|
||
By
From the Department of Microbiology and Immunology, Kimmel Cancer Center, Jefferson Medical
College, Philadelphia, Pennsylvania 19107
Accumulating evidence shows that the repertoire of major histocompatibility complex class
I-restricted epitopes extends beyond conventional translation reading frames. Previously, we
reported that scanthrough translation, where the initiating AUG of a primary open reading
frame is bypassed, is most likely to account for the presentation of cryptic epitopes from alternative reading frames within the influenza A PR/8/34 nucleoprotein gene. Here, we confirm
and extend these findings using an epitope cassette construct that features two well-defined
CD8+ T cell (TCD8+) epitopes in alternative reading frames, each preceded by a single start
codon. Expression of one epitope depends on scanning of the ribosome over the first AUG
with translation initiation occurring at the second AUG. We find that scanthrough translation
has great potency in our system, with its impact being modulated, as predicted, by the base
composition surrounding the first initiation codon, the number of start codons preceding the point of alternate reading frame initiation, and the efficiency with which the epitope itself is
generated. Additionally, we investigated the efficiency of eukaryotic translation termination
codons, to assess codon readthrough as a mechanism for cryptic epitope expression from 3
untranslated regions. In contrast with initiation codons, eukaryotic stop codons appear to be
highly efficient at preventing expression of epitopes encoded in 3
untranslated regions, suggesting that 3
untranslated regions are not a common source of cryptic epitope substrate. We
conclude that scanthrough is a powerful mechanism for the expression of epitopes encoded in
upstream alternative open reading frames that may contribute significantly to TCD8+ responses
and to tolerance induction.
This article has been cited by other articles:
| TABLE OF CONTENTS |
|