scholarly journals Signaling Cascades Triggered by Bacterial Metabolic End Products during Reactivation of Kaposi's Sarcoma-Associated Herpesvirus

2007 ◽  
Vol 81 (11) ◽  
pp. 6032-6042 ◽  
Author(s):  
T. L. Morris ◽  
R. R. Arnold ◽  
J. Webster-Cyriaque
Keyword(s):  
Protein Kinase ◽  
Kaposi's Sarcoma ◽  
Mapk Pathway ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Viral Reactivation ◽  
Mitogen Activated Protein Kinase ◽  
End Products ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT The present studies explore the role of polymicrobial infection in the reactivation of Kaposi's sarcoma-associated herpesvirus (KSHV) and analyze signaling pathways activated upon this induction. We hypothesized that activation of the cellular stress-activated mitogen-activated protein kinase (MAPK) p38 pathway would play a key role in the bacterium-mediated disruption of viral latency similar to that of previously reported results obtained with other inducers of gammaherpesvirus lytic replication. KSHV within infected BCBL-1 cells was induced to replicate following exposure to metabolic end products from gram-negative or -positive bacteria that were then simultaneously exposed to specific inhibitors of signal transduction pathways. We have determined that bacterium-mediated induction of lytic KSHV infection is significantly reduced by the inhibition of the p38 MAPK pathway. In contrast, inhibition of the phosphatidylinositol 3-kinase pathway did not impair induction of lytic replication or p38 phosphorylation. Protein kinase C, though activated, was not the major pathway used for bacterium-induced viral reactivation. Furthermore, hyperacetylation of histones 3 and 4 was detected. Collectively, our results show that metabolic end products from these pathogens induce lytic replication of KSHV in BCBL-1 cells primarily via the activation of a stress-activated MAPK pathway. Importantly, we demonstrate for the first time a mechanism by which polymicrobial bacterial infections result in KSHV reactivation and pathogenesis.

scholarly journals Activation of p90 Ribosomal S6 Kinase by ORF45 of Kaposi's Sarcoma-Associated Herpesvirus and Its Role in Viral Lytic Replication

2007 ◽  
Vol 82 (4) ◽  
pp. 1838-1850 ◽  
Author(s):  
Ersheng Kuang ◽  
Qiyi Tang ◽  
Gerd G. Maul ◽  
Fanxiu Zhu
Keyword(s):  
Kaposi's Sarcoma ◽  
Mapk Pathway ◽  
Specific Inhibitor ◽  
Kaposi’S Sarcoma ◽  
Mapk Signaling ◽  
Lytic Replication ◽  
Mitogen Activated Protein Kinase ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Ribosomal S6 Kinase ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT The extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) pathway is essential for infection by a variety of viruses. The p90 ribosomal S6 kinases (RSKs) are direct substrates of ERK and functional mediators of ERK MAPK signaling, but their roles in viral infection have never been examined. We demonstrate that ORF45 of Kaposi's sarcoma-associated herpesvirus (KSHV) interacts with RSK1 and RSK2 and strongly stimulates their kinase activities. The activation of RSK by ORF45 is correlated with ERK activation but does not require MEK. We further demonstrate that RSK1/RSK2 is activated during KSHV primary infection and reactivation from latency; a subset of RSK1/RSK2 is present in the viral replication compartment in the nucleus. Depletion of RSK1/RSK2 by small interfering RNA or the specific inhibitor BI-D1870 suppresses KSHV lytic gene expression and progeny virion production, suggesting an essential role of RSK1/RSK2 in KSHV lytic replication.

scholarly journals Kaposi's Sarcoma-Associated Herpesvirus Transactivator RTA Promotes Degradation of the Repressors To Regulate Viral Lytic Replication

2008 ◽  
Vol 82 (7) ◽  
pp. 3590-3603 ◽  
Author(s):  
Zhilong Yang ◽  
Zhangcai Yan ◽  
Charles Wood
Keyword(s):  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Viral Reactivation ◽  
Common Mechanism ◽  
Ubiquitin Proteasome Pathway ◽  
Ubiquitin Proteasome ◽  
Proteasome Pathway ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8 (KSHV/HHV-8) RTA is an important protein involved in the induction of KSHV lytic replication from latency through activation of the lytic cascade. A number of cellular and viral proteins, including K-RBP, have been found to repress RTA-mediated transactivation and KSHV lytic replication. However, it is unclear as to how RTA overcomes the suppression during lytic reactivation. In this study, we found that RTA can induce K-RBP degradation through the ubiquitin-proteasome pathway and that two regions in RTA are responsible. Moreover, we found that RTA can promote the degradation of several other RTA repressors. RTA mutants that are defective in inducing K-RBP degradation cannot activate RTA responsive promoter as efficiently as wild-type RTA. Interference of the ubiquitin-proteasome pathway affected RTA-mediated transactivation and KSHV reactivation from latency. Our results suggest that KSHV RTA can stimulate the turnover of repressors to modulate viral reactivation. Since herpes simplex virus type 1 transactivator ICP0 and human cytomegalovirus transactivator pp71 also stimulate the degradation of cellular silencers, it is possible that the promotion of silencer degradation by viral transactivators may be a common mechanism for regulating the lytic replication of herpesviruses.

scholarly journals Effects of the NEDD8-Activating Enzyme Inhibitor MLN4924 on Lytic Reactivation of Kaposi's Sarcoma-Associated Herpesvirus

2017 ◽  
Vol 91 (19) ◽  
Author(s):  
Pey-Jium Chang ◽  
Lee-Wen Chen ◽  
Li-Yu Chen ◽  
Chien-Hui Hung ◽  
Ying-Ju Shih ◽  
...  
Keyword(s):  
Transcriptional Regulation ◽  
Cell Lines ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Lytic Cycle ◽  
Viral Reactivation ◽  
Lytic Reactivation ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT The switch of Kaposi's sarcoma-associated herpesvirus (KSHV) from latency to lytic replication is a key event for viral dissemination and pathogenesis. MLN4924, a novel neddylation inhibitor, reportedly causes the onset of KSHV reactivation but impairs later phases of the viral lytic program in infected cells. Thus far, the molecular mechanism involved in the modulation of the KSHV lytic cycle by MLN4924 is not yet fully understood. Here, we confirmed that treatment of different KSHV-infected primary effusion lymphoma (PEL) cell lines with MLN4924 substantially induces viral lytic protein expression. Due to the key role of the virally encoded ORF50 protein in the latent-to-lytic switch, we investigated its transcriptional regulation by MLN4924. We found that MLN4924 activates the ORF50 promoter (ORF50p) in KSHV-positive cells (but not in KSHV-negative cells), and the RBP-Jκ-binding elements within the promoter are critically required for MLN4924 responsiveness. In KSHV-negative cells, reactivation of the ORF50 promoter by MLN4924 requires the presence of the latency-associated nuclear antigen (LANA). Under such a condition, LANA acts as a repressor to block the ORF50p activity, whereas MLN4924 treatment relieves LANA-mediated repression. Importantly, we showed that LANA is a neddylated protein and can be deneddylated by MLN4924. On the other hand, we revealed that MLN4924 exhibits concentration-dependent biphasic effects on 12-O-tetradecanoylphorbol-13-acetate (TPA)- or sodium butyrate (SB)-induced viral reactivation in PEL cell lines. In other words, low concentrations of MLN4924 promote activation of TPA- or SB-mediated viral reactivation, whereas high concentrations of MLN4924, conversely, inhibit the progression of TPA- or SB-mediated viral lytic program. IMPORTANCE MLN4924 is a neddylation (NEDD8 modification) inhibitor, which currently acts as an anti-cancer drug in clinical trials. Although MLN4924 has been reported to trigger KSHV reactivation, many aspects regarding the action of MLN4924 in regulating the KSHV lytic cycle are not fully understood. Since the KSHV ORF50 protein is the key regulator of viral lytic reactivation, we focus on its transcriptional regulation by MLN4924. We here show that activation of the ORF50 gene by MLN4924 involves the relief of LANA-mediated transcriptional repression. Importantly, we find that LANA is a neddylated protein. To our knowledge, this is the first report showing that neddylation occurs in viral proteins. Additionally, we provide evidence that different concentrations of MLN4924 have opposite effects on TPA-mediated or SB-mediated KSHV lytic cycle activation. Therefore, in clinical application, we propose that MLN4924 needs to be used with caution in combination therapy to treat KSHV-positive subjects.

scholarly journals Suppression of Kaposi's Sarcoma-Associated Herpesvirus Infection and Replication by 5′-AMP-Activated Protein Kinase

2016 ◽  
Vol 90 (14) ◽  
pp. 6515-6525 ◽  
Author(s):  
Fan Cheng ◽  
Meilan He ◽  
Jae U. Jung ◽  
Chun Lu ◽  
Shou-Jiang Gao
Keyword(s):  
Protein Kinase ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Energy Sensor ◽  
Ampk Activity ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus ◽  
Amp Activated Protein Kinase ◽  
Lytic Genes

ABSTRACTThe host intracellular antiviral restriction factors inhibit viral infection and replication. The 5′-AMP-activated protein kinase (AMPK) is a cellular energy sensor regulating metabolic homeostasis. Activated AMPK inhibits the replication of numerous RNA viruses but enhances the entry of vaccinia virus. However, the role of AMPK in herpesvirus infection is unclear. In this study, we showed that the constitutive AMPK activity restricted Kaposi's sarcoma-associated herpesvirus (KSHV) lytic replication in primary human umbilical vein endothelial cells while KSHV infection did not markedly affect the endogenous AMPK activity. Knockdown of the AMPKα1 considerably enhanced the expression of viral lytic genes and the production of infectious virions, while overexpression of a constitutively active AMPK had the opposite effects. Accordingly, an AMPK inhibitor, compound C, augmented viral lytic gene expressions and virion productions but an AMPK agonist, 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), suppressed both. Furthermore, a common diabetes drug, metformin, which carries an AMPK-agonistic activity, drastically inhibited the expression of viral lytic genes and the production of infectious virions, suggesting the use of metformin as a therapeutic agent for KSHV infection and replication. Together, these results identify the host AMPK as a KSHV restriction factor that can serve as a potential therapeutic target.IMPORTANCEHost cells encode specific proteins to restrict viral infection and replication. Kaposi's sarcoma-associated herpesvirus (KSHV) is a human tumor virus associated with several cancers. In this study, we have identified 5′-AMP-activated protein kinase (AMPK), a cellular energy sensor, as a restriction factor of KSHV lytic replication during primary infection. Activation of AMPK suppresses, while inhibition of AMPK enhances, KSHV lytic replication by regulating the expression of viral genes. AICAR and metformin, both of which are AMPK agonists currently used in clinics for the treatment of conditions associated with metabolic disorders, inhibit KSHV lytic replication. Thus, our work has identified AMPK as a potential therapeutic target and AICAR and metformin as potential therapeutic agents for KSHV-associated cancers.

scholarly journals An essential role of ERK signalling in TPA-induced reactivation of Kaposi's sarcoma-associated herpesvirus

2006 ◽  
Vol 87 (4) ◽  
pp. 795-802 ◽  
Author(s):  
Adina Cohen ◽  
Chaya Brodie ◽  
Ronit Sarid
Keyword(s):  
Protein Kinase ◽  
Kaposi's Sarcoma ◽  
Primary Effusion Lymphoma ◽  
Kaposi’S Sarcoma ◽  
Mitogen Activated Protein Kinase ◽  
Potent Inducer ◽  
Erk Phosphorylation ◽  
Gf 109203X ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV) is implicated causally in the development of several human malignancies, including primary effusion lymphoma (PEL). PEL cells serve as tools for KSHV research, as most of them are latently infected and allow lytic virus replication in response to various stimuli. 12-O-Tetradecanoyl-phorbol-13-acetate (TPA) is the most potent inducer of lytic KSHV reactivation; nevertheless, the exact mechanism by which it induces reactivation remains unknown. It has previously been reported by our group that the protein kinase C (PKC) δ isoform plays a crucial role in TPA-mediated KSHV reactivation. Here, the activation pathway was dissected and it was demonstrated that TPA induces KSHV reactivation via stimulation of the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway. Western blot analysis revealed a rapid phosphorylation of ERK1/2. Cells treated with MAPK/ERK inhibitors before TPA addition demonstrated repression of ERK1/2 phosphorylation, which was associated with a block of KSHV lytic-gene expression. This inhibition prevented c-Fos accumulation, yet increased c-Jun phosphorylation. Similar results were obtained in response to rottlerin, a selective PKCδ inhibitor. Notably, the PKC inhibitor GF 109203X reduced ERK1/2 phosphorylation, c-Fos accumulation, c-Jun phosphorylation and KSHV reactivation. It is proposed that TPA induces KSHV reactivation through at least two arms. The first involves PKCδ, ERK phosphorylation and c-Fos accumulation, whilst the second requires another PKC isoform that induces the phosphorylation of c-Jun. c-Fos and c-Jun jointly form an active AP-1 complex, which functions to activate the lytic cascade of KSHV.

scholarly journals Screening of the Human Kinome Identifies MSK1/2-CREB1 as an Essential Pathway Mediating Kaposi's Sarcoma-Associated Herpesvirus Lytic Replication during Primary Infection

2015 ◽  
Vol 89 (18) ◽  
pp. 9262-9280 ◽  
Author(s):  
Fan Cheng ◽  
Tanvee Vinod Sawant ◽  
Ke Lan ◽  
Chun Lu ◽  
Jae U. Jung ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Protein Kinase ◽  
Primary Infection ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Kshv Infection ◽  
Cellular Pathways ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACTViruses often hijack cellular pathways to facilitate infection and replication. Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic gammaherpesvirus etiologically associated with Kaposi's sarcoma, a vascular tumor of endothelial cells. Despite intensive studies, cellular pathways mediating KSHV infection and replication are still not well defined. Using an antibody array approach, we examined cellular proteins phosphorylated during primary KSHV infection of primary human umbilical vein endothelial cells. Enrichment analysis identified integrin/mitogen-activated protein kinase (integrin/MAPK), insulin/epidermal growth factor receptor (insulin/EGFR), and JAK/STAT as the activated networks during primary KSHV infection. The transcriptional factor CREB1 (cyclic AMP [cAMP]-responsive element-binding protein 1) had the strongest increase in phosphorylation. While knockdown of CREB1 had no effect on KSHV entry and trafficking, it drastically reduced the expression of lytic transcripts and proteins and the production of infectious virions. Chemical activation of CREB1 significantly enhanced viral lytic replication. In contrast, CREB1 neither influenced the expression of the latent gene LANA nor affected KSHV infectivity. Mechanistically, CREB1 was not activated through the classic cAMP/protein kinase A (cAMP/PKA) pathway or via the AKT, MK2, and RSK pathways. Rather, CREB1 was activated by the mitogen- and stress-activated protein kinases 1 and 2 (MSK1/2). Consequently, chemical inhibition or knockdown of MSKs significantly inhibited the KSHV lytic replication program; however, it had a minimal effect on LANA expression and KSHV infectivity. Together, these results identify the MSK1/2-CREB1 proteins as novel essential effectors of KSHV lytic replication during primary infection. The differential effect of the MSK1/2-CREB1 pathway on the expression of viral latent and lytic genes might control the robustness of viral lytic replication, and therefore the KSHV replication program, during primary infection.IMPORTANCEKaposi's sarcoma-associated herpesvirus (KSHV) is a human tumor virus associated with several cancers. Through genome-wide kinase screening, we found that KSHV activates the MSK1/2-CREB1 pathway during primary infection and that it depends on this pathway for viral lytic replication. Inhibition of this pathway blocks KSHV lytic replication. These results illustrate a mechanism by which KSHV hijacks a cellular pathway for its replication, and they identify a potential therapeutic target.

scholarly journals Discovery of a Coregulatory Interaction between Kaposi's Sarcoma-Associated Herpesvirus ORF45 and the Viral Protein Kinase ORF36

2016 ◽  
Vol 90 (13) ◽  
pp. 5953-5964 ◽  
Author(s):  
Denis Avey ◽  
Sarah Tepper ◽  
Benjamin Pifer ◽  
Amritpal Bahga ◽  
Hunter Williams ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Viral Protein ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Viral Protein Kinase ◽  
Important Interaction ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACTKaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of three human malignancies. KSHV ORF36 encodes a serine/threonine viral protein kinase, which is conserved throughout all herpesviruses. Although several studies have identified the viral and cellular substrates of conserved herpesvirus protein kinases (CHPKs), the precise functions of KSHV ORF36 during lytic replication remain elusive. Here, we report that ORF36 interacts with another lytic protein, ORF45, in a manner dependent on ORF36 kinase activity. We mapped the regions of ORF36 and ORF45 involved in the binding. Their association appears to be mediated by electrostatic interactions, since deletion of either the highly basic N terminus of ORF36 or an acidic patch of ORF45 abolished the binding. In addition, the dephosphorylation of ORF45 protein dramatically reduced its association with ORF36. Importantly, ORF45 enhances both the stability and kinase activity of ORF36. Consistent with previous studies of CHPK homologs, we detected ORF36 protein in extracellular virions. To investigate the roles of ORF36 in the context of KSHV lytic replication, we used bacterial artificial chromosome mutagenesis to engineer both ORF36-null and kinase-dead mutants. We found that ORF36-null/mutant virions are moderately defective in viral particle production and are further deficient in primary infection. In summary, our results uncover a functionally important interaction between ORF36 and ORF45 and indicate a significant role of ORF36 in the production of infectious progeny virions.IMPORTANCEKaposi's sarcoma-associated herpesvirus (KSHV) is a human tumor virus with a significant public health burden. KSHV ORF36 encodes a serine/threonine viral protein kinase, whose functions throughout the viral life cycle have not been elucidated. Here, we report that ORF36 interacts with another KSHV protein, ORF45. We mapped the regions of ORF36 and ORF45 involved in their association and further characterized the consequences of this interaction. We engineered ORF36 mutant viruses in order to investigate the functional roles of ORF36 in the context of KSHV lytic replication, and we confirmed that ORF36 is a component of KSHV virions. Moreover, we found that ORF36 mutants are defective in virion production and primary infection. In summary, we discovered and characterized a functionally important interaction between KSHV ORF36 and ORF45, and our results suggest a significant role of ORF36 in the production of infectious progeny virions, a process critical for KSHV pathogenesis.

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