Multi-Faceted Proteomic Characterization of Host Protein Complement of Rift Valley Fever Virus Virions and Identification of Specific Heat Shock Proteins, Including HSP90, as Important Viral Host Factors

Rift Valley fever is a potentially fatal disease of humans and domestic animals caused by Rift Valley fever virus (RVFV). Infection with RVFV in ruminants can cause near 100% abortion rates and recent outbreaks in naïve human populations have suggested case fatality rates of greater than thirty percent. To elucidate the roles that host proteins play during RVFV infection, proteomic analysis of RVFV virions was conducted using complementary analytical approaches, followed by functional validation studies of select identified host factors. Coupling the more traditional Gel LC/MS/MS approach (SDS PAGE followed by liquid chromatography tandem mass spectrometry) with an alternative technique that preserves protein complexes allowed the protein complement of these viral particles to be thoroughly examined. In addition to viral proteins present within the virions and virion-associated host proteins, multiple macromolecular complexes were identified. Bioinformatic analysis showed that host chaperones were among over-represented protein families associated with virions, and functional experiments using siRNA gene silencing and small molecule inhibitors identified several of these heat shock proteins, including heat shock protein 90 (HSP90), as important viral host factors. Further analysis indicated that HSP inhibition effects occur during the replication/transcription phase of the virus life cycle, leading to significant lowering of viral titers without compromising the functional capacity of released virions. Overall, these studies provide much needed further insight into interactions between RVFV and host cells, increasing our understanding of the infection process and suggesting novel strategies for anti-viral development. In particular, considering that several HSP90 inhibitors have been advancing through clinical trials for cancer treatment, these results also highlight the exciting potential of repurposing HSP90 inhibitors to treat RVF.

裂谷热（Rift Valley fever）是一种由裂谷热病毒（Rift Valley fever virus, RVFV）引发的可感染人类与家养动物的致死性疾病。反刍动物感染RVFV后，流产率可接近100%；近期在无免疫人群中暴发的疫情显示，该病的病死率超过30%。

为阐明宿主蛋白在RVFV感染过程中发挥的作用，本研究采用互补分析方法对RVFV病毒粒子开展蛋白质组学分析，并对筛选出的部分已鉴定宿主因子进行功能验证研究。研究将传统的凝胶液相色谱-串联质谱法（即先经十二烷基硫酸钠聚丙烯酰胺凝胶电泳（SDS-PAGE），再行液相色谱串联质谱分析）与另一项可保留蛋白质复合物完整结构的新技术相结合，对这些病毒颗粒的蛋白组成进行了全面解析。

除病毒粒子内部的病毒蛋白及与病毒粒子结合的宿主蛋白外，本研究还鉴定出多种大分子复合物。生物信息学分析显示，宿主分子伴侣是与病毒粒子相关的富集蛋白家族之一；通过小干扰RNA（siRNA）基因沉默与小分子抑制剂开展的功能实验，证实包括热休克蛋白90（heat shock protein 90, HSP90）在内的数种热休克蛋白为重要的病毒宿主因子。

进一步分析表明，HSP90抑制作用发生于病毒生命周期的复制/转录阶段，可在不影响释放的病毒粒子功能活性的前提下，显著降低病毒滴度。总体而言，本研究为RVFV与宿主细胞间的相互作用提供了亟需的深入见解，加深了我们对感染过程的理解，并为抗病毒药物开发提供了全新策略。尤其值得关注的是，多款HSP90抑制剂已进入癌症治疗的临床试验阶段，本研究结果也凸显了将此类抑制剂重定位用于RVF治疗的极具前景的潜力。