Alam Syed Benazir, Rochon D'Ann
Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, Canada.
Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, Canada Summerland Research and Development Centre, Agriculture and Agri-Food Canada, Summerland, British Columbia, Canada
J Virol. 2015 Dec 30;90(7):3302-17. doi: 10.1128/JVI.02833-15.
RNA viruses often depend on host factors for multiplication inside cells due to the constraints of their small genome size and limited coding capacity. One such factor that has been exploited by several plant and animal viruses is heat shock protein 70 (HSP70) family homologs which have been shown to play roles for different viruses in viral RNA replication, viral assembly, disassembly, and cell-to-cell movement. Using next generation sequence analysis, we reveal that several isoforms of Hsp70 and Hsc70 transcripts are induced to very high levels during cucumber necrosis virus (CNV) infection of Nicotiana benthamiana and that HSP70 proteins are also induced by at least 10-fold. We show that HSP70 family protein homologs are co-opted by CNV at several stages of infection. We have found that overexpression of Hsp70 or Hsc70 leads to enhanced CNV genomic RNA, coat protein (CP), and virion accumulation, whereas downregulation leads to a corresponding decrease. Hsc70-2 was found to increase solubility of CNV CP in vitro and to increase accumulation of CNV CP independently of viral RNA replication during coagroinfiltration in N. benthamiana. In addition, virus particle assembly into virus-like particles in CP agroinfiltrated plants was increased in the presence of Hsc70-2. HSP70 was found to increase the targeting of CNV CP to chloroplasts during infection, reinforcing the role of HSP70 in chloroplast targeting of host proteins. Hence, our findings have led to the discovery of a highly induced host factor that has been co-opted to play multiple roles during several stages of the CNV infection cycle.
Because of the small size of its RNA genome, CNV is dependent on interaction with host cellular components to successfully complete its multiplication cycle. We have found that CNV induces HSP70 family homologs to a high level during infection, possibly as a result of the host response to the high levels of CNV proteins that accumulate during infection. Moreover, we have found that CNV co-opts HSP70 family homologs to facilitate several aspects of the infection process such as viral RNA, coat protein and virus accumulation. Chloroplast targeting of the CNV CP is also facilitated, which may aid in CNV suppression of host defense responses. Several viruses have been shown to induce HSP70 during infection and others to utilize HSP70 for specific aspects of infection such as replication, assembly, and disassembly. We speculate that HSP70 may play multiple roles in the infection processes of many viruses.
由于RNA病毒基因组较小且编码能力有限，它们在细胞内繁殖通常依赖宿主因子。几种植物和动物病毒利用的一种此类因子是热休克蛋白70（HSP70）家族同源物，已证明其在病毒RNA复制、病毒组装、拆卸以及细胞间移动过程中对不同病毒发挥作用。通过下一代测序分析，我们发现，在本氏烟草受黄瓜坏死病毒（CNV）感染期间，Hsp70和Hsc70转录本的几种亚型被诱导至非常高的水平，并且HSP70蛋白也被诱导至少10倍。我们表明，HSP70家族蛋白同源物在感染的几个阶段被CNV利用。我们发现，Hsp70或Hsc70的过表达导致CNV基因组RNA、衣壳蛋白（CP）和病毒粒子积累增加，而下调则导致相应减少。发现Hsc70 - 2在体外增加CNV CP的溶解度，并在本氏烟草中进行共浸润时独立于病毒RNA复制增加CNV CP的积累。此外，在CP浸润植物中，在Hsc70 - 2存在的情况下，病毒粒子组装成病毒样颗粒增加。发现HSP70在感染期间增加CNV CP向叶绿体的靶向，加强了HSP70在宿主蛋白叶绿体靶向中的作用。因此，我们的发现导致发现了一种高度诱导的宿主因子，该因子在CNV感染周期的几个阶段被利用来发挥多种作用。
由于其RNA基因组较小，CNV依赖于与宿主细胞成分相互作用以成功完成其繁殖周期。我们发现，CNV在感染期间将HSP70家族同源物诱导至高水平，这可能是宿主对感染期间积累的高水平CNV蛋白作出反应的结果。此外，我们发现CNV利用HSP70家族同源物促进感染过程的几个方面，如病毒RNA、衣壳蛋白和病毒积累。CNV CP向叶绿体的靶向也得到促进，这可能有助于CNV抑制宿主防御反应。已表明几种病毒在感染期间诱导HSP70，其他病毒利用HSP70进行感染的特定方面，如复制、组装和拆卸。我们推测HSP70可能在许多病毒的感染过程中发挥多种作用。
