The human JC polyomavirus is a bit of a mystery. Many people are infected with it, but few become ill as a result. This virus bides its time, waiting for your immune systen to let its guard down, then wham! People infected with HIV, those who have AIDS, or those receiving immunomodulatory therapies for autoimmune diseases are at serious risk for progressive multifocal leukoencephalopathy (PML), where the virus can spread from the kidney to the central nervous system and cause a fatal, demyelinating disease.
Recent reports have shown that virus isolates from PML patients often have distinct changes within the major capsid protein. This paper shows that that these mutations result in abolished engagement of the carbohydrate receptor motif necessary for infection. Viruses with PML-associated mutations are not infectious in glial cells, suggesting that they may play an alternative role in PML. Interesting stuff, suggesting that interaction with cell surface receptors is an important determinant of tissue tropism and JC virus pathogenesis for PML, even though the best defence remains a healthy immune system.
Progressive Multifocal Leukoencephalopathy-Associated Mutations in the JC Polyomavirus Capsid Disrupt Lactoseries Tetrasaccharide c Binding. (2013) mBio 4(3): e00247-13 doi: 10.1128/mBio.00247-13
The human JC polyomavirus (JCPyV) is the causative agent of the fatal, demyelinating disease progressive multifocal leukoencephalopathy (PML). The Mad-1 prototype strain of JCPyV uses the glycan lactoseries tetrasaccharide c (LSTc) and serotonin receptor 5-HT2A to attach to and enter into host cells, respectively. Specific residues in the viral capsid protein VP1 are responsible for direct interactions with the α2,6-linked sialic acid of LSTc. Viral isolates from individuals with PML often contain mutations in the sialic acid-binding pocket of VP1 that are hypothesized to arise from positive selection. We reconstituted these mutations in the Mad-1 strain of JCPyV and found that they were not capable of growth. The mutations were then introduced into recombinant VP1 and reconstituted as pentamers in order to conduct binding studies and structural analyses. VP1 pentamers carrying PML-associated mutations were not capable of binding to permissive cells. High-resolution structure determination revealed that these pentamers are well folded but no longer bind to LSTc due to steric clashes in the sialic acid-binding site. Reconstitution of the mutations into JCPyV pseudoviruses allowed us to directly quantify the infectivity of the mutants in several cell lines. The JCPyV pseudoviruses with PML-associated mutations were not infectious, nor were they able to engage sialic acid as measured by hemagglutination of human red blood cells. These results demonstrate that viruses from PML patients with single point mutations in VP1 disrupt binding to sialic acid motifs and render these viruses noninfectious.
Since their discovery in 1971, the polyomaviruses JC (JCPyV) and BK (BKPyV), isolated from patients with progressive multifocal leukoencephalopathy and polyomavirus-associated nephropathy, respectively, remained for decades as the only known members of the Polyomaviridae family of viruses of human origin. Over the past five years, the application of new genomic amplification technologies has facilitated the discovery of several novel human polyomaviruses (HPyVs), bringing the present number to 10. These HPyVs share many fundamental features in common such as genome size and organization. Infection by all HPyVs is widespread in the human population, but they show important differences in their tissue tropism and association with disease. Much remains unknown about these new viruses.
This review discusses the problems associated with studying HPyVs, such as the lack of culture systems for the new viruses and the gaps in our basic understanding of their biology, and summarizes what is known so far about their distribution, life cycle, tissue tropism, their associated pathologies (if any), and future research directions. The Rapidly Expanding Family of Human Polyomaviruses: Recent Developments in Understanding Their Life Cycle and Role in Human Pathology. (2013) PLoS Pathog 9(3): e1003206. doi:10.1371/journal.ppat.1003206
Until a few years ago the polyomavirus family (Polyomaviridae) included a dozen viruses identified in avian and mammal hosts. Two of these, the JC and BK-polyomaviruses isolated long time ago, are known to infect humans and cause severe illness in immunocompromized hosts. Since 2007 an unprecedented number of eight new polyomaviruses was discovered in humans. Among them are the KI and WU-polyomaviruses identified in respiratory samples, the Merkel cell polyomavirus found in skin carcinomas, and the polyomavirus associated with trichodysplasia spinulosa, a skin disease of transplant patients. Another four new human polyomaviruses were identified, HPyV6, HPyV7, HPyV9, and the Malawi polyomavirus, so far not associated with any disease. In the same period several new mammal polyomaviruses were described.
This review summarizes the recent developments in studying the new human polyomaviruses, and touches upon several aspects of polyomavirus virology, pathogenicity, epidemiology and phylogeny. From Stockholm to Malawi: recent developments in studying human polyomaviruses. J Gen Virol. 19 Dec 2012
The large tumor antigen (T antigen) encoded by simian virus 40 is an amazing molecular machine because it orchestrates viral infection by modulating multiple fundamental viral and cellular processes. T antigen is required for viral DNA replication, transcription, and virion assembly. In addition, T antigen targets multiple cellular pathways, including those that regulate cell proliferation, cell death, and the inflammatory response. Ectopic T antigen expression results in the immortalization and transformation of many cell types in culture and T antigen induces neoplasia when expressed in rodents. The analysis of the mechanisms by which T antigen carries out its many functions has proved to be a powerful way of gaining insights into cell biology. The accelerating pace at which new polyomaviruses are being discovered provides a collection of novel T antigens that, like simian virus 40, can be used to discover and study key cellular regulatory systems.
For decades I’ve been telling the students who take my virology course that, as long as your immune system is healthy, the consequence of JC virus infection is … not so much. But sexually transmitted infectious agents are some of the main causes of human infertility. In recent years the incidence of male infertility has increased. A new study has found a much higher prevalence of JC virus in the semen and urine of infertile men than in matched controls, suggesting that the JC virus should be taken into consideration as a common infectious agent responsible for male infertility.
Association between the JC Polyomavirus Infection and Male Infertility. (2012) PLoS ONE 7(8): e42880. doi:10.1371/journal.pone.0042880
In recent years the incidence of male infertility has increased. Many risk factors have been taken into consideration, including viral infections. Investigations into viral agents and male infertility have mainly been focused on human papillomaviruses, while no reports have been published on polyomaviruses and male infertility. The aim of this study was to verify whether JC virus and BK virus are associated with male infertility. Matched semen and urine samples from 106 infertile males and 100 fertile males, as controls, were analyzed. Specific PCR analyses were carried out to detect and quantify large T (Tag) coding sequences of JCV and BKV. DNA sequencing, carried out in Tag JCV-positive samples, was addressed to viral protein 1 (VP1) coding sequences. The prevalence of JCV Tag sequences in semen and urine samples from infertile males was 34% (72/212), whereas the BKV prevalence was 0.94% (2/212). Specifically, JCV Tag sequences were detected in 24.5% (26/106) of semen and 43.4% (46/106) of urine samples from infertile men. In semen and urine samples from controls the prevalence was 11% and 28%, respectively. A statistically significant difference (p<0.05) in JCV prevalence was disclosed in semen and urine samples of cases vs. controls. A higher JC viral DNA load was detected in samples from infertile males than in controls. In samples from infertile males the JC virus type 2 strain, subtype 2b, was more prevalent than ubiquitous type 1. JCV type 2 strain infection has been found to be associated with male infertility. These data suggest that the JC virus should be taken into consideration as an infectious agent which is responsible for male infertility.
Polyomaviruses are naked viruses with an icosahedral capsid that surrounds a circular double-stranded DNA molecule of about 5000 base-pairs. Their genome encodes at least five proteins: large and small tumor antigens and the capsid proteins VP1, VP2 and VP3. The tumor antigens are expressed during early stages of the viral life cycle and are implicated in the regulation of viral transcription and DNA replication, while the capsid proteins are produced later during infection.
Some mammalian polyomaviruses encode an additional protein, referred to as the agnoprotein, a relatively small polypeptide that exerts multiple functions. This review discusses the structure, post-translational modifications, and functions of agnoprotein, and speculates why not all polyomaviruses express this protein.
Virion Assembly Factories in the Nucleus of Polyomavirus-Infected Cells. (2012) PLoS Pathog 8(4): e1002630. doi:10.1371/journal.ppat.1002630
Polyomaviruses are infectious pathogens of mammals and birds that have been linked to the development of cancers in their hosts. Members of the polyomavirus family are associated with human disease, such as JCV and BKV, and over the past few years, several more human polyomaviruses (WUV, KIV and MCV) have been discovered in immune-suppressed individuals. We are studying the way in which these viruses assemble in cells in order to identify critical points where anti-viral therapies could target these viruses. Using a structural, biochemical and cell biological approach, we set out to define sites of virus assembly and virus intermediates. We identified virus-specific structures that we termed “virus factories”. We believe that these sites serve as an assembly line for the production of new viruses. Our study provides new evidence for the presence and composition of virus assembly factories, and identifies a host protein that may be important for infection by polyomaviruses.
BK virus (BKV) and JC virus (JCV) are widespread human polyomaviruses, and their pathogenic potential during immunodeficiency has been clearly documented. Primary infection usually occurs asymptomatically (or with only mild respiratory symptoms) during childhood, after which the polyomaviruses persist latently in various organs, mainly in the urogenital system, brain and circulating leukocytes. Reactivation of both viruses is common, and frequently associated with asymptomatic viruria. The natural history of infection is well established, but it is still not clear how BKV and JCV are transmitted, although the hypotheses include respiratory, oral-fecal and urinary transmission. Furthermore, on the basis of the frequency of Polyomavirus (PV) infection in childhood, and as has been previously demonstrated in the case of animal homologue polyomaviruses such as the Murine and Simian polyomaviruses (SV-40), some authors have investigated the possibility of vertical transmission, but with conflicting results. So how are these pathogenic viruses transmitted between humans?
Serologic evidence of vertical transmission of JC and BK polyomaviruses in humans. J Gen Virol. Feb 9 2011
Vertical transmission of JC virus and BK virus has been investigated by few authors, with conflicting results. We performed a combined serological and genomic study of 19 unselected pregnant women and their newborns. Blood and urine samples were collected during each gestational trimester in the pregnant women; umbilical cord blood, peripheral blood, urine, and nasopharyngeal secretion samples were taken from newborns at delivery, one week and one month of life. Polyomavirus DNA was detected by nested-PCR. Polyomavirus IgG, IgM and IgA specific antibodies were measured in maternal and newborn serum samples using virus-like particle-based ELISA method. BKV and JCV DNA was detected in urine from 4 (21%) and 5 (26%) women, respectively. BKV and JCV seroprevalence in the pregnant women was 84% and 42%, respectively. Using a rise in the IgG level or the transient appearance of an IgA or IgM response as evidence of infection in the newborn we detected BKV and JCV infections in four (21%) and three (16%) newborns respectively. Three infants had serological evidence of infection with both BKV and JCV. In two of the four possible BKV infected newborns, the mothers seroconverted during pregnancy, while another mother was viruric and IgA seropositive. The mother of one of three possible JCV infected newborn was viruric and IgA seropositive, another mother was viruric. These results suggest JC virus and BK virus can be transmitted from mother to newborn during pregnancy or soon after birth.
In the past three years, remarkable discoveries have added three new human polyomaviruses (KI virus (KIV), WU virus (WUV) and Merkel cell virus (MCV)) to a class that previously had only two disease-causing members (BK virus (BKV) and JC virus (JCV)) identified. Two monkey polyomaviruses, simian virus (SV)40 and B-cell lymphotropic polyomavirus (LPV) are also present in humans. KIV and WUV lack the agnoprotein coding sequence and regulatory micro (mi)RNA clusters of BKV, JCV and SV40. MCV lacks the agnoprotein sequence but generates miRNAs. KIV, WUV and MCV are all widespread in humans. Although they have distinctive tissue tropisms, all these viruses are probably acquired in childhood. Of these viruses, only MCV has thus far been strongly linked to cancer. Marshalled evidence from diverse sources implicates MCV as an etiological agent of Merkel cell carcinoma. This review compares the structural features of the new and previously known polyomaviruses, with the aim of identifying approaches to molecular pathology.
BK virus (BKV) belongs to the polyomavirus family and is ubiquitous in the human population. The viral capsid is icosahedral and has a diameter of 45–50 nm. The genome consists of a closed circular double-stranded DNA molecule with approximately 5 kb. BKV infection typically occurs during childhood, without specific symptoms, followed by a state of non-replicative infection in various tissues, with the urogenital tract as the principal site. In the setting of relative or absolute cell-mediated immunosuppression, dramatic increase in BK viral replication occurs, resulting in the lytic destruction of infected uroepithelial cells, which in turn induces the influx of inflammatory immune cells. This destruction of kidney cells most often occurs in 5–8% of kidney transplants resulting in organ loss in half of these cases and is termed BKV-associated nephropathy. Rise in the incidence of Polyomavirus viruria and viremia has been detected in recipients of bone marrow, kidney and heart transplants, as well as an increase in viruria in HIV-infected individuals. The potential for BK replication at distant sites such as the salivary gland may certainly exist in the setting of HIV infection.
While it is clear that BKV infection is an ubiquitous childhood infection, BKV transmission is not currently well understood. The present studies were undertaken to determine whether BKV could infect and replicate within salivary gland cells resulting in virus production and potentially transmission. BKV has been detected in the saliva of patients with HIV-associated salivary gland pathology and in healthy individuals. In order to begin to decipher BKV pathogenesis within the salivary gland cell it was essential to develop an in vitro model system. Submandibular and parotid gland cell lines were able to support virus entry, transcription, translation and virion production and BKV infection could be inhibited by saturating the capsid protein with its ganglioside receptor. This data demonstrates for the first time, BKV detection in saliva and evidence that human salivary gland cells can be productively infected with BK virus. This suggests that while kidney/uroepithelial cells have long been known to be a site of BKV replication and latency, the salivary gland may also constitute an infectious reservoir for BKV. Although the natural route of BKV transmission has not been resolved, this study suggests a potential for oral BKV transmission.
BK virus has tropism for human salivary gland cells in vitro: Implications for transmission. Virology Sep 24 2009
In this study, it was determined that BKV is shed in saliva and an in vitro model system was developed whereby BKV can productively infect both submandibular (HSG) and parotid (HSY) salivary gland cell lines. BKV was detected in oral fluids using quantitative real-time PCR (QRTPCR). BKV infection was determined using quantitative RT-PCR, immunofluorescence and immunoblotting assays. The infectivity of BKV was inhibited by pre-incubation of the virus with gangliosides that saturated the major capsid protein, VP1, halting receptor mediated BKV entry into salivary gland cells. Examination of infected cultures by transmission electron microscopy revealed 45-50 nm BK virions clearly visible within the cells. Subsequent to infection, encapsidated BK virus was detected in the supernatant. We thus demonstrated that BKV was detected in oral fluids and that BK infection and replication occur in vitro in salivary gland cells. These data collectively suggest the potential for BKV oral route of transmission and oral pathogenesis.
The human JC polyomavirus is a bit of a mystery. Many people are infected with it, but few become ill as a result. This virus bides its time, waiting for your immune systen to let its guard down, then wham! People infected with HIV, those who have AIDS, or those receiving immunomodulatory therapies for autoimmune diseases are at serious risk for progressive multifocal leukoencephalopathy (PML), where the virus can spread from the kidney to the central nervous system and cause a fatal, demyelinating disease.
