Growth characteristics of cytomegalovirus in human fibroblasts with demonstration of protein synthesis early in viral replication

Sulphated glucuronomannan tetramer and hexamer from Sargassum thunbergii exhibit anti-human cytomegalovirus activity by blocking viral entry

Human cytomegalovirus (HCMV) remains a major public health burden worldwide. The anti-HCMV activity of glucuronomannan oligosaccharides (Gs) and sulphated glucuronomannan oligosaccharides (SGs) was investigated. Among these Gs and SGs, G4S1 and G6S1 (higher sulphated glucuronomannan tetramer and hexamer) showed satisfactory anti-HCMV activity starting at 50 μg/mL and 10 μg/mL, respectively. The results of the morphology, western blotting, qPCR and TCID50 assay showed that they prevented lytic cytopathic changes, inhibited the expression of IE1/2 and UL44, and reduced the UL123 copy number and virus titre significantly. It was interesting to note that degree of sulphation and polymerization was more important for anti-HCMV activity. Moreover, the anti-HCMV activities of G4S1 and G6S1 were stable when stored at 4 °C, -20 °C, and -80 °C for at least three months and mainly occurred in the early stage of HCMV infection through the negative charge of the sulphate groups and the interaction between SGs and the host cells.

Tricin inhibits the CCL5 induction required for efficient growth of human cytomegalovirus

Treatment of human embryonic lung fibroblast (HEL) cells with tricin (4', 5, 7-trihydroxy-3', 5'-dimethoxyflavone) following infection with human cytomegalovirus (HCMV) reportedly significantly suppresses HCMV replication. In the present work, the mechanisms for the anti-HCMV effects of tricin in HEL cells were examined. It was found that exposure of HEL cells to tricin inhibited HCMV replication, with concomitant decreases in amounts of transcripts of the CC chemokine RANTES (CCL5)-encoding gene and in expression of the CCL5 protein. It was also found that transcripts of HCMV immediate early 1 (IE1), and HCMV UL54 (encoding DNA polymerase) and replication of HCMV was significantly lower in CCL5 gene-knockdown cells. These results suggest that the anti-HCMV activity of tricin differs from that of ganciclovir and that CCL5 is one of the chemokines involved in HCMV replication. In addition, it is possible that chemokine CCL5 is one of the targets of tricin.

An in silico-designed flavone derivative, 6-fluoro-4'-hydroxy-3',5'-dimetoxyflavone, has a greater anti-human cytomegalovirus effect than ganciclovir in infected cells

A novel type of antiviral agent for human cytomegalovirus (HCMV) is required, because the appearance of ganciclovir (GCV) resistant viruses has been reported. Tricin (4',5,7-trihydroxy-3',5'-dimethoxyflavone) has been shown to suppress significantly HCMV replication in human embryonic lung (HEL) fibroblast cells. Recently, we revealed that the action of tricin is different from that of GCV and cyclin-dependent kinase 9 (CDK9) is one of the target proteins of tricin. These results suggested that tricin is considered as a novel type of anti-HCMV agent. However, its anti-HCMV potency is not greater than that of GCV. This study tried to develop novel compounds with much greater anti-HCMV activity than GCV. We first made modifications to tricin by introducing fluorine atom, and then performed molecular docking simulations using the designed compounds and CDK9. The calculated binding energies showed that 6F-tricin (6-fluoro-4'-hydroxy-3',5'-dimetoxyflavone) binds to CDK9 much stronger than tricin. Based on these results, 6F-tricin was synthesized, and then its anti-HCMV effect was analyzed in HEL cell cultures. As a result, 6F-tricin strongly suppressed HCMV replication in a dose-dependent manner. The anti-HCMV activity with a 50% effective concentration (EC₅₀) was 0.126 nM, corresponding to about 1/200 and 1/400 of EC₅₀ of GCV (27.5 nM) and tricin (54.3 nM), respectively. Moreover, 6F-tricin had no cytotoxicity against HEL cells at concentrations up to 10 μM. We further performed detailed analysis on the amino acid contributions to the binding energies and found that the strong binding affinity for 6F-tricin to CDK9 is attributed to the specific binding orientation of 6F-tricin in the ATP-binding site. These results suggest that 6F-tricin is a promising candidate for anti-HCMV drug development.

The anti-human cytomegalovirus drug tricin inhibits cyclin-dependent kinase 9

4′,5,7‐trihydroxy‐3′,5′‐dimethoxyflavone (tricin), derived from Sasa albo‐marginata, has been reported to suppress significantly human cytomegalovirus (HCMV) replication in human embryonic lung (HEL) fibroblast cells. However, the target protein of tricin remains unclear. This study focused on the anti‐HCMV activity of tricin in terms of its binding affinity to cyclin‐dependent kinase 9 (CDK9). A molecular docking study predicted that tricin binds well to the ATP‐binding site of CDK9. Experimental measurements then revealed that tricin inhibits the kinase activity of CDK9 and affects the phosphorylation of the carboxy‐terminal domain of RNA polymerase II. Based on these results, we conclude that CDK9 is one of the target proteins of tricin. We also found that tricin possesses anti‐HCMV activity with no cytotoxicity against HEL cells.

The M25 gene products are critical for the cytopathic effect of mouse cytomegalovirus

Cell rounding is a hallmark of the cytopathic effect induced by cytomegaloviruses. By screening a panel of deletion mutants of mouse cytomegalovirus (MCMV) a mutant was identified that did not elicit cell rounding and lacked the ability to form typical plaques. Altered cell morphology was assigned to the viral M25 gene. We detected an early 2.8 kb M25 mRNA directing the synthesis of a 105 kDa M25 protein, and confirmed that a late 3.1 kb mRNA encodes a 130 kDa M25 tegument protein. Virions lacking the M25 tegument protein were of smaller size because the tegument layer between capsid and viral envelope was reduced. The ΔM25 mutant did not provoke the rearrangement of the actin cytoskeleton observed after wild-type MCMV infection, and isolated expression of the M25 proteins led to cell size reduction, confirming that they contribute to the morphological changes. Yields of progeny virus and cell-to-cell spread of the ΔM25 mutant in vitro were diminished and replication in vivo was impaired. The identification of an MCMV gene involved in cell rounding provides the basis for investigating the role of this cytopathic effect in CMV pathogenesis.

Inhibition of Ganciclovir-Resistant Human Cytomegalovirus Replication by Kampo (Japanese Herbal Medicine)

We examined the effect of Kampo on the replication of ganciclovir (GCV)-resistant human cytomegalovirus (HCMV) in the human embryonic fibroblast cell line MRC-5. Treatment of HCMV-infected cells with Sho-seiryu-to (SST; Xiao-Qing-Long-Tang in Chinese) resulted in the inhibition of viral replication without affecting the cell growth. SST treatment decreased the synthesis of viral DNA, but had no virucidal effect on cell-free HCMV. However, the inhibitory effect of SST on HCMV replication was ablated by anti-interferon-β (IFN-β) antibody suggesting that SST inhibits the replication of GCV-resistant HCMV through the induction of IFN-β. These results suggest that SST is a novel compund with potential as an anti-HCMV.

Human cytomegalovirus replication supported by virus-induced activation of CCL2-CCR2 interactions

We previously revealed that human cytomegalovirus (HCMV) infection can cause aberrant expression of the chemokine IL-8/CXCL8. We first examined the effects of HCMV infection on the expression of another chemokine, CCL2. HCMV infection induced CCL2 expression at the mRNA and protein levels in human embryonic lung fibroblasts cells (HEL). Moreover, HCMV induced the mRNA expression of CCR2, a specific receptor for CCL2. CCL2 siRNA treatment reduced HCMV virion production, and this reduction was reversed by the addition of CCL2. We further observed that CCL2 siRNA, but not control siRNA, reduced the expression of HCMV immediate early gene (IE1) and HCMV UL54 gene (DNA polymerase) in a dose-dependent manner. Thus, HCMV infection is able to activate the CCL2-CCR2 interactions to further enhance HCMV infection and/or replication.

Systems-level metabolic flux profiling identifies fatty acid synthesis as a target for antiviral therapy

Viruses rely on the metabolic network of their cellular hosts to provide energy and building blocks for viral replication. We developed a flux measurement approach based on liquid chromatography-tandem mass spectrometry to quantify changes in metabolic activity induced by human cytomegalovirus (HCMV). This approach reliably elucidated fluxes in cultured mammalian cells by monitoring metabolome labeling kinetics after feeding cells (13)C-labeled forms of glucose and glutamine. Infection with HCMV markedly upregulated flux through much of the central carbon metabolism, including glycolysis. Particularly notable increases occurred in flux through the tricarboxylic acid cycle and its efflux to the fatty acid biosynthesis pathway. Pharmacological inhibition of fatty acid biosynthesis suppressed the replication of both HCMV and influenza A, another enveloped virus. These results show that fatty acid synthesis is essential for the replication of two divergent enveloped viruses and that systems-level metabolic flux profiling can identify metabolic targets for antiviral therapy.

Anti-Human Cytomegalovirus Activity of Constituents from Sasa Albo-Marginata (Kumazasa in Japan)

Background:

Effective new anti-human cytomegalovirus (HCMV) agents and regimens need to be developed. We examined the anti-HCMV properties of crude extract (True World Extract of Bambuseae sasa [TWEBS]) and five compounds ( p-coumaric acid, 3-hydroxy-4-methoxyben-zaldehyde [vanillin], p-hydroxybenzaldehyde, 3-hydroxypyridine and 4',5,7-trihydroxy-3',5'-dimethoxyflavone [tricin]), isolated from Sasa albo-marginata, a bamboo known in Japan as Sasa.

Methods:

Among TWEBS and five compounds screened in a plaque reduction assay, four showed anti-HCMV activity in the MRC-5 human embryonic fibroblast cell line. The anti-HCMV mechanisms of the TWEBS was examined by western blot analysis using primary antibody specific for an immediate early (IE) antigen of HCMV, for a structural late antigen of HCMV and for β-actin.

Results:

Treatment of cells with ⩾0.001% of TWEBS inhibited the observable cytopathic effects of HCMV on infected cells. Western blot analysis demonstrated that TWEBS decreased the expression of IE antigen and late antigen of HCMV in the infected cells. Next, we examined the anti-HCMV properties of five compounds isolated from TWEBS. In a viral plaque reduction assay, tricin showed dose-dependent inhibitory properties with a 50% effective concentration of 0.17 µug/ml (selective index =1,205.8).

Conclusions:

The hot water extract (TWEBS) of Sasa albo-marginata, with tricin isolated from it, has anti-HCMV activity in MRC-5 cells. TWEBS and/or tricin are a novel compound with potential anti-HCMV activity. Future studies should evaluate these findings in vivo.

Anticytomegalovirus activity of pristimerin, a triterpenoid quinone methide isolated from Maytenus heterophylla (Eckl. & Zeyh.)

We examined the anticytomegalovirus properties of four compounds: pristimerin, the pristimerin analogue, lupeol and 2-acetylphenol-1-beta-D-glucopyranosyl (1 --> 6)-beta-D-xylpyranoside (acetophenol glycoside), isolated from Maytenus heterophylla, a Kenyan medicinal plant. The effects were studied on human cytomegalovirus (HCMV) replication in the human embryonic fibroblast cell line, MRC-5. In a viral plaque-reduction assay, pristimerin showed dose-dependent inhibitory properties with a 50% inhibitory concentration of 0.53 microg/ml (selective index = 27.9). The cells treated with pristimerin inhibited the cytopathic effects in HCMV-infected cells. Moreover, pristimerin suppressed viral replication without affecting the cell growth. Pristimerin inhibited the synthesis of viral DNA but had no virucidal effect on cell-free HCMV. Furthermore, Western blot analysis demonstrated that pristimerin decreased the amount of immediate early (IE) antigen (especially IE2) expression in the infected cells. These results suggest that pristimerin is a unique compound with potential anti-HCMV activity.

Dynamics of the cellular metabolome during human cytomegalovirus infection

Viral replication requires energy and macromolecular precursors derived from the metabolic network of the host cell. Despite this reliance, the effect of viral infection on host cell metabolic composition remains poorly understood. Here we applied liquid chromatography-tandem mass spectrometry to measure the levels of 63 different intracellular metabolites at multiple times after human cytomegalovirus (HCMV) infection of human fibroblasts. Parallel microarray analysis provided complementary data on transcriptional regulation of metabolic pathways. As the infection progressed, the levels of metabolites involved in glycolysis, the citric acid cycle, and pyrimidine nucleotide biosynthesis markedly increased. HCMV-induced transcriptional upregulation of specific glycolytic and citric acid cycle enzymes mirrored the increases in metabolite levels. The peak levels of numerous metabolites during infection far exceeded those observed during normal fibroblast growth or quiescence, demonstrating that HCMV markedly disrupts cellular metabolic homeostasis and institutes its own specific metabolic program.

Viruses are parasites. They depend on the biochemical infrastructure of host cells to grow. A key element of the infrastructure provided by the host cell is its metabolic machinery, which viruses rely upon to provide the energy and building blocks necessary for their replication. The way in which viruses interact with host cell metabolism remains, however, poorly understood. The authors have used an advanced measurement technique, liquid chromatography-mass spectrometry, to quantitate directly the levels of a large number of metabolic compounds (energy molecules and biochemical building blocks) during cytomegalovirus infection of cultured human cells. They find that viral infection leads to dramatic increases in the levels of many metabolites and that these increases substantially exceed those associated with normal transitions of cells between resting and growing states. In several cases, enhanced metabolite levels induced by the virus coincide with an apparent increase in host cell production of the machinery (enzymes) involved in making those metabolites. This work represents the first comprehensive characterization of the metabolic environment of virally infected cells and identifies a number of profound metabolic effects of the virus, some of which may eventually prove fruitful targets for antiviral therapy.

Analysis of human cytomegalovirus UL144 variability in low-passage clinical isolates in Japan

To explore a possible role for viral genes as determinants of virulence, portions of the UL144 tumor necrosis factor-like receptor gene and the UL55 envelope glycoprotein B gene from 42 patients with congenital human cytomegalovirus (HCMV) infection or other diseases were sequenced. Of the 42 patients, 16 (38%) had UL144 group 1 [group 1A, 15 of 16 (94%); group 1B, 1 of 16 (6%); group 1C, 0 of 16 (0%)], 5 patients (12%) had UL144 group 2, and 21 patients (50%) had UL144 group 3. Although group 1C was not found in Japan strains (0%), it was found in USA strains (22%). Other HCMV polymorphisms should be further evaluated for their potential relevance to neonatal infection, and acquired immunodeficiency syndrome-associated HCMV diseases.

In Vitro Anti-Cytomegalovirus Activity of Kampo (Japanese Herbal) Medicine

We examined the effect of three types of Kampo medicines on human cytomegalovirus (CMV) replication in the human embryonic fibroblast cell line, MRC-5. Treatment of cells with at least 0.01 μg/ml of Kampo medicines inhibited the cytopathic effects of CMV-infected MRC-5 cells. Moreover, Kampo medicine decreased the replication of CMV without affecting the inhibition of host cells, with a concomitant decrease in CMV DNA levels. However, Kampo medicine demonstrated no virocidal effect on cell-free CMV. Furthermore, western blotting analysis demonstrated that the Kampo medicine decreased the amount of 65 kDa late antigen expression in the infected cells. These results suggest that Kampo medicine may be sufficient to inhibit viral DNA replication and late protein synthesis, resulting in anti-CMV effects. Therefore, these three Kampo medicines have the potential of being a source of new powerful anti-CMV compounds.

2,3,7,8-Tetrachlorodibenzo-p-dioxin is a possible activator of human cytomegalovirus replication in a human fibroblast cell line

We examined the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on human cytomegalovirus (CMV) replication in the human embryonic fibroblast cell line, MRC-5. Treatment of cells with 0.0001pg/ml TCDD augmented the cytopathic effects of CMV-infected MRC-5 cells. Moreover, TCDD increased the replication of intracellular CMV without affecting the proliferation of host cells, with a concomitant increase in CMV UL54 DNA levels. However, TCDD demonstrated no virocidal effect on cell-free CMV. Furthermore, CMV-infected MRC-5 cells expressed transcripts of the aryl hydrocarbon receptor (AhR) and AhR nuclear translocator. These results suggest that TCDD may contribute to the development of opportunistic diseases by reactivation of latently infected CMV and that TCDD regulates CMV replication through the dependence on AhR.

Histopathologic findings in cutaneous cytomegalovirus infection

When cytomegalovirus (CMV) involves the skin, viral inclusions are typically present within mesenchymal cells, e.g., endothelial cells, fibrocytes, and sometimes within inflammatory cells, e.g., macrophages, in contrast to infection in other organs in which inclusions are usually present within ductal epithelial cells. Two cases of cutaneous CMV are presented, one showing prominent findings within eccrine ductal epithelium and the other revealing mostly endothelial cells affected by CMV. Due to the range of cytologic changes induced by CMV observed in these cases, there seem to be early, fully developed, and late cellular changes brought about by CMV analogous to how herpesvirus (varicella, zoster, simplex) induces different changes depending on its stage of infection.

Human cytomegalovirus induces interleukin-8 production by a human monocytic cell line, THP-1, through acting concurrently on AP-1- and NF-kappaB-binding sites of the interleukin-8 gene

Cytomegalovirus (CMV) infection induced interleukin-8 (IL-8) gene transcription in a human monocytic cell line, THP-1 cells, leading to IL-8 secretion. The functional analysis of the IL-8 gene revealed that both AP-1- and NF-kappaB factor-binding elements were involved in conferring the responsiveness to CMV. Moreover, electrophoretic mobility shift assays demonstrated that CMV induced the formation of NF-kappaB and AP-1 complexes. These results suggest that CMV activates these transcriptional factors, resulting in IL-8 gene expression.

Human cytomegalovirus infection inhibits G1/S transition

Cell cycle progression during cytomegalovirus infection was investigated by fluorescence-activated cell sorter (FACS) analysis of the DNA content in growth-arrested as well as serum-stimulated human fibroblasts. Virus-infected cells maintained in either low (0.2%) or high (10%) serum failed to progress into S phase and failed to divide. DNA content analysis in the presence of G1/S (hydroxyurea and mimosine) and G2/M (nocodazole and colcemid) inhibitors demonstrated that upon virus infection of quiescent (G0) cells, the cell cycle did not progress beyond the G1/S border even after serum stimulation. Proteins which normally indicate G1/S transition (proliferating cell nuclear antigen [PCNA]) or G2/M transition (cyclin B1) were elevated by virus infection. PCNA levels were induced in infected cells and exhibited a punctate pattern of nuclear staining instead of the diffuse pattern observed in mock-infected cells. Cyclin B1 was induced in infected cells which exhibited a G1/S DNA content by FACS analysis, suggesting that expression of this key cell cycle function was dramatically altered by viral functions. These data demonstrate that contrary to expectations, cytomegalovirus inhibits normal cell cycle progression. The host cell is blocked prior to S phase to provide a favorable environment for viral replication.

Enhancement human cytomegalovirus replication in a human lung fibroblast cell line by interleukin-8

We examined the effects of interleukin-8 (IL-8) on cytomegalovirus (CMV) replication in human fibroblasts. Exposure of fibroblasts to IL-8 augmented both infectious virus production and replication of CMV, with concomitant increases in the levels of both the transcript of the CMV pp71 genome and the synthesis of the CMV late antigen. We also found that CMV selectively induced transcripts of the IL-8 type 1 receptor in fibroblasts. These results suggest that IL-8 also contributes to inflammatory diseases by enhancing CMV replication and that CMV regulates its production through induction of IL-8 receptor.

Antibodies to human cytomegalovirus 65-kilodalton Fc binding protein in rheumatoid arthritis: idiotypic mimicry hypothesis of rheumatoid factor production

We previously reported that rheumatoid factors (RFs) might bear the internal image of Fc gamma-binding proteins (FcBPs) of herpes family viruses, suggesting the possibility that some RFs may be produced as antiidiotypic antibodies to anti-viral FcBP antibodies. Since human cytomegalovirus (HCMV) has been implicated in the pathogenesis of RA, we made an attempt to detect antibodies to 65 KD major HCMV FcBP in sera and synovial fluid from patients with RA. Western blotting was performed using HCMV-infected MRC-5 cell lysate as the antigen. Eleven of 23 patients with RA possessed strong serum antibodies to HCMV-65 KD protein, whereas such antibodies were found in only 2 of 23 normal controls. In the synovial fluid, 10 of 19 RA patients showed anti-HCMV 65 KD reactivity. Pepsin-digested IgG retained anti-65 KD reactivity, indicating that false-positive reaction due to the presence of IgG Fc portion and/or RF was unlikely. 65 KD protein was shown to be different from human heat shock proteins (hsps) using monoclonal antibodies against human hsps. Patients' IgG F(ab')2 also reacted with the 65 KD protein of purified HCMV virion itself. These results support the possibility that some RFs could be produced as antiidiotypic antibodies to anti-viral FcBP antibodies.

Human cytomegalovirus nuclear and cytoplasmic dense bodies

One of the characteristic features of cytomegalovirus (CMV) replication is the formation of cytoplasmic dense bodies. Recent findings revealed similar structures also in the nuclei of CMV-infected cells. By transmission electron microscopy, immuno electronmicroscopy, and cytochemistry, we have studied the morphogenetic steps and macromolecular composition of both structures. Our results show that both structures contain DNA, RNA and viral antigenic proteins. Nuclear dense bodies are probably an expression of a stimulated cellular metabolism, while cytoplasmic dense bodies may represent the site where surplus cellular and viral molecules are stored before being eliminated.

Recognition of compartmentalized intracellular analogs of glycoprotein H of human cytomegalovirus

Infected cell proteins immunoprecipitated from human cytomegalovirus (HCMV)-infected fibroblasts with glycoprotein H (gH)-specific conformation-dependent monoclonal antibody (mab 14-4 b) were found to consist of three components of 86 kDa, 89 kDa, and 125 kDa (gp 86, 89, and 125). Affinity purified antibodies from human convalescent serum reactive with an NH2-terminal epitope of gH recognized three polypeptides of comparable size in immunoblots, suggesting antigenic relatedness of these three components of the gH-complex. Using subcellular fractions for immunoblotting, gp 86 was identified as an endoglycosidase H (endo H)-sensitive gH-form present in the nuclear fraction whereas gp 89 and gp 125 were endo H-resistant and present in the membrane fraction or in virions. Incomplete endo H-digestion suggested that four of six predicted N-glycosylation sites of the gH molecule were occupied by carbohydrate side chains. Analysis under nonreducing conditions revealed that the compartmentalized as well as virion-associated gH analogs form high molecular weight complexes. The relation of the recognized gH analogs to the processing pathway of gH is discussed.

Methionine dependence of virus-infected cells

Mouse embryo cells nonproductively infected with human cytomegalovirus differed from noninfected cells by the impaired ability to grow in the medium containing homocysteine instead of methionine. Virus infection of mouse embryo cells grown in both kinds of media resulted in the increase of protein synthesis. In the infected cells grown on homocysteine this increase was followed by a quick decrease. The effects of homocysteine substitution could be abolished by the addition of low amounts of methionine (0.1 mM). Methionine uptake in the infected cells grown on homocysteine for 48 h was significantly higher than that in the noninfected cells.

Inhibition of endoproteolytic cleavage of cytomegalovirus (HCMV) glycoprotein B by palmitoyl-peptidyl-chloromethyl ketone

Endoproteolytic cleavage of glycoprotein B (gB) of human cytomegalovirus (HCMV) is inhibited by palmitoylated peptidyl-chloromethyl ketone (palFAKR-CEK) at concentrations above 30 microM. Inhibitor treatment of HCMV-infected human fibroblasts neither interfered with exposure of gB on the plasma membrane, detected by surface membrane immunostaining, nor reduced production of intracellular infectious viral progeny. Release of infectious virus, on the other hand, was impaired.

Nuclear compartmentation of glycoprotein B of human cytomegalovirus

Maturation of glycoprotein B (gB) of human cytomegalovirus (HCMV) includes a series of sequential glycosylation steps followed by proteolytic cleavage of the precursor protein. Inhibitors of glycosylation and glycoprotein processing, including tunicamycin, monensin, and bromoconduritol, were used to define further the processing pathway of HCMV gB. The results of these studies indicated that cotranslational glycosylation and intracellular transport are essential for subsequent cleavage of the precursor; early trimming in the endoplasmic reticulum is not a prerequisite but facilitates this processing event. Analysis of purified nuclei with gB-specific monoclonal antibody suggested that the mannose-rich gB-precursor intermediate(s) is (are) compartmentalized in the nuclear fraction. Immunoelectron microscopy revealed that HCMV gB was localized in the outer as well as in the inner nuclear membranes of HCMV-infected fibroblasts.

Biological response modifier enhances the activity of natural killer cell against human cytomegalovirus-infected cells

Peripheral blood lymphocytes (PBL) from two human cytomegalovirus (CMV)-seronegative donors and eight CMV-seropositive donors were cultured for 3 days with or without the biological response modifier OK-432 and examined for lysis of K562 cells and CMV-infected MRC-5 cells. OK-432-stimulated PBL exhibited significantly greater natural killer (NK) activity than did unstimulated PBL. There was no difference in activity of NK cells in PBL prepared from CMV-seronegative and -seropositive donors. Antibody-complement depletion studies suggested that OK-432-stimulated NK activity was associated with Leu-7-positive cells. The ability of OK-432 to sustain the NK activity in PBL was decreased when the CD4-positive population of lymphocytes was eliminated by antibody-complement depletion prior to OK-432 stimulation. The ability of OK-432 to sustain the NK activity of PBL was also significantly decreased in the presence of monoclonal antibody against recombinant human interleukin-2. The results suggest that the activity of human NK cells against K562 and CMV-infected MRC-5 target cells can be sustained in vitro by OK-432-stimulated T-helper cells and that the effect of the T-helper cells is mediated, at least in part, by interleukin-2.

Cytomegalovirus infection and trans-activation of HIV-1 and HIV-2 LTRs in human astrocytoma cells

Susceptibility of a human astrocytoma cell line to human cytomegalovirus (HCMV) infection was investigated. Infection of U-373MG astrocytoma cells with two strains of HCMV resulted in both production of extracellular, infectious virus and expression of immediate early and early antigens within 18 hours and late antigens after 72 hours of infection. The kinetics of infection in U-373MG cells were the same as in human diploid fibroblasts (MRC-5). Since HCMV and human immunodeficiency virus (HIV) have reportedly been found in astrocytic cells in vivo, we studied the possible interaction between HCMV and HIV long terminal repeat (LTR) elements in this cellular environment. HCMV infection transactivated the LTR of HIV-1 and HIV-2 to similar levels. Interestingly, transfection of these cells with infectious HIV-1 provirus did not result in expression of gag, env, or F proteins detectable by immunofluorescence. However, provirus gene expression was not completely silent, since it transactivated HIV-1 LTR. The level of this transactivation was similar to that seen following cotransfection with a tat expression vector. These results suggest that opportunistic infection with HCMV may reactivate latent HIV genomes in glial cells.

Induction by sodium butyrate of cytomegalovirus replication in human endothelial cells

Cultured endothelial cells are shown to be induced in regard to permissiveness to human cytomegalovirus by temporary treatment postinfection with sodium butyrate (1-2 mM). Drug-treated cells are demonstrated to exhibit expression of immediate early and early viral antigens, synthesis of viral DNA and viral structural glycoprotein B. Progeny virus could be visualized by electron microscopy.

Comparative study with monospecific and monoclonal antibodies against a 65 K human cytomegalovirus protein

Immunofluorescence assay using monospecific and monoclonal antibodies to the 65 K major protein of human cytomegalovirus (HCMV) was carried out to monitor the expression of this protein in infected cells. Regardless of differences in the reactivity of the monoclonal antibodies, as determined by immunoblotting and immunofluorescent staining, all stained cytoplasmic inclusion bodies localized to the site of the HCMV-induced receptor for the Fc portion of IgG, suggesting that most of the 65 K major protein of HCMV colocalizes with the HCMV-induced FcR.

Beta interferon production in primed and unprimed cells infected with human cytomegalovirus

Human cytomegalovirus induced beta interferon in cultures of human foreskin cells. The inhibitor was first released between 8 and 16 hours after infection, about 48 hours before progeny virus. In cultures infected with low concentrations of virus, interferon was produced as the infection spread, and then in amounts larger than expected. After infection with cytomegalovirus, cells which had been primed for 48 hours with purified beta interferon produced significantly more interferon than unprimed cells, and the interferon was produced earlier, between 2 and 8 hours after infection. CMV-induced interferon also was able to prime cells. The data suggest that the relatively large quantities of interferon detected in cultures infected with low concentrations of cytomegalovirus result from endogenous priming: those cells infected early first produce interferon which primes uninfected cells, then virus which induces the primed cells to produce interferon in relatively high concentrations.

Analysis by immunoblotting of human cytomegalovirus antibody in sera of renal transplant recipient

Human cytomegalovirus-infected cell polypeptides were immunoreacted by sera of renal transplant recipients and compared with those reactive with sera of healthy adult donors by means of the Western immunoblotting technique. At least 15 polypeptides with molecular weights of 155K, 123K, 102K, 89K, 79K, 71K, 65K, 60K, 55K, 50K, 46K, 42K, 38K, 33K, and 28K were immunoreacted. Sera obtained serially from renal transplant recipients reacted with most of these polypeptides and reacted more frequently and intensely with the smaller polypeptide species such as 38K, 33K, and 28K, compared with sera of healthy seropositive adults. The implications of these findings are discussed.

Inhibition by monensin of human cytomegalovirus DNA replication

Monensin, at concentrations which depended on the multiplicity of infection, was found to prevent DNA replication of human cytomegalovirus (HCMV) as well as production of viral progeny in human foreskin fibroblasts. The drug did not affect DNA replication of herpes simplex virus. Inhibition of consecutive HCMV DNA synthesis was also observed following delayed addition of the drug within 12-24 hours postinfection, but was fully reversible upon its removal. Viral replication proceeded, however, without impairment in cultures treated with monensin prior to infection. Induction of viral DNA polymerase activity was not impeded by the inhibitor. Analysis of protein- and glycoprotein synthesis revealed that monensin interfered with the production of a number of HCMV-specific polypeptides. Furthermore, evidence was obtained that the drug may hinder intracellular transport of a 135 kd glycopolypeptide.

The importance of primary cytomegalovirus infection in childhood cancer

Sixty-eight paediatric patients with malignant tumours or leukaemia were followed for signs of infection with human cytomegalovirus (HCMV) over 1 year. HCMV was isolated from 24 out of 68 patients at some point during the observation period; from urine in 14, from both urine and throat in 9 patients, and from throat alone in 1 patient. Previous antibody analysis indicated the presence of HCMV antibodies in 10 of the 24 virus-shedding patients, while 7 patients were seronegative and 7 undefined. Thus the incidence of reactivation appears to be higher than that of primary infection in these immunocompromised patients. The mean duration of virus shedding was 4.2 months in the primary infection group, 1.7 months in the reactivation group and 1.1 months in the undefined group. No difference in the incidence of HCMV-associated illness was observed between patients with leukaemia and those with malignant tumours. Clinical symptoms associated with HCMV infection (pneumonia (2), fever (6) and hepatitis (1)) were observed in all patients with primary infections and in only five patients with reactivated infection.

Differentiation of TERA-2 human embryonal carcinoma cells into neurons and HCMV permissive cells. Induction by agents other than retinoic acid

Retinoic acid induces the differentiation of NTERA-2 cl. D1 human embryonal carcinoma (EC) cells into neurons, cells permissive for the replication of human cytomegalovirus (HCMV), and other cell types that cannot as yet be classified but are distinguishable from the stem cells. We tested several additional agents for their ability to induce the differentiation of these EC cells. No differentiation was induced by butyrate, cyclic AMP, cytosine arabinoside, the tumor promoter 12-0-tetradecanoylphorbol 13-acetate (TPA), or the chemotherapeutic agent cis-diaminedichloroplatinum, although morphological changes were detected at the highest concentrations of these agents that permitted cell survival. However, retinal, retinol, 5-bromouracil 2'deoxyribose (BUdR), 5-iodouracil 2'deoxyribose (IUdR), hexamethylene bisacetamide (HMBA), dimethylacetamide (DMA), and dimethylsulfoxide (DMSO) all induced some neuronal differentiation, but to a lesser extent than retinoic acid. Also, BUdR, IUdR, HMBA, and DMA induced the appearance of many cells permissive for the replication of HCMV. Differentiation was, in all cases, accompanied by the loss of SSEA-3, a globoseries glycolipid antigen characteristically expressed by human EC cells. However, another glycolipid antigen, A2B5, which appears in 60%-80% of differentiated cells 7 days following retinoic acid induction, was detected in less than 20% of the cells induced by the other agents studied. This implies that the HCMV-permissive cells induced by retinoic acid are not identical to those induced by BUdR, IUdR, and DMA.

Preparation of highly purified human cytomegalovirus envelope antigen

A human cytomegalovirus (HCMV) envelope preparation was highly purified by immunoaffinity column chromatography using an anti-cellular-IgG column. The purified envelope induced high titre antibodies to HCMV in guinea-pigs. Analysis of the guinea-pig immune sera by RIA and immunofluorescence (IF) showed that this envelope preparation, unlike its unpurified counterpart, did not induce antibody to cellular contaminants. Dot-blot assay revealed viral proteins in the flow-through fraction and cellular proteins in the bound fractions. Results of sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of flow-through and bound fractions suggest that a number of proteins previously identified as virus-specific may, in fact, reflect cellular contamination of the envelope preparation, or crossreactivity of some virus-specific proteins with cellular proteins.

Distinction of viral and host-derived glycopolypeptides induced by "early" functions of human cytomegalovirus

Human cytomegalovirus is shown to induce in phosphonoacetic acid-treated human fibroblasts glycosylation of five polypeptides with approximate molecular weights of 200-250, 150, 135, 130 and 100 kilodaltons (kd). Except for the 130 kd product, these glycopolypeptides (gp) separate with the cytoplasmic fraction, only one (200-250 kd) with the chromatin fraction as well. The gp of 135 and 100 kd were found to be virus-specified as determined by immunoblotting and immunoprecipitation. The gp of 200-250 kd exhibited an immunological relatedness to fibronectin and are therefore considered host-specific products. Both subsets of gp participate in virus-induced surface membrane alterations as documented by living cell immunofluorescence.

Activation of the major immediate early gene of human cytomegalovirus by cis-acting elements in the promoter-regulatory sequence and by virus-specific trans-acting components

Upstream of the major immediate early gene of human cytomegalovirus (Towne) is a strong promoter-regulatory region that promotes the synthesis of 1.95-kilobase mRNA (D. R. Thomsen, R. M. Stenberg, W. F. Goins, and M. F. Stinski, Proc. Natl. Acad. Sci. U.S.A. 81:659-663, 1984; M. F. Stinski, D. R. Thomsen, R. M. Stenberg, and L. C. Goldstein, J. Virol. 46:1-14, 1983). The wild-type promoter-regulatory region as well as deletions within this region were ligated upstream of the thymidine kinase, chloramphenicol acetyltransferase, or ovalbumin genes. These gene chimeras were constructed to investigate the role of the regulatory sequences in enhancing downstream expression. The regulatory region extends to approximately 465 nucleotides upstream of the cap site for the initiation of transcription. The extent and type of regulatory sequences upstream of the promoter influences the level of in vitro transcription as well as the amount of in vivo expression of the downstream gene. The regulatory elements for cis-activation appear to be repeated several times within the regulatory region. A direct correlation was established between the distribution of the 19 (5' CCCCAGTTGACGTCAATGGG 3')- and 18 (5' CACTAACGGGACTTTCCAA 3')-nucleotide repeats and the level of downstream expression. In contrast, the 16 (5' CTTGGCAGTACATCAA 3')-nucleotide repeat is not necessary for the enhancement of downstream expression. In a domain associated with the 19- or 18-nucleotide repeats are elements that can be activated in trans by a human cytomegalovirus-specified component but not a herpes simplex virus-specified component. Therefore, the regulatory sequences of the major immediate early gene of human cytomegalovirus have an important role in interacting with cellular and virus-specific factors of the transcription complex to enhance downstream expression of this critical viral gene.

Sodium butyrate selectively inhibits host cell glycoprotein synthesis in human fibroblasts infected with cytomegalovirus

Host cell as well as viral DNA synthesis in human fibroblasts infected with human cytomegalovirus was found to be largely resistant even to high concentrations of sodium butyrate. Likewise, production of viral progeny was reduced by 1-2 orders of magnitude but not abolished. On the other hand, the drug allowed (modified) glycosylation only of viral polypeptides whereas that of host proteins was suppressed. Immunofluorescence studies on living cells suggested that butyrate may interfere with processing and intracellular transport of virus-specific surface membrane antigens.

Catalytic properties of a human cytomegalovirus-induced protein kinase

Human cytomegalovirus, a DNA virus whose genome contains a fragment of transforming DNA, induces a threonine-serine protein kinase having a molecular mass of 68 kDa (p68). p68 was extracted from cells 96-144 h after infection, and immunoprecipitated with a monoclonal antibody (F6b). Antibody-enzyme complexes were immobilized on heat/formaldehyde-inactivated Staphylococcus aureus. The best substrates for p68 were acidic proteins, phosvitin and casein. Glycogen synthase, phosphorylase alpha and histones were phosphorylated at rates not higher than 1-4% that obtained with phosvitin as substrate. ATP and GTP were equally good substrates of p68. p68 is able to autophosphorylate at the same residues (i.e. threonine and serine) as the protein substrates. Autophosphorylation does not seem to represent an intermediate in substrate phosphorylation. The protein kinase activity of p68 was not enhanced by cAMP, calcium ions, or polyamines like spermine or spermidine. Only at low Mg2+ concentration spermine enhanced by 68% the rate of casein phosphorylation. Heparin, a potent inhibitor of casein kinase II, inhibits p68 activity too, but ten-times higher concentrations were required for the same degree of inhibition. Quercetin, a bioflavonoid, acts as a strong inhibitor of p68 protein kinase activity. The inhibitory effect of quercetin was competitive towards the nucleotide substrate (Ki = 2.8 microM), and non-competitive towards the protein substrate (Ki = 15 microM).

Abortive infection with human cytomegalovirus induces an alteration of growth pattern: morphological changes with cytocidal effect in rabbit kidney epithelial cells. Brief report

Rabbit kidney epithelial cells (RK13) exhibited a cytopathic effect (CPE) characterized by cell rounding after infection with human cytomegalovirus (HCMV). Although HCMV-specific immediate early and early antigens were detected by indirect immunofluorescence techniques, neither late antigens nor infectious progeny virus could be observed in virus-infected RK13 cells. HCMV-infected RK13 cells showed a prolonged doubling time and a decreased saturation density in cell growth compared to uninfected control cells. Moreover, colony forming ability (CFA) of virus-infected cells decreased by approximately 70 per cent compared to that of uninfected cells during the first 24 hours after infection. These results indicate that an abortive infection of RK13 cells with HCMV induces an alteration of growth pattern including morphological changes with cytocidal effect.