DNA解旋酶调控恶性疟原虫致病性因子表达的机制研究

Plasmodium falciparum is the most deadly parasite of human malaria. P. falciparum var gene family encodes ~60 surface antigens that contribute to the major pathogenesis in severe malaria. Through a mutually exclusive expression of var genes, P. falciparum could escape the host antibody response and parasite killing as an immune evasion mechanism. Our latest study revealed that var genes expression was significantly decreased upon knock-out of DNA helicases (PfWRN or PfRecQ1). Additionally, we have established parasites where DNA helicase was knocked out or tagged in. In order to explore the mechanism of WRN and RecQ1 in regulation of var genes expression, I plan to : 1) identify the binding sites of two DNA helicases on chromatin ; 2) reveal the role of DNA helicase in the regulation of the var genes' spatial location in nucleus; 3) analyze how active transcription marker or silencing marker plays together with DNA helicases to regulate var gene expression 4) identify proteins which associate with DNA helicases in transcriptional regulation of var genes; 5) characterize functional roles of key partner proteins in controlling var genes expression. In conclusion, this study will reveal the mechanism of DNA helicases in transcriptional regulation of var genes, shed light on understanding how P. falciparum escapes human immune system, and then provide new targets for the development of malaria vaccines and antimalarials.

恶性疟原虫是致命性最强的疟疾寄生虫，由var基因家族编码的表面抗原蛋白是该寄生虫的致病因子。某个时期每个疟原虫只能表达一个var基因，这种相互排斥性表达帮助其逃避人体免疫反应。我们最新研究发现DNA解旋酶WRN和RecQ1调控了var基因的表达；任何一个酶的缺失都能导致var基因家族表达受抑制。为进一步探索WRN和RecQ1调节var 基因表达的机制，本项目拟开展如下研究：1）鉴定DNA解旋酶在染色质上的结合位点；2）揭示解旋酶调节var基因核周空间位置重排的作用方式；3）分析H3K4me3或H3K9me3等基因转录/沉默标记与DNA解旋酶互作而协同调控var基因表达的模式；4）筛选与解旋酶互作的蛋白网络；5）明确互作因子与解旋酶协同调控var基因表达的机制。本研究对于系统阐明var基因家族参与恶性疟原虫免疫逃逸的机制具有重要意义，也将为疟疾疫苗及抗疟药的研发提供新的靶点。

恶性疟原虫是致病性最强的疟疾寄生虫；其var基因家族所编码的PfEMP1蛋白，是疟原虫致病过程中的一个关键组分。通过表观遗传机制的调节，每个疟原虫在某个时刻只能表达一个var基因，从而帮助其逃避人体免疫反应。我们应用表观遗传学理论，首次揭示了PfRecQ1 DNA解旋酶通过减少var基因转录起始位点区域的H3K9me3修饰及调节var基因所在DNA在核周上的定位，从而维持了var基因的表达，相关研究已经发表在PNAS 2019杂志上（项目承担人为共同通讯作者）。此外，我们还发现并开展了PfRecQ1之外的新研究方向，找到了一个新的表观遗传调控因子DM蛋白；该蛋白通过维持蛋白转运家族的表达，而保障了PfEMP1蛋白在受感染红细胞膜表面的呈递；目前我们正在深入研究其机制。总之，本研究阐明了调控PfEMP1病原蛋白表达、转运及呈递的新机制，为疟疾疫苗及抗疟药的研发提供了新靶点。