A novel exogenous retrovirus sequence identified in humans

Evolutionary studies on the betaretrovirus RERV-H in the Leporidae family reveal an endogenization in the ancestor of Oryctolagus, Bunolagus and Pentalagus at 9 million years ago

RERV-H was first identified in human tissues and mistaken for a human exogenous retrovirus. However, the integration sites carried by this virus showed that it was instead a European rabbit (Oryctolagus cuniculus) endogenous retrovirus. The first clones retrieved from European rabbit samples represented defective proviruses, although estimation of proviral copy numbers found in the European rabbit genome ranged from hundreds to thousands. Screening for the presence of RERV-H showed the absence of the virus in two other lagomorphs, pika (Ochotona) and hares (Lepus), which diverged from rabbits about 35 and 12 million years ago, respectively. Using a PCR-based approach, samples of seven different Lagomorph genera were tested for the presence of RERV-H. It was possible to amplify a proviral fragment corresponding to RNaseH from Oryctolagus, Bunolagus and Pentalagus genomic samples. The amplification of proviral DNA in species other than Oryctolagus revealed that this virus was endogenized in their common ancestor, roughly 9 million years ago. Using the European rabbit genome sequence OryCun2.0, it was possible to find multiple copies spread throughout the genome and several complete proviral genomes were retrieved. Some copies contained full open reading frames for all viral components. The lack of a complete genome in the other Lagomorph species did not allow further analyses of the provirus, although more deleterious mutations were found in Bunolagus and Pentalagus than in Oryctolagus RNaseH-amplified sequences. To what extent RERV-H and other endogenous viruses might have had an impact on the rabbit genome and its immune system remains elusive.

Tales from the crypt and coral reef: the successes and challenges of identifying new herpesviruses using metagenomics

Herpesviruses are ubiquitous double-stranded DNA viruses infecting many animals, with the capacity to cause disease in both immunocompetent and immunocompromised hosts. Different herpesviruses have different cell tropisms, and have been detected in a diverse range of tissues and sample types. Metagenomics—encompassing viromics—analyses the nucleic acid of a tissue or other sample in an unbiased manner, making few or no prior assumptions about which viruses may be present in a sample. This approach has successfully discovered a number of novel herpesviruses. Furthermore, metagenomic analysis can identify herpesviruses with high degrees of sequence divergence from known herpesviruses and does not rely upon culturing large quantities of viral material. Metagenomics has had success in two areas of herpesvirus sequencing: firstly, the discovery of novel exogenous and endogenous herpesviruses in primates, bats and cnidarians; and secondly, in characterizing large areas of the genomes of herpesviruses previously only known from small fragments, revealing unexpected diversity. This review will discuss the successes and challenges of using metagenomics to identify novel herpesviruses, and future directions within the field.

Expression of human cationic trypsinogen (PRSS1) in murine acinar cells promotes pancreatitis and apoptotic cell death

Hereditary pancreatitis (HP) is an autosomal dominant disease that displays the features of both acute and chronic pancreatitis. Mutations in human cationic trypsinogen (PRSS1) are associated with HP and have provided some insight into the pathogenesis of pancreatitis, but mechanisms responsible for the initiation of pancreatitis have not been elucidated and the role of apoptosis and necrosis has been much debated. However, it has been generally accepted that trypsinogen, prematurely activated within the pancreatic acinar cell, has a major role in the initiation process. Functional studies of HP have been limited by the absence of an experimental system that authentically mimics disease development. We therefore developed a novel transgenic murine model system using wild-type (WT) human PRSS1 or two HP-associated mutants (R122H and N29I) to determine whether expression of human cationic trypsinogen in murine acinar cells promotes pancreatitis. The rat elastase promoter was used to target transgene expression to pancreatic acinar cells in three transgenic strains that were generated: Tg(Ela-PRSS1)NV, Tg(Ela-PRSS1*R122H)NV and Tg(Ela-PRSS1*N29I)NV. Mice were analysed histologically, immunohistochemically and biochemically. We found that transgene expression is restricted to pancreatic acinar cells and transgenic PRSS1 proteins are targeted to the pancreatic secretory pathway. Animals from all transgenic strains developed pancreatitis characterised by acinar cell vacuolisation, inflammatory infiltrates and fibrosis. Transgenic animals also developed more severe pancreatitis upon treatment with low-dose cerulein than controls, displaying significantly higher scores for oedema, inflammation and overall histopathology. Expression of PRSS1, WT or mutant, in acinar cells increased apoptosis in pancreatic tissues and isolated acinar cells. Moreover, studies of isolated acinar cells demonstrated that transgene expression promotes apoptosis rather than necrosis. We therefore conclude that expression of WT or mutant human PRSS1 in murine acinar cells induces apoptosis and is sufficient to promote spontaneous pancreatitis, which is enhanced in response to cellular insult.

Viruses and salivary gland disease (SGD): lessons from HIV SGD

Viral infections are often associated with salivary gland pathology. Here we review the pathogenesis of HIV-associated salivary gland disease (HIV-SGD), a hallmark of diffuse infiltrative lymphocytosis syndrome. We investigate the presence and contributions of viral diseases to the pathogenesis of salivary gland diseases, particularly HIV-SGD. We have detected BK viral shedding in the saliva of HIV-SGD patients consistent with viral infection and replication, suggesting a role for oral transmission. For further investigation of BKV pathogenesis in salivary glands, an in vitro model of BKV infection is described. Submandibular (HSG) and parotid (HSY) gland salivary cell lines were capable of permissive BKV infection, as determined by BKV gene expression and replication. Analysis of these data collectively suggests the potential for a BKV oral route of transmission and salivary gland pathogenesis within HIV-SGD.

Is Sjögren's syndrome a retroviral disease?

Circumstantial evidence suggests that retroviruses play a role in the pathogenesis of Sjögren's syndrome. Such evidence, derived from studies of patients with Sjögren's syndrome, includes the following: the presence of serum antibodies cross-reactive with retroviral Gag proteins; the occurrence of reverse transcriptase activity in salivary glands; the detection of retroviral antigens, retrovirus-like particles, or novel retroviral sequences in salivary glands; the occurrence of Sjögren's syndrome-like illnesses in patients having confirmed systematic infections with retroviruses such as human immunodeficiency virus-1 (HIV-1) and human T lymphotropic virus type 1; and the beneficial effect of anti-retroviral treatment on the occurrence of HIV-1-associated sicca syndrome. Additional evidence is provided by animal models.

Broadly reactive pan-paramyxovirus reverse transcription polymerase chain reaction and sequence analysis for the detection of Canine distemper virus in a case of canine meningoencephalitis of unknown etiology

Despite the immunologic protection associated with routine vaccination protocols, Canine distemper virus (CDV) remains an important pathogen of dogs. Antemortem diagnosis of systemic CDV infection may be made by reverse transcription polymerase chain reaction (RT-PCR) and/or immunohistochemical testing for CDV antigen; central nervous system infection often requires postmortem confirmation via histopathology and immunohistochemistry. An 8-month-old intact male French Bulldog previously vaccinated for CDV presented with multifocal neurologic signs. Based on clinical and postmortem findings, the dog's disease was categorized as a meningoencephalitis of unknown etiology. Broadly reactive, pan-paramyxovirus RT-PCR using consensus-degenerate hybrid oligonucleotide primers, combined with sequence analysis, identified CDV amplicons in the dog's brain. Immunohistochemistry confirmed the presence of CDV antigens, and a specific CDV RT-PCR based on the phosphoprotein gene identified a wild-type versus vaccinal virus strain. This case illustrates the utility of broadly reactive PCR and sequence analysis for the identification of pathogens in diseases with unknown etiology.

Primary Sjogren's syndrome: too dry and too tired

Chronic fatigue is one of the most prevalent and debilitating symptoms in primary SS (pSS). Approximately 70% of pSS patients suffer from disabling fatigue, which is associated with reduced health-related quality of life. In this article, we review the instruments used for evaluating pSS-related fatigue, our current understanding of the underlying psychosocial and physiological mechanisms of fatigue in pSS and the therapeutic strategies that have been studied in the management of fatigue in pSS.

Conventional and molecular diagnostic testing for the acute neurologic patient

OBJECTIVE

The aim of this review is to describe and evaluate both conventional and molecular diagnostic testing utilized in dogs and cats with acute neurologic diseases. Various types of polymerase chain reaction (PCR) are explored along with novel molecular diagnostic testing that ultimately may prove useful in the critical care setting.

DATA SOURCES

PUBMED was searched to obtain relevant references material using keywords: 'canine OR feline meningitis AND meningoencephalitis,''feline infectious peritonitis,''canine distemper,''canine OR feline AND toxoplasma,''canine neospora,''canine OR feline AND rickettsia,''granulomatous meningoencephalitis,''steroid responsive meningitis arteritis,''necrotizing encephalitis,''novel neurodiagnostics,''canine OR feline AND CNS borrelia,''canine OR feline AND CNS bartonella,''canine OR feline AND CNS fungal,''nested OR multiplex OR degenerate OR consensus OR CODEHOP AND PCR.' Research findings from the authors' laboratory and current veterinary textbooks also were utilized.

HUMAN DATA SYNTHESIS

Molecular diagnostic testing including conventional, real-time, and consensus and degenerate PCR and microarray analysis are utilized routinely for the antemortem diagnosis of infectious meningoencephalitis (ME) in humans. Recently, PCR using consensus degenerate hybrid primers (CODEHOP) has been used to identify and characterize a number of novel human viruses.

VETERINARY DATA SYNTHESIS

Molecular diagnostic testing such as conventional and real-time PCR aid in the diagnosis of several important central nervous system infectious agents including canine distemper virus, Toxoplasma gondii, Neospora caninum, rickettsial species, and others. Recently, broadly reactive consensus and degenerate PCR reactions have been applied to canine ME including assays for rickettsial organisms, Borrelia spp. and Bartonella spp., and various viral families.

CONCLUSIONS

In the acute neurologic patient, there are several key infectious diseases that can be pursued by a combination of conventional and molecular diagnostic testing. It is important that the clinician understands the utility, as well as the limitations, of the various neurodiagnostic tests that are available.

Sensitive and broadly reactive reverse transcription-PCR assays to detect novel paramyxoviruses

We have developed a set of reverse transcription-PCR assays for the detection and identification of known and novel paramyxoviruses in clinical specimens. Primers were designed from the conserved motifs of the polymerase pol gene sequences to detect members of the Paramyxovirinae or Pneumovirinae subfamily or groups of genera within the Paramyxovirinae subfamily. The consensus-degenerate hybrid oligonucleotide primer design and seminested or nested PCR assay design were used to enhance the breadth of reactivity and sensitivity of the respective assays. Using expressed RNA and 10-fold dilution series of virus-infected tissue culture isolates from different members of the family or genera, these assays were able to detect on average between 100 and 500 copies of template RNA. The assays were specific to the respective group of genera or subfamily viruses. This set of primers enhances our ability to look for novel viruses in outbreaks and diseases of unknown etiology.

Human RNA "rumor" viruses: the search for novel human retroviruses in chronic disease

Retroviruses are an important group of pathogens that cause a variety of diseases in humans and animals. Four human retroviruses are currently known, including human immunodeficiency virus type 1, which causes AIDS, and human T-lymphotropic virus type 1, which causes cancer and inflammatory disease. For many years, there have been sporadic reports of additional human retroviral infections, particularly in cancer and other chronic diseases. Unfortunately, many of these putative viruses remain unproven and controversial, and some retrovirologists have dismissed them as merely "human rumor viruses." Work in this field was last reviewed in depth in 1984, and since then, the molecular techniques available for identifying and characterizing retroviruses have improved enormously in sensitivity. The advent of PCR in particular has dramatically enhanced our ability to detect novel viral sequences in human tissues. However, DNA amplification techniques have also increased the potential for false-positive detection due to contamination. In addition, the presence of many families of human endogenous retroviruses (HERVs) within our DNA can obstruct attempts to identify and validate novel human retroviruses. Here, we aim to bring together the data on "novel" retroviral infections in humans by critically examining the evidence for those putative viruses that have been linked with disease and the likelihood that they represent genuine human infections. We provide a background to the field and a discussion of potential confounding factors along with some technical guidelines. In addition, some of the difficulties associated with obtaining formal proof of causation for common or ubiquitous agents such as HERVs are discussed.

Persistent viral infection in primary Sjogren's syndrome: review and perspectives

Exocrine gland pathology in primary Sjogren's syndrome is characterized by destruction of acinar epithelial cells and chronic lymphocytic infiltrates surrounding ductal epithelial cells. These cells seem to be activated, as it is inferred by their immunophenotype. The cause of this activation and the chronic inflammatory response that targets epithelial cells remain unknown. Here, we will review the evidence pointing to a persistent viral infection as a probable cause of primary Sjogren's syndrome and discuss potential directions for future research.

Jaagsiekte sheep retrovirus is not detected in human lung adenocarcinomas expressing antigens related to the Gag polyprotein of betaretroviruses

A proportion of human lung adenocarcinomas (hLACs) express an antigen related to the major capsid protein (CA) of Jaagsiekte sheep retrovirus (JSRV), a Betaretrovirus that causes a transmissible lung cancer in sheep. In this study, we have investigated whether JSRV or related betaretroviruses are expressed in hLACs. Results obtained indicate that JSRV is not associated with human lung adenocarcinomas. However, a proportion of hLACs reacted positively in immunohistochemistry with antibodies specific towards different domains of the JSRV Gag suggesting that a bona fide retrovirus antigen could be expressed in these tumours. Further studies will be necessary to ascertain whether the detection of antigens cross-reacting with betaretrovirus Gag antisera in some hLACs is due to expression of a human endogenous retrovirus or, more unlikely, of an uncharacterized exogenous retrovirus.

Retinoic acid receptor beta silences human papillomavirus-18 oncogene expression by induction of de novo methylation and heterochromatinization of the viral control region

Retinoic acid receptor beta2 (RAR beta2) is often down-regulated during the multistep process to cervical cancer. In that way, its inhibitory function on the transcription factor AP-1, indispensable to maintain human papillomavirus (HPV) gene expression is relieved. Using HPV-18 positive HeLa cells as a model system, we show that ectopic expression of RAR beta2 is able to down-regulate HPV-18 transcription by selectively abrogating the binding of AP-1 to the viral regulatory region in a ligand-independent manner. This resulted in down-regulation of the viral mRNAs at the level of initiation of transcription. Decreased oncogene expression was accompanied by a re-induction of cell cycle inhibitory proteins such as p53, p21(CIP1), and p27(KIP) as well as by a cessation of cellular growth. Reduced transcriptional activity as a consequence of AP-1 reduction by selective c-Jun degradation apparently targets the HPV-18 regulatory region for epigenetic modification such as de novo methylation and nucleosomal condensation. This mechanism is otherwise counterbalanced by active and abundant viral transcription in malignant cells, because RAR beta2 itself becomes inactivated during cervical carcinogenesis. Hence, our study shows that the temporal co-existence of a potential repressor and viral oncoproteins is mutually exclusive and provides evidence of a cross-talk between a nuclear receptor, AP-1, and the epigenetic machinery.

Lack of detection of human retrovirus-5 proviral DNA in synovial tissue and blood specimens from individuals with rheumatoid arthritis or osteoarthritis

OBJECTIVE

Prior studies have suggested an association of human retrovirus 5 with rheumatoid arthritis. The purpose of this study was to determine if human retrovirus-5 proviral DNA is present in synovial tissue and blood specimens from patients with rheumatoid arthritis or osteoarthritis, or those without joint disease.

METHODS

Synovial tissue and whole blood from 75 patients with rheumatoid arthritis, 75 patients with osteoarthritis, and 50 patients without a primary arthritis diagnosis were assayed by real-time quantitative polymerase chain reaction (PCR) using primers that amplify a 186-bp fragment of human retrovirus-5 proviral DNA.

RESULTS

A total of 200 tissue specimens, 200 mononuclear cells, and 196 of 200 granulocyte specimens tested negative for human retrovirus-5 proviral DNA. No association between human retrovirus 5 and rheumatoid arthritis or osteoarthritis (P = 0.516) was identified. Granulocyte specimens from 4 patients, 2 with rheumatoid arthritis and 2 with osteoarthritis, yielded a low positive human retrovirus-5 proviral DNA signal (83-1,365 copies of human retrovirus-5 proviral DNA/ml blood).

CONCLUSION

Contrary to prior reports, we did not find an association between human retrovirus 5 and rheumatoid arthritis or osteoarthritis using a real-time PCR assay. Our findings are consistent with the recent finding that human retrovirus 5 is actually rabbit endogenous retrovirus H.

Loss of Net as Repressor Leads to Constitutive Increased c-fos Transcription in Cervical Cancer Cells

We have investigated the expression of c-fos in cervical carcinoma cells and in somatic cell hybrids derived therefrom. In malignant cells, c-fos was constitutively expressed even after serum starvation. Dissection of the c-fos promoter showed that expression was mainly controlled by the SRE motif, which was active in malignant cells, but repressed in their non-malignant counterparts. Constitutive SRE activity was not mediated by sustained mitogen-activated protein kinase activity but because of inefficient expression of the ternary complex factor Net, which was either very low or even barely discernible. Chromatin immunoprecipitation assays revealed that Net directly binds to the SRE nucleoprotein complex in non-tumorigenic cells, but not in malignant segregants. Small interfering RNA targeted against Net resulted in enhanced c-fos transcription, clearly illustrating its repressor function. Conversely, stable ectopic expression of Net in malignant cells negatively regulated endogenous c-fos, resulting in a disappearance of the c-Fos protein from the AP-1 transcription complex. These data indicate that loss of Net and constitutive c-fos expression appear to be a key event in the transformation of cervical cancer cells.

Association of human endogenous retroviruses with multiple sclerosis and possible interactions with herpes viruses

The hypothesis that human endogenous retroviruses (HERVs) play a role in autoimmune diseases is subject to increasing attention. HERVs represent both putative susceptibility genes and putative pathogenic viruses in the immune-mediated neurological disease multiple sclerosis (MS). Gammaretroviral HERV sequences are found in reverse transcriptase-positive virions produced by cultured mononuclear cells from MS patients, and they have been isolated from MS samples of plasma, serum and CSF, and characterised to some extent at the nucleotide, protein/enzyme, virion and immunogenic level. Two types of sequences, HERV-H and HERV-W, have been reported. No known HERV-H or HERV-W copy contains complete ORFs in all prerequisite genes, although several copies have coding potential, and several such sequences are specifically activated in MS, apparently resulting in the production of complete, competent virions. Increased antibody reactivity to specific Gammaretroviral HERV epitopes is found in MS serum and CSF, and cell-mediated immune responses have also been reported. Further, HERV-encoded proteins can have neuropathogenic effects. The activating factor(s) in the process resulting in protein or virion production may be members of the Herpesviridae. Several herpes viruses, such as HSV-1, VZV, EBV and HHV-6, have been associated with MS pathogenesis, and retroviruses and herpes viruses have complex interactions. The current understanding of HERVs, and specifically the investigations of HERV activation and expression in MS are the major subjects of this review, which also proposes to synergise the herpes and HERV findings, and presents several possible pathogenic mechanisms for HERVs in MS.

Ectopic expression of nonliganded retinoic acid receptor beta abrogates AP-1 activity by selective degradation of c-Jun in cervical carcinoma cells

Expression of the nuclear retinoic acid receptor beta2 (RARbeta2) gene is often disturbed in cervical carcinoma cells. One important mechanism by which RARbeta2 can exert growth inhibitory function is based on its ability to repress the AP-1 transcription factor in a ligand-dependent manner. Because less is known about the biological effects of RARbeta in the absence of ligand, the corresponding cDNA was stably introduced into HPV18-positive HeLa cervical carcinoma cells. In the present study we describe a novel mechanism by which AP-1 becomes inactivated. Constitutive expression of nonliganded RARbeta abrogated both AP-1 binding affinity and activity by a selective degradation of the c-Jun protein as major dimerization partner, without substitution by other members of the Jun family. Blockage of the proteasomal pathway completely rescued c-Jun and reconstituted the AP-1 function. Moreover, HeLa RARbeta2 clones treated either with tumor necrosis factor-alpha or transfected with a constitutive active upstream mitogen-activated protein kinase (MEKK1Delta) also resulted in c-Jun phosphorylation and restoration of AP-1 affinity and functionality similar to that found in nontransfected parental HeLa cells. These data revealed an important cross-talk between trans-repression of AP-1 and nonliganded RARbeta in human papillomavirus-positive cells. Because AP-1 activity was not irreversibly disturbed, but could be switched on through activation of the Jun N-terminal kinase pathway, a model for the transient activation of AP-1 even in the presence of RARbeta as repressor is suggested.

HDAC inhibitors trigger apoptosis in HPV-positive cells by inducing the E2F-p73 pathway

Histone deacetylase (HDAC) inhibitors induce an intrinsic type of apoptosis in human papillomavirus (HPV)-positive cells by disrupting the mitochondrial transmembrane potential (deltapsim). Loss of deltapsim was only detected in E7, but not in E6 oncogene-expressing cells. HDAC inhibition led to a time-dependent degradation of the pocket proteins pRb, p107 and p130, releasing 'free' E2F-1 following initial G1 arrest. Inhibition of proteasomal proteolysis, but not of caspase activity rescued pRb from degradation and functionally restored its inhibitory effect on the cyclin E gene, known to be suppressed by pRb-E2F-1 in conjunction with HDAC1. Using siRNA targeted against p53, E2F-1 still triggered apoptosis by inducing the E2F-responsive proapoptotic alpha- and beta-isoforms of p73. These data may determine future therapeutic strategies in which HDAC inhibitors can effectively eliminate HPV-positive cells by an apoptotic route that does not rely on the reactivation of the 'classical' p53 pathway through a preceding shut-off of viral gene expression.

Single-tube nested quantitative PCR: a rational and sensitive technique for detection of retroviral DNA. Application to RERV-H/HRV-5 and confirmation of its rabbit origin

It was reported earlier that a few patients suffering from non-Hodgkin's lymphoma had low amounts of DNA from the so-called fifth human exogenous retrovirus, HRV-5. A sensitive and rational method for large-scale screening for HRV-5 DNA was therefore developed. It is a single-tube nested quantitative PCR (stnQPCR), which uses two functionally isolated primer pairs and one probe target distinct from related endogenous retroviral sequences, yet encompassing known HRV-5 variation, allowing optimal use of sequence conservation. DNA from lymphoma, myeloma, and follicular dendritic cell lines was tested for HRV-5 positivity, as was DNA from whole blood of blood donors, non-Hodgkin's lymphoma and systemic lupus erythematosus patients, as well as DNA from lymph node biopsies of rheumatoid arthritis patients with lymphoma. One blood donor, one systemic lupus erythematosus patient, two previously known positive non-Hodgkin's lymphoma patients, and one rheumatoid arthritis lymphoma patient, came out positive. They had 24, 2, 148, 480 and 30 proviral copies per microg of DNA from PBMC or lymphoma tissue, respectively. During the completion of this work it was reported that HRV-5 is a rabbit endogenous retrovirus (RERV-H), and that HRV-5 positivity was due to presence of rabbit DNA. DNA from six RERV-H/HRV-5 positive samples was therefore retested. Three also contained rabbit mitochondrial DNA. A search for HRV-5 antibodies using synthetic peptides was negative in sera from three RERV-H/HRV-5 positive individuals, as well as in 144 other sera, according with a noninfectious origin of the RERV-H/HRV-5 DNA in human samples. A search for possible sources of rabbit DNA contamination was negative. Methods for prevention of PCR contamination were strictly adhered to. Three samples from RERV-H/HRV-5 positive individuals positive at the Uppsala laboratory were retested at one or two other laboratories, and all three were positive. Two other samples, which were positive in the Riga laboratory, were tested also in London and also found positive. One non-Hodgkin's lymphoma patient was RERV-H/HRV-5 positive in four consecutive samples, showing that positivity was a property of that patient. It is concluded that the stnQPCR developed to detect and quantify minute amounts of RERV-H/HRV-5 DNA is a principle which can be applied widely and HRV-5 is a RERV-H. Its presence in a few human blood samples could not be explained.

Pathogenesis of Sjögren's syndrome

The pathogenesis of Sjögren's syndrome is poorly understood. Genetic and environmental factors appear to contribute to the development of this syndrome. Viral infection is one of the most likely environmental factors. The primary lesion of Sjögren's syndrome is in the exocrine glands. A majority of the infiltrating cells in the lesion are CD(4+) CD45RO(+) memory T cells. Although antigen-presentation to T cells seems to occur in the exocrine tissues, these T cells are not fully activated. On the other hand, B cells comprise approximately 20% of the infiltrating cells, and several features of this syndrome are attributed to stimulated B cells. The presence of autoantibodies, such as anti-SS-A/Ro and SS-B/La antibodies, is one of the characteristic features and is associated with severe disorders. Some antibodies appear to play a direct pathogenic role, for example, in cases of congenital heart block and sicca symptoms. Chronic inflammation with possible T cell-dependent antigen stimulation appears to induce neoplastic transformation of lymphocytes.

Rabbit endogenous retrovirus-H encodes a functional protease

Recent studies have revealed that 'human retrovirus-5' sequences found in human samples belong to a rabbit endogenous retrovirus family named RERV-H. A part of the gag-pro region of the RERV-H genome was amplified by PCR from DNA in human samples and several forms of RERV-H protease were expressed in bacteria. The RERV-H protease was able to cleave itself from a precursor protein and was also able to cleave the RERV-H Gag polyprotein precursor in vitro whereas a form of the protease with a mutation engineered into the active site was inactive. Potential N- and C-terminal autocleavage sites were characterized. The RERV-H protease was sensitive to pepstatin A, showing it to be an aspartic protease. Moreover, it was strongly inhibited by PYVPheStaAMT, a pseudopeptide inhibitor specific for Mason-Pfizer monkey virus and avian myeloblastosis-associated virus. A structural model of the RERV-H protease was constructed that, together with the activity data, confirms that this is a retroviral aspartic protease.

Novel endogenous retrovirus in rabbits previously reported as human retrovirus 5

Human retrovirus 5 (HRV-5) represented a fragment of a novel retrovirus sequence identified in human RNA and DNA preparations. In this study, the genome of HRV-5 was cloned and sequenced and integration sites were analyzed. Using PCR and Southern hybridization, we showed that HRV-5 is not integrated into human DNA. A survey of other species revealed that HRV-5 is present in the genomic DNA of the European rabbit (Oryctolagus cuniculus) and belongs to an endogenous retrovirus family found in rabbits. The presence of rabbit sequences flanking HRV-5 proviruses in human DNA extracts suggested that rabbit DNA was present in our human extracts, and this was confirmed by PCR analysis that revealed the presence of rabbit mitochondrial DNA sequences in four of five human DNA preparations tested. The origin of the rabbit DNA and HRV-5 in human DNA preparations remains unclear, but laboratory contamination cannot explain the preferential detection of HRV-5 in inflammatory diseases and lymphomas reported previously. This is the first description of a retrovirus genome in rabbits, and sequence analysis shows that it is related to but distinct from A-type retroelements of mice and other rodents. The species distribution of HRV-5 is restricted to rabbits; other species, including other members of the order Lagomorpha, do not contain this sequence. Analysis of HRV-5 expression by Northern hybridization and reverse transcriptase PCR indicates that the virus is transcribed at a low level in many rabbit tissues. In light of these findings we propose that the sequence previously designated HRV-5 should now be denoted RERV-H (for rabbit endogenous retrovirus H).

Autoantibodies to human endogenous retrovirus-K are frequently detected in health and disease and react with multiple epitopes

A number of studies have found increased levels of antibodies to human endogenous retroviruses (HERVs) in autoimmune rheumatic diseases. It is not clear whether this immune response is driven by the HERV itself or by cross-reactions with an exogenous virus or an autoantigen. To address this question, we examined the antibody response to the Env protein of two closely related members of the HERV-K family, HERV-K10 and IDDMK1,222. By immunoblotting of recombinant proteins, antibodies were found in 32-47% of 84 sera from patients with autoimmune rheumatic disease, and 29% of 35 normal controls. Epitope mapping with overlapping 15mers identified multiple reactive peptides on both antigens, with one (GKTCPKEIPKGSKNT) containing immunodominant epitope(s). By ELISA, the median titre of antibody to this peptide was significantly increased in 39 patients with SLE compared to 39 healthy controls and 86 patients with other rheumatic diseases (P < 0.003). We have shown that there is a high frequency of IgG antibodies to HERV-K env sequences in human sera, both in health and autoimmune rheumatic disease, and that the response is to multiple epitopes. This supports the hypothesis that the autoimmune response to HERV-K is antigen-driven and may be an early stage in the chain of events that leads to tolerance breakdown to other autoantigens.

Endogenous retroviruses in systemic lupus erythematosus: candidate lupus viruses

Although the etiology of systemic lupus erythematosus (SLE) remains unclear, there is substantial circumstantial evidence that the development of SLE is dependent on environmental, genetic, and retroviral factors. SLE patients produce high titer antibodies to various retroviral proteins, including Gag, Env, and Nef of HIV and HTLV, in the absence of overt retroviral infection. We review the factors linking HERVs to SLE and consider the various processes utilized by endogenous retroviruses in the etiopathogenesis of SLE. In particular, we consider the role of HTLV-1-related endogenous sequence (HRES-1) in SLE. We propose that molecular mimicry between HRES-1 and the small ribonucleoprotein complex initiates the production of autoantibodies, leading to immune complex formation, complement fixation, and pathological tissue deposition.

The genetics of the target tissue in rheumatoid arthritis

The genetic mechanisms that are complementary in predisposing and then establishing disease are yet to be fully elucidated. During a lifetime, the genetic composition of the host is not only hereditary but undergoes rearrangements, integrations, and more subtle single-base pair alterations. These changes can be inconsequential or lead to aberrant and deleterious pathologic changes. In a complex multifactorial disease such as RA, the relative roles of the dynamic versus germline elements of the disease have yet to be fully determined. Further studies of large populations are likely to segregate out factors affecting specific ethnic, clinical, and genetic subgroups.

Restoration of p53 expression sensitizes human papillomavirus type 16 immortalized human keratinocytes to CD95-mediated apoptosis

To understand the function of the individual oncogenes of HPV16 in modulating the cellular response to apoptogenic signals, we used human keratinocytes immortalized with either E6, E7 or E6/E7 oncoproteins as model system. Applying CD95 antibodies or recombinant CD95 ligand, only the E7-immortalized cells underwent extensive apoptosis. In contrast, E6- and E6/E7-expressing keratinocytes were resistant. Dominance of E6 correlated with significant down-regulation of p53, c-Myc, p21 and Bcl-2. CD95 was found to be reduced in resistant HPV-positive cells, while there were no quantitative differences in expression levels of FADD, FLICE/caspase-8 or caspase-3. Notably, in contrast to primary human keratinocytes, all immortalized cells showed a general reduction of c-FLIP, an inhibitory protein which normally prevents unscheduled CD95-induced apoptosis. E6- and E6/E7-positive keratinocytes, however, can be sensitized to CD95 apoptosis by blocking proteasome-mediated proteolysis. CD95-resistant HPV-positive cells underwent apoptosis within 3-5 h upon co-incubation with MG132 and agonistic antibodies or CD95 ligand, which was preceded by a strong re-expression of p53 and c-Myc, but not of other half-life controlled proteins such as Bax or IkappaBalpha. Blockage of proteasomal activity alone did not result in apoptosis, although the same set of pro-apoptotic proteins was up-regulated. Performing similar experiments with cervical carcinoma cells expressing mutated p53 (C33a) or with p53-'null' lung carcinoma cells (H1299), no CD95 cell killing occurred even though c-Myc was strongly induced. These data indicate that the reduced bioavailability of p53 is a key-regulatory event in perturbation of CD95 signaling in HPV16 immortalized keratinocytes.

Disturbance of tumor necrosis factor alpha-mediated beta interferon signaling in cervical carcinoma cells

In the present study we show that malignant human papillomavirus (HPV)-positive cells lost their ability to synthesize endogenous beta interferon (IFN-beta) upon tumor necrosis factor alpha (TNF-alpha) treatment. IFN-beta transcription, however, was reinducible in nonmalignant HPV-positive cells, which was confirmed in functional protection assays against encephalomyocarditis virus or vesicular stomatitis virus infections. Addition of neutralizing antibodies against IFN-beta blocked the antiviral effect, excluding the possibility that other IFN types were involved. Conversely, both malignant and immortalized cells could be protected against viral cytolysis when either IFN-beta, IFN-alpha, or IFN-gamma was added exogenously. This indicates that only the cross talk between TNF-alpha and the IFN-beta pathways, and not IFN-alpha/beta and IFN-gamma signaling in general, is perturbed in cervical carcinoma cells. Notably, full virus protection was restricted exclusively to nonmalignant cells, indicating that the antiviral effect correlates with the growth-inhibitory and virus-suppressive properties of TNF-alpha. The IFN-regulatory factors IRF-1 and p48 (ISGF3gamma) emerged as key regulatory molecules in the differential IFN-beta response, since their transcription was either absent or only inefficiently enhanced in tumorigenic cells upon treatment with TNF-alpha. Inducibility of both genes, however, became reestablished in cervical carcinoma cells, which were complemented to nontumorigenicity after somatic cell hybridization. Complementation was paralleled by the entire reconstitution of cytokine-mediated IFN-beta expression and the ability of TNF-alpha to exert an antiviral state. In contrast, under conditions where tumor suppression was not accomplished upon somatic cell hybridization, neither expression of IRF-1, p48, and IFN-beta nor antiviral activity could be restored.

Use of muscarinic agonists in the treatment of Sjögren's syndrome

Two muscarinic agonists (pilocarpine and cevimeline) have recently been approved for the treatment of symptoms of xerostomia in Sjögren's syndrome (SS). These agents stimulate the M1 and M3 receptors present on salivary glands, leading to increased secretory function. The use of these agents emphasizes the importance of neuroendocrine mechanisms in SS, which is considered an autoimmune disorder. We review recent studies on the release of cytokines and metalloproteinases in SS-affected glands and their influence on the release of and response to neurotransmitters. Also, we review the structure and function of muscarinic receptors as they may relate to SS and the potential use of novel muscarinic agonists in SS.

Identification, phylogeny, and evolution of retroviral elements based on their envelope genes

Phylogenetic analyses of retroviral elements, including endogenous retroviruses, have relied essentially on the retroviral pol gene expressing the highly conserved reverse transcriptase. This enzyme is essential for the life cycle of all retroid elements, but other genes are also endowed with conserved essential functions. Among them, the transmembrane (TM) subunit of the envelope gene is involved in virus entry through membrane fusion. It has also been reported to contain a domain, named the immunosuppressive domain, that has immunosuppressive properties most probably essential for virus spread within the host. This domain is conserved among a large series of retroviral elements, and we have therefore attempted to generate phylogenetic links between retroviral elements identified from databases following tentative alignments of the immunosuppressive domain and adjacent sequences. This allowed us to unravel a conserved organization among TM domains, also found in the Ebola and Marburg filoviruses, and to identify a large number of human endogenous retroviruses (HERVs) from sequence databases. The latter elements are part of previously identified families of HERVs, and some of them define new families. A general phylogenetic analysis based on the TM proteins of retroelements, and including those with no clearly identified immunosuppressive domain, could then be derived and compared with pol-based phylogenetic trees, providing a comprehensive survey of retroelements and definitive evidence for recombination events in the generation of both the endogenous and the present-day infectious retroviruses.

Role of viruses in systemic lupus erythematosus and Sjögren syndrome

Systemic lupus erythematosus and Sjögren syndrome remain elusive in the description of their underlying etiologic causes and pathogenic mechanisms. Although underlying genetic predisposition appears to contribute to both diseases based on twin and other genetic studies, additional factors must play a role. Over the decades additional factors, such as hormonal influence, UV light, environmental exposures (e.g., silica, solvents), and infectious agents have been postulated to play a role. Over the past few years additional information has been published concerning roles of various infectious agents in both lupus and Sjögren syndrome. Although the understanding of this field is still incomplete, significant advances are being made.

Characterization of a late entry event in the replication cycle of human immunodeficiency virus type 2

Certain human cell lines and primary macrophage cultures are restricted to infection by some primary isolates of human immunodeficiency virus type 2 (HIV-2), although early steps of the viral life cycle such as fusion at the plasma membrane and reverse transcription are fully supported. The late postintegration events, transcription, translation, assembly, budding, and maturation into infectious virions are functional in restrictive cells. Apart from primary macrophages, the restrictive cell types are actively dividing, and nuclear import of preintegration complexes (PICs) is not required for infection. We therefore postulate that the PICs are trapped in a cellular compartment, preventing subsequent steps in the replication cycle that lead to integration of the provirus. To test this we showed that HIV-2 particles pseudotyped with vesicular stomatitis virus envelope G protein, which delivers HIV into an endocytic compartment, could overcome the block to infection. We suggest that delivery of the viral core into an appropriate cellular compartment is a critical step during the entry process of HIV.

Human retrovirus type 5 sequences in non-Hodgkin's lymphoma of T cell origin

DNA of a recently described fifth exogenous retrovirus (HRV-5) has been found in blood samples from patients with autoimmune diseases and lymphoma. We analyzed HRV-5 sequence in DNA extracted from whole blood of 17 patients with T cell non-Hodgkin's lymphoma (NHL) and 186 patients with hematological malignancies other than NHL, using a sensitive PCR technique. While all samples of patients with hematological malignancies other than NHL were negative, 2 of the 17 patients with T cell NHL were HRV-5 DNA positive. Both HRV-5-positive patients had T cell NHL of high-grade malignancy (stage IV) and diffuse distribution of the lymphoma, including infiltration of bone marrow or lung and pleura. The difference in HRV-5 DNA detection frequency between NHL and control groups is significant (p value of 0.0004 judged by the Fisher exact test). These data, together with our previous finding of HRV-5 DNA in three B cell NHL cases, are compatible with an association between HRV-5 and NHL, of both T cell and B cell origin.

Infectious agents in chronic rheumatic diseases

The possible role of infectious microorganisms in the disease process of both arthritis and autoimmunity continue to attract both basic and clinical researchers. However, proving a causal role for these suspects is a very difficult and complicated task. This article provides an update on various mechanisms in which microbes may play roles as inciting or perpetuating factors in the pathogenesis of connective tissue disease. It also focuses on current theories that specific microorganisms may play a role in rheumatoid arthritis and ankylosing spondylitis.

Hepatitis C and D, retroviruses and autoimmune manifestations

Chronic infections with hepatitis C virus (HCV) are associated with various autoimmune manifestations, i.e. mixed cryoglobulinemia, membranoproliferative glomerulonephritis, autoimmune thyroid diseases, sporadic porphyria cutanea tarda and B cell lymphoma. Since exacerbation of hepatitis occurs in 5-10% of HCV patients receiving interferon-alpha treatment and may be successfully treated by immunosuppression afterwards, hepatitis C was also suspected to be associated with autoimmune hepatitis. LKM3 autoantibodies in chronic hepatitis D virus (HDV) infection and epitope recognition are discussed. Lately, endogenous and exogenous retroviruses have been investigated for the induction of autoimmune diseases. Human A type retroviral particles (HIAP), reverse transcriptase activity and anti-HIAP autoantibodies were detected in patients with Sjögren's syndrome. Anti-HIAP and anti-HIV p24 autoantibodies are seen in systemic lupus erythematosus, primary biliary cirrhosis and multiple sclerosis. Multiple sclerosis was even associated with a new human retrovirus called multiple sclerosis associated retrovirus (MSRV). In diabetes long terminal repeats (LTR) were detected in the HLA DQB1 locus, which was shown to associate with an increased risk of diabetes. A second retrovirus called IDDMK(1,2)22 was reported to code for a superantigen, which was implicated as a potential cause of diabetes. This hypothesis, however, was challenged repeatedly. Until now it is unknown whether endogenous retroviruses are aetiological agents of autoimmune diseases or an epiphenomenon, induced by coinfecting viruses (e.g. herpes viruses) and inflammatory processes.

A novel type D simian retrovirus naturally infecting the Indian Hanuman langur (Semnopithecus entellus)

As a simian species, the langurs are not known to harbor simian retroviruses, except for one report on a simian Type D endogenous retrovirus from the spectacled langur (Trachypithecus obscurus) from Malaysia. The present report describes for the first time natural infection of the common Hanuman langur (Semnopithecus entellus) from India by a novel simian retrovirus (SRV). The new SRV is phylogenetically related to but distinct from the three molecularly characterized serotypes, SRV 1-3, of the five known serotypes of SRVs, based on sequence analyses from the 3'orf and env regions of the viral genome. The novel SRV isolated from the Indian Hanuman langur is provisionally named SRV-6.

The human endogenous retrovirus K Rev response element coincides with a predicted RNA folding region

Human endogenous retrovirus K (HERV-K) is the name given to an approximately 30-million-year-old family of endogenous retroviruses present at >50 copies per haploid human genome. Previously, the HERV-K were shown to encode a nuclear RNA export factor, termed K-Rev, that is the functional equivalent of the H-Rev protein encoded by human immunodeficiency virus type 1. HERV-K was also shown to contain a cis-acting target element, the HERV-K Rev response element (K-RRE), that allowed the nuclear export of linked RNA transcripts in the presence of either K-Rev or H-Rev. Here, we demonstrate that the functionally defined K-RRE coincides with a statistically highly significant unusual RNA folding region and present a potential RNA secondary structure for the approximately 416-nt K-RRE. Both in vitro and in vivo assays of sequence specific RNA binding were used to map two primary binding sites for K-Rev, and one primary binding site for H-Rev, within the K-RRE. Of note, all three binding sites map to discrete predicted RNA stem-loop subdomains within the larger K-RRE structure. Although almost the entire 416-nt K-RRE was required for the activation of nuclear RNA export in cells expressing K-Rev, mutational inactivation of the binding sites for K-Rev resulted in the selective loss of the K-RRE response to K-Rev but not to H-Rev. Together, these data strongly suggest that the K-RRE, like the H-RRE, coincides with an extensive RNA secondary structure and identify specific sites within the K-RRE that can recruit either K-Rev or H-Rev to HERV-K RNA transcripts.

Mutational definition of functional domains within the Rev homolog encoded by human endogenous retrovirus K

Nuclear export of the incompletely spliced mRNAs encoded by several complex retroviruses, including human immunodeficiency virus type 1 (HIV-1), is dependent on a virally encoded adapter protein, termed Rev in HIV-1, that directly binds both to a cis-acting viral RNA target site and to the cellular Crm1 export factor. Human endogenous retrovirus K, a family of ancient endogenous retroviruses that is not related to the exogenous retrovirus HIV-1, was recently shown to also encode a Crm1-dependent nuclear RNA export factor, termed K-Rev. Although HIV-1 Rev and K-Rev display little sequence identity, they share the ability not only to bind to Crm1 and to RNA but also to form homomultimers and shuttle between nucleus and cytoplasm. We have used mutational analysis to identify sequences in the 105-amino-acid K-Rev protein required for each of these distinct biological activities. While mutations in K-Rev that inactivate any one of these properties also blocked K-Rev-dependent nuclear RNA export, several K-Rev mutants were comparable to wild type when assayed for any of these individual activities yet nevertheless defective for RNA export. Although several nonfunctional K-Rev mutants acted as dominant negative inhibitors of K-Rev-, but not HIV-1 Rev-, dependent RNA export, these were not defined by their inability to bind to Crm1, as is seen with HIV-1 Rev. In total, this analysis suggests a functional architecture for K-Rev that is similar to, but distinct from, that described for HIV-1 Rev and raises the possibility that viral RNA export mediated by the approximately 25 million-year-old K-Rev protein may require an additional cellular cofactor that is not required for HIV-1 Rev function.

Retroviruses and psoriasis

Psoriasis occurs with at least undiminished frequency in HIV infected individuals. The behaviour of psoriasis in HIV disease is of interest, both in terms of pathogenesis and therapy, because of the background of profound immunodysregulation. It is paradoxical that, while drugs that target T lymphocytes are effective in psoriasis, the condition should be exacerbated by HIV infection. Antiretroviral therapy may improve psoriasis in tandem with improvement in the overall clinical and virological condition of the patient. The aetiopathogenesis of psoriasis is unknown but genetic and environmental factors are thought to be involved. There are controversial issues regarding the immunological basis of psoriasis and the role of CD4+ versus CD8+ T lymphocytes. Current opinion favours an autoimmune basis for psoriasis, although the precipitating activating signal(s) within psoriatic plaques remains unknown. The immunodysregulation resulting from HIV infection may trigger psoriasis in those genetically predisposed by the Cw*0602 allele. Since CD8+ T cells recognize antigen in the context of class I molecules, the identification of a human leucocyte antigen class I association in HIV-associated psoriasis strengthens the argument for an important role for CD8+ T lymphocytes in the immunopathogenesis of psoriasis. HLA-Cw*0602 could act as a cross-reactive target for cytotoxic T lymphocytes responding to processed peptides from microorganisms. Human retrovirus-5 is a recently described, partially characterized retrovirus and has been implicated in the pathogenesis of psoriatic arthropathy but not psoriasis.

Human retrovirus 5 sequences in peripheral blood cells of patients with B-cell non-Hodgkin's lymphoma

A recently described sequence from a probable 5th human exogenous retrovirus, HRV-5, is related to type A, B and D retroviruses. It was initially detected in a salivary gland biopsy from a patient with Sjögren's syndrome, but it is not consistently associated with this disease. We searched for the HRV-5 sequence in DNA extracted from whole blood of 300 blood donors, 81 patients with hematological malignancy and 21 patients with neurological disease using PCR. While samples from none of the blood donors and the neurological patients became positive, 3 of the 81 patients with hematological malignancy were HRV-5 DNA positive. All 3 had B-cell non-Hodgkin's lymphoma of low grade. The difference in frequency between NHL and controls is statistically significant. HRV-5 DNA was found in DNA from whole blood and in plastic-adherent cells but not in tumor cell DNA. Thus, monocytes/macrophages may be preferred targets for HRV-5. Our result, together with a previous finding of HRV-5 DNA in 2 NHL cases, is compatible with an association between HRV-5 and NHL, whether causal or not.

Accumulation of common T cell clonotypes in the salivary glands of patients with human T lymphotropic virus type I-associated and idiopathic Sjögren's syndrome

To clarify the pathogenesis of human T lymphotropic virus type I (HTLV-I)-associated Sjögren's syndrome (SS), the TCR Vbeta gene usage by the infiltrating lymphocytes in the target organ was examined. The Vbeta families predominantly used in the labial salivary gland (LSG) from the HTLV-I-seropositive (HTLV-I+) SS patients were more restricted than those from the HTLV-I-seronegative (idiopathic) SS patients, and were commonly Vbeta5.2, Vbeta6, and Vbeta7. The single-strand conformation polymorphism analysis revealed that T cell clonotypes with Vbeta5.2, Vbeta6, and Vbeta7 accumulate in the LSG from the HTLV-I+ and idiopathic SS patients. Among junctional sequences of the most dominant Vbeta7 transcripts, the conserved amino acid motif (QDXG: X is any amino acid) was found in six of the five HTLV-I+ SS patients and was also detected in two of the five idiopathic SS patients. Using the probes specific to the motif, the Vbeta7 transcripts with the motif were detected in the LSG from all of the seven HTLV-I+ and five of the six idiopathic SS patients, but not from eight healthy subjects. The Vbeta7 transcripts with this motif were also detected in the HTLV-I-infected T cell lines obtained from the LSG of an HTLV-I+ SS patient. The accumulation of HTLV-I-infected T cells expressing TCR with the conserved motif was thus indicated. These T cells were commonly present in patients with idiopathic SS and are strongly suggested to most likely be involved in the pathogenesis of both HTLV-I-associated and idiopathic SS.

An ancient family of human endogenous retroviruses encodes a functional homolog of the HIV-1 Rev protein

The human endogenous retrovirus K (HERV-K) family of endogenous retroviruses consists of approximately 50 proviral copies per haploid human genome. Herein, the HERV-Ks are shown to encode a sequence-specific nuclear RNA export factor, termed K-Rev, that is functionally analogous to the HIV-1 Rev protein. Like HIV-1 Rev, K-Rev binds to both the Crm1 nuclear export factor and to a cis-acting viral RNA target to activate nuclear export of unspliced RNAs. Surprisingly, this HERV-K RNA sequence, which is encoded within the HERV-K long terminal repeat, is also recognized by HIV-1 Rev. These data provide surprising evidence for an evolutionary link between HIV-1 and a group of endogenous retroviruses that first entered the human genome approximately 30 million years ago.

Retroviruses: ancient and modern

Retroviruses are transmitted in two distinct ways: as infectious virions and as 'endogenous' proviral DNA integrated in the germ line of their hosts. Modern infectious viruses such as HIV recently infected mankind from simian hosts, whereas human endogenous retroviral genomes have been present throughout old world primate evolution. Recently we have characterised novel retroviruses in humans and pigs. Human retrovirus 5 (HRV-5) is detected as an exogenous genome in association with arthritis and systemic lupus erythematosus. Porcine endogenous retroviruses (PERV) are carried in swine DNA but can be activated to produce virions that are infectious for human cells, which has implications for xenotransplantation. A brief account of HRV-5 and PERV is given here.