Lysine methylation is an important posttranslational modification, implicated in various biological pathological conditions. The transcription factor interferon regulatory factor 3 (IRF3) is essential for antiviral innate immunity, yet the mechanism for methylation control of IRF3 activation remains unclear. In this paper, we discovered monomethylation of IRF3 at K366 is critical for IRF3 transcription activity in antiviral innate immunity. By mass spectrometry analysis of IRF3-associated proteins, we identified nuclear receptor–binding SET domain 3 (NSD3) as the lysine methyltransferase that directly binds to the IRF3 C-terminal region through its PWWP1 domain and methylates IRF3 at K366 via its SET domain. Deficiency of NSD3 impairs the antiviral innate immune response in vivo. Mechanistically, NSD3 enhances the transcription activity of IRF3 dependent on K366 monomethylation, which maintains IRF3 phosphorylation by promoting IRF3 dissociation of protein phosphatase PP1cc and consequently promotes type I interferon production. Our study reveals a critical role of NSD3-mediated IRF3 methylation in enhancing antiviral innate immunity.

赖氨酸甲基化是重要的翻译后修饰，与多种生物学病理条件有关。转录因子干扰素调节因子3（IRF3）对于抗病毒先天免疫至关重要，但是IRF3激活的甲基化控制机制仍不清楚。在本文中，我们发现IRF3在K366处的单甲基化对于抗病毒先天免疫中的IRF3转录活性至关重要。通过对IRF3相关蛋白的质谱分析，我们确定了结合核受体的SET结构域3（NSD3）是赖氨酸甲基转移酶，可通过其PWWP1结构域直接与IRF3 C末端区域结合，并通过其SET结构域对K366处的IRF3进行甲基化。NSD3的缺乏会损害体内的抗病毒先天性免疫反应。从机制上讲，NSD3增强了依赖于K366单甲基化的IRF3的转录活性，该作用通过促进蛋白磷酸酶PP1cc的IRF3解离来维持IRF3磷酸化，从而促进I型干扰素的产生。我们的研究揭示了NSD3介导的IRF3甲基化在增强抗病毒先天免疫中的关键作用。