Antiviral potencies of BV-araU and related nucleoside analogues against varicella-zoster virus in different cell lines

1-beta-D-Arabinofuranosyl-E-5-(2-bromovinyl)uracil (BV-araU) and nine other antiherpesviral nucleoside analogues were compared for their potencies against four strains of varicella-zoster virus (VZV) on three different cell lines: HEL cells, Vero cells, and MS cells established from a human malignant schwannoma. In contrast to the activity against herpes simplex virus type 1 previously reported, BV-araU showed extremely marked antiviral activity against VZV even on Vero cells. ED50, 50% plaque reduction dose, of BV-araU for VZV was 0.20-3.1 and 0.14-0.63 ng/ml on Vero cells and on HEL cells, respectively. Potency of BV-araU on MS cells was similar to that on these cell lines. There was not significant variation in anti-VZV activities of other nucleoside analogues on these three different cell lines except a few combinations of VZV strain and test compound.     

Synthesis of mitochondrial macromolecules in herpes simplex type 1 virus infected Vero cells

How viral infections affect host cell mitochondrial functions is largely unknown. In this study, uptake of radiolabeled precursors was used to assess how a herpes simplex virus type 1 (HSV 1) infection influences synthesis of macromolecules comprising Vero cell mitochondria. Total macromolecular synthesis in infected cells was determined for comparative purposes. Mitochondrial and total cellular DNA syntheses were approximately halved at 1-2.5 h postinfection (PI). Mitochondrial DNA synthesis in infected cells then rose to 3.5-fold that in control cells at 3-4.5 h PI. Total DNA synthesis in infected cells also rose, but more slowly, reaching threefold that for control cells at 5-6.5 h PI. Mitochondrial and total RNA synthesis in infected cells were both decreased by approximately 40% at 1-3 h PI. Over the next 4 h, total RNA synthesis in infected cells slowly continued to decrease, while that in mitochondria recovered to control levels. Synthesis of mitochondrial proteins in infected cells decreased progressively, dropping to about 60% of control levels by 5-6.5 h PI. With the metabolic inhibitors ethidium bromide and cycloheximide, it was determined that nuclear DNA and mitochondrial DNA and mitochondrial DNA directed synthesis of mitochondrial proteins were each partially inhibited in infected cells. Total cellular protein synthesis was decreased by 30% at 1-2.5 h PI and then recovered to control levels by 5-6.5 h PI. Finally, phospholipid synthesis in mitochondria from infected cells was elevated 2.3-fold at 1-5 h PI, but dropped to 14% below control levels during 4-8 h PI.(ABSTRACT TRUNCATED AT 250 WORDS)     

The mode of entry of herpes simplex virus type 1 into Vero cells

The mode of entry of herpes simplex virus type 1 (HSV-1) into Vero cells was investigated quantitatively with biological techniques. The entry of virus occurred rapidly when the virus-adsorbed cells were incubated at 37 C. The kinetics of virus entry was found to be similar to that of the process of uncoating, indicating that the uncoating of HSV-1 occurs simultaneously with the entry of virus into the cell. Experiments with ammonium chloride revealed that acidity in endosomes is not necessary for the entry or uncoating of HSV-1, in contrast with the cases of enveloped RNA viruses. In addition, endocytosis of the virus seems to be one of the processes of entry for HSV-1. However, the kinetics of endocytosis showed that the cell-bound virus is endocytosed gradually and suggested that the endocytosis of HSV-1 does not lead the virus to an uncoating process. These results are most consistent with a mechanism of entry for HSV-1 involving fusion of the viral envelope with the plasma membrane of the host cell.     

Search for inhibitors against herpes simplex virus type-I in cell extracts derived from human lymphoblastoid cell lines.

Cell extracts obtained from KB cells and 5 human lymphoblastoid cell lines including 2 from Burkitt's lymphoma (P3HR-1 and Raji), one each from nasopharyngeal carcinoma (no.223), acute lymphatic leukemia (MOLT-4) and a healthy person (NC-37) were tested for their inhibitory effects on the growth of herpes simplex virus type-1 (HSV-1) in green monkey kidney (GMK) cells by the plaque titration method. The relationship between the production of HSV-1 inhibitors and the degree of Epstein-Barr virus (EBV) genome repression in lymphoblastoid cells were also examined. Among the cell lines used P3HR-1 and no.223 cells produced a few EBV particles, Raji and NC-37 cells contained EBV genomes only, and MOLT-4 as well as KB cells were EBV genome-negative. The results revealed that P3HR-1 cell extract showed a tendency to inhibit HSV-1 growth in GMK cells but the other 4 lymphoblastoid cell lines and KB cells did not produce HSV-1 inhibitors, indicating that EBV genomes governing the formation of EBV structural antigens were not related to the production of HSV-1 growth inhibitors. The extracts from MOLT-4 cells, which are only a T lymphocyte cell line used in this study, stimulated HSV-1 growth in GMK cells significantly.     

Expression of herpes simplex virus type 1 glycoproteins in interferon-treated human neuroblastoma cells.

Human alpha interferon (IFN) significantly inhibits the replication of herpes simplex virus type 1 in human neuroblastoma cells. This inhibitory effect can be blocked by pretreatment with antiserum to IFN. We observed no significant differences in the expression of major nucleocapsid proteins, including VP5, between IFN-treated and untreated neuroblastoma cells. Electron micrographs demonstrated that there were distinct viral nucleocapsids within IFN-treated neuroblastoma cells. The expression of glycoproteins B and E was significantly reduced in these IFN-treated cells. On the other hand, glycoprotein D, although reduced in quantity, was expressed after IFN treatment. An immunofluorescence assay of the IFN-treated and virus-infected cells detected glycoprotein D in the Golgi complexes and in the nuclear membranes. Our results indicate that human alpha IFN may be useful in the study of gene expression in IFN-treated cells of neuronal origin.     

Characterization of a herpes simplex virus type 2 75,000-molecular-weight glycoprotein antigenically related to herpes simplex virus type 1 glycoprotein C.

Evidence is presented that the herpes simplex virus type 2 glycoprotein previously designated gF is antigenically related to herpes simplex virus type 1 gC (gC-1). An antiserum prepared against type 1 virion envelope proteins immunoprecipitated gF of type 2 (gF-2), and competition experiments revealed that the anti-gC-1 component of the antiserum was responsible for the anti-gF-2 cross-reactivity. An antiserum prepared against fully denatured purified gF-2, however, and three anti-gF-2 monoclonal antibodies failed to precipitate any type 1 antigen, indicating that the extent of cross-reactivity between gC-1 and gF-2 may be limited. Several aspects of gF-2 synthesis and processing were investigated. Use of the enzymes endo-beta-N-acetylglucosaminidase H and alpha-D-N-acetylgalactosaminyl oligosaccharidase revealed that the fully processed form of gF-2 (about 75,000 [75K] apparent molecular weight) had both complex-type N-linked and O-linked oligosaccharides, whereas newly synthesized forms (67K and 69K) had only high-mannose N-linked oligosaccharides. These last two forms were both reduced in size to 54K by treatment with endo-beta-N-acetylglucosaminidase H and therefore appear to differ only in the number of N-linked chains. Neutralization tests and radioiodination experiments revealed that gF-2 is exposed on the surfaces of virions and that the 75K form of gF-2 is exposed on cell surfaces. The similarities and differences of gF-2 and gC-1 are discussed in light of recent mapping results which suggest collinearity of their respective genes.     

Persistence of herpes simplex virus type 1 in rat neurotumor cells.

Herpes simplex virus type 1 (HSV-1) infection of a rat central nervous system tumor cell line led to almost complete destruction of the cells. Cells that survived the infection could be isolated and shown to produce infectious HSV particles for variable lengths of time in culture ranging from 20 to 57 passages. Even though infectious virus production eventually ceased, the cell lines continued to produce herpes-specified proteins as measured by immunological techniques. These cells also showed herpesvirus-like structures in the electron microscope. The persistently infected cells that produced HSV antigens and bore HSV sequences were resistant to superinfection by HSV-1. The resistance was not due to failure of adsorption of the virus or to the production of interferon by the cells. The nature of the block in HSV replication in these neurotumor cells, which contain and partially express the HSV genome, is unknown, but may offer an interesting parallel to the known latency of HSV in neural tissues.     

Ribonucleotide reductase of herpes simplex virus type 2 resembles that of herpes simplex virus type 1.

The ribonucleotide reductase (ribonucleoside-diphosphate reductase; EC 1.17.4.1) induced by herpes simplex virus type 2 infection of serum-starved BHK-21 cells was purified to provide a preparation practically free of both eucaryotic ribonucleotide reductase and contaminating enzymes that could significantly deplete the substrates. Certain key properties of the herpes simplex virus type 2 ribonucleotide reductase were examined to define the extent to which it resembled the herpes simplex virus type 1 ribonucleotide reductase. The herpes simplex virus type 2 ribonucleotide reductase was inhibited by ATP and MgCl2 but only weakly inhibited by the ATP X Mg complex. Deoxynucleoside triphosphates were at best only weak inhibitors of this enzyme. ADP was a competitive inhibitor (K'i, 11 microM) of CDP reduction (K'm, 0.5 microM), and CDP was a competitive inhibitor (K'i, 0.4 microM) of ADP reduction (K'm, 8 microM). These key properties closely resemble those observed for similarly purified herpes simplex virus type 1 ribonucleotide reductase and serve to distinguish these virally induced enzymes from other ribonucleotide reductases.     

Age-dependent role for CCR5 in antiviral host defense against herpes simplex virus type 2

Elimination of viral infections is dependent on rapid recruitment and activation of leukocytes with antiviral activities to infected areas. Chemokines constitute a class of cytokines that have regulatory effects on leukocyte migration and activity. In this study we have studied the role of CC chemokine receptor 1 (CCR1) and CCR5 in host defense during a generalized herpes simplex virus type 2 (HSV-2) infection. Whereas both 4- and 8-week-old CCR1(-/-) mice resembled wild-type mice (C57BL/6) with respect to defense against the infection, significantly higher virus titers were seen in the livers and brains of 4-week-old CCR5(-/-) mice. At the age of 8 weeks, CCR5(-/-) were indistinguishable from wild-type mice and cleared the infection from liver and spleen. Although 4-week-old CCR5(-/-) mice were able to recruit natural killer (NK) cells to the site of infection, these cells had reduced cytotoxic activity compared to NK cells from wild-type mice. This was not due to lower production of alpha/beta interferon or interleukin-12, two well-described activators of cytotoxic activity in NK cells. We also noted that the spleens of young CCR5(-/-) mice did not increase in size during infection as did the spleens of wild-type and CCR1(-/-) mice. This observation was accompanied by impaired proliferation of CCR5(-/-) splenocytes (SCs) ex vivo. Moreover, migration of CD8(+) T cells to the liver in response to infection was impaired in CCR5(-/-) mice, and adoptive transfer of SCs from CCR5(-/-) mice infected for 6 days into newly infected wild-type mice did not improve antiviral activity in the liver, in contrast to what was seen in mice receiving immune SCs from wild-type mice. Altogether, this study shows that CCR5 plays an age-dependent role in host defense against HSV-2 by supporting both the innate and adaptive immune response.     

Direct lymphocytotoxicity against herpes simplex virus infected cells.

This study was undertaken to determine if direct cytotoxicity (DC) against herpes simplex virus infected cells, perhaps mediated by T cells, could be demonstrated in individuals subject to recurrent herpes labialis. The mononuclear cells from 7 out of 17 individuals with recurrent herpes expressed DC whereas no DC was ever exhibited by 7 individuals without a previous history of herpes infections. Several approaches were used to show that the cytotoxicity being detected was predominately of the direct type rather than antibody-dependent cell cytotoxicity (ADCC). Since the effector cells of the DC were sensitive to trypsin treatment and behaved as do natural killer (NK) cells upon cell fractionation, the results were taken to imply that the DC was attributable to a NK-effector cell type rather than a classical T lymphocyte.     

Rolling circle DNA replication by extracts of herpes simplex virus type 1-infected human cells.

Whole-cell extracts of herpes simplex virus type 1-infected human cells (293 cells) can promote the rolling circle replication of circular duplex DNA molecules. The products of the reaction are longer than monomer unit length and are the result of semiconservative DNA replication by the following criteria: (i) resistance to DpnI and susceptibility to MboI restriction enzymes, (ii) shift in density on a CsCl gradient of the products synthesized in the presence of bromo-dUTP to a position on the gradient consistent with those of molecules composed mainly of one parental DNA strand and one newly synthesized DNA strand, and (iii) the appearance in the electron microscope of molecules consisting of duplex circles with multiunit linear appendages, a characteristic of a rolling circle mode of DNA replication. The reaction requires ATP and is dependent on herpes simplex virus type 1-encoded DNA polymerase.     

Enhanced lysis of herpes simplex virus type 1-infected mouse cell lines by NC and NK effectors

Spontaneously cytotoxic murine lymphocytes lysed certain cell types infected by herpes simplex virus type 1 (HSV-1) better than uninfected cells. The levels of virus-directed lysis varied widely from target to target, and we found that differences in virus-directed lytic efficiency could be attributed both to the characteristics of HSV-1 replication in the different targets and to the subgroup of natural effector cells which mediated lysis. Although HSV-1 adsorbed to the surface of all the target cells, those in which the virus replicated more efficiently were lysed to a greater extent. As targets, we used cell lines that, when uninfected, were spontaneously lysed by NK cells (YAC-1) or by NC cells (WEHI-164). We also used a fibroblastoid cell line (M50) and a monocytic tumor line (PU51R), which were not spontaneously killed. Using complement-mediated elimination of Qa-5-positive or asialo-GM1-positive NK cells to distinguish NK from NC activity, we found that NK cells lysed HSV-1-infected YAC cells better than uninfected cells, and an NC-like activity selectively lysed HSV-1-infected WEHI cells. In addition, we showed that both NK and NC cytotoxicities contributed to the lysis against the HSV-1-infected fibroblastoid line, M50, but the infected PU51R cells were killed by only NK effectors. These findings were consistent with the results of experiments performed to define the role of interferon in induction of virus-augmented cytolysis. Increased lysis of YAC-HSV and PU51R-HSV was entirely due to interferon activation and was completely abolished by performing the 51Cr-release assay in the presence of anti-interferon serum. Because NC activity was not augmented by interferon, virus-enhanced NC lysis of M50-HSV and WEHI-HSV was not due to this nonspecific mechanism. Together, our data show that HSV-1 infection of NK/NC targets induces increased cytotoxicity, but the effector cell responsible for lysis is determined by the uninfected target, or by an interaction between the virus and target cell, rather than by a viral determinant alone.     

Induction of human cell DNA synthesis by herpes simplex virus type 2.

The effect of herpes simplex virus type 2 (HSV-2) infection on the synthesis of DNA in human embryonic fibroblast cells was determined at temperatures permissive (37 C) and nonpermissive (42 C) for virus multiplication. During incubation of HSV-2 infected cultures at 42 C for 2 to 4 days or after shift-down from 42 to 37 C, incorporation of (3H)TdR into total DNA was increased 2-to 30-fold as compared with mock-infected cultures. Analysis of the (3H)DNA suggested that host cell DNA synthesis was induced by HSV-2 infection. Induction of host cell DNA synthesis by HSV-2 also occurred in cells arrested in DNA replication by low serum concentration. The three strains of HSV-2 tested were capable of stimulating cellular DNA synthesis. Virus inactivated by UV irradiation, heat, or neutral red dye and light did not induce cellular DNA synthesis, suggesting that an active viral genome is necessary for induction.     

Susceptibility of a herpes simplex virus ribonucleotide reductase null mutant to deoxyribonucleosides and antiviral nucleoside analogs.

A herpes simplex virus ribonucleotide reductase (RR) null mutant, ICP6 delta, exhibited hypersensitivity to hydroxyurea, and to the precursors of allosteric inhibitors of cellular RR. The mutant was also much more sensitive than the parental KOS to all of antiviral nucleoside analogs tested, including acyclovir (ACV), ganciclovir (DHPG) and BVaraU. Our data indicate that cellular RR is essential for the growth of ICP6 delta, and suggest that inhibitors of viral RR could act as potentiators of all of anti-herpetic nucleoside analogs whose targets are viral DNA polymerase.