Tellam Judy T, Zhong Jie, Lekieffre Lea, Bhat Purnima, Martinez Michelle, Croft Nathan P, Kaplan Warren, Tellam Ross L, Khanna Rajiv
QIMR Centre for Immunotherapy and Vaccine Development and Tumour Immunology, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia.
Medical School, Australian National University, Canberra, Australian Capital Territory, Australia.
PLoS Pathog. 2014 Oct 9;10(10):e1004423. doi: 10.1371/journal.ppat.1004423. eCollection 2014 Oct.
Recent studies have shown that virally encoded mRNA sequences of genome maintenance proteins from herpesviruses contain clusters of unusual structural elements, G-quadruplexes, which modulate viral protein synthesis. Destabilization of these G-quadruplexes can override the inhibitory effect on self-synthesis of these proteins. Here we show that the purine-rich repetitive mRNA sequence of Epstein-Barr virus encoded nuclear antigen 1 (EBNA1) comprising G-quadruplex structures, limits both the presentation of MHC class I-restricted CD8(+) T cell epitopes by CD11c(+) dendritic cells in draining lymph nodes and early priming of antigen-specific CD8(+) T-cells. Destabilization of the G-quadruplex structures through codon-modification significantly enhanced in vivo antigen presentation and activation of virus-specific T cells. Ex vivo imaging of draining lymph nodes by confocal microscopy revealed enhanced antigen-specific T-cell trafficking and APC-CD8(+) T-cell interactions in mice primed with viral vectors encoding a codon-modified EBNA1 protein. More importantly, these antigen-specific T cells displayed enhanced expression of the T-box transcription factor and superior polyfunctionality consistent with the qualitative impact of translation efficiency. These results provide an important insight into how viruses exploit mRNA structure to down regulate synthesis of their viral maintenance proteins and delay priming of antigen-specific T cells, thereby establishing a successful latent infection in vivo. Furthermore, targeting EBNA1 mRNA rather than protein by small molecules or antisense oligonucleotides will enhance EBNA1 synthesis and the early priming of effector T cells, to establish a more rapid immune response and prevent persistent infection.
最近的研究表明，来自疱疹病毒的基因组维持蛋白的病毒编码mRNA序列含有异常结构元件簇——G-四链体，其可调节病毒蛋白合成。这些G-四链体的去稳定化可克服对这些蛋白自身合成的抑制作用。在此，我们表明，包含G-四链体结构的爱泼斯坦-巴尔病毒编码核抗原1（EBNA1）的富含嘌呤的重复mRNA序列，限制了引流淋巴结中CD11c(+)树突状细胞对MHC I类限制性CD8(+) T细胞表位的呈递以及抗原特异性CD8(+) T细胞的早期启动。通过密码子修饰使G-四链体结构去稳定化，可显著增强体内抗原呈递以及病毒特异性T细胞的激活。通过共聚焦显微镜对引流淋巴结进行体外成像显示，在用编码密码子修饰的EBNA1蛋白的病毒载体免疫的小鼠中，抗原特异性T细胞的转运以及抗原呈递细胞与CD8(+) T细胞的相互作用增强。更重要的是，这些抗原特异性T细胞显示出T盒转录因子的表达增强以及卓越的多功能性，这与翻译效率的定性影响一致。这些结果为病毒如何利用mRNA结构下调其病毒维持蛋白的合成并延迟抗原特异性T细胞的启动，从而在体内建立成功的潜伏感染提供了重要见解。此外，通过小分子或反义寡核苷酸靶向EBNA1 mRNA而非蛋白，将增强EBNA1的合成以及效应T细胞的早期启动，以建立更快速的免疫反应并预防持续性感染。
