University of Chinese Academy of Sciences, Beijing, China.
Key Laboratory of Insect Developmental and Evolutionary Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai, China.
PLoS Genet. 2021 Aug 9;17(8):e1009718. doi: 10.1371/journal.pgen.1009718. eCollection 2021 Aug.
Insects depend on the innate immune response for defense against a wide array of pathogens. Central to Drosophila immunity are antimicrobial peptides (AMPs), released into circulation when pathogens trigger either of the two widely studied signal pathways, Toll or IMD. The Toll pathway responds to infection by Gram-positive bacteria and fungi while the IMD pathway is activated by Gram-negative bacteria. During activation of the IMD pathway, the NF-κB-like transcription factor Relish is phosphorylated and then cleaved, which is crucial for IMD-dependent AMP gene induction. Here we show that loss-of-function mutants of the unconventional histone variant H2Av upregulate IMD-dependent AMP gene induction in germ-free Drosophila larvae and adults. After careful dissection of the IMD pathway, we found that Relish has an epistatic relationship with H2Av. In the H2Av mutant larvae, SUMOylation is down-regulated, suggesting a possible role of SUMOylation in the immune phenotype. Eventually we demonstrated that Relish is mostly SUMOylated on amino acid K823. Loss of the potential SUMOylation site leads to significant auto-activation of Relish in vivo. Further work indicated that H2Av regulates Relish SUMOylation after physically interacting with Su(var)2-10, the E3 component of the SUMOylation pathway. Biochemical analysis suggested that SUMOylation of Relish prevents its cleavage and activation. Our findings suggest a new mechanism by which H2Av can negatively regulate, and thus prevent spontaneous activation of IMD-dependent AMP production, through facilitating SUMOylation of the NF-κB like transcription factor Relish.
昆虫依靠先天免疫反应来防御各种病原体。在果蝇免疫中起核心作用的是抗菌肽（AMPs），当病原体触发两种广泛研究的信号通路（Toll 或 IMD）之一时，它们会被释放到循环中。Toll 通路对革兰氏阳性菌和真菌的感染有反应，而 IMD 通路则被革兰氏阴性菌激活。在 IMD 通路的激活过程中，NF-κB 样转录因子 Relish 被磷酸化，然后被切割，这对 IMD 依赖的 AMP 基因诱导至关重要。在这里，我们表明非常规组蛋白变体 H2Av 的功能丧失突变体可上调无菌果蝇幼虫和成虫中 IMD 依赖的 AMP 基因诱导。在仔细剖析 IMD 通路后，我们发现 Relish 与 H2Av 具有上位性关系。在 H2Av 突变体幼虫中，SUMOylation 被下调，这表明 SUMOylation 可能在免疫表型中起作用。最终，我们证明 Relish 主要在氨基酸 K823 上 SUMO 化。失去潜在的 SUMO 化位点会导致 Relish 在体内的显著自动激活。进一步的工作表明，H2Av 通过与 SUMOylation 途径的 E3 成分 Su(var)2-10 物理相互作用来调节 Relish 的 SUMOylation。生化分析表明，Relish 的 SUMO 化可防止其切割和激活。我们的研究结果表明，H2Av 可以通过促进 NF-κB 样转录因子 Relish 的 SUMO 化，负调控（并因此防止 IMD 依赖的 AMP 产生的自发激活），从而提供了一种新的机制。
