HSP90 binds TBK1 and IRF3

During viral infection, cytosolic viral RNA triggers activation of mitochondrial antiviral-signaling protein (MAVS) and the formation of MAVS signalosome (Kawai T et al. 2005; Seth RB et al. 2005; Xu LG et al. 2005). Activated MAVS recruits TANK-binding kinase 1 (TBK1), interferon regulatory factor 3 (IRF3) and IRF7 to the mitochondria leading to the activation of IRF3/IRF7 and subsequent production of type I interferons (Kawai T et al. 2005; Seth RB et al. 2005; Xu LG et al. 2005).<p>Co-immunoprecipitation assay showed that both TBK1 and IRF3 associated with heat shock protein 90kDa (HSP90), which facilitated signal transduction from TBK1 to IRF3 in Sendai virus (SeV)-infected human embryonic kidney (HEK293) cells (Yang K et l. 2006). MAVS, TBK1 and IRF3 were found to associate with mitochondrial import receptor subunit TOM70 (TOMM70) in HEK293 cells (Liu XY et al. 2010). TOMM70 localizes on the outer membrane of the mitochondria to mediate the translocation of mitochondrial protein precursors from the cytosol into the mitochondria (reviewed in Fan AC & Young JC 2011; Sokol AM et al. 2014; Kreimendahl S & Rassow J 2020). The molecular chaperone complexes of HSP90 and HSP70 were shown to deliver precursor proteins to TOMM70 for subsequent import (Young JC et al. 2003; Zanphorlin LM et al. 2016). The C-terminal motif (EEVD) of HSP90 was found to bind the N-terminal TPR clamp-type domain of TOMM70 (Liu XY et al. 2010; Gava LM et al. 2011). Knockdown of HSP90 by small interfering RNA (siRNA) decreased the association of TOMM70 with TBK1 and IRF3 in HEK293T cells (Liu XY et al. 2010). Further, in SeV-stimulated HEK293 cells, cytosolic BAX translocated to the mitochondrial outer membrane and induced apoptosis in the IRF3-dependent manner via the formation of the TOMM70:HSP90:IRF3:BAX protein complex (Wei B et al. 2015). The data suggest that HSP90 forms a complex with TBK1 and IRF3 in the cytosol and deliver them to the MAVS signalosome on the mitochondria.<p>Interaction between HSP90 and US11, a viral protein derived from human herpesvirus 1 (HHV-1, also known as herpes simplex virus 1, HSV-1) disrupted the formation of the HSP90:TBK1:IRF3 complex and induced degradation of TBK1 through a proteasome-dependent pathway in mouse embryonic fibroblasts (MEFs) (Liu X et al. 2018).

在病毒感染过程中，细胞质中的病毒RNA激活了线粒体抗病毒信号蛋白（MAVS）及其信号复合物的形成（Kawai T 等，2005；Seth RB 等，2005；Xu LG 等，2005）。活化的MAVS招募TANK结合激酶1（TBK1）、干扰素调节因子3（IRF3）和IRF7至线粒体，进而引发IRF3/IRF7的激活并随后产生I型干扰素（Kawai T 等，2005；Seth RB 等，2005；Xu LG 等，2005）。共免疫沉淀实验表明，TBK1和IRF3与热休克蛋白90kDa（HSP90）相联系，并在感染新泻病毒（SeV）的人胚胎肾（HEK293）细胞中促进了TBK1至IRF3的信号转导（Yang K 等，2006）。在HEK293细胞中，MAVS、TBK1和IRF3被发现与线粒体导入受体亚基TOM70（TOMM70）相联系（Liu XY 等，2010）。TOMM70定位于线粒体外膜，以介导细胞质中线粒体蛋白前体向线粒体的转位（参见Fan AC & Young JC，2011；Sokol AM 等，2014；Kreimendahl S & Rassow J，2020）。研究表明，HSP90和HSP70的分子伴侣复合物将前体蛋白递送到TOMM70以实现后续的导入（Young JC 等，2003；Zanphorlin LM 等，2016）。HSP90的C端基序（EEVD）被发现与TOMM70的N端TPR夹型结构域结合（Liu XY 等，2010；Gava LM 等，2011）。通过小干扰RNA（siRNA）敲低HSP90可降低TOMM70与TBK1和IRF3在HEK293T细胞中的关联（Liu XY 等，2010）。此外，在SeV刺激的HEK293细胞中，细胞质中的BAX蛋白转位至线粒体外膜，并通过TOMM70:HSP90:IRF3:BAX蛋白复合物的形成，在IRF3依赖的方式下诱导细胞凋亡（Wei B 等，2015）。数据表明，HSP90在细胞质中与TBK1和IRF3形成复合物，并将它们递送到线粒体上的MAVS信号复合物中。<p>HSP90与来自人疱疹病毒1（HHV-1，亦称单纯疱疹病毒1，HSV-1）的病毒蛋白US11的相互作用破坏了HSP90:TBK1:IRF3复合物的形成，并在小鼠胚胎成纤维细胞（MEFs）中通过蛋白酶体依赖途径诱导TBK1的降解（Liu X 等，2018）。