Hsp90 Chaperones Bluetongue Virus Proteins and Prevents Proteasomal Degradation.

Bjorn-Patrick Mohl,Polly Roy,Tom Gallagher

doi:10.1128/jvi.00898-19

Bjorn-Patrick Mohl, Polly Roy + Show 1 more

Open Access

https://doi.org/10.1128/jvi.00898-19

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Abstract

The molecular chaperone machinery is important for the maintenance of protein homeostasis within the cells. The principle activities of the chaperone machinery are to facilitate protein folding and organize conformationally dynamic client proteins. Prominent among the members of the chaperone family are heat shock protein 70 (Hsp70) and 90 (Hsp90). Like cellular proteins, viral proteins depend upon molecular chaperones to mediate their stabilization and folding. Bluetongue virus (BTV), which is a model system for the Reoviridae family, is a nonenveloped arbovirus that causes hemorrhagic disease in ruminants. This constitutes a significant burden upon animals of commercial significance, such as sheep and cattle. Here, for the first time, we examined the role of chaperone proteins in the viral lifecycle of BTV. Using a combination of molecular, biochemical, and microscopic techniques, we examined the function of Hsp90 and its relevance to BTV replication. We demonstrate that Hsp70, the chaperone that is commonly usurped by viral proteins, does not influence virus replication, while Hsp90 activity is important for virus replication by stabilizing BTV proteins and preventing their degradation via the ubiquitin-proteasome pathway. To our knowledge this is the first report showing the involvement of Hsp90 as a modulator of BTV infection.IMPORTANCE Protein chaperones are instrumental for maintaining protein homeostasis, enabling correct protein folding and organization; prominent members include heat shock proteins 70 and 90. Virus infections place a large burden on this homeostasis. Identifying and understanding the underlying mechanisms that facilitate Bluetongue virus replication and spread through the usurpation of host factors is of primary importance for the development of intervention strategies. Our data identify and show that heat shock protein 90, but not heat shock protein 70, stabilizes bluetongue virus proteins, safeguarding them from proteasomal degradation.

Highlights

The molecular chaperone machinery is important for the maintenance of protein homeostasis within the cells
In order to obtain direct evidence that Hsp90 activity is involved during the virus life cycle, we used a specific inhibitor for Hsp90, geldanamycin, which binds the N-terminal ATP/ ADP-binding domain of Hsp90 and interferes with its ability to stabilize client proteins [6]
Lysates were analyzed by Western blotting using specific antibodies, which showed comparable decreases in both structural (VP2, VP5, and VP7) and nonstructural (NS1, NS2, and NS3) protein levels, while Hsp90 protein levels remained unperturbed by the inhibition (Fig. 1A)

Summary

Introduction

The molecular chaperone machinery is important for the maintenance of protein homeostasis within the cells. We demonstrate that Hsp, the chaperone that is commonly usurped by viral proteins, does not influence virus replication, while Hsp activity is important for virus replication by stabilizing BTV proteins and preventing their degradation via the ubiquitin-proteasome pathway. To our knowledge this is the first report showing the involvement of Hsp as a modulator of BTV infection. BTV utilizes a number of essential host factors to facilitate successful infection, replication, and viral spread These include, but are not limited to, the late endosome-specific lipid lysobisphosphatidic acid [18], casein kinase 2 [19, 20], calpactin [21], and the NEDD4 family of proteins [22], respectively. BTV has been found to require multi vesicular body components and exocytic pathway proteins for infectious virus production [22]

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