Superoxide generation by monocytes following infection with human cytomegalovirus

ASFV pD345L protein negatively regulates NF-κB signalling by inhibiting IKK kinase activity

The NF-κB pathway is an essential signalling cascade in the defence against viral infections, including African swine fever virus (ASFV) infection. ASFV encodes more than 151 proteins via its own transcription machinery and possesses a great capacity to evade or subvert antiviral innate immune responses. Although some of these viral proteins have been reported, many remain unknown. Here, we show that pD345L, an ASFV-encoded lambda-like exonuclease, acts as an inhibitor of cGAS/STING-mediated NF-κB signalling by blocking the IkappaB kinase (IKKα/β) activity. Specifically, we showed that overexpression of pD345L suppresses cGAS/STING-induced IFNβ and NF-κB activation, resulting in decreased transcription of IFNβ and several proinflammatory cytokines, including IL-1α, IL-6, IL-8, and TNFα. In addition, we showed that pD345L acts at or downstream of IKK and upstream of p65. Importantly, we found that pD345L associates with the KD and HLH domains of IKKα and the LZ domain of IKKβ and thus interrupts their kinase activity towards the downstream substrate IκBα. Finally, we showed that pD345L-mediated inhibition of NF-κB signalling was independent of its exonuclease activity. Considering these results collectively, we concluded that pD345L blocks IKKα/β kinase activity via protein–protein interactions and thus disrupts cGAS/STING-mediated NF-κB signalling.

Viruses in colorectal cancer

Increasing evidence suggests that microorganisms might represent at least highly interesting cofactors in colorectal cancer (CRC) oncogenesis and progression. Still, associated mechanisms, specifically in colonocytes and their microenvironmental interactions, are still poorly understood. Although, currently, at least seven viruses are being recognized as human carcinogens, only three of these – Epstein–Barr virus (EBV), human papillomavirus (HPV) and John Cunningham virus (JCV) – have been described, with varying levels of evidence, in CRC. In addition, cytomegalovirus (CMV) has been associated with CRC in some publications, albeit not being a fully acknowledged oncovirus. Moreover, recent microbiome studies set increasing grounds for new hypotheses on bacteriophages as interesting additional modulators in CRC carcinogenesis and progression. The present Review summarizes how particular groups of viruses, including bacteriophages, affect cells and the cellular and microbial microenvironment, thereby putatively contributing to foster CRC. This could be achieved, for example, by promoting several processes – such as DNA damage, chromosomal instability, or molecular aspects of cell proliferation, CRC progression and metastasis – not necessarily by direct infection of epithelial cells only, but also by interaction with the microenvironment of infected cells. In this context, there are striking common features of EBV, CMV, HPV and JCV that are able to promote oncogenesis, in terms of establishing latent infections and affecting p53‐/pRb‐driven, epithelial–mesenchymal transition (EMT)‐/EGFR‐associated and especially Wnt/β‐catenin‐driven pathways. We speculate that, at least in part, such viral impacts on particular pathways might be reflected in lasting (e.g. mutational or further genomic) fingerprints of viruses in cells. Also, the complex interplay between several species within the intestinal microbiome, involving a direct or indirect impact on colorectal and microenvironmental cells but also between, for example, phages and bacterial and viral pathogens, and further novel species certainly might, in part, explain ongoing difficulties to establish unequivocal monocausal links between specific viral infections and CRC.

Decrease in 3-nitrotyrosine in the amniotic fluid of women with cytomegalovirus infection

The aim of this study was to assess oxidative stress in pregnant women infected with cytomegalovirus on the basis of 3-nitrotyrosine levels in amniotic fluid (AF). The 3-nitrotyrosine (3-NT) level in AF was measured using the competitive ELISA method. The study groups were as follows: group I consisted of women with IgM and/or IgA; group II were women with only IgG anti-CMV antibodies and group III were seronegative women, used as the control group. Age, gestational age and socioeconomic status were also assessed. The average level of 3-nitrotyrosine in group II and the control group was similar: 53.14 nM 3-NT and 49.78 nM 3-NT, respectively. However, in group I, the lowest level 3-NT in AF was observed - 39.17 nM 3-NT and statistical analysis showed significant differences in levels of 3-NT between group I and the control group (p < 0.01). We conclude that significantly lower levels of 3-nitrotyrosine in pregnant women with CMV infection may indicate an increase in the antioxidant defence mechanisms in these patients.

Repair of base damage and genome maintenance in the nucleo-cytoplasmic large DNA viruses

Among the DNA viruses, the so-called nucleo-cytoplasmic large DNA viruses (NCLDV) constitute a monophyletic group that currently consists of seven families of viruses infecting a very broad variety of eukaryotes, from unicellular marine protists to humans. Many recent papers have analyzed the sequence and structure of NCLDV genomes and their phylogeny, providing detailed analysis about their genomic structure and evolutionary history and proposing their inclusion in a new viral order named Megavirales that, according to some authors, should be considered as a fourth domain of life, aside from Bacteria, Archaea and Eukarya. The maintenance of genetic information protected from environmental attacks and mutations is essential not only for the survival of cellular organisms but also viruses. In cellular organisms, damaged DNA bases are removed in two major repair pathways: base excision repair (BER) and nucleotide incision repair (NIR) that constitute the major pathways responsible for repairing most endogenous base lesions and abnormal bases in the genome by precise repair procedures. Like cells, many NCLDV encode proteins that might constitute viral DNA repair pathways that would remove damages through BER/NIR pathways. However, the molecular mechanisms and, specially, the biological roles of those viral repair pathways have not been deeply addressed in the literature so far. In this paper, we review viral-encoded BER proteins and the genetic and biochemical data available about them. We propose and discuss probable viral-encoded DNA repair mechanisms and pathways, as compared with the functional and molecular features of known homologs proteins.

Involvement of the reparative DNA polymerase Pol X of African swine fever virus in the maintenance of viral genome stability in vivo

The function of the African swine fever virus (ASFV) reparative DNA polymerase, Pol X, was investigated in the context of virus infection. Pol X is a late structural protein that localizes at cytoplasmic viral factories during DNA replication. Using an ASFV deletion mutant lacking the Pol X gene, we have shown that Pol X is not required for virus growth in Vero cells or swine macrophages under one-step growth conditions. However, at a low multiplicity of infection, when multiple rounds of replication occur, the growth of the mutant virus is impaired in swine macrophages but not in Vero cells, suggesting that Pol X is needed to repair the accumulated DNA damage. The replication of the mutant virus in Vero cells presents sensitivity to oxidative damage, and mutational analysis of viral DNA shows that deletion of Pol X results in an increase in the mutation frequency in macrophages. Therefore, our data reveal a biological role for ASFV Pol X in the context of the infected cell in the preservation of viral genetic information.

Consensus on the role of human cytomegalovirus in glioblastoma

The human cytomegalovirus (HCMV) and glioma symposium was convened on April 17, 2011 in Washington, DC, and was attended by oncologists and virologists involved in studying the relationship between HCMV and gliomas. The purpose of the meeting was to reach a consensus on the role of HCMV in the pathology of gliomas and to clarify directions for future research. First, the group summarized data that describe how HCMV biology overlaps with the key pathways of cancer. Then, on the basis of published data and ongoing research, a consensus was reached that there is sufficient evidence to conclude that HCMV sequences and viral gene expression exist in most, if not all, malignant gliomas, that HCMV could modulate the malignant phenotype in glioblastomas by interacting with key signaling pathways; and that HCMV could serve as a novel target for a variety of therapeutic strategies. In summary, existing evidence supports an oncomodulatory role for HCMV in malignant gliomas, but future studies need to focus on determining the role of HCMV as a glioma-initiating event.

NAD(P)H oxidase and eNOS play differential roles in cytomegalovirus infection-induced microvascular dysfunction

Primary cytomegalovirus (CMV) infection promotes oxidative stress and reduces nitric oxide (NO) bioavailability in endothelial cells. These events are among the earliest vascular responses to cardiovascular risk factors. We assessed the roles of NAD(P)H oxidase and NO bioavailability in microvascular responses to persistent CMV infection alone or with hypercholesterolemia. Wild-type (WT) or gp91(phox) (NAD(P)H oxidase subunit) knockout mice received mock inoculum or 3×10(4) PFU murine CMV (mCMV) ip 5 weeks before placement on a normal or high-cholesterol diet (HC) for 4 weeks before assessment of arteriolar function and venular blood cell recruitment using intravital microscopy. Some WT groups received sepiapterin (a precursor of the nitric oxide synthase cofactor tetrahydrobiopterin) or apocynin (NAD(P)H oxidase inhibitor/antioxidant). Endothelium-dependent vasodilation was impaired in mCMV vs mock WT, regardless of diet. This was not affected by sepiapterin, and pharmacological inhibition of nitric oxide synthase reduced dilation similarly in mock and mCMV mice. Apocynin or deficiency of total, but not blood cell or vascular wall only (tested using bone marrow chimeras), gp91(phox) protected against arteriolar dysfunction. Blood cell recruitment was induced by mCMV-HC. Sepiapterin, but not NAD(P)H oxidase deficiency/apocynin, reduced leukocyte accumulation, whereas platelet adhesion was reduced by sepiapterin, apocynin, or total, platelet-specific, or vascular wall gp91(phox) deficiency. These data implicate activation of both hematopoietic and vessel wall NAD(P)H oxidase in mCMV-induced arteriolar dysfunction and platelet and vascular NAD(P)H oxidase in the thrombogenic phenotype induced by mCMV-HC. In contrast, findings with sepiapterin suggest that eNOS dysfunction, perhaps uncoupling, mediates venular, but not arteriolar, responses to mCMV-HC, thus indicating that NAD(P)H oxidase and eNOS differentially regulate microvascular responses to mCMV.

P-selectin mediates the microvascular dysfunction associated with persistent cytomegalovirus infection in normocholesterolemic and hypercholesterolemic mice

OBJECTIVE

  Cytomegalovirus has been implicated in cardiovascular disease, possibly through the induction of inflammatory processes. P-selectin and L-selectin are adhesion molecules that mediate early microvascular responses to inflammatory stimuli. This study examined the role of these selectins in the microvascular dysfunction that occurs during persistent CMV infection.

METHODS

  C57Bl/6, P- or L-selectin-deficient mice were mock-inoculated or infected with murine CMV, and five weeks later placed on normal diet or high cholesterol diet for six weeks. P-selectin expression was measured or intravital microscopy was performed to determine arteriolar vasodilation and venular blood cell recruitment.

RESULTS

  P-selectin expression was significantly increased in the heart, lung, and spleen of mCMV-ND, but not mCMV-HC C57Bl/6. mCMV-ND and mCMV-HC exhibited impaired arteriolar function, which was reversed by treatment with an anti-P-selectin antibody, but not L-selectin deficiency. mCMV-HC also showed elevated leukocyte and platelet recruitment. P-selectin inhibition abrogated, whereas L-selectin deficiency partially reduced these responses.

CONCLUSIONS

  We provide the first evidence for P-selectin upregulation by persistent mCMV infection and implicate this adhesion molecule in the associated arteriolar dysfunction. P-selectin, and to a lesser extent L-selectin, mediates the leukocyte and platelet recruitment induced by CMV infection combined with hypercholesterolemia.

Is HCMV a tumor promoter?

Human cytomegalovirus (HCMV) is a beta-herpesvirus that causes persistent infection in humans and can cause severe disease in fetuses and immunocompromised individuals. Although HCMV is not currently causally implicated in human cancer, emerging evidence suggests that HCMV infection and expression may be specifically associated with human malignancies including malignant glioma, colon, and prostate cancer. In addition, multiple investigators have demonstrated that HCMV can dysregulate signaling pathways involved in initiation and promotion of malignancy, including tumor suppressor, mitogenic signaling, inflammatory, immune regulation, angiogenesis and invasion, and epigenetic mechanisms. This review highlights some of the recent evidence that HCMV might play a role in modulating the tumor microenvironment as well as in the initiation and promotion of tumor cells themselves.

African swine fever virus AP endonuclease is a redox-sensitive enzyme that repairs alkylating and oxidative damage to DNA

African swine fever virus (ASFV) encodes an AP endonuclease (pE296R) which is essential for virus growth in swine macrophages. We show here that the DNA repair functions of pE296R (AP endonucleolytic, 3′ → 5′ exonuclease, 3′-diesterase and nucleotide incision repair (NIR) activities) and DNA binding are inhibited by reducing agents. Protein pE296R contains one intramolecular disulfide bond, whose disruption by reducing agents might perturb the interaction of the viral AP endonuclease with the DNA substrate. The characterization of the 3′ → 5′ exonuclease and 3′-repair diesterase activities of pE296R indicates that it has strong preference for mispaired and oxidative base lesions at the 3′-termini of single-strand breaks. Finally, the viral protein protects against DNA damaging agents in both prokaryotic and eukaryotic cells, emphasizing its importance in vivo. The biochemical and genetic properties of ASFV AP endonuclease are consistent with the repair of DNA damage generated by the genotoxic intracellular environment of the host macrophage.

Broad distribution of the JC virus receptor contrasts with a marked cellular restriction of virus replication

To investigate the early events of JC virus (JCV) infection, including attachment, penetration, transport to the nuclei, and replication of the virus, we analyzed the susceptibility of 15 different cell lines to infection using a semiquantitative polymerase chain reaction (PCR) assay, in situ hybridization, laser scanning confocal microscopy, and a viral replication assay. The cell lines examined were human permissive and nonpermissive cells as well as cells of monkey and mouse origin. JCV entry into the nuclei of the all cell lines was observed within 10 min after inoculation, demonstrating that the virus receptor is widely distributed among mammalian cells. Inhibition of viral entry by an anti-JCV VP1 antibody and sialidase treatment to remove sialic acid residues, which are considered a candidate for the JCV receptor, suggested that VP1 may interact with the cellular surface sialic acid. In addition, chlorpromazine, a clathrin-dependent pathway inhibitor, significantly suppressed entry of JCV into nuclei. In spite of the broad spectrum of cells susceptible to JCV entry, replication of the virus occurred exclusively in human neuroblastoma cell lines. These results suggest that whereas JCV can enter a wide variety of cell types and localize to the nuclei, cell-specific intranuclear mechanisms are required for virus replication.