and produce functional proteins, for example, the ERVW-1 envelope gene Syncytin-1, essential for placentogenesis, but also deregulated in human tumours. Data concerning ERV expression in the AH and related endocrine tumours are missing. Syncytin-1 protein was analysed in normal AH (n = 15) and compared with five PA subtypes (n = 117) by immunohistochemistry. Absolute gene expression of 20 ERV functional envelope genes and ERVW-5 gag was measured. PA tissues were examined for Syncytin-1 and the cAMP signalling marker phospho-CREB-Ser133 using immunohistochemistry. Isolated primary human PA cells were treated with different hormones. Murine embryonic and adult pituitary gland ERV expressions were compared with human AH. Syncytin-1 protein colocalized with corticotropic cells of AH. In contrast, all PA demonstrated significant Syncytin-1 protein overexpression, supporting deregulation. All other ERV genes showed significant up-regulations in different PA subtypes. Phospho-CREB-Ser133 and Syncytin-1 colocalized in PA cells. Cultivated primary PA cells with ACTH or CRH induced their respective receptors and ERV genes. Syncytin-A/-B, murine orthologues to human Syncytin-1/-2, localized to embryonic and adult pituitary glands demonstrating functional mammalian conservation. Deregulated ERV genes may contribute to PA development via cAMP signalling.

Identification and analysis of HML2 sequences in human genome assembly GRCh37/hg19

Background Human endogenous retroviruses (HERVs) originated from exogenous retroviral infections of the human germ line cells and spread in the human population through vertical transmission over millions of years. Among HERVs, the HML2 proviruses [1] are the most recently integrated and show the most intact proviral genomes. HML-2 expression has tentatively been associated with different pathological conditions, including Hodgkin’s lymphoma, melanoma, breast and testicular cancer. A comprehensive recent study identified 91 HML2 proviruses [2].

Abstract 4800: Reactivation of codogenic endogenous retroviral (ERV) envelope genes in human endometrial carcinoma and prestages: emergence of new molecular targets.

Abstract Endometrial carcinoma (EnCa) is the most common invasive gynaecologic carcinoma. Over 85% of EnCa are classified as endometrioid, expressing steroid hormone receptors and mostly involve pathological prestages. Evolutionarily occurring exogenous retroviral infections into germ lines generated human endogenous retroviruses (ERV) and represent today ∼8% of the human genome. Our research parallels similarities between placentogenesis, where ERV envelope (env) genes have essential functions, and tumorigenesis. Previously, we demonstrated that Syncytin-1 (ERVW-1 env gene) up regulation was involved in EnCa cell fusion and steroid hormone proliferation regulated by TGF-ß. Additionally, Syncytin-1 was up regulated in EnCa tissues from tamoxifen treated breast carcinoma patients. The majority of ERV env coding genes are either not present or not consistently represented on gene expression microarrays. For the first time all 21 ERV env genes, including 19 codogenic and two env genes with premature stop codons were cloned and analysed for their absolute gene expression in 38 EnCa, 31 endometrium, 9 endometrial hyperplasia and 20 polyps. ERV env genes showed a stepwise increase of expression from the benign to malignant states. We classified env expression into three different categories. For example, EnCa demonstrated seven genes with high &amp;gt;200 mol/ng cDNA expression where Syncytin-1 was the highest single gene; two middle &amp;gt;50 mol/ng cDNA expressed (e.g. erv-3) and 12 low &amp;lt;50 mol/ng cDNA expressed (e.g. Syncytin-2). Overall, ERV env genes were in part similar in their expression hierarchy when compared to 34 term placentas, supporting parallel functions. Regarding tumor parameters, Syncytin-1 and Syncytin-2 were significantly up regulated in advanced stage pT2 compared to pT1b. In less differentiated EnCa Syncytin-1, erv-3, envT and envFc2 were up regulated. Using immunohistochemistry Syncytin-1, Syncytin-2 and erv-3 specifically localized to glandular epithelial cells of polyps, hyperplasia and EnCa. As noted in patient-matched EnCa compared to endometrium, increased Syncytin-1 expression correlated with ERVW-1 5’long terminal repeat (LTR) hypomethylation, including the ERE and CRE overlapping MeCP2 sites. This hypomethylation state was similar to human placental cytotrophoblasts. Functional analyses showed 10 additional env genes also regulated by methylation in EnCa cell lines. Co-transfection of an estrogen receptor (ER) negative EnCa cell line with an ERα and ERVW-1 5’LTR-luciferase reporter constructs, resulted in increased activity following treatment with estradiol and tamoxifen, which was suppressed by methylation. Reactivated and overexpressed ERV env genes could serve to promote tumorigenesis of pathological pre-stages and EnCa. A comparative model involving ERV in placentogenesis versus EnCa is presented. Citation Format: Pamela L. Strissel, Matthias Ruebner, Falk Thiel, David Wachter, Arif B. Ekici, Florentine Koppitz, Matthias W. Beckmann, Reiner Strick. Reactivation of codogenic endogenous retroviral (ERV) envelope genes in human endometrial carcinoma and prestages: emergence of new molecular targets. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4800. doi:10.1158/1538-7445.AM2013-4800

Application of next generation sequencing in mammalian embryogenomics: Lessons learned from endogenous betaretroviruses of sheep

Endogenous retroviruses (ERVs) are present in the genome of all vertebrates and are remnants of ancient exogenous retroviral infections of the host germline transmitted vertically from generation to generation. The sheep genome contains 27 JSRV-related endogenous betaretroviruses (enJSRVs) related to the pathogenic Jaagsiekte sheep retrovirus (JSRV) that have been integrating in the host genome for the last 5–7 million years. The exogenous JSRV is a causative agent of a transmissible lung cancer in sheep, and enJSRVs are able to protect the host against JSRV infection. In sheep, the enJSRVs are most abundantly expressed in the uterine epithelia as well as in the conceptus (embryo and associated extraembryonic membranes) trophectoderm. Sixteen of the 27 enJSRV loci contain an envelope (env) gene with an intact open reading frame, and in utero loss-of-function experiments found the enJSRVs Env to be essential for trophoblast outgrowth and conceptus elongation. Collectively, available evidence supports the ideas that genes captured from ancestral retroviruses were pivotal in the acquisition of new, important functions in mammalian evolution and were positively selected for biological roles in genome plasticity, protection of the host against infection of related pathogenic and exogenous retroviruses, and a convergent physiological role in placental morphogenesis and thus mammalian reproduction. The discovery of ERVs in mammals was initially based on molecular cloning discovery techniques and will be boosted forward by next generation sequencing technologies and in silico discovery techniques.

Endogenous Retroviruses of Sheep: A Model System for Understanding Physiological Adaptation to an Evolving Ruminant Genome

Endogenous retroviruses (ERVs) are present in the genome of all vertebrates and are remnants of ancient exogenous retroviral infections of the host germline transmitted vertically from generation to generation. Sheep betaretroviruses offer a unique model system to study the complex interaction between retroviruses and their host. The sheep genome contains 27 endogenous betaretroviruses (enJSRVs) related to the exogenous and pathogenic Jaagsiekte sheep retrovirus (JSRV), the causative agent of a transmissible lung cancer in sheep. The enJSRVs can protect their host against JSRV infection by blocking early and late steps of the JSRV replication cycle. In the female reproductive tract, enJSRVs are specifically expressed in the uterine luminal and glandular epithelia as well as in the conceptus (embryo and associated extraembryonic membranes) trophectoderm and in utero loss-of-function experiments found the enJSRVs envelope (env) to be essential for conceptus elongation and trophectoderm growth and development. Collectively, available evidence in sheep and other mammals indicate that ERVs coevolved with their hosts for millions of years and were positively selected for biological roles in genome plasticity and evolution, protection of the host against infection of related pathogenic and exogenous retroviruses, and placental development.

Conservation of ancient full-length open reading frames in vertebrate endogenous retroviruses

Background Endogenous retroviruses (ERVs) are genetic remnants of exogenous retroviral infections that have endured selective processes and made their way into ancestral host genomes. While many of them have deteriorated beyond the ability to code for detectable proteins, some still retain activity or the potential for coding activity [1-3]. A few active ERVs have been coopted into fully functional genes that play important roles in development or disease [1, 2, 4]. New high throughput data revealed that these ERVs are far more common than previously thought and different software packages have been created to search genomes for these structures. In this study, we build on such a tool to look at several vertebrate genomes, search for ERV remnants and identify loci with long, intact open reading frames for the major retroviral genes and dating these loci of interest using the long terminal repeat (LTR) divergence method [5].