Systematic Identification of Cellular Signals Reactivating Kaposi Sarcoma–Associated Herpesvirus

Department of Laboratory Medicine, University of Washington Seattle, Seattle, Washington, United States
PLoS Pathogens (Impact Factor: 7.56). 03/2007; 3(3):e44. DOI: 10.1371/journal.ppat.0030044
Source: PubMed


The herpesvirus life cycle has two distinct phases: latency and lytic replication. The balance between these two phases is critical for viral pathogenesis. It is believed that cellular signals regulate the switch from latency to lytic replication. To systematically evaluate the cellular signals regulating this reactivation process in Kaposi sarcoma-associated herpesvirus, the effects of 26,000 full-length cDNA expression constructs on viral reactivation were individually assessed in primary effusion lymphoma-derived cells that harbor the latent virus. A group of diverse cellular signaling proteins were identified and validated in their effect of inducing viral lytic gene expression from the latent viral genome. The results suggest that multiple cellular signaling pathways can reactivate the virus in a genetically homogeneous cell population. Further analysis revealed that the Raf/MEK/ERK/Ets-1 pathway mediates Ras-induced reactivation. The same pathway also mediates spontaneous reactivation, which sets the first example to our knowledge of a specific cellular pathway being studied in the spontaneous reactivation process. Our study provides a functional genomic approach to systematically identify the cellular signals regulating the herpesvirus life cycle, thus facilitating better understanding of a fundamental issue in virology and identifying novel therapeutic targets.

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Available from: Ting-Ting Wu
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    • "The establishment of persistent infection depends on the activation of these cellular signaling pathways (Walia et al., 2005; Pan et al., 2006). Similarly, reactivation of latently infected cells leads to the activation of MAPK pathways (Ford et al., 2006; Yu et al., 2007; Xie et al., 2008). KSHV LANA is involved in the activation of the serum response element and MAPK pathways through its interaction with a mediator complex (Roupelieva et al., 2010). "
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    ABSTRACT: Kaposi’ssarcomaassociatedherpesvirus(KSHV)orhumanherpesvirus8(HHV8)isamajoretiologicalagentformultipleseveremalignanciesinimmune-compromisedpatients.KSHVestablisheslifetimepersistenceintheinfectedindividualsanddisplaystwodistinctlifecycles,generallyaprolongedpassivelatent,andashortproductiveorlyticcycle.Duringlatentphase,theviralepisomeistetheredtothehostchromosomeandreplicatesonceduringeverycelldivision.Latency-associatednuclearantigen(LANA)isapredominantmultifunctionalnuclearproteinexpressedduringlatency,whichplaysacentralroleinepisometethering,replicationandperpetualsegregationoftheepisomesduringcelldivision.LANAbindscooperativelytoLANAbindingsites(LBS)withintheterminalrepeat(TR)regionoftheviralepisomeaswellastothecellularnucleosomalproteinstotetherviralepisometothehostchromosome.LANAhasbeenshowntomodulatemultiplecellularsignalingpathwaysandrecruitsvariouscellularproteinssuchaschromatinmodifyingenzymes,replicationfactors,transcriptionfactors,andcellularmitoticframeworktomaintainasuccessfullatentinfection.Although,manyotherregionswithintheKSHVgenomecaninitiatereplication,KSHVTRisimportantforlatentDNAreplicationandpossiblesegregationofthereplicatedepisomes.BindingofLANAtoLBSfavorstherecruitmentofvariousreplicationfactorstoinitiateLANAdependentDNAreplication.Inthisreview,wediscussthemolecularmechanismsrelevanttoKSHVgenomereplication,segregation,andmaintenanceoflatency.
    Full-text · Article · Feb 2016 · Frontiers in Microbiology
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    • "In this study, transfection of cells with egr-1/pCDNA3.1(+) resulted in a significant increase in virus-encoded ORF50 transcription followed by the expression of early-lytic ORF59 protein and late-lytic gene (ORF8) encoding gB (Fig. 4B, C); all of which are indicators of an active lytic replication of KSHV [12], [28], [29]. MAPK signaling was observed to regulate Egr-1 expression in cells transfected with egr-1/pCDNA3.1(+) "
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    ABSTRACT: In the field of herpesvirus research, the exact molecular mechanism by which such viruses reactivate from latency remains elusive. Kaposi's sarcoma-associated herpesvirus (KSHV) primarily exists in a latent state, while only 1-3% of cells support lytic infection at any specific time. KSHV reactivation from latency is an exceedingly intricate process mediated by the integration of viral and cellular factors. Previously, our lab has described early growth response-1 (Egr-1) as an essential component for the KSHV reactivation process via its ability to mediate transcription of KSHV ORF50, the gene encoding for replication and transcription activator (RTA), a viral component known to control the switch from latent to lytic infection. In here, electrophoretic mobility shift assays (EMSA) and chromatin immunoprecipitation (ChIP) experiments revealed that Egr-1 binds KSHV ORF50 promoter (ORF50P) in at least two different GC-rich binding domains. Expression profiles of cellular egr-1 and KSHV-encoded ORF50 follow a similar pattern during de novo KSHV infection. Over-expressing Egr-1, a signaling component downstream of Raf>MEK>ERK1/2, in KSHV-infected cells activates KSHV lytic replication. Through performing more physiologically relevant experiments, we analyzed the effect of a dietary supplement containing resveratrol on KSHV-infected cells. Our results, for the first time, demonstrate resveratrol to act in lowering ERK1/2 activity and expression of Egr-1 in KSHV-infected cells, resulting in the suppression of virus reactivation from latency. Taken together, these findings will undoubtedly contribute to future studies on not only combating KSHV related disease conditions, but also on other herpesviruses-induced pathogenesis.
    Full-text · Article · Mar 2012 · PLoS ONE
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    • "Cohen et al. also showed an essential role of ERK signaling in TPA-induced reactivation of KSHV by using MEK-specific inhibitors [43]. Yu et al. revealed that Raf/MEK/ERK pathway mediated Ras-induced KSHV reactivation and the same pathway also mediated TPA-induced KSHV reactivation and spontaneous reactivation in PEL cells, by screening expression of a mammalian cDNA library [44]. A more recent study also showed that alloferon inhibited lytic reactivation of KSHV through down-regulation of ERK [45]. "
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    ABSTRACT: Kaposi's sarcoma-associated herpesvirus (KSHV) is causally linked to several acquired immunodeficiency syndrome-related malignancies, including Kaposi's sarcoma (KS), primary effusion lymphoma (PEL) and a subset of multicentric Castleman's disease. Regulation of viral lytic replication is critical to the initiation and progression of KS. Recently, we reported that herpes simplex virus type 1 (HSV-1) was an important cofactor that activated lytic cycle replication of KSHV. Here, we further investigated the possible signal pathways involved in HSV-1-induced reactivation of KSHV. By transfecting a series of dominant negative mutants and protein expressing constructs and using pharmacologic inhibitors, we found that either Janus kinase 1 (JAK1)/signal transducer and activator of transcription 3 (STAT3) or JAK1/STAT6 signaling failed to regulate HSV-1-induced KSHV replication. However, HSV-1 infection of BCBL-1 cells activated phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB, also called AKT) pathway and inactivated phosphatase and tensin homologue deleted on chromosome ten (PTEN) and glycogen synthase kinase-3β (GSK-3β). PTEN/PI3K/AKT/GSK-3β pathway was found to be involved in HSV-1-induced KSHV reactivation. Additionally, extracellular signal-regulated protein kinase (ERK) mitogen-activated protein kinase (MAPK) pathway also partially contributed to HSV-1-induced KSHV replication. HSV-1 infection stimulated PI3K/AKT and ERK MAPK signaling pathways that in turn contributed to KSHV reactivation, which provided further insights into the molecular mechanism controlling KSHV lytic replication, particularly in the context of HSV-1 and KSHV co-infection.
    Full-text · Article · Oct 2011 · BMC Microbiology
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