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Critical role of galectin-9 in EBV-driven transformation of human B-lymphocytes

ABSTRACT: Background: In several types of malignancies, especially EBV-associated nasopharyngeal carcinomas, high Galectin-9 (Gal-9) expression is indicative of an aggressive tumor phenotype. The contribution of Gal-9 to the oncogenesis of B-cell lymphomas (BCLs) has not yet been investigated. Methods: The expression of Gal-9, STING, and EBNA1 was measured by immunohistochemical (IHC) staining on tumor sections from 66 BCL patients. Artificial EBV infection of normal primary B cells in vitro was used as an experimental model. The dynamic changes of the transcriptome of EBV-infected B cells undergoing transformation were investigated by bulk RNA-sequencing and bioinformatics analysis. The oncogenic role of Gal-9 was investigated in vitro by addition of recombinant Gal-9 to EBV-infected primary B-cells, and growth assays. The underlying molecular mechanisms were investigated by immunoblotting and immunofluorescent (IF) staining, CHIP and luciferase reporter assays. Results: In clinical specimens of BCLs, Gal-9 expression was significantly associated with tumor stage, latent EBV infection and abundance of the viral latent protein EBNA1. Looking at the transcriptome changes occurring in vitro during EBV-driven B-cell transformation, we could identify a series of genes undergoing long term activation and remaining highly expressed in mature LCLs. The Gal-9 gene is one of them. Its expression is enhanced during the transformation process at the mRNA level and even more at the protein level. This up-regulation results at least in part from its transactivation by EBNA1 which can bind its promoter. Reciprocally, we find that addition of extra-cellular Gal-9 promotes B-cell transformation and establishment of the latent phase of EBV-infection. Concomitantly, extra-cellular Gal-9 blocks STING signaling and enhances STAT3 phosphorylation. Inhibition of Sting signaling or STAT3 phosphorylation blocks B-cell transformation, even in the presence of Gal-9. Conclusion: our data unveil a role of amplification and acceleration for Gal-9 in the process of EBV-driven B-cell transformation. This process might be relevant to the pathogenesis of EBV-associated BCLs.

ORGANISM(S): Homo sapiens

PROVIDER: GSE162516 | GEO | 2022/06/30

REPOSITORIES: GEO

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Project description:The Epstein-Barr virus (EBV) switches between latent and lytic phases in hosts that are important in developing related diseases. However, the underlying mechanism of how the viral latent-lytic switch is controlled and how EBV itself mediates this regulation remains largely unknown. This study identified the upregulated histone acetyl reader bromodomain-containing protein 7 (BRD7) during EBV latent infection. Based on the ChIP-sequencing of endogenous BRD7 in Burkitt lymphoma cells, we found that EBV drove BRD7 to regulate cellular and viral genomic loci, including the transcriptional activation of c-Myc, a recently reported regulator of EBV latency. Additionally, EBV-mediated BRD7 signals enriched around the FUSE site in chromosome 8, and the enhancer LOC108348026 in the lgH locus, which might activate the c-Myc alleles. Mechanically, EBV-encoded nuclear antigen 1 (EBNA1) bound and recruited BRD7 to colocalize at promotor regions of the related genes, thus serving as cofactors for the maintenance of viral latency. Moreover, the disruption of BRD7 decreased the c-Myc expression, induced the BZLF1 expression, and reactivated the lytic cycle. Our findings reveal the unique role of BRD7 hijacked by EBV in maintaining the viral latency state via chromatin remodeling. The study paved the way for understanding the new molecular mechanism of EBV-induced chromatin remodeling and latent-lytic switch regulation, providing novel therapeutic candidate targets for EBV persistent infection. With establishing persistent infection in most human hosts, EBV is usually at a latent infection state. How the viral latency is maintained in cells remains largely unknown. c-Myc was recently reported to act as a controller of the lytic switch, while whether and how EBV regulates it remains to be explored. Here, we identified that BRD7 is involved in controlling EBV latency. We found that EBV-mediated BRD7 was enriched in both the normal promoter regions and the translocation alleles of c-Myc, and the disruption of BRD7 decreased c-Myc expression to reactivate the lytic cycle. We also demonstrated that EBV-encoded EBNA1 bound to and regulated BRD7. Therefore, we reveal a novel mechanism by which EBV can regulate its infection state by hijacking host BRD7 to target c-Myc. Our findings will help future therapeutic intervention strategies of EBV infection and pathogenesis.

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Critical role of galectin-9 in EBV-driven transformation of human B-lymphocytes

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