DNA helicase RecQ1 regulates mutually exclusive expression of virulence genes in Plasmodium falciparum via heterochromatin alteration
DNA helicase RecQ1 regulates mutually exclusive expression of virulence genes in Plasmodium falciparum via heterochromatin alteration
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DNA解旋酶RecQ1通过异染色质改变调节恶性疟原虫毒力基因的互斥表达
DOI：
10.1073/pnas.1811766116
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
Jiang Lubin
中科院分区：
文献类型：
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作者：
Li Zhou;Yin Shigang;Sun Maoxin;Cheng Xiu;Wei Jieqiong;Gilbert Nicolas;Miao Jun;Cui Liwang;Huang Zhenghui;Dai Xueyu;Jiang Lubin
意义var基因家族的互斥表达与恶性疟原虫抗原变异和免疫逃逸有关。我们的工作表明，整个var基因家族在敲除PfRecQ1 DNA解旋酶时沉默。我们的研究表明，PfRecQ1可能通过介导var基因家族的核外周定位和减少var基因位点的异染色质组蛋白修饰来维持var基因的克隆表达。这项工作揭示了var基因通过染色质结构调控的途径，并确定了PfRecQ1作为抗疟疾药物开发的靶点。恶性疟原虫var基因家族编码约60种表面抗原，寄生虫通过var基因的克隆表达逃避宿主免疫应答。然而，控制这种与染色质组装改变相关的互斥性的机制尚不清楚。在这里，我们确定了var基因家族的表达是如何由两个RecQ DNA解旋酶家族成员PfRecQ1和PfWRN在恶性疟原虫中调控的。通过基因操作，我们发现在敲除PfRecQ1时，完整的var库被沉默，而当敲除PfWRN时，它们的表达没有明显变化。更重要的是，通过PfRecQ1的互补可以挽救var基因的互斥表达。此外，敲除这两个解旋酶基因中的任何一个都改变了亚端粒和亚端粒变异基因的核周簇分布。虽然PfRecQ1的缺失增加了var基因upsC1转录起始位点（TSS）的异染色质标记三甲基化（H3K9me3），但该缺失对H3K9me3在包括var基因在内的基因体上的全球分布没有影响。ChIP-seq分析结果显示，PfRecQ1在所有基因的tss位点上富集，而pfwrn在var基因家族的基因小体上富集，其他基因和所有基因的tss位点上均不富集。在PfRecQ1缺失时，upsC1 var基因从活跃的核周转录区移动到upsC型的沉默区。这些发现表明，PfRecQ1，而不是PfWRN，是维持var基因克隆表达所必需的。
Significance Mutually exclusive expression of the var gene family contributes to antigenic variation and immune evasion in Plasmodium falciparum. Our work reveals that the entire var gene family is silenced on knockout of the PfRecQ1 DNA helicase. Our study shows that PfRecQ1 maintains var gene clonal expression, possibly by mediating the nuclear periphery localization of the var gene family and decreasing heterochromatic histone modifications at the var gene loci. This work reveals a path of var gene regulation through chromatin structure and identifies PfRecQ1 as a target for antimalarial drug development. The Plasmodium falciparum var gene family encodes ∼60 surface antigens by which parasites escape the host immune responses via clonal expression of var genes. However, the mechanism controlling this mutual exclusivity, associated with alterations in chromatin assembly, is not understood. Here, we determined how expression of the var gene family is regulated by two RecQ DNA helicase family members, PfRecQ1 and PfWRN, in P. falciparum. Through genetic manipulation, we found that the complete var repertoire was silenced on PfRecQ1 knockout, whereas their expression did not show noticeable changes when PfWRN was knocked out. More important, mutually exclusive expression of var genes could be rescued by complementation of PfRecQ1. In addition, knocking out either of these two helicase genes changed the perinuclear cluster distribution of subtelomeres and subtelomeric var genes. Whereas deletion of PfRecQ1 increased the heterochromatin mark trimethylated (H3K9me3) at the transcription start site (TSS) of the var gene upsC1, that deletion had no effect on the global distribution of H3K9me3 over gene bodies, including those for the var genes. ChIP-seq assay showed that PfRecQ1 was enriched globally at the TSSs of all genes, whereas PfWRN-enriched regions occurred at the gene bodies of the var gene family, but not of other genes or at TSSs of all genes. On PfRecQ1 deletion, the upsC1 var gene moved from the active perinuclear transcription region to a silenced region of the upsC type. These findings imply that PfRecQ1, but not PfWRN, is essential for maintaining the clonal expression of var genes.