A mutation in the DE loop of the VP1 protein that prevents polyomavirus transcription and replication

Proteome profiling of polyomavirus nuclear replication centers using iPOND

Polyomaviruses (PyVs) cause diverse diseases in a variety of mammalian hosts. During the life cycle, PyVs recruit nuclear host factors to viral genomes to facilitate replication and transcription. While host factors involved in DNA replication, DNA damage sensing and repair, and cell cycle regulation have been observed to bind PyV DNA, the complete set of viral and host proteins comprising the PyV replisome remains incompletely characterized. Here, the iPOND-MS technique (Isolation of Proteins on Nascent DNA coupled with Mass Spectrometry) was used to identify the proteome bound to murine PyV (MuPyV) DNA immediately following synthesis and 2 hours post-synthesis. Several novel MuPyV DNA interactors were identified on newly synthesized viral DNA (vDNA), including MCM complex members, DNA primase, DNA polymerase alpha, DNA ligase, and replication factor C. Though displaying partial overlap, the host and viral proteins bound to MuPyV DNA 2 hours post-synthesis lacked many of the replication proteins found on newly synthesized vDNA. These data help distinguish between the host factors critical for MuPyV DNA replication and those involved in downstream processing.IMPORTANCEPolyomaviruses are the causative agents of serious diseases in humans, including progressive multifocal leukoencephalopathy (PML), BK virus nephropathy, and Merkel cell carcinoma. The exact mechanisms by which the virus replicates, and which host cell proteins are required, are incompletely characterized. Identifying the host proteins necessary for efficient viral replication in the cell may reveal targets for downstream targets that may suppress viral replication in vivo.

Litopenaeus vannamei peroxiredoxin 2-like is involved in WSSV infection by interaction with wsv089 and VP26

White spot syndrome virus (WSSV) is one of the most dangerous pathogen in shrimp aquaculture, which can cause extremely high mortality of shrimp. A full understanding of virus-host interactions is important to prevent viral infection. In the present study, wsv089-interacting molecule Litopenaeus vannamei peroxiredoxins2-like (LvPrx2-L) was selected by the yeast two-hybrid (Y2H) method. The interaction between wsv089 and LvPrx2-L was confirmed by far-western blotting assay. Interestingly, a further study indicated that LvPrx2-L interacted with VP26, and the molecular docking analysis supported the interaction between LvPrx2-L and VP26. Tissues distribution assay showed that LvPrx2-L was detected in all sampled tissues. The highest expression of LvPrx2-L was appeared in hemocytes. Following WSSV challenge, LvPrx2-L mRNA transcripts were significantly increased in the hemocytes and gill. In addition, the relative expression of IE1 and VP28 were remarkably up-regulated in the hepatopancreas and intestines of LvPrx2-L-knockdown shrimp. Moreover, the cumulative survival rate was significantly lower in the LvPrx2-L- silenced group compared with the control and blank groups. Furthermore, LvPrx2-L could regulate the expression of proPO, crustin, ALF3, and CAT at the mRNA level. These findings would further deepen our understanding of WSSV-host interaction and shrimp antiviral response. All these data might useful for assessing the function of LvPrx2-L in the immune response of crustacean.

Regulation of Polyomavirus Transcription by Viral and Cellular Factors

Polyomavirus infection is widespread in the human population. This family of viruses normally maintains latent infection within the host cell but can cause a range of human pathologies, especially in immunocompromised individuals. Among several known pathogenic human polyomaviruses, JC polyomavirus (JCPyV) has the potential to cause the demyelinating disease progressive multifocal leukoencephalopathy (PML); BK polyomavirus (BKPyV) can cause nephropathy in kidney transplant recipients, and Merkel cell polyomavirus (MCPyV) is associated with a highly aggressive form of skin cancer, Merkel cell carcinoma (MCC). While the mechanisms by which these viruses give rise to the relevant diseases are not well understood, it is clear that the control of gene expression in each polyomavirus plays an important role in determining the infectious tropism of the virus as well as their potential to promote disease progression. In this review, we discuss the mechanisms governing the transcriptional regulation of these pathogenic human polyomaviruses in addition to the best-studied simian vacuolating virus 40 (SV40). We highlight the roles of viral cis-acting DNA elements, encoded proteins and miRNAs that control the viral gene expression. We will also underline the cellular transcription factors and epigenetic modifications that regulate the gene expression of these viruses.

The Major Capsid Protein, VP1, of the Mouse Polyomavirus Stimulates the Activity of Tubulin Acetyltransferase 1 by Microtubule Stabilization

Viruses have evolved mechanisms to manipulate microtubules (MTs) for the efficient realization of their replication programs. Studying the mechanisms of replication of mouse polyomavirus (MPyV), we observed previously that in the late phase of infection, a considerable amount of the main structural protein, VP1, remains in the cytoplasm associated with hyperacetylated microtubules. VP1–microtubule interactions resulted in blocking the cell cycle in the G2/M phase. We are interested in the mechanism leading to microtubule hyperacetylation and stabilization and the roles of tubulin acetyltransferase 1 (αTAT1) and deacetylase histone deacetylase 6 (HDAC6) and VP1 in this mechanism. Therefore, HDAC6 inhibition assays, αTAT1 knock out cell infections, in situ cell fractionation, and confocal and TIRF microscopy were used. The experiments revealed that the direct interaction of isolated microtubules and VP1 results in MT stabilization and a restriction of their dynamics. VP1 leads to an increase in polymerized tubulin in cells, thus favoring αTAT1 activity. The acetylation status of MTs did not affect MPyV infection. However, the stabilization of MTs by VP1 in the late phase of infection may compensate for the previously described cytoskeleton destabilization by MPyV early gene products and is important for the observed inhibition of the G2→M transition of infected cells to prolong the S phase.

Exploitation of stable nanostructures based on the mouse polyomavirus for development of a recombinant vaccine against porcine circovirus 2

The aim of this study was to develop a suitable vaccine antigen against porcine circovirus 2 (PCV2), the causative agent of post-weaning multi-systemic wasting syndrome, which causes significant economic losses in swine breeding. Chimeric antigens containing PCV2b Cap protein sequences based on the mouse polyomavirus (MPyV) nanostructures were developed. First, universal vectors for baculovirus-directed production of chimeric MPyV VLPs or pentamers of the major capsid protein, VP1, were designed for their exploitation as vaccines against other pathogens. Various strategies were employed based on: A) exposure of selected immunogenic epitopes on the surface of MPyV VLPs by insertion into a surface loop of the VP1 protein, B) insertion of foreign protein molecules inside the VLPs, or C) fusion of a foreign protein or its part with the C-terminus of VP1 protein, to form giant pentamers of a chimeric protein. We evaluated these strategies by developing a recombinant vaccine against porcine circovirus 2. All candidate vaccines induced the production of antibodies against the capsid protein of porcine circovirus after immunization of mice. The candidate vaccine, Var C, based on fusion of mouse polyomavirus and porcine circovirus capsid proteins, could induce the production of antibodies with the highest PCV2 neutralizing capacity. Its ability to induce the production of neutralization antibodies was verified after immunization of pigs. The advantage of this vaccine, apart from its efficient production in insect cells and easy purification, is that it represents a DIVA (differentiating infected from vaccinated animals) vaccine, which also induces an immune response against the mouse polyoma VP1 protein and is thus able to distinguish between vaccinated and naturally infected animals.

VP1, the major capsid protein of the mouse polyomavirus, binds microtubules, promotes their acetylation and blocks the host cell cycle

VP1, the major structural protein of the mouse polyomavirus (MPyV), is the major architectural component of the viral capsid. Its pentamers are able to self-assemble into capsid-like particles and to non-specifically bind DNA. Surface loops of the protein interact with sialic acid of ganglioside receptors. Although the replication cycle of the virus, including virion morphogenesis, proceeds in the cell nucleus, a substantial fraction of the protein is detected in the cytoplasm of late-phase MPyV-infected cells. In this work, we detected VP1 mainly in the cytoplasm of mammalian cells transfected with plasmid expressing VP1. In the cytoplasm, VP1-bound microtubules, including the mitotic spindle, and the interaction of VP1 with microtubules resulted in cell cycle block at the G2/M phase. Furthermore, in the late phase of MPyV infection and in cells expressing VP1, microtubules were found to be hyperacetylated. We then sought to understand how VP1 interacts with microtubules. Dynein is not responsible for the VP1-microtubule association, as neither overexpression of p53/dynamitin nor treatment with ciliobrevin-D (an inhibitor of dynein activity) prevented binding of VP1 to microtubules. A pull-down assay for VP1-interacting proteins identified the heat shock protein 90 (Hsp90) chaperone, and Hsp90 was also detected in the VP1-microtubule complexes. Although Hsp90 is known to be associated with acetylated microtubules, it does not mediate the interaction between VP1 and microtubules. Our study provides insight into the role of the major structural protein in MPyV replication, indicating that VP1 is a multifunctional protein that participates in the regulation of cell cycle progression in MPyV-infected cells.

Mutation in the VP1-LDV motif of the murine polyomavirus affects viral infectivity and conditions virus tissue tropism in vivo

The first contact of a virus with the host cell surface and further entry are important steps for a successful outcome of the infection process and for the virus-associated pathogenicity. We have previously shown that the entry of the murine Polyomavirus (Py) into fibroblasts is a multi-step process involving, at least, the attachment to primary sialic acids (SA)-containing cell receptors followed by post-binding interaction with secondary receptors, such as the alpha4beta1 integrin, likely through the VP1-LDV motif. Here we report on the functional role of the VP1-LDV motif in Py infectivity and in vivo virus tissue tropism. For this purpose, we have characterized a recombinant virus mutant, PyLNV, harboring a single aa substitution in this motif (D138N). Although not critical for virus viability, the D138N substitution abrogates the post-attachment Py-alpha4beta1 interaction, rendering the PyLNV mutant virus twofold less infectious than the Py wild-type (Wt) in alpha4beta1-positive fibroblasts. To study the putative role of the VP1-LDV motif in vivo, newborn C57BL/6 mice were inoculated with PyWt or PyLNV and, after six days, organs were analyzed for the presence of viral DNA. Intriguingly, PyLNV showed an altered spectrum of in vivo replication compared with PyWt, particularly in the skin and in the kidney. The implication of Py-alpha4beta1 integrin interaction in conditioning tissue-specificity of virus replication is discussed.

PARP-1 interaction with VP1 capsid protein regulates polyomavirus early gene expression

Poly(ADP-ribose)polymerases are involved in fundamental cellular events as well as they seem to be associated to some viral infection process. In this work, the poly(ADP-ribose)polymerase-1 (PARP-1) role in the polyomavirus life cycle has been investigated. Early viral transcription was reduced by competitive inhibitors of PARPs in Swiss 3T3 cells and almost abolished in PARP-1 knockout fibroblasts and in wild-type fibroblasts when PARP-1 was silenced by RNA interference. In vivo chromatin immunoprecipitation assays showed that poly(ADP-ribosyl)ation (poly(ADP-ribose)) facilitates the release of the capsid protein viral protein 1 (VP1) from the chromatin of infecting virions. In vitro experiments demonstrated that VP1 stimulates the enzymatic activity of PARP-1 and binds non-covalently both protein-free and PARP-1-bound poly(ADP-ribose). Our studies suggest that PARP-1 promotes the complete VP1 displacement from viral DNA favouring the viral early transcription.

Arenavirus diversity and evolution: quasispecies in vivo

Arenaviruses exist as viral quasispecies due to the high mutation rates of the low-fidelity viral RNA-dependent RNA polymerase (RdRp). This genomic heterogeneity is advantageous to the population, allowing for adaptation to rapidly changing environments that present varying types and degrees of selective pressure. The significant variation in biological properties observed among lymphocytic choriomeningitis virus (LCMV) strains, the prototypic arenavirus, indicates to what extent a quasispecies dynamics may play a role in arenavirus adaptability and pathogenesis. Several aspects of arenavirus variability and its contribution to pathogenesis will be discussed.

Conformational changes of murine polyomavirus capsid proteins induced by sialic acid binding

Murine polyomavirus (Py) infection initiates by the recognition of cell membrane molecules containing terminal sialic acid (SA) residues through specific binding pockets formed at the major capsid protein VP1 surface. VP1 Pockets 1, 2, and 3 bind terminal SA, Gal, and second branched SA, respectively. The consequence of recognition on viral cell entry remains elusive. In this work, we show that preincubation of Py with soluble compounds within Pocket 1 (N-acetyl or N-glycolyl neuraminic acids) increases Py cell binding and infectivity in murine 3T6 fibroblasts. In contrast, Gal does not significantly alter Py binding nor infectivity, whereas sialyllactose, in Pockets 1 and 2, decreases cell binding and infectivity. Binding experiments with Py virus-like particles confirmed the direct involvement of VP1 in this effect. To determine whether such results could reflect VP1 conformational changes induced by SA binding, protease digestion assays were performed after pretreatment of Py or virus-like particles with soluble receptor fragments. Binding of SA with the VP1 Pocket 1, but not of compounds interacting with Pocket 2, was associated with a transition of this protein from a protease-sensitive to a protease-resistant state. This effect was transmitted to the minor capsid proteins VP2 and VP3 in virus particles. Attachment of Py to cell monolayers similarly led to a VP1 trypsin-resistant pattern. Taken together, these data present evidence that initial binding of Py to terminal SA induces conformational changes in the viral capsid, which may influence subsequent virus cell entry steps.

Chromosome-protein interactions in polyomavirus virions

In this work, we sought to determine whether the components of the murine polyomavirus capsid establish specific interactions with the minichromosome encapsidated into the mature viral particles by using the cis-diamminedichloroplatinum(II) cross-linking reagent. Our data indicated that VP1, but not minor capsid proteins, interacts with the viral genome in vivo. In addition, semiquantitative PCR assays performed on cross-linked DNA complexes revealed that VP1 binds to all regions of the viral genome but significantly more to the regulatory region. The implications of such an interaction for viral infectivity are discussed.

Role of sialic acid-containing molecules and the α4β1 integrin receptor in the early steps of polyomavirus infection

Murine polyomavirus (MPyV) infection occurs through recognition of sialic acid (SA) residues present on the host cell membrane, but the nature of the molecules involved and the exact role of this interaction in virus cell entry still need to be clarified. In this work, mutations at residues R(77) or H(298) of the MPyV VP1 protein were shown to lead to a complete loss of virus infectivity, which, however, could be restored by lipofection of virus particles into the cytoplasm of the host cells. Using virus-like particles (VLPs), it was demonstrated that the non-infectivity of these mutants was due to impaired cell entry caused by total abrogation of SA-dependent cell binding. This indicates that SA residues are essential primary cell receptors for MPyV. As the alpha4beta1 integrin has been identified recently as a cell receptor for MPyV, the relationship, if any, was investigated between SA-containing and alpha4beta1 integrin receptors. The ability of mutants R(77)Q and H(298)Q and wt VLPs to bind to cells overexpressing the alpha4beta1 integrin was studied in SA-positive (BALB/c 3T3 cells and Pro-5 cells) and SA-deficient (Pro5-derived Lec-2 cells) backgrounds. Overexpression of alpha4beta1 integrin did not restore binding of mutant VLPs in any of these cell lines or, indeed, that of wt VLPs in a SA-deficient background. Moreover, evidence is provided that overexpression of the sialylated alpha4beta1 integrin enhances wt VLP cell binding, suggesting that, in addition to its function at a post-attachment level, alpha4beta1 integrin acts also as one of the SA-containing receptors for initial cell binding.

Alpha4beta1 integrin acts as a cell receptor for murine polyomavirus at the postattachment level

The initial interaction of murine polyomavirus (Py) with host cells occurs through direct binding of the major capsid protein VP1 with cell membrane molecules containing terminal sialic acids; however, these Py receptor molecules have not yet been identified. Analysis of the capsid protein primary sequences of all murine strains revealed the presence of integrin ligand motifs in the DE and EF loops of VP1 (LDV and DLXXL, respectively) and at the N terminus of VP2 (DGE). We show that infectivity of the Py A2 strain in mouse Swiss 3T3 fibroblasts is significantly reduced only in the presence of natural integrin ligands carrying an LDV motif or antibodies directed against the alpha4 and beta1 integrin subunits. Furthermore, we demonstrate that expression of the alpha4 subunit in the alpha4-deficient BALB/c 3T3 cells increases viral infectivity. Addition of alpha4 function-blocking antibodies, prior to or after virus adsorption, blocks this increased infectivity without affecting virus binding to cells. Taken together, these data indicate that expression of alpha4 integrin enhances permissivity to Py, probably by acting as one of the postattachment receptors.

Genomic instability of prawn white spot bacilliform virus (WSBV) and its association to virus virulence

Prawn White Spot Bacilliform Virus (WSBV) is a major pathogen that causes prawn diseases. In this study, we examined the sequence of WSBV genome DNA in the shrimp Penaeus japonicus, P. vannamei, P. Monodon, P. chinensis and Metapenaeus ensis through successive PCR amplification of the DNA fragments in the whole WSBV genome. We found a sequence deletion hotspot in the WSBV genome that is 305107 bp in length. The sizes of the deleted fragments were 4.6, 4.8 or 8.1 kbp depending on the species of prawn. Since the mortality of shrimp infected by the intact WSBV was always significantly higher than that of shrimp infected by DNA fragment-deleted WSBV, we suggest that this deletion be somehow linked to the virulence of the virus itself. This result may lead to the discovery of the molecular mechanism of the pathogenicity of WSBV in shrimps.

Immunization of T-cell deficient mice against polyomavirus infection using viral pseudocapsids or temperature sensitive mutants

A murine experimental model system aimed at developing potential vaccines to papovavirus infection in immunosuppressed individuals was explored. A VP1-pseudocapsid based on the major capsid protein of the murine polyomavirus A2 strain and a mutant, M17-pseudocapsid as well as four temperature sensitive (ts)-mutants were used as immunogens. T-cells deficient CD4-/-8-/- mice were immunized four times with each immunogen and then together with non-immunized control mice challenged with polyomavirus. In contrast to all control mice, only half of the immunized mice exhibited presence of polyoma DNA when assayed by PCR. The results indicate that pseudocapsids and ts-mutant immunization may potentially protect mice with an impaired T-cell function from polyomavirus infection.

Natural biology of polyomavirus middle T antigen

"It has been commented by someone that 'polyoma' is an adjective composed of a prefix and suffix, with no root between--a meatless linguistic sandwich" (C. J. Dawe). The very name "polyomavirus" is a vague mantel: a name given before our understanding of these viral agents was clear but implying a clear tumor life-style, as noted by the late C. J. Dawe. However, polyomavirus are not by nature tumor-inducing agents. Since it is the purpose of this review to consider the natural function of middle T antigen (MT), encoded by one of the seemingly crucial transforming genes of polyomavirus, we will reconsider and redefine the virus and its MT gene in the context of its natural biology and function. This review was motivated by our recent in vivo analysis of MT function. Using intranasal inoculation of adult SCID mice, we have shown that polyomavirus can replicate with an MT lacking all functions associated with transformation to similar levels to wild-type virus. These observations, along with an almost indistinguishable replication of all MT mutants with respect to wild-type viruses in adult competent mice, illustrate that MT can have a play subtle role in acute replication and persistence. The most notable effect of MT mutants was in infections of newborns, indicating that polyomavirus may be highly adapted to replication in newborn lungs. It is from this context that our current understanding of this well-studied virus and gene is presented.