Hsp90 function is required for stable transcription of the baculovirus transactivator ie-1 gene

A molecular chaperone heat shock protein 90 (Hsp90) is required for efficient infection by several viruses. Hsp90 has been recently implicated in baculovirus infection, but its exact role remains obscure. This study investigated the effect of 17-N-allylamino-17-demethoxygeldanamycin (17-AAG), an Hsp90-specific inhibitor, on Bombyx mori nucleopolyhedrovirus (BmNPV) infection. The 17-AAG treatment significantly decreased the production of budded viruses and occlusion bodies in BmNPV-infected Bombyx mori cultured cells. Immunoblot and SDS-PAGE analyses showed that the expression of early and delayed early gene products, DBP and BRO, was delayed and dysregulated, and the very late gene product POLH was almost completely diminished. RT-qPCR experiments revealed that 17-AAG treatment did not affect initiation of the immediate early gene ie-1 expression, but the expression decreased by ∼50 % during the late stage of infection. 17-AAG treatment also decreased ie-1 promoter activity by ∼50 %. In addition, the expression of delayed early and late genes was dysregulated and inhibited, respectively. These results indicated that Hsp90 function is required for stable ie-1 transcription. Inhibiting Hsp90 function negatively affects ie-1 expression, resulting in dysregulation of delayed early genes and a severe decrease in late and very late gene expression.