Expression of novel proteins by polyomaviruses and recent advances in the structural and functional features of agnoprotein of JC virus, BK virus, and simian virus 40.

Polyomavirus family consists of a highly diverse group of small DNA viruses. The founding family member (MPyV) was first discovered in the newborn mouse in the late 1950s, which induces solid tumors in a wide variety of tissue types that are the epithelial and mesenchymal origin. Later, other family members were also isolated from a number of mammalian, avian and fish species. Some of these viruses significantly contributed to our current understanding of the fundamentals of modern biology such as transcription, replication, splicing, RNA editing, and cell transformation. After the discovery of first two human polyomaviruses (JC virus [JCV] and BK virus [BKV]) in the early 1970s, there has been a rapid expansion in the number of human polyomaviruses in recent years due to the availability of the new technologies and brought the present number to 14. Some of the human polyomaviruses cause considerably serious human diseases, including progressive multifocal leukoencephalopathy, polyomavirus-associated nephropathy, Merkel cell carcinoma, and trichodysplasia spinulosa. Emerging evidence suggests that the expression of the polyomavirus genome is more complex than previously thought. In addition to encoding universally expressed regulatory and structural proteins (LT-Ag, Sm t-Ag, VP1, VP2, and VP3), some polyomaviruses express additional virus-specific regulatory proteins and microRNAs. This review summarizes the recent advances in polyomavirus genome expression with respect to the new viral proteins and microRNAs other than the universally expressed ones. In addition, a special emphasis is devoted to the recent structural and functional discoveries in the field of polyomavirus agnoprotein which is expressed only by JCV, BKV, and simian virus 40 genomes.

Structure-based release analysis of the JC virus agnoprotein regions: A role for the hydrophilic surface of the major alpha helix domain in release.

Agnoprotein (Agno) is an important regulatory protein of JC virus (JCV), BK virus (BKV) and simian virus 40 (SV40) and these viruses are unable to replicate efficiently in the absence of this protein. Recent 3D-NMR structural data revealed that Agno contains two alpha-helices (a minor and a major) while the rest of the protein adopts an unstructured conformation (Coric et al., 2017, J Cell Biochem). Previously, release of the JCV Agno from the Agno-positive cells was reported. Here, we have further mapped the regions of Agno responsible for its release by a structure-based systematic mutagenesis approach. Results revealed that amino acid residues (Lys22, Lys23, Phe31, Glu34, and Asp38) located either on or adjacent to the hydrophilic surface of the major alpha-helix domain of Agno play critical roles in release. Additionally, Agno was shown to strongly interact with unidentified components of the cell surface when cells are treated with Agno, suggesting additional novel roles for Agno during the viral infection cycle.

Discovery and characterization of novel trans-spliced products of human polyoma JC virus late transcripts from PML patients.

Although the human neurotropic polyomavirus, JC virus (JCV), was isolated almost a half century ago, understanding the molecular mechanisms governing its biology remains highly elusive. JCV infects oligodendrocytes and astrocytes in the central nervous system (CNS) and causes a rare fatal brain disease known as progressive multifocal leukoencephalopathy (PML) in immunocompromised individuals including AIDS. It has a small circular DNA genome (∼5 kb) and generates two primary transcripts from its early and late coding regions, producing several predicted alternatively spliced products mainly by cis-splicing. Here, we report the discovery and characterization of two novel open reading frames (ORF1 and ORF2) associated with JCV late transcripts, generated by an unusual splicing process called trans-splicing. These ORFs result from (i) the trans-splicing of two different lengths of the 5'-short coding region of VP1 between the coding regions of agnoprotein and VP2 after replacing the intron located between these two coding regions and (ii) frame-shifts occurring within the VP2 coding sequences terminated by a stop codon. ORF1 and ORF2 are capable of encoding 58 and 72 aa long proteins respectively and are expressed in infected cells and PML patients. Each ORF protein shares a common coding region with VP1 and has a unique coding sequence of their own. When the expression of the unique coding regions of ORFs is blocked by a stop codon insertion in the viral background, the mutant virus replicates less efficiently when compared to wild-type, suggesting that the newly discovered ORFs play critical roles in the JCV life cycle.

Nuclear Magnetic Resonance Structure of the Human Polyoma JC Virus Agnoprotein.

Agnoprotein is an important regulatory protein of the human polyoma JC virus (JCV) and plays critical roles during the viral replication cycle. It forms highly stable dimers and oligomers through its Leu/Ile/Phe-rich domain, which is important for the stability and function of the protein. We recently resolved the partial 3D structure of this protein by NMR using a synthetic peptide encompassing amino acids Thr17 to Gln52, where the Leu/Ile/Phe- rich region was found to adopt a major alpha-helix conformation spanning amino acids 23-39. Here, we report the resolution of the 3D structure of full-length JCV agnoprotein by NMR, which not only confirmed the existence of the previously reported major α-helix domain at the same position but also revealed the presence of an additional minor α-helix region spanning amino acid residues Leu6 to lys13. The remaining regions of the protein adopt an intrinsically unstructured conformation. J. Cell. Biochem. 118: 3268-3280, 2017. © 2017 Wiley Periodicals, Inc.

Emerging From the Unknown: Structural and Functional Features of Agnoprotein of Polyomaviruses.

Agnoprotein is an important regulatory protein of polyomaviruses, including JCV, BKV, and SV40. In the absence of its expression, these viruses are unable to sustain their productive life cycle. It is a highly basic phosphoprotein that localizes mostly to the perinuclear area of infected cells, although a small amount of the protein is also found in nucleus. Much has been learned about the structure and function of this important regulatory protein in recent years. It forms highly stable dimers/oligomers in vitro and in vivo through its Leu/Ile/Phe-rich domain. Structural NMR studies revealed that this domain adopts an alpha-helix conformation and plays a critical role in the stability of the protein. It associates with cellular proteins, including YB-1, p53, Ku70, FEZ1, HP1α, PP2A, AP-3, PCNA, and α-SNAP; and viral proteins, including small t antigen, large T antigen, HIV-1 Tat, and JCV VP1; and significantly contributes the viral transcription and replication. This review summarizes the recent advances in the structural and functional properties of this important regulatory protein. J. Cell. Physiol. 231: 2115-2127, 2016. © 2016 Wiley Periodicals, Inc.

The Brd4 acetyllysine-binding protein is involved in activation of polyomavirus JC.

Brd4 is an epigenetic reader protein and a member of the BET (bromodomain and extra terminal domain) family of proteins with two bromodomains that recognize acetylated lysine residues. Brd4 specifically binds to acetylated transcription factor NF-κB p65 and coactivates transcription. Polyomavirus JC (JCV) is regulated by a noncoding control region (NCCR) containing promoter/enhancer elements for viral gene expression including a binding site for NF-κB, which responds to proinflammatory cytokines such as TNF-α, the DNA damage response, calcium signaling and acetylation of the NF-κB p65 subunit on lysine residues K218 and K221. Earlier studies indicated that NF-κB is involved in the reactivation of persistent/latent JCV in glial cells to cause progressive multifocal leukoencephalopathy (PML), a severe demyelinating disease of the brain caused by replication of JCV in glial cells. To investigate the mechanism of action of NF-κB acetylation on JCV transcription, we examined Brd4 and found that JCV early transcription was stimulated by Brd4 via the JCV NF-κB site and that p65 K218 and K221 were involved. Treatment with the Brd4 inhibitor JQ1(+) or mutation of either K218 or K221 to glutamine (K218R or K221) inhibited this stimulation and decreased the proportion of p65 in the nucleus. We conclude that Brd4 is involved in the regulation of the activation status of JCV in glial cells.

Nuclear magnetic resonance structure revealed that the human polyomavirus JC virus agnoprotein contains an α-helix encompassing the Leu/Ile/Phe-rich domain.

UNLABELLED: Agnoprotein is a small multifunctional regulatory protein required for sustaining the productive replication of JC virus (JCV). It is a mostly cytoplasmic protein localizing in the perinuclear area and forms highly stable dimers/oligomers through a Leu/Ile/Phe-rich domain. There have been no three-dimensional structural data available for agnoprotein due to difficulties associated with the dynamic conversion from monomers to oligomers. Here, we report the first nuclear magnetic resonance (NMR) structure of a synthetic agnoprotein peptide spanning amino acids Thr17 to Glu55 where Lys23 to Phe39 encompassing the Leu/Ile/Phe-rich domain forms an amphipathic α-helix. On the basis of these structural data, a number of Ala substitution mutations were made to investigate the role of the α-helix in the structure and function of agnoprotein. Single L29A and L36A mutations exhibited a significant negative effect on both protein stability and viral replication, whereas the L32A mutation did not. In addition, the L29A mutant displayed a highly nuclear localization pattern, in contrast to the pattern for the wild type (WT). Interestingly, a triple mutant, the L29A+L32A+L36A mutant, yielded no detectable agnoprotein expression, and the replication of this JCV mutant was significantly reduced, suggesting that Leu29 and Leu36 are located at the dimer interface, contributing to the structure and stability of agnoprotein. Two other single mutations, L33A and E34A, did not perturb agnoprotein stability as drastically as that observed with the L29A and L36A mutations, but they negatively affected viral replication, suggesting that the role of these residues is functional rather than structural. Thus, the agnoprotein dimerization domain can be targeted for the development of novel drugs active against JCV infection. IMPORTANCE: Agnoprotein is a small regulatory protein of JC virus (JCV) and is required for the successful completion of the viral replication cycle. It forms highly stable dimers and oligomers through its hydrophobic (Leu/Ile/Phe-rich) domain, which has been shown to play essential roles in the stability and function of the protein. In this work, the Leu/Ile/Phe-rich domain has been further characterized by NMR studies using an agnoprotein peptide spanning amino acids T17 to Q54. Those studies revealed that the dimerization domain of the protein forms an amphipathic α-helix. Subsequent NMR structure-based mutational analysis of the region highlighted the critical importance of certain amino acids within the α-helix for the stability and function of agnoprotein. In conclusion, this study provides a solid foundation for developing effective therapeutic approaches against the dimerization domain of the protein to inhibit its critical roles in JCV infection.

Epigenetic regulation of polyomavirus JC involves acetylation of specific lysine residues in NF-κB p65.

Progressive multifocal leukoencephalopathy (PML) is a fatal demyelinating disease caused by neurotropic polyomavirus, JC virus (JCV), a virus that causes lytic infection of CNS glial cells. After primary infection, JCV is controlled by the immune system but virus persists asymptomatically. Rarely, when immune function is impaired, it can reemerge to cause PML. The mechanisms of JCV persistence and reactivation are not well understood but our earlier work implicated epigenetic control by protein acetylation since histone deacetylase inhibitors such as trichostatin A (TSA) strongly stimulate JCV transcription. Since both TNF-α and TSA activate JCV transcription via the same unique NF-κB site in the JCV control region, we investigated a role for acetylation of NF-κB in JCV regulation. A site-directed mutagenesis strategy was employed targeting the known lysine acetylation sites of NF-κB p65: K218, K221, and K310. We individually mutated each lysine to arginine, which cannot be acetylated and retains a positive charge like lysine. K218R and K221R impaired transactivation of JCV early promoter transcription either alone or combined with TSA treatment or coexpression of acetyltransferase transcriptional coactivator p300 but K310R was largely without effect. Mutation of lysine to glutamine gives mutants with a negative charge like acetyllysine. However, K218Q and K221Q showed impaired activity and only K310Q showed enhanced transactivation. NF-κB acetylation can regulate several aspects of the process of activation including complex formation with IκB, translocation to the nucleus, and DNA binding and transcriptional activation. Cell fractionation studies revealed that the mutants had no defect in translocation to the nucleus whereas gel shift studies revealed reduced binding to the JCV NF-κB site. Thus, acetylation regulates NF-κB p65 activity toward JCV at the level of p65 binding to the JCV control region and activation of JCV transcription.

Epigenetic regulation of polyomavirus JC.

BACKGROUND: Polyomavirus JC (JCV) causes the CNS demyelinating disease progressive multifocal leukoencephalopathy (PML), which occurs almost exclusively in people with immune deficiencies, such as HIV-1/AIDS patients. JCV infection is very common and usually occurs early in life. After primary infection, virus is controlled by the immune system but, rarely when immune function is impaired, it can re-emerge and multiply in the astrocytes and oligodendrocytes in the brain and cause PML. Thus a central question in PML pathogenesis is the nature of the molecular mechanisms maintaining JCV in a latent state and then allowing reactivation. METHODS: Since transcription can be regulated by epigenetic mechanisms including DNA methylation and histone acetylation, we investigated their role in JCV regulation by employing inhibitors of epigenetic events. RESULTS: The histone deacetylase inhibitors trichostatin A (TSA) and sodium butyrate powerfully stimulated JCV early and late transcription while the DNA methylation inhibitor 5-azacytidine had no effect. Analysis of JCV mutants showed that this effect was mediated by the KB element of the JCV control region, which binds transcription factors NF-κB p65, NFAT4 and C/EBPß and mediates stimulation by TNF-α. Stimulation of transcription by p65 was additive with TSA as was cotransfection with transcriptional coactivators/acetyltransferase p300 whereas depletion of endogenous p65 by RNA interference inhibited the effect of TSA. EMSA with a KB oligonucleotide showed p65 expression, TNF-α stimulation or TSA treatment each caused a gel shift that was further shifted by antibody to p65. CONCLUSIONS: We conclude that JCV is regulated epigenetically by protein acetylation events and that these involve the NF-κB p65 binding site in the JCV control region.

Human neurotropic polyomavirus, JC virus, late coding region encodes a novel nuclear protein, ORF4, which targets the promyelocytic leukemia nuclear bodies (PML-NBs) and modulates their reorganization.

We previously reported the discovery and characterization of two novel proteins (ORF1 and ORF2) generated by the alternative splicing of the JC virus (JCV) late coding region. Here, we report the discovery and partial characterization of three additional novel ORFs from the same coding region, ORF3, ORF4 and ORF5, which potentially encode 70, 173 and 265 amino acid long proteins respectively. While ORF3 protein exhibits a uniform distribution pattern throughout the cells, we were unable to detect ORF5 expression. Surprisingly, ORF4 protein was determined to be the only JCV protein specifically targeting the promyelocytic leukemia nuclear bodies (PML-NBs) and inducing their reorganization in nucleus. Although ORF4 protein has a modest effect on JCV replication, it is implicated to play major roles during the JCV life cycle, perhaps by regulating the antiviral response of PML-NBs against JCV infections and thus facilitating the progression of the JCV-induced disease in infected individuals.

Infection by agnoprotein-negative mutants of polyomavirus JC and SV40 results in the release of virions that are mostly deficient in DNA content.

BACKGROUND: Human polyomavirus JC (JCV) is the etiologic agent of a brain disease, known as progressive multifocal leukoencephalopathy (PML). The JCV genome encodes a small multifunctional phospho-protein, agnoprotein, from the late coding region of the virus, whose regulatory functions in viral replication cycle remain elusive. In this work, the functional role of JCV and SV40 agnoproteins in virion release was investigated using a point mutant (Pt) of each virus, where the ATG codon of agnoprotein was mutated to abrogate its expression. RESULTS: Analysis of both viral protein expression and replication using Pt mutant of each virus revealed that both processes were substantially down-regulated in the absence of agnoprotein compared to wild-type (WT) virus. Complementation studies in cells, which are constitutively expressing JCV agnoprotein and transfected with the JCV Pt mutant genome, showed an elevation in the level of viral DNA replication near to that observed for WT. Constitutive expression of large T antigen was found to be not sufficient to compensate the loss of agnoprotein for efficient replication of neither JCV nor SV40 in vivo. Examination of the viral release process for both JCV and SV40 Pt mutants showed that viral particles are efficiently released from the infected cells in the absence of agnoprotein but were found to be mostly deficient in viral DNA content. CONCLUSIONS: The results of this study provide evidence that agnoprotein plays an important role in the polyomavirus JC and SV40 life cycle. Infection by agnoprotein-negative mutants of both viruses results in the release of virions that are mostly deficient in DNA content.

Human neurotropic polyomavirus, JC virus, agnoprotein targets mitochondrion and modulates its functions.

JC virus encodes an important regulatory protein, known as Agnoprotein (Agno). We have recently reported Agno's first protein-interactome with its cellular partners revealing that it targets various cellular networks and organelles, including mitochondria. Here, we report further characterization of the functional consequences of its mitochondrial targeting and demonstrated its co-localization with the mitochondrial networks and with the mitochondrial outer membrane. The mitochondrial targeting sequence (MTS) of Agno and its dimerization domain together play major roles in this targeting. Data also showed alterations in various mitochondrial functions in Agno-positive cells; including a significant reduction in mitochondrial membrane potential, respiration rates and ATP production. In contrast, a substantial increase in ROS production and Ca2+ uptake by the mitochondria were also observed. Finally, findings also revealed a significant decrease in viral replication when Agno MTS was deleted, highlighting a role for MTS in the function of Agno during the viral life cycle.

Regulation of gene expression in primate polyomaviruses.

Polyomaviruses are a growing family of small DNA viruses with a narrow tropism for both the host species and the cell type in which they productively replicate. Species host range may be constrained by requirements for precise molecular interactions between the viral T antigen, host replication proteins, including DNA polymerase, and the viral origin of replication, which are required for viral DNA replication. Cell type specificity involves, at least in part, transcription factors that are necessary for viral gene expression and restricted in their tissue distribution. In the case of the human polyomaviruses, BK virus (BKV) replication occurs in the tubular epithelial cells of the kidney, causing nephropathy in kidney allograft recipients, while JC virus (JCV) replication occurs in the glial cells of the central nervous system, where it causes progressive multifocal leukoencephalopathy. Three new human polyomaviruses have recently been discovered: MCV was found in Merkel cell carcinoma samples, while Karolinska Institute Virus and Washington University Virus were isolated from the respiratory tract. We discuss control mechanisms for gene expression in primate polyomaviruses, including simian vacuolating virus 40, BKV, and JCV. These mechanisms include not only modulation of promoter activities by transcription factor binding but also enhancer rearrangements, restriction of DNA methylation, alternate early mRNA splicing, cis-acting elements in the late mRNA leader sequence, and the production of viral microRNA.

A Comprehensive Proteomics Analysis of the JC Virus (JCV) Large and Small Tumor Antigen Interacting Proteins: Large T Primarily Targets the Host Protein Complexes with V-ATPase and Ubiquitin Ligase Activities While Small t Mostly Associates with Those Having Phosphatase and Chromatin-Remodeling Functions.

The oncogenic potential of both the polyomavirus large (LT-Ag) and small (Sm t-Ag) tumor antigens has been previously demonstrated in both tissue culture and animal models. Even the contribution of the MCPyV tumor antigens to the development of an aggressive human skin cancer, Merkel cell carcinoma, has been recently established. To date, the known primary targets of these tumor antigens include several tumor suppressors such as pRb, p53, and PP2A. However, a comprehensive list of the host proteins targeted by these proteins remains largely unknown. Here, we report the first interactome of JCV LT-Ag and Sm t-Ag by employing two independent "affinity purification/mass spectroscopy" (AP/MS) assays. The proteomics data identified novel targets for both tumor antigens while confirming some of the previously reported interactions. LT-Ag was found to primarily target the protein complexes with ATPase (v-ATPase and Smc5/6 complex), phosphatase (PP4 and PP1), and ligase (E3-ubiquitin) activities. In contrast, the major targets of Sm t-Ag were identified as Smarca1/6, AIFM1, SdhA/B, PP2A, and p53. The interactions between "LT-Ag and SdhB", "Sm t-Ag and Smarca5", and "Sm t-Ag and SDH" were further validated by biochemical assays. Interestingly, perturbations in some of the LT-Ag and Sm t-Ag targets identified in this study were previously shown to be associated with oncogenesis, suggesting new roles for both tumor antigens in novel oncogenic pathways. This comprehensive data establishes new foundations to further unravel the new roles for JCV tumor antigens in oncogenesis and the viral life cycle.

A comprehensive proteomics analysis of JC virus Agnoprotein-interacting proteins: Agnoprotein primarily targets the host proteins with coiled-coil motifs.

JC virus (JCV) Agnoprotein (Agno) plays critical roles in successful completion of the viral replication cycle. Understanding its regulatory roles requires a complete map of JCV-host protein interactions. Here, we report the first Agno interactome with host cellular targets utilizing "Two-Strep-Tag" affinity purification system coupled with mass spectroscopy (AP/MS). Proteomics data revealed that Agno primarily targets 501 cellular proteins, most of which contain "coiled-coil" motifs. Agno-host interactions occur in several cellular networks including those involved in protein synthesis and degradation; and cellular transport; and in organelles, including mitochondria, nucleus and ER-Golgi network. Among the Agno interactions, Rab11B, Importin and Crm-1 were first validated biochemically and further characterization was done for Crm-1, using a HIV-1 Rev-M10-like Agno mutant (L33D + E34L), revealing the critical roles of L33 and E34 residues in Crm-1 interaction. This comprehensive proteomics data provides new foundations to unravel the critical regulatory roles of Agno during the JCV life cycle.

Small tumor antigen of polyomaviruses: role in viral life cycle and cell transformation.

The regulatory proteins of polyomaviruses, including small and large T antigens, play important roles, not only in the viral life cycle but also in virus-induced cell transformation. Unlike many other tumor viruses, the transforming proteins of polyomaviruses have no cellular homologs but rather exert their effects mostly by interacting with cellular proteins that control fundamental processes in the regulation of cell proliferation and the cell cycle. Thus, they have proven to be valuable tools to identify specific signaling pathways involved in tumor progression. Elucidation of these pathways using polyomavirus transforming proteins as tools is critically important in understanding fundamental regulatory mechanisms and hence to develop effective therapeutic strategies against cancer. In this short review, we will focus on the structural and functional features of one polyomavirus transforming protein, that is, the small t-antigen of the human neurotropic JC virus (JCV) and the simian virus, SV40.

Evidence for dysregulation of cell cycle by human polyomavirus, JCV, late auxiliary protein.

The late region of the human neurotropic JC virus encodes a 71 amino acid protein, named Agnoprotein, whose biological function remains elusive. Here we demonstrate that in the absence of other viral proteins, expression of Agnoprotein can inhibit cell growth by deregulating cell progression through the cell cycle stages. Cells with constitutive expression of Agnoprotein were largely accumulated at the G2/M stage and that decline in the activity of cyclins A and B is observed in these cells. Agnoprotein showed the ability to augment p21 promoter activity in transient transfection assay and a noticeable increase in the level of p21 is detected in cells continuously expressing Agnoprotein. Results from binding studies revealed the interaction of Agnoprotein with p53 through the N-terminal of the Agnoprotein spanning residues 1-36. Co-expression of p53 and Agnoprotein further stimulated transcription of the p21 promoter. Thus, the interaction of p53 and Agnoprotein can lead to a higher level of p21 expression and suppression of cell cycle progression during the cell cycle.

T-antigen of human polyomavirus JC cooperates withIGF-IR signaling system in cerebellar tumors of the childhood-medulloblastomas.

Polyomaviruses are implicated in a number of cancers, and the transforming activity of their early protein, large T-antigen, has been documented in a variety of cell types and in experimental animals (1). Although the pathways by which T-antigen induces uncontrolled cell growth are not fully defined, T-antigen mediated inactivation of tumor suppressors, p53 and pRB, is well-documented in some malignancies (2). Here we postulate that functional interaction between the insulin-like growth factor (IGF-IR) and the T-antigen of human polyomavirus JC (JCV T-antigen) may contribute to the process of malignant transformation in medulloblastomas: (i) the IGF-IR signaling system is strongly activated in medulloblastoma cell lines and medulloblastoma biopsies; (ii) the cytoplasmic protein, insulin receptor substrate 1 (IRS-1), is translocated to the nucleus in the presence of JCV T-antigen; (iii) molecular characterization of the interaction between IRS-1 and JCV T-antigen indicates that the binding involves the N-terminal portion of IRS-1 (PH/PTB domain) and the C-terminal region of JCV T-antigen (aa 411-628); and finally (iv) competition for the IRS-1-JCV T-antigen binding attenuates anchorage-independent growth of T-antigen positive medulloblastoma cells in culture. Based on these findings, we propose a novel role for IRS-1 in JCV T-antigen-mediated deregulation of cellular equilibrium, which may involve uncoupling of IRS-1 from the surface receptor and translocation of its function to the nuclear compartment of the cell.

Human polyoma JC virus minor capsid proteins, VP2 and VP3, enhance large T antigen binding to the origin of viral DNA replication: evidence for their involvement in regulation of the viral DNA replication.

JC virus (JCV) lytically infects the oligodendrocytes in the central nervous system in a subset of immunocompromized patients and causes the demyelinating disease, progressive multifocal leukoencephalopathy. JCV replicates and assembles into infectious virions in the nucleus. However, understanding the molecular mechanisms of its virion biogenesis remains elusive. In this report, we have attempted to shed more light on this process by investigating molecular interactions between large T antigen (LT-Ag), Hsp70 and minor capsid proteins, VP2/VP3. We demonstrated that Hsp70 interacts with VP2/VP3 and LT-Ag; and accumulates heavily in the nucleus of the infected cells. We also showed that VP2/VP3 associates with LT-Ag through their DNA binding domains resulting in enhancement in LT-Ag DNA binding to Ori and induction in viral DNA replication. Altogether, our results suggest that VP2/VP3 and Hsp70 actively participate in JCV DNA replication and may play critical roles in coupling of viral DNA replication to virion encapsidation.

Essential roles of Leu/Ile/Phe-rich domain of JC virus agnoprotein in dimer/oligomer formation, protein stability and splicing of viral transcripts.

Agnoprotein is one of the key regulatory proteins of polyomaviruses, including JCV, BKV and SV40 and is required for a productive viral life cycle. We have recently reported that agnoprotein forms stable dimer/oligomers mediated by a predicted amphipathic α-helix, spanning amino acids (aa), 17 to 42. Deletion of the α-helix renders a replication incompetent virus. Here, we have further characterized this region by a systematic deletion and substitution mutagenesis and demonstrated that a Leu/Ile/Phe-rich domain, (spanning aa 28-39) within α-helix is indispensable for agnoprotein structure and function. Deletion of aa 30-37 severely affects the dimer/oligomer formation and stable expression of the protein. Mutagenesis data also indicate that the residues, 34-36, may be involved in regulation of the splicing events of JCV transcripts. Collectively, these data suggest that the Leu/Ile/Phe-rich domain plays critical roles in agnoprotein function and thus represents a potential target for developing novel therapeutics against JCV infections.