Initiation codon scanthrough versus termination codon readthrough demonstrates strong potential for major histocompatibility complex class I-restricted cryptic epitope expression.
Initiation codon scanthrough versus termination codon readthrough demonstrates strong potential for major histocompatibility complex class I-restricted cryptic epitope expression.
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DOI：
10.1084/jem.186.7.1051
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发表时间：
1997-10-06
期刊：
影响因子：
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通讯作者：
Eisenlohr LC
中科院分区：
文献类型：
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作者：
Bullock TN;Patterson AE;Franlin LL;Notidis E;Eisenlohr LC
越来越多的证据表明，主要组织相容性复合体I类限制性表位的库超出了传统的翻译阅读框架。以前，我们报道了扫描翻译，其中一个主要的开放阅读框的起始AUG被绕过，是最有可能解释的潜在表位从替代阅读框架内的流感病毒A PR/8/34核蛋白基因的介绍。在这里，我们确认和扩展这些发现使用表位盒构建体，其特征在于两个定义明确的CD 8 + T细胞（TCD 8+）表位在替代阅读框架，每个前面有一个单一的起始密码子。一个表位的表达依赖于核糖体在第一个AUG上的扫描，翻译起始发生在第二个AUG。我们发现，扫描翻译在我们的系统中具有很大的效力，其影响如预测的那样受到第一个起始密码子周围的碱基组成、交替阅读框起始点之前的起始密码子的数量、以及表位本身产生的效率。此外，我们研究了真核生物翻译终止密码子的效率，以评估密码子通读作为3′非翻译区表达隐蔽表位的机制。与起始密码子相比，真核生物终止密码子似乎在阻止3′非翻译区编码的表位表达方面非常有效，这表明3′非翻译区不是隐蔽表位底物的常见来源。我们的结论是，扫描是一个强大的机制，表达表位编码的上游替代开放阅读框架，可能有助于显着TCD 8+反应和耐受诱导。
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.