KAP1-mediated epigenetic suppression in anti-RNA viral responses by direct targeting RIG-I and MDA5. KAP1-mediated epigenetic suppression in anti-RNA viral responses by direct targeting RIG-I and MDA5

Retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), including RIG-I (encoded by Ddx58) and MDA5 (melanoma-differentiation-associated gene 5, encoded by Ifih1), are crucial for initiating antiviral responses. Endogenous retroviral elements (ERVs) are transposable elements derived from exogenous retrovirus that integrated into the genome. KRAB-associated protein 1 (KAP1) is a master epigenetic suppressor of ERVs, and thereby protects cells from detrimental genome instability. Increased ERV transcripts are sensed by RLRs and trigger innate immune signaling. However, whether KAP1 could directly control RLRs activity remain unclear. Here we show that KAP1 attenuates RNA viral infection induced type I IFNs and facilitates viral replication by inhibiting RIG-I/MDA5 expression in primary peritoneal macrophages of C57BL/6J mice. Kap1 deficiency increased IFN-β expression and inhibited VSV replication in C57BL/6J mice in vivo. Mechanistically, KAP1 binds to the promoter regions of Ddx58 and Ifih1, and promotes the establishment of repressive histone marks in primary peritoneal macrophages of C57BL/6J mice. Concordantly, KAP1 suppresses the expression of RIG-I and MDA5 at transcriptional level in primary peritoneal macrophages of C57BL/6J mice. Our results establish that KAP1 epigenetically suppresses host antiviral responses by direct targeting RIG-1 and MDA5, and thus facilitates the immune escape of RNA viruses. Overall design: Examination of KAP1 bound genes in primary peritoneal macrophages.

视黄酸诱导基因-I样受体（Retinoic acid-inducible gene-I-like receptors, RLRs），包括由Ddx58基因编码的视黄酸诱导基因-I（Retinoic acid-inducible gene-I, RIG-I）以及由Ifih1基因编码的黑色素瘤分化相关基因5（melanoma-differentiation-associated gene 5, MDA5），在启动抗病毒免疫应答过程中发挥关键作用。内源性逆转录病毒元件（Endogenous retroviral elements, ERVs）是源自外源性逆转录病毒并整合至宿主基因组的转座元件。KRAB相关蛋白1（KRAB-associated protein 1, KAP1）是ERVs的核心表观遗传抑制因子，可保护细胞免受有害基因组不稳定的侵扰。增多的ERV转录本可被RLRs识别并触发先天免疫信号通路。然而，KAP1是否能够直接调控RLRs的活性目前仍不明确。本研究结果显示，KAP1可通过抑制C57BL/6J小鼠原代腹腔巨噬细胞中RIG-I/MDA5的表达，减弱RNA病毒感染诱导的I型干扰素（type I interferons, IFNs）产生，并促进病毒复制。在体实验表明，Kap1基因缺陷可上调C57BL/6J小鼠体内IFN-β的表达，并抑制水疱性口炎病毒（vesicular stomatitis virus, VSV）的复制。机制上，KAP1可结合Ddx58与Ifih1的启动子区域，并在C57BL/6J小鼠原代腹腔巨噬细胞中促进抑制性组蛋白修饰的建立。相应地，KAP1可在转录水平抑制C57BL/6J小鼠原代腹腔巨噬细胞中RIG-I与MDA5的表达。本研究证实，KAP1通过直接靶向RIG-I与MDA5，以表观遗传方式抑制宿主抗病毒应答，从而助力RNA病毒实现免疫逃逸。整体实验设计：检测原代腹腔巨噬细胞中KAP1结合的基因。