Role of reactive oxygen intermediates in cytomegalovirus gene expression and in the response of human smooth muscle cells to viral infection

Complex roles for proliferating cell nuclear antigen in restricting human cytomegalovirus replication

DNA viruses at once elicit and commandeer host pathways, including DNA repair pathways, for virus replication. Despite encoding its own DNA polymerase and processivity factor, human cytomegalovirus (HCMV) recruits the cellular processivity factor, proliferating cell nuclear antigen (PCNA) and specialized host DNA polymerases involved in translesion synthesis (TLS) to replication compartments (RCs) where viral DNA (vDNA) is synthesized. While the recruitment of TLS polymerases is important for viral genome stability, the role of PCNA is poorly understood. PCNA function in DNA repair is regulated by monoubiquitination (mUb) or SUMOylation of PCNA at lysine 164 (K164). We find that mUb-PCNA increases over the course of infection, and modification of K164 is required for PCNA-mediated restriction of virus replication. mUb-PCNA plays important known roles in recruiting TLS polymerases to DNA, which we have shown are important for viral genome integrity and diversity, represented by structural variants and single nucleotide variants (SNVs), respectively. We find that PCNA drives SNVs on vDNA similar to Y-family TLS polymerases, but this did not require modification at K164. Unlike TLS polymerases, depeletion of PCNA did not result in large-scale rearrangements on vDNA. These striking results suggest separable PCNA-dependent and -independent functions of TLS polymerases on vDNA. By extension, these results imply roles for TLS polymerase beyond their canonical function in TLS in host biology. These findings highlight PCNA as a complex restriction factor for HCMV infection, likely with multiple distinct roles, and provide new insights into the PCNA-mediated regulation of DNA synthesis and repair in viral infection.IMPORTANCEGenome synthesis is a critical step of virus life cycles and a major target of antiviral drugs. Human cytomegalovirus (HCMV), like other herpesviruses, encodes machinery sufficient for viral DNA synthesis and relies on host factors for efficient replication. We have shown that host DNA repair factors play important roles in HCMV replication, but our understanding of this is incomplete. Building on previous findings that specialized host DNA polymerases contribute to HCMV genome integrity and diversity, we sought to determine the importance of proliferating cell nuclear antigen (PCNA), the central polymerase regulator. PCNA is associated with nascent viral DNA and restricts HCMV replication. While PCNA is dispensable for genome integrity, it contributes to genome diversity. Our findings suggest that host polymerases function on viral genomes by separable PCNA-dependent and -independent mechanisms. Through revealing complex roles for PCNA in HCMV replication, this study expands the repertoire of host DNA synthesis and repair proteins hijacked by this ubiquitous herpesvirus.

Discovery of bimodal hepatitis B virus ribonuclease H and capsid assembly inhibitors

Hepatitis B virus (HBV) ribonuclease H (RNaseH) inhibitors are a potent class of antivirals that prevent degradation of the viral pregenomic RNA during reverse transcription and block formation of mature HBV DNAs. Development of HBV RNaseH inhibitors is entering advanced preclinical analyses. To ensure the mechanism of action was fully understood, we defined the effects of RNaseH inhibitors on other steps of HBV replication. Some N-hydroxypyridinedione (HPD) HBV RNaseH inhibitors significantly reduced accumulation of capsids in HBV-replicating cells. A representative HPD 1466, with a 50% effective concentration against HBV replication of 0.25 µM, decreased capsid and core protein accumulation by 50-90% in HepDES19 and HepG2.2.15 cells. Surprisingly, 1466 did not affect pregenomic RNA encapsidation, demonstrating a specific effect on empty capsids. HBV genomic replication was not necessary for 1466's inhibitory effect as it decreased capsid accumulation in cells transfected with replication-deficient mutants blocking pgRNA encapsidation (Δ-bulge), DNA synthesis (YMHA), and RNaseH (D702A) activities. 1466 also decreased capsid and core protein accumulation in cells transfected with a core protein expression plasmid, indicating that other HBV products are unneeded. 1466 reduced initial capsid assembly rates in biochemical assembly reactions employing purified core protein (Cp149), demonstrating a specific effect on HBV core protein. We conclude that the bimodal HPD HBV RNaseH inhibitor 1466 is the prototypic member of a new class of capsid assembly modulators (CAM) that inhibits capsid assembly rather than accelerating it, as all other CAM classes do. We propose that this class be called CAM-I, for CAM-inhibitor. These results lay the foundation for identifying bimodal HBV antivirals targeting the RNaseH and capsid assembly.

Modulation of Monocyte Effector Functions and Gene Expression by Human Cytomegalovirus Infection

Monocytes are crucial players in innate immunity. The human cytomegalovirus (CMV) infection has significant impacts on monocyte effector functions and gene expression. CMV, a β-herpesvirus, disrupts key monocyte roles, including phagocytosis, antigen presentation, cytokine production, and migration, impairing their ability to combat pathogens and activate adaptive immune responses. CMV modulates monocyte gene expression, decreasing their capacity for antigen presentation and phagocytosis while increasing pro-inflammatory cytokine production, which can contribute to tissue damage and chronic inflammation. CMV also alters monocyte migration to sites of infection while promoting trans-endothelial migration, thus aiding viral dissemination. Additionally, the virus affects reactive oxygen species (ROS) production, thereby contributing to end-organ disease associated with CMV infection. Overall, these changes enhance viral persistence during acute infection and facilitate immune evasion during latency. We highlight the clinical significance of these disruptions, particularly in immunocompromised patients such as transplant recipients, where the modulation of monocyte function by CMV exacerbates risks for infection, inflammation, and graft rejection. An understanding of these mechanisms will inform therapeutic strategies to mitigate CMV-related complications in vulnerable populations.

Cytomegalovirus-induced peroxynitrite promotes virus entry and contributes to pathogenesis in a murine model of infection

There are no licensed vaccines for human cytomegalovirus (HCMV), and current antiviral drugs that target viral proteins are toxic and prone to resistance. Targeting host pathways essential for virus replication provides an alternate strategy that may reduce opportunities for drug resistance to occur. Oxidative stress is triggered by numerous viruses including HCMV. Peroxynitrite is a reactive nitrogen species that is formed during oxidative stress. Herein, we identified that HCMV rapidly induces the generation of intracellular peroxynitrite upon infection in a manner partially dependent upon xanthine oxidase generation. Peroxynitrite promoted HCMV infection in both cell-free and cell-associated infection systems in multiple cell types. Inhibiting peroxynitrite within the first 24 hours of infection prevented HCMV replication and peroxynitrite promoted cell entry and pp65 translocation into the host cell nuclei. Furthermore, using the murine cytomegalovirus model, we demonstrated that antagonizing peroxynitrite significantly reduces cytomegalovirus replication and pathogenesis in vivo. Overall, our study highlights a proviral role for peroxynitrite in CMV infection and implies that RNS and/or the mechanisms that induce their production could be targeted as a novel strategy to inhibit HCMV infection.

IMPORTANCE

Human cytomegalovirus (HCMV) causes significant disease in individuals with impaired or immature immune systems, such as transplant patients and after congenital infection. Antiviral drugs that target the virus directly are toxic and are susceptible to antiviral drug resistance due to virus mutations. An alternate strategy is to target processes within host cells that are required by the virus for replication. Herein, we show that HCMV infection triggers a highly reactive molecule, peroxynitrite, during the initial stages of infection. Peroxynitrite was required for the initial entry of the virus into the cell and promotes virus replication in multiple cell types, suggesting a broad pro-viral function. Importantly, targeting peroxynitrite dramatically inhibited cytomegalovirus replication in cells in the laboratory and in mice, suggesting that therapeutic targeting of this molecule and/or the cellular functions it regulates could represent a novel strategy to inhibit HCMV infection.

Biliary atresia

Biliary atresia (BA) is a progressive inflammatory fibrosclerosing disease of the biliary system and a major cause of neonatal cholestasis. It affects 1:5,000-20,000 live births, with the highest incidence in Asia. The pathogenesis is still unknown, but emerging research suggests a role for ciliary dysfunction, redox stress and hypoxia. The study of the underlying mechanisms can be conceptualized along the likely prenatal timing of an initial insult and the distinction between the injury and prenatal and postnatal responses to injury. Although still speculative, these emerging concepts, new diagnostic tools and early diagnosis might enable neoadjuvant therapy (possibly aimed at oxidative stress) before a Kasai portoenterostomy (KPE). This is particularly important, as timely KPE restores bile flow in only 50-75% of patients of whom many subsequently develop cholangitis, portal hypertension and progressive fibrosis; 60-75% of patients require liver transplantation by the age of 18 years. Early diagnosis, multidisciplinary management, centralization of surgery and optimized interventions for complications after KPE lead to better survival. Postoperative corticosteroid use has shown benefits, whereas the role of other adjuvant therapies remains to be evaluated. Continued research to better understand disease mechanisms is necessary to develop innovative treatments, including adjuvant therapies targeting the immune response, regenerative medicine approaches and new clinical tests to improve patient outcomes.

Virus-Induced MicroRNA Modulation and Systemic Sclerosis Disease

MicroRNAs (miRNAs) are short noncoding RNA sequences that regulate gene expression at the post-transcriptional level. They are involved in the regulation of multiple pathways, related to both physiological and pathological conditions, including autoimmune diseases, such as Systemic Sclerosis (SSc). Specifically, SSc is recognized as a complex and multifactorial disease, characterized by vascular abnormalities, immune dysfunction, and progressive fibrosis, affecting skin and internal organs. Among predisposing environmental triggers, evidence supports the roles of oxidative stress, chemical agents, and viral infections, mostly related to those sustained by beta-herpesviruses such as HCMV and HHV-6. Dysregulated levels of miRNA expression have been found in SSc patients compared to healthy controls, at both the intra- and extracellular levels, providing a sort of miRNA signature of the SSc disease. Notably, HCMV/HHV-6 viral infections were shown to modulate the miRNA profile, often superposing that observed in SSc, potentially promoting pathological pathways associated with SSc development. This review summarizes the main data regarding miRNA alterations in SSc disease, highlighting their potential as prognostic or diagnostic markers for SSc disease, and the impact of the putative SSc etiological agents on miRNA modulation.

Mitochondrial Oxidative Phosphorylation in Viral Infections

Mitochondria have been identified as the "powerhouse" of the cell, generating the cellular energy, ATP, for almost seven decades. Research over time has uncovered a multifaceted role of the mitochondrion in processes such as cellular stress signaling, generating precursor molecules, immune response, and apoptosis to name a few. Dysfunctional mitochondria resulting from a departure in homeostasis results in cellular degeneration. Viruses hijack host cell machinery to facilitate their own replication in the absence of a bonafide replication machinery. Replication being an energy intensive process necessitates regulation of the host cell oxidative phosphorylation occurring at the electron transport chain in the mitochondria to generate energy. Mitochondria, therefore, can be an attractive therapeutic target by limiting energy for viral replication. In this review we focus on the physiology of oxidative phosphorylation and on the limited studies highlighting the regulatory effects viruses induce on the electron transport chain.

Polyploid Giant Cancer Cells Generated from Human Cytomegalovirus-Infected Prostate Epithelial Cells

BACKGROUND

Prostate cancer is the most commonly diagnosed malignancy and the sixth leading cause of cancer death in men worldwide. Chromosomal instability (CIN) and polyploid giant cancer cells (PGCCs) have been considered predominant hallmarks of cancer. Recent clinical studies have proven the association of CIN, aneuploidy, and PGCCs with poor prognosis of prostate cancer (PCa). Evidence of HCMV transforming potential might indicate that HCMV may be involved in PCa.

METHODS

Herein, we underline the role of the high-risk HCMV-DB and -BL clinical strains in transforming prostate epithelial cells and assess the molecular and cellular oncogenic processes associated with PCa.

RESULTS

Oncogenesis parallels a sustained growth of "CMV-Transformed Prostate epithelial cells" or CTP cells that highly express Myc and EZH2, forming soft agar colonies and displaying stemness as well as mesenchymal features, hence promoting EMT as well as PGCCs and a spheroid appearance.

CONCLUSIONS

HCMV-induced Myc and EZH2 upregulation coupled with stemness and EMT traits in IE1-expressing CTP might highlight the potential role of HCMV in PCa development and encourage the use of anti-EZH2 and anti-HCMV in PCa treatment.

Targeting the Host Mitochondria as a Novel Human Cytomegalovirus Antiviral Strategy

Human cytomegalovirus (HCMV) exploits host mitochondrial function to promote viral replication. HCMV gene products have been described to directly interact and alter functional or structural aspects of host mitochondria. Current antivirals against HCMV, such as ganciclovir and letermovir, are designed against viral targets. Concerns with the current antivirals include toxicity and viral resistance. Targeting host mitochondrial function is a promising alternative or complimentary antiviral approach as (1) drugs targeting host mitochondrial function interact with host targets, minimizing viral resistance, and (2) host mitochondrial metabolism plays key roles in HCMV replication. This review describes how HCMV alters mitochondrial function and highlights pharmacological targets that can be exploited for novel antiviral development.

The Human Cytomegalovirus β2.7 Long Non-Coding RNA Prevents Induction of Reactive Oxygen Species to Maintain Viral Gene Silencing during Latency

Human cytomegalovirus (HCMV) is a significant source of disease for the immunosuppressed and immunonaive. The treatment of HCMV is made more problematic by viral latency, a lifecycle stage in which the virus reduces its own gene expression and produces no infectious virus. The most highly expressed viral gene during HCMV latency is the viral β2.7 long non-coding RNA. Although we have recently shown that the β2.7 lncRNA lowers levels of reactive oxygen species (ROS) during infection in monocytes, how this impacts latency is unclear. We now show that β2.7 is important for establishing and maintaining HCMV latency by aiding the suppression of viral lytic gene expression and that this is directly related to its ability to quench reactive oxygen species (ROS). Consistent with this, we also find that exogenous inducers of ROS cause reactivation of latent HCMV. These effects can be compensated by treatment with an antioxidant to lower ROS levels. Finally, we show that ROS-mediated reactivation is independent of myeloid differentiation, but instead relies on NF-κB activation. Altogether, these results reveal a novel factor that is central to the complex process that underpins HCMV latency. These findings may be of particular relevance in the transplant setting, in which transplanted tissue/organs are subject to very high ROS levels, and HCMV reactivation poses a significant threat.

Poxviruses package viral redox proteins in lateral bodies and modulate the host oxidative response

All poxviruses contain a set of proteinaceous structures termed lateral bodies (LB) that deliver viral effector proteins into the host cytosol during virus entry. To date, the spatial proteotype of LBs remains unknown. Using the prototypic poxvirus, vaccinia virus (VACV), we employed a quantitative comparative mass spectrometry strategy to determine the poxvirus LB proteome. We identified a large population of candidate cellular proteins, the majority being mitochondrial, and 15 candidate viral LB proteins. Strikingly, one-third of these are VACV redox proteins whose LB residency could be confirmed using super-resolution microscopy. We show that VACV infection exerts an anti-oxidative effect on host cells and that artificial induction of oxidative stress impacts early and late gene expression as well as virion production. Using targeted repression and/or deletion viruses we found that deletion of individual LB-redox proteins was insufficient for host redox modulation suggesting there may be functional redundancy. In addition to defining the spatial proteotype of VACV LBs, these findings implicate poxvirus redox proteins as potential modulators of host oxidative anti-viral responses and provide a solid starting point for future investigations into the role of LB resident proteins in host immunomodulation.

A Viral Long Non-Coding RNA Protects against Cell Death during Human Cytomegalovirus Infection of CD14+ Monocytes

Long non-coding RNA β2.7 is the most highly transcribed viral gene during latent human cytomegalovirus (HCMV) infection. However, as yet, no function has ever been ascribed to β2.7 during HCMV latency. Here we show that β2.7 protects against apoptosis induced by high levels of reactive oxygen species (ROS) in infected monocytes, which routinely support latent HCMV infection. Monocytes infected with a wild-type (WT) virus, but not virus deleted for the β2.7 gene (Δβ2.7), are protected against mitochondrial stress and subsequent apoptosis. Protected monocytes display lower levels of ROS and additionally, stress-induced death in the absence of β2.7 can be reversed by an antioxidant which reduces ROS levels. Furthermore, we show that infection with WT but not Δβ2.7 virus results in strong upregulation of a cellular antioxidant enzyme, superoxide dismutase 2 (SOD2) in CD14+ monocytes. These observations identify a role for the β2.7 viral transcript, the most abundantly expressed viral RNA during latency but for which no latency-associated function has ever been ascribed, and demonstrate a novel way in which HCMV protects infected monocytes from pro-death signals to optimise latent carriage.

Effect of Reactive Oxygen Species on the Endoplasmic Reticulum and Mitochondria during Intracellular Pathogen Infection of Mammalian Cells

Oxidative stress, particularly reactive oxygen species (ROS), are important for innate immunity against pathogens. ROS directly attack pathogens, regulate and amplify immune signals, induce autophagy and activate inflammation. In addition, production of ROS by pathogens affects the endoplasmic reticulum (ER) and mitochondria, leading to cell death. However, it is unclear how ROS regulate host defense mechanisms. This review outlines the role of ROS during intracellular pathogen infection, mechanisms of ROS production and regulation of host defense mechanisms by ROS. Finally, the interaction between microbial pathogen-induced ROS and the ER and mitochondria is described.

Host Mitochondrial Requirements of Cytomegalovirus Replication

Purpose of Review

Metabolic rewiring of the host cell is required for optimal viral replication. Human cytomegalovirus (HCMV) has been observed to manipulate numerous mitochondrial functions. In this review, we describe the strategies and targets HCMV uses to control different aspects of mitochondrial function.

Recent Findings

The mitochondria are instrumental in meeting the biosynthetic and bioenergetic needs of HCMV replication. This is achieved through altered metabolism and signaling pathways. Morphological changes mediated through biogenesis and fission/fusion dynamics contribute to strategies to avoid cell death, overcome oxidative stress, and maximize the biosynthetic and bioenergetic outputs of mitochondria.

Summary

Emerging data suggests that cytomegalovirus relies on intact, functional host mitochondria for optimal replication. HCMV large size and slow replication kinetics create a dependency on mitochondria during replication. Targeting the host mitochondria is an attractive antiviral target.

The role of human cytomegalovirus in atherosclerosis: a systematic review

Atherosclerosis is a progressive vascular disease with increasing morbidity and mortality year by year in modern society. Human cytomegalovirus (HCMV) infection is closely associated with the development of atherosclerosis. HCMV infection may accelerate graft atherosclerosis and the development of transplant vasculopathy in organ transplantation. However, our current understanding of HCMV-associated atherosclerosis remains limited and is mainly based on clinical observations. The underlying mechanism of the involvement of HCMV infection in atherogenesis remains unclear. Here, we summarized current knowledge regarding the multiple influences of HCMV on a diverse range of infected cells, including vascular endothelial cells, vascular smooth muscle cells, monocytes, macrophages, and T cells. In addition, we described potential HCMV-induced molecular mechanisms, such as oxidative stress, endoplasmic reticulum stress, autophagy, lipid metabolism, and miRNA regulation, which are involved in the development of HCMV-associated atherogenesis. Gaining an improved understanding of these mechanisms will facilitate the development of novel and effective therapeutic strategies for the treatment of HCMV-related cardiovascular disease.

Monocytes Latently Infected with Human Cytomegalovirus Evade Neutrophil Killing

One site of latency of human cytomegalovirus (HCMV) in vivo is in undifferentiated cells of the myeloid lineage. Although latently infected cells are known to evade host T cell responses by suppression of T cell effector functions, it is not known if they must also evade surveillance by other host immune cells. Here we show that cells latently infected with HCMV can, indeed, be killed by host neutrophils but only in a serum-dependent manner. Specifically, antibodies to the viral latency-associated US28 protein mediate neutrophil killing of latently infected cells. To address this mechanistically, a full proteomic screen was carried out on latently infected monocytes. This showed that latent infection downregulates the neutrophil chemoattractants S100A8/A9, thus suppressing neutrophil recruitment to latently infected cells. The ability of latently infected cells to inhibit neutrophil recruitment represents an immune evasion strategy of this persistent human pathogen, helping to prevent clearance of the latent viral reservoir.

The Human Cytomegalovirus US27 Gene Product Constitutively Activates Antioxidant Response Element-Mediated Transcription through Gβγ, Phosphoinositide 3-Kinase, and Nuclear Respiratory Factor 1

Human cytomegalovirus (HCMV) is a widespread pathogen that modulates host chemokine signaling during persistent infection in the host. HCMV encodes four proteins with homology to the chemokine receptor family of G protein-coupled receptors (GPCRs): US27, US28, UL33, and UL78. Each of the four receptors modulates host CXCR4 signaling. US28, UL33, and UL78 impair CXCR4 signaling outcomes, while US27 enhances signaling, as evidenced by increased calcium mobilization and cell migration to CXCL12. To investigate the effects of US27 on CXCR4 during virus infection, fibroblasts were infected with bacterial artificial chromosome-derived clinical strain HCMV TB40/E-mCherry (wild type [WT]), mutants lacking US27 (TB40/E-mCherry-US27Δ [US27Δ]) or all four GPCRs (TB40 E-mCherry-allΔ), or mutants expressing only US27 but not US28, UL33, or UL78 (TB40/E-mCherry-US27wt [US27wt]). CXCR4 gene expression was significantly higher in WT- and US27wt-infected fibroblasts. This effect was evident at 3 h postinfection, suggesting that US27 derived from the parental virion enhanced CXCR4 expression. Reporter gene assays demonstrated that US27 increased transcriptional activity regulated by the antioxidant response element (ARE), and small interfering RNA treatment indicated that this effect was mediated by NRF-1, the primary transcription factor for CXCR4. Increased translocation of NRF-1 into the nucleus of WT-infected cells compared to mock- or US27Δ-infected cells was confirmed by immunofluorescence microscopy. Chemical inhibitors targeting G_βγ and phosphoinositide 3-kinase (PI3K) ablated the increase in ARE-driven transcription, implicating these proteins as mediators of US27-stimulated gene transcription. This work identifies the first signaling pathway activated by HCMV US27 and may reveal a novel regulatory function for this orphan viral receptor in stimulating stress response genes during infection.IMPORTANCE Human cytomegalovirus (HCMV) is the most common congenital infection worldwide, causing deafness, blindness, and other serious birth defects. CXCR4 is a human chemokine receptor that is crucial for both fetal development and immune responses. We found that the HCMV protein US27 stimulates increased expression of CXCR4 through activation of the transcription factor nuclear respiratory factor 1 (NRF-1). NRF-1 regulates stress response genes that contain the antioxidant response element (ARE), and HCMV infection is associated with increased expression of many stress response genes when US27 is present. Our results show that the US27 protein activates the NRF-1/ARE pathway, stimulating higher expression of CXCR4 and other stress response genes, which is likely to be beneficial for virus replication and/or immune evasion.

Human cytomegalovirus infection and coronary heart disease: a systematic review

Background

Human cytomegalovirus (HCMV) infection is closely associated with coronary heart disease.

Main body of the abstract

In 1987, Adam et al. were the first to report an association between HCMV infection and atherosclerosis (AS), and later, many serum epidemiology and molecular biology studies showed that HCMV-infected endothelial cells play an important role in the development of AS. As patients with HCMV are generally susceptible to coronary heart disease, and with the increasing elderly population, a review of recent studies focusing on the relationships of HCMV infection and coronary heart disease is timely and necessary.

Short conclusion

The role of HCMV infection in the development of AS needs further study, since many remaining issues need to be explored and resolved. For example, whether HCMV promotes the development of coronary AS, and what the independent factors that lead to coronary artery AS by viral infection are. A comprehensive understanding of HCMV infection is needed in order to develop better strategies for preventing AS.

Pathogenesis of developmental anomalies of the central nervous system induced by congenital cytomegalovirus infection

In humans, the herpes virus family member cytomegalovirus (CMV) is the most prevalent mediator of intrauterine infection-induced congenital defect. Central nervous system (CNS) dysfunction is a distinguishing symptom of CMV infection, and characterized by ventriculoencephalitis and microglial nodular encephalitis. Reports on the initial distribution of CMV particles and its receptors on the blood brain barrier (BBB) are rare. Nevertheless, several factors are suggested to affect CMV etiology. Viral particle size is the primary factor in determining the pattern of CNS infections, followed by the expression of integrin β1 in endothelial cells, pericytes, meninges, choroid plexus, and neural stem progenitor cells (NSPCs), which are the primary targets of CMV infection. After initial infection, CMV disrupts BBB structural integrity to facilitate the spread of viral particles into parenchyma. Then, the initial meningitis and vasculitis eventually reaches NSPC-dense areas such as ventricular zone and subventricular zone, where viral infection inhibits NSPC proliferation and differentiation and results in neuronal cell loss. These cellular events clinically manifest as brain malformations such as a microcephaly. The purpose of this review is to clearly delineate the pathophysiological basis of congenital CNS anomalies caused by CMV.

Inhibition of cyclophilin A suppresses H2O2-enhanced replication of HCMV through the p38 MAPK signaling pathway

Human cytomegalovirus (HCMV) infection can be accelerated by intracellular and extracellular hydrogen peroxide (H₂O₂) stimulation, mediated by the activation of the p38 mitogen‐activated protein kinase (MAPK) pathway. However, it remains unknown whether host gene expression is involved in H₂O₂‐upregulated HCMV replication. Here, we show that the expression of the host gene, cyclophilin A (CyPA), could be facilitated by treatment with H₂O₂ in a dose‐dependent manner. Experiments with CyPA‐specific siRNA, or with cyclosporine A, an inhibitor of CyPA, confirmed that H₂O₂‐mediated upregulation of HCMV replication is specifically mediated by upregulation of CyPA expression. Furthermore, depletion or inhibition of CyPA reduced H₂O₂‐induced p38 activation, consistent with that of H₂O₂‐upregulated HCMV lytic replication. These results show that H₂O₂ is capable of activating ROS‐CyPA–p38 MAPK interactions to enhance HCMV replication.

Human Cytomegalovirus pTRS1 and pIRS1 Antagonize Protein Kinase R To Facilitate Virus Replication

Human cytomegalovirus (HCMV) counteracts host defenses that otherwise act to limit viral protein synthesis. One such defense is the antiviral kinase protein kinase R (PKR), which inactivates the eukaryotic initiation factor 2 (eIF2) translation initiation factor upon binding to viral double-stranded RNAs. Previously, the viral TRS1 and IRS1 proteins were found to antagonize the antiviral kinase PKR outside the context of HCMV infection, and the expression of either pTRS1 or pIRS1 was shown to be necessary for HCMV replication. In this study, we found that expression of either pTRS1 or pIRS1 is necessary to prevent PKR activation during HCMV infection and that antagonism of PKR is critical for efficient viral replication. Consistent with a previous study, we observed decreased overall levels of protein synthesis, reduced viral protein expression, and diminished virus replication in the absence of both pTRS1 and pIRS1. In addition, both PKR and eIF2α were phosphorylated during infection when pTRS1 and pIRS1 were absent. We also found that expression of pTRS1 was both necessary and sufficient to prevent stress granule formation in response to eIF2α phosphorylation. Depletion of PKR prevented eIF2α phosphorylation, rescued HCMV replication and protein synthesis, and reversed the accumulation of stress granules in infected cells. Infection with an HCMV mutant lacking the pTRS1 PKR binding domain resulted in PKR activation, suggesting that pTRS1 inhibits PKR through a direct interaction. Together our results show that antagonism of PKR by HCMV pTRS1 and pIRS1 is critical for viral protein expression and efficient HCMV replication.

IMPORTANCE

To successfully replicate, viruses must counteract host defenses that limit viral protein synthesis. We have identified inhibition of the antiviral kinase PKR by the viral proteins TRS1 and IRS1 and shown that this is a critical step in HCMV replication. Our results suggest that inhibiting pTRS1 and pIRS1 function or restoring PKR activity during infection may be a successful strategy to limit HCMV disease.

Suppressive effects of sirtinol on human cytomegalovirus (hCMV) infection and hCMV-induced activation of molecular mechanisms of senescence and production of reactive oxygen species

Substantial evidence suggests that chronic human cytomegalovirus (hCMV) infection contributes significantly to T-cell immunosenescence and adverse health outcomes in older adults. As such, it is important to search for compounds with anti-hCMV properties. Studies have shown that resveratrol, a sirtuin activator, suppresses hCMV infection. Here we report suppressive effects of sirtinol, a sirtuin antagonist, on hCMV infection and its cellular and molecular consequences. Human diploid fibroblast WI-38 cells were infected by hCMV Towne strain in the absence or presence of sirtinol. hCMV replication was measured using qPCR. Senescent phenotype was determined by senescence-associated β galactosidase (SA-β-Gal) activity. Expression of hCMV immediate early (IE) and early (E) proteins and senescence-associated proteins (pRb and Rb, p16(INK4), and p53) and production of reactive oxygen species (ROS) were assessed using standard laboratory assays. The results demonstrated that sirtinol suppressed hCMV infection as well as hCMV-induced activation of molecular mechanisms of senescence and ROS production. While underlying molecular mechanisms remain to be elucidated, these findings indicate sirtinol as a novel and potent anti-hCMV agent with the potential to be developed as an effective treatment for chronic hCMV infection and its cellular and molecular consequences that are important to ageing and health of older adults.

Hydrogen Peroxide Induce Human Cytomegalovirus Replication through the Activation of p38-MAPK Signaling Pathway

Human cytomegalovirus (HCMV) is a major risk factor in transplantation and AIDS patients, which induces high morbidity and mortality. These patients infected with HCMV experience an imbalance of redox homeostasis that cause accumulation of reactive oxygen species (ROS) at the cellular level. H₂O₂, the most common reactive oxygen species, is the main byproduct of oxidative metabolism. However, the function of H₂O₂ on HCMV infection is not yet fully understood and the effect and mechanism of N-acetylcysteine (NAC) on H₂O₂-stimulated HCMV replication is unclear. We, therefore, examined the effect of NAC on H₂O₂-induced HCMV production in human foreskin fibroblast cells. In the present study, we found that H₂O₂ enhanced HCMV lytic replication through promoting major immediate early (MIE) promoter activity and immediate early (IE) gene transcription. Conversely, NAC inhibited H₂O₂-upregulated viral IE gene expression and viral replication. The suppressive effect of NAC on CMV in an acute CMV-infected mouse model also showed a relationship between antioxidants and viral lytic replication. Intriguingly, the enhancement of HCMV replication via supplementation with H₂O₂ was accompanied with the activation of the p38 mitogen-activated protein kinase pathway. Similar to NAC, the p38 inhibitor SB203580 inhibited H₂O₂-induced p38 phosphorylation and HCMV upregulation, while upregulation of inducible ROS was unaffected. These results directly relate HCMV replication to H₂O₂, suggesting that treatment with antioxidants may be an attractive preventive and therapeutic strategy for HCMV.

Kaposi's sarcoma-associated herpesvirus induces Nrf2 activation in latently infected endothelial cells through SQSTM1 phosphorylation and interaction with polyubiquitinated Keap1

Nuclear factor erythroid 2-related factor 2 (Nrf2), the cellular master regulator of the antioxidant response, dissociates from its inhibitor Keap1 when activated by stress signals and participates in the pathogenesis of viral infections and tumorigenesis. Early during de novo infection of endothelial cells, KSHV induces Nrf2 through an intricate mechanism involving reactive oxygen species (ROS) and prostaglandin E2 (PGE2). When we investigated the Nrf2 activity during latent KSHV infection, we observed increased nuclear serine-40-phosphorylated Nrf2 in human KS lesions compared to that in healthy tissues. Using KSHV long-term-infected endothelial cells (LTC) as a cellular model for KS, we demonstrated that KSHV infection induces Nrf2 constitutively by extending its half-life, increasing its phosphorylation by protein kinase Cζ (PKCζ) via the infection-induced cyclooxygenase-2 (COX-2)/PGE2 axis and inducing its nuclear localization. Nrf2 knockdown in LTC decreased expression of antioxidant genes and genes involved in KS pathogenesis such as the NAD(P)H quinone oxidase 1 (NQO1), gamma glutamylcysteine synthase heavy unit (γGCSH), the cysteine transporter (xCT), interleukin 6 (IL-6), and vascular endothelial growth factor A (VEGF-A) genes. Nrf2 activation was independent of oxidative stress but dependent on the autophagic protein sequestosome-1 (SQSTM1; p62). SQSTM1 levels were elevated in LTC, a consequence of protein accumulation due to decreased autophagy and Nrf2-mediated transcriptional activation. SQSTM1 was phosphorylated on serine-351 and -403, while Keap1 was polyubiquitinated with lysine-63-ubiquitin chains, modifications known to increase their mutual affinity and interaction, leading to Keap1 degradation and Nrf2 activation. The latent KSHV protein Fas-associated death domain-like interleukin-1β-converting enzyme-inhibitory protein (vFLIP) increased SQSTM1 expression and activated Nrf2. Collectively, these results demonstrate that KSHV induces SQSTM1 to constitutively activate Nrf2, which is involved in the regulation of genes participating in KSHV oncogenesis.

IMPORTANCE

The transcription factor Nrf2 is activated by stress signals, including viral infection, and responds by activating the transcription of cytoprotective genes. Recently, Nrf2 has been implicated in oncogenesis and was shown to be activated during de novo KSHV infection of endothelial cells through ROS-dependent pathways. The present study was undertaken to determine the mechanism of Nrf2 activation during prolonged latent infection of endothelial cells, using an endothelial cell line latently infected with KSHV. We show that Nrf2 activation was elevated in KSHV latently infected endothelial cells independently of oxidative stress but dependent on the autophagic protein sequestosome-1 (SQSTM1), which was involved in the degradation of the Nrf2 inhibitor Keap1. Furthermore, our results indicated that the KSHV latent protein vFLIP participates in Nrf2 activation. This study suggests that KSHV hijacks the host's autophagic protein SQSTM1 to induce Nrf2 activation, thereby manipulating the infected host gene regulation to promote KS pathogenesis.

Protective effect of curcumin against cytomegalovirus infection in Balb/c mice

Curcumin has been found to suppress the activity of human cytomegalovirus (HCMV) in vitro, whereas its protective effects against HCMV infection in vivo remain unclear. In this study, we aimed to investigate the protective effects of curcumin against HCMV infection in Balb/c mice. Mice were randomly divided into the control, model, model+ganciclovir (positive control), and model+high-dose, model+middle-dose, and model+low-dose curcumin groups. In the model groups, each mouse was given HCMV by tail injection intravenously. Positive control animals were given ganciclovir. Animals in the curcumin treatment groups were given different concentrations of curcumin. The anti-HCMV activities of ganciclovir and curcumin were assessed by serological examination and pathology. Ganciclovir and curcumin treatment reduced the HCMV IgM level and HCMV DNA load; decreased the serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatine kinase (CK), and lactate dehydrogenase (LDH) as well as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) generation in infected mice. These treatments also suppressed malondialdehyde (MDA) content and upregulated superoxide dismutase (SOD) and glutathione (GSH) levels. In addition, both treatments prevented pathological changes of the lung, kidney, liver, and heart tissues in infected mice. Our findings indicate that curcumin protected Balb/c mice against HCMV infection possibly by its anti-inflammatory and antioxidant effects.

Ultrafast diffusion of a fluorescent cholesterol analog in compartmentalized plasma membranes

Cholesterol distribution and dynamics in the plasma membrane (PM) are poorly understood. The recent development of Bodipy488-conjugated cholesterol molecule (Bdp-Chol) allowed us to study cholesterol behavior in the PM, using single fluorescent-molecule imaging. Surprisingly, in the intact PM, Bdp-Chol diffused at the fastest rate ever found for any molecules in the PM, with a median diffusion coefficient (D) of 3.4 µm²/second, which was ∼10 times greater than that of non-raft phospholipid molecules (0.33 µm²/second), despite Bdp-Chol's probable association with raft domains. Furthermore, Bdp-Chol exhibited no sign of entrapment in time scales longer than 0.5 milliseconds. In the blebbed PM, where actin filaments were largely depleted, Bdp-Chol and Cy3-conjugated dioleoylphosphatidylethanolamine (Cy3-DOPE) diffused at comparable Ds (medians = 5.8 and 6.2 µm²/second, respectively), indicating that the actin-based membrane skeleton reduces the D of Bdp-Chol only by a factor of ∼2 from that in the blebbed PM, whereas it reduces the D of Cy3-DOPE by a factor of ∼20. These results are consistent with the previously proposed model, in which the PM is compartmentalized by the actin-based membrane-skeleton fence and its associated transmembrane picket proteins for the macroscopic diffusion of all of the membrane molecules, and suggest that the probability of Bdp-Chol passing through the compartment boundaries, once it enters the boundary, is ∼10× greater than that of Cy3-DOPE. Since the compartment sizes are greater than those of the putative raft domains, we conclude that raft domains coexist with membrane-skeleton-induced compartments and are contained within them.

Are reactive oxygen species always detrimental to pathogens?

Reactive oxygen species (ROS) are deadly weapons used by phagocytes and other cell types, such as lung epithelial cells, against pathogens. ROS can kill pathogens directly by causing oxidative damage to biocompounds or indirectly by stimulating pathogen elimination by various nonoxidative mechanisms, including pattern recognition receptors signaling, autophagy, neutrophil extracellular trap formation, and T-lymphocyte responses. Thus, one should expect that the inhibition of ROS production promote infection. Increasing evidences support that in certain particular infections, antioxidants decrease and prooxidants increase pathogen burden. In this study, we review the classic infections that are controlled by ROS and the cases in which ROS appear as promoters of infection, challenging the paradigm. We discuss the possible mechanisms by which ROS could promote particular infections. These mechanisms are still not completely clear but include the metabolic effects of ROS on pathogen physiology, ROS-induced damage to the immune system, and ROS-induced activation of immune defense mechanisms that are subsequently hijacked by particular pathogens to act against more effective microbicidal mechanisms of the immune system. The effective use of antioxidants as therapeutic agents against certain infections is a realistic possibility that is beginning to be applied against viruses.

Upregulation of Nrf2 expression by human cytomegalovirus infection protects host cells from oxidative stress

NF-E2 related factor 2 (Nrf2) is a transcription factor that plays a key role(s) in cellular defence against oxidative stress. In this study, we showed that the expression of Nrf2 was upregulated in primary human foreskin fibroblasts (HFFs), following human cytomegalovirus (HCMV/HHV-5) infection. The expression of haem oxygenase-1, a downstream target of Nrf2, was also increased by HCMV infection, and this induction was suppressed in HFFs expressing a small hairpin RNA (shRNA) against Nrf2. The HCMV-mediated increase in Nrf2 expression was abolished when UV-irradiated virus was used or when the activity of casein kinase 2 was inhibited. Host cells infected by HCMV had higher survival rates following oxidative stress induced by buthionine sulfoximine compared with uninfected control cells, but this cell-protective effect was abolished by the use of Nrf2 shRNA. Our results suggest that HCMV-mediated activation of Nrf2 might be beneficial to the virus by increasing the host cell's ability to cope with oxidative stress resulting from viral infection and/or inflammation.

Neutrophil in viral infections, friend or foe?

Polymorphonuclear leukocytes or neutrophils are the first immune cells to the site of injury and microbial infection. Neutrophils are crucial players in controlling bacterial and fungal infections, and in particular secondary infections, by phagocytosis, degranulation and neutrophil extracellular traps (NETs). While neutrophils have been shown to play important roles in viral pathogenesis, there is a lack of detailed investigation. In this article, we will review recent progresses toward understanding the role of neutrophils in viral pathogenesis.

Human cytomegalovirus induces multiple means to combat reactive oxygen species

Reactive oxygen species (ROS) are generated as by-products of many cellular processes and can modulate cellular signaling pathways. However, high ROS levels are toxic; thus, intracellular ROS need to be tightly controlled. Therefore, cells use a group of antioxidant molecules and detoxifying enzymes that remove or detoxify reactive species. We found that the level of the antioxidant glutathione is greatly increased in human cytomegalovirus (HCMV)-infected cells due to activation of glutathione synthetic enzymes. In addition, our data suggest that virus-specific mechanisms are used to induce the expression of target antioxidant and detoxifying enzymes critical for the success of the infection. As a result of this virus-induced anti-ROS environment, key signaling kinases, such as the mammalian target of rapamycin (mTOR) kinase in mTOR complex 1 (mTORC1), are protected from inhibition by exogenous hydrogen peroxide (H(2)O(2)). In this regard, we found that phosphorylation of mTOR kinase at serine 2448 (suggested to be activating) was maintained during infection even under ROS stress conditions that inhibited it in uninfected cells. We also show that AMP-dependent kinase (AMPK)-mediated phosphorylation of serine 792 of raptor, the specificity subunit of mTORC1, increases in infected cells after H(2)O(2) treatment. This phosphorylation is normally inhibitory for mTORC1. However, in infected cells this did not result in inhibition of mTORC1 activity, suggesting that inhibitory effects of raptor phosphorylation are circumvented. Overall, our data suggest that HCMV utilizes virus-specific mechanisms to activate a variety of means to protect the cell and mTORC1 from the effects of ROS.

Human cytomegalovirus infection increases mitochondrial biogenesis

Fibroblasts infected by Human Cytomegalovirus (CMV) undergo a robust increase in mitochondrial biogenesis with a corresponding increase in mitochondrial activity that is partly dependent on the viral anti-apoptotic pUL37x1 protein (vMIA). The increased respiration activity is blocked by the mitochondrial translation inhibitor chloramphenicol, which additionally suppresses viral production. Intriguingly, chloramphenicol and pUL37x1 depletion have different effects on respiration capacity but similar effects on CMV production, suggesting that pUL37x1 promotes viral replication by efficient utilization of new mitochondria. These results argue for a role of pUL37x1 beyond controlling apoptosis.

Construction of green fluorescent protein-tagged recombinant iridovirus to assess viral replication

Green fluorescent protein-tagged recombinant virus has been successfully applied to observing the infective dynamics and evaluating viral replication. Here, we identified soft-shelled turtle iridovirus (STIV) ORF55 as an envelope protein (VP55), and developed a recombinant STIV expressing an enhanced green fluorescent protein (EGFP) fused to VP55 (EGFP-STIV). Recombinant EGFP-STIV shared similar single-step growth curves and ultrastructural morphology with wild type STIV (wt-STIV). The green fluorescence distribution during EGFP-STIV infection was consistent with the intracellular distribution of VP55 which was mostly co-localized with virus assembly sites. Furthermore, EGFP-STIV could be used to evaluate viral replication conveniently under drug treatment, and the result showed that STIV replication was significantly inhibited after the addition of antioxidant pyrrolidine dithiocarbamate (PDTC). Thus, the EGFP-tagged recombinant iridovirus will not only be useful for further investigations on the viral replicative dynamics, but also provide an alternative simple strategy to screen for antiviral substances.

Human cytomegalovirus is protected from inactivation by reversible binding to villous trophoblasts

Human cytomegalovirus (HCMV) is the leading cause of congenital disease in the developed world. Transmission of HCMV to the fetus can occur through the villous placenta. Previously, we have shown that although syncytiotrophoblast (ST) can be productively infected, it is more likely that HCMV reaches the fetus through breaks in the ST than through basal release of progeny virus from infected ST. Progeny virus released on the maternal side could interact back with the ST and accumulate. In pregnancy, the organ distribution of disease burden is dramatically shifted, with the placenta reported as a reservoir for some pathogens. Thus, we propose that the ST layer functions as a viral reservoir, where HCMV is harbored and ultimately protected from degradation. Using primary cytotrophoblasts differentiated into an ST culture in vitro and challenged with HCMV, we have defined reversible binding between the virus and trophoblasts that protects the virus from degradation. This is blocked by treatment with low pH and neutralizing intravenous immunoglobulin. This reversible binding likely is to heparan sulfate proteoglycans, because heparin treatment blocks it. Importantly, we show that bound and released virus maintained in culture for at least 48 h results from inoculum and not progeny virus. Thus, the placenta has the potential to accumulate a relatively high steady-state level of virus within the intervillous space resulting from localized binding and release at the ST. A better understanding of the molecular interactions between HCMV and ST will provide insights regarding interventions to prevent or minimize congenital transmission.

Differential effects on nitric oxide-mediated vasodilation in mesenteric and uterine arteries from cytomegalovirus-infected mice

Chronic cytomegalovirus (CMV) infections are implicated in vascular diseases. Recently, we showed that an active mouse CMV (mCMV) infection in nonpregnant mice increased endothelial-dependent vasodilation in isolated mesenteric and uterine arteries. In late pregnancy, while increased vasodilation was found in mesenteric arteries from infected mice, there was a dramatic decrease in uterine arteries. Understanding the mechanisms for these vascular changes during CMV infections is important for pregnancy outcomes and long-term consequences of this chronic infection. Increased nitric oxide (NO) is implicated in CMV-associated atherosclerosis, and CMV replication is dependent on prostaglandin H synthase (PGHS) activity. Alternatively, CMV infections decrease NO under inflammatory conditions. We therefore hypothesized that changes in the contribution by NO or PGHS-induced vasodilators would explain the increased or decreased endothelial-dependent vasodilation in arteries from nonpregnant and late pregnant mice, respectively. We found that the contribution by NO to methacholine-induced vasodilation was significantly increased in mesenteric, but not uterine, arteries isolated from nonpregnant and pregnant mCMV-infected mice. Prostaglandin inhibition did not affect endothelial-dependent vasodilation in any group. Vasodilation responses to sodium nitroprusside, an NO donor, were increased in mesenteric and uterine arteries isolated only from mCMV-infected nonpregnant mice. These results explain the increased vasodilation responses observed in mesenteric arteries from mCMV-infected mice; however, the decreased vasodilation in uterine arteries from pregnant mice could not be explained by these mechanisms. Thus CMV infection affects the contribution of NO differently in endothelial-dependent vasodilation in pregnant compared with nonpregnant mice and also in the mesenteric compared with the uterine vascular bed.

Impaired vascular function in mice with an active cytomegalovirus infection

Human cytomegalovirus (CMV) is implicated in vascular complications through endothelial dysfunction. However, the effect of in vivo infections on vascular function in isolated arteries has not been examined. In pregnancy, systemic and uterine vascular adaptations accommodate increased blood volume through several mechanisms, including decreased sensitivity to vasoconstrictors and increased production of endothelial-dependent vasodilators. We hypothesized that an active in vivo CMV infection would reduce vasodilation of isolated arteries to the endothelial-dependent vasodilator methacholine and increase vasoconstriction to the α1-adrenergic receptor agonist phenylephrine and that these CMV-induced changes would be accentuated in late pregnancy. A mouse CMV infection model was used to study vascular responses in isolated mesenteric and uterine arteries from nonpregnant and late pregnant mice. In the mouse, CMV is not transmitted to the fetus. Accordingly, there was no evidence of active infection in any fetus examined, even though an active infection was found in salivary glands, uterine and mesenteric arteries, and placentas. Contrary to our hypothesis, increased endothelial-dependent vasodilation was found in mesenteric arteries from infected compared with uninfected nonpregnant and pregnant mice These data implicate active CMV infections in hypotensive disorders. Similarly, increased vasodilation was found in uterine arteries from infected vs. uninfected nonpregnant mice. However, this was completely reversed in infected compared with uninfected late pregnant mice in which vasodilation in uterine arteries was significantly reduced. Uterine arteries from infected pregnant mice also showed increased vasoconstriction to phenylephrine. Maternal infection led to decreased placental weights but had no effect on fetal weights in late pregnancy. These novel data demonstrate abnormal systemic and uterine vascular responses during an active CMV infection in both nonpregnant and late pregnant mice. Importantly, despite reduced placental weights, fetal weights were maintained, suggesting effective intrauterine compensation in the mouse model.

APOE epsilon3 gene transfer attenuates brain damage after experimental stroke

Apolipoprotein E (apoE, protein; APOE, gene) is the major lipid-transport protein in the brain and plays an important role in modulating the outcome and regenerative processes after acute brain injury. The aim of the present study was to determine if gene transfer of the epsilon3 form of APOE improves outcome in a murine model of transient focal cerebral ischaemia. Mice received an intrastriatal injection of vehicle, a second-generation adenoviral vector containing the green fluorescent protein gene (Ad-GFP) or a vector containing the APOE epsilon3 gene (Ad-APOE) 3 days before 60 mins focal ischaemia. Green fluorescent protein expression was observed in cells throughout the striatum and subcortical white matter indicating successful gene transfer and expression. ApoE levels in the brain were significantly increased after Ad-APOE compared with Ad-GFP or vehicle treatment. Ad-APOE treatment reduced the volume of ischaemic damage by 50% compared with Ad-GFP or vehicle treatment (13+/-3 versus 29+/-4 versus 27+/-5 mm(3)). The extent of postischaemic apoE immunoreactivity was enhanced in Ad-APOE compared with Ad-GFP or vehicle treated mice. These results show the ability of APOE gene transfer to markedly improve outcome after cerebral ischaemia and suggest that modulating apoE levels may be a potential strategy in human stroke therapy.

Infection as a risk factor for stroke

Persisting disability requiring professional healthcare or help in daily life activities can be expected in a third to a half of all stroke survivors. It is mainly the elderly that are affected. For the increasingly aging population of Western societies, stroke represents an increasing social and economic burden. Besides the existing therapeutic options, additional treatment and prevention strategies are needed. Traditional risk factors do not explain all clinical and epidemiological features of stroke. Recently, the association between infectious and inflammatory processes and the occurrence of vascular disease has been established. This review summarizes the current evidence of infections as stroke risk factors and of potential anti-infective strategies as future methods of stroke prevention.

Stimulation of interferon-β gene expression by human cytomegalovirus via nuclear factor kappa B and phosphatidylinositol 3-kinase pathway

Infection of human foreskin fibroblast (HFF) cells with human cytomegalovirus (HCMV) induces the secretion of soluble factors including interferon (IFN)-beta that stimulates human leukocyte antigen (HLA) class I expression. In this study, the mechanism of IFN-beta induction by HCMV was investigated. In HCMV-infected HFF cells, IFN-beta secretion increased at 6h post infection (h.p.i.). Reverse transcription polymerase chain reaction (RT-PCR) analysis using ultra violet (UV)-inactivated HCMV indicated that viral gene expression is not necessary for the stimulation of IFN-beta. Stimulation of IFN-beta by HCMV infection was not blocked by cycloheximide, an inhibitor of protein synthesis, further suggesting that the expression of HCMV genes is not required for the stimulation of IFN-beta gene transcription. IFN-beta may be produced from virus-infected cells as an inflammatory response and nuclear factor kappa B (NF-kappaB) plays a central role in inflammatory response. HCMV failed to induce the IFN-beta expression, when the virus-infected cells were treated with pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-kappaB, or LY294002 and wortmannin, inhibitors of phosphatidylinositol 3-kinase (PI3-K). The result suggests that PI3-K and/or NF-kappaB may be related with the induction pathway of IFN-beta by HCMV.

Renal ischemia/reperfusion injury activates the enhancer domain of the human cytomegalovirus major immediate early promoter

Reactivation of latent human cytomegalovirus is of significant concern in immunocompromised transplant patients and is likely to occur through transcriptional activation of immediate early (ie) gene expression through mechanisms that are not well understood. TNF-mediated activation of NF-kappaB has been proposed to be one pathway leading to transcriptional activation of CMV ie gene expression. Using transgenic mice carrying a lacZ reporter gene under the control of the HCMV major ie promoter/enhancer (MIEP-lacZ mice) and MIEP-lacZ mice deficient in TNF receptor 1 and TNF receptor 2 (MIEP-lac Z TNFR DKO mice), we demonstrate that renal ischemia/reperfusion (I/R) injury activates the HCMV enhancer independently of TNF. Induction of MIEP-lacZ expression was preceded by TNFR-independent formation of reactive oxygen species (ROS), weak and transient activation of NF-kappaB and strong and sustained activation of AP-1. Our studies show that, in addition to TNF-mediated signaling, TNF-independent signaling induced by I/R injury can contribute to the activation of the HCMV enhancer. This likely occurs through ROS-mediated activation of AP-1. Targeting MAP kinase signaling pathways as well as NF-kappaB may be of therapeutic value in patients with CMV infection.

Up-regulation of the interferon-inducible IFI16 gene by oxidative stress triggers p53 transcriptional activity in endothelial cells

Reactive oxygen species (ROS), including hydrogen peroxide (H2O2), induces injury of endothelium in a variety of pathophysiological conditions, such as inflammation, aging, and cancer. In our study, we characterized the signaling pathway linking oxidative stress induced by sublethal concentrations of H2O2 to p53 in primary human endothelial cells through the interferon (IFN)-inducible gene IFI16. Induction of IFI16 by H2O2 was concentration- and time-dependent (maximum at 50 microM, 6 h after treatment) and down-regulated by pretreatment with N-acetyl-L-cysteine, which acts as an antioxidant. This pathway is a general response to ROS and not specific to H2O2 treatment, as two other ROS-generating compounds, i.e., S-nitroso-N-acetylpenicillamine and tert-butyl hydroperoxide, were equally capable to induce IFI16. Moreover, IFI16 up-regulation is a result of protein accumulation, as expression of corresponding mRNA, assessed by real-time polymerase chain reaction, was not affected. To investigate the mechanism of IFI16 accumulation, cells were incubated for 6 h in the presence of H2O2 or IFN-beta, and then cycloheximide was added to inhibit further protein synthesis. The half-life of IFI16 protein was found to be significantly increased in H2O2-treated cells compared with IFN-beta-treated cells (t1/2 = 120 min vs. > 30 min in H2O2- vs. IFN-beta-treated cells, respectively). An increase of IFI16 was accompanied by interaction with p53 phosphorylated at its N terminus, as shown by immunoprecipitation experiments. Moreover, binding to IFI16 resulted in its transcriptional activation as shown by an increase in the activity of a reporter gene driven by p53-responsive sequences derived from the p21(WAF1) promoter, along with an increase in the p21 mRNA and protein levels. Altogether, these results demonstrate a novel role of IFI16 in the signal transduction pathway that leads to p53 activation by oxidative stress in endothelial cells.

3,4',5-Trihydroxy-trans-stilbene (resveratrol) inhibits human cytomegalovirus replication and virus-induced cellular signaling

Resveratrol is a polyphenolic natural product that is present in red wine and peanuts and has inhibitory activity against inflammation, heart disease, and cancer. Here we describe its inhibition of human cytomegalovirus replication (IC50 = 1-2 microM). At least 50-fold higher concentrations of compound were required to produce cytotoxicity against growing or stationary human embryonic lung fibroblasts. Mechanism of action studies determined that resveratrol blocked virus-induced activation of the epidermal growth factor receptor (EGFR) and phosphatidylinositol-3-kinase signal transduction as well as NF-kappaB and Sp1 transcription factor activation shortly following infection. Resveratrol prevented the appearance of immediate-early, early, and late viral proteins. Human cytomegalovirus DNA replication was reduced to undetectable levels by treatment with resveratrol, as were the second (late) phases of virus-induced phosphatidylinositol-3-kinase signaling and transcription factor activation. Resveratrol lost substantial antiviral activity when its addition was delayed until 4 h postinfection. Compound reversibility and preincubation studies were inconsistent with a virucidal mechanism of action. These data indicated that this compound likely operated during attachment and entry. We hypothesize that the primary molecular target for resveratrol may be blockage of epidermal growth factor receptor activation and its downstream effectors.

Cellular stress and signal transduction responses to human cytomegalovirus infection

Human cytomegalovirus (HCMV) receptor-ligand interactions and viral entry excite cellular responses such as receptor tyrosine kinase and mitogen-activated protein kinase signaling, cytoskeletal rearrangement, and the induction of transcription factors, prostaglandins, and cytokines. Bi-phasic stimulation of these pathways, excepting interferon, facilitates productive viral infection and likely contributes to viral pathogenesis.

Replication-incompetent virions of Japanese encephalitis virus trigger neuronal cell death by oxidative stress in a culture system

It has been shown that replication of the Japanese encephalitis virus (JEV) can trigger infected cells to undergo apoptosis. In the present study, it is further demonstrated that replication-incompetent virions of JEV, obtained by short-wavelength ultraviolet (UV) irradiation, could also induce host-cell death. It was found that UV-inactivated JEV (UV-JEV) caused cell death in neuronal cells such as mouse neuroblastoma N18 and human neuronal NT-2 cells, but not in non-neuronal baby hamster kidney BHK-21 fibroblast or human cervical HeLa cells. Only actively growing, but not growth-arrested, cells were susceptible to the cytotoxic effects of UV-JEV. Killing of UV-JEV-infected N18 cells could be antagonized by co-infection with live, infectious JEV, suggesting that virions of UV-JEV might engage an as-yet-unidentified receptor-mediated death-signalling pathway. Characteristically, mitochondrial alterations were evident in UV-JEV-infected N18 cells, as revealed by electron microscopy and a loss of membrane potential. N18 cells infected by UV-JEV induced generation of reactive oxygen species (ROS) as well as the activation of nuclear factor kappa B (NF-kappaB), and the addition of anti-oxidants or specific NF-kappaB inhibitors to the media greatly reduced the cytotoxicity of UV-JEV. Together, the results presented here suggest that replication-incompetent UV-JEV damages actively growing neuronal cells through a ROS-mediated pathway.

Enhanced cytomegalovirus infection in atherosclerotic human blood vessels

Human cytomegalovirus (CMV) is a possible co-factor in atherogenesis and vascular occlusion, but its ability to actively infect medium and large blood vessels is unclear. A vascular explant model was adapted to investigate CMV infection in human coronary artery, internal mammary artery (IMA), and saphenous vein (SV). Vascular explants were inoculated with CMV Towne or low-passage clinical isolate and examined in situ for CMV cytopathic effect and immediate-early and early antigens, as indicators of active infection. At 5 to 7 days after inoculation, we found that CMV Towne actively infected eight of eight different atherosclerotic blood vessel explants (coronary artery, n = 4; SV and IMA grafts, n = 4), whereas it only infected 2 of 14 nonatherosclerotic blood vessel explants (SV, n = 10; IMA, n = 4) (P = 0.001). The CMV clinical isolate actively infected none of six sets of nonatherosclerotic SV explants at 5 to 7 days after inoculation. The active CMV infections involved adventitial and, less frequently, intimal cells. A small subset of infected cells in atherosclerotic tissue expresses the endothelial cell marker CD31. Smooth muscle cells residing in both atherosclerotic and nonatherosclerotic blood vessels were free of active CMV infections even after all vascular tissue layers were exposed to the virus. In contrast, active CMV Towne infection was evident at 2 days after inoculation in smooth muscle cells and endothelial cells previously isolated from the SV tissues. We conclude that active CMV infection is enhanced in atherosclerotic blood vessels compared to atherosclerosis-free vascular equivalents, and this viral activity is restricted to subpopulations of intimal and adventitial cells.

Mechanisms governing maintenance of Cdk1/cyclin B1 kinase activity in cells infected with human cytomegalovirus

Previous work has demonstrated dysregulation of key cell cycle components in human cytomegalovirus (HCMV)-infected human fibroblasts, resulting in cell cycle arrest (F. M. Jault, J.-M. Jault, F. Ruchti, E. A. Fortunato, C. L. Clark, J. Corbeil, D. D. Richman, and D. H. Spector, J. Virol. 69:6697-6704, 1995). The activation of the mitotic kinase Cdk1/cyclin B, which was detected as early as 8 h postinfection (p.i.) and maintained throughout the time course, was particularly interesting. To understand the mechanisms underlying the induction of this kinase activity, we have examined the pathways that regulate the activation of Cdk1/cyclin B1 complexes. The accumulation of the cyclin B1 subunit in HCMV-infected cells is the result of increased synthesis and reduced degradation of the protein. In addition, the catalytic subunit, Cdk1, accumulates in its active form in virus-infected cells. The decreased level of the Tyr15-phosphorylated form of Cdk1 in virus-infected fibroblasts is due in part to the down-regulation of the expression and activity of the Cdk1 inhibitory kinases Myt1 and Wee1. Increased degradation of Wee1 via the proteasome also accounts for its absence at 24 h p.i. At late times, we observed accumulation of the Cdc25 phosphatases that remove the inhibitory phosphates from Cdk1. Interestingly, biochemical fractionation studies revealed that the active form of Cdk1, a fraction of total cyclin B1, and the Cdc25 phosphatases reside predominantly in the cytoplasm of infected cells. Collectively, these data suggest that the maintenance of Cdk1/cyclin B1 activity observed in HCMV-infected cells can be explained by three mechanisms: the accumulation of cyclin B1, the inactivation of negative regulatory pathways for Cdk1, and the accumulation of positive factors that promote Cdk1 activity.

Effects of hydrogen peroxide on bovine leukemia virus expression

Several activators of bovine leukemia virus (BLV) expression, including lipopolysaccharides, phorbol esters and calcium ionophores, are known to generate reactive oxygen species (ROS). Therefore the influence of H2O2 on BLV expression in two BLV producing cell lines was investigated. The effect of H2O2 on BLV expression is apparently dose-dependent. Incubation of FLK/BLV cells with low concentrations of H2O2 (2.5 to 10 microM) induced a marked enhancement of BLV p24 synthesis and an activation of the long terminal repeat (LTR). Higher concentrations resulted in a decrease of proliferation, induction of apoptosis and in a decrease of BLV synthesis. Furthermore, in both cell lines H2O2 treatment led to the activation of NF-kappaB. Pretreatment of cells with antioxidants abrogated the H2O2-induced BLV expression. Taken together, our findings suggest that oxidative stress stimulates BLV expression via activation of NF-kappaB, raising the possibility that biological sources of H2O2, such as stimulated phagocytes, may influence BLV expression.