内含子保留在T细胞活化过程中的基因调控作用及分子机制

One major finding of the post-genomics era is the pervasive transcription of mammalian genomes. Supporting this notion, emerging evidences have suggested an unprecedented complexity of eukaryotic transcriptome. Using human CD4+ T cells as a model system, we have recently uncovered widespread intron retentions under the resting condition. The extent of intron retention decreases dramatically upon T cell activation. Further analyses supported the notion that intron retention might play an important role in regulating proper gene expression required for cell activation. These observations strongly suggest that a novel paradigm of post transcriptional gene regulation, which might be broadly involved in T-cell activation. In this proposed study, we aim to study the molecular mechanism underlying the regulated intron retention and to characterize its potential biological significance in gene activation. In addition, a prominent feature of the T cell activation process is the shortening of 3' untranslated regions (3' UTRs) by using proximal alternative polyadenylation sites. Because of the intrinsic connectivity of transcription, splicing and polyadenylation in mRNA biogenesis, we will investigate the genome-wide coordination between intron retention and alternative polyadenylation, which potentially will shed light on the molecular mechanism of shortening of 3' UTRs that has so far remained unknown. These aims will be achieved by integration of genomics, epigenomics and computational biology approaches, and the resulting findings will be further validated by molecular biology experiments.

人类CD4阳性T细胞是HIV病毒的靶细胞，在艾滋病发病时急剧减少。T细胞在接受树突状细胞抗原呈递后活化并分泌白细胞介素2，从而调控自身和其它免疫细胞的基因表达，是免疫应答的重要过程。申请人通过前期工作在这一过程中发现了一个新的全基因组水平内含子保留现象。T细胞休眠时，超过800个基因有高水平的内含子保留，并且这些基因的内含子保留水平在活化后至少下降2倍。进一步的分析显示，内含子保留水平的下降与基因的表达水平变化呈负相关。申请人据此推测全基因组水平的内含子保留可能是T细胞活化过程中一个非常广泛的基因调控机制。本项目结合基因组学、表观遗传学、计算生物学及分子生物学等多种手段，研究内含子保留在T细胞活化过程中的分子机制，阐明内含子保留的基因调控功能，发现并验证内含子保留与T细胞活化时全局性3端非翻译区变短之间的内在联系，从而验证并完善申请人的假说，为深入理解免疫应答中的基因调控新机制奠定基础。

本项目前期发现免疫T细胞在休眠时有大量基因出现内含子保留这一特殊形式的可变剪接的有趣现象，并且在活化后内含子保留水平显著下降，进而深入探索内含子保留介导的基因调控在T细胞中的作用、分子机制及其与另一个重要现象（选择性多聚腺苷酸化/polyA加尾）之间的关系。4年来，围绕T细胞中内含子保留的各个方面展开了深入研究，阐明了内含子保留是全基因组水平的一种调控机制，通过使得内含子保留的转录本滞留在细胞核中并降解的方式来实现免疫过程的快速应答，并进而回答了人和小鼠的CD4阳性T细胞中均存在内含子保留介导的基因调控功能，并发现受内含子保留调控的基因更倾向于使用近端polyA位点。总之，我们的研究发现了内含子保留介导的转录后调控是免疫T细胞响应环境刺激的快速应答新机制。这些研究进展按照计划执行，取得了良好的成绩。核心发现以第一作者和通讯作者的身份发表在《Nucleic Acids Research》，另有3篇标注本基金号的相关研究论文发表，获授权中国专利1项。