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Signal transducer and activator of transcription 3 limits Epstein-Barr virus lytic activation in B lymphocytes.

ABSTRACT: Lytic activation of Epstein-Barr virus (EBV) is central to its life cycle and to most EBV-related diseases. However, not every EBV-infected B cell is susceptible to lytic activation. This lack of uniform susceptibility to lytic activation also directly impacts the success of viral oncolytic therapy for EBV cancers, yet determinants of susceptibility to lytic induction signals are not well understood. To determine if host factors influence susceptibility to EBV lytic activation, we developed a technique to separate lytic from refractory cells and reported that EBV lytic activation occurs preferentially in cells with lower levels of signal transducer and activator of transcription 3 (STAT3). Using this tool to detect single cells, we now extend the correlation between STAT3 and lytic versus refractory states to EBV-infected circulating B cells in patients with primary EBV infection, leading us to investigate whether STAT3 controls susceptibility to EBV lytic activation. In loss-of-function and gain-of-function studies in EBV-positive B lymphoma and lymphoblastoid cells, we found that the levels of functional STAT3 regulate susceptibility to EBV lytic activation. This prompted us to identify a pool of candidate cellular genes that might be regulated by STAT3 to limit EBV lytic activation. From this pool, we confirmed increases in transcript levels in refractory cells of a set of genes known to participate in transcription repression. Taken together, our findings place STAT3 at a critical crossroads between EBV latency and lytic activation, processes fundamental to EBV lymphomagenesis.

SUBMITTER: Hill ER

PROVIDER: S-EPMC3807321 | biostudies-literature | 2013 Nov

REPOSITORIES: biostudies-literature

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Signal transducer and activator of transcription 3 limits Epstein-Barr virus lytic activation in B lymphocytes.

Hill Erik R ER Koganti Siva S Zhi Jizu J Megyola Cynthia C Freeman Alexandra F AF Palendira Umaimainthan U Tangye Stuart G SG Farrell Paul J PJ Bhaduri-McIntosh Sumita S

Journal of virology 20130821 21

Lytic activation of Epstein-Barr virus (EBV) is central to its life cycle and to most EBV-related diseases. However, not every EBV-infected B cell is susceptible to lytic activation. This lack of uniform susceptibility to lytic activation also directly impacts the success of viral oncolytic therapy for EBV cancers, yet determinants of susceptibility to lytic induction signals are not well understood. To determine if host factors influence susceptibility to EBV lytic activation, we developed a te ...[more]

PMID: 23966384

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Project description:UnlabelledA major hurdle to killing Epstein-Barr virus (EBV)-infected tumor cells using oncolytic therapy is the presence of a substantial fraction of EBV-infected cells that does not support the lytic phase of EBV despite exposure to lytic cycle-promoting agents. To determine the mechanism(s) underlying this refractory state, we developed a strategy to separate lytic from refractory EBV-positive (EBV(+)) cells. By examining the cellular transcriptome in separated cells, we previously discovered that high levels of host STAT3 (signal transducer and activator of transcription 3) curtail the susceptibility of latently infected cells to lytic cycle activation signals. The goals of the present study were 2-fold: (i) to determine the mechanism of STAT3-mediated resistance to lytic activation and (ii) to exploit our findings to enhance susceptibility to lytic activation. We therefore analyzed our microarray data set, cellular proteomes of separated lytic and refractory cells, and a publically available STAT3 chromatin immunoprecipitation sequencing (ChIP-Seq) data set to identify cellular PCBP2 [poly(C)-binding protein 2], an RNA-binding protein, as a transcriptional target of STAT3 in refractory cells. Using Burkitt lymphoma cells and EBV(+) cell lines from patients with hypomorphic STAT3 mutations, we demonstrate that single cells expressing high levels of PCBP2 are refractory to spontaneous and induced EBV lytic activation, STAT3 functions via cellular PCBP2 to regulate lytic susceptibility, and suppression of PCBP2 levels is sufficient to increase the number of EBV lytic cells. We expect that these findings and the genome-wide resources that they provide will accelerate our understanding of a longstanding mystery in EBV biology and guide efforts to improve oncolytic therapy for EBV-associated cancers.ImportanceMost humans are infected with Epstein-Barr virus (EBV), a cancer-causing virus. While EBV generally persists silently in B lymphocytes, periodic lytic (re)activation of latent virus is central to its life cycle and to most EBV-related diseases. However, a substantial fraction of EBV-infected B cells and tumor cells in a population is refractory to lytic activation. This resistance to lytic activation directly and profoundly impacts viral persistence and the effectiveness of oncolytic therapy for EBV(+) cancers. To identify the mechanisms that underlie susceptibility to EBV lytic activation, we used host gene and protein expression profiling of separated lytic and refractory cells. We find that STAT3, a transcription factor overactive in many cancers, regulates PCBP2, a protein important in RNA biogenesis, to regulate susceptibility to lytic cycle activation signals. These findings advance our understanding of EBV persistence and provide important leads on devising methods to improve viral oncolytic therapies.

Project description:Study questionAre STAT3 signaling molecules differentially expressed in endometriosis?Summary answerLevels of phospho-STAT3 and HIF1A, its downstream signaling molecule, are significantly higher in eutopic endometrium from women with endometriosis when compared with women without the disease.What is known alreadyEndometriosis is an estrogen-dependent inflammatory condition. Interleukin 6 (IL-6) is an inflammatory survival cytokine known to induce prolonged activation of STAT3 via association with the IL-6 receptor.Study design, size, durationCross-sectional measurements of STAT3 and HIF1A protein levels in eutopic endometrium from women with endometriosis versus those without.Participants/materials, setting, methodsLevels of phospho-STAT3 (pSTAT3) and HIF1A were examined in the endometrium of patients with and without endometriosis as well as in a non-human primate animal model using western blot and immunohistochemical analysis.Main results and the role of chanceLevels of pSTAT3 were significantly higher in the eutopic endometrium from women with endometriosis when compared with women without the disease in both the proliferative and secretory phases. HIF1A is known to be stabilized by STAT3 and IL-6. Our immunohistochemistry results show abundant HIF1A expression within the eutopic endometrial epithelial cells of women with endometriosis. Furthermore, pSTAT3 and HIF1A proteins are co-localized in endometriosis. This aberrant activation of pSTAT3 and HIF1A is confirmed by sequential analysis of eutopic endometrium using a baboon animal model of induced endometriosis. Lastly, we confirmed this IL-6 induction of both STAT3 phosphorylation and HIF1A mRNA expression in Ishikawa human endometrial adenocarcinoma cell line.Limitations, reasons for cautionIshikawa cancer cell line was used to study a benign disease. The peritoneal fluid contains various inflammatory cytokines in addition to IL-6 and so it is possible that other cytokines may affect the activity and expression of STAT3 signaling molecules.Wider implications of the findingsOur results imply that aberrant activation of STAT3 signaling plays an important role in the pathogenesis of endometriosis. Our findings could progress in our understanding of the etiology and pathophysiology of endometriosis and potential therapeutic interventions by targeted pharmacological.Study funding/competing interestsThis work was supported by NIH R01 HD067721 (to S.L.Y and B.A.L) and NIH R01 HD057873 and American Cancer Society Research Grant RSG-12-084-01-TBG (to J.-W.J.). There are no conflicts of interest.

Dataset Information

Signal transducer and activator of transcription 3 limits Epstein-Barr virus lytic activation in B lymphocytes.

Publications

Signal transducer and activator of transcription 3 limits Epstein-Barr virus lytic activation in B lymphocytes.

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