HITS-CLIP analysis uncovers a link between the Kaposi's sarcoma associated herpesvirus ORF57 protein and host pre-mRNA metabolism
ABSTRACT: The Kaposi's sarcoma associated herpesvirus (KSHV) is an oncogenic virus that causes Kaposi's sarcoma, primary effusion lymphoma (PEL), and some forms of multicentric Castleman's disease. The KSHV ORF57 protein is a conserved posttranscriptional regulator of gene expression that is essential for virus replication. ORF57 is multifunctional, but most of its activities are directly linked to its ability to bind RNA. We globally identified virus and host RNAs bound by ORF57 during lytic reactivation in PEL cells using high-throughput sequencing of RNA isolated by crosslinking immunoprecipitation (HITS-CLIP). As expected, ORF57-bound RNA fragments mapped throughout the KSHV genome, including the known ORF57 ligand PAN RNA. In agreement with previously published ChIP results, we observed that ORF57 bound RNAs near the oriLyt regions of the genome. Examination of the host RNA fragments revealed that a subset of the ORF57-bound RNAs was derived from transcript 5´ ends. The position of these 5´-bound fragments correlated closely with the 5´-most exonintron junction of the pre-mRNA. We selected four candidates (BTG1, EGR1, ZFP36, and TNFSF9) and analyzed their pre-mRNA and mRNA levels during lytic phase. Analysis of both steady-state and newly made RNAs revealed that these candidate ORF57-bound pre-mRNAs persisted for longer periods of time throughout infection than control RNAs, consistent with a role for ORF57 in pre-mRNA metabolism. In addition, exogenous expression of ORF57 was sufficient to increase the pre-mRNA levels and, in one case, the mRNA levels of the putative ORF57 targets. These results demonstrate that ORF57 interacts with specific host pre-mRNAs during lytic reactivation and alters their processing, likely by stabilizing pre-mRNAs. These data suggest that ORF57 is involved in modulating host gene expression in addition to KSHV gene expression during lytic reactivation. HITS-CLIP was performed on TREx BCBL-Rta cells 20 hpi using antibodies against ORF57. Three biological replicates were performed.
Project description:The objective of this study was to identify the binding sites of KSHV encoded imemdiate early protein, RTA and early protein, K8 on KSHV genome by chromatin immunoprecipitation assay and sequencing of the DNA bound to RTA and K8 Overall design: KSHV infected, TRExBCBL1-RTA cells were induced with doxycycline for 24h to trigger the lytic reactivation, cells were crosslinked and subjected for chromatin isolation and sonication. ChIP assay was performed using purified antibodies for RTA and K8.
Project description:The objective of this study was to identify the symmetric methylation sites on KSHV genome during latency and lytic reactivation Overall design: KSHV infected iSLKBac16WT cells were induced with doxycycline for 24h to trigger the lytic reactivation, cells were crosslinked and subjected for chromatin isolation and sonication. ChIP assay was performed using specific antibodies.
Project description:The objective of this study was to identify the symmetric methylation sites on KSHV genome during latency and lytic reactivation Overall design: KSHV infected, TRExBCBL1-RTA cells were induced with doxycycline for 24h to trigger the lytic reactivation, cells were crosslinked and subjected for chromatin isolation and sonication. ChIP assay was performed using anti-H4R3sym antibody
Project description:The objective of this study was to identify the symmetric methylation sites on KSHV genome during latency and lytic reactivation Overall design: KSHV infected, TRExBCBL1-RTA or iSLKBac16WT cells were induced with doxycycline for 12h or 24h to trigger the lytic reactivation, cells were crosslinked and subjected for chromatin isolation and sonication. ChIP assay was performed using specific antibodies.
Project description:The objective of this study was to identify the symmetric methylation sites on KSHV genome during latency and lytic reactivation Overall design: KSHV infected, TRExBCBL1-RTA cells were induced with doxycycline for 12h to trigger the lytic reactivation, cells were crosslinked and subjected for chromatin isolation and sonication. ChIP assay was performed using anti-H4R3sym antibody, Control IgG antibody, or Histone H4 antibody.
Project description:Lytic reactivation from latency is critical for the pathogenesis of KSHV. We previously demonstrated that the 691 amino acid KSHV Rta transcriptional transactivator is necessary and sufficient to reactivate the virus from latency. Viral lytic cycle genes, including those expressing additional transactivators and putative oncogenes, are induced in a cascade fashion following Rta expression. In this study, we sought to define Rta’s direct targets during reactivation by generating a conditionally nuclear variant of Rta. WT Rta protein is constitutively localized to cell nuclei, and contains two putative nuclear localization signals (NLSs). Only one NLS (NLS-2; aa 516-530) was required for nuclear localization of Rta, and relocalized eGFP exclusively to cell nuclei. Analyses of Rta NLS mutants demonstrated that proper nuclear localization of Rta was required for transactivation and stimulation of viral reactivation. Fusion of Rta_NLS-1,2 to the hormone binding domain of the murine estrogen receptor generated a variant of Rta whose nuclear localization and ability to transactivate and induce reactivation were tightly controlled post-translationally by the synthetic hormone tamoxifen. We used this strategy in KSHV-infected cells treated with protein synthesis inhibitors to identify direct transcriptional targets of Rta. Only eight KSHV genes were activated by Rta in the absence of de novo protein synthesis. These direct transcriptional targets of Rta were transactivated to different magnitudes, and included the genes nut-1/PAN, ORF57/Mta, ORF56/Primase, K2/vIL-6, ORF37/SOX, K14/vOX, K9/vIRF1, and ORF52. Our data suggest that induction of most of the KSHV lytic cycle genes requires additional protein expression post-Rta. Keywords: Comparative transcriptome analysis by oligonucleotide microarray Overall design: KSHV infected cells were transfected with empty expression vector or with vector expressing RtadeltaNLS1,2-ER (RtadeltaNLS1,2 fused to murine hormone binding domain of estrogen receptor (ER)). Cells were treated with 4-hydroxytamoxifen (4-OHT) to induce nuclear re-localization of Rta fusion protein. Cells were pre-treated with hygromycin to eliminate de novo cellular and viral protein expression. Direct transcriptional targets of Rta were identified by comparing Rta +/- 4-OHT to vector (negative control) +/- 4-OHT.
Project description:Chromatin-organizing factors, like CTCF and cohesins, have been implicated in the control of complex viral regulatory programs. We investigated the role of CTCF and cohesin in the control of the latent to lytic switch for Kaposi's Sarcoma-Associated Herpesvirus (KSHV). We found that cohesin subunits, but not CTCF, were required for the repression of KSHV immediate early gene transcription. Depletion of cohesin subunits Rad21, SMC1, or SMC3 resulted in lytic cycle gene transcription and viral DNA replication. In contrast, depletion of CTCF failed to induce lytic transcription or DNA replication. ChiP-Seq analysis revealed that cohesins and CTCF bound to several sites within the immediate early control regions for ORF50 and more distal 5' sites that also regulate the divergently transcribed ORF45-46-47 gene cluster. Rad21 depletion led to a robust increase in ORF45 and ORF47 transcripts, with similar kinetics to that observed with chemical induction by sodium butyrate. During latency, the chromatin between the ORF45 and ORF50 transcription start sites was enriched in histone H3K4me3 with elevated H3K9ac at the ORF45 promoter and elevated H3K27me3 at the ORF50 promoter. A paused form of RNA pol II was loosely associated with the ORF45 promoter region during latency, but was converted to an active elongating form upon reactivation induced by Rad21 depletion. Butyrate-induced transcription of ORF45 and ORF47 was resistant to cyclohexamide, suggesting that these genes have immediate early features similar to ORF50. Butyrate-treatment caused the rapid dissociation of cohesins and loss of CTCF binding at the immediate early gene locus, suggesting that cohesins may be a direct target of butyrate-mediated lytic induction. Our findings implicate cohesins as a major repressor of KSHV lytic gene activation, and function coordinately with CTCF to regulate the switch between latent and lytic gene activity. Study of chromatin-organizing factors, like CTCF and cohesins.
Project description:The establishment of latency is an essential step for the life-long persistent infection and pathogenesis of Kaposi’s sarcoma-associated herpesvirus (KSHV). While the KSHV genome is chromatin-free in the virions, the viral DNA in latently infected cells has a chromatin structure that is characterized by a specific pattern of activating and repressive histone modifications that ultimately promote latent gene expression while suppressing lytic gene expression. To investigate the molecular events involved in the establishment of the latent chromatin structure during the pre-latency phase of KSHV infection, we performed a comprehensive epigenetic study to analyze the recruitment of chromatin regulatory factors onto the KSHV genome at various time-points following de novo infection of SLK and TIME cells. This showed that the KSHV genome undergoes a biphasic chromatinization following de novo infection. Initially, a transcriptionally active chromatin (euchromatin), characterized by high levels of the H3K4me3 and acetylated H3K27 (H3K27ac) activating histone marks, was deposited on the viral episome and was accompanied by the temporary induction of a limited number of lytic genes. Interestingly, transient expression of the RTA protein facilitated the increases of H3K4me3 and H3K27ac occupancy on the KSHV episome during de novo infection. Between 24-72 hours post-infection, as the levels of these activating histone marks declined on the KSHV genome, the levels of the repressive H3K27me3 and H2AK119ub histone marks increased concomitantly with the decline of lytic gene expression. Importantly, this transition to heterochromatin was dependent on both the Polycomb Repressive Complex 2 and 1. In contrast, upon infection of human gingiva-derived epithelial cells, the KSHV genome underwent a continuously transcription-active euchromatinization, resulting in efficient lytic gene expression. Our data demonstrate that the KSHV genome undergoes a temporally ordered biphasic euchromatin-to-heterochromatin transition in endothelial cells, leading to latent infection, whereas KSHV preferentially adopts a transcriptionally active euchromatin in oral epithelial cells, resulting in lytic gene expression. Our results suggest that the differential epigenetic modification of the KSHV genome in distinct cell types is a potential determining factor for latent infection vs. lytic replication of KSHV. Please see above. 16 hybridizations: ChIP and Input DNA
Project description:Primary effusion lymphoma (PEL) is an aggressive subtype of non-Hodgkin lymphoma caused by Kaposi's sarcoma-associated herpesvirus (KSHV) infection. Currently, treatment options for patients with PEL are limited. Oncolytic viruses have been engineered as anticancer agents and have recently shown increased therapeutic promise. Similarly, lytic activation of endogenous viruses from latently infected tumor cells can also be applied as a cancer therapy. In theory, such a therapeutic strategy would induce oncolysis by viral replication, while simultaneously stimulating an immune response to viral lytic cycle antigens. We examined the combination of the FDA-approved drug ingenol-3-angelate (PEP005) with epigenetic drugs as a rational therapeutic approach for KSHV-mediated malignancies. JQ1, a bromodomain and extra terminal (BET) protein inhibitor, in combination with PEP005, not only robustly induced KSHV lytic replication, but also inhibited IL6 production from PEL cells. Using the dosages of these agents that was found to be effective in reactivating HIV (as a means to clear latent virus with highly active antiretroviral therapy), we were able to inhibit PEL growth in vitro and delay tumor growth in a PEL xenograft tumor model. KSHV reactivation was mediated by activation of NF-kB pathway by PEP005, which led to increased occupancy of RNA polymerase II onto the KSHV 33 genome. RNA-sequencing analysis further revealed cellular targets of PEP005, JQ1, and the synergistic effects of both. Thus, combination of PEP005 with a BET inhibitor may be considered as a rational therapeutic approach for the treatment of PEL. Overall design: The goal of these studies was to perform genome-wide mapping of BRD4 binding sites across the KSHV genome during viral reactivation using ChIP-Sequencing (ChIP-Seq). This was performed in the context of the BCBL-1 cell line model, which is derived from a KSHV-infected human primary effusion lymphoma (PEL) and contains latent KSHV genomes. For these studies, we utilized an engineered subline, referred to as TREx-K-Rta BCBL-1, which contains a Tetracycline/Doxycycline (Dox)-inducible Flagx3- and HAx3-tagged K-Rta expression cassette. Viral reactivation is then stimulated by inducing K-Rta expression in individual TREx-K-Rta BCBL-1 cultures by treatment with Dox for 24 hours. Following treatment, the cells were then processed for ChIP-Seq analyses by formaldehyde cross-linking, chromatin solubilization, and chromatin immunoprecipitation (ChIP) with anti-BRD4 antibody. Subsequently, DNA was isolated from the ChIP and total chromatin (Input) samples, and followed by library preparation and next-generation sequencing (NGS).
Project description:Purpose: Kaposi’s sarcoma associated-herpesvirus (KSHV) causes several hyperproliferative disorders, including Kaposi’s sarcoma, primary effusion lymphoma and multicentric Castleman’s disease. KSHV encodes for a number of microRNAs (miRNAs), and KSHV infection can affect the expression of cellular miRNAs. Hypoxia has been shown to induce KSHV reactivation, directly induce several KSHV lytic genes, and also induce the most abundant latent viral protein, LANA. Also, several KSHV proteins can stabilize and increase the cellular levels of hypoxia-inducible factor (HIF-1α). However, the degree to which hypoxic pathways are utilized by KSHV has yet to be determined. Methods: We investigated the interplay between hypoxia and KSHV infection by comparing the 31effects of hypoxia and KSHV infection on miRNA and mRNA expression, and by examining the 32effects of hypoxia on uninfected and KSHV-infected cells. This was accomplished using next-33generation sequencing (NGS), qRT-PCR, Taqman assays, and pathway analysis. Results: NGS analysis of human mRNAs revealed striking similarities (~34%) between the transcriptomic response to hypoxia and the transcriptomic response to KSHV infection. Additionally, hsa-miR-210, a key hypoxia-inducible miRNA with pro-angiogenic and anti-apoptotic properties, was found significantly up-regulated by both KSHV infection and hypoxia using Taqman assays. Finally, KSHV infected cells differed somewhat in their response to hypoxia compared to KSHV-uninfected controls. Conclusions: These results demonstrate that KSHV harnesses a part of the hypoxic cellular response and induces miR-210 up-regulation. The understanding of how these miRNAs, genes and pathways are regulated by HIF-1α and KSHV infection are essential to a better understanding of the biology of KSHV-associated diseases. Overall design: 6 samples analyzed. Two experimental conditions: hypoxic uninfected cells (SLK cells) and hypoxic chronically KSHV-infected cells (SLKK cells) (n=3). Two sequencing platforms: microRNA-Seq and mRNA-Seq.