Development of broadly targeted human endogenous gammaretroviral pol-based real time PCRs

Syncytin-1, a fusogenic protein encoded by a human endogenous retrovirus of the W family (HERV-W) element (ERVWE1), is expressed in the syncytiotrophoblast layer of the placenta. This locus is transcriptionally repressed in adult tissues through promoter CpG methylation and suppressive histone modifications. Whereas syncytin-1 appears to be crucial for the development and functioning of the human placenta, its ectopic expression has been associated with pathological conditions, such as multiple sclerosis and schizophrenia. We previously reported on the transactivation of HERV-W elements, including ERVWE1, during influenza A/WSN/33 virus infection in a range of human cell lines. Here we report the results of quantitative PCR analyses of transcripts encoding syncytin-1 in both cell lines and primary fibroblast cells. We observed that spliced ERVWE1 transcripts and those encoding the transcription factor glial cells missing 1 (GCM1), acting as an enhancer element upstream of ERVWE1, are prominently upregulated in response to influenza A/WSN/33 virus infection in nonplacental cells. Knockdown of GCM1 by small interfering RNA followed by infection suppressed the transactivation of ERVWE1. While the infection had no influence on CpG methylation in the ERVWE1 promoter, chromatin immunoprecipitation assays detected decreased H3K9 trimethylation (H3K9me3) and histone methyltransferase SETDB1 levels along with influenza virus proteins associated with ERVWE1 and other HERV-W loci in infected CCF-STTG1 cells. The present findings suggest that an exogenous influenza virus infection can transactivate ERVWE1 by increasing transcription of GCM1 and reducing H3K9me3 in this region and in other regions harboring HERV-W elements. IMPORTANCESyncytin-1, a protein encoded by the env gene in the HERV-W locus ERVWE1, appears to be crucial for the development and functioning of the human placenta and is transcriptionally repressed in nonplacental tissues. Nevertheless, its ectopic expression has been associated with pathological conditions, such as multiple sclerosis and schizophrenia. In the present paper, we report findings suggesting that an exogenous influenza A virus infection can transactivate ERVWE1 by increasing the transcription of GCM1 and reducing the repressive histone mark H3K9me3 in this region and in other regions harboring HERV-W elements. These observations have implications of potential relevance for viral pathogenesis and for conditions associated with the aberrant transcription of HERV-W loci.

Section: Discussionsupporting

confidence: 83%

Transcriptional Derepression of the ERVWE1 Locus following Influenza A Virus Infection

Nellåker

Sabunciyan

et al. 2014

“…The human genome sequencing project revealed that 8 to 9% of the human genome is of retroviral origin (23). Around 826 of these elements (class II HERVs) are betaretrovirus-like and therefore distantly related to exogenous MMTV (33).Although the majority of HERVs are noninfectious, replication-defective retroviral fossils, at least some members of each HERV family were found to still be transcriptionally active (12,33,42,43). Furthermore, tissue-specific HERV expression profiles could be established for all human tissues investigated so far, confirming that HERVs are permanent components of the human transcriptome (13, 42).…”

mentioning

confidence: 99%

“…Although the majority of HERVs are noninfectious, replication-defective retroviral fossils, at least some members of each HERV family were found to still be transcriptionally active (12,33,42,43). Furthermore, tissue-specific HERV expression profiles could be established for all human tissues investigated so far, confirming that HERVs are permanent components of the human transcriptome (13,42).…”

mentioning

confidence: 99%

Variable Transcriptional Activity of Endogenous Retroviruses in Human Breast Cancer

Frank

Verbeke

Schwarz

et al. 2008

Human endogenous retroviruses (HERVs) account for up to 9% of the human genome and include more than 800 elements related to betaretroviruses. While mouse mammary tumor virus (MMTV) is the accepted etiological agent of mammary tumors in mice, the role of retroviral elements in human breast cancer remains elusive. Here, we performed a comprehensive microarray-based analysis of overall retroviral transcriptional activities in 46 mammary gland tissue specimens representing pairs of nonmalignant and tumor samples from 23 patients. An analysis of nonmalignant tissue samples revealed a distinct, mammary gland-specific HERV expression profile that consists of 18 constitutively active HERV taxa. For corresponding tumor samples, a general trend toward lower levels of HERV transcription was observed, suggesting common regulatory mechanisms. In various subsets of patients, however, increased transcript levels of single class I HERV families (HERV-T, HERV-E, and HERV-F) and several class II families, including HML-6, were detected. An analysis of transcribed HML-6 sequences revealed either the activation of some or the increased activity of several proviral loci. No evidence for MMTV or human MMTV-like virus transcripts was found, indicating that transcriptionally active, MMTV analogous, exogenous viruses were not present in the breast cancer samples analyzed.Great efforts have been invested in searching for the etiology of human breast cancer, a malignancy accounting for one-fifth of all female cancers worldwide. Although many studies have identified several risk factors, such as age, diet, hormonal balance, and genetic predisposition, a clear underlying cause for the disease, especially for sporadic cases of breast cancer, remains unknown. The current data suggest that breast cancer most likely is a multifactorial disease encompassing many different causes and factors (2, 30). Moreover, it has been suggested that an infectious agent contributes to the development of human breast cancer (16,45). Of note, a novel human retrovirus (xenotropic murine leukemia virus) has recently been associated with human prostate cancer (7, 48).Since type B mouse mammary tumor virus (MMTV) is the major etiological agent of mammary gland neoplasia in laboratory mice, researchers have searched extensively for a related human retrovirus that could be responsible for human breast cancer. The existence of such a virus, although postulated for many years, has not been conclusively demonstrated, although a long line of indirect evidence for it exists. This evidence is reflected by reports on the expression of type B envelope glycoprotein (gp52) (32) and the occurrence of virus-like particles in breast cancer biopsy specimens (8), in milk (38), and in cultures of breast cancer-derived cell lines (20, 40) as well as the detection of antibodies directed against gp52 in breast cancer patients (52). However, supporting observations have been confounded by a failure to continually observe virus particles in human tumors and by numerous controversial repo...

“…However, in the cases where it has been examined, repetitive DNA and HERVs in particular have been shown to be a component of the human transcriptome (13,24,32,34). While tissue-specific patterns of HERV expression have been demonstrated, all tissues analyzed to date express at least some elements.…”

mentioning

confidence: 99%

Expression Profiles of Endogenous Retroviruses in Old World Monkeys

Stengel

Roos

Hunsmann

et al. 2006

Human endogenous retroviruses (HERVs) are a major component of the human genome and an active part of the transcriptome. Some HERVs play vital biological roles, while others potentially contribute to diseases. Many HERVs are relatively new in the primate genome, having entered or expanded after the lineages leading to the platyrrhines (New World monkeys) and catarrhines (Old World monkeys and apes) separated. Most HERVs are active in at least some tissues, though tissue specificity is common for most elements. We analyzed multiple tissues from several Old World monkeys using retroviral pol-based DNA microarrays and quantitative PCR methods to determine their ERV expression profiles. The results demonstrate that while many ERVs are active in nonhuman primates, overall the tissue expression specificity is unique to each species. Most striking is that while the majority of HERVs analyzed in this study are expressed in human brain, almost none are expressed in Old World monkey brains or are only weakly expressed.