EMT转录因子Zeb1调控滤泡辅助性T细胞分化的细胞和分子机制

T cell help to B cells is a fundamental aspect of adaptive immunity and the generation of immunological memory. Follicular helper CD4+ T (TFH) cells are the specialized providers of such help. However, the molecular mechanisms that regulate the differentiation of TFH cells remain poorly understood. Our preliminary data showed that, overexpression of Zeb1 impaired TFH differentiation, while its knockdown enhanced TFH differentiation as well as B cell response and virus-specific antibody production. Further results indicated that Bcl-6 might be one of target genes of Zeb1. We will first dissect the spatiotemporal regulation of TFH differentiation by Zeb1 using conditional gene knockout mice. Then, we will analyze ubiquitination of Zeb1 and its functional consequence in TFH differentiation. Finally, by using RNA-seq and Chip-seq, we will identify the target genes of Zeb1 and investigate whether Zeb1 and Tcf3/12 competitively bind to regulatory elements of those target genes. The completion of this project may provide new insights into current model of TFH differentiation, and may be useful in both therapeutic intervention of human infectious diseases, autoimmunity diseases, and rational vaccine design.

T细胞对B细胞的帮助是适应性免疫和免疫记忆的最根本要素，而滤泡辅助性T细胞(TFH)正是此方面的专业提供者。TFH细胞分化的机制还有很多不清楚的地方。我们前期结果表明，Zeb1在T细胞过表达抑制TFH细胞的分化；而在T细胞敲低Zeb1则增强TFH细胞的分化以及B细胞反应和病毒特异性抗体的产生。进一步研究表明，Bcl-6可能是Zeb1的靶基因之一。首先我们将利用条件性敲除小鼠分析Zeb1抑制TFH细胞分化的时空效应；然后分析Zeb1的泛素化修饰及其在TFH细胞分化的作用；之后我们将利用组学方法鉴定Zeb1的下游靶基因，并确定Zeb1在这些靶基因的调控元件与Tcf3/12的竞争性关系。本研究的完成有望进一步完善TFH细胞分化调控的分子机制，为传染性疾病、自身免疫疾病以及疫苗的优化提供理论依据。

本项目计划探究转录抑制因子Zeb1调控TFH细胞分化的分子机制，但是我们后来发现，Zeb1在T细胞的缺失导致T细胞更容易走向凋亡，导致我们无法研究Zeb1在TFH细胞分化中的直接作用。然而我们发现Zeb1的泛素E3连接酶Cul4-Ddb1复合物和E蛋白E2A及HEB是病毒急性感染后TFH细胞分化、生发中心反应和抗体应答所必需的。Ddb1的缺失造成p53蛋白和DNA损伤的异常累积，同时引起p53和Chk1细胞周期检查点的激活进而引起细胞周期G2/M期的阻滞和Caspase依赖的细胞死亡，继而导致效应CD4+ T细胞扩增能力的急剧下降，最终导致Ddb1条件性敲除小鼠的TFH细胞分化和功能的缺陷。我们还发现E2A和HEB通过直接促进TFH细胞分化相关基因包括Cxcr5的表达而调控TFH细胞分化。本研究的成果进一步完善TFH细胞分化调控的分子机制，为传染性疾病、自身免疫疾病以及疫苗的优化提供理论依据。