NP220 mediates silencing of unintegrated retroviral DNA
NP220 mediates silencing of unintegrated retroviral DNA
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DOI：
10.1038/s41586-018-0750-6
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发表时间：
2018-12-13
期刊：
影响因子：
64.8
通讯作者：
Goff, Stephen P.
中科院分区：
文献类型：
--
作者：
Zhu, Yiping;Wang, Gary Z.;Goff, Stephen P.
外源DNA进入许多哺乳动物细胞类型触发先天免疫系统，这是一套复杂的反应，以防止病原体感染。这种反应的一个方面是对进入的病毒DNA（包括逆转录病毒感染后立即形成的染色体外DNA）进行有效的表观遗传沉默1。这些未整合的病毒DNA在所有细胞中转录非常差，甚至在允许细胞中，与病毒整合后观察到的稳健表达相反（2-5）。导致这种低表达的因素尚未确定。在这里，我们对沉默整合酶缺陷型MLV-GFP报告病毒所需的基因进行了全基因组CRISPR-Cas9筛选，以探索人类细胞中抑制未整合病毒DNA的机制。我们的筛选鉴定了DNA结合蛋白NP 220、构成HUSH复合物的三种蛋白质（MPP 8、TASOR和PPHLN 1）-其使异染色质中的前病毒沉默（6）和逆转录转座子沉默（7，8）-组蛋白甲基转移酶SETDB 1和沉默所需的其他宿主因子。染色质免疫沉淀的进一步测试表明，NP 220是募集HUSH复合物、SETDB 1和组蛋白脱乙酰酶HDAC 1和HDAC 4以沉默未整合的逆转录病毒DNA的关键蛋白。NP 220的敲除加速逆转录病毒的复制。这些实验确定了使染色体外逆转录病毒DNA沉默的分子机制。
The entry of foreign DNA into many mammalian cell types triggers the innate immune system, a complex set of responses to prevent infection by pathogens. One aspect of the response is the potent epigenetic silencing of incoming viral DNAs1, including the extrachromosomal DNAs that are formed immediately after infection by retroviruses. These unintegrated viral DNAs are very poorly transcribed in all cells, even in permissive cells, in contrast to the robust expression that is observed after viral integration(2-5). The factors that are responsible for this low expression have not yet been identified. Here we performed a genome-wide CRISPR-Cas9 screen for genes that are required for silencing an integrase-deficient MLV-GFP reporter virus to explore the mechanisms responsible for repression of unintegrated viral DNAs in human cells. Our screen identified the DNA-binding protein NP220, the three proteins (MPP8, TASOR and PPHLN1) that comprise the HUSH complex-which silences proviruses in heterochromatin(6) and retrotransposons(7,8)-the histone methyltransferase SETDB1, and other host factors that are required for silencing. Further tests by chromatin immunoprecipitation showed that NP220 is the key protein that recruits the HUSH complex, SETDB1 and the histone deacetylases HDAC1 and HDAC4 to silence the unintegrated retroviral DNA. Knockout of NP220 accelerates the replication of retroviruses. These experiments identify the molecular machinery that silences extrachromosomal retroviral DNA.