Interferon regulatory factor 8 regulates caspase-1 expression to facilitate Epstein-Barr virus reactivation in response to B cell receptor stimulation and chemical induction

Targeted eradication of EBV-positive cancer cells by CRISPR/dCas9-mediated EBV reactivation in combination with ganciclovir

Epstein-Barr virus (EBV) is a ubiquitous human tumor virus that establishes lifelong, persistent infections in B cells. The presence of EBV in cancer cells presents an opportunity to target these cells by reactivating the virus from latency. In this study, we developed a novel approach for EBV reactivation termed clustered regularly interspaced short palindromic repeats (CRISPR)/dCas9-mediated EBV reactivation (CMER) strategy. Using modified CRISPR-associated protein 9 (dCas9) fused with VP64, we designed 10 single guide RNAs (sgRNAs) to target and activate the EBV immediate-early gene promoter. In Akata Burkitt lymphoma cells, 9 out of 10 CMER sgRNAs effectively reactivated EBV. Among these, CMER sgRNA-5 triggered robust reactivation across various cell types, including lymphoma, gastric cancer, and nasopharyngeal carcinoma cells. Importantly, the combination of CMER and ganciclovir selectively eliminated EBV-positive cells, regardless of their cell origin. These findings indicate that targeted virus reactivation by CMER, combined with nucleoside analog therapy, holds promise for EBV-associated cancer treatment.

IMPORTANCE

This study explores a novel strategy called clustered regularly interspaced short palindromic repeats (CRISPR)/dCas9-mediated Epstein-Barr virus (EBV) reactivation (CMER) to reactivate the Epstein-Barr virus in cancer cells. EBV is associated with various cancers, and reactivating EBV from latency offers a potential therapeutic strategy. We utilized an enzymatically inactive CRISPR-associated protein 9 (dCas9) fused with VP64 and designed 10 single guide RNAs to target the EBV immediate-early gene promoter. Nine of these sgRNAs effectively reactivated EBV in Burkitt lymphoma cells, with CMER sgRNA-5 demonstrating strong reactivation across different cancer cell types. Combining CMER with ganciclovir selectively eliminated EBV-positive cells, showing promise for EBV-associated cancer treatment.

SUMOylation of the m6A reader YTHDF2 by PIAS1 promotes viral RNA decay to restrict EBV replication

YTH N6-methyladenosine RNA-binding protein F2 (YTHDF2) is a member of the YTH protein family that binds to N6-methyladenosine (m6A)-modified RNA, regulating RNA stability and restricting viral replication, including Epstein-Barr virus (EBV). PIAS1 is an E3 small ubiquitin-like modifier (SUMO) ligase known as an EBV restriction factor, but its role in YTHDF2 SUMOylation remains unclear. In this study, we investigated the functional regulation of YTHDF2 by PIAS1. We found that PIAS1 promotes the SUMOylation of YTHDF2 at three specific lysine residues (K281, K571, and K572). Importantly, PIAS1 synergizes with wild-type YTHDF2, but not a SUMOylation-deficient mutant, to limit EBV lytic replication. Mechanistically, YTHDF2 lacking SUMOylation exhibits reduced binding to EBV transcripts, leading to increased viral mRNA stability. Furthermore, PIAS1 mediates SUMOylation of YTHDF2's paralogs, YTHDF1 and YTHDF3, to restrict EBV replication. These results collectively uncover a unique mechanism whereby YTHDF family proteins control EBV replication through PIAS1-mediated SUMOylation, highlighting the significance of SUMOylation in regulating viral mRNA stability and EBV replication.IMPORTANCEm6A RNA modification pathway plays important roles in diverse cellular processes and viral life cycle. Here, we investigated the relationship between PIAS1 and the m6A reader protein YTHDF2, which is involved in regulating RNA stability by binding to m6A-modified RNA. We found that both the N-terminal and C-terminal regions of YTHDF2 interact with PIAS1. We showed that PIAS1 promotes the SUMOylation of YTHDF2 at three specific lysine residues. We also demonstrated that PIAS1 enhances the anti-EBV activity of YTHDF2. We further revealed that PIAS1 mediates the SUMOylation of other YTHDF family members, namely, YTHDF1 and YTHDF3, to limit EBV replication. These findings together illuminate an important regulatory mechanism of YTHDF proteins in controlling viral RNA decay and EBV replication through PIAS1-mediated SUMOylation.

Membrane-bound CD95 ligand modulates CD19-mediated B cell receptor signaling and EBV activation

Post-transplant lymphoproliferative disorders (PTLDs) are associated with Epstein-Barr virus (EBV) infection in transplant recipients. Most of lymphoblastoid cell lines (LCLs) derived from EBV-immortalized B cells or PTLDs are sensitive to CD95-mediated apoptosis and cytotoxic T cell (CTL) killing. CD95 ligand (CD95L) exists as a transmembrane ligand (mCD95L) or a soluble form (sCD95L). Using recombinant mCD95L and sCD95L, we observed that sCD95L does not affect LCLs. While high expression of mCD95L in CTLs promotes apoptosis of LCLs, low expression induces clathrin-dependent CD19 internalization, caspase-dependent CD19 cleavage, and proteasomal/lysosomal-dependent CD19 degradation. The CD95L/CD95-mediated CD19 degradation impairs B cell receptor (BCR) signaling and inhibits BCR-mediated EBV activation. Interestingly, although inhibition of the caspase activity restores CD19 expression and CD19-mediated BCR activation, it fails to rescue BCR-mediated EBV lytic gene expression. EBV-specific CTLs engineered to overexpress mCD95L exhibit a stronger killing activity against LCLs. This study highlights that engineering EBV-specific CTLs to express a higher level of mCD95L could represent an attractive therapeutic approach to improve T cell immunotherapy for PTLDs.

Shikonin, an inhibitor of inflammasomes, inhibits Epstein-Barr virus reactivation

Epstein-Barr virus (EBV) is a highly prevalent human herpesvirus that persists for life in more than 95% of the adult population. EBV usually establishes an asymptomatic life-long infection, but it is also associated with malignancies affecting B lymphocytes and epithelial cells mainly. The virus alternates between a latent phase and a lytic phase, both of which contribute to the initiation of the tumor process. So far, there is only a limited number of antiviral molecules against the lytic phase, most of them targeting viral replication. Recent studies provided evidence that EBV uses components of the NLRP3 inflammasome to enter the productive phase of its cycle following activation in response to various stimuli. In the present work, we demonstrate that shikonin, a natural molecule with low toxicity which is known to inhibit inflammasome, can efficiently repress EBV reactivation. Similar results were obtained with apigenin and OLT 1177, two other NLRP3 inflammasome inhibitors. It is shown herein that shikonin repressed the transcription of reactivation-induced NLRP3 thereby inhibiting inflammasome activation and EBV lytic phase induction.

SUMOylation of the m6A reader YTHDF2 by PIAS1 promotes viral RNA decay to restrict EBV replication

YTHDF2 is a member of the YTH protein family that binds to N6-methyladenosine (m6A)-modified RNA, regulating RNA stability and restricting viral replication, including Epstein-Barr virus (EBV). PIAS1 is an E3 SUMO ligase known as an EBV restriction factor, but its role in YTHDF2 SUMOylation remains unclear. In this study, we investigated the functional regulation of YTHDF2 by PIAS1. We found that PIAS1 promotes the SUMOylation of YTHDF2 at three specific lysine residues (K281, K571, and K572). Importantly, PIAS1 enhances the antiviral activity of YTHDF2, and SUMOylation-deficient YTHDF2 shows reduced anti-EBV activity. Mechanistically, YTHDF2 lacking SUMOylation exhibits reduced binding to EBV transcripts, leading to increased viral mRNA stability. Furthermore, PIAS1 mediates SUMOylation of YTHDF2's paralogs, YTHDF1 and YTHDF3. These results collectively uncover a unique mechanism whereby YTHDF2 controls EBV replication through PIAS1-mediated SUMOylation, highlighting the significance of SUMOylation in regulating viral mRNA stability and EBV replication.

Hypomethylated interferon regulatory factor 8 recruits activating protein-2α to attenuate porcine epidemic diarrhea virus infection in porcine jejunum

Interferon regulatory factor 8 (IRF8) is a key regulator of innate immune receptor signaling that resists pathogen invasion by regulating cell growth and differentiation. Porcine epidemic diarrhea virus (PEDV) targets the intestine and damages the mucosal barrier. However, whether IRF8 regulates PEDV replication remains unclear. We revealed that PEDV infection activated IRF8 expression. Moreover, IRF8 deletion drastically promoted PEDV replication and invasion, increasing the virus copies and titers. Hypomethylation enrichment of activating protein (AP)-2α was significantly negatively correlated with high IRF8 expression, and AP-2α directly targeted the IRF8 promoter to regulate PEDV replication. Furthermore, IRF8 overexpression decreased the cellular reactive oxygen species levels and mitochondrial membrane potential and increased the antioxidant enzyme activities to alleviate PEDV-induced oxidative damage. IRF8 overexpression suppressed apoptotic gene expression, thereby inhibiting apoptosis in response to PEDV stimulation. Taken together, this study demonstrates that AP-2α is involved in PEDV-induced epigenetic modification of IRF8 to reduce cell apoptosis and oxidative stress and facilitate host resistance to PEDV in the intestinal epithelium.

Piperlongumine conjugates induce targeted protein degradation

Proteolysis targeting chimeras (PROTACs) are bifunctional molecules that degrade target proteins through recruiting E3 ligases. However, their application is limited in part because few E3 ligases can be recruited by known E3 ligase ligands. In this study, we identified piperlongumine (PL), a natural product, as a covalent E3 ligase recruiter, which induces CDK9 degradation when it is conjugated with SNS-032, a CDK9 inhibitor. The lead conjugate 955 can potently degrade CDK9 in a ubiquitin-proteasome-dependent manner and is much more potent than SNS-032 against various tumor cells in vitro. Mechanistically, we identified KEAP1 as the E3 ligase recruited by 955 to degrade CDK9 through a TurboID-based proteomics study, which was further confirmed by KEAP1 knockout and the nanoBRET ternary complex formation assay. In addition, PL-ceritinib conjugate can degrade EML4-ALK fusion oncoprotein, suggesting that PL may have a broader application as a covalent E3 ligase ligand in targeted protein degradation.

Screening Host Antiviral Proteins under the Enhanced Immune Responses Induced by a Variant Strain of Porcine Epidemic Diarrhea Virus

While discussing the ideal candidates of viral restriction factor, the interferon (IFN) and interferon-stimulated genes (ISGs) could be considered potential targets. However, numerous viruses have evolved multiple strategies to modulate the host innate immune signaling for optimal infection, including the porcine epidemic diarrhea virus (PEDV), a coronavirus spreading widely around the world with high morbidity and mortality in piglets. The immunosuppression mediated by PEDV infection creates an impediment for studying the host-virus interactions and screening the antiviral ISGs. Here, the PEDV variant strain 85-7^C40 was screened using the continuous passaging, which showed significantly attenuated viral replication compared with its parent on MARC-145 cells. The comparative transcriptome analysis (accession nos. SRR13154018 to SRR13154026) indicated that 85-7^C40 infection led to enhanced immune response on MARC-145 cells, particularly to the IFN antiviral signaling, which mediated the stronger activation of numerous ISGs. Numerous ISGs activated by 85-7^C40 showed antiviral effects against the wild-type strain infection, particularly the IFI44 (an ISG upregulated specifically by the 85-7^C40 infection) and OASL (upregulated higher in 85-7^C40 than 85-7-infected cells), exhibited powerful antiviral activity. IFI44 promoted the production of RIG-I, while the OASL interacted directly with RIG-I, and then they both activated the phosphorylation of STAT1, indicating that they restricted PEDV replication by positively regulating the type I IFN response. Our results provided insight into the ISGs with antiviral activity against PEDV infection and also expanded our understanding of the innate immune response to PEDV infection, which may promote the development of novel therapeutics.

IMPORTANCE Host innate immune responses, particularly interferon (IFN) antiviral signaling, can activate diverse downstream ISGs to exert antiviral effects. However, porcine epidemic diarrhea virus (PEDV) infection has evolved multiple strategies to escape from this immune clearance. The immunosuppression mediated by PEDV infection creates an impediment for studying the host-virus interactions. We screened a PEDV variant strain, 85-7^C40, which induced enhanced immune responses on MARC-145 cells and thus mediated the stronger activation of numerous ISGs. The laboratory-generated variant might induce inconsistent immune responses with a natural wild-type strain during infection, while numerous ISGs activated by 85-7^C40 showed antiviral effects against the wild-type strain infection, particularly the IFI44 and OASL, restricted PEDV replication by positively regulating the type I IFN response. These findings were suggestive of the immune-enhanced variant being capable of using as an ideal viral model for screening the efficient antiviral proteins and elucidating the underlying mechanisms between PEDV and host innate immune responses.

Host Cells Actively Resist Porcine Reproductive and Respiratory Syndrome Virus Infection via the IRF8-MicroRNA-10a-SRP14 Regulatory Pathway

MicroRNAs (miRNAs) play an important role in the virus-host interaction. Our previous work has indicated that the expression level of miR-10a increased in porcine alveolar macrophages (PAMs) during porcine reproductive and respiratory syndrome virus (PRRSV) infection and further inhibited viral replication through downregulates the expression of host molecule signal-recognition particle 14 (SRP14) protein. However, the molecular mechanism of miR-10a increased after PRRSV infection remains unknown. In the present study, transcription factor interferon regulatory factor 8 (IRF8) was identified as a negative regulator of miR-10a. PRRSV infection decreases the expression level of IRF8 in PAMs, leading to upregulating miR-10a expression to play an anti-PRRSV role. Meanwhile, this work first proved that IRF8 promoted PRRSV replication in an miR-10a-dependent manner. Further, we explained that SRP14, the target gene of miR-10a, promotes the synthesis of the PRRSV genome by interacting with the viral components Nsp2, thus facilitating PRRSV replication. In conclusion, we identified a novel IRF8-miR-10a-SRP14 regulatory pathway against PRRSV infection, which provides new insights into virus-host interactions and suggests potential new antiviral strategies to control PRRSV. IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) has rapidly spread to the global pig industry and caused incalculable economic damage since first discovered in the 1980s. However, conventional vaccines do not provide satisfactory protection. Understanding the molecular mechanisms of host resistance to PRRSV infection is necessary to develop safe and effective strategies to control PRRSV. During viral infection, miRNAs play vital roles in regulating the expression of viral or host genes at the posttranscriptional level. The significance of our study is that we revealed the transcriptional regulation mechanism of the antiviral molecule miR-10a after PRRSV infection. Moreover, our research also explained the mechanism of host molecule SRP14, the target gene of miR-10a regulating PRRSV replication. Thus, we report a novel regulatory pathway of IRF8-miR-10a-SRP14 against PRRSV infection, which provides new insights into virus-host interactions and suggests potential new control measures for future PRRSV outbreaks.

Caspase-Mediated Cleavage of the Transcription Factor Sp3: Possible Relevance to Cancer and the Lytic Cycle of Kaposi's Sarcoma-Associated Herpesvirus

The open reading frame 50 (ORF50) protein of Kaposi's sarcoma-associated herpesvirus (KSHV) is the master regulator essential for initiating the viral lytic cycle. Previously, we have demonstrated that the ORF50 protein can cooperate with Sp3 to synergistically activate a set of viral and cellular gene promoters through highly conserved ORF50-responsive elements that harbor a Sp3-binding motif. Herein, we show that Sp3 undergoes proteolytic cleavage during the viral lytic cycle, and the cleavage of Sp3 is dependent on caspase activation. Since similar cleavage patterns of Sp3 could be detected in both KSHV-positive and KSHV-negative lymphoma cells undergoing apoptosis, the proteolytic cleavage of Sp3 could be a common event during apoptosis. Mutational analysis identifies 12 caspase cleavage sites in Sp3, which are situated at the aspartate (D) positions D17, D19, D180, D273, D275, D293, D304 (or D307), D326, D344, D530, D543, and D565. Importantly, we noticed that three stable Sp3 C-terminal fragments generated through cleavage at D530, D543, or D565 encompass an intact DNA-binding domain. Like the full-length Sp3, the C-terminal fragments of Sp3 could still retain the ability to cooperate with ORF50 protein to activate specific viral and cellular gene promoters synergistically. Collectively, our findings suggest that despite the proteolytic cleavage of Sp3 under apoptotic conditions, the resultant Sp3 fragments may retain biological activities important for the viral lytic cycle or for cellular apoptosis. IMPORTANCE The ORF50 protein of Kaposi's sarcoma-associated herpesvirus (KSHV) is the key viral protein that controls the switch from latency to lytic reactivation. It is a potent transactivator that can activate target gene promoters via interacting with other cellular DNA-binding transcription factors, such as Sp3. In this report, we show that Sp3 is proteolytically cleaved during the viral lytic cycle, and up to 12 caspase cleavage sites are identified in Sp3. Despite the proteolytic cleavage of Sp3, several resulting C-terminal fragments that have intact zinc-finger DNA-binding domains still retain substantial influence in the synergy with ORF50 to activate specific gene promoters. Overall, our studies elucidate the caspase-mediated cleavage of Sp3 and uncover how ORF50 utilizes the cleavage fragments of Sp3 to transactivate specific viral and cellular gene promoters.

Genetic errors of immunity distinguish pediatric nonmalignant lymphoproliferative disorders

BACKGROUND

Pediatric nonmalignant lymphoproliferative disorders (PLPDs) are clinically and genetically heterogeneous. Long-standing immune dysregulation and lymphoproliferation in children may be life-threatening, and a paucity of data exists to guide evaluation and treatment of children with PLPD.

OBJECTIVE

The primary objective of this study was to ascertain the spectrum of genomic immunologic defects in PLPD. Secondary objectives included characterization of clinical outcomes and associations between genetic diagnoses and those outcomes.

METHODS

PLPD was defined by persistent lymphadenopathy, lymph organ involvement, or lymphocytic infiltration for more than 3 months, with or without chronic or significant Epstein-Barr virus (EBV) infection. Fifty-one subjects from 47 different families with PLPD were analyzed using whole exome sequencing.

RESULTS

Whole exome sequencing identified likely genetic errors of immunity in 51% to 62% of families (53% to 65% of affected children). Presence of a genetic etiology was associated with younger age and hemophagocytic lymphohistiocytosis. Ten-year survival for the cohort was 72.4%, and patients with viable genetic diagnoses had a higher survival rate (82%) compared to children without a genetic explanation (48%, P = .03). Survival outcomes for individuals with EBV-associated disease and no genetic explanation were particularly worse than outcomes for subjects with EBV-associated disease and a genetic explanation (17% vs 90%; P = .002). Ascertainment of a molecular diagnosis provided targetable treatment options for up to 18 individuals and led to active management changes for 12 patients.

CONCLUSIONS

PLPD defines children at high risk for mortality, and whole exome sequencing informs clinical risks and therapeutic opportunities for this diagnosis.

Development of a BCL-xL and BCL-2 dual degrader with improved anti-leukemic activity

PROteolysis-TArgeting Chimeras (PROTACs) have emerged as an innovative drug development platform. However, most PROTACs have been generated empirically because many determinants of PROTAC specificity and activity remain elusive. Through computational modelling of the entire NEDD8-VHL Cullin RING E3 ubiquitin ligase (CRL^VHL)/PROTAC/BCL-xL/UbcH5B(E2)-Ub/RBX1 complex, we find that this complex can only ubiquitinate the lysines in a defined band region on BCL-xL. Using this approach to guide our development of a series of ABT263-derived and VHL-recruiting PROTACs, we generate a potent BCL-xL and BCL-2 (BCL-xL/2) dual degrader with significantly improved antitumor activity against BCL-xL/2-dependent leukemia cells. Our results provide experimental evidence that the accessibility of lysines on a target protein plays an important role in determining the selectivity and potency of a PROTAC in inducing protein degradation, which may serve as a conceptual framework to guide the future development of PROTACs.

Molecular Basis of Epstein-Barr Virus Latency Establishment and Lytic Reactivation

Epstein–Barr virus (EBV) is a causative agent of infectious mononucleosis and several types of cancer. Like other herpesviruses, it establishes an asymptomatic, life-long latent infection, with occasional reactivation and shedding of progeny viruses. During latency, EBV expresses a small number of viral genes, and exists as an episome in the host–cell nucleus. Expression patterns of latency genes are dependent on the cell type, time after infection, and milieu of the cell (e.g., germinal center or peripheral blood). Upon lytic induction, expression of the viral immediate-early genes, BZLF1 and BRLF1, are induced, followed by early gene expression, viral DNA replication, late gene expression, and maturation and egress of progeny virions. Furthermore, EBV reactivation involves more than just progeny production. The EBV life cycle is regulated by signal transduction, transcription factors, promoter sequences, epigenetics, and the 3D structure of the genome. In this article, the molecular basis of EBV latency establishment and reactivation is summarized.

ΔNp63α promotes Epstein-Barr virus latency in undifferentiated epithelial cells

Epstein-Barr virus (EBV) is a human herpesvirus that causes infectious mononucleosis and contributes to both B-cell and epithelial-cell malignancies. EBV-infected epithelial cell tumors, including nasopharyngeal carcinoma (NPC), are largely composed of latently infected cells, but the mechanism(s) maintaining viral latency are poorly understood. Expression of the EBV BZLF1 (Z) and BRLF1 (R) encoded immediate-early (IE) proteins induces lytic infection, and these IE proteins activate each other's promoters. ΔNp63α (a p53 family member) is required for proliferation and survival of basal epithelial cells and is over-expressed in NPC tumors. Here we show that ΔNp63α promotes EBV latency by inhibiting activation of the BZLF1 IE promoter (Zp). Furthermore, we find that another p63 gene splice variant, TAp63α, which is expressed in some Burkitt and diffuse large B cell lymphomas, also represses EBV lytic reactivation. We demonstrate that ΔNp63α inhibits the Z promoter indirectly by preventing the ability of other transcription factors, including the viral IE R protein and the cellular KLF4 protein, to activate Zp. Mechanistically, we show that ΔNp63α promotes viral latency in undifferentiated epithelial cells both by enhancing expression of a known Zp repressor protein, c-myc, and by decreasing cellular p38 kinase activity. Furthermore, we find that the ability of cis-platinum chemotherapy to degrade ΔNp63α contributes to the lytic-inducing effect of this agent in EBV-infected epithelial cells. Together these findings demonstrate that the loss of ΔNp63α expression, in conjunction with enhanced expression of differentiation-dependent transcription factors such as BLIMP1 and KLF4, induces lytic EBV reactivation during normal epithelial cell differentiation. Conversely, expression of ΔNp63α in undifferentiated nasopharyngeal carcinoma cells and TAp63α in Burkitt lymphoma promotes EBV latency in these malignancies.

Stress-Induced Epstein-Barr Virus Reactivation

Epstein-Barr virus (EBV) is typically found in a latent, asymptomatic state in immunocompetent individuals. Perturbations of the host immune system can stimulate viral reactivation. Furthermore, there are a myriad of EBV-associated illnesses including various cancers, post-transplant lymphoproliferative disease, and autoimmune conditions. A thorough understanding of this virus, and the interplay between stress and the immune system, is essential to establish effective treatment. This review will provide a summary of the interaction between both psychological and cellular stressors resulting in EBV reactivation. It will examine mechanisms by which EBV establishes and maintains latency and will conclude with a brief overview of treatments targeting EBV.

Caspases Switch off the m6A RNA Modification Pathway to Foster the Replication of a Ubiquitous Human Tumor Virus

The methylation of RNA at the N6 position of adenosine (m⁶A) orchestrates multiple biological processes to control development, differentiation, and cell cycle, as well as various aspects of the virus life cycle. How the m⁶A RNA modification pathway is regulated to finely tune these processes remains poorly understood. Here, we discovered the m⁶A reader YTHDF2 as a caspase substrate via proteome-wide prediction, followed by in vitro and in vivo validations. We further demonstrated that cleavage-resistant YTHDF2 blocks, while cleavage-mimicking YTHDF2 fragments promote, the replication of a common human oncogenic virus, Epstein-Barr virus (EBV). Intriguingly, our study revealed a feedback regulation between YTHDF2 and caspase-8 via m⁶A modification of CASP8 mRNA and YTHDF2 cleavage during EBV replication. Further, we discovered that caspases cleave multiple components within the m⁶A RNA modification pathway to benefit EBV replication. Our study establishes that caspase disarming of the m⁶A RNA modification machinery fosters EBV replication. IMPORTANCE The discovery of an N⁶-methyladenosine (m⁶A) RNA modification pathway has fundamentally altered our understanding of the central dogma of molecular biology. This pathway is controlled by methyltransferases (writers), demethylases (erasers), and specific m⁶A binding proteins (readers). Emerging studies have linked the m⁶A RNA modification pathway to the life cycle of various viruses. However, very little is known regarding how this pathway is subverted to benefit viral replication. In this study, we established an unexpected linkage between cellular caspases and the m⁶A modification pathway, which is critical to drive the reactivation of a common tumor virus, Epstein-Barr virus (EBV).

Hippo signaling effectors YAP and TAZ induce Epstein-Barr Virus (EBV) lytic reactivation through TEADs in epithelial cells

The Epstein-Barr virus (EBV) human herpesvirus is associated with B-cell and epithelial-cell malignancies, and both the latent and lytic forms of viral infection contribute to the development of EBV-associated tumors. Here we show that the Hippo signaling effectors, YAP and TAZ, promote lytic EBV reactivation in epithelial cells. The transcriptional co-activators YAP/TAZ (which are inhibited by Hippo signaling) interact with DNA-binding proteins, particularly TEADs, to induce transcription. We demonstrate that depletion of either YAP or TAZ inhibits the ability of phorbol ester (TPA) treatment, cellular differentiation or the EBV BRLF1 immediate-early (IE) protein to induce lytic EBV reactivation in oral keratinocytes, and show that over-expression of constitutively active forms of YAP and TAZ reactivate lytic EBV infection in conjunction with TEAD family members. Mechanistically, we find that YAP and TAZ interact with, and activate, the EBV BZLF1 immediate-early promoter. Furthermore, we demonstrate that YAP, TAZ, and TEAD family members are expressed at much higher levels in epithelial cell lines in comparison to B-cell lines, and find that EBV infection of oral keratinocytes increases the level of activated (dephosphorylated) YAP and TAZ. Finally, we have discovered that lysophosphatidic acid (LPA), a known YAP/TAZ activator that plays an important role in inflammation, induces EBV lytic reactivation in epithelial cells through a YAP/TAZ dependent mechanism. Together these results establish that YAP/TAZ are powerful inducers of the lytic form of EBV infection and suggest that the ability of EBV to enter latency in B cells at least partially reflects the extremely low levels of YAP/TAZ and TEADs in this cell type.

PIAS1 potentiates the anti-EBV activity of SAMHD1 through SUMOylation

BACKGROUND

Sterile alpha motif and HD domain 1 (SAMHD1) is a deoxynucleotide triphosphohydrolase (dNTPase) that restricts the infection of a variety of RNA and DNA viruses, including herpesviruses. The anti-viral function of SAMHD1 is associated with its dNTPase activity, which is regulated by several post-translational modifications, including phosphorylation, acetylation and ubiquitination. Our recent studies also demonstrated that the E3 SUMO ligase PIAS1 functions as an Epstein-Barr virus (EBV) restriction factor. However, whether SAMHD1 is regulated by PIAS1 to restrict EBV replication remains unknown.

RESULTS

In this study, we showed that PIAS1 interacts with SAMHD1 and promotes its SUMOylation. We identified three lysine residues (K469, K595 and K622) located on the surface of SAMHD1 as the major SUMOylation sites. We demonstrated that phosphorylated SAMHD1 can be SUMOylated by PIAS1 and SUMOylated SAMHD1 can also be phosphorylated by viral protein kinases. We showed that SUMOylation-deficient SAMHD1 loses its anti-EBV activity. Furthermore, we demonstrated that SAMHD1 is associated with EBV genome in a PIAS1-dependent manner.

CONCLUSION

Our study reveals that PIAS1 synergizes with SAMHD1 to inhibit EBV lytic replication through protein-protein interaction and SUMOylation.

Nur77 Attenuates Inflammasome Activation by Inhibiting Caspase-1 Expression in Pulmonary Vascular Endothelial Cells

Inflammasomes are intracellular multiprotein complexes that help trigger and maintain the inflammatory response as part of the innate immune system. Recently, it has been increasingly recognized that aberrant inflammasome activation is critically involved endothelial dysfunction in a variety of human diseases, such as atherosclerosis, acute lung injury (ALI), and type 2 diabetes. The molecular mechanisms underlying endothelial inflammasome activation, however, are not completely elucidated. In the present study, we identified orphan nuclear receptor Nur77 as a novel regulator in controlling inflammasome activation in vascular endothelial cells (ECs). We demonstrated that LPS-induced inflammasome activation was significantly inhibited by ectopic overexpression of Nur77, predominantly through transcriptionally suppression of caspase-1 expression in vascular ECs. Consistent with this observation, we found that LPS-induced inflammasome activation was significantly augmented in lung ECs isolated from Nur77 knockout (KO) mice. Mechanistically, we showed that Nur77-induced inhibition of caspase-1 expression was due to an inhibition of Interferon Regulatory Factor 1 (IRF1) expression and its subsequent binding to the caspase-1 promoter. Importantly, in a mouse model of LPS-induced acute lung injury (ALI), Nur77 KO led to a marked activation of caspase-1 in the lung, increased alveolar and circulating IL-1β levels, and exacerbated ALI, all of which were substantially inhibited by administration of caspase-1 inhibitor. Together, our results support an important role for Nur77 in controlling inflammasome activation in vascular ECs and suggest that Nur77 could be a novel therapeutic target for the treatment of human diseases associated with aberrant inflammasome activation, such as ALI and atherosclerosis.

OmpA Protein-Deficient Acinetobacter baumannii Outer Membrane Vesicles Trigger Reduced Inflammatory Response

Multidrug resistant Acinetobacter baumannii shows a growing number of nosocomial infections worldwide during the last decade. The outer membrane vesicles (OMVs) produced by this bacterium draw increasing attention as a possible treatment target. OMVs have been implicated in the reduction of antibiotic level in the surrounding environment, transfer of virulence factors into the host cells, and induction of inflammatory response. Although the evidence on the involvement of OMVs in A. baumannii pathogenesis is currently growing, their role during inflammation is insufficiently explored. It is likely that bacteria, by secreting OMVs, can expand the area of their exposure and prepare surrounding matrix for infection. Here, we investigated the impact of A. baumannii OMVs on activation of macrophages in vitro. We show that OmpA protein present in A. baumannii OMVs substantially contributes to the proinflammatory response in J774 murine macrophages and to the cell death in both lung epithelium cells and macrophages. The loss of OmpA protein in OMVs, obtained from A. baumannii ∆ompA mutant, resulted in the altered expression of genes coding for IL-6, NLRP3 and IL-1β proinflammatory molecules in macrophages in vitro. These results imply that OmpA protein in bacterial OMVs could trigger a more intense proinflammatory response.

Integrative Informatics Analysis of Transcriptome and Identification of Interacted Genes in the Glomeruli and Tubules in CKD

Chronic kidney disease (CKD) is a complex disease in which the renal function is compromised chronically. Many studies have indicated the crosstalk between the tubule and the glomerulus in CKD progression. However, our understanding of the interaction of tubular and glomerular injury remains incomplete. In this study, we applied a meta-analysis approach on the transcriptome of the tubules and glomeruli of CKD patients to identify differentially expressed genes (DEGs) signature. Functional analysis of pathways and Gene Ontology found that tubular DEGs were mainly involved in cell assembly and remodeling, glomerular DEGs in cell proliferation and apoptosis, and overlapping DEGs mainly in immune response. Correlation analysis was performed to identify the associated DEGs in the tubules and glomeruli. Secreted protein comparison and verification experiments indicated that WFDC2 from the tubule could downregulate PEX19 mRNA and protein levels at the glomeruli in diabetic kidney disease (DKD). This study revealed the distinctive pathways of the tubules and glomeruli and identified interacted genes during CKD progression.

TRIM21 - A potential novel therapeutic target in cancer

Tripartite motif-containing protein 21 (TRIM21) is well known to be involved in innate immunity, systemic lupus erythematosus and Sjögren's syndrome. In addition, TRIM21 involvement in cancer proliferation has been observed. However, the clinical significance of TRIM21 and its role in cancer cell proliferation and suppression remains elusive. Here we discuss the effects of TRIM21 on major cancer promoting proteins such as NF-κB, STAT3, BCL2, p53, p27 and Snail, comparing its signaling pathways under normal conditions and in the presence of a variety of carcinogenesis effectors (oncogenic, genotoxic and UV irradiation). Depending on the cancer type and the carcinogenesis effector, TRIM21 may enhance cancer proliferation, or alternatively it may increase the ubiquitination of many cancer-triggering proteins, resulting in their proteasomal degradation. This indicates the importance of TRIM21 in cancer proliferation and/or apoptosis and suggests its potential as a novel cancer therapeutic target.

BRLF1 suppresses RNA Pol III-mediated RIG-I inflammasome activation in the early EBV lytic lifecycle

Latent infection with herpesviruses constitutively activates inflammasomes, while lytic replication suppresses their activation through distinct mechanisms. However, how Epstein-Barr virus (EBV) lytic replication inhibits the activation of inflammasomes remains unknown. Here, we reveal that the EBV immediate-early protein BRLF1 inhibits inflammasome activation, and BRLF1 deficiency significantly increases the activation of inflammasomes and pyroptosis during early lytic lifecycle. BRLF1 interacts with RNA polymerase III subunits to suppress immunostimulatory small RNA transcription, RIG-I inflammasome activation, and antiviral responses. Consequently, BRLF1-deficient EBV primary infection induces robust T-cell and NK cell activation and killing through IL-1β and IL-18. A BRLF1-derived peptide that inhibits inflammasome activation is sufficient to suppress T-cell and NK cell responses during BRLF1-deficient EBV primary infection in lymphocytes. These results reveal a novel mechanism involved in the evasion of inflammasome activation and antiviral responses during EBV early lytic infection and provide a promising approach for the manipulation of inflammasomes against infection of oncogenic herpesviruses.

Potentialities of selenium nanoparticles in biomedical science

Selenium nanoparticles (SeNPs) have revolutionized biomedical domain and are still developing rapidly. Hence, this perspective elaborates SeNPs properties, synthesis, and biomedical applications, together with their potential for management of SARS-CoV-2.

Recurrent tonsillitis and parental perceptions of tonsillectomy during the COVID-19 pandemic

OBJECTIVES

The coronavirus outbreak has triggered the implementation of nationwide social distancing measures. We aimed to investigate the impact on patients with recurrent tonsillitis and parental perceptions towards tonsillectomy during the COVID-19 pandemic.

METHODS

A telephone questionnaire was conducted for all children awaiting tonsillectomy for recurrent tonsillitis after social distancing for 2 months at our centre. The COVID-19 lockdown period was compared with the 2 months prior to lockdown.

RESULTS

Forty-four children had been social distancing at home during lockdown. There was a significant reduction in tonsillitis episodes during the 2-month lockdown period in comparison with 2 months prior to lockdown (p = 0.0001). In 70% (n = 31) of cases parents wanted their child's tonsillectomy during the coronavirus outbreak.

CONCLUSION

These findings demonstrate that viral exposure is a key factor in the pathophysiology of recurrent tonsillitis and that social distancing measures can reduce the frequency of recurrent tonsillitis. Despite the overall reduction in tonsillitis frequency during the lockdown period, the majority of parents wanted their child's tonsillectomy during the coronavirus outbreak. This demonstrates the impact tonsillitis has on the patient and their family's quality of life.

Transcriptional Regulation of Inflammasomes

Inflammasomes are multimolecular complexes with potent inflammatory activity. As such, their activity is tightly regulated at the transcriptional and post-transcriptional levels. In this review, we present the transcriptional regulation of inflammasome genes from sensors (e.g., NLRP3) to substrates (e.g., IL-1β). Lineage-determining transcription factors shape inflammasome responses in different cell types with profound consequences on the responsiveness to inflammasome-activating stimuli. Pro-inflammatory signals (sterile or microbial) have a key transcriptional impact on inflammasome genes, which is largely mediated by NF-κB and that translates into higher antimicrobial immune responses. Furthermore, diverse intrinsic (e.g., circadian clock, metabolites) or extrinsic (e.g., xenobiotics) signals are integrated by signal-dependent transcription factors and chromatin structure changes to modulate transcriptionally inflammasome responses. Finally, anti-inflammatory signals (e.g., IL-10) counterbalance inflammasome genes induction to limit deleterious inflammation. Transcriptional regulations thus appear as the first line of inflammasome regulation to raise the defense level in front of stress and infections but also to limit excessive or chronic inflammation.

Conserved Herpesvirus Protein Kinases Target SAMHD1 to Facilitate Virus Replication

To ensure a successful infection, herpesviruses have developed elegant strategies to counterbalance the host anti-viral responses. Sterile alpha motif and HD domain 1 (SAMHD1) was recently identified as an intrinsic restriction factor for a variety of viruses. Aside from HIV-2 and the related simian immunodeficiency virus (SIV) Vpx proteins, the direct viral countermeasures against SAMHD1 restriction remain unknown. Using Epstein-Barr virus (EBV) as a primary model, we discover that SAMHD1-mediated anti-viral restriction is antagonized by EBV BGLF4, a member of the conserved viral protein kinases encoded by all herpesviruses. Mechanistically, we find that BGLF4 phosphorylates SAMHD1 and thereby inhibits its deoxynucleotide triphosphate triphosphohydrolase (dNTPase) activity. We further demonstrate that the targeting of SAMHD1 for phosphorylation is a common feature shared by beta- and gamma-herpesviruses. Together, our findings uncover an immune evasion mechanism whereby herpesviruses exploit the phosphorylation of SAMHD1 to thwart host defenses.

Herpesviruses have evolved elegant strategies to dampen the host anti-viral responses. Zhang et al. discover a mechanism by which herpesviruses evade SAMHD1-mediated host defenses through phosphorylation, expanding the functional repertoire of viral protein kinases in herpesvirus biology.

Discovery of IAP-recruiting BCL-XL PROTACs as potent degraders across multiple cancer cell lines

Targeting BCL-X_L via PROTACs is a promising strategy in reducing BCL-X_L inhibition associated platelet toxicity. Recently, we reported potent BCL-X_L PROTAC degraders that recruit VHL or CRBN E3 ligase. However, low protein expression or mutation of the responsible E3 ligase has been known to result in decreased protein degradation efficiency of the corresponding PROTACs. To overcome these mechanisms of resistance, PROTACs based on recruiting alternative E3 ligases could be generated. Thus, we designed and synthesized a series of PROTACs that recruit IAP E3 ligases for BCL-X_L degradation. Among those PROTACs, compound 8a efficiently degrades BCL-X_L in malignant T-cell lymphoma cell line MyLa 1929 while CRBN-based PROTACs that have high potency in other cancer cell lines show compromised potency, likely due to the low CRBN expression. Moreover, compared with the parent compound ABT-263, PROTAC 8a shows comparable cell killing effects in MyLa 1929 cells whereas the on-target platelet toxicity is significantly reduced. Our findings expand the anti-tumor spectra of BCL-X_L degraders and further highlight the importance of selecting suitable E3 members to achieve effective cellular activity.

Using proteolysis-targeting chimera technology to reduce navitoclax platelet toxicity and improve its senolytic activity

Small molecules that selectively kill senescent cells (SCs), termed senolytics, have the potential to prevent and treat various age-related diseases and extend healthspan. The use of Bcl-xl inhibitors as senolytics is largely limited by their on-target and dose-limiting platelet toxicity. Here, we report the use of proteolysis-targeting chimera (PROTAC) technology to reduce the platelet toxicity of navitoclax (also known as ABT263), a Bcl-2 and Bcl-xl dual inhibitor, by converting it into PZ15227 (PZ), a Bcl-xl PROTAC, which targets Bcl-xl to the cereblon (CRBN) E3 ligase for degradation. Compared to ABT263, PZ is less toxic to platelets, but equally or slightly more potent against SCs because CRBN is poorly expressed in platelets. PZ effectively clears SCs and rejuvenates tissue stem and progenitor cells in naturally aged mice without causing severe thrombocytopenia. With further improvement, Bcl-xl PROTACs have the potential to become safer and more potent senolytic agents than Bcl-xl inhibitors.

MYC Controls the Epstein-Barr Virus Lytic Switch

Epstein-Barr virus (EBV) is associated with multiple human malignancies. To evade immune detection, EBV switches between latent and lytic programs. How viral latency is maintained in tumors or in memory B cells, the reservoir for lifelong EBV infection, remains incompletely understood. To gain insights, we performed a human genome-wide CRISPR/Cas9 screen in Burkitt lymphoma B cells. Our analyses identified a network of host factors that repress lytic reactivation, centered on the transcription factor MYC, including cohesins, FACT, STAGA, and Mediator. Depletion of MYC or factors important for MYC expression reactivated the lytic cycle, including in Burkitt xenografts. MYC bound the EBV genome origin of lytic replication and suppressed its looping to the lytic cycle initiator BZLF1 promoter. Notably, MYC abundance decreases with plasma cell differentiation, a key lytic reactivation trigger. Our results suggest that EBV senses MYC abundance as a readout of B cell state and highlights Burkitt latency reversal therapeutic targets.

Toward targeting inflammasomes: insights into their regulation and activation

Inflammasomes are multi-component signaling complexes critical to the initiation of pyroptotic cell death in response to invading pathogens and cellular damage. A number of innate immune receptors have been reported to serve as inflammasome sensors. Activation of these sensors leads to the proteolytic activation of caspase-1, a proinflammatory caspase responsible for the cleavage of proinflammatory cytokines interleukin-1β and interleukin-18 and the effector of pyroptotic cell death, gasdermin D. Though crucial to the innate immune response to infection, dysregulation of inflammasome activation can lead to the development of inflammatory diseases, neurodegeneration, and cancer. Therefore, clinical interest in the modulation of inflammasome activation is swiftly growing. As such, it is imperative to develop a mechanistic understanding of the regulation of these complexes. In this review, we divide the regulation of inflammasome activation into three parts. We discuss the transcriptional regulation of inflammasome components and related proteins, the post-translational mechanisms of inflammasome activation, and advances in the understanding of the structural basis of inflammasome activation.

A promiscuous inflammasome sparks replication of a common tumor virus

Viruses activate inflammasomes but then subvert resulting inflammatory responses to avoid elimination. We asked whether viruses could instead use such activated or primed inflammasomes to directly aid their propagation and spread. Since herpesviruses are experts at coopting cellular functions, we investigated whether Epstein-Barr virus (EBV), an oncoherpesvirus, exploits inflammasomes to activate its replicative or lytic phase. Indeed, our experiments reveal that EBV exploits several inflammasome sensors to actually activate its replicative phase from quiescence/latency. In particular, TXNIP, a key inflammasome intermediary, causes assembly of the NLRP3 inflammasome, resulting in caspase-1-mediated depletion of the heterochromatin-inducing epigenetic repressor KAP1/TRIM28 in a subpopulation of cells. As a result, only TXNIPhiKAP1lo cells, that is, in a primed/prolytic state, turn expression of the replication/lytic/reactivation switch protein on to enter the replicative phase. Our findings 1) demonstrate that EBV dovetails its escape strategy to a key cellular danger-sensing mechanism, 2) indicate that transcription may be regulated by KAP1 abundance aside from canonical regulation through its posttranslational modification, 3) mechanistically link diabetes, which frequently activates the NLRP3 inflammasome, to deregulation of a tumor virus, and 4) demonstrate that B lymphocytes from NOMID (neonatal onset multisystem inflammatory disease) patients who have NLRP3 mutations and suffer from hyperactive innate responses are defective in controlling a herpesvirus.

A selective BCL-XL PROTAC degrader achieves safe and potent antitumor activity

BCL-X_L is a well-validated cancer target. However, the on-target and dose-limiting thrombocytopenia limits the use of BCL-X_L inhibitors such as ABT263 as safe and effective anticancer agents. To reduce the toxicity of ABT263, we converted it into DT2216, a BCL-X_L proteolysis targeting chimera (PROTAC), that targets BCL-X_L to the Von Hippel-Lindau (VHL) E3 ligase for degradation. We found that DT2216 was more potent against various BCL-X_L-dependent leukemia and cancer cells but significantly less toxic to platelets than ABT263 in vitro because VHL is poorly expressed in platelets. In vivo, DT2216 effectively inhibits the growth of several xenograft tumors as a single agent or in combination with other chemotherapeutic agents, without causing significant thrombocytopenia. These findings demonstrate the potential to use PROTAC technology to reduce on-target drug toxicities and rescue the therapeutic potential of previously undruggable targets. Furthermore, DT2216 may be developed as a safe first-in-class anticancer agent targeting BCL-X_L.

Protein inhibitor of activated STAT1 (PIAS1) inhibits IRF8 activation of Epstein-Barr virus lytic gene expression

Epstein-Barr virus (EBV), a major human oncogenic pathogen, establishes life-long persistent infections. In latently infected B lymphocytes, the virus persists as an episome in the nucleus. Periodic reactivation of latent virus is controlled by both viral and cellular factors. Our recent studies showed that interferon regulatory factor 8 (IRF8) is required for EBV lytic reactivation while protein inhibitor of activated STAT1 (PIAS1) functions as an EBV restriction factor to block viral reactivation. Here, we show that IRF8 directly binds to the EBV genome and regulates EBV lytic gene expression together with PU.1 and EBV transactivator RTA. Furthermore, our study reveals that PIAS1 antagonizes IRF8/PU.1-mediated lytic gene activation through binding to and inhibiting IRF8. Together, our study establishes IRF8 as a transcriptional activator in promoting EBV reactivation and defines PIAS1 as an inhibitor of IRF8 to limit lytic gene expression.

Duckling short beak and dwarfism syndrome virus infection activates host innate immune response involving both DNA and RNA sensors

Duckling short beak and dwarfism syndrome virus (SBDSV), a newly identified goose parvovirus, causes devastating disease in domestic waterfowl and considerable economic losses to Chinese waterfowl industry. The molecular pathogenesis of SBDSV infection, nature and dynamics of host immune responses against SBDSV infection remained elusive. In this study, we systematically explored the relative mRNA expression profiles of major innate immune-related genes in SBDSV infected duck embryo fibroblasts. We found that SBDSV infection effectively activated host innate immune responses and resulted in significant up-regulation of IFN-β and several vital IFN-stimulated genes (ISGs). These up-regulation responses were mainly attributed to viral genomic DNA and dsRNA replication intermediates. Importantly, the expression of cGAS was significantly induced, whereas the expression of other DNA receptors including DDX41, STING, ZBP1, LSM14A and LRRFIP1 have no significant change. Furthermore, SBDSV infection also activates the up-regulation of TLR3 and inhibited the expression of TLR2 and TLR4; however, no effect was observed on the expression of TLR1, TLR5, TLR7, TLR15 and TLR21. Intriguingly, SBDSV infection significantly up-regulated the expression of RNA sensors such as MDA5 and LGP2, and resulted in a delayed but significant up-regulation of RIG-I gene. Taken together, these data indicate that host multiple sensors including DNA sensor (cGAS) and RNA sensors (TLR3, MDA5 and LGP2) are involved in recognizing a variety of different pathogen associated molecular patterns (PAMPs) including viral genomic ssDNA and dsRNA replication intermediates, which trigger an effective antiviral innate immune response.

Global Mapping of H3K4 Trimethylation (H3K4me3) and Transcriptome Analysis Reveal Genes Involved in the Response to Epidemic Diarrhea Virus Infections in Pigs

Porcine epidemic diarrhea virus (PEDV) is currently detected as the main pathogen causing severe diarrhea in pig farms. The phenotypic alterations induced by pathogenic infections are usually tightly linked with marked changes in epigenetic modification and gene expression. We performed global mapping of H3K4 trimethylation (H3K4me3) and transcriptomic analyses in the jejunum of PEDV-infected and healthy piglets using chromatin immunoprecipitation sequencing and RNA-seq techniques. A total of 1885 H3K4me3 peaks that are associated with 1723 genes were characterized. Moreover, 290 differentially expressed genes were identified, including 104 up-regulated and 186 down-regulated genes. Several antiviral genes including 2'-5'-oligoadenylate synthetase 1 (OAS1), 2'-5'-oligoadenylate synthetase 2 (OAS2), ephrin B2 (EFNB2), and CDC28 protein kinase regulatory subunit 1B (CKS1B) with higher H3K4me3 enrichment and expression levels in PEDV-infected samples suggested the potential roles of H3K4me3 deposition in promoting their expressions. Transcription factor annotation analysis highlighted the potential roles of two transcription factors interferon regulatory factor 8 (IRF8) and Kruppel like factor 4 (KLF4) in modulating the differential expression of genes involved in PEDV infection. The results provided novel insights into PEDV infection from the transcriptomic and epigenetic layers and revealed previously unknown and intriguing elements potentially involved in the host responses.

IL-10 knockdown with siRNA enhances the efficacy of Doxorubicin chemotherapy in EBV-positive tumors by inducing lytic cycle via PI3K/p38 MAPK/NF-kB pathway

High levels of IL-10 expression in Epstein-Barr virus (EBV) associated tumors have been reported and it is likely to be important for maintaining EBV latency and EBV-associated tumors. The switch from the latent form of EBV to the lytic form in tumor cells can lead to tumor cell lysis. Here, we found that knockdown of IL-10 induced EBV lytic replication. Subsequently, we demonstrated that IL-10 knockdown activated BZLF1 promoter through PI3K-p38 MAPK-NF-κB signaling pathway. Interestingly, we verified that VEGF-A was required for IL-10 knockdown to activate PI3K signaling and the accompanying EBV lytic induction. Exogenous recombinant human VEGF-A induced PI3K activation and EBV lytic infection, and inhibition of VEGF-A signaling prevented the PI3K/AKT phosphorylation and EBV reactivation responded to IL-10 knockdown. Most importantly, IL-10 knockdown synergized with chemotherapeutic agent Doxorubicin to kill EBV associated tumor cells in vitro and repress EBV-positive tumor growth in vivo. Our results suggest that inhibition of IL-10 has the potential to serve as a new supplemental strategy for the treatment of EBV-associated tumors.

Epstein-Barr Virus and Innate Immunity: Friends or Foes?

Epstein–Barr virus (EBV) successfully persists in the vast majority of adults but causes lymphoid and epithelial malignancies in a small fraction of latently infected individuals. Innate immunity is the first-line antiviral defense, which EBV has to evade in favor of its own replication and infection. EBV uses multiple strategies to perturb innate immune signaling pathways activated by Toll-like, RIG-I-like, NOD-like, and AIM2-like receptors as well as cyclic GMP-AMP synthase. EBV also counteracts interferon production and signaling, including TBK1-IRF3 and JAK-STAT pathways. However, activation of innate immunity also triggers pro-inflammatory response and proteolytic cleavage of caspases, both of which exhibit proviral activity under some circumstances. Pathogenic inflammation also contributes to EBV oncogenesis. EBV activates NFκB signaling and induces pro-inflammatory cytokines. Through differential modulation of the proviral and antiviral roles of caspases and other host factors at different stages of infection, EBV usurps cellular programs for death and inflammation to its own benefits. The outcome of EBV infection is governed by a delicate interplay between innate immunity and EBV. A better understanding of this interplay will instruct prevention and intervention of EBV-associated cancers.

Pomalidomide increases immune surface marker expression and immune recognition of oncovirus-infected cells

Most chronic viruses evade T-cell and natural killer (NK) immunity through downregulation of immune surface markers. Previously we showed that Pomalidomide (Pom) increases surface expression of major histocompatibility complex class I (MHC-I) in Kaposi sarcoma-associated herpesvirus-infected latent and lytic cells and restores ICAM-1 and B7-2 in latent cells. We explored the ability of Pom to increase immune surface marker expression in cells infected by other chronic viruses, including human T-cell leukemia virus type-1 (HTLV-1), Epstein-Barr virus (EBV), human papilloma virus (HPV), Merkel cell polyoma virus (MCV), and human immunodeficiency virus type-1 (HIV-1). Pom increased MHC-1, ICAM-1, and B7-2/CD86 in immortalized T-cell lines productively infected with HTLV-1 and also significantly increased their susceptibility to NK cell-mediated cytotoxicity. Pom enhancement of MHC-I and ICAM-1 in primary cells infected with HTLV-1 was abrogated by knockout of HTLV-1 orf-1. Pom increased expression of ICAM-1, B7-2 and MHC class I polypeptide related sequence A (MICA) surface expression in the EBV-infected Daudi cells and increased their T-cell activation and susceptibility to NK cells. Moreover, Pom increased expression of certain of these surface markers on Akata, Raji, and EBV lymphoblastic cell lines. The increased expression of immune surface markers in these virus-infected lines was generally associated with a decrease in IRF4 expression. By contrast, Pom treatment of HPV, MCV and HIV-1 infected cells did not increase these immune surface markers. Pom and related drugs may be clinically beneficial for the treatment of HTLV-1 and EBV-induced tumors by rendering infected cells more susceptible to both innate and adaptive host immune responses.

Restriction of H1N1 influenza virus infection by selenium nanoparticles loaded with ribavirin via resisting caspase-3 apoptotic pathway

INTRODUCTION

Ribavirin (RBV) is a broad-spectrum antiviral drug. Selenium nanoparticles (SeNPs) attract much attention in the biomedical field and are used as carriers of drugs in current research studies. In this study, SeNPs were decorated by RBV, and the novel nanoparticle system was well characterized. Madin-Darby Canine Kidney cells were infected with H1N1 influenza virus before treatment with RBV, SeNPs, and SeNPs loaded with RBV (Se@RBV).

METHODS AND RESULTS

MTT assay showed that Se@RBV nanoparticles protect cells during H1N1 infection in vitro. Se@RBV depressed virus titer in the culture supernatant. Intracellular localization detection revealed that Se@RBV accumulated in lysosome and escaped to cytoplasm as time elapsed. Furthermore, activation of caspase-3 was resisted by Se@RBV. Expressions of proteins related to caspase-3, including cleaved poly-ADP-ribose polymerase, caspase-8, and Bax, were downregulated evidently after treatment with Se@RBV compared with the untreated infection group. In addition, phosphorylations of phosphorylated 38 (p38), JNK, and phosphorylated 53 (p53) were inhibited as well. In vivo experiments indicated that Se@RBV was found to prevent lung injury in H1N1-infected mice through hematoxylin and eosin staining. Tunel test of lung tissues present that DNA damage reached a high level but reduced substantially when treated with Se@RBV. Immunohistochemical test revealed an identical result with the in vitro experiment that activations of caspase-3 and proteins on the apoptosis pathway were restrained by Se@RBV treatment.

CONCLUSION

Taken together, this study elaborates that Se@RBV is a novel promising agent against H1N1 influenza virus infection.

Emerging Proviral Roles of Caspases during Lytic Replication of Gammaherpesviruses

Due to their roles in the regulation of programmed cell death and inflammation, the cellular caspase proteases are considered antiviral factors. However, recent studies have revealed examples of proviral functions for caspases. Here, we review a growing body of literature on the role of caspases in promoting the replication of human gammaherpesviruses. We propose that gammaherpesviruses have evolved ways to redirect these enzymes and to use their activation to support viral replication and immune evasion.

Investigating genetic-and-epigenetic networks, and the cellular mechanisms occurring in Epstein-Barr virus-infected human B lymphocytes via big data mining and genome-wide two-sided NGS data identification

Epstein-Barr virus (EBV), also known as human herpesvirus 4, is prevalent in all human populations. EBV mainly infects human B lymphocytes and epithelial cells, and is therefore associated with their various malignancies. To unravel the cellular mechanisms during the infection, we constructed interspecies networks to investigate the molecular cross-talk mechanisms between human B cells and EBV at the first (0-24 hours) and second (8-72 hours) stages of EBV infection. We first constructed a candidate genome-wide interspecies genetic-and-epigenetic network (the candidate GIGEN) by big database mining. We then pruned false positives in the candidate GIGEN to obtain the real GIGENs at the first and second infection stages in the lytic phase by their corresponding next-generation sequencing data through dynamic interaction models, the system identification approach, and the system order detection method. The real GIGENs are very complex and comprise protein-protein interaction networks, gene/microRNA (miRNA)/long non-coding RNA regulation networks, and host-virus cross-talk networks. To understand the molecular cross-talk mechanisms underlying EBV infection, we extracted the core GIGENs including host-virus core networks and host-virus core pathways from the real GIGENs using the principal network projection method. According to the results, we found that the activities of epigenetics-associated human proteins or genes were initially inhibited by viral proteins and miRNAs, and human immune responses were then dysregulated by epigenetic modification. We suggested that EBV exploits viral proteins and miRNAs, such as EBNA1, BPLF1, BALF3, BVRF1 and miR-BART14, to develop its defensive mechanism to defeat multiple immune attacks by the human immune system, promotes virion production, and facilitates the transportation of viral particles by activating the human genes NRP1 and CLIC5. Ultimately, we propose a therapeutic intervention comprising thymoquinone, valpromide, and zebularine to act as inhibitors of EBV-associated malignancies.