A yeast model for the mechanism of the Epstein‐Barr virus immune evasion identifies a new therapeutic target to interfere with the virus stealthiness

Abstract

The oncogenic Epstein-Barr virus (EBV) evades the immune system but has an Achilles heel: its genome maintenance protein EBNA1. Indeed, EBNA1 is essential for viral genome replication and maintenance but also highly antigenic. Hence, EBV evolved a system in which the glycine-alanine repeat (GAr) of EBNA1 limits the translation of its own mRNA at a minimal level to ensure its essential function thereby, at the same time, minimizing immune recognition. Defining intervention points where to interfere with EBNA1 immune evasion is an important step to trigger an immune response against EBV-carrying cancers. Thanks to a yeast-based assay that recapitulates all the aspects of EBNA1 selflimitation of expression, a recent study by Lista et al.[Nature Communications (2017) 7, 435-444] has uncovered the role of the host cell nucleolin (NCL) in this process via a direct interaction of this protein with Gquadruplexes (G4) formed in GAr-encoding sequence of EBNA1 mRNA. In addition, the G4 ligand PhenDC3 prevents NCL binding on EBNA1 mRNA and reverses GAr-mediated repression of translation and antigen presentation. This shows that the NCL-EBNA1 mRNA interaction is a relevant therapeutic target to unveil EBV-carrying cancers to the immune system and that the yeast model can be successfully used for uncovering drugs and host factors that interfere with EBV stealthiness.Yeast-based chemobiological models for a number of human diseases involving functionally conserved physiopathological factors have been quite largely and successfully developed for about fifteen years. However, yeast assays based on the expression of key physiopathological players that do not exist in yeast are also possible (e.g.: yeast models for Huntington and Parkinson diseases). Here we briefly describe how we developed a yeast model to identify drugs and host cell factors that interfere with the capacity of the Epstein-Barr virus (EBV) to evade the host immune system. EBV is the first oncogenic virus discovered in human and has been linked to various cancers that include Burkitt and Hodgkin lymphomas, the nasopharyngeal carcinoma and 10% of gastric cancers. EBV evades the host immune system but, fortunately, has an Achilles heel: its genome maintenance protein EBNA1 which is, on the one hand, essential for EBV genome replication and maintenance and as such expressed in all dividing EBV-infected cells. On the other hand, EBNA1 is highly antigenic and CD8 + T cells directed towards EBNA1 epitopes exist in all infected individuals. Hence, in order to avoid the immune

G-quadruplexes and G-quadruplex ligands: targets and tools in antiviral therapy

“…G4s in EBNA1 mRNA have been shown to modulate the endogenous presentation of EBNA1-specific CD8 + T-cell epitopes, which are involved in persistent infections ( 72 ). The cellular protein nucleolin counteracts this mechanism by interacting with EBNA1 mRNA G4s and thus downregulating EBNA1 protein expression and antigen presentation ( 73 , 74 ). G4s can also be observed in the mRNAs of other genome maintenance proteins that are known to regulate their self-synthesis, suggesting that G4s are exploited as structural regulatory elements by the virus ( 75 ).…”

Guidelines and recommendations on yeast cell death nomenclature

“…In addition, studies on yeast have shed light on human diseases, providing a cellular platform to examine, for instance, prion biology, virus-host interactions, metabolic diseases, neurodegenerative disorders, cancer, or aging 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 . Among the pathophysiologically relevant pathways that can readily be explored in yeast are those governing cellular demise.…”

Novel cationic bis(acylhydrazones) as modulators of Epstein–Barr virus immune evasion acting through disruption of interaction between nucleolin and G-quadruplexes of EBNA1 mRNA

“…Along these lines, we have previously developed a yeast (Saccharomyces cerevisiae)-based assay reproducing all the aspects of the GAr-based inhibition of translation, including the GAr-length dependency [18]. This allowed us to decipher the mechanisms of GAr-mediated mRNA translation suppression in cis and, in particular, to identify the cellular factors involved [19,20]. The yeast assay was successfully used first to identify small molecular-weight compounds that can stimulate EBNA1 expression both in yeast and in mammalian cells and relieve the GAr-based limitation of antigen presentation [18,20].…”

“…This allowed us to decipher the mechanisms of GAr-mediated mRNA translation suppression in cis and, in particular, to identify the cellular factors involved [19,20]. The yeast assay was successfully used first to identify small molecular-weight compounds that can stimulate EBNA1 expression both in yeast and in mammalian cells and relieve the GAr-based limitation of antigen presentation [18,20]. More recently, this model was employed for a genetic screen that aimed at identifying host cell genes involved in the GAr-mediated inhibition of translation.…”