Human endogenous retroviruses and cancer:Causality and therapeutic possibilities

A substantial part of the human genome is derived from transposable elements;remnants of ancient retroviral infections.Conservative estimates set the percentage of human endogenous retroviruses(HERVs) in the genome at 8%.For the most part,the interplay between mutations,epigenetic mechanisms and posttranscriptional regulations silence HERVs in somatic cells.We first highlight mechanisms by which activation of members of several HERV families may be associated with tumor development before discussing the arising chances for both diagnosis and therapy.It has been shown that at least in some cases,tumor cells expressing HERV open reading frames(ORFs) thus gain tumor-promoting functions.However,since these proteins are not expressed in healthy tissues,they become prime target structures.Of potential pharmacological interest are the prevention of HERV transposition,the inhibition of HERV-encoded protein expression and the interference with these proteins' activities.Evidence from recent studies unequivocally proves that HERV ORFs represent a very interesting source of novel tumor-specific antigens with even the potential to surpass entity boundaries.The development of new tumor(immune-) therapies is a very active field and true tumor-specific targets are of outstanding interest since they minimize the risk of autoimmunity and could reduce side effects.Finally,we postulate on main future research streams in order to stimulate discussion on this hot topic.

Cloning and Sequence Analysis of Genome from the Inner Mongolia Strain of the Endogenous Betaretroviruses (enJSRV)

In order to amplify the complete genome of enJSRV from the strain of Inner Mongolia (enJSRV-NM), we used enJSRV-specific and JSRV-specific DNA probes in dot blot hybridization. Seven pairs of primers were designed based on Genbank sequences. Seven fragments were obtained by PCR and were cloned into the PMD19-T vectors. The recombinant plasmids were sequenced and analyzed. The results showed that the genome was 7 942 bp in length and contained four overlapping open reading frames corresponding to the gag, pro, pol and env genes as well as an additional open reading frame (orf-x) that overlaps the 3' end of the pol gene. The nucleotide acid sequences of the enJSRV-NM loci were compared with the sequences of South Africa enJS56A1 strain (Accession No. AF153615) and USA JSRV21 strain (Accession No. AF105220). The nucleotide acid identities were 99.2% and 92.3% respectively. Two zinc fingers were found in the NC region in the predicted amino acid sequence. However, the YXXM motif, which is a reliable molecular marker for the infectious exogenous virus, was not found in the TM region. It was found that the enJSRV-NM region was 90%-98% identical at the amino acid level to its exogenous infectious counterparts in most of the retroviral genome. This is the first nucleotide sequence of enJSRV reported in P.R China. The resource work has provided a wide range of information useful not only for expression genomics and annotation of genomic DNA sequence, but also for further research on the clinical diagnosis of OPA.

Classification of Retroviruses Based on Genomic Data Using RVGC

Retroviruses are a large group of infectious agents with similar virion structures and replication mechanisms.AIDS,cancer,neurologic disorders,and other clinical conditions can all be fatal due to retrovirus infections.Detection of retroviruses by genome sequence is a biological problem that benefits from computational methods.The National Center for Biotechnology Information(NCBI)promotes science and health by making biomedical and genomic data available to the public.This research aims to classify the different types of rotavirus genome sequences available at the NCBI.First,nucleotide pattern occurrences are counted in the given genome sequences at the preprocessing stage.Based on some significant results,the number of features used for classification is reduced to five.The classification shall be carried out in two phases.The first phase of classification shall select only two features.Unclassified data in the first phase is transferred to the next phase,where the final decision is taken with the remaining three features.Three data sets of animals and human retroviruses are selected;the training data set is used to minimize the classifier’s number and training;the validation data set is used to validate the models.The performance of the classifier is analyzed using the test data set.Also,we use decision tree,naive Bayes,knearest neighbors,and vector support machines to compare results.The results show that the proposed approach performs better than the existing methods for the retrovirus’s imbalanced genome-sequence dataset.

Differentiation of wild boar and domestic pig populations based on the frequency of chromosomes carrying endogenous retroviruses

Analysis of the frequencies of chromosomes carrying various classes of porcine endogenous retroviruses (PERVs) and combinations of these classes was performed in the swine species Sus scrofa L. by using maps constructed in two principal component coordinates. Four population clusters can be recognized in the maps. Cluster 1 is formed by wild boars,cluster 2 by domestic meat breeds, cluster 3 by meat-and-lard (universal) breeds, and cluster 4 by miniature pigs. The maps indicate that modern domesticated swine meat breeds are the closest to the wild type. Meat-and-lard domestic swine breeds are more distant from wild boars, and miniature pigs are diverged the most. The maps showed that microevolution processes associated with PERV carriership frequency had two basic dimensions, or vectors: the vector of fat deposition variation and the “minus” selection vector (determination of commercial traits). Thus, PERVs may cause variation in pig physiology.

Gene therapy strategies for treating brain tumors: Retroviruses are still good candidates for therapeutic vectors

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor in adults. In the past few decades, many efforts have been made to improve the prognosis of GBM, however, with limited success. Many gene therapy strategies for GBM have been developed and a few have progressed to clinical trials. Retroviral vectors have superior features for gene therapy in brain cancers, including tumor specificity, immunogenicity, and longer half-life. Early gene therapy trials in GBM patients based on transplantation of retrovirus-producing cells into the brain failed to prove efficacious. Adenoviral vectors, which can be prepared as high-titer virus solutions and undergo efficient transduction in tumor cells, failed in clinical trials, likely due to immunogenicity and instability of gene expression. Alternative therapeutics such as oncolytic viruses that specifically target and destroy cancer cells are currently under investigation. In addition to novel vectors, retroviral vectors are still attractive candidates for use in gene therapy against brain tumors. Since yields of properly-packaged viral particles from virus-producing cells have been very limited so far, gene therapy by direct injection of hightiter retroviral vectors into the patients’ brains was not possible. To overcome these disadvantages, a packaging cell line that yields high-titer retroviral solutions was established by our group, enabling the direct injection of massive retroviral vector stocks directly into the brain. Mouse glioma models were effectively cured with a combination of a suicide gene/ prodrug system and a highly-concentrated retrovirus solution. Preclinical assessments, including that of replication-competent retroviruses and tumorigenicity of the combination method, have confirmed the safety of the highly-concentrated retrovirus solution. Addi tional studies are needed to address the clinical utility of such combination gene therapies. Taken together, these data suggest that retroviral vectors are still good candidates for development in gene therapy applications.

Regulation of endogenous retroviruses in murine embryonic stem cells and early embryos

Endogenous retroviruses(ERVs)are important components of transposable elements that constitute∼40%of the mouse genome.ERVs exhibit dynamic expression patterns during early embryonic development and are engaged in numerous biological processes.Therefore,ERV expression must be closely monitored in cells.Most studies have focused on the regulation of ERV expression in mouse embryonic stem cells(ESCs)and during early embryonic development.This review touches on the classification,expression,and functions of ERVs in mouse ESCs and early embryos and mainly discusses ERV modulation strategies from the perspectives of transcription,epigenetic modification,nucleosome/chromatin assembly,and post-transcriptional control.

The diversity and evolution of retroviruses:Perspectives from viral“fossils”

Retroviruses exclusively infect vertebrates,causing a variety of diseases.The replication of retroviruses requires reverse transcription and integration into host genomes.When infecting germline cells,retroviruses become inherited vertically,forming endogenous retroviruses(ERVs).ERVs document past viral infections,providing molecular fossils for studying the evolutionary history of retroviruses.In this review,we summarize the recent advances in understanding the diversity and evolution of retroviruses from the perspectives of viral fossils,and discuss the effects of ERVs on the evolution of host biology.

Human Endogenous Retroviruses as Biomedicine Markers

Human endogenous retroviruses(HERVs)were formed via ancient integration of exogenous retroviruses into the human genome and are considered to be viral“fossils”.The human genome is embedded with a considerable amount of HERVs,witnessing the long-term evolutionary history of the viruses and the host.Most HERVs have lost coding capability during selection but still function in terms of HERV-mediated regulation of host gene expression.In this review,we summarize the roles of HERV activation in response to viral infections and diseases,and emphasize the potential use of HERVs as biomedicine markers in the early diagnosis of diseases such as cancer,which provides a new perspective for the clinical application of HERVs.

Construction and expression of retroviruses encoding dual drug resistance genes in human umbilical cord blood CD34^+ cells

A series of retroviral vectors encoding human mdrl gene alone as well as in combination with either human mgmt gene or human mutant Ser31-dftfrgene are engineered. The resultant retroviruses are used to transduce human umbilical cord blood CD34+ cells. It has been shown that expression of dual drug resistance genes in transduced cells confers a broad range of resistance to both kinds of corresponding drugs. These data suggest a rationale for the use of such double chemoresistance gene constructs in an in vivo model in which transduced hematopoietic cells will acquire multiple protection against the cytotoxic side effects of combination chemotherapy and may have future application in chemoprotection of normal tissues, thus killing tumor cells more effectively.

Transcriptome Analyses Implicate Endogenous Retroviruses Involved in the Host Antiviral Immune System through the Interferon Pathway

Human endogenous retroviruses(HERVs) are the remains of ancient retroviruses that invaded our ancestors’ germline cell and were integrated into the genome. The expression of HERVs has always been a cause for concern because of its association with various cancers and diseases. However, few previous studies have focused on specific activation of HERVs by viral infections. Our previous study has shown that dengue virus type 2(DENV-2) infection induces the transcription of a large number of abnormal HERVs loci;therefore, the purpose of this study was to explore the relationship between exogenous viral infection and HERV activation further. In this study, we retrieved and reanalyzed published data on 21 transcriptomes of human cells infected with various viruses. We found that infection with different viruses could induce transcriptional activation of HERV loci. Through the comparative analysis of all viral datasets, we identified 43 key HERV loci that were up-regulated by DENV-2, influenza A virus, influenza B virus, Zika virus, measles virus, and West Nile virus infections. Furthermore, the neighboring genes of these HERVs were simultaneously up-regulated, and almost all such neighboring genes were interferon-stimulated genes(ISGs), which are enriched in the host’s antiviral immune response pathways. Our data supported the hypothesis that activation of HERVs, probably via an interferon-mediated mechanism, plays an important role in innate immunity against viral infections.

Ancient origin and complex evolution of porcine endogenous retroviruses

Porcine endogenous retroviruses(PERVs)are proviruses that have medical value in xenotransplantation.However,the evolutionary process leading to the generation of modern PERVs is not well understood.In this study,we in silico mined 14 pig genomes and other available 304 mammalian genomes,which led to the documentation of 185 full-length PERVs or PERV-like sequences.Notably,we found that lesser Egyptian jerboa(Jaculus jaculus),rock hyrax(Procavia capensis)and eight Muridae species all harbored ancestral PERV-like sequences,indicative of ancient cross-species transmission events from none-porcine species to pigs.We also revealed that 11 genomic rearrangement events were mediated via PERVs,during the process of porcine evolution.In conclusion,these new findings help us to understand the complex evolution of the modern PERVs.

Human Endogenous Retroviruses and Hematological Malignant Tumors

Human endogenous retrovirus(HERV)gene sequences are remnants of retroviruses that infected the ancestors of humans millions of years ago and were integrated into human chromosomes,accounting for approximately 8%-9%of the human genome.Most integrated HERVs have lost their coding capacity and remain silent due to frame shifts,mutations,and sequence deletions or insertions over the millions of years,but their expression is highly regulated by epigenetic and host defense mechanisms.However,there are still some HERV genes that have intact open reading frames due to recent integration into the human genome or positive selective pressure.The abnormal activation of HERVs may contribute to diseases or their pathology,such as malignant tumors,autoimmune diseases,and nervous system diseases.The occurrence and development of hematological malignant tumors(HMTs)is a complex process involving interactions of multiple genetic and environmental factors.The abnormal activation of HERVs may contribute to the pathology of HMTs via indirect mechanisms.In this review,we address the discovery of endogenous retroviruses in vertebrates,and the classification and genomic structure of HERVs.Among HERV family members,HERV-K is the latest type of HERV integrated into the human genome and it has the strongest transcriptional activity.We explore the currently known expression of HERV-K proto-oncogenes in HMTs and further address potential research and therapeutic approaches.However,much remains to be learned about not only the impact of HERVs on the occurrence of HMTs,but also the potential value of HERVs as diagnostic and therapeutic targets for HMTs.

Advances on genetic and genomic studies of ALV resistance

Avian leukosis(AL)is a general term for a variety of neoplastic diseases in avian caused by avian leukosis virus(ALV).No vaccine or drug is currently available for the disease.Therefore,the disease can result in severe economic losses in poultry flocks.Increasing the resistance of poultry to ALV may be one effective strategy.In this review,we provide an overview of the roles of genes associated with ALV infection in the poultry genome,including endogenous retroviruses,virus receptors,interferon-stimulated genes,and other immune-related genes.Furthermore,some methods and techniques that can improve ALV resistance in poultry are discussed.The objectives are willing to provide some valuable references for disease resistance breeding in poultry.

Effects of TRPC6 on invasibility of low-differentiated prostate cancer cells

Objective:To study the expression of TRPC6 among prostate cancer cells,establish high expression cell lines of TRPC6,and to provide potential cell mode for prostate cancer oncogenesis and development.Methods:Occurrence and development of prostate cancer cells,PC3,PC—3m DU145,22 rvl,LNCaP and normal prostate epithelial cells in the PrEC TRPC6 expression level were detected by QPCR method.Calcium phosphate transfection method was used to package retrovirus pLEGFP-Nl-TRPC6 and pLEGFP-Nl-vector and infect the prostate cancer cells,a stable high expression of TRPC6 prostate cancer cells.Sable cell lines of TRPC6,matrix metalloproteinase(MMP)2,MMP9 expression was detected by QPCR and Western blot.Change of cell invasion ability was detected by Transwell.Results:The expression level of prostate cancer cells TRPC6 were higher than control group PrEC cells.Among TPRC6 the expression of cell line PC 3 transfer potential wre the lowest,and high transfer cell tone PC-3M express was the highest.Real-time fluorescent quantitative PCR and western blot results showed that after filter,the seventh generation of cell TRPC6 protein and mRNA expression levels were higher than the control group obviously.Transwell experimental results showed that the overexpression of TRPC6could promote the invasion ability of PC.3 prostate cancer cells.Conclusions:TRPC6 expressed in prostate cancer cells is in disorder,and its action may be associated with the invasion and metastasis of prostate cancer cells;successful establishment of stable high expression of TRPC6prostate cancer cells primarily confirm the invasion-trigger ability of TRPC6 on prostate cancer,and lay down the foundation for exploring the TRPC6's role in the occurrence and development of prostate cancer

Human T-lymphotropic virus type 1-associated myelopathy/tropical spastic paraparesis: Clinical presentation and pathophysiology

Human T-cell lymphotropic virus type 1(HTLV-1)-associated myelopathy/tropical spastic paraparesis(HAM/TSP) is a slowly progressive neurodegenerative disorder in which lesions of the central nervous system cause progressive weakness, stiffness, and a lower limb spastic paraparesis. In some cases, polymyositis, inclusion bodymyositis, or amyotrophic lateral sclerosis-like syndromes are associated with HTLV-1. TSP was first described in Jamaica in 1888 and known as Jamaican peripheral neuritis before TSP was related to HTLV-1 virus, the first retrovirus being identified, and the disease is since named HAM/TSP. There is no established treatment program for HAM/TSP. Prevention is difficult in lowincome patients(i.e., HTLV-1 infected breast feeding mothers in rural areas, sex workers). Thus, there is a need for new therapeutic avenues. Therapeutic approaches must be based on a better understanding, not only of clinical and clinicopathological data, but also of the pathophysiology of the affection. Consequently, a better understanding of existing or newly developed animal models of HAM/TSP is a prerequisite step in the development of new treatments.

Lineage tracing of direct astrocyte-to-neuron conversion in the mouse cortex

Regenerating functional new neurons in the adult mammalian central nervous system has been proven to be very challenging due to the inability of neurons to divide and repopulate themselves after neuronal loss.Glial cells,on the other hand,can divide and repopulate themselves under injury or diseased conditions.We have previously reported that ectopic expression of NeuroD1 in dividing glial cells can directly convert them into neurons.Here,using astrocytic lineage-tracing reporter mice(Aldh1l1-CreERT2 mice crossing with Ai14 mice),we demonstrate that lineage-traced astrocytes can be successfully converted into NeuNpositive neurons after expressing NeuroD1 through adeno-associated viruses.Retroviral expression of NeuroD1 further confirms that dividing glial cells can be converted into neurons.Importantly,we demonstrate that for in vivo cell conversion study,using a safe level of adeno-associated virus dosage(10^10–10^12 gc/mL,1μL)in the rodent brain is critical to avoid artifacts caused by toxic dosage,such as that used in a recent bioRxiv study(2×10^13 gc/mL,1μL,mouse cortex).For therapeutic purpose under injury or diseased conditions,or for non-human primate studies,adeno-associated virus dosage needs to be optimized through a series of dose-finding experiments.Moreover,for future in vivo gliato-neuron conversion studies,we recommend that the adeno-associated virus results are further verified with retroviruses that mainly express transgenes in dividing glial cells in order to draw solid conclusions.The study was approved by the Laboratory Animal Ethics Committee of Jinan University,China(approval No.IACUC-20180330-06)on March 30,2018.

RETROVIRAL MEDIATED EFFICIENT TRANSFER ANDEXPRESSION OF MULTIPLE DRUG RESISTANCE GENE TO HUMAN LEUKEMIC CELLS

Objective: To investigate retroviral-mediated transfer and expression of human multidrug resistance (MDR) gene MDR1 in leukemic cells. Methods: Human myeloid cells, K562 and NB4, were infected by MDR retrovirus from the producer PA317/HaMDR, and the resistant cells were selected with cytotoxic drug. The transfer and expression of MDR1 gene was analyzed by using polymerase chain reaction (PCR), flow cytometry (FCM) and semisolid colonies cultivation. Results: The resistant cells, K562/MDR and NB4/MDR, in which integration of the exogenous MDR1 gene was confirmed by PCR analysis, displayed a typical MDR phenotype. The expression of MDR1 transgene was detected on truncated as well as full-length transcripts. Moreover, the resistant cells were P-glycoprotein postiive at 78.0% to 98.7% analyzed with FCM. The transduction efficieny in K562 cells was studied on suspension cultures and single-cell colonies. The transduction was more efficient in coculture system (67.9%-72.5%) than in supernatant system (33.1%~46.8%), while growth factors may improve the efficiency. Conclusion: Retrovirus could allow a functional transfer and expression of MDR1 gene in human leukemia cells, and MDR1 might act as a dominant selectable gene for coexpression with the genes of interest in gene therapy.

Prevalence of porcine endogenous retrovirus in Chinese pig breeds and in patients treated with a porcine liver cell-based bioreactor

AIM： To determine the prevalence of porcine endogenous retrovirus （PERV） in various pig breeds raised in China including Chinese experimental mini-pigs by PERV-reverse transcriptase （PERV-RT enzyme）. Moreover, the potential for infection of PERV was investigated in patients treated with a bioreactor based on porcine liver cells （n = 3）. METHODS： Pig serum, liver and muscle cell-free supernatants were collected from various Chinese pig breeds. Porcine hepatocytes were isolated with a two-step perfusion method. Three patients with acute or chronic liver failure were treated with a bioartificial liver support system （BALSS） for 8-12 h and serum samples were collected from the patients before, immediately after and 30 d after treatment. RESULTS： The activities of PERV-RT enzyme in pig liver and muscle cell-free supernatants were higher than in normal human controls. PERV-TR enzyme activity did not increase in patients before and after 1 mo of treatment. PERV-RT activities were not significantly different when compared with pre-treatment group （1.544±0.155576）, the post-treatment groups （1.501±0.053507, 1.461±0.033808 and 1.6006667±0.01963 for 0, 14 and 30 d post-treatment, respectively, P〉0.05）, and normal control group （1.440±1.0641, P〉0.05）. RT enzyme activity in Chinese experimental mini-pigs was higher than in normal human control group （1.440±1.0641 U/mL, P〈0.05）, and not significantly different （P〉0.05） when compared with the pig breeds except in the muscle supernatants. All the samples including muscle and liver cell supernatants from the Chinese mini-experimental pigs and the four domestic Chinese pig breeds contained PERVs. CONCLUSION： These results suggest that the risk of PERV infection through BALSS containing porcine liver cells without immunosuppressants may be quite low. Although there were PERVs in Chinese experimental mini-pigs and porcine liver cell culture suspensions, we did not find any evidence of persistent PERV infection in patients treated with this porcine hepatocyte-based bioartificial liver.

Protective effects of pLNCX-SOD gene transfection on hepatocyte injury induced by obstructive jaundice in rats

BACKGROUND: Hydrophobic bile acids lead to the generation of oxygen free radicals in mitochondria. Accordingly, this study is to investigate if gene delivery of superoxide dismutase (SOD) will reduce hepatocyte injury caused by experimental cholestasis. METHODS: The recombinant of pLNCX-SOD gene packaged with lipofection of AMINE was transfected into hepatocytes in vitro, which stably expressed the SOD gene. RESULTS: After transfection, hepatocytes enhanced the protective effect against injury to bile and the toxicity of serum in obstructive jaundice. The inhibition of bile at the concentration of 2% (v: v, bile: DMEM 1: 50) decreased obviously from (78.80 +/- 12.35)% to (43.35 +/- 9.69)% in 12 hours, from (82.55 +/- 11.27)% to (-26.64 +/- 7.66)% in 24 hours, and from (83.83 +/- 18.69)% to (-19.27 +/- 14.38)% in 48 hours, compared with that of the untransfected cells (P < 0.01). The inhibition of serum at the obstructive jaudice concentration of 2.5% was obviously decreased from (89.72 +/- 1.52)% to (14.68 +/- 14.33)% in 12 hours, from (92.2 +/- 11.27)% to (41.39 +/- 7.66)% in 24 hours, and from (94.25 +/- 8.96)% to (22.71 +/- 4.38)% in 48 hours (P < 0.01). CONCLUSION: Hepatocytes transfected with the pLNCX-SOD gene could obviously be resistant to the toxicity of bile and serum from rat with obstructive jaundice.

Influence of chitosan nanofiber scaffold on porcine endogenous retroviral expression and infectivity in pig hepatocytes

AIM: To investigate the influence of chitosan nanofiber scaffold on the production and infectivity of porcine endogenous retrovirus (PERV) expressed by porcine hepatocytes. METHODS: Freshly isolated porcine hepatocytes were cultured with or without chitosan nanofiber scaffold (defined as Nano group and Hep group) for 7 d. The daily collection of culture medium was used to detect reverse transcriptase (RT) activity with RT activity assaykits and PERV RNA by reverse transcription-polymerase chain reaction (PCR) and real time PCR with the PERV specific primers. And Western blotting was performed with the lysates of daily retrieved cells to determine the PERV protein gag p30. Besides, the in-vitro infectivity of the supernatant was tested by incubating the human embryo kidney 293 (HEK293) cells. RESULTS: The similar changing trends between two groups were observed in real time PCR, RT activity assay and Western blotting. Two peaks of PERV expression at 10H and Day 2 were found and followed by a regular decline. No significant difference was found between two groups except the significantly high level of PERV RNA at Day 6 and PERV protein at Day 5 in Nano group than that in Hep group. And in the in-vitro infection experiment, no HEK293 cell was infected by the supernatant. CONCLUSION: Chitosan nanofiber scaffold might prolong the PERV secreting time in pig hepatocytes but would not obviously influence its productive amount and infectivity, so it could be applied in the bioartificial liver without the increased risk of the virus transmission.