Division of Immunology and Pathogenesis, Department of Molecular and Cell Biology, University of California, Berkeley, California, United States of America.
PLoS One. 2010 Jan 21;5(1):e8692. doi: 10.1371/journal.pone.0008692.
Cytotoxic T cells detect intracellular pathogens by surveying peptide loaded MHC class I molecules (pMHC I) on the cell surface. Effective immune surveillance also requires infected cells to present pMHC I promptly before viral progeny can escape. Rapid pMHC I presentation apparently occurs because infected cells can synthesize and present peptides from antigenic precursors called defective ribosomal products (DRiPs). The molecular characteristics of DRiPs are not known.
METHODOLOGY/PRINCIPAL FINDINGS: Here, using a novel method for detecting antigenic precursors and proteolytic intermediates, we tracked the synthesis and processing of Epstein-Barr Virus encoded nuclear antigen 1 (EBNA1). We find that ribosomes initiated translation appropriately, but rapidly produced DRiPs representing approximately 120 amino acid truncated EBNA1 polypeptides by premature termination. Moreover, specific sequences in EBNA1 mRNA strongly inhibited the generation of truncated DRiPs and pMHC I presentation.
Our results reveal the first characterization of virus DRiPs as truncated translation products. Furthermore, production of EBNA1-derived DRiPs is down-regulated in cells, possibly limiting the antigenicity of EBNA1.
细胞毒性 T 细胞通过检测细胞表面上加载有肽的 MHC Ⅰ类分子（pMHCⅠ）来检测细胞内病原体。有效的免疫监测还需要受感染的细胞在病毒产物逃逸之前迅速呈现 pMHCⅠ。pMHCⅠ的快速呈现显然是因为受感染的细胞可以从称为核糖体缺陷产物（DRiPs）的抗原前体中合成和呈现肽。DRiPs 的分子特征尚不清楚。
方法/主要发现：在这里，我们使用一种检测抗原前体和蛋白水解中间产物的新方法，追踪了 Epstein-Barr 病毒编码的核抗原 1（EBNA1）的合成和加工。我们发现核糖体适当地起始了翻译，但通过过早终止，迅速产生了代表大约 120 个氨基酸截断的 EBNA1 多肽的 DRiPs。此外，EBNA1 mRNA 中的特定序列强烈抑制了截断的 DRiPs 和 pMHCⅠ呈现的产生。
我们的结果首次揭示了病毒 DRiPs 作为截断翻译产物的特征。此外，EBNA1 衍生的 DRiPs 的产生在细胞中受到下调，可能限制了 EBNA1 的抗原性。
