Molecular biology of jaagsiekte sheep retrovirus

A novel strategy for developing vaccine candidate against Jaagsiekte sheep retrovirus from the envelope and gag proteins: an in-silico approach

BACKGROUND

Sheep pulmonary adenocarcinoma (OPA) is a contagious lung cancer of sheep caused by the Jaagsiekte retrovirus (JSRV). OPA typically has a serious economic impact worldwide. A vaccine has yet to be developed, even though the disease has been globally spread, along with its complications. This study aimed to construct an effective multi-epitopes vaccine against JSRV eliciting B and T lymphocytes using immunoinformatics tools.

RESULTS

The designed vaccine was composed of 499 amino acids. Before the vaccine was computationally validated, all critical parameters were taken into consideration; including antigenicity, allergenicity, toxicity, and stability. The physiochemical properties of the vaccine displayed an isoelectric point of 9.88. According to the Instability Index (II), the vaccine was stable at 28.28. The vaccine scored 56.51 on the aliphatic index and -0.731 on the GRAVY, indicating that the vaccine was hydrophilic. The RaptorX server was used to predict the vaccine's tertiary structure, the GalaxyWEB server refined the structure, and the Ramachandran plot and the ProSA-web server validated the vaccine's tertiary structure. Protein-sol and the SOLPro servers showed the solubility of the vaccine. Moreover, the high mobile regions in the vaccine's structure were reduced and the vaccine's stability was improved by disulfide engineering. Also, the vaccine construct was docked with an ovine MHC-1 allele and showed efficient binding energy. Immune simulation remarkably showed high levels of immunoglobulins, T lymphocytes, and INF-γ secretions. The molecular dynamic simulation provided the stability of the constructed vaccine. Finally, the vaccine was back-transcribed into a DNA sequence and cloned into a pET-30a ( +) vector to affirm the potency of translation and microbial expression.

CONCLUSION

A novel multi-epitopes vaccine construct against JSRV, was formed from B and T lymphocytes epitopes, and was produced with potential protection. This study might help in controlling and eradicating OPA.

JSRV Intragenic Enhancer Element Increases Expression from a Heterologous Promoter and Promotes High Level AAV-mediated Transgene Expression in the Lung and Liver of Mice

Jaagsiekte sheep retrovirus (JSRV) induces tumors in the distal airways of sheep and goats. A putative intragenic enhancer, termed JE, localized to the 3' end of the JSRV env gene, has been previously described. Herein we provide further evidence that the JE functions as a transcriptional enhancer, as it was able to enhance gene expression when placed in either forward or reverse orientation when combined with a heterologous chicken beta actin promoter. We then generated novel composite promoters designed to improve transgene expression from adeno-associated virus (AAV) gene therapy vectors. A hybrid promoter consisting of the shortest JE sequence examined (JE71), the U3 region of the JSRV long terminal repeat (LTR), and the chicken beta actin promoter, demonstrated robust expression in vitro and in vivo, when in the context of AAV vectors. AAV-mediated transgene expression in vivo from the hybrid promoter was marginally lower than that observed for AAV vectors encoding the strong CAG promoter, but greatly reduced in the heart, making this promoter/enhancer combination attractive for non-cardiac applications, particularly respiratory tract or liver directed therapies. Replacement of the murine leukemia virus intron present in the original vector construct with a modified SV40 intron reduced the promoter/enhancer/intron cassette size to 719 bp, leaving an additional ~4 kb of coding capacity when packaged within an AAV vector. Taken together, we have developed a novel, compact promoter that is capable of directing high level transgene expression from AAV vectors in both the liver and lung with diminished transgene expression in the heart.

Ovine Pulmonary Adenocarcinoma: A Unique Model to Improve Lung Cancer Research

Lung cancer represents a major worldwide health concern; although advances in patient management have improved outcomes for some patients, overall 5-year survival rates are only around 15%. In vitro studies and mouse models are commonly used to study lung cancer and their use has increased the molecular understanding of the disease. Unfortunately, mouse models are poor predictors of clinical outcome and seldom mimic advanced stages of the human disease. Animal models that more accurately reflect human disease are required for progress to be made in improving treatment outcomes and prognosis. Similarities in pulmonary anatomy and physiology potentially make sheep better models for studying human lung function and disease. Ovine pulmonary adenocarcinoma (OPA) is a naturally occurring lung cancer that is caused by the jaagsiekte sheep retrovirus. The disease is endemic in many countries throughout the world and has several features in common with human lung adenocarcinomas, including histological classification and activation of common cellular signaling pathways. Here we discuss the in vivo and in vitro OPA models that are currently available and describe the advantages of using pre-clinical naturally occurring OPA cases as a translational animal model for human lung adenocarcinoma. The challenges and options for obtaining these OPA cases for research purposes, along with their use in developing novel techniques for the evaluation of chemotherapeutic agents or for monitoring the tumor microenvironment in response to treatment, are also discussed.

A cis-Acting Element Downstream of the Mouse Mammary Tumor Virus Major Splice Donor Critical for RNA Elongation and Stability

BACKGROUND

The mouse mammary tumor virus (MMTV) encodes a functional signal peptide, a cleavage product of envelope and Rem proteins. Signal peptide interacts with a 3' cis-acting RNA element, the Rem-responsive element (RmRE), to facilitate expression of both unspliced genomic (gRNA) and spliced mRNAs. An additional RmRE has been proposed at the 5' end of the genome, facilitating nuclear export of the unspliced gRNA, whereas the 3' RmRE could facilitate translation of all other mRNAs, including gRNA.

RESULTS

To address this hypothesis, a series of mutations were introduced into a 24-nt region found exclusively in the unspliced gRNA. Mutant clones using MMTV or human cytomegalovirus promoters were tested in both transient and stable transfections to determine their effect on gRNA nuclear export, stability, and translation. Nuclear export of the gRNA was affected only in a small mutant subset in stably transfected Jurkat T cells. Quantitative real-time RT-PCR of actinomycin D-treated cells expressing MMTV revealed that multiple mutants were severely compromised for RNA expression and stability. Both genomic and spliced nuclear RNAs were reduced, leading to abrogation of Gag and Env protein expressed from unspliced and spliced mRNAs, respectively. RT-PCRs with multiple primer pairs indicated failure to elongate genomic MMTV transcripts beyond ~500 nt compared to the wild type in a cell line-dependent manner.

CONCLUSIONS

MMTV contains a novel cis-acting element downstream of the major splice donor critical for facilitating MMTV gRNA elongation and stability. Presence of a mirror repeat within the element may represent important viral/host factor binding site(s) within MMTV gRNA.

Changes in blood parameters induced by experimental jaagsiekte sheep retrovirus infection

The aim of the study was to assess the changes of blood parameters in 12 three-week-old Polish Merino sheep subjected to experimental jaagsiekte sheep retrovirus (JSRV) infection.

Material and Methods: Haematological (WBC with leukocyte subpopulations: GRA, LYM, MID, and RBC, MCV, MCH, MCHC, HGB, HCT, PLT, and MPV) and biochemical blood parameters (acid/base balance, cation/anion content, and gasometry) were determined in blood samples collected one month after JSRV infection, then at four-week intervals for five consecutive months.

Results: A decrease in RBC, HCT, MCV, PLT, MPV, and LYM values in comparison with controls was found in the last month of observation. On the other hand, at the same time, an increase in HGB, MCH, MCHC, WBC, MID, and GRA indices was observed. Moreover, at the end of experiment blood gasometric indices such as pCO2, HCO3, and tCO2, and Na and K ion concentrations were higher in the affected lambs than in the healthy animals. The pH values of the challenged animals exhibited less alkaline character than in the case of controls, which was associated with a decrease in O2% saturation. However, the majority of differences between JSRV inoculated and control groups was not statistically significant.

Conclusion: The observed changes in the examined blood parameters can be considered as prodromal symptoms in the preclinical phase of adenocarcinoma development associated with JSRV infection.

Seroconversion of sheep experimentally infected with enzootic nasal tumor virus

BACKGROUND

Enzootic nasal tumor virus (ENTV-1) is an exogenous betaretrovirus of sheep that transforms epithelial cells lining the ethmoid turbinates leading to a disease called enzootic nasal adenocarcinoma (ENA). A unique feature of ENA is the apparent absence of a specific humoral immune response to the virus, despite the highly productive infection in nasal tumors. The sheep genome contains approximately 27 copies of endogenous ovine betaretroviral sequences (enJSRVs) and expression of enJSRVs in the ovine placenta and uterine endometrium throughout gestation is thought to induce immunological tolerance to exogenous ovine betaretroviruses, a factor that may influence the likelihood of exogenous ENTV infection and disease outcome. Nevertheless, we recently demonstrated the presence of neutralizing antibodies directed against the ENTV-1 envelope glycoprotein in sheep naturally exposed to ENTV-1.

FINDINGS

Here, we employed an ENTV-1 envelope glycoprotein surface subunit specific ELISA and a virus neutralization assay to monitor serum antibody responses to ENTV-1 in a group of lambs experimentally infected with ENTV-1 virus containing filtered ENA tumor homogenate. Seroconversion and development of neutralizing antibodies was detected in one of six experimentally infected lambs.

CONCLUSIONS

Our results demonstrate that sheep can respond immunologically and seroconvert following ENTV-1 infection suggesting that anti-viral immune responses may play a role in the development of ENA.

"Ménage à Trois": the evolutionary interplay between JSRV, enJSRVs and domestic sheep

Sheep betaretroviruses represent a fascinating model to study the complex evolutionary interplay between host and pathogen in natural settings. In infected sheep, the exogenous and pathogenic Jaagsiekte sheep retrovirus (JSRV) coexists with a variety of highly related endogenous JSRVs, referred to as enJSRVs. During evolution, some of them were co-opted by the host as they fulfilled important biological functions, including placental development and protection against related exogenous retroviruses. In particular, two enJSRV loci, enJS56A1 and enJSRV-20, were positively selected during sheep domestication due to their ability to interfere with the replication of related competent retroviruses. Interestingly, viruses escaping these transdominant enJSRVs have recently emerged, probably less than 200 years ago. Overall, these findings suggest that in sheep the process of endogenization is still ongoing and, therefore, the evolutionary interplay between endogenous and exogenous sheep betaretroviruses and their host has not yet reached an equilibrium.

The sheep tetherin paralog oBST2B blocks envelope glycoprotein incorporation into nascent retroviral virions

Bone marrow stromal cell antigen 2 (BST2) is a cellular restriction factor with a broad antiviral activity. In sheep, the BST2 gene is duplicated into two paralogs termed oBST2A and oBST2B. oBST2A impedes viral exit of the Jaagsiekte sheep retroviruses (JSRV), most probably by retaining virions at the cell membrane, similar to the "tethering" mechanism exerted by human BST2. In this study, we provide evidence that unlike oBST2A, oBST2B is limited to the Golgi apparatus and disrupts JSRV envelope (Env) trafficking by sequestering it. In turn, oBST2B leads to a reduction in Env incorporation into viral particles, which ultimately results in the release of virions that are less infectious. Furthermore, the activity of oBST2B does not seem to be restricted to retroviruses, as it also acts on vesicular stomatitis virus glycoproteins. Therefore, we suggest that oBST2B exerts antiviral activity using a mechanism distinct from the classical tethering restriction observed for oBST2A.

IMPORTANCE

BST2 is a powerful cellular restriction factor against a wide range of enveloped viruses. Sheep possess two paralogs of the BST2 gene called oBST2A and oBST2B. JSRV, the causative agent of a transmissible lung cancer of sheep, is known to be restricted by oBST2A. In this study, we show that unlike oBST2A, oBST2B impairs the normal cellular trafficking of JSRV envelope glycoproteins by sequestering them within the Golgi apparatus. We also show that oBST2B decreases the incorporation of envelope glycoprotein into JSRV viral particles, which in turn reduces virion infectivity. In conclusion, oBST2B exerts a novel antiviral activity that is distinct from those of BST2 proteins of other species.

Ovine pulmonary adenocarcinoma in slaughtered sheep: a pathological and polymerase chain reaction study

Ovine pulmonary adenocarcinoma (OPA) is a contagious tumour in sheep caused by jaagsiekte sheep retrovirus (JSRV). This tumour originates from the pneumocyte type II and Clara cells and grossly appears as hard, prominent nodules in different lobes. The clinical signs of the disease are similar to those of other chronic respiratory diseases and are not pathogonomic. Therefore, post mortem examinations and histopathological studies are the most reliable ways to diagnose OPA, particularly subclinical cases of this neoplasm. In this study, out of 1000 sheep lungs grossly inspected, 50 animals were suspected of OPA. The suspected lungs as well as 25 apparently normal lungs were examined by histopathological and PCR methods. The proviral DNA was detected in 1/25 apparently normal lungs and 8/50 of the suspected lungs and subsequently confirmed by histopathological studies. The PCR-positive lung samples from five sheep revealed lesions of 'atypical' OPA and those from three sheep showed the 'classic' form of the disease. The tumours were multifocal and the masses were distributed throughout the cranioventral and diaphragmatic lung lobes. The stroma of the tumours in the atypical cases was more severely affected with inflammatory cell infiltration and connective tissue proliferation. The histopathological characteristics of maedi including hyperplasia of the perivascular and peribronchiolar lymphoid cells, interstitial lymphoplasmacytic infiltration and smooth muscle hyperplasia were also associated with OPA, especially the atypical form of this adenocarcinoma. Atypical OPA was more prevalent than the classic form. Geographic and climatic conditions, duration of exposure to the virus and the immune status of individual animals might be responsible for the differences between the two pathological entities of OPA.

Diagnosis and phylogenetic analysis of ovine pulmonary adenocarcinoma in China

Ovine pulmonary adenocarcinoma (OPA) is a lung tumor of sheep caused by jaagsiekte sheep retrovirus (JSRV). OPA is common in sheep, and it is most commonly observed in China. Without preventative vaccines and serological diagnostic tools for assay of OPA, identification of JSRV based on reverse transcription polymerase chain reaction (RT-PCR) is very important for prevention and control measures for OPA in practice management. In this study, the diagnosis of OPA was made from analysis of clinical signs, pathological observations, JSRV-like particle discovery, and RT-PCR of the target env gene. The phylogenetic analysis showed that the China Shandong (SD) strain studied in this article belonged to exogenous JSRV, and it was very similar to 92k3, which was isolated from sheep in the Kenya (Y18305). The current study reported a severe outbreak of OPA in Shandong Province, China. The observations could offer a comparative view of the env gene of JSRV.

Structural and functional comparisons of retroviral envelope protein C-terminal domains: still much to learn

Retroviruses are a family of viruses that cause a broad range of pathologies in animals and humans, from the apparently harmless, long-term genomic insertion of endogenous retroviruses, to tumors induced by the oncogenic retroviruses and acquired immunodeficiency syndrome (AIDS) resulting from human immunodeficiency virus infection. Disease can be the result of diverse mechanisms, including tumorigenesis induced by viral oncogenes or immune destruction, leading to the gradual loss of CD4 T-cells. Of the virally encoded proteins common to all retroviruses, the envelope (Env) displays perhaps the most diverse functionality. Env is primarily responsible for binding the cellular receptor and for effecting the fusion process, with these functions mediated by protein domains localized to the exterior of the virus. The remaining C-terminal domain may have the most variable functionality of all retroviral proteins. The C-terminal domains from three prototypical retroviruses are discussed, focusing on the different structures and functions, which include fusion activation, tumorigenesis and viral assembly and lifecycle influences. Despite these genetic and functional differences, however, the C-terminal domains of these viruses share a common feature in the modulation of Env ectodomain conformation. Despite their differences, perhaps each system still has information to share with the others.

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.

Jaagsiekte sheep retrovirus and enzootic nasal tumor virus promoters drive gene expression in all airway epithelial cells of mice but only induce tumors in the alveolar region of the lungs

Jaagsiekte sheep retrovirus (JSRV) induces tumors in the distal airways of sheep and goats, while the closely related enzootic nasal tumor virus type 1 (ENTV-1) and ENTV-2 induce tumors in the nasal epithelium of sheep and goats, respectively. When expressed using a strong Rous sarcoma virus promoter, the envelope proteins of these viruses induce tumors in the respiratory tract of mice, but only in the distal airway. To examine the role of the retroviral long terminal repeat (LTR) promoters in determining tissue tropism, adeno-associated virus (AAV) vectors expressing alkaline phosphatase under the control of the JSRV, ENTV-1, or ENTV-2 LTRs were generated and administered to mice. The JSRV LTR was active in all airway epithelial cells, while the ENTV LTRs were active in the nasal epithelium and alveolar type II cells but poorly active in tracheal and bronchial epithelial cells. When vectors were administered systemically, the ENTV-1 and -2 LTRs were inactive in major organs examined, whereas the JSRV showed high-level activity in the liver. When a putative transcriptional enhancer from the 3' end of the env gene was inserted upstream of the JSRV and ENTV-1 LTRs in the AAV vectors, a dramatic increase in transgene expression was observed. However, intranasal administration of AAV vectors containing any combination of ENTV or JSRV LTRs and Env proteins induced tumors only in the lower airway. Our results indicate that mice do not provide an adequate model for nasal tumor induction by ENTV despite our ability to express genes in the nasal epithelium.

Jaagsiekte sheep retrovirus biology and oncogenesis

Jaagsiekte sheep retrovirus (JSRV) is the causative agent of a lung cancer in sheep known as ovine pulmonary adenocarcinoma (OPA). The disease has been identified around the world in several breeds of sheep and goats, and JSRV infection typically has a serious impact on affected flocks. In addition, studies on OPA are an excellent model for human lung carcinogenesis. A unique feature of JSRV is that its envelope (Env) protein functions as an oncogene. The JSRV Env-induced transformation or oncogenesis has been studied in a variety of cell systems and in animal models. Moreover, JSRV studies have provided insights into retroviral genomic RNA export/expression mechanisms. JSRV encodes a trans-acting factor (Rej) within the env gene necessary for the synthesis of Gag protein from unspliced viral RNA. This review summarizes research pertaining to JSRV-induced pathogenesis, Env transformation, and other aspects of JSRV biology.

Interplay between ovine bone marrow stromal cell antigen 2/tetherin and endogenous retroviruses

Endogenous betaretroviruses (enJSRVs) of sheep are expressed abundantly in the female reproductive tract and play a crucial role in conceptus development and placental morphogenesis. Interestingly, the colonization of the sheep genome by enJSRVs is likely still ongoing. During early pregnancy, enJSRV expression correlates with the production of tau interferon (IFNT), a type I IFN, by the developing conceptus. IFNT is the pregnancy recognition signal in ruminants and possesses potent antiviral activity. In this study, we show that IFNT induces the expression of bone marrow stromal cell antigen 2 (BST2) (also termed CD317/tetherin) both in vitro and in vivo. The BST2 gene is duplicated in ruminants. Transfection assays found that ovine BST2 proteins (oBST2A and oBST2B) block release of viral particles produced by intact enJSRV loci and of related exogenous and pathogenic jaagsiekte sheep retrovirus (JSRV). Ovine BST2A appears to restrict enJSRVs more efficiently than oBST2B. In vivo, the expression of BST2A/B and enJSRVs in the endometrium increases after day 12 and remains high between days 14 and 20 of pregnancy. In situ hybridization analyses found that oBST2A is expressed mainly in the endometrial stromal cells but not in the luminal and glandular epithelial cells, in which enJSRVs are highly expressed. In conclusion, enJSRVs may have coevolved in the presence of oBST2A/B by being expressed in different cellular compartments of the same organ. Viral expression in cells unable to express BST2 may be one of the mechanisms used by retroviruses to escape restriction.

Full-length genome sequence analysis of enzootic nasal tumor virus reveals an unusually high degree of genetic stability

Enzootic nasal tumor virus (ENTV) is a betaretrovirus of sheep (ENTV-1) and goats (ENTV-2) associated with neoplastic transformation of epithelial cells of the ethmoid turbinate. Confirmation of the role of ENTV in the pathogenesis of enzootic nasal adenocarcinoma (ENA) has yet to be resolved due to the lack of an infectious molecular clone and the inability to culture the virus. Very little is known about the prevalence of this disease, particularly in North America, and only one full-length sequence is available for each of ENTV-1 and ENTV-2. In order to understand the molecular evolution of ENTV-1, the full-length genome sequence of ten ENTV-1 proviruses derived from clinical samples of ENA isolated from conventionally reared sheep in Canada and the United States was determined. The North American ENTV-1 (ENTV-1(NA)) genomes shared greater than 96% sequence identity with the European ENTV-1 sequence (ENTV-1(EU)). Most of the amino acid differences were found in Orf-x, which in the corresponding ENTV-1(EU) genome is truncated by 44 amino acids. Apart from Orf-x, the long terminal repeat (LTR) is where the majority of differences between ENTV-1(NA) and ENTV-1(EU) reside. Overall, there was an unusually high degree of amino acid conservation among the isolates suggesting that ENTV-1 is under stabilizing selection and K(a)/K(s) ratios calculated for each of the viral genes support this hypothesis. The unusually high degree of genetic stability of the ENTV-1 genome enabled us to develop a hemi-nested PCR assay for detection of ENTV-1 in clinical samples. Additionally, multiple nasal tumor cell clones were established and while most had lost the provirus by passage 5; one polyclonal line retained the provirus and attempts are being made to culture these cells. These tumor cells, the first of their kind, may provide a system for studying ENTV-1 in vitro. This work represents an important step in the study of ENTV and sets the foundation for the construction of an infectious molecular clone of ENTV-1.

The signal peptide of a simple retrovirus envelope functions as a posttranscriptional regulator of viral gene expression

Retroviruses use different strategies to regulate transcription and translation and exploit the cellular machinery involved in these processes. This study shows that the signal peptide of the envelope glycoprotein (Env) of Jaagsiekte sheep retrovirus (JSRV) plays a major role in posttranscriptional viral gene expression. Expression of the JSRV Env in trans increases viral particle production by mechanisms dependent on (i) its leader sequence, (ii) an intact signal peptide cleavage site, (iii) a cis-acting RNA-responsive element located in the viral genome, (iv) Crm1, and (v) B23. The signal peptide of the JSRV Env (JSE-SP) is 80 amino acid residues in length and contains putative nuclear localization and export signals, in addition to an arginine-rich RNA binding motif. JSE-SP localizes both in the endoplasmic reticulum and in the nucleus, where it colocalizes with nucleolar markers. JSE-SP is a multifunctional protein, as it moderately enhances nuclear export of unspliced viral mRNA and considerably increases viral particle release by favoring a posttranslational step of the replication cycle.

Immunohistochemical detection of pulmonary surfactant proteins and retroviral antigens in the lungs of sheep with pulmonary adenomatosis

The lungs and mediastinal and bronchial lymph nodes from 26 sheep with ovine pulmonary adenomatosis (OPA) were examined. Microscopically, the tumour was disseminated throughout the lungs and displayed acinar or papillary growth. The neoplastic cells were cuboidal or columnar with clear cytoplasm and a low mitotic rate. Retrovirus antigen (Jaagsiekte Sheep Retrovirus Capsid Protein, JSRV CA) was demonstrated in the cytoplasm of tumour cells in the lung and lymph nodes by immunohistochemistry. The neoplastic cells had more diffuse and intense expression of pulmonary surfactant protein-A (SP-A) compared with the expression of SP-B or SP-C. SP-A and SP-B expression was localized to the apical cytoplasm of the neoplastic cells, whereas SP-C was most strongly expressed in the perinuclear area of the tumour cells. In the lungs of two sheep, low numbers of tumour cells expressed Clara cell secretory protein (CCSP). The nuclei of the neoplastic epithelial cells and of the germinal centre lymphocytes within the peribronchiolar lymphoid tissue expressed the proliferating cell nuclear antigen (PCNA). CD3(+) T lymphocytes infiltrated the pulmonary tissue and surrounded the neoplastic foci. The results of this study demonstrate that JSRV continues to replicate in neoplastic cells after they have been transformed, and that the neoplastic cells produce pulmonary surfactant proteins. A local T-cell response occurs within affected lungs.

Coevolution of endogenous betaretroviruses of sheep and their host

Sheep betaretroviruses offer a unique model system to study the complex interaction between retroviruses and their host. Jaagsiekte sheep retrovirus (JSRV) is a pathogenic exogenous retrovirus and the causative agent of ovine pulmonary adenocarcinoma. The sheep genome contains at least 27 copies of endogenous retroviruses (enJSRVs) highly related to JSRV. enJSRVs have played several roles in the evolution of the domestic sheep as they are able to block the JSRV replication cycle and play a critical role in sheep conceptus development and placental morphogenesis. Available data strongly suggest that some dominant negative enJSRV proviruses (i.e. able to block JSRV replication) have been positively selected during evolution. Interestingly, viruses escaping the transdominant enJSRV loci have recently emerged (less than 200 years ago). Thus, endogenization of these retroviruses may still be occurring today. Therefore, sheep provide an exciting and unique system to study retrovirus-host coevolution. (Part of a multi-author review).

A large animal model to evaluate the effects of Hsp90 inhibitors for the treatment of lung adenocarcinoma

Ovine pulmonary adenocarcinoma (OPA) is a naturally occurring lung cancer of sheep caused by Jaagsiekte sheep retrovirus (JSRV). The JSRV envelope glycoprotein (Env) functions as a dominant oncoprotein in vitro and in vivo. In order to develop the basis for the use of OPA as a lung cancer model, we screened a variety of signal transduction inhibitors for their ability to block transformation by the JSRV Env. Most inhibitors were not effective in blocking JSRV Env-induced transformation. On the contrary, various Hsp90 inhibitors efficiently blocked JSRV transformation. This phenomenon was at least partly due to Akt degradation, which is activated in JSRV-transformed cells. Hsp90 was found expressed in tumor cells of sheep with naturally occurring OPA. In addition, Hsp90 inhibitors specifically inhibited proliferation of immortalized and moreover primary cells derived from OPA tumors. Thus, OPA could be used as a large animal model for comprehensive studies investigating the effects of Hsp90 inhibitors in lung adenocarcinoma.

Jaagsiekte Sheep Retrovirus (JSRV): from virus to lung cancer in sheep

Jaagsiekte Sheep Retrovirus (JSRV) is a betaretrovirus infecting sheep. This virus is responsible for a pulmonary adenocarcinoma, by transformation of epithelial cells from the bronchioli and alveoli. This animal cancer is similar to human bronchioloalveolar cancer (BAC), a specific form of human lung cancer for which a viral aetiology has not yet been identified. JSRV interacts with target cells through the membrane receptor Hyal2. The JSRV genome is simple and contains no recognised oncogene. It is now well established that the viral envelope protein is oncogenic by itself, via the cytoplasmic domain of the transmembrane glycoprotein and some domains of the surface glycoprotein. Activation of the PI3K/Akt and MAPK pathways participates in the envelope-induced transformation. Tumour development is associated with telomerase activation. This review will focus on the induction of cancer by JSRV.

Expression of the jaagsiekte sheep retrovirus envelope glycoprotein is sufficient to induce lung tumors in sheep

Jaagsiekte sheep retrovirus (JSRV) is the causative agent of ovine pulmonary adenocarcinoma (OPA). The expression of the JSRV envelope (Env) alone is sufficient to transform a variety of cell lines in vitro and induce lung cancer in immunodeficient mice. In order to determine the role of the JSRV Env in OPA tumorigenesis in sheep, we derived a JSRV replication-defective virus (JS-RD) which expresses env under the control of its own long terminal repeat (LTR). JS-RD was produced by transiently transfecting 293T cells with a two plasmid system, involving (i) a packaging plasmid, with the putative JSRV packaging signal deleted, expressing the structural and enzymatic proteins Gag, Pro, and Pol, and (ii) a plasmid which expresses env in trans for JS-RD particles and provides the genomes necessary to deliver JSRV env upon infection. During the optimization of the JS-RD system we determined that both R-U5 (in the viral 5' LTR) and the env region are important for JSRV particle production. Two independent experimental transmission studies were carried out with newborn lambs. Four of five lambs inoculated with JS-RD showed OPA lesions in the lungs at various times between 4 and 12 months postinoculation. Abundant expression of JSRV Env was detected in tumor cells of JS-RD-infected animals and PCR assays confirmed the presence of the deleted JS-RD genome. These data strongly suggest that the JSRV Env functions as a dominant oncoprotein in the natural immunocompetent host and that JSRV can induce OPA in the absence of viral spread.

Mouse mammary tumor virus encodes a self-regulatory RNA export protein and is a complex retrovirus

Mouse mammary tumor virus (MMTV) has been classified as a simple retrovirus with two accessory genes, dut and sag. Cloned MMTV proviruses carrying a trimethoprim (trim) cassette in the envelope gene were defective for Gag protein production and the nuclear export of unspliced gag-pol RNA. Complementation experiments indicated that a trans-acting product was responsible for the Gag defect of such mutants. Analysis of MMTV-infected cells revealed the presence of a novel, doubly spliced RNA that encodes a putative product of 301 amino acids. Overexpression of cDNA from this RNA increased Gag levels from env mutant proviruses or reporter gene expression from unspliced mRNAs and allowed detection of a 33-kDa protein product, which has been named regulator of export of MMTV mRNA, or Rem. The Rem N terminus has motifs similar to the Rev-like export proteins of complex retroviruses, and mutation of the nuclear localization signal (NLS) abolished RNA export and detection within the nucleus. The Rem C terminus has few identifiable features, but removal of this domain increased Rem-mediated export, suggesting an autoregulatory function. A reporter vector developed from the 3' end of the MMTV provirus was Rem responsive and required both the presence of the MMTV env-U3 junction and a functional Crm1 pathway. The identification of a third accessory protein from a doubly spliced transcript suggests that MMTV is the first murine complex retrovirus to be documented. Manipulation of the MMTV genome may provide mouse models for human retroviral diseases, such as AIDS.

Multiple domains of the Jaagsiekte sheep retrovirus envelope protein are required for transformation of rodent fibroblasts

Jaagsiekte sheep retrovirus (JSRV) is an exogenous retrovirus of sheep that induces a contagious lung cancer, ovine pulmonary adenocarcinoma. We previously showed that the gene encoding JSRV envelope protein (Env) appears to function as an oncogene, since it can transform mouse NIH 3T3 cells. The cytoplasmic tail of the Env transmembrane protein (TM) is necessary for the transformation. However, previous experiments did not exclude the involvement of the Env surface protein (SU) in transformation. In this study, we created a series of nested deletion mutants through the SU domain and assessed their ability to transform rodent fibroblasts. All SU deletion mutants downstream of the predicted signal peptide were unable to transform murine NIH 3T3 or rat 208F cells. Transport to the plasma membrane of selected deleted Env proteins was confirmed by confocal immunofluorescence microscopy of hemagglutinin-tagged versions. Additional sequential SU deletion mutants lacking 50-amino-acid (aa) blocks throughout SU also were unable to transform. Furthermore, minimal insertion mutants of two amino acids (Leu/Gln) at various positions in SU also abolished transformation. These data indicate that domains in SU facilitate efficient JSRV transformation. This could reflect a necessity of SU for appropriate configuration of the Env protein or independent activation by SU of a signaling pathway necessary for transformation. Complementation between SU and TM mutants for transformation supported the latter hypothesis. Cotransfection with DeltaGP Y590F (mutant in the TM cytoplasmic tail) with DeltaGP SUDelta103-352 (lacking most of SU) resulted in efficient transformation. The resulting transformants showed evidence for the presence and expression of both mutant plasmids.