Viral Factor Research Articles

A novel antisense RNA ASPACT confers multi-level suppression of PACT and associated signalling

ABSTRACTThe innate immune system is the frontline host protection against pathogens. Effective antiviral immunity is elicited upon recognition of viral RNAs by the host pattern recognition receptors. One of the major viral RNA sensors is retinoic acid inducible gene-1, which triggers the production of interferons (IFNs). In turn, this protective response requires another viral sensor and immunity factor interferon-inducible protein kinase RNA activator (PACT/PRKRA). Here, we report the identification and characterization of a novel antisense PACT gene that expresses a non-coding RNA in a convergent and interferon-inducible manner. Publicly available gene structure and expression data revealed that this gene, that we termed ASPACT, overlaps with the 3′ -end of the PACT locus and is highly expressed during viral infection. Our results confirm the IFN-β-inducibility of ASPACT, which is dependent on STAT-1/2. We further discovered that downregulation of ASPACT impacts both the expression and localization of the PACT transcript. At the transcription level, ChIP and ChIRP assays demonstrated that the ASPACT non-coding RNA occupies distinct chromatin regions of PACT gene and is important for promoter recruitment of the epigenetic silencer HDAC1. In parallel, ASPACT was also found to mediate nuclear retention of the PACT mRNA via direct RNA–RNA interaction, as revealed by RNA antisense purification assay. In summary, our results support the model that the non-coding RNA ASPACT acts as a negative regulator of PACT at multiple levels, and reveal a novel regulator of the viral counteractive response.

Cylindrical Inclusion Protein of Wheat Yellow Mosaic Virus Is Involved in Differential Infection of Wheat Cultivars.

Wheat yellow mosaic virus (WYMV) belongs to the genus Bymovirus in the family Potyviridae and has a bipartite genome (RNA1 and RNA2). WYMV in Japan is classified into three pathotypes (I to III) based on its pathogenicity to wheat cultivars. Among these three, pathotypes I and II are discriminated by their pathogenicity to the wheat cultivar Fukuho; pathotype I infects Fukuho but pathotype II does not. In the present study, the genomic regions that are involved in such pathogenicity were examined using infectious viral cDNA clones of pathotypes I and II. Reassortant experiments between viral RNA1 and RNA2 revealed the presence of a viral factor related to pathogenicity in RNA1. A chimeric pathotype II virus harboring a cylindrical inclusion (CI) cistron from pathotype I facilitated systemic infection of Fukuho, indicating that CI protein is involved in pathogenicity. Furthermore, analysis of chimeric and site-directed mutants revealed that three amino acids at the N-terminal region of CI protein were involved in pathogenicity to Fukuho. On the other hand, at the single-cell level, pathotype II replicated in protoplasts of Fukuho similar to that of pathotype I virus. These data suggest that differential pathogenicity between pathotypes I and II was considered to depend on the ability of cell-to-cell or long-distance viral movement, in which CI protein is involved. To the best of our knowledge, this is the first report to show the involvement of the bymoviral CI protein in pathogenicity.

Stimulating DDX3 expression by serotonin 5-HT receptor 7 through phosphorylation of p53 via the AC-PKA-ERK signaling pathway.

DDX3 is a host viral factor that can inhibit the hepatitis B virus-induced innate immune responses. In this study, the 20 bioactive compounds have screened the effects on DDX3 and we found that 5-HT upregulated DDX3 promoter activity via the 5-HT7 receptor on liver hepatocellular cells (HepG2 cells) by using a luciferase assay, reverse transcription-polymerase chain reaction analysis, and Western blot analysis. Furthermore, we are trying to elucidate the pathways involved in the stimulating effect of 5-HT on DDX3 expression to induce innate immune responses against hepatitis B virus infection. A knockdown of the 5-HT7 receptor by transfection si-5-HT7 receptors or si-control into HepG2 cells treated by 5-HT (or 5-HT plus agonist) confirmed the role of the 5-HT7 receptor in DDX3 expression. The IFN-β-Luc expression and level of hepatitis B virus surface Antigen (HBsAg) showed that DDX3 mediated by the 5-HT7 agonist (AS-19) increased IFN-β expression and inhibited HBV replication. Luciferase assays showed the involvement of 5-HT7 receptors in DDX3 expression via cAMP/AC/PKA pathways by using protein kinase A (PKA) and adenylyl cyclase inhibitor (MDL 12330A). AS-19 mediated DDX3 promoter activated PKA extracellular signal-regulated kinase ERK signaling the p53 phosphorylation (-1080/-1070) resulted in upregulation of DDX3 promoter transactivation via the 5-HT7 receptors agonist. Overall, 5-HT7 was found to be a new potential target to inhibit hepatitis B infection by activating AC/PKA/ERK pathways by phosphorylating p53 via the 5-HT7 agonist response by mediating DDX3 expression.

Structure and Function of the Influenza A Virus Non-Structural Protein 1.

The influenza A virus is a highly infectious respiratory pathogen that sickens many people with respiratory disease annually. To prevent outbreaks of this viral infection, an understanding of the characteristics of virus-host interaction and development of an anti-viral agent is urgently needed. The influenza A virus can infect mammalian species including humans, pigs, horses and seals. Furthermore, this virus can switch hosts and form a novel lineage. This so-called zoonotic infection provides an opportunity for virus adaptation to the new host and leads to pandemics. Most influenza A viruses express proteins that antagonize the antiviral defense of the host cell. The non-structural protein 1 (NS1) of the influenza A virus is the most important viral regulatory factor controlling cellular processes to modulate host cell gene expression and double-stranded RNA (dsRNA)-mediated antiviral response. This review focuses on the influenza A virus NS1 protein and outlines current issues including the life cycle of the influenza A virus, structural characterization of the influenza A virus NS1, interaction between NS1 and host immune response factor, and design of inhibitors resistant to the influenza A virus.

Structural Determinants of the APOBEC3G N-Terminal Domain for HIV-1 RNA Association.

APOBEC3G (A3G) is a cellular protein that inhibits HIV-1 infection through virion incorporation. The interaction of the A3G N-terminal domain (NTD) with RNA is essential for A3G incorporation in the HIV-1 virion. The interaction between A3G-NTD and RNA is not completely understood. The A3G-NTD is also recognized by HIV-1 Viral infectivity factor (Vif) and A3G-Vif binding leads to A3G degradation. Therefore, the A3G-Vif interaction is a target for the development of antiviral therapies that block HIV-1 replication. However, targeting the A3G-Vif interactions could disrupt the A3G-RNA interactions that are required for A3G's antiviral activity. To better understand A3G-RNA binding, we generated in silico docking models to simulate the RNA-binding propensity of A3G-NTD. We simulated the A3G-NTD residues with high RNA-binding propensity, experimentally validated our prediction by testing A3G-NTD mutations, and identified structural determinants of A3G-RNA binding. In addition, we found a novel amino acid residue, I26 responsible for RNA interaction. The new structural insights provided here will facilitate the design of pharmaceuticals that inhibit A3G-Vif interactions without negatively impacting A3G-RNA interactions.

Intrinsic conformational dynamics of the HIV-1 genomic RNA 5′UTR

The highly conserved 5' untranslated region (5'UTR) of the HIV-1 RNA genome is central to the regulation of virus replication. NMR and biochemical experiments support a model in which the 5'UTR can transition between at least two conformational states. In one state the genome remains a monomer, as the palindromic dimerization initiation site (DIS) is sequestered via base pairing to upstream sequences. In the second state, the DIS is exposed, and the genome is competent for kissing loop dimerization and packaging into assembling virions where an extended dimer is formed. According to this model the conformation of the 5'UTR determines the fate of the genome. In this work, the dynamics of this proposed conformational switch and the factors that regulate it were probed using multiple single-molecule and in-gel ensemble FRET assays. Our results show that the HIV-1 5'UTR intrinsically samples conformations that are stabilized by both viral and host factor binding. Annealing of tRNALys3, the primer for initiation of reverse transcription, can promote the kissing dimer but not the extended dimer. In contrast, HIV-1 nucleocapsid (NC) promotes formation of the extended dimer in both the absence and presence of tRNALys3 Our data are consistent with an ordered series of events that involves primer annealing, genome dimerization, and virion assembly.

Vaccinia virus E5 is a dominant inhibitor of the cytosolic DNA sensor cGAS

Abstract The cytosolic DNA sensor cGAS plays an important role in detecting viral nucleic acid, which leads to type I IFN production. We have previously shown that infection with conventional dendritic cells with modified vaccinia virus Ankara (MVA), a highly attenuated vaccinia strain (VACV), induces IFN production via a cGAS/STING-dependent mechanism. However, MVA or VACV infection triggers cGAS degradation and its mechanism is still unknown. VACV is a cytoplasmic DNA virus, which encodes more than 200 genes. In this study, we screened 70 vaccinia viral early genes for inhibition of cGAS/STING pathway using a dual luciferase system. We found that vaccinia E5 is a dominant inhibitor of cGAS and is the key protein mediating cGAS degradation. MVAΔE5R induces much higher levels of type I IFN than MVA in multiple cell types, including bone marrow derived dendritic cells (BMDC), bone marrow-derived macrophages (BMDM), and skin primary fibroblasts. MVAΔE5R-mediated type I IFN production is dependent on cGAS. Furthermore, MVAΔE5R gains replication capability in cGAS−/− skin fibroblasts. As a vaccine vector, skin scarification or intradermal vaccination with MVAΔE5R-OVA leads to much higher OVA-specific CD8+ T cell responses than MVA-OVA in vivo. Intratumoral injection of MVAΔE5R leads to stronger anti-tumor immune responses and better survival compared with MVA. Finally, in an intranasal infection model, VACVΔE5R is at least 100-fold attenuated compared with WT VACV. Taken together, our results provide strong evidence that E5 is a key viral virulence factor targeting the cytosolic DNA sensor cGAS and thereby inhibits type I IFN production.

HTLV-1 HBZ Protein Resides Exclusively in the Cytoplasm of Infected Cells in Asymptomatic Carriers and HAM/TSP Patients.

Human T cell lymphotropic virus type 1 (HTLV-1) is the causative agent of adult T cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) in a subset of infected subjects. Two viral proteins, Tax-1 and HTLV-1 basic leucine zipper factor (HBZ), play important roles in the pathogenesis of both diseases. We recently demonstrated that HBZ, previously considered a nuclear protein, is exclusively localized in the cytoplasm of peripheral blood mononuclear cells (PBMCs) of HAM/TSP patients. Here, the analysis of a larger panel of HAM/TSP cases confirmed that HBZ is a cytoplasmic protein, while Tax-1 preferentially localized in the cytoplasm with fewer speckle-like dots in the nucleus. More importantly, here we report for the first time that HBZ, when expressed in asymptomatic carriers (AC), is also confined in the cytoplasm. Similarly, Tax-1 was preferentially expressed in the cytoplasm in a significant proportion of AC. Interestingly, in both HAM/TSP and AC patients, the expression of HBZ and Tax-1 was rarely found in the same cell. We observed only few cases coexpressing the two oncoprotein in a very limited number of cells. In representative AC and HAM/TSP patients, cells expressing cytoplasmic HBZ were almost exclusively found in the CD4+ T cell compartment and very rarely in CD8+ T cells. Interestingly, at least in the cases analyzed, the expression of thymocite-expressed molecule involved in selection (THEMIS) is dispensable for the cytoplasmic localization of HBZ in both AC and HAM/TSP. The study of an HTLV-1-immortalized cell line established from an HAM/TSP patient confirmed HBZ as a resident cytoplasmic protein not shuttling between the cytoplasm and nucleus. These results extend our previous observation on the dichotomy of HBZ localization between HAM/TSP and ATL, pointing to the exclusive either cytoplasmic or nuclear localization in the two diseased states, respectively. Moreover, they show a rather selective expression in distinct cells of either HBZ or Tax-1. The unprecedented observation that HBZ is expressed only in the cytoplasm in AC strongly suggests a progressive modification of HBZ localization during the disease states associated to HTLV-1 infection. Future studies will clarify whether the distinct HBZ intracellular localization is a marker or a causative event of disease evolution.

The Antiresection Activity of the X Protein Encoded by Hepatitis Virus B

Chronic infection of hepatitis B virus (HBV) is associated with an increased incidence of hepatocellular carcinoma (HCC). HBV encodes an oncoprotein, hepatitis B x protein (HBx), that is crucial for viral replication and interferes with multiple cellular activities including gene expression, histone modifications, and genomic stability. To date, it remains unclear how disruption of these activities contributes to hepatocarcinogenesis. Here, we report that HBV exhibits antiresection activity by disrupting DNA end resection, thus impairing the initial steps of homologous recombination (HR). This antiresection activity occurs in primary human hepatocytes undergoing a natural viral infection–replication cycle as well as in cells with integrated HBV genomes. Among the seven HBV‐encoded proteins, we identified HBx as the sole viral factor that inhibits resection. By disrupting an evolutionarily conserved Cullin4A–damage‐specific DNA binding protein 1–RING type of E3 ligase, CRL4WDR70, through its H‐box, we show that HBx inhibits H2B monoubiquitylation at lysine 120 at double‐strand breaks, thus reducing the efficiency of long‐range resection. We further show that directly impairing H2B monoubiquitylation elicited tumorigenesis upon engraftment of deficient cells in athymic mice, confirming that the impairment of CRL4WDR70 function by HBx is sufficient to promote carcinogenesis. Finally, we demonstrate that lack of H2B monoubiquitylation is manifest in human HBV‐associated HCC when compared with HBV‐free HCC, implying corresponding defects of epigenetic regulation and end resection. Conclusion: The antiresection activity of HBx induces an HR defect and genomic instability and contributes to tumorigenesis of host hepatocytes.

BZLF1 interacts with chromatin remodelers promoting escape from latent infections with EBV.

A hallmark of EBV infections is its latent phase, when all viral lytic genes are repressed. Repression results from a high nucleosome occupancy and epigenetic silencing by cellular factors such as the Polycomb repressive complex 2 (PRC2) and DNA methyltransferases that, respectively, introduce repressive histone marks and DNA methylation. The viral transcription factor BZLF1 acts as a molecular switch to induce transition from the latent to the lytic or productive phase of EBV's life cycle. It is unknown how BZLF1 can bind to the epigenetically silenced viral DNA and whether it directly reactivates the viral genome through chromatin remodeling. We addressed these fundamental questions and found that BZLF1 binds to nucleosomal DNA motifs both in vivo and in vitro. BZLF1 co-precipitates with cellular chromatin remodeler ATPases, and the knock-down of one of them, INO80, impaired lytic reactivation and virus synthesis. In Assay for Transposase-Accessible Chromatin-seq experiments, non-accessible chromatin opens up locally when BZLF1 binds to its cognate sequence motifs in viral DNA. We conclude that BZLF1 reactivates the EBV genome by directly binding to silenced chromatin and recruiting cellular chromatin-remodeling enzymes, which implement a permissive state for lytic viral transcription. BZLF1 shares this mode of action with a limited number of cellular pioneer factors, which are instrumental in transcriptional activation, differentiation, and reprogramming in all eukaryotic cells.

Conformational Dynamics of the HIV-Vif Protein Complex

Human immunodeficiency virus-1 viral infectivity factor (Vif) is an intrinsically disordered protein responsible for the ubiquitination of the APOBEC3 (A3) antiviral proteins. Vif folds when it binds Cullin-RING E3 ligase 5 and the transcription cofactor CBF-β. A five-protein complex containing the substrate receptor (Vif, CBF-β, Elongin-B, Elongin-C (VCBC)) and Cullin5 (CUL5) has a published crystal structure, but dynamics of this VCBC-CUL5 complex have not been characterized. Here, we use molecular dynamics (MD) simulations and NMR to characterize the dynamics of the VCBC complex with and without CUL5 and an A3 protein bound. Our simulations show that the VCBC complex undergoes global dynamics involving twisting and clamshell opening of the complex, whereas VCBC-CUL5 maintains a more static conformation, similar to the crystal structure. This observation from MD is supported by methyl-transverse relaxation-optimized spectroscopy NMR data, which indicates that the VCBC complex without CUL5 is dynamic on the μs-ms timescale. Our NMR data also show that the VCBC complex is more conformationally restricted when bound to the antiviral APOBEC3F (one of the A3 proteins), consistent with our MD simulations. Vif contains a flexible linker region located at the hinge of the VCBC complex, which changes conformation in conjunction with the global dynamics of the complex. Like other substrate receptors, VCBC can exist alone or in complex with CUL5 and other proteins in cells. Accordingly, the VCBC complex could be a good target for therapeutics that would inhibit full assembly of the ubiquitination complex by stabilizing an alternate VCBC conformation.

Broad spectrum anti-flavivirus pyridobenzothiazolones leading to less infective virions

We report the design, synthesis, and biological evaluation of a class of 1H-pyrido[2,1-b][1,3]benzothiazol-1-ones originated from compound 1, previously identified as anti-flavivirus agent. Some of the new compounds showed activity in low μM range with reasonable selectivity against Dengue 2, Yellow fever (Bolivia strain), and West Nile viruses. One of the most interesting molecules, compound 16, showed broad antiviral activity against additional flaviviruses such as Dengue 1, 3 and 4, Zika, Japanese encephalitis, several strains of Yellow fever, and tick-borne encephalitis viruses. Compound 16 did not exert any effect on alphaviruses and phleboviruses and its activity was maintained in YFV infected cells from different species. The activity of 16 appears specific for flavivirus with respect to other virus families, suggesting, but not proving, that it might be targeting a viral factor. We demonstrated that the antiviral effect of 16 is not related to reduced viral RNA synthesis or virion release. On the contrary, viral particles grown in the presence of 16 showed reduced infectivity, being unable to perform a second round of infection. The chemical class herein presented thus emerges as suitable to provide pan-flavivirus inhibitors.

Insights into ligand binding by a viral tumor necrosis factor (TNF) decoy receptor yield a selective soluble human type 2 TNF receptor

Etanercept is a soluble form of the tumor necrosis factor receptor 2 (TNFR2) that inhibits pathological tumor necrosis factor (TNF) responses in rheumatoid arthritis and other inflammatory diseases. However, besides TNF, etanercept also blocks lymphotoxin-α (LTα), which has no clear therapeutic value and might aggravate some of the adverse effects associated with etanercept. Poxviruses encode soluble TNFR2 homologs, termed viral TNF decoy receptors (vTNFRs), that display unique specificity properties. For instance, cytokine response modifier D (CrmD) inhibits mouse and human TNF and mouse LTα, but it is inactive against human LTα. Here, we analyzed the molecular basis of these immunomodulatory activities in the ectromelia virus-encoded CrmD. We found that the overall molecular mechanism to bind TNF and LTα from mouse and human origin is fairly conserved in CrmD and dominated by a groove under its 50s loop. However, other ligand-specific binding determinants optimize CrmD for the inhibition of mouse ligands, especially mouse TNF. Moreover, we show that the inability of CrmD to inhibit human LTα is caused by a Glu-Phe-Glu motif in its 90s loop. Importantly, transfer of this motif to etanercept diminished its anti-LTα activity in >60-fold while weakening its TNF-inhibitory capacity in 3-fold. This new etanercept variant could potentially be used in the clinic as a safer alternative to conventional etanercept. This work is the most detailed study of the vTNFR-ligand interactions to date and illustrates that a better knowledge of vTNFRs can provide valuable information to improve current anti-TNF therapies.

Genome replication affects transcription factor binding mediating the cascade of herpes simplex virus transcription

In herpes simplex virus type 1 (HSV-1) infection, the coupling of genome replication and transcription regulation has been known for many years; however, the underlying mechanism has not been elucidated. We performed a comprehensive transcriptomic assessment and factor-binding analysis for Pol II, TBP, TAF1, and Sp1 to assess the effect genome replication has on viral transcription initiation and elongation. The onset of genome replication resulted in the binding of TBP, TAF1, and Pol II to previously silent late promoters. The viral transcription factor, ICP4, was continuously needed in addition to DNA replication for activation of late gene transcription initiation. Furthermore, late promoters contain a motif that closely matches the consensus initiator element (Inr), which robustly bound TAF1 postreplication. Continued DNA replication resulted in reduced binding of Sp1, TBP, and Pol II to early promoters. Therefore, the initiation of early gene transcription is attenuated following DNA replication. Herein, we propose a model for how viral DNA replication results in the differential utilization of cellular factors that function in transcription initiation, leading to the delineation of kinetic class in HSV-productive infection.

Integral evaluation of hematological indicators in community-acquired pneumonia in children of different ages

Community-acquired pneumonia is a serious problem in pediatric practice. It would be interesting to use an integral evaluation of hematological indicators in diagnosis verification, which can help to determine not only patient's condition severity, but also to predict the risk of infectious process complications as well as to assess the effectiveness of therapy. The purpose of our study was to investigate the variability and clinical significance of blood count and basic leukocyte indices in case of community-acquired pneumonia in children of different ages. Materials and methods. Blood counts of 238 children between the ages of 1 and 18 years with community-acquired pneumonia were retrospectively analyzed. The main clinical signs and blood count parameters were evaluated using standard laboratory techniques, as well as the main leukocyte indices were calculated: neutrophil to lymphocyte ratio (NLR), absolute lymphocyte count (ALC), leukocyte index of intoxication by Ya. Ya. Kalf-Kalif formula (LII). Results. The differences in both the disease clinical manifestations and hematological changes in children of different age groups were detected. Thus, in young children, the disease debut was characterized by a significant severity of the condition and a viral trigger factor prevailed. In adolescent, the trigger factor was bacterial and debut of the disease was characterized by a severe intoxication. The revealed peculiarities were confirmed by hematological criteria and calculation of the corresponding leukocyte indices. Conclusions. The calculation of hematological indices is an informative method assessing the condition in children of different ages with community-acquired pneumonia that should be further considered when choosing the type and amount of therapy.

Single-Stranded DNA Binding and Crosslinking Activities of the Viral Restriction Factor Apobec3G Characterized by Force Spectroscopy

APOBEC3G (A3G) is a human deaminase able to inhibit human immunodeficiency virus type 1 (HIV-1). A3G reduces HIV-1 infectivity via two independent mechanisms, including enzymatic hyper-mutation of the viral genome, and non-enzymatic stalling of the reverse transcription. However, the physical mechanism of these A3G activities remain unclear. Here we use force spectroscopy to show that the ssDNA-bound A3G exists in the rapid (1-10 s) conformational equilibrium between its “globular” state with its NTD and CTD bound to each other, with free energy ∼2.4 kBT, and its extended “dumbbell” state with its domains unbound, but connected by ∼0.6 nm flexible 7 aa linker. Low free energy and fast kinetics of this conformational transition in ssDNA-bound A3G suggest that both of these states are functionally important. We also measure much slower rates of monomeric A3G binding to and unbinding from ssDNA, which are of 107 M−1.s−1 and 0.014 s−1, respectively. However, while all of dimerization deficient FW A3G mutant dissociates with that rate, the a majority of the WT A3G oligomerizes upon binding within 10 s, and does not dissociate for over 10 min. We show that the A3G monomers can crosslink two DNA strands, leading to major construct shortening. For the WT A3G oligomerized on ssDNA the strand crosslinking process takes ∼300 s, while it only takes ∼10 s for the FW A3G mutant. In both cases crosslinking is rate-limited by one of the A3G domain unbinding one ssDNA strand and re-binding another strand. Taken together with other published data, our results suggest that the ssDNA-crosslinking A3G monomers are calalyticalycatalytically active, while the oligomerized A3Gs are catalytically inactive, and present a reverse transcription road block.

The deletion of the AcMNPV ac124 gene resulted in a decrease in chitinase transcription

The Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ac124 gene has been previously characterized as a viral pathogenicity factor. In this study, an ac124-knockout virus (vAc124KO) was generated to examine the role of the ac124 gene in the context of the AcMNPV genome during infection. Our results showed that the absence of ac124 does not affect the production of budded virus (BV) and occlusion bodies (OBs) in infected Sf9 cells. Western blotting analysis showed that the deletion of ac124 does not affect the temporal expression and the relative levels of GP64, VP39, P6.9, and polyhedrin. qRT-PCR analysis showed that the transcription level of chitinase but not the adjacent cathepsin in vAc124KO infected cells was significantly lower than that of the vAcWT infected cells from 24 to 96 h p.i. Luciferase assays showed that the overexpression of Ac124 could significantly improve the ability of chitinase promoter to initiate reporter genes. Based on the above data, we hypothesize that Ac124 binds to the promoter of chitinase to regulate the expression of chitinase gene.

Oncogenic KSHV-encoded interferon regulatory factor upregulates HMGB2 and CMPK1 expression to promote cell invasion by disrupting a complex lncRNA-OIP5-AS1/miR-218-5p network.

Kaposi’s sarcoma (KS), a highly disseminated tumor of hyperproliferative spindle endothelial cells, is the most common AIDS-associated malignancy caused by infection of Kaposi’s sarcoma-associated herpesvirus (KSHV). KSHV-encoded viral interferon regulatory factor 1 (vIRF1) is a viral oncogene but its role in KSHV-induced tumor invasiveness and motility remains unknown. Here, we report that vIRF1 promotes endothelial cell migration, invasion and proliferation by down-regulating miR-218-5p to relieve its suppression of downstream targets high mobility group box 2 (HMGB2) and cytidine/uridine monophosphate kinase 1 (CMPK1). Mechanistically, vIRF1 inhibits p53 function to increase the expression of DNA methyltransferase 1 (DNMT1) and DNA methylation of the promoter of pre-miR-218-1, a precursor of miR-218-5p, and increases the expression of a long non-coding RNA OIP5 antisense RNA 1 (lnc-OIP5-AS1), which acts as a competing endogenous RNA (ceRNA) of miR-218-5p to inhibit its function and reduce its stability. Moreover, lnc-OIP5-AS1 increases DNA methylation of the pre-miR-218-1 promoter. Finally, deletion of vIRF1 from the KSHV genome reduces the level of lnc-OIP5-AS1, increases the level of miR-218-5p, and inhibits KSHV-induced invasion. Together, these results define a novel complex lnc-OIP5-AS1/miR-218-5p network hijacked by vIRF1 to promote invasiveness and motility of KSHV-induced tumors.

A viral expression factor behaves as a prion

Prions are proteins that can fold into multiple conformations some of which are self-propagating. Such prion-forming proteins have been found in animal, plant, fungal and bacterial species, but have not yet been identified in viruses. Here we report that LEF-10, a baculovirus-encoded protein, behaves as a prion. Full-length LEF-10 or its candidate prion-forming domain (cPrD) can functionally replace the PrD of Sup35, a widely studied prion-forming protein from yeast, displaying a [PSI+]-like phenotype. Furthermore, we observe that high multiplicity of infection can induce the conversion of LEF-10 into an aggregated state in virus-infected cells, resulting in the inhibition of viral late gene expression. Our findings extend the knowledge of current prion proteins from cellular organisms to non-cellular life forms and provide evidence to support the hypothesis that prion-forming proteins are a widespread phenomenon in nature.

Cross-talking between baculoviruses and host insects towards a successful infection.

Baculoviridae is a family of large DNA viruses that infect insects. They have been extensively used as safe and efficient biological agents for the control of insect pests. As a result of coevolution with their hosts, baculoviruses developed unique life cycles characterized by the production of two distinctive virion phenotypes, occlusion-derived virus and budded virus, which are responsible for mediating primary infection in insect midgut epithelia and spreading systemic infection within infected insects, respectively. In this article, advances associated with virus-host interactions during the baculovirus life cycle are reviewed. We mainly focus on how baculoviruses exploit versatile strategies to overcome diverse host barriers and establish successful infections. For example, in the midgut, baculoviruses encode enzymes to degrade peritrophic membranes and use a series of per os infectivity factors to initiate primary infection. A viral fibroblast growth factor is expressed to attract tracheoblasts that spread the virus for systemic infection. Baculoviruses use different strategies to suppress host defence systems, including apoptosis, melanization and RNA interference. Additionally, baculoviruses can manipulate host physiology and induce 'tree-top disease' for optimal virus replication and dispersal. These advances in our understanding of baculoviruses will greatly inform the development of more effective baculoviral pesticides. This article is part of the theme issue 'Biotic signalling sheds light on smart pest management'.