Identification of heat-shock protein 90 beta in Japanese encephalitis virus-induced secretion proteins

Five host cellular proteins were identified in the secretion medium from Japanese encephalitis virus (JEV)-infected baby hamster kidney-21 (BHK-21) cells, including three molecular chaperones: Hsp70, GRP78 and Hsp90. Hsp90 isoforms were characterized further. Hsp90 alpha was observed to be retained inside the nuclei, whereas Hsp90 beta associated with virus particles during assembly and was released into the secretion medium upon JEV infection. The association of Hsp90 beta and viral E protein was demonstrated by using sucrose-density fractionation and Western blot analysis. Moreover, JEV viral RNA replication was not affected by treatment with geldanamycin, an Hsp90 inhibitor, but impaired virus infectivity that was determined by a plaque-forming assay. Our results show that Hsp90 beta, not Hsp90 alpha, is present in the JEV-induced secretion medium and is required for JEV infectivity in BHK-21 cells.