Upregulation of Leukocytic Syncytin-1 in Acute Myeloid Leukemia Patients

Molecular mechanisms of syncytin-1 in tumors and placental development related diseases

Human endogenous retroviruses (HERVs) have evolved from exogenous retroviruses and account for approximately 8% of the human genome. A growing number of findings suggest that the abnormal expression of HERV genes is associated with schizophrenia, multiple sclerosis, endometriosis, breast cancer, bladder cancer and other diseases. HERV-W env (syncytin-1) is a membrane glycoprotein which plays an important role in placental development. It includes embryo implantation, fusion of syncytiotrophoblasts and of fertilized eggs, and immune response. The abnormal expression of syncytin-1 is related to placental development-related diseases such as preeclampsia, infertility, and intrauterine growth restriction, as well as tumors such as neuroblastoma, endometrial cancer, and endometriosis. This review mainly focused on the molecular interactions of syncytin-1 in placental development-related diseases and tumors, to explore whether syncytin-1 can be an emerging biological marker and potential therapeutic target.

Serum circulating free DNA of syncytin-1 as a novel molecular marker for early diagnosis of non-small-cell lung cancer

Background: Liquid biopsy has been receiving attention as an emerging detection technology in the clinical application of non-small-cell lung cancer (NSCLC). Methods: We quantified serum circulating free DNA (cfDNA) of syncytin-1 in 126 patients and 106 controls, analyzed the correlation of level with pathological parameters and explored diagnostic utility. Results: The cfDNA of syncytin-1 levels in NSCLC patients were higher than healthy controls (p < 0.0001). These levels were associated with smoking history (p = 0.0393). The area under the curve of cfDNA of syncytin-1 was 0.802, and combination of cfDNA of syncytin-1/cytokeratin 19 fragment antigen 21-1/carcinoembryonic antigen markers improved diagnostic efficiency. Conclusion: The cfDNA of syncytin-1 was detected in NSCLC patients and can be used as a novel molecular marker for early diagnosis.

Enhanced Expression of Human Endogenous Retroviruses, TRIM28 and SETDB1 in Autism Spectrum Disorder

Human endogenous retroviruses (HERVs) are relics of ancestral infections and represent 8% of the human genome. They are no longer infectious, but their activation has been associated with several disorders, including neuropsychiatric conditions. Enhanced expression of HERV-K and HERV-H envelope genes has been found in the blood of autism spectrum disorder (ASD) patients, but no information is available on syncytin 1 (SYN1), SYN2, and multiple sclerosis-associated retrovirus (MSRV), which are thought to be implicated in brain development and immune responses. HERV activation is regulated by TRIM28 and SETDB1, which are part of the epigenetic mechanisms that organize the chromatin architecture in response to external stimuli and are involved in neural cell differentiation and brain inflammation. We assessed, through a PCR realtime Taqman amplification assay, the transcription levels of pol genes of HERV-H, -K, and -W families, of env genes of SYN1, SYN2, and MSRV, as well as of TRIM28 and SETDB1 in the blood of 33 ASD children (28 males, median 3.8 years, 25–75% interquartile range 3.0–6.0 y) and healthy controls (HC). Significantly higher expressions of TRIM28 and SETDB1, as well as of all the HERV genes tested, except for HERV-W-pol, were found in ASD, as compared with HC. Positive correlations were observed between the mRNA levels of TRIM28 or SETDB1 and every HERV gene in ASD patients, but not in HC. Overexpression of TRIM28/SETDB1 and several HERVs in children with ASD and the positive correlations between their transcriptional levels suggest that these may be main players in pathogenetic mechanisms leading to ASD.

Therapeutic potential of the human endogenous retroviral envelope protein HEMO: a pan-cancer analysis

Human endogenous retroviruses represent approximately 8% of our genome. Most of these sequences are defective except for a few genes such as the ancestral retroviral HEMO envelope gene (Human Endogenous MER34 ORF), recently characterized by our group. In this study, we characterized transcriptional activation of HEMO in primary tumors from The Cancer Genome Atlas (TCGA) and in metastatic tumors from a Gustave Roussy cohort. Pan‐cancer detection of the HEMO protein in a series of patient samples validated these results. Differential gene expression analysis in various TCGA datasets revealed a link between HEMO expression and activation of Wnt/β‐catenin signaling, in particular in endometrial cancer. Studies on cell models led us to propose that the Wnt/β‐catenin pathway could act as an upstream regulator of this retroviral endogenous sequence in tumor condition. Characterization of transcriptomic profiles of both HEMO^Low and HEMO^High tumors suggested that activation of HEMO is negatively associated with immune response signatures. Taken together, these results highlight that HEMO, as an endogenous retroviral envelope protein specifically expressed in tumors, represents a promising tumor biomarker and therapeutic target.

Correlation Between Promoter Hypomethylation and Increased Expression of Syncytin-1 in Non-Small Cell Lung Cancer

Introduction

Syncytin-1 is a human endogenous retroviral (HERVW) envelope protein, which has been implicated in trophoblast and cancer cell fusions as well as in immunomodulatory functions. We investigated syncytin-1 expression and promoter methylation in non-small cell lung cancer (NSCLC) and the adjacent, para-carcinoma tissues. In addition, the correlation to patient survival differentiation of between 5-year survival and death group was analyzed.

Methods

Survival ratio was calculated by Kaplan-Meier survival curve. Death risk assessment was executed by Cox risk regression model. The 5ʹ-LTR methylation level of HERVW promoter was detected by EpiTYPER method.

Results

Syncytin-1 expression in NSCLC tissue was found to be significantly higher than in para-carcinoma tissues. Moreover, the 5-year survival group has a lower syncytin-1 expression than the death group. Clinical stage and the percentage of syncytin-1 positive cells were top risk factors according to Cox ratio risk regression model analysis. While the methylation level of the 5ʹ-LTR in HERVW gene promoter was relatively lower in NSCLC than para-carcinoma tissues, the methylation status of a CpG-2 site overlapping the Oct-1 binding site was found to be an important element potentially involved in the epigenetic regulation of HERVW gene expression.

Conclusion

These findings suggest that syncytin-1 could be a biomarker for the diagnosis/prognosis of NSCLC, and further studies are required to elucidate the exact role of syncytin-1 in the development of NSCLC as well as the underlying molecular mechanism for syncytin-1 function and regulation.

Chronic HCV Infection Is Associated with Overexpression of Human Endogenous Retroviruses that Persists after Drug-Induced Viral Clearance

Chronic hepatitis C virus (HCV) infection is associated with several hepatic and extrahepatic complications, including cancers and autoimmune disorders, whose frequency is reduced but not abolished after drug-induced viral clearance. The causes of these complications and of their persistence are ill-defined. Human endogenous retroviruses (HERVs) are remnants of ancestral infections and constitute 8% of the human genome. Most HERV elements are inactive, but some are transcribed. HERV overexpression is associated with many cancers and autoimmune diseases with a putative pathogenetic role. Several viral infections trigger HERV activation, but there are no studies on HCV-infected subjects. We assessed, through a PCR real-time amplification assay, the transcription levels of the pol genes of HERV-H, -K, and -W, and of their repressor TRIM28 in white blood cells (WBCs) of vertically infected children, both before and after therapy with direct-acting antivirals (DAAs). The results documented significantly higher expressions of HERV-H-pol and HERV-K-pol, not of HERV-W-pol, in HCV-infected subjects as compared to age-matched controls. HERV RNA levels remained unchanged after DAA-driven viral clearance. No significant variations in transcription levels of TRIM28 were observed in infected subjects. Our findings demonstrate HERV-H-pol and HERV-K-pol overexpression in subjects with chronic HCV infection, without variations after a positive response to DAAs; this might justify their predisposition to cancers and autoimmune disorders that persist after a DAA-induced resolution of viremia.

Syncytin-1/HERV-W envelope is an early activation marker of leukocytes and is upregulated in multiple sclerosis patients

Syncytin-1 is the envelope protein of the human endogenous retrovirus W (HERV-W). It has been related to multiple sclerosis (MS) but its role in cellular immunity and its pathogenic mechanism in the autoimmune context are not fully understood. We analyzed syncytin-1 levels in peripheral blood mononuclear cells (PBMC) subsets from healthy donors, MS patients in relapse or remission, and patients with acute infections by flow cytometry. PBMC cultures were also prepared to analyze protein expression kinetics. MS patients had higher levels of syncytin-1 levels than controls. We found that syncytin-1 is elevated in monocytes during MS relapses and infections. Cells expressing syncytin-1, including monocytes, T and B lymphocytes, and NKs presented mainly an activated phenotype and, upon stimulation with LPS, its levels increased rapidly on antigen-presenting cells. Syncytin-1 ligation promoted the activation of monocytes, as demonstrated by the upregulation of CD80 and the nonclassical subset CD14^low CD16⁺ . Our results suggest an important role for syncytin-1 in the activation of leukocytes. Given that the expression of syncytin-1 is upregulated in MS patients, this protein might be contributing to the autoimmune cascade in the disease.

Cancer cell fusion: a potential target to tackle drug-resistant and metastatic cancer cells

Cell fusion is an integral, established phenomenon underlying various physiological processes in the cell cycle. Although research in cancer metastasis has hypothesised numerous molecular mechanisms and signalling pathways responsible for invasion and metastasis, the origin and progression of metastatic cells within primary tumours remains unclear. Recently, the role of cancer cell fusion in cancer metastasis and development of multidrug resistance (MDR) in tumours has gained prominence. However, evidence remains lacking to justify the role of cell fusion in cancer metastasis and drug resistance. Here, we highlight plausible mechanisms governing cell fusion with different cell types in the tumour microenvironment (TME), the clinical relevance of cancer cell fusion, its potential as a target for overcoming MDR and inhibiting metastasis, and putative modes of treatment.