The basis for modeling progressive multifocal leukoencephalopathy pathogenesis

The Risk of Progressive Multifocal Leukoencephalopathy in the Biologic Era: Prevention and Management

Progressive multifocal leukoencephalopathy (PML) is a rare, typically fatal, demyelinating central nervous system infection caused by reactivation of the John Cunningham virus that generally occurs in immunosuppressed patients. With an evolving understanding of a greater clinical heterogeneity of PML and significant implications for therapy, PML should be considered in the differential diagnosis of neurologic presentations of rheumatic diseases. Increased awareness of PML among rheumatologists is required, as earlier diagnosis and restoration of immune function may improve the otherwise grim prognosis associated with PML.

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.

Sorting out the risks in progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a rare, opportunistic infection of the central nervous system, caused by reactivation of the ubiquitous JC virus. PML is a devastating disease that is frequently fatal, and although survival rates have improved, patients who survive PML often experience considerable neurological deficits. PML was associated with a variety of immunosuppressive therapies in the past decade, but attribution of causality is difficult owing to the presence of confounding factors and to an inadequate understanding of the underlying pathogenesis of this disease. This uncertainty has hindered efforts for shared decision-making between physicians and their patients and, in some cases, discouraged the use of potentially beneficial therapies. We propose a categorization of immunosuppressive agents according to their risk of PML to support a better-informed decision-making process when evaluating the risks and benefits of these therapies.

Rad51 activates polyomavirus JC early transcription

The human neurotropic polyomavirus JC (JCV) causes the fatal CNS demyelinating disease progressive multifocal leukoencephalopathy (PML). JCV infection is very common and after primary infection, the virus is able to persist in an asymptomatic state. Rarely, and usually only under conditions of immune impairment, JCV re-emerges to actively replicate in the astrocytes and oligodendrocytes of the brain causing PML. The regulatory events involved in the reactivation of active viral replication in PML are not well understood but previous studies have implicated the transcription factor NF-κB acting at a well-characterized site in the JCV noncoding control region (NCCR). NF-κB in turn is regulated in a number of ways including activation by cytokines such as TNF-α, interactions with other transcription factors and epigenetic events involving protein acetylation – all of which can regulate the transcriptional activity of JCV. Active JCV infection is marked by the occurrence of rapid and extensive DNA damage in the host cell and the induction of the expression of cellular proteins involved in DNA repair including Rad51, a major component of the homologous recombination-directed double-strand break DNA repair machinery. Here we show that increased Rad51 expression activates the JCV early promoter. This activation is co-operative with the stimulation caused by NF-κB p65, abrogated by mutation of the NF-κB binding site or siRNA to NFκB p65 and enhanced by the histone deacetylase inhibitor sodium butyrate. These data indicate that the induction of Rad51 resulting from infection with JCV acts through NF-κB via its binding site to stimulate JCV early transcription. We suggest that this provides a novel positive feedback mechanism to enhance viral gene expression during the early stage of JCV infection.

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

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.

Rituximab in the treatment of non-Hodgkin's lymphoma--a critical evaluation of randomized controlled trials

INTRODUCTION

The use of rituximab has led to significant improvements in the outcome of both aggressive and indolent Non-Hodgkin's lymphoma (NHL). It is the first targeted therapy to be developed for the treatment of lymphoma which has been widely adopted.

AREAS COVERED

This paper discusses the use of rituximab in NHL, mainly concentrating on diffuse large B cell lymphoma (DLBCL) and follicular lymphoma (FL), with a brief discussion about use in other types of NHL including mantle cell lymphoma (MCL). The use of rituximab in chronic lymphocytic leukemia (CLL) has been recently published in this journal by Robak (Robak T. Rituximab for chronic lymphocytic Leukemia. Expert Opin Biol. Ther. 2012;12(4):503-15). Non hematological indications for rituximab are also not discussed. A Pubmed search was conducted using key words of rituximab, DLBCL, FL, MCL, Burkitt's lymphoma and MALToma. Papers shortlisted for review included randomized control trials and scientific papers discussing CD20.

EXPERT OPINION

In conclusion this paper has critically evaluated the use of rituximab in the treatment mainly of DLBCL, FL and MCL both at diagnosis and relapsed disease, and briefly discuses its use in other subtypes of lymphoma. Rituximab has significantly improved the outcome of patients with B cell NHL, in particular those with DLBCL and FL. Patients usually tolerate the treatment well, and studies have shown it to be a cost effective treatment.

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.

In vivo analysis of kallikrein-related peptidase 6 (KLK6) function in oligodendrocyte development and the expression of myelin proteins

Oligodendrocytes are important for not only nerve conduction but also central nervous system (CNS) development and neuronal survival in a variety of conditions. Kallikrein-related peptidase 6 (KLK6) is expressed in oligodendrocytes in the CNS and its expression is changed in several physiological and pathological conditions, especially following spinal cord injury (SCI) and experimental autoimmune encephalomyelitis. In this study, we investigated the functions of KLK6 in oligodendrocyte lineage cell development and the production of myelin proteins using KLK6-deficient (KLK6(-/-)) mice. KLK6(-/-) mice were born without apparent defects and lived as long as wild-type (WT) mice. There was no significant difference in the numbers of oligodendrocyte precursor cells and mature oligodendrocytes in the adult naive spinal cord between WT and KLK6(-/-) mice. However, there were fewer mature oligodendrocytes in the KLK6(-/-) spinal cord than in the WT spinal cord at postnatal day 7 (P7). Expression of myelin basic protein (MBP) and oligodendrocyte-specific protein/claudin-11, major myelin proteins, was also decreased in the KLK6(-/-) spinal cord compared with the WT spinal cord at P7-21. Moreover, after SCI, the amount of MBP in the damaged spinal cords of KLK6(-/-) mice was significantly less than that in the damaged spinal cords of WT mice. These results indicate that KLK6 plays a functional role in oligodendrocyte development and the expression of myelin proteins.

JC virus agnoprotein enhances large T antigen binding to the origin of viral DNA replication: evidence for its involvement in viral DNA replication

Agnoprotein is required for the successful completion of the JC virus (JCV) life cycle and was previously shown to interact with JCV large T-antigen (LT-Ag). Here, we further characterized agnoprotein's involvement in viral DNA replication. Agnoprotein enhances the DNA binding activity of LT-Ag to the viral origin (Ori) without directly interacting with DNA. The predicted amphipathic α-helix of agnoprotein plays a major role in this enhancement. All three phenylalanine (Phe) residues of agnoprotein localize to this α-helix and Phe residues in general are known to play critical roles in protein-protein interaction, protein folding and stability. The functional relevance of all Phe residues was investigated by mutagenesis. When all were mutated to alanine (Ala), the mutant virus (F31AF35AF39A) replicated significantly less efficiently than each individual Phe mutant virus alone, indicating the importance of Phe residues for agnoprotein function. Collectively, these studies indicate a close involvement of agnoprotein in viral DNA replication.

JCV agnoprotein-induced reduction in CXCL5/LIX secretion by oligodendrocytes is associated with activation of apoptotic signaling in neurons

An indispensable role for oligodendrocytes in the protection of axon function and promotion of neuronal survival is strongly supported by the finding of progressive neuron/axon degeneration in human neurological diseases that affect oligodendrocytes. Imaging and pathological studies of the CNS have shown the presence of neuroaxonal injury in progressive multifocal leukoencephalopathy (PML), a demyelinating disease of the CNS, resulting from destruction of oligodendrocytes upon productive replication of the pathogenic neurotropic polyomavirus JC. Here, we examined the extracellular factors involved in communication between oligodendrocytes and neurons. Culturing cortical neurons with conditioned medium (CM) from rat CG4 oligodendrocytic cells that express the JCV agnoprotein showed that CXCL5/LIX, which is a chemokine closely related to the human CXCL5/ENA78 and CXCL6/GCP-2 chemokines, is essential for neuronal cell survival. We found that in CM from agnoprotein-producing CG-4 cells level of CXC5/LIX is decreased compared to control cells. We also demonstrated that a reduced expression of CXCL5/LIX by CG4 GFP-Agno cells triggered a cascade of signaling events in cortical neurons. Analysis of mitogen-activated protein kinases (MAPK) and glycogen synthase kinase (GSK3) pathways showed that they are involved in mechanisms of neuronal apoptosis in response to the depletion of CXCL5/LIX signaling. These data suggest that agnoprotein-induced dysregulation of chemokine production by oligodendrocytes may contribute to neuronal/axonal injury in the pathogenesis of PML lesions.

Cooperative roles of NF-κB and NFAT4 in polyomavirus JC regulation at the KB control element

The human polyomavirus JC (JCV) is the causative agent of the CNS demyelinating disease progressive multifocal leukoencephalopathy (PML). Infection by JCV is extremely common and after primary infection, JCV persists in a latent state. However, PML is a very rare disease suggesting that the virus is tightly regulated. Previously, we showed that NF-κB and C/EBPβ regulate the JCV early and late promoters via a DNA control element, KB, which also mediates the stimulatory effects of proinflammatory cytokines such as TNF-α on JCV gene expression. Other studies have implicated NFAT4 in JCV regulation. We now report that NFAT4 and NF-κB interact at the KB element to co-operatively activate both JCV early and late transcription and viral DNA replication. This interplay is inhibited by C/EBPβ and by agents that block the calcineurin/NFAT signaling pathway. The importance of these events in the regulation of JCV latency and reactivation is discussed.

Prevalence of JC virus in Chinese patients with colorectal cancer

Background

JCV is a DNA polyomavirus very well adapted to humans. Although JCV DNA has been detected in colorectal cancers (CRC), the association between JCV and CRC remains controversial. In China, the presence of JCV infection in CRC patients has not been reported. Here, we investigated JCV infection and viral DNA load in Chinese CRC patients and to determine whether the JCV DNA in peripheral blood (PB) can be used as a diagnostic marker for JCV-related CRC.

Methodology/Principal Findings

Tumor tissues, non-cancerous tumor-adjacent tissues and PB samples were collected from 137 CRC patients. In addition, 80 normal colorectal tissue samples from patients without CRC and PB samples from 100 healthy volunteers were also harvested as controls. JCV DNA was detected by nested PCR and glass slide-based dot blotting. Viral DNA load of positive samples were determined by quantitative real-time PCR. JCV DNA was detected in 40.9% (56/137) of CRC tissues at a viral load of 49.1 to 10.3×10⁴ copies/µg DNA. Thirty-four (24.5%) non-cancerous colorectal tissues (192.9 to 4.4×10³ copies/µg DNA) and 25 (18.2%) PB samples (81.3 to 4.9×10³ copies/µg DNA) from CRC patients were positive for JCV. Tumor tissues had higher levels of JCV than non-cancerous tissues (P = 0.003) or PB samples (P<0.001). No correlation between the presence of JCV and demographic or medical characteristics was observed. The JCV prevalence in PB samples was significantly associated with the JCV status in tissue samples (P<0.001). Eleven (13.8%) normal colorectal tissues and seven (7.0%) PB samples from healthy donors were positive for JCV.

Conclusions/Significance

JCV infection is frequently present in colorectal tumor tissues of CRC patients. Although the association between JCV presence in PB samples and JCV status in tissue samples was identified in this study, whether PB JCV detection can serve as a marker for JCV status of CRC requires further study.

Pre-existing T- and B-cell defects in one progressive multifocal leukoencephalopathy patient

Progressive multifocal leukoencephalopathy (PML) usually occurs in patients with severe immunosuppression, hematological malignancies, chronic inflammatory conditions or receiving organ transplant. Recently, PML has also been observed in patients treated with monoclonal antibodies. By taking advantage of the availability of samples from a multiple sclerosis (MS) patient treated with natalizumab, the antibody anti-α4 integrin, who developed PML and was monitored starting before therapy initiation, we investigated the fate of T and B lymphocytes in the onset of PML. Real-time PCR was used to measure new T- and B-cell production by means of T-cell receptor excision circle (TREC) and K-deleting recombination excision circle (KREC) analysis and to quantify transcripts for CD34, terminal-deoxynucleotidyltransferase, and V pre-B lymphocyte gene 1. T- and B-cell subsets and T-cell heterogeneity were measured by flow cytometry and spectratyping. The data were compared to those of untreated and natalizumab-treated MS patients and healthy donors. Before therapy, a patient who developed PML had a low TREC and KREC number; TRECs remained low, while KRECs and pre-B lymphocyte gene 1 transcripts peaked at 6 months of therapy and then decreased at PML diagnosis. Flow cytometry confirmed the deficient number of newly produced T lymphocytes, counterbalanced by an increase in TEMRA cells. The percentage of naive B cells increased by approximately 70% after 6 months of therapy, but B lymphocyte number remained low for the entire treatment period. T-cell heterogeneity and immunoglobulins were reduced.

Although performed in a single patient, all results showed that an immune deficit, together with an increase in newly produced B cells a few months after therapy initiation, may predispose the patient to PML. These findings indicate the TREC/KREC assay is a potential tool to identify patients at risk of developing PML and may provide insights into the immunological involvement of monoclonal antibody-associated therapies.