Hepatitis B virus HBx protein deregulates cell cycle checkpoint controls.

The human hepatitis B virus (HBV) HBx protein is a small transcriptional activator that is essential for virus infection. HBx is thought to be involved in viral hepatocarcinogenesis because it promotes tumorigenesis in transgenic mice. HBx activates the RAS-RAF-mitogen-activated protein (MAP) kinase signaling cascade, through which it activates transcription factors AP-1 and NF-kappa B, and stimulates cell DNA synthesis. We show that HBx stimulates cell cycle progression, shortening the emergence of cells from quiescence (G0) and entry into S phase by at least 12 h, and accelerating transit through checkpoint controls at G0/G1 and G2/M. Compared with serum stimulation, HBx was found to strongly increase the rate and level of activation of the cyclin-dependent kinases CDK2 and CDC2, and their respective active association with cyclins E and A or cyclin B. HBx is also shown to override or greatly reduce serum dependence for cell cycle activation. Both HBx and serum were found to require activation of RAS to stimulate cell cycling, but only HBx could shorten checkpoint intervals. HBx therefore stimulates cell proliferation by activating RAS and a second unknown effector, which may be related to its reported ability to induce prolonged activation of JUN or to interact with cellular p53 protein. These data suggest a molecular mechanism by which HBx likely contributes to viral carcinogenesis. By deregulating checkpoint controls, HBx could participate in the selection of cells that are genetically unstable, some of which would accumulate unrepaired transforming mutations.

Delivery of herpesvirus and adenovirus to nude rat intracerebral tumors after osmotic blood-brain barrier disruption.

The delivery of viral vectors to the brain for treatment of intracerebral tumors is most commonly accomplished by stereotaxic inoculation directly into the tumor. However, the small volume of distribution by inoculation may limit the efficacy of viral therapy of large or disseminated tumors. We have investigated mechanisms to increase vector delivery to intracerebral xenografts of human LX-1 small-cell lung carcinoma tumors in the nude rat. The distribution of Escherichia coli lacZ transgene expression from primary viral infection was assessed after delivery of recombinant virus by intratumor inoculation or intracarotid infusion with or without osmotic disruption of the blood-brain barrier (BBB). These studies used replication-compromised herpes simplex virus type 1 (HSV; vector RH105) and replication-defective adenovirus (AdRSVlacZ), which represent two of the most commonly proposed viral vectors for tumor therapy. Transvascular delivery of both viruses to intracerebral tumor was demonstrated when administered intraarterially (i.a.) after osmotic BBB disruption (n = 9 for adenovirus; n = 7 for HSV), while no virus infection was apparent after i.a. administration without BBB modification (n = 8 for adenovirus; n = 4 for HSV). The thymidine kinase-negative HSV vector infected clumps of tumor cells as a result of its ability to replicate selectively in dividing cells. Osmotic BBB disruption in combination with i.a. administration of viral vectors may offer a method of global delivery to treat disseminated brain tumors.

Hydrophobic cluster analysis predicts an amino-terminal domain of varicella-zoster virus open reading frame 10 required for transcriptional activation.

Varicella-zoster virus open reading frame 10 (ORF10) protein, the homolog of the herpes simplex virus protein VP16, can transactivate immediate-early promoters from both viruses. A protein sequence comparison procedure termed hydrophobic cluster analysis was used to identify a motif centered at Phe-28, near the amino terminus of ORF10, that strongly resembles the sequence of the activating domain surrounding Phe-442 of VP16. With a series of GAL4-ORF10 fusion proteins, we mapped the ORF10 transcriptional-activation domain to the amino-terminal region (aa 5-79). Extensive mutagenesis of Phe-28 in GAL4-ORF10 fusion proteins demonstrated the importance of an aromatic or bulky hydrophobic amino acid at this position, as shown previously for Phe-442 of VP16. Transactivation by the native ORF10 protein was abolished when Phe-28 was replaced by Ala. Similar amino-terminal domains were identified in the VP16 homologs of other alphaherpesviruses. Hydrophobic cluster analysis correctly predicted activation domains of ORF10 and VP16 that share critical characteristics of a distinctive subclass of acidic activation domains.

High-affinity RNA-binding domains of alfalfa mosaic virus coat protein are not required for coat protein-mediated resistance.

A virus-based vector was used for the transient expression of the alfalfa mosaic virus coat protein (CP) gene in protoplasts and plants. The accumulation of wild-type CP conferred strong protection against subsequent alfalfa mosaic virus infection, enabling the efficacy of CP mutants to be determined without developing transgenic plants. Expression of the CP mRNA alone without CP accumulation conferred weaker protection against infection. The activity of the N-terminal mutant CPs in protection did not correlate with their activities in genome activation. The activity of a C-terminal mutant suggested that encapsidation did not have a role in protection. Our results indicate that interaction of the CP with alfalfa mosaic virus RNA is not important in protection, thereby leaving open the possibility that interactions with host factors lead to protection.

Managing atypical and typical herpetic central nervous system infections: results of a multinational study

There have been many studies pertaining to the management of herpetic meningoencephalitis (HME), but the majority of them have focussed on virologically unconfirmed cases or included only small sample sizes. We have conducted a multicentre study aimed at providing management strategies for HME. Overall, 501 adult patients with PCR-proven HME were included retrospectively from 35 referral centres in 10 countries; 496 patients were found to be eligible for the analysis. Cerebrospinal fluid (CSF) analysis using a PCR assay yielded herpes simplex virus (HSV)-1 DNA in 351 patients (70.8%), HSV-2 DNA in 83 patients (16.7%) and undefined HSV DNA type in 62 patients (12.5%). A total of 379 patients (76.4%) had at least one of the specified characteristics of encephalitis, and we placed these patients into the encephalitis presentation group. The remaining 117 patients (23.6%) had none of these findings, and these patients were placed in the nonencephalitis presentation group. Abnormalities suggestive of encephalitis were detected in magnetic resonance imaging (MRI) in 83.9% of the patients and in electroencephalography (EEG) in 91.0% of patients in the encephalitis presentation group. In the nonencephalitis presentation group, MRI and EEG data were suggestive of encephalitis in 33.3 and 61.9% of patients, respectively. However, the concomitant use of MRI and EEG indicated encephalitis in 96.3 and 87.5% of the cases with and without encephalitic clinical presentation, respectively. Considering the subtle nature of HME, CSF HSV PCR, EEG and MRI data should be collected for all patients with a central nervous system infection.

Herpesvirus-specific CD8 T cell immunity in old age: Cytomegalovirus impairs the response to a coresident EBV infection

Aging in humans is associated with increased infections and the reduced proliferative capacity of T cells, part of the more global phenomenon termed immune senescence. The etiology of immune senescence is unknown but the accumulation of virus-specific memory T cells may be a contributory factor. We have examined CD8 T cell responses to two persistent herpesvirus infections, CMV and EBV, and to a recurrent virus infection, influenza, in different age cohorts of healthy donors using HLA-peptide tetramers and intracellular cytokine detection. Of these, CMV appears to be the most immunogenic, with the CD8 T cell response representing over 10% of the CD8 pool in many elderly donors. Interestingly, the effect of age upon EBV-specific responses depends upon donor CMV sero-status. In CMV seropositive donors, the magnitude of the EBV-specific immune response is stable with age, but in CMV seronegative donors, the response to EBV increases significantly with age. By contrast, the influenza-specific CD8 T cell immune response decreases with age, independent of CMV status. The functional activity of the herpesvirus-specific immune response decreases in elderly donors, although the characteristic phenotypes of CMV- and EBV-specific memory populations are retained. This demonstrates that aging is associated with a marked accumulation of CMV-specific CD8 T cells together with a decrease in immediate effector function. Moreover, infection with CMV can reduce prevailing levels of immunity to EBV, another persistent virus. These results suggest that carriage of CMV may be detrimental to the immunocompetent host by suppressing heterologous virus-specific immunity during aging.

Regulation of antigen processing and presentation molecules in West Nile virus-infected human skin fibroblasts

Infection of humans with the West Nile flavivirus principally occurs via tick and mosquito bites. Here, we document the expression of antigen processing and presentation molecules in West Nile virus (WNV)-infected human skin fibroblast (HFF) cells. Using a new Flavivirus-specific antibody, 4G4, we have analyzed cell surface human leukocyte antigen (HLA) expression on virus-infected cells at a single cell level. Using this approach, we show that West Nile Virus infection alters surface HLA expression on both infected HFF and neighboring uninfected HFF cells. Interestingly, increased surface HLA evident on infected HFF cultures is almost entirely due to virus-induced interferon (IFN)alpha/beta because IFNalpha/beta-neutralizing antibodies completely prevent increased surface HLA expression. In contrast, RT-PCR analysis indicates that WNV infection results in increased mRNAs for HLA-A, -B, and -C genes, and HLA-associated molecules low molecular weight polypeptide-2 (LMP-2) and transporter associated with antigen presentation-1 (TAP-1), but induction of these mRNAs is not diminished in HFF cells cultured with IFNalpha/beta-neutralizing antibodies. Taken together, these data support the idea that that both cytokine-dependent and cytokine-independent mechanisms account for WNV-induced HLA expression in human skin fibroblasts. (C) 2004 Elsevier Inc. All rights reserved.

Contemporaneous fluctuations in T cell responses to persistent herpes virus infections

The classical paradigm for T cell dynamics suggests that the resolution of a primary acute virus infection is followed by the generation of a long-lived pool of memory T cells that is thought to be highly stable. Very limited alteration in this repertoire is expected until the immune system is re-challenged by reactivation of latent viruses or by cross-reactive pathogens. Contradicting this view, we show here that the T cell repertoire specific for two different latent herpes viruses in the peripheral blood displayed significant contemporaneous co-fluctuations of virus-specific CD8(+) T cells. The coordinated responses to two different viruses suggest that the fluctuations within the T cell repertoire may be driven by sub-clinical viral reactivation or a more generalized 'bystander' effect. The later contention was supported by the observation that, while absolute number of CD3(+) T cells and their subsets and also the cell surface phenotype of antigen-specific T cells remained relatively constant, a loss of CD62L expression in the total CD8(+) T cell population was coincident with the expansion of tetramer-positive virus-specific T cells. This study demonstrates that the dynamic process of T cell expansion and contractions in persistent viral infections is not limited to the acute phase of infection, but also continues during the latent phase of infection.

Oral viral infections and the therapeutic use of antiviral agents in dentistry

This paper reviews the current concepts of viral classification, infection and replication. The clinical presentation of common oral viral infections encountered in the dental practice are discussed, including: herpes simplex virus types 1 and 2; Epstein-Barr virus; varicella-zoster virus; Coxsackie virus; human papilloma virus; and human immunodeficiency virus. The diagnosis, principles of management and pharmacological agents available for the treatment of oral viral infections are also discussed.

Synthesis, biological activity, and preliminary pharmacokinetic evaluation of analogues of a phosphosulfomannan angiogenesis inhibitor (PI-88)

The phosphosulfomannan 1 (PI-88) is a mixture of highly sulfated oligosaccharides that is currently undergoing clinical evaluation in cancer patients. As well as it's anticancer properties, 1 displays a number of other interesting biological activities. A series of analogues of 1 were synthesized with a single carbon (pentasaccharide) backbone to facilitate structural characterization and interpretation of biological results. In a fashion similar to 1, all compounds were able to inhibit heparanase and to bind tightly to the proangiogenic growth factors FGF-1, FGF-2, and VEGF. The compounds also inhibited the infection of cells and cell-to-cell spread of herpes simplex virus (HSV-1). Preliminary pharmacokinetic data indicated that the compounds displayed different pharmacokinetic behavior compared with 1. Of particular note was the n-octyl derivative, which was cleared 3 times less rapidly than 1 and may provide increased systemic exposure.

Regulated Cleavages at the West Nile Virus NS4A-2K-NS4B Junctions Play a Major Role in Rearranging Cytoplasmic Membranes and Golgi Trafficking of the NS4A Protein

A common feature associated with the replication of most RNA viruses is the formation of a unique membrane environment encapsulating the viral replication complex. For their part, flaviviruses are no exception, whereupon infection causes a dramatic rearrangement and induction of unique membrane structures within the cytoplasm of infected cells. These virus-induced membranes, termed paracrystalline arrays, convoluted membranes, and vesicle packets, all appear to have specific functions during replication and are derived from different organelles within the host cell. The aim of this study was to identify which protein(s) specified by the Australian strain of West Nile virus, Kunjin virus (KUNV), are responsible for the dramatic membrane alterations observed during infection. Thus, we have shown using immunolabeling of ultrathin cryosections of transfected cells that expression of the KUNV polyprotein intermediates NS4A-4B and NS213-34A, as well as that of individual NS4A proteins with and without the C-terminal transmembrane domain 2K, resulted in different degrees of rearrangement of cytoplasmic membranes. The formation of the membrane structures characteristic for virus infection required coexpression of an NS4A-NS4B cassette with the viral protease NS2B-3pro which was shown to be essential for the release of the individual NS4A and NS4B proteins. Individual expression of NS4A protein retaining the C-terminal transmembrane domain 2K resulted in the induction of membrane rearrangements most resembling virus-induced structures, while removal of the 2K domain led to a less profound membrane rearrangement but resulted in the redistribution of the NS4A protein to the Golgi apparatus. The results show that cleavage of the KUNV polyprotein NS4A-4B by the viral protease is the key initiation event in the induction of membrane rearrangement and that the NS4A protein intermediate containing the uncleaved C-terminal transmembrane domain plays an essential role in these membrane rearrangements.

Transgenic gene silencing strategies for virus control

Co-suppression of transgenes and their homologous viral sequences by RNA silencing is a powerful strategy for achieving high-level virus resistance in plants. This review provides a brief overview of RNA silencing mechanisms in plants and discusses important transgene construct design features underpinning successful RNA silencing-mediated transgenic virus control. Application of those strategies to protect horticultural and field crops from virus infection and results of field tests are also provided. The effectiveness and stability of RNA-mediated transgenic resistance are assessed taking into account effects of viral, plant and environmental factors.

Insights to substrate binding and processing by West Nile Virus NS3 protease through combined modeling, protease mutagenesis, and kinetic studies

West Nile Virus is becoming a widespread pathogen, infecting people on at least four continents with no effective treatment for these infections or many of their associated pathologies. A key enzyme that is essential for viral replication is the viral protease NS2B-NS3, which is highly conserved among all flaviviruses. Using a combination of molecular fitting of substrates to the active site of the crystal structure of NS3,site-directed enzyme and cofactor mutagenesis, and kinetic studies on proteolytic processing of panels of short peptide substrates, we have identified important enzyme-substrate interactions that define substrate specificity for NS3 protease. In addition to better understanding the involvement of S2, S3, and S4 enzyme residues in substrate binding, a residue within cofactor NS2B has been found to strongly influence the preference of flavivirus proteases for lysine or arginine at P2 in substrates. Optimization of tetrapeptide substrates for enhanced protease affinity and processing efficiency has also provided important clues for developing inhibitors of West Nile Virus infection.