Role of heat-shock protein 90 in hepatitis E virus capsid trafficking.

p239 is a virus-like particle constituted from hepatitis E virus (HEV) recombinant proteins. It can be used as a surrogate for HEV and as an investigative tool to study cellular interactions because of its ability to adsorb to and penetrate HepG2 cellular membranes. Our objective was to use p239 to define the role of HEV capsid proteins during the early stages of infection. Pull-down and MALDI-TOF MS experiments identified three host-cell proteins, Grp 78/Bip, alpha-tubulin and heat-shock protein 90 (HSP90), and the latter was investigated further. Antibodies to p239 alone or HSP90 alone could detect p239 or HSP90, suggesting the formation of a complex between p239 and HSP90. In the HepG2 cell, geldanamycin (GA), an HSP90-specific inhibitor, blocked intracellular transportation of p239, but had no effect on the binding and cellular entry of p239, suggesting that HSP90 was important for HEV capsid intracellular transportation. RT-PCR results showed that the efficiency of wild-type HEV infection was inhibited significantly by GA treatment, suggesting the importance of HSP90 in virus infectivity. It was concluded that HSP90 plays a crucial role in the intracellular transportation of viral capsids in the early stage of HEV infection.