Department of Entomology, University of Georgia, Athens, Georgia, USA.
PLoS Pathog. 2012;8(5):e1002722. doi: 10.1371/journal.ppat.1002722. Epub 2012 May 24.
Recent studies have greatly increased understanding of how the immune system of insects responds to infection, whereas much less is known about how pathogens subvert immune defenses. Key regulators of the insect immune system are Rel proteins that form Nuclear Factor-κB (NF-κB) transcription factors, and inhibitor κB (IκB) proteins that complex with and regulate NF-κBs. Major mortality agents of insects are parasitoid wasps that carry immunosuppressive polydnaviruses (PDVs). Most PDVs encode ank genes that share features with IκBs, while our own prior studies suggested that two ank family members from Microplitis demolitor bracovirus (MdBV) (Ank-H4 and Ank-N5) behave as IκB mimics. However, the binding affinities of these viral mimics for Rel proteins relative to endogenous IκBs remained unclear. Surface plasmon resonance (SPR) and co-immunoprecipitation assays showed that the IκB Cactus from Drosophila bound Dif and Dorsal homodimers more strongly than Relish homodimers. Ank-H4 and -N5 bound Dif, Dorsal and Relish homodimers with higher affinity than the IκB domain of Relish (Rel-49), and also bound Relish homodimers more strongly than Cactus. Ank-H4 and -N5 inhibited processing of compound Relish and reduced the expression of several antimicrobial peptide genes regulated by the Imd signaling pathway in Drosophila mbn2 cells. Studies conducted in the natural host Pseudoplusia includens suggested that parasitism by M. demolitor also activates NF-κB signaling and that MdBV inhibits this response. Overall, our data provide the first quantitative measures of insect and viral IκB binding affinities, while also showing that viral mimics disable Relish processing.
最近的研究极大地提高了人们对昆虫免疫系统如何对感染做出反应的理解，而对于病原体如何颠覆免疫防御则知之甚少。昆虫免疫系统的关键调节因子是 Rel 蛋白，它形成核因子-κB（NF-κB）转录因子，以及与 NF-κB 结合并调节其活性的抑制κB（IκB）蛋白。昆虫的主要致死因子是携带免疫抑制多粒病毒（PDV）的寄生蜂。大多数 PDV 编码 ank 基因，这些基因与 IκB 具有相似的特征，而我们之前的研究表明，来自 Microplitis demolitor bracovirus（MdBV）的两个 ank 家族成员（Ank-H4 和 Ank-N5）表现为 IκB 模拟物。然而，这些病毒模拟物与内源性 IκB 相比与 Rel 蛋白的结合亲和力仍不清楚。表面等离子体共振（SPR）和共免疫沉淀实验表明，果蝇的 IκB Cactus 与 Dif 和 Dorsal 同源二聚体的结合比 Relish 同源二聚体更强。Ank-H4 和 -N5 与 Dif、Dorsal 和 Relish 同源二聚体的结合亲和力高于 Relish 的 IκB 结构域（Rel-49），并且与 Cactus 的结合也比 Relish 同源二聚体更强。Ank-H4 和 -N5 抑制了复合 Relish 的加工，并降低了果蝇 mbn2 细胞中 Imd 信号通路调控的几种抗菌肽基因的表达。在 Pseudoplusia includens 的天然宿主中进行的研究表明，M. demolitor 的寄生也激活了 NF-κB 信号通路，而 MdBV 抑制了这种反应。总的来说，我们的数据提供了昆虫和病毒 IκB 结合亲和力的第一个定量测量值，同时也表明病毒模拟物使 Relish 加工失活。
