G-quadruplexes formed by Varicella-Zoster virus reiteration sequences suppress expression of glycoprotein C and regulate viral cell-to-cell spread.

G-quadruplex (G4) formed by repetitive guanosine-rich sequences plays important roles in diverse cellular processes; however, its roles in viral infection are not fully understood. In this study, we investigated the genome-wide distribution of G4-forming sequences (G4 motifs) in Varicella-Zoster virus (VZV) and found that G4 motifs are enriched in the internal repeat short and the terminal repeat short regions flanking the unique short region and also in some reiteration (R) sequence regions. A high density of G4 motifs in the R2 region was found on the template strand of ORF14, which encodes glycoprotein C (gC), a virulent factor for viral growth in skin. Analyses such as circular dichroism spectroscopy, thermal difference spectra, and native polyacrylamide gel electrophoresis with oligodeoxynucleotides demonstrated that several G4 motifs in ORF14 form stable G4 structures. In transfection assays, gC expression from the G4-disrupted ORF14 gene was increased at the transcriptional level and became more resistant to suppression by G4-ligand treatment. The recombinant virus containing the G4-disrupted ORF14 gene expressed a higher level of gC mRNA, while it showed a slightly reduced growth. This G4-disrupted ORF14 virus produced smaller plaques than the wild-type virus. Our results demonstrate that G4 formation via reiteration sequences suppresses gC expression during VZV infection and regulates viral cell-to-cell spread.

Dynamic bidirectional regulation of NLRC3 and gammaherpesviruses during viral latency in B lymphocytes.

While most NOD-like receptors (NLRs) are predominately expressed by innate immune cells, NLRC3, an inhibitory NLR of immune signaling, exhibits the highest expression in lymphocytes. The role of NLRC3 or any NLRs in B lymphocytes is completely unknown. Gammaherpesviruses, including human Epstein-Barr virus (EBV) and murine gammaherpesvirus 68 (MHV-68), establish latent infection in B lymphocytes, which requires elevated NF-κB. This study shows that during latent EBV infection of human B cells, viral-encoded latent membrane protein 1 (LMP1) decreases NLRC3 transcript. LMP1-induced-NF-κB activation suppresses the promoter activity of NLRC3 via p65 binding to the promoter. Conversely, NLRC3 inhibits NF-κB activation by promoting the degradation of LMP1 in a proteasome-dependent manner. In vivo, MHV-68 infection reduces Nlrc3 transcripts in splenocytes, and Nlrc3-deficient mice show greater viral latency than controls. These results reveal a bidirectional regulatory circuit in B lymphocytes, where viral latent protein LMP1 reduces NLRC3 expression, while NLRC3 disrupts gammaherpesvirus latency, which is an important step for tumorigenesis.

Epstein-Barr Virus Viral Processivity Factor EA-D Facilitates Virus Lytic Replication by Inducing Poly(ADP-Ribose) Polymerase 1 Degradation.

Gammaherpesviruses, including Epstein-Barr virus (EBV), are important human pathogens because they are associated with various tumors. Poly(ADP-ribose) polymerase 1 (PARP1) is a multifunctional host nuclear protein responsible for poly(ADP-ribosyl)ation (PARylation) of target proteins. While PARP1 acts as a negative regulator that suppresses the lytic replication of gammaherpesviruses, viruses are often equipped with various strategies to overcome PARP1 inhibition. However, the mechanisms of how EBV may modulate a repressive host protein, PARP1, are still elusive. In this study, we found that EBV reactivation induced PARP1 downregulation in EBV-infected cells. EBV DNA polymerase processivity factor EA-D, encoded by the BMRF1 gene, directly interacted with the central automodification domain (AD) of PARP1 and was necessary and sufficient to downregulate PARP1 via K29-linked polyubiquitination. Moreover, knockdown of EA-D in B95.8 cells restored PARP1 levels and abrogated the expression of ZTA (also known as ZEBRA), a switch molecule of the EBV life cycle during reactivation. Interestingly, PARP1 PARylated RTA, another key switch molecule, and decreased RTA transactivation on the promoters of the ZTA, BMRF1, and BMLF1 genes. EA-D alleviated the PARylation of RTA and further enhanced RTA-mediated transactivation of these lytic promoters in reporter assays. Taken together, our results suggest that EBV viral processivity factor plays a key role in facilitating lytic replication by inducing PARP1 degradation via its interaction with the PARP1 AD, which is a highly conserved mechanism among gammaherpesviruses to counteract host repressive activity of PARP1 against viral lytic replication. IMPORTANCE PARP1 acts as a negative regulator of lytic replication in EBV. To successfully enter the reactivation cycle, EBV has developed multiple strategies to counteract the host's repressive mechanisms. In this study, we investigated how EBV manipulated the host repressive factor PARP1 to facilitate lytic replication. The EBV processivity factor EA-D downregulated PARP1 in a proteasome-dependent manner via its direct binding with PARP1 AD. The knockdown of EA-D restored the PARP1 level and inhibited ZTA expression during reactivation. Interestingly, PARP1 PARylated RTA and EA-D reduced the PARylation of RTA, thereby promoting the ZTA promoter activity. These results suggest that EA-D plays a key role in EBV lytic replication by inducing PARP1 degradation in addition to supporting DNA replication as a viral processivity factor. Given that the KSHV processivity factor also induces PARP1 degradation and enhances RTA function, gammaherpesviruses share a conserved molecular mechanism to overcome the inhibitory effects of PARP1, promoting lytic replication.

Kaposi's sarcoma-associated herpesvirus processivity factor (PF-8) recruits cellular E3 ubiquitin ligase CHFR to promote PARP1 degradation and lytic replication.

Kaposi's sarcoma-associated herpesvirus (KSHV), which belongs to the gammaherpesvirus subfamily, is associated with the pathogenesis of various tumors. Nuclear enzyme poly(ADP-ribose) polymerase 1 (PARP1) catalyzes the polymerization of ADP-ribose units on target proteins. In KSHV-infected cells, PARP1 inhibits replication and transcription activator (RTA), a molecular switch that initiates lytic replication, through direct interaction. Thus, for efficient replication, KSHV has to overcome the molecular barrier in the form of PARP1. Previously, we have demonstrated that KSHV downregulates the expression of PARP1 through PF-8, a viral processivity factor. PF-8 induces ubiquitin-proteasome system-mediated degradation of PARP1 via direct physical association and enhances RTA transactivation activity. Here, we showed that dimerization domains of PF-8 are crucial not only for PARP1 interaction and degradation but also for enhancement of the RTA transactivation activity. PF-8 recruited CHFR for the PARP1 degradation. A knockdown of CHFR attenuated the PF-8-induced PARP1 degradation and enhancement of the RTA transactivation activity, leading to reduced KSHV lytic replication. These findings reveal a mechanism by which KSHV PF-8 recruits a cellular E3 ligase to curtail the inhibitory effect of PARP1 on KSHV lytic replication.

Optimization and validation of a fluorogenic dipeptidyl peptidase 4 enzymatic assay in human plasma.

During the development of a specific dipeptidyl peptidase 4 (DPP4) inhibitor to treat type 2 diabetes, a fluorogenic kinetic analysis for DPP4 enzymatic activity using Gly-Pro-Aminomethylcoumarin (AMC) as a substrate was optimized and validated for recombinant DPP4 and human plasma samples. The sensitivity, calibration curve, detection range, accuracy, precision, recovery efficiency, Km constant, short/long-term stability, and stability after freezing-thawing cycles were analyzed. DPP4 enzymatic activity (mU/min) was measured as the initial velocity (Vo) of the enzymatic reaction over time. The sensitivity of the Vo value was 14,488 mU/min for recombinant DPP4 and 17,995 mU/min for human plasma samples. The dynamic ranges of the calibration curve were linear and reliable between 1.11 × 104-1.86 × 106 mU/min of the mean Vo value and in the DPP4 concentration range of 23.4-3,000 ng/mL. The assay's accuracy and precision met acceptance criteria for all samples. Plasma DPP4 was stable under various storage temperatures, even after three freeze-thaw cycles. Our optimized, validated bioanalytic method for measuring DPP4 activity in plasma samples was successfully employed to evaluate the effect of evogliptin (DA-1229) tartrate, which irreversibly and dose-dependently inhibits DPP4 enzymatic activity, without the dilution effect of human plasma samples and irrespective of the co-treated metformin.

A DNA-sensing-independent role of a nuclear RNA helicase, DHX9, in stimulation of NF-κB-mediated innate immunity against DNA virus infection.

DExD/H-box helicase 9 (DHX9), or RNA helicase A (RHA), is an abundant multifunctional nuclear protein. Although it was previously reported to act as a cytosolic DNA sensor in plasmacytoid dendritic cells (pDCs), the role and molecular mechanisms of action of DHX9 in cells that are not pDCs during DNA virus infection are not clear. Here, a macrophage-specific knockout and a fibroblast-specific knockdown of DHX9 impaired antiviral innate immunity against DNA viruses, leading to increased virus replication. DHX9 enhanced NF-κB-mediated transactivation in the nucleus, which required its ATPase-dependent helicase (ATPase/helicase) domain, but not the cytosolic DNA-sensing domain. In addition, DNA virus infection did not induce cytoplasmic translocation of nuclear DHX9 in macrophages and fibroblasts. Nuclear DHX9 was associated with a multiprotein complex including both NF-κB p65 and RNA polymerase II (RNAPII) in chromatin containing NF-κB-binding sites. DHX9 was essential for the recruitment of RNAPII rather than NF-κB p65, to the corresponding promoters; this function also required its ATPase/helicase activity. Taken together, our results show a critical role of nuclear DHX9 (as a transcription coactivator) in the stimulation of NF-κB-mediated innate immunity against DNA virus infection, independently of DHX9's DNA-sensing function.

BST2 inhibits infection of influenza A virus by promoting apoptosis of infected cells.

BST2 is an antiviral factor that inhibits the release of enveloped virus at the plasma membrane via an unusual topology in which its N-terminal is in the cytosol while its C-terminal is anchored by glycophosphatidylinositol (GPI). BST2-deficient cells showed substantially higher release of virions than wild type cells. Influenza-infected BST2-deficient cells showed greatly reduced cytopathic effect (CPE) than wild type cells despite their generally robust virus production. This finding prompted us to determine whether BST2 was involved in the apoptotic process of virus-infected host cells. Our results revealed that BST2 might be involved in IRE1α-mediated ER stress pathway by increasing spliced form XBP-1. Consequently, levels of cytochrome C, caspase-3, caspase-9, and PARP as representative molecules of apoptosis were significantly increased in wild type cells than those in BST2-deficient cells. These results suggest that BST2 might participate in innate host defense by augmenting ER-stress-induced apoptotic signaling to inhibit the replication and spread of virus.

The structure of the pleiotropic transcription regulator CodY provides insight into its GTP-sensing mechanism.

GTP and branched-chain amino acids (BCAAs) are metabolic sensors that are indispensable for the determination of the metabolic status of cells. However, their molecular sensing mechanism remains unclear. CodY is a unique global transcription regulator that recognizes GTP and BCAAs as specific signals and affects expression of more than 100 genes associated with metabolism. Herein, we report the first crystal structures of the full-length CodY complex with sensing molecules and describe their functional states. We observed two different oligomeric states of CodY: a dimeric complex of CodY from Staphylococcus aureus with the two metabolites GTP and isoleucine, and a tetrameric form (apo) of CodY from Bacillus cereus Notably, the tetrameric state shows in an auto-inhibitory manner by blocking the GTP-binding site, whereas the binding sites of GTP and isoleucine are clearly visible in the dimeric state. The GTP is located at a hinge site between the long helical region and the metabolite-binding site. Together, data from structural and electrophoretic mobility shift assay analyses improve understanding of how CodY senses GTP and operates as a DNA-binding protein and a pleiotropic transcription regulator.

Enhancing the natural killer cell activity and anti-influenza effect of heat-treated Lactobacillus plantarum nF1-fortified yogurt in mice.

Influenza A virus (IAV) infection is a global public health concern. It causes respiratory diseases ranging from mild illness to fatal disease. Natural killer (NK) cells are an innate immune component that kill infected cells and secrete cytokines to modulate the adaptive immune system; they constitute the first-line defense and play important roles in controlling IAV infection. This study evaluated the effect of daily administration of heat-treated Lactobacillus plantarum nF1-fortified yogurt on immunity and protection against IAV infection. Mice administered with heat-treated L. plantarum nF1-fortified yogurt showed elevated NK cell-related cytokine expression levels. Daily administration of the L. plantarum nF1-fortified yogurt before IAV infection also enhanced splenic NK activity, lung inflammatory cytokine responses, and survival rate. Thus, daily administration of nF1-fortified yogurt enhances host immunity and helps prevent IAV infection.

Regulation of the viral life cycle by murine gammaherpesvirus 68 microRNAs.

γ-Herpesviruses (γHV) such as Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus are important human pathogens involved in lymphoproliferation and tumorigenesis. Murine gammaherpesvirus 68 (MHV-68, γHV-68) is an effective model for the study of γHV pathogenesis and host-virus interaction because it is closely related to human γHV. Similarly to human γHV, MHV-68 encodes 15 microRNAs (miRNAs). Although their functions remain unknown, they are thought to regulate the viral life cycle or host-virus interactions, similarly to other human γHV. Herein, we established stable cell lines expressing MHV-68 miRNAs and investigated the role of MHV-68 miRNAs in the regulation of viral life cycle. We found that mghv-miR-M1-1, -3, -5, -7, -8, -9, -10, -11, -13, and -15 repressed MHV-68 lytic replication by down-regulating expression of the replication and transcription activator (RTA) gene, whereas mghv-miR-M1-2, -4, -6, and -12 induced lytic replication by up-regulating RTA. We confirmed that the decrease in viral replication caused by mghv-miR-M1-1 was abolished by inhibition of miRNA expression via miRNA inhibitor treatment. In addition, we observed that mghv-miR-M1-1 down-regulated c-Jun indirectly and decreased cytokine production, suggesting that mghv-miR-M1-1 may inhibit MHV-68 lytic replication by inhibiting the activator protein 1 (AP-1) signaling pathway.

Downregulation of Poly(ADP-Ribose) Polymerase 1 by a Viral Processivity Factor Facilitates Lytic Replication of Gammaherpesvirus.

UNLABELLED: In Kaposi's sarcoma-associated herpesvirus (KSHV), poly(ADP-ribose) polymerase 1 (PARP-1) acts as an inhibitor of lytic replication. Here, we demonstrate that KSHV downregulated PARP-1 upon reactivation. The viral processivity factor of KSHV (PF-8) interacted with PARP-1 and was sufficient to degrade PARP-1 in a proteasome-dependent manner; this effect was conserved in murine gammaherpesvirus 68. PF-8 knockdown in KSHV-infected cells resulted in reduced lytic replication upon reactivation with increased levels of PARP-1, compared to those in control cells. PF-8 overexpression reduced the levels of the poly(ADP-ribosyl)ated (PARylated) replication and transcription activator (RTA) and further enhanced RTA-mediated transactivation. These results suggest a novel viral mechanism for overcoming the inhibitory effect of a host factor, PARP-1, thereby promoting the lytic replication of gammaherpesvirus. IMPORTANCE: Gammaherpesviruses are important human pathogens, as they are associated with various kinds of tumors and establish latency mainly in host B lymphocytes. Replication and transcription activator (RTA) of Kaposi's sarcoma-associated herpesvirus (KSHV) is a central molecular switch for lytic replication, and its expression is tightly regulated by many host and viral factors. In this study, we investigated a viral strategy to overcome the inhibitory effect of poly(ADP-ribose) polymerase 1 (PARP-1) on RTA's activity. PARP-1, an abundant multifunctional nuclear protein, was downregulated during KSHV reactivation. The viral processivity factor of KSHV (PF-8) directly interacted with PARP-1 and was sufficient and necessary to degrade PARP-1 protein in a proteasome-dependent manner. PF-8 reduced the levels of PARylated RTA and further promoted RTA-mediated transactivation. As this was also conserved in another gammaherpesvirus, murine gammaherpesvirus 68, our results suggest a conserved viral modulation of a host inhibitory factor to facilitate its lytic replication.

Phosphatidylinositol-3-kinase and Akt are required for RIG-I-mediated anti-viral signalling through cross-talk with IPS-1.

Retinoic acid-inducible gene I (RIG-I) is a cytosolic pattern-recognition receptor that recognizes viruses and triggers anti-viral immune responses. Activation of intracellular RIG-I signalling is mediated through interferon-ß (IFN-ß) promoter stimulator-1 (IPS-1), an adaptor of RIG-I, which induces IFN regulatory factor (IRF) 3 activation and type I IFN expression. The phosphatidylinositol-3-kinase (PI3K) and Akt pathway is activated in host immune cells upon viral infection. However, the mechanism as to how they work in RIG-I signalling has not been fully elucidated. Therefore, we investigated the role of PI3K and Akt in the regulation of RIG-I-mediated IRF3 activation and type I IFN expression in macrophages. Our results show that Sendai virus infection, which is recognized by RIG-I, led to IRF3 activation and IFN-ß expression and these responses were attenuated by the PI3K inhibitor (LY294002) and an Akt dominant-negative mutant in the macrophage cell line(RAW264.7). IRF3 phosphorylation and dimerization as well as IFN-ß expression induced by a synthetic RIG-I agonist, short poly(I:C), were suppressed by LY294002 or siRNA-Akt in bone marrow-derived macrophages. Suppression of PI3K and Akt using a dominant-negative mutant and siRNA knockdown resulted in attenuation of IRF3 activation and IFN-ß expression induced by RIG-I itself or its adaptor, IPS-1. Association of Akt with IPS-1 increased with short poly(I:C) stimulation and required the pleckstrin homology domain of Akt and caspase-recruitment domain in IPS-1. Collectively, our results show that PI3K and Akt are required downstream of IPS-1 for RIG-I-mediated anti-viral immune responses. The results describe a novel, interactive relationship between RIG-I downstream signalling molecules resulting in efficient anti-viral immunity.

Murine gammaherpesvirus 68 encoding open reading frame 11 targets TANK binding kinase 1 to negatively regulate the host type I interferon response.

UNLABELLED: Upon viral infection, type I interferons, such as alpha and beta interferon (IFN-α and IFN-ß, respectively), are rapidly induced and activate multiple antiviral genes, thereby serving as the first line of host defense. Many DNA and RNA viruses counteract the host interferon system by modulating the production of IFNs. In this study, we report that murine gammaherpesvirus 68 (MHV-68), a double-stranded DNA virus, encodes open reading frame 11 (ORF11), a novel immune modulator, to block IFN-ß production. ORF11-deficient recombinant viruses induced more IFN-ß production in fibroblast and macrophage cells than the MHV-68 wild type or a marker rescue virus. MHV-68 ORF11 decreased IFN-ß promoter activation by various factors, the signaling of which converges on TBK1-IRF3 activation. MHV-68 ORF11 directly interacted with both overexpressed and endogenous TBK1 but not with IRF3. Physical interactions between ORF11 and endogenous TBK1 were further confirmed during virus replication in fibroblasts using a recombinant virus expressing FLAG-ORF11. ORF11 efficiently reduced interaction between TBK1 and IRF3 and subsequently inhibited activation of IRF3, thereby negatively regulating IFN-ß production. Our domain-mapping study showed that the central domain of ORF11 was responsible for both TBK1 binding and inhibition of IFN-ß induction, while the kinase domain of TBK1 was sufficient for ORF11 binding. Taken together, these results suggest a mechanism underlying inhibition of IFN-ß production by a gammaherpesvirus and highlight the importance of TBK1 in DNA virus replication. IMPORTANCE: Gammaherpesviruses are important human pathogens, as they are associated with various kinds of tumors. Upon virus infection, the type I interferon pathway is activated by a series of signaling molecules and stimulates antiviral gene expression. To subvert such interferon antiviral responses, viruses are equipped with multiple factors that can inhibit its critical steps. In this study, we took an unbiased genomic approach using a mutant library of murine gammaherpesvirus 68 to screen a novel viral immune modulator that negatively regulates the type I interferon pathway and identified ORF11 as a strong candidate. ORF11-deficient virus infection produced more interferon than the wild type in both fibroblasts and macrophages. During virus replication, ORF11 directly bound to TBK1, a key regulatory protein in the interferon pathway, and inhibited TBK1-mediated interferon production. Our results highlight a crucial role of TBK1 in controlling DNA virus infection and a viral strategy to curtail host surveillance.

Plasma proteomic analysis of patients infected with H1N1 influenza virus.

This study profiled the plasma proteins of patients infected by the 2011 H1N1 influenza virus. Differential protein expression was identified in plasma obtained from noninfected control subjects (n = 15) and H1N1-infected subjects (n = 15). Plasma proteins were separated by a 2DE large gel system and identified by nano-ultra performance LC-MS. Western blot assays were performed to validate proteins. Eight plasma proteins were upregulated and six proteins were downregulated among 3316 plasma proteins in the H1N1-infected group as compared with the control group. Of 14 up- and downregulated proteins, nine plasma proteins were validated by Western blot analysis. Putative protein FAM 157A, leucine-rich alpha 2 glycoprotein, serum amyloid A protein, and dual oxidase 1 showed significant differential expression. The identified plasma proteins could be potential candidates for biomarkers of H1N1 influenza viral infection. Further studies are needed to develop these proteins as diagnostic biomarkers.

The virion-associated open reading frame 49 of murine gammaherpesvirus 68 promotes viral replication both in vitro and in vivo as a derepressor of RTA.

Replication and transcription activator (RTA), an immediate-early gene, is a key molecular switch to evoke lytic replication of gammaherpesviruses. Open reading frame 49 (ORF49) is conserved among gammaherpesviruses and shown to cooperate with RTA in regulating virus lytic replication. Here we show a molecular mechanism and in vivo functions of murine gammaherpesvirus 68 (MHV-68 or γHV-68) ORF49. MHV-68 ORF49 was transcribed and translated as a late gene. The ORF49 protein was associated with a virion, interacting with the ORF64 large tegument protein and the ORF25 capsid protein. Moreover, ORF49 directly bound to RTA and its negative cellular regulator, poly(ADP-ribose) polymerase-1 (PARP-1), and disrupted the interactions of RTA and PARP-1. Productive replication of an ORF49-deficient mutant virus (49S) was attenuated in vivo as well as in vitro. Likewise, latent infection was also impaired in the spleen of 49S-infected mice. Taken together, our results suggest that the virion-associated ORF49 protein may promote virus replication both in vitro and in vivo by providing an optimal environment in the early phase of virus infection as a derepressor of RTA.

Liquid-liquid phase separation drives herpesvirus assembly in the cytoplasm.

Liquid-liquid phase separation (LLPS) has emerged as a fundamental mechanism to compartmentalize biomolecules into membraneless organelles. In this issue, Zhou et al. (2022. J. Cell Biol.https://doi.org/10.1083/jcb.202201088), report that MHV-68 ORF52 undergoes LLPS to form cytoplasmic virion assembly compartments, regulating the spatiotemporal compartmentalization of viral components.

Stabilization of RNA G-quadruplexes in the SARS-CoV-2 genome inhibits viral infection via translational suppression.

The G-quadruplex (G4) formed in single-stranded DNAs or RNAs plays a key role in diverse biological processes and is considered as a potential antiviral target. In the genome of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), 25 putative G4-forming sequences are predicted; however, the effects of G4-binding ligands on SARS-CoV-2 replication have not been studied in the context of viral infection. In this study, we investigated whether G4-ligands suppressed SARS-CoV-2 replication and whether their antiviral activity involved stabilization of viral RNA G4s and suppression of viral gene expression. We found that pyridostatin (PDS) suppressed viral gene expression and genome replication as effectively as the RNA polymerase inhibitor remdesivir. Biophysical analyses revealed that the 25 predicted G4s in the SARS-CoV-2 genome formed a parallel G4 structure. In particular, G4-644 and G4-3467 located in the 5' region of ORF1a, formed a G4 structure that could be effectively stabilized by PDS. We also showed that PDS significantly suppressed translation of the reporter genes containing these G4s. Taken together, our results demonstrate that stabilization of RNA G4s by PDS in the SARS-CoV-2 genome inhibits viral infection via translational suppression, highlighting the therapeutic potential of G4-ligands in SARS-CoV-2 infection.

Virus-Host Interplay Between Poly (ADP-Ribose) Polymerase 1 and Oncogenic Gammaherpesviruses.

The gammaherpesviruses, include the Epstein-Barr virus, Kaposi's sarcoma-associated herpesvirus, and murine gammaherpesvirus 68. They establish latent infection in the B lymphocytes and are associated with various lymphoproliferative diseases and tumors. The poly (ADP-ribose) polymerase-1 (PARP1), also called ADP-ribosyltransferase diphtheria-toxin-like 1 (ARTD1) is a nuclear enzyme that catalyzes the transfer of the ADP-ribose moiety to its target proteins and participates in important cellular activities, such as the DNA-damage response, cell death, transcription, chromatin remodeling, and inflammation. In gammaherpesvirus infection, PARP1 acts as a key regulator of the virus life cycle: lytic replication and latency. These viruses also develop various strategies to regulate PARP1, facilitating their replication. This review summarizes the roles of PARP1 in the viral life cycle as well as the viral modulation of host PARP1 activity and discusses the implications. Understanding the interactions between the PARP1 and oncogenic gammaherpesviruses may lead to the identification of effective therapeutic targets for the associated diseases.

Effects of the Antidiabetic Drugs Evogliptin and Sitagliptin on the Immune Function of CD26/DPP4 in Th1 Cells.

This study aimed to investigate whether the antidiabetic drugs dipeptidyl peptidase 4 (DPP4) inhibitors such as evogliptin and sitagliptin affect the membrane DPP4 (mDPP4) enzymatic activity and immune function of T helper1 (Th1) cells in terms of cytokine expression and cell profiles. The mDPP4 enzymatic activity, cytokine expression, and cell profiles, including cell counts, cell viability, DNA synthesis, and apoptosis, were measured in pokeweed mitogen (PWM)-activated CD4+CD26+ H9 Th1 cells with or without the DPP4 inhibitors, evogliptin and sitagliptin. PWM treatment alone strongly stimulated the expression of mDPP4 and cytokines such as interleukin (IL)-2, IL-10, tumor necrosis factor-alpha, interferon-gamma, IL-13, and granulocyte-macrophage colony stimulating factor in the CD4+CD26+ H9 Th1 cells. Evogliptin or sitagliptin treatment potently inhibited mDPP4 activity in a dose-dependent manner but did not affect either the cytokine profile or cell viability in PWM-activated CD4+CD26+ H9 Th1 cells. These results suggest that, following immune stimulation, Th1 cell signaling pathways for cytokine expression function normally after treatment with evogliptin or sitagliptin, which efficiently inhibit mDPP4 enzymatic activity in Th1 cells.