Inhibition of cytomegalovirus immediate early gene expression: a therapeutic option?

Challenges, Recent Advances and Perspectives in the Treatment of Human Cytomegalovirus Infections

Human cytomegalovirus (HCMV) is ubiquitous worldwide and elicits global health problems. The diseases associated with HCMV are a serious threat to humans, especially for the sick, infant, elderly and immunocompromised/immunodeficient individuals. Although traditional antiviral drugs (e.g., ganciclovir, valganciclovir, cidofovir, foscarnet) can be used to treat or prevent acute HCMV infections, their efficacy is limited because of toxicity, resistance issues, side effects and other problems. Fortunately, novel drugs (e.g., letermovir and maribavir) with less toxicity and drug/cross-resistance have been approved and put on the market in recent years. The nucleic acid-based gene-targeting approaches including the external guide sequences (EGSs)-RNase, the clustered regularly interspaced short palindromic repeats (CRISPRs)/CRISPRs-associated protein 9 (Cas9) system and transcription activator-like effector nucleases (TALENs) have been investigated to remove both lytic and latent CMV in vitro and/or in vivo. Cell therapy including the adoptive T cell therapy (ACT) and immunotherapy have been tried against drug-resistant and recurrent HCMV in patients receiving hematopoietic stem cell transplantation (HSCT) or solid organ transplant (SOT), and they have also been used to treat glioblastoma (GBM) associated with HCMV infections. These newly developed antiviral strategies are expected to yield fruitful results and make a significant contribution to the treatment of HCMV infections. Despite this progress, the nucleic acid-based gene-targeting approaches are still under study for basic research, and cell therapy is adopted in a small study population size or only successful in case reports. Additionally, no current drugs have been approved to be indicated for latent infections. Therefore, the next strategy is to develop antiviral strategies to elevate efficacy against acute and/or latent infections and overcome challenges such as toxicity, resistance issues, and side effects. In this review, we would explore the challenges, recent advances and perspectives in the treatment of HCMV infections. Furthermore, the suitable therapeutic strategies as well as the possibility for compassionate use would be evaluated.

Multiple AT-rich sequences function as a cis-element in the ORF3 promoter in channel catfish virus (Ictaluridherpesvirus 1)

The expression of herpesvirus genes during infection of tissue culture cells can be classified into three main classes: immediate-early (IE), early and late. The transcriptional regulation of herpesvirus IE genes is a critical regulatory step in the initiation of viral infection, with their regulation differing from that of early and late genes. Herein, we report that an IE gene (ORF3) promoter in channel catfish virus (CCV, Ictalurid herpesvirus 1) can be activated regardless of the presence or absence of CCV infection, indicating that the ORF3 promoter is efficiently driven by host-cell transcription factors in a viral infection-independent manner. The analysis of truncated promoter activity suggested that several transcription elements play a role in activating the ORF3 promoter, with the key cis-elements seemingly located in the flanking sequence of the start codon ATG. We further found that this flanking sequence contained multiple AT-rich sequences, and systematic mutational analyses showed that these AT-rich sequences affected normal transcription levels of the ORF3 promoter. To summarize, multiple AT-rich domains, representing the novel architecture of IE gene promoters in Ictalurid herpesvirus 1, serve as a cis-element for ORF3 transcription.

Potential Therapeutic Approaches Against Brain Diseases Associated with Cytomegalovirus Infections

Cytomegalovirus (CMV) is one of the major human health threats worldwide, especially for immunologically comprised patients. CMV may cause opportunistic infections, congenital infections, and brain diseases (e.g., mental retardation and glioblastoma). The etiology of brain diseases associated with human CMV (HCMV) infections is usually complex and it is particularly difficult to treat because HCMV has a life-long infection in its hosts, high mutation rate, and latent infections. Moreover, it is almost impossible to eradicate latent viruses in humans. Although there has been progress in drug discovery recently, current drugs used for treating active CMV infections are still limited in efficacy due to side effects, toxicity, and viral resistance. Fortunately, letermovir which targets the HCMV terminase complex rather than DNA polymerase with fewer adverse reactions has been approved to treat CMV infections in humans. The researchers are focusing on developing approaches against both productive and latent infections of CMV. The gene or RNA targeting approaches including the external guide sequences (EGSs)-RNase, the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system and transcription activator-like effector nucleases (TALENs) are being investigated to remove acute and/or latent CMV infections. For the treatment of glioblastoma, vaccine therapy through targeting specific CMV antigens has improved patients’ survival outcomes significantly and immunotherapy has also emerged as an alternative modality. The advanced research for developing anti-CMV agents and approaches is promising to obtain significant outcomes and expecting to have a great impact on the therapy of brain diseases associated with CMV infections.

Bright and Early: Inhibiting Human Cytomegalovirus by Targeting Major Immediate-Early Gene Expression or Protein Function

The human cytomegalovirus (HCMV), one of eight human herpesviruses, establishes lifelong latent infections in most people worldwide. Primary or reactivated HCMV infections cause severe disease in immunosuppressed patients and congenital defects in children. There is no vaccine for HCMV, and the currently approved antivirals come with major limitations. Most approved HCMV antivirals target late molecular processes in the viral replication cycle including DNA replication and packaging. “Bright and early” events in HCMV infection have not been exploited for systemic prevention or treatment of disease. Initiation of HCMV replication depends on transcription from the viral major immediate-early (IE) gene. Alternative transcripts produced from this gene give rise to the IE1 and IE2 families of viral proteins, which localize to the host cell nucleus. The IE1 and IE2 proteins are believed to control all subsequent early and late events in HCMV replication, including reactivation from latency, in part by antagonizing intrinsic and innate immune responses. Here we provide an update on the regulation of major IE gene expression and the functions of IE1 and IE2 proteins. We will relate this insight to experimental approaches that target IE gene expression or protein function via molecular gene silencing and editing or small chemical inhibitors.

Antiviral Agents as Therapeutic Strategies Against Cytomegalovirus Infections

Cytomegalovirus (CMV) is a threat to human health in the world, particularly for immunologically weak patients. CMV may cause opportunistic infections, congenital infections and central nervous system infections. CMV infections are difficult to treat due to their specific life cycles, mutation, and latency characteristic. Despite recent advances, current drugs used for treating active CMV infections are limited in their efficacy, and the eradication of latent infections is impossible. Current antiviral agents which target the UL54 DNA polymerase are restricted because of nephrotoxicity and viral resistance. CMV also cannot be prevented or eliminated with a vaccine. Fortunately, letermovir which targets the human CMV (HCMV) terminase complex has been recently approved to treat CMV infections in humans. The growing point is developing antiviral agents against both lytically and latently infected cells. The nucleic acid-based therapeutic approaches including the external guide sequences (EGSs)-RNase, the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system and transcription activator-like effector nucleases (TALENs) are being explored to remove acute and/or latent CMV infections. HCMV vaccine is being developed for prophylaxis. Additionally, adoptive T cell therapy (ACT) has been experimentally used to combate drug-resistant and recurrent CMV in patients after cell and/or organ transplantation. Developing antiviral agents is promising in this area to obtain fruitful outcomes and to have a great impact on humans for the therapy of CMV infections.

The Thrombopoietin Receptor Agonist Eltrombopag Inhibits Human Cytomegalovirus Replication Via Iron Chelation

The thrombopoietin receptor agonist eltrombopag was successfully used against human cytomegalovirus (HCMV)-associated thrombocytopenia refractory to immunomodulatory and antiviral drugs. These effects were ascribed to the effects of eltrombopag on megakaryocytes. Here, we tested whether eltrombopag may also exert direct antiviral effects. Therapeutic eltrombopag concentrations inhibited HCMV replication in human fibroblasts and adult mesenchymal stem cells infected with six different virus strains and drug-resistant clinical isolates. Eltrombopag also synergistically increased the anti-HCMV activity of the mainstay drug ganciclovir. Time-of-addition experiments suggested that eltrombopag interfered with HCMV replication after virus entry. Eltrombopag was effective in thrombopoietin receptor-negative cells, and the addition of Fe³⁺ prevented the anti-HCMV effects, indicating that it inhibits HCMV replication via iron chelation. This may be of particular interest for the treatment of cytopenias after hematopoietic stem cell transplantation, as HCMV reactivation is a major reason for transplantation failure. Since therapeutic eltrombopag concentrations are effective against drug-resistant viruses, and synergistically increase the effects of ganciclovir, eltrombopag is also a drug-repurposing candidate for the treatment of therapy-refractory HCMV disease.

The isoquinoline alkaloid berberine inhibits human cytomegalovirus replication by interfering with the viral Immediate Early-2 (IE2) protein transactivating activity

The identification and validation of new small molecules able to inhibit the replication of human cytomegalovirus (HCMV) remains a priority to develop alternatives to the currently used DNA polymerase inhibitors, which are often burdened by long-term toxicity and emergence of cross-resistance. To contribute to this advancement, here we report on the characterization of the mechanism of action of a bioactive plant-derived alkaloid, berberine (BBR), selected in a previous drug repurposing screen expressly devised to identify early inhibitors of HCMV replication. Low micromolar concentrations of BBR were confirmed to suppress the replication of different HCMV strains, including clinical isolates and strains resistant to approved DNA polymerase inhibitors. Analysis of the HCMV replication cycle in infected cells treated with BBR then revealed that the bioactive compound compromised the progression of virus cycle at a stage prior to viral DNA replication and Early (E) genes expression, but after Immediate-Early (IE) proteins expression. Mechanistic studies in fact highlighted that BBR interferes with the transactivating functions of the viral IE2 protein, thus impairing efficient E gene expression and the progression of HCMV replication cycle. Finally, the mechanism of the antiviral activity of BBR appears to be conserved among different CMVs, since BBR suppressed murine CMV (MCMV) replication and inhibited the transactivation of the prototypic MCMV E1 gene by the IE3 protein, the murine homolog of IE2. Together, these observations warrant for further experimentation to obtain proof of concept that BBR could represent an attractive candidate for alternative anti-HCMV therapeutic strategies.

Human cytomegalovirus may promote tumour progression by upregulating arginase-2

BACKGROUND

Both arginase (ARG2) and human cytomegalovirus (HCMV) have been implicated in tumorigenesis. However, the role of ARG2 in the pathogenesis of glioblastoma (GBM) and the HCMV effects on ARG2 are unknown. We hypothesize that HCMV may contribute to tumorigenesis by increasing ARG2 expression.

RESULTS

ARG2 promotes tumorigenesis by increasing cellular proliferation, migration, invasion and vasculogenic mimicry in GBM cells, at least in part due to overexpression of MMP2/9. The nor-NOHA significantly reduced migration and tube formation of ARG2-overexpressing cells. HCMV immediate-early proteins (IE1/2) or its downstream pathways upregulated the expression of ARG2 in U-251 MG cells. Immunostaining of GBM tissue sections confirmed the overexpression of ARG2, consistent with data from subsets of Gene Expression Omnibus. Moreover, higher levels of ARG2 expression tended to be associated with poorer survival in GBM patient by analyzing data from TCGA.

METHODS

The role of ARG2 in tumorigenesis was examined by proliferation-, migration-, invasion-, wound healing- and tube formation assays using an ARG2-overexpressing cell line and ARG inhibitor, N (omega)-hydroxy-nor-L-arginine (nor-NOHA) and siRNA against ARG2 coupled with functional assays measuring MMP2/9 activity, VEGF levels and nitric oxide synthase activity. Association between HCMV and ARG2 were examined in vitro with 3 different GBM cell lines, and ex vivo with immunostaining on GBM tissue sections. The viral mechanism mediating ARG2 induction was examined by siRNA approach. Correlation between ARG2 expression and patient survival was extrapolated from bioinformatics analysis on data from The Cancer Genome Atlas (TCGA).

CONCLUSIONS

ARG2 promotes tumorigenesis, and HCMV may contribute to GBM pathogenesis by upregulating ARG2.

Inhibition of human cytomegalovirus immediate-early gene expression and replication by the ethyl acetate (EtOAc) fraction of Elaeocarpus sylvestris in vitro

Background

In immunocompromised patients, human cytomegalovirus (HCMV) infection can lead to severe, life-threatening diseases, such as pneumonitis, hepatitis, gastrointestinal tract disease, and retinitis. We previously reported that a 70% ethanol extract of Elaeocarpus sylvestris leaves (ESE) inhibits human cytomegalovirus (HCMV) replication in vitro. In the present study, we determined the solvent fraction of ESE that inhibits HCMV replication using activity-guided fractionation.

Methods

Activity-guided fractionation of ESE was performed to determine the solvent fraction that inhibits HCMV replication. Effects of solvent fractions on HCMV lytic gene expression and major immediate-early (MIE) enhancer/promoter activity were further investigated.

Results

Among the solvent fractions tested, the EtOAc fraction of ESE markedly reduced HCMV lytic gene expression and viral replication in vitro without exerting significant cytotoxic effects against human foreskin fibroblasts (HFF). Furthermore, the EtOAc fraction negatively affected HCMV MIE enhancer/promoter activity.

Conclusion

Our data collectively indicate that the EtOAc fraction of ESE contains active constituents that inhibit HCMV MIE enhancer/promoter activity and viral replication. The EtOAc fraction of ESE is a good source of novel drug candidates for treatment of HCMV-associated diseases.

The immunological footprint of CMV in HIV-1 patients stable on long-term ART

Background

Most HIV-infected persons are cytomegalovirus (CMV) seropositive and retain latent virus that can be reactivated by immune activation. Their T cell populations express markers reflecting a late stage of differentiation, but the contributions of HIV and CMV to this profile are unclear. We investigated the immunological “footprint” of CMV in HIV patients who had a history of extreme immunodeficiency but were now stable on antiretroviral therapy (ART).

Results

Twenty CMV seropositive HIV patients >50 years old with nadir CD4 T-cell counts <200 cells/μl were studied after >12 years on ART. 16 CMV seropositive and 9 CMV seronegative healthy controls were included. CMV antibody titres were higher in HIV patients than controls (P < 0.001-0.003). Levels of soluble B-cell activating factor (sBAFF) were elevated in patients (P = 0.002) and correlated with levels of CMV antibodies (P = 0.03-0.002), with no clear relationship in controls. CD8 T-cell IFNγ responses to the IE1 peptide (VLE) remained elevated in HIV patients (P = 0.005). The CD57⁺CD45RA⁺CD27⁻ phenotype of CD8 T-cells correlated with age (r = 0.60, P = 0.006), antibodies against CMV IE1 protein (r = 0.44, P = 0.06) and CD4 T-cell IFNγ response to CMV lysate (r = 0.45, P = 0.05).

Conclusions

Humoral and T-cell responses to CMV remained elevated in HIV patients after >12 years on ART. Age and presence of CMV disease influenced CD8 T-cell phenotypes. Elevated levels of sBAFF may be a consequence of HIV disease and contribute to high titres of CMV antibody.

Electronic supplementary material

The online version of this article (doi:10.1186/s12979-015-0041-0) contains supplementary material, which is available to authorized users.

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.

The 6-Aminoquinolone WC5 inhibits different functions of the immediate-early 2 (IE2) protein of human cytomegalovirus that are essential for viral replication

The human cytomegalovirus (HCMV) immediate-early 2 (IE2) protein is a multifunctional factor essential for viral replication. IE2 modulates both viral and host gene expression, deregulates cell cycle progression, acts as an immunomodulator, and antagonizes cellular antiviral responses. Based on these facts, IE2 has been proposed as an important target for the development of innovative antiviral approaches. We previously identified the 6-aminoquinolone WC5 as a promising inhibitor of HCMV replication, and here, we report the dissection of its mechanism of action against the viral IE2 protein. Using glutathione S-transferase (GST) pulldown assays, mutagenesis, cell-based assays, and electrophoretic mobility shift assays, we demonstrated that WC5 does not interfere with IE2 dimerization, its interaction with TATA-binding protein (TBP), and the expression of a set of cellular genes that are stimulated by IE2. On the contrary, WC5 targets the regulatory activity exerted by IE2 on different responsive viral promoters. Indeed, WC5 blocked the IE2-dependent negative regulation of the major immediate-early promoter by preventing IE2 binding to the crs element. Moreover, WC5 reduced the IE2-dependent transactivation of a series of indicator constructs driven by different portions of the early UL54 gene promoter, and it also inhibited the transactivation of the murine CMV early E1 promoter by the IE3 protein, the murine cytomegalovirus (MCMV) IE2 homolog. In conclusion, our results indicate that the overall anti-HCMV activity of WC5 depends on its ability to specifically interfere with the IE2-dependent regulation of viral promoters. Importantly, our results suggest that this mechanism is conserved in murine CMV, thus paving the way for further preclinical evaluation in an animal model.

Human cytomegalovirus induces upregulation of arginase II: possible implications for vasculopathies

Both human cytomegalovirus (HCMV) and arginase II (ARG II) have been implicated in the pathogenesis of cardiovascular diseases. The effects of HCMV on ARG II are unknown. The aim of this study was to investigate the effects of HCMV on ARG II expression in endothelial and vascular smooth muscle cells (SMC) both in vitro and ex vivo. Endothelial and SMC were infected with either HCMV or UV-irradiated HCMV. Expression of ARG II, endothelial or inducible nitric oxide synthase (eNOS and iNOS, respectively) and viral immediate early (IE) was quantified using quantitative PCR. Ganciclovir and short interfering RNA were used to determine the viral gene mediating the effects on ARG II. Detection of viral antigens and ARG II expression was performed by immunofluorescence or immunohistochemistry. HCMV infection increased both ARG II mRNA and protein levels in the examined cells; this effect was mediated by the HCMV IE2-p86 protein. The upregulation of ARG II was accompanied by a downregulation of eNOS but an induction of iNOS in HCMV-infected endothelial cells. Both eNOS and iNOS expressions were induced in HCMV-infected SMC. ARG II was abundantly expressed in endothelial cells, foam cells and SMC and was importantly significantly upregulated in HCMV-immunoreactive human carotid atherosclerotic plaques. HCMV IE2-p86 mediates ARG II upregulation in vitro and ARG II is co-expressed with HCMV antigens in human carotid atherosclerotic plaques. We speculate that HCMV may contribute to endothelial dysfunction via ARG II induction and reduced eNOS production.

Human cytomegalovirus immediate early proteins promote degradation of connexin 43 and disrupt gap junction communication: implications for a role in gliomagenesis

A lack of gap junctional intercellular communication (GJIC) is common in cancer. Many oncogenic viruses have been shown to downregulate the junctional protein connexin 43 (Cx43) and reduce GJIC. Human cytomegalovirus (HCMV) is a ubiquitous, species-specific betaherpesvirus that establishes life-long latency after primary infection. It encodes two viral gene products, immediate early (IE) proteins IE1 and IE2, which are crucial in viral replication and pathogenesis of many diseases. Emerging evidence demonstrates that HCMV DNA and proteins are highly prevalent in glioblastoma multiforme (GBM) and in other tumors, but HCMV's role in tumorigenesis remains obscure. In the present study, we examined the effects of HCMV infection on Cx43 expression and GJIC as well as the viral mechanism mediating the effects in human GBM cells and tissue samples. We found that HCMV downregulated Cx43 protein, resulting in disruption of functional GJIC as assayed by fluorescent dye transfer assay. We show that both HCMV-IE72 and IE86 mediate downregulation of Cx43 by silencing RNA targeting either IE72 or IE86 coupled with ganciclovir. This finding was further validated by transfection with expression vectors encoding IE72 or IE86, and we show that viral-mediated Cx43 depletion involved proteasomal degradation. Importantly, we also observed that the Cx43 protein levels and IE staining correlated inversely in 10 human GBM tissue specimens. Thus, HCMV regulates Cx43 expression and GJIC, which may contribute to gliomagenesis.

Interplay between human cytomegalovirus and intrinsic/innate host responses: a complex bidirectional relationship

The interaction between human cytomegalovirus (HCMV) and its host is a complex process that begins with viral attachment and entry into host cells, culminating in the development of a specific adaptive response that clears the acute infection but fails to eradicate HCMV. We review the viral and cellular partners that mediate early host responses to HCMV with regard to the interaction between structural components of virions (viral glycoproteins) and cellular receptors (attachment/entry receptors, toll-like receptors, and other nucleic acid sensors) or intrinsic factors (PML, hDaxx, Sp100, viperin, interferon inducible protein 16), the reactions of innate immune cells (antigen presenting cells and natural killer cells), the numerous mechanisms of viral immunoevasion, and the potential exploitation of events that are associated with early phases of virus-host interplay as a therapeutic strategy.

RNA interference-mediated targeting of human cytomegalovirus immediate-early or early gene products inhibits viral replication with differential effects on cellular functions

Viral drug toxicity, resistance, and an increasing immunosuppressed population warrant continued research into new avenues for limiting diseases associated with human cytomegalovirus (HCMV). In this study, a small interfering RNA (siRNA), siX3, was designed to target coding sequences within shared exon 3 of UL123 and UL122 transcripts encoding IE1 and IE2 immediate-early proteins of HCMV. Pretreatment of cells with siX3 reduced the levels of viral protein expression, DNA replication, and progeny virus production compared to control siRNA. Two siRNAs against UL54 and overlapping transcripts (UL55-57) were compared to siX3 in HCMV infection and were also found to be effective at inhibiting HCMV replication. Further investigation into the effects of the siRNAs on viral replication showed that pretreatment with each of the siRNAs resulted in an inhibition in the formation of mature replication compartments. The ability of these siRNAs to prevent or reduce certain cytopathic effects associated with HCMV infection was also examined. Infected cells pretreated with siX3, but not siUL54, retained promyelocytic leukemia (PML) protein in cellular PML bodies, an essential component of this host intrinsic antiviral defense. DNA damage response proteins, which are localized in nuclear viral replication compartments, were reduced in the siX3- and siUL54-treated cells. siX3, but not siUL54, prevented DNA damage response signaling early after infection. Therapeutic efficacy was demonstrated by treating cells with siRNAs after HCMV replication had commenced. Together, these findings suggest that siRNAs targeting exon 3 of the major IE genes or the UL54-57 transcripts be further studied for their potential development into anti-HCMV therapeutics.

The multi-targeted kinase inhibitor sorafenib inhibits human cytomegalovirus replication

Human cytomegalovirus (HCMV) is a major pathogen in immunocompromised individuals. Here, non-toxic concentrations of the anti-cancer kinase inhibitor sorafenib were shown to inhibit replication of different HCMV strains (including a ganciclovir-resistant strain) in different cell types. In contrast to established anti-HCMV drugs, sorafenib inhibited HCMV major immediate early promoter activity and HCMV immediate early antigen (IEA) expression. Sorafenib is known to inhibit Raf. Comparison of sorafenib with the MEK inhibitor U0126 suggested that sorafenib inhibits HCMV IEA expression through inhibition of Raf but independently of signaling through the Raf downstream kinase MEK 1/2. In concordance, siRNA-mediated depletion of Raf but not of MEK-reduced IEA expression. In conclusion, sorafenib diminished HCMV replication in clinically relevant concentrations and inhibited HCMV IEA expression, a pathophysiologically relevant event that is not affected by established anti-HCMV drugs. Moreover, we demonstrated for the first time that Raf activation is involved in HCMV IEA expression.

The 6-aminoquinolone WC5 inhibits human cytomegalovirus replication at an early stage by interfering with the transactivating activity of viral immediate-early 2 protein

WC5 is a 6-aminoquinolone that potently inhibits the replication of human cytomegalovirus (HCMV) but has no activity, or significantly less activity, against other herpesviruses. Here we investigated the nature of its specific anti-HCMV activity. Structure-activity relationship studies on a small series of analogues showed that WC5 possesses the most suitable pattern of substitutions around the quinolone scaffold to give potent and selective anti-HCMV activity. Studies performed to identify the possible target of WC5 indicated that it prevents viral DNA synthesis but does not significantly affect DNA polymerase activity. In yield reduction experiments with different multiplicities of infection, the anti-HCMV activity of WC5 appeared to be highly dependent on the viral inoculum, suggesting that WC5 may act at an initial stage of virus replication. Consistently, time-of-addition and time-of-removal studies demonstrated that WC5 affects a phase of the HCMV replicative cycle that precedes viral DNA synthesis. Experiments to monitor the effects of the compound on virus attachment and entry showed that it does not inhibit either process. Evaluation of viral mRNA and protein expression revealed that WC5 targets an event of the HCMV replicative cycle that follows the transcription and translation of immediate-early genes and precedes those of early and late genes. In cell-based assays to test the effects of WC5 on the transactivating activity of the HCMV immediate-early 2 (IE2) protein, WC5 markedly interfered with IE2-mediated transactivation of viral early promoters. Finally, WC5 combined with ganciclovir in checkerboard experiments exhibited highly synergistic activity. These findings suggest that WC5 deserves further investigation as a candidate anti-HCMV drug with a novel mechanism of action.

New cell-based indicator assays for the detection of human cytomegalovirus infection and screening of inhibitors of viral immediate-early 2 protein activity

AIMS

Expression of early (E) genes of human cytomegalovirus (HCMV) is stimulated cooperatively by the activities of host cell transcription factors and the viral immediate-early 2 (IE2) protein. Taking advantage of the IE2-dependent inducibility of E gene promoters, in this study, we generated cell-based assays in which the expression of the enhanced green fluorescence protein (EGFP) reporter gene was driven by the UL54 or UL112/113 E promoters.

METHODS AND RESULTS

Cell clones derived from a stably transfected human cell line permissive to HCMV replication showed a specific and inducible dose- and time-dependent EGFP response to HCMV infection. The sensitivity of these indicator cells for detecting infectious particles of clinical isolates of HCMV was comparable to that of a conventional plaque assay. The HCMV-induced EGFP expression was completely prevented by treatment of indicator cells with fomivirsen, an antisense oligodeoxynucleotide designed to block IE2 expression, and this inhibitory activity was also observed when the IE2 protein alone was constitutively expressed in EGFP indicator cells.

CONCLUSIONS

The EGFP-based cell assays have proved to be a rapid, sensitive, quantitative and specific system for detection of HCMV and selection of antivirals.

SIGNIFICANCE AND IMPACT OF THE STUDY

These new cell-based assays can be exploited as functional assays to detect infectious HCMV particles, as well as to screen antiviral compounds that interfere with IE2 activity.

Molecular targets for antiviral therapy of cytomegalovirus infections

Human cytomegalovirus infections are still associated with severe morbidity and mortality in immunocompromised individuals, despite the availability of five drugs that are currently licensed for antiviral therapy. Furthermore, human cytomegalovirus is the most frequent cause of congenital infections for which antiviral treatment options are very limited. Thus, the need for a potent, safe and well-tolerated antiviral drug remains. This review focuses on target molecules that are implicated in the development of innovative anticytomegaloviral approaches, such as viral immediate-early and DNA replication proteins, as well as regulatory protein kinases. Special emphasis is given to promising host factors, in particular the receptor tyrosine kinase PDGF and cyclin-dependent protein kinases, since a combined targeting of viral and cellular factors that are critical for viral replication may alleviate the emergence of drug-resistant virus variants.

Human cytomegalovirus DNA replication: antiviral targets and drugs

Human cytomegalovirus (HCMV) infection is associated with severe morbidity and mortality in immunocompromised individuals, in particular transplant recipients and AIDS patients, and is the most frequent congenital viral infection in humans. There are currently five drugs approved for HCMV treatment: ganciclovir and its prodrug valganciclovir, foscarnet, cidofovir and fomivirsen. These drugs have provided a major advance in HCMV disease management, but they suffer from poor bioavailability, significant toxicity and limited effectiveness, mainly due to the development of drug resistance. Fortunately, there are several novel and potentially very effective new compounds which are under pre-clinical and clinical evaluation and may address these limitations. This review focuses on HCMV proteins that are directly or indirectly involved in viral DNA replication and represent already established or potential novel antiviral targets, and describes both currently available drugs and new compounds against such protein targets.

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.

Phosphorothioate-modified oligodeoxynucleotides inhibit human cytomegalovirus replication by blocking virus entry

Studies in animal models have provided evidence that Toll-like receptor 9 (TLR9) agonists, such as synthetic oligodeoxynucleotides (ODNs) that contain immunostimulatory deoxycytidyl-deoxyguanosine (CpG) motifs (CpG ODNs), protect against a wide range of viral pathogens. This antiviral activity has been suggested to be indirect and secondary to CpG-induced cytokines and inflammatory responses triggered through TLR9 activation. However, few studies have addressed the potential of CpG ODNs as direct antiviral agents. Here, we report on the ability of some CpG ODNs to directly suppress, almost completely, human cytomegalovirus (HCMV) replication in both primary fibroblasts and endothelial cells. Murine CMV replication was inhibited as well, whereas no inhibition was observed for herpes simplex virus type 1, adenovirus, or vesicular stomatitis virus. The antiviral activity of these ODNs was significantly reduced when they were added after virus adsorption, indicating that their action may be primarily targeted to the very early phases of the HCMV cycle. In fact, the B-class prototype CpG ODN 2006 effectively prevented the nuclear localization of pp65 and input viral DNA, which suggests that it inhibits HCMV entry. Moreover, a CpG 2006 control, ODN 2137 without CpG motifs, also showed a potent inhibitory activity on the HCMV entry phase, indicating that the anticytomegaloviral activity is independent of the CpG motif. In contrast, a phosphodiester version of CpG 2006 showed reduced antiviral activity, indicating that the inhibitory activity is dependent on the phosphorothioate backbone of the ODN. These results suggest that this yet-unrecognized activity of CpG ODNs may be of interest in the development of novel anticytomegaloviral molecules.

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.

Targeting the NF-kappaB pathway through pharmacological inhibition of IKK2 prevents human cytomegalovirus replication and virus-induced inflammatory response in infected endothelial cells

Endothelial cells are important reservoirs for human cytomegalovirus (HCMV) replication, dissemination and persistence. HCMV infection of endothelial cells has been associated with a proinflammatory response characterized by an increased expression of chemokines and adhesion molecules and modulation of angiogenesis. Many of the host proinflammatory genes augmented in HCMV-infected endothelial cells are regulated, at least in part, by the NF-kappaB pathway. HCMV is a potent activator of NF-kappaB through the IKK-IkappaB signaling axis. To explore whether inhibition of HCMV-induced NF-kappaB activation may interfere with the onset of virus-associated inflammatory response, we measured the effects of the specific IKK2 inhibitor AS602868 on the expression of a panel of proinflammatory genes in HUVEC cells infected with a clinical isolate. Treatment of infected HUVEC with AS602868 was shown to impair HCMV-induced NF-kappaB activity, IE gene expression, viral replication and to prevent HCMV-induced upregulation of ICAM-1, IL-8, RANTES, IP-10, I-TAC and COX-2 gene expression. Consistent with these results, HCMV-mediated upregulation of another NF-kappaB-dependent gene, the plasminogen inhibitor type-1, a regulatory factor of endothelial proliferation and angiogenesis, was abrogated by AS602868. These results suggest that inhibition of HCMV-induced IKK-NF-kappaB activation may be of interest to limit the virus-induced inflammatory response of infected endothelial cells.

Experimental study on the action of allitridin against human cytomegalovirus in vitro: Inhibitory effects on immediate-early genes

Garlic (Allium sativum) extraction has been reported having anti-HCMV efficacy. This study was aimed to investigate the effect of allitridin (diallyl trisulfide, a compound from A. sativum extraction) on the replication of HCMV and the expression of viral immediate-early genes. In HCMV plaque-reduction assay, allitridin appeared a dose-dependent inhibitory ability with EC(50) value of 4.2 microg/ml (selective index, SI=16.7). Time-of-addition and time-of-removal studies showed that allitridin inhibited HCMV replication in earlier period of viral cycle before viral DNA synthesis. Both immediate early gene (ie1) transcription and IEA (IE(1)72 and IE(2)86) expression was suppressed by allitridin, but not by GCV in a single HCMV cycle format. In addition, allitridin appeared stronger inhibition on IE(2)86 than on IE(1)72. Decrease of viral DNA load in infected cells was also detected under allitridin treatment, probably due to an indirect consequence of the reduction in ie gene transcription. In summary, this study indicated that allitridin has anti-HCMV activity and the mechanism is associated with suppression of ie gene transcription.

Oligonucleotides as antivirals: dream or realistic perspective?

Many reports have been published on antiviral activity of synthetic oligonucleotides, targeted to act either by a true antisense effect or via non-sequence specific interactions. This short review will try to evaluate the current status of the field by focusing on the effects as reported for inhibition of either HSV-1, HCMV or HIV-1. Following an introduction with a historical background and a brief discussion on the different types of constructs and mechanisms of action, the therapeutic potential of antisense oligonucleotides as antivirals, as well as possible pitfalls upon their evaluation will be discussed.

Circadian Regulation of a Viral Gene Promoter in Live Transgenic Mice Expressing Firefly Luciferase

PURPOSE

This study was conducted to test for possible circadian control of viral infection in live animals using bioluminescence imaging of a firefly luciferase transgene.

METHODS

Transgenic mice expressing the firefly luciferase gene under the control of the promoter and enhancer of the human cytomegalovirus major immediate-early gene (CMV::luc) were examined through whole-animal imaging. Mice were crossed with HRS/J hairless albino mice to improve imaging of deep structures.

RESULTS

Transgene expression in the extremities and head was elevated around dusk in mice maintained in cycles of light and dark. Signal was also elevated during the animal's night in mice maintained in extended darkness. The viral promoter was induced during the active phase of the circadian locomotor rhythm in several tissues. Both the acinar cells and islets expressed the transgene in dissociated pancreas cultures.

CONCLUSIONS

These results suggest that viruses may exploit the circadian system for optimal timing of infection at particular phases in several tissue types.

HIV patients on antiretroviral therapy have high frequencies of CD8 T cells specific for Immediate Early protein-1 of cytomegalovirus

OBJECTIVE

To assess the frequency and phenotype of cytomegalovirus (CMV)-specific CD8 T cells in previously immunocompromised HIV patients with stable undetectable HIV viremia due to highly active antiretroviral therapy (HAART).

METHODS

Twenty-one CMV-seropositive HIV patients with nadir CD4 T-cell counts < 50 x 10(6) cells/l, at least 4 years on HAART and 6 months of complete viral suppression (< 50 HIV RNA copies/ml) and 12 CMV-seropositive, HIV-seronegative age/sex-matched controls were studied. CD4 and CD8 T-cell responses to whole CMV and two HLA-A*02 restricted CMV peptides [NLV from pp65 and VLE from Immediate Early 1 (IE1)] were measured by interferon (IFN)gamma ELISpot. Phenotypes of peptide-specific CD8 T cells were determined by tetramer staining.

RESULTS

In the ELISpot assay, HIV patients had significantly more CD8 T cells producing IFN gamma in response to VLE than controls, whereas numbers of NLV-specific and CMV-specific IFN gamma spots were similar. Four HIV patients and one control had large VLE and/or NLV-specific CD8 T-cell populations despite the absence of CMV-specific CD4 T cells. The majority of peptide-specific CD8 T cells from HIV patients and controls were CD28-, CD45RO+ and CD45RA-. However, a significantly higher proportion of VLE-specific CD8 T cells expressed perforin compared to NLV-specific CD8 T cells in HIV patients.

CONCLUSIONS

HIV patients had elevated numbers of IE1-specific, IFNgamma-producing perforin-positive CD8 T cells compared to controls. As IE1 is expressed early during CMV reactivation, these cells may be important for preventing CMV replication to pathogenic levels. In addition, CMV-specific CD4 T cells are not essential for maintenance of large populations of CMV-specific CD8 T cells in aviremic HIV patients on HAART.

Oncomodulatory signals by regulatory proteins encoded by human cytomegalovirus: a novel role for viral infection in tumor progression

A high frequency of human cytomegalovirus (HCMV) genome and antigens in tumor samples of patients with different malignancies is now well documented, although the causative role for HCMV in the development of the neoplasias remains to be established. HCMV infection can modulate multiple cellular regulatory and signalling pathways in a manner similar to that of oncoproteins of small DNA tumor viruses such as human papilloma virus or adenoviruses. However, in contrast to these DNA tumor viruses, HCMV infection fails to transform susceptible normal human cells. There is now growing evidence that tumor cells with disrupted regulatory and signalling pathways enable HCMV to modulate their properties including stimulation of cell proliferation, survival, invasion, production of angiogenic factors, and immunogenic properties. In contrast to previously suggested "hit and run" transformation we suggest that persistence in tumor cells is essential for HCMV to fully express its oncomodulatory effects. These effects are observed particularly in persistent HCMV infection and are mediated mainly by activity of HCMV regulatory proteins. In persistently HCMV-infected tumor cell lines - a selection of novel, slowly growing virus variants with changes in coding sequences for virus regulatory proteins takes place. As a result, oncomodulatory effects of HCMV infection may lead to a shift to more malignant phenotype of tumor cells contributing to tumor progression.

Experimental study on the prevention and treatment of murine cytomegalovirus hepatitis by using allitridin

Allitridin (diallyl trisulfide), a main effective compound of Allium sativum (garlic), was previously shown to inhibit the expression of immediate-early antigens and viral proliferation of human cytomegalovirus (HCMV) in vitro. Here we have examined the prophylactic and therapeutic efficacy of allitridin in a non-lethal murine cytomegalovirus (MCMV) hepatitis in methylprednisolone-immunosuppressed BALB/c mice. Allitridin was administered at 25mg/kg per day (equal to the mean human dose) and 75 mg/kg per day in two regimens: prophylaxis plus therapy beginning at 2 days before infection and lasting for 18 days, and therapy lasting for 14 days initiated at 2 days after infection. Ganciclovir (GCV)-treated, infected, and non-infected mice served as controls. MCMV DNA load in the liver, plasma alanine aminotransferase (ALT) level and Knodell's histological activity index (HAI) score of liver section were evaluated. We found that MCMV DNA load was significantly decreased in all allitridin- and GCV-treated mice, compared with infected controls. Concomitantly, histopathological lesions in the liver and plasma ALT levels were reduced. Statistically, no significant differences were detected between the combined allitridin prophylaxis plus therapeutic and therapeutic groups regardless of dose and the GCV groups. Our results demonstrate the therapeutic efficacy of allitridin in mouse models with MCMV hepatitis.

Thrombin induces Sp1-mediated antiviral effects in cytomegalovirus-infected human retinal pigment epithelial cells

Human cytomegalovirus (HCMV) retinitis causing retinal detachment and destruction of the blood-retina barrier is closely related to retinal hemorrhage/coagulation. However, the effects of procoagulants on HCMV (re)activation in retinal cells have not been investigated yet. Therefore, we studied whether thrombin modulates the expression of HCMV immediate early (IE) and late (L) genes in cultured human retinal pigment epithelial cells (RPE). Thrombin specifically stimulated the protease-activated receptor-1 (PAR-1) on RPE and, surprisingly, inhibited basal and 12,0-tetradecanoylphorbol 13-acetate-stimulated HCMV IE gene expression in infected RPE. On the other hand, HCMV strongly induced Sp1 DNA binding activity, which was prevented by thrombin/PAR1-mediated Sp1 hyperphosphorylation. Our data suggest that thrombin/PAR-1 may inhibit Sp1-dependent HCMV replication, which might be an important regulatory mechanism for HCMV persistence and replication in RPE.

Monitoring immediate-early gene expression through firefly luciferase imaging of HRS/J hairless mice

BACKGROUND

Gene promoters fused to the firefly luciferase gene (luc) are useful for examining gene regulation in live transgenic mice and they provide unique views of functioning organs. The dynamics of gene expression in cells and tissues expressing luciferase can be observed by imaging this enzyme's bioluminescent oxidation of luciferin. Neural pathways involved in specific behaviors have been identified by localizing expression of immediate-early genes such as c-fos. A transgenic mouse line with luc controlled by the human c-fos promoter (fos::luc) has enabled gene expression imaging in brain slice cultures. To optimize imaging of immediate-early gene expression throughout intact mice, the present study examined fos::luc mice and a second transgenic mouse containing luc controlled by the human cytomegalovirus immediate-early gene 1 promoter and enhancer (CMV::luc). Because skin pigments and hair can significantly scatter light from underlying structures, the two transgenic lines were crossed with a hairless albino mouse (HRS/J) to explore which deep structures could be imaged. Furthermore, live anesthetized mice were compared with overdosed mice.

RESULTS

Bioluminescence imaging of anesthetized mice over several weeks corresponded with expression patterns in mice imaged rapidly after a lethal overdose. Both fos::luc and CMV::luc mice showed quantifiable bright bioluminescence in ear, nose, paws, and tail whether they were anesthetized or overdosed. CMV::luc and fos::luc neonates had bioluminescence patterns similar to those of adults, although intensity was significantly higher in neonates. CMV::luc mice crossed with HRS/J mice had high expression in bone, claws, head, pancreas, and skeletal muscle, but less in extremities than haired CMV::luc mice. Imaging of brain bioluminescence through the neonatal skull was also practical. By imaging luciferin autofluorescence it was clear that substrate distribution did not restrict bioluminescence imaging to capillaries after injection. Luciferin treatment and anesthesia during imaging did not adversely affect circadian rhythms in locomotor activity.

CONCLUSIONS

Imaging of gene expression patterns with luciferase can be extended from studies of live animals to rapid imaging of mice following a pentobarbital overdose before significant effects from postmortem changes occurs. Bioluminescent transgenic mice crossed with HRS/J mice are valuable for examining gene expression in deep tissues.

Ex vivo profiling of CD8+-T-cell responses to human cytomegalovirus reveals broad and multispecific reactivities in healthy virus carriers

Human cytomegalovirus (HCMV) can establish both nonproductive (latent) and productive (lytic) infections. Many of the proteins expressed during these phases of infection could be expected to be targets of the immune response; however, much of our understanding of the CD8(+)-T-cell response to HCMV is mainly based on the pp65 antigen. Very little is known about T-cell control over other antigens expressed during the different stages of virus infection; this imbalance in our understanding undermines the importance of these antigens in several aspects of HCMV disease pathogenesis. In the present study, an efficient and rapid strategy based on predictive bioinformatics and ex vivo functional T-cell assays was adopted to profile CD8(+)-T-cell responses to a large panel of HCMV antigens expressed during different phases of replication. These studies revealed that CD8(+)-T-cell responses to HCMV often contained multiple antigen-specific reactivities, which were not just constrained to the previously identified pp65 or IE-1 antigens. Unexpectedly, a number of viral proteins including structural, early/late antigens and HCMV-encoded immunomodulators (pp28, pp50, gH, gB, US2, US3, US6, and UL18) were also identified as potential targets for HCMV-specific CD8(+)-T-cell immunity. Based on this extensive analysis, numerous novel HCMV peptide epitopes and their HLA-restricting determinants recognized by these T cells have been defined. These observations contrast with previous findings that viral interference with the antigen-processing pathway during lytic infection would render immediate-early and early/late proteins less immunogenic. This work strongly suggests that successful HCMV-specific immune control in healthy virus carriers is dependent on a strong T-cell response towards a broad repertoire of antigens.

Subclinical activation of latent cytomegalovirus (CMV) infection and anti-CMV immune response in patients with atopic dermatitis

BACKGROUND

Microbiological infections are considered to be of pathophysiological importance in atopic dermatitis (AD). As yet, no information is available regarding cytomegalovirus (CMV) infection in this disease. This, however, is of interest because of the high prevalence of latent infections in the general population, the frequent reactivation in inflammatory diseases, and the immunomodulating capacity of CMV.

OBJECTIVES

To investigate the prevalence of latent CMV infection, the frequency of active CMV infection, and the immune response to CMV in patients with moderate to severe AD. Methods To detect active infection we analysed CMV antigen expression by peripheral blood mononuclear cells (PBMC) from 27 patients with moderate to severe AD in comparison with 53 healthy volunteers. We used three monoclonal antibodies recognizing different CMV-encoded antigens and immunocytological staining (alkaline phosphatase-antialkaline phosphatase technique).

RESULTS

Patients with AD had a higher mean frequency of CMV-positive PBMC: 2.25 per 10 000 vs. 0.74 per 10 000 in controls (P = 0.001) as well as a higher incidence of CMV antigenaemia: 29.6% vs. 7.5% (P < 0.01). Seropositivity for anti-CMV IgG antibodies indicated subclinical activation of latent infection. Remarkably, a clearance of CMV antigenaemia was observed during anti-eczematous treatment. Significantly higher plasma levels of tumour necrosis factor-alpha, which is involved in CMV reactivation, and interleukin-12, which is crucial for an antiviral cellular immune response, were observed in AD patients in comparison with healthy volunteers. Furthermore, a significantly enhanced frequency of circulating activated HLA-DR+ T cells especially in CMV-seropositive AD patients (19.3% vs. 13.5% in seronegative AD patients vs. 10.2% in controls) suggested that the active CMV infection triggers a cellular immune response. This was also supported by a high frequency of CMV-specific interferon-gamma-producing T cells in CMV-seropositive patients with AD.

CONCLUSIONS

Our data suggest that active, subclinical CMV infection is more frequent in patients with moderate to severe AD and may have immunopathophysiological relevance.

Human cytomegalovirus retinitis: pathogenicity, immune evasion and persistence

Human cytomegalovirus (HCMV) retinitis frequently occurs in severely naturally and iatrogenically immunocompromised patients. It has been shown that the immune-privileged retinal pigment epithelium (RPE) is a major site of persistent HCMV. Recently, evidence has accumulated to show that HCMV immediate early (IE) gene expression in RPE cells deviates ocular antiviral inflammation via FasL. Moreover, unlike in other cell types, the HCMV major IE1/2 enhancer promoter (MIEP) resists activation by proinflammatory stimuli mediated by the transcription factor NF-kappaB. However, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) found at elevated levels in transplant recipients and AIDS patients with retinitis sensitize RPE cells and other retinal cells to FasL-mediated apoptosis, thus contributing to retina destruction and necrosis rather than inflammation. These specific features of RPE cells in conjunction with deregulated immune responses of immunocompromised patients seem to contribute to virus persistence and pathogenesis within the immune-privileged ocular retina.

NF-kappaB--a potential therapeutic target for inhibition of human cytomegalovirus (re)activation?

From clinical studies the proinflammatory cytokine TNFalpha was proposed to play a key role in human cytomegalovirus (HCMV) reactivation from latency. In vitro experiments confirmed that TNFalpha stimulates the activity of the HCMV IE1/2 enhancer/promoter, which controls immediate early protein IE1 and IE2 gene expression via activation of the transcription factor NF-kappaB and its binding to putative binding sites in the IE1/2 enhancer. NF-kappaB was also proposed to be involved in IE1-mediated autostimulation of this promoter. The IE1/2 enhancer of HCMV contains four putative NF-kappaB binding sites which differ in their distance to the transcription start site as well as in their sequence. Construction and testing of a series of promoter mutants demonstrated that NF-kappaB is essential for both TNFalpha and IE1 stimulation. Furthermore, we were able to show that although all four NF-kappaB sites bind NF-kappaB with similar affinity in vitro, the contribution to TNFalpha and IE1 stimulation differs in correlation with the distance to the transcription start site and the sequence. Site 1 and 3 play the most dominant role and site 2 an intermediate, while site 4, which is conserved in sequence but far distant from the transcription start site, had no influence on NF-kappaB-mediated regulation of the IE1/2 promoter. Specific inhibition of NF-kappaB signalling by co-expression of a dominant-negative IkappaB variant reduced TNFalpha stimulation of the IE1/2 enhancer/promoter by up to 80%. From this data, inhibitors of NF-kappaB activation are suggested to be an alternative therapeutical strategy to interfere with HCMV (re)activation in undifferentiated monocyte/granulocyte progenitor cells in patients with a high risk of inflammation-related HCMV (re)activation.

Proteasome Inhibitors: A Novel Tool to Suppress Human Cytomegalovirus Replication and Virus-Induced Immune Modulation

Recently, we like others, demonstrated that systemic inflammation is the most important mechanism involved in (re)activation of human cytomegalovirus (HCMV) in both immunocompromised and immunocompetent patients. By in vitro studies the eukaryotic transcription factor NF-κB could be identified as the key mediator of TNF-α- and IE1-dependent stimulation of the HCMV IE1/2 enhancer/promoter activity, which is crucial for initiation of viral gene expression during reactivation from latency as well as productive infection. The enzymatic proteasome complex plays a central role in regulating intracellular processes, including the activation of NF-κB. As present antiviral strategies target mainly late events in HCMV replication (DNA replication, virus assembly) that do not completely prevent virus mediated immunopathogenesis, we wondered whether proteasome inhibitors might be a novel tool for targeting the interaction between inflammation and HCMV (re)activation. Here, proteasome inhibitors like MG132, PSI, II and III (MG262) have been shown to block both TNF-α-associated up-regulation of the HCMV IE1/2 enhancer/promoter in monocytic cells in an in vitro transient transfection system and HCMV replication in permissive human embryonal lung fibroblasts. Importantly, ganciclovir-resistant HCMV strains are sensitive to proteasome inhibitors. The effect of proteasome inhibitors on HCMV replication was found to be specific as replication of other herpes viruses, like HSV-1 and HSV-2, under identical experimental conditions was not influenced. Inhibition of HCMV replication correlated with a delayed and significantly reduced expression of IE proteins, particularly of the IE2 protein, suggesting that MG132 blocks HCMV replication at an immediate early stage of infection. Early and late protein synthesis as shown exemplary for the pp52 (DNA-binding protein) and p68 (structural protein) protein production and viral DNA synthesis were also inhibited. Suppression of HCMV replication could be correlated with an increased cytosolic accumulation of IκB as well as a reduced NF-κB binding activity in nuclear extracts of MG132-treated cells, which mainly regards NF-κB p50. MG132 also reduced the immune modulatory activity of the virus by abrogating virus-induced up-regulation of cellular ICAM-1. These data suggest that short-term therapy with proteasome inhibitors might be an alternative strategy to prevent (re)activation, replication and immune modulatory activity of HCMV in patients with systemic inflammation.

Direct targeting of human cytomegalovirus protein kinase pUL97 by kinase inhibitors is a novel principle for antiviral therapy

The protein kinase pUL97, encoded by human cytomegalovirus (HCMV), is an important determinant of virus replication. Recently, indolocarbazoles were identified as a class of substances that inhibit the pUL97 kinase activity in vitro. In parallel, it was shown that indolocarbazoles interfere with HCMV replication; however, the causal relationship between inhibition of pUL97 kinase activity and virus replication has not been clarified. Here evidence is provided that indolocarbazole-mediated inhibition of virus replication is a direct result of diminished pUL97 protein kinase activity. In cell culture infections, a strong and selective antiviral activity was measured with respect to several strains of HCMV in contrast with other related or non-related viruses. For fine quantification, recombinant HCMVs expressing green fluorescent protein were used, demonstrating the high sensitivity towards compounds NGIC-I and Gö6976. Interestingly, a ganciclovir-resistant virus mutant (UL97-M460I) showed increased sensitivity to both compounds. Supporting this concept, transfection experiments with cloned pUL97 revealed that ganciclovir-resistant mutants were characterized by reduced levels of autophosphorylation compared with wild-type and possessed particularly high sensitivity to indolocarbazoles. Moreover, the Epstein-Barr virus-encoded homologous kinase, BGLF4, which showed a similar pattern of autophosphorylation and ganciclovir phosphorylation activities, was not inhibited. Importantly, a cytomegalovirus deletion mutant, lacking a functional UL97 gene and showing a severe impairment of replication, was completely insensitive to indolocarbazoles. Thus, our findings indicate that a specific block in the activity of pUL97 is the critical step in indolocarbazole-mediated inhibition of virus replication and that pUL97 might be targeted very efficiently by a novel antiviral therapy.

Efficient and tightly regulated expression systems for the human cytomegalovirus major transactivator protein IE2p86 in permissive cells

The 86-kDa IE2 protein (IE2p86) of human cytomegalovirus is a pleiotropic regulatory polypeptide that is essential for activation of viral early promoters and thus, for the entire viral replication cycle. Moreover, this protein modulates cellular gene expression and contributes to the pathogenic features of HCMV. The full spectrum of IE2p86 mediated effects on cellular gene expression has not been defined yet, since efficient expression systems for this protein in HCMV permissive cells are, so far, limited. Here, we report the establishment of two efficient model systems that allow a tightly regulated expression of IE2p86 in various permissive cell types including primary human fibroblasts, primary endothelial cells and U373MG cells. Firstly, we generated a tetracycline-regulated U373MG cell line, which expresses high levels of IE2p86 upon tetracycline removal from the culture medium. Secondly, a recombinant baculovirus was constructed, which expresses IE2p86 under the control of the HCMV major immediate early enhancer/promoter upon transduction of various cell types. Importantly, IE2p86 was functional in both systems, since strong transactivation of luciferase promoter constructs could be measured. Furthermore, a cell cycle arrest was detectable after infection of primary human fibroblasts with IE2p86-expressing baculoviruses. Both expression systems represent useful tools to fully define the effects of this pleiotropic transactivator on cellular gene expression and to establish screening systems for novel antiviral drugs targeting this critical immediate early protein of HCMV.