Epstein barr virus-encoded EBNA1 interference with MHC class I antigen presentation reveals a close correlation between mRNA translation initiation and antigen presentation

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Abstract

Viruses are known to employ different strategies to manipulate the major histocompatibility (MHC) class I antigen presentation pathway to avoid recognition of the infected host cell by the immune system. However, viral control of antigen presentation via the processes that supply and select antigenic peptide precursors is yet relatively unknown. The Epstein-Barr virus (EBV)-encoded EBNA1 is expressed in all EBV-infected cells, but the immune system fails to detect and destroy EBV-carrying host cells. This immune evasion has been attributed to the capacity of a Gly-Ala repeat (GAr) within EBNA1 to inhibit MHC class I restricted antigen presentation. Here we demonstrate that suppression of mRNA translation initiation by the GAr in cis is sufficient and necessary to prevent presentation of antigenic peptides from mRNAs to which it is fused. Furthermore, we demonstrate a direct correlation between the rate of translation initiation and MHC class I antigen presentation from a certain mRNA. These results support the idea that mRNAs, and not the encoded full length proteins, are used for MHC class I restricted immune surveillance. This offers an additional view on the role of virus-mediated control of mRNA translation initiation and of the mechanisms that control MHC class I restricted antigen presentation in general. © 2010 Apcher et al.

Figures

  • Figure 1. Inhibition of EBNA1 synthesis prevents presentation of peptides derived from the EBNA1 mRNA. A) Cartoon illustrating the different constructs. The location of the exogenous antigenic peptide sequence SIINFEKL (SL8) of the chicken ovalbumin (Ova) in the EBNA1-SL8 and the EBNA1DGA-SL8 constructs is indicated. B) The presentation of SL8 peptide on endogenous MHC class I Kb molecules on (0.56105) EL4 cells (left) or on human cells co-expressing a genomic Kb construct (right) was determined using B3Z CD8+ T cells [23]. The GAr domain suppresses presentation of SL8 by over 90% in either cell type. C) Autoradiograph of a 1 hour 35S-methionine pulse label in the presence of proteasome inhibitors shows that
  • Figure 2. Inhibition of protein degradation is not essential for the GAr sequence to prevent endogenous antigen presentation for the MHC class I restricted pathway. A) The SL8 epitope was inserted in the 39UTR of the GAr open reading frame (ORF) (GAr-1), in another
  • Figure 3. GAr suppresses antigen presentation by targeting the mRNA translation initiation process. A) Cartoon illustrating the c-myc Internal Ribosomal Entry Sites (IRES) constructs. IRESs offer alternative cap-independent mechanisms of mRNA translation initiation. B) Autoradiograph of 35S-methionine metabolic pulse labelling. Insertion of the c-myc IRES in the 59UTR of the GAr-Ova mRNA (c-myc-GAr-Ova)
  • Table 1. GAr-dependent inhibition of antigen presentation in different cell lines from different origins.
  • Figure 4. Domain 1 of the c-myc IRES is responsible for the effect of the c-myc IRES on GAr-dependent translation control. A) Cartoons illustrating the predicted structure and functional domains of the human c-myc IRES and domains 1 and 2 and the ribosome entry window are indicated. B) Domain 1 was deleted while retaining the ribosome entry window and domain 2 (Dc-myc IRES). C) Autoradiograph of 35Smethionine metabolic pulse labelling and presentation of SL8 derived from the indicated constructs in H1299 cells. Insertion of the Dc-myc IRES in the 59UTR of the GAr-Ova mRNA (Dc-myc-GAr-Ova) does not restore translation as compare to the intact c-myc IRES (c-myc-GAr-Ova). Neither Dc-myc IRES nor c-myc IRES affect translation when inserted in the 59UTR of Ova alone. Data are representative of three or more independent experiments with SD. doi:10.1371/journal.ppat.1001151.g004
  • Figure 5. The rate of mRNA translation initiation directly correlates with the amount of antigen presented from a given mRNA. A) A 30 amino acid GAr sequence from the EBV-encoded EBNA1was fused to the N-terminus of Ova (30GAr-EBV-Ova). The GAr sequence from the EBNA1like protein of the Papio virus carries four single inserted serine residues (30GAr-Papio-Ova). B) Autoradiograph of a 30 minutes 35S-methionine pulse
  • Figure 6. Antigenic peptides (A.P.) can be derived from the main open reading frame as well as cryptic peptides from alternative reading frames (yellow) and from the 39UTR (pink) [25]. The nascent GAr polypeptide (red) of the EBNA1 prevents translation initiation throughout the entire mRNA, including its own reading frame and cryptic peptides. This allows the EBV to evade the MHC class I restricted antigen presentation of peptides from the EBNA1 message and helps the virus to evade the immune system. The GAr also prevents the synthesis of the EBNA1 full length protein but its long half life ensures that functional levels of EBNA1 are expressed. doi:10.1371/journal.ppat.1001151.g006

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APA

Apcher, S., Daskalogianni, C., Manoury, B., & Fåhraeus, R. (2010). Epstein barr virus-encoded EBNA1 interference with MHC class I antigen presentation reveals a close correlation between mRNA translation initiation and antigen presentation. PLoS Pathogens, 6(10). https://doi.org/10.1371/journal.ppat.1001151

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