Heat-shock protein 90α is involved in maintaining the stability of VP16 and VP16-mediated transactivation of a genes from herpes simplex virus-1

Background: Numerous host cellular factors are exploited by viruses to facilitate infection. Our previous studies and those of others have shown heat-shock protein 90 (Hsp90), a cellular molecular chaperone, is involved in herpes simplex virus (HSV)-1 infection. However, the function of the dominant Hsp90 isoform and the relationship between Hsp90 and HSV-1 alpha genes remain unclear. Methods and results: Hsp90 alpha knockdown or inhibition significantly inhibited the promoter activity of HSV-1 alpha genes and downreoulated virion protein 16(VP16) expression from virus and plasmids. The Hsp90 alpha knockdown-induced suppression of alpha genes promoter activity and downregulation of alpha genes was reversed by VP16 overexpression, indicating that Hsp90 alpha is involved in VP16-mediated transcription of HSV-1 alpha genes. Co-immunoprecipitation experiments indicated that VP16 interacted with Hsp90 alpha through the conserved core domain within VP16. Based on using autophagy inhibitors and the presence of Hsp90 inhibitors in ATG7(-/-) (autophagy-deficient) cells, Hsp90 inhibition-induced degradation of VP16 is dependent on macroautophagy-mediated degradation but not chaperonemediated autophagy (CMA) pathway. In vivo studies demonstrated that treatment with gels containing Hsp90 inhibitor effectively reduced the level of VP16 and alpha genes, which may contribute to the amelioration of the skin lesions in an HSV-1 infection mediated zosteriform model. Conclusion: Our study provides new insights into the mechanisms by which Hsp90 alpha facilitates the transactivation of HSV-1 alpha genes and viral infection, and highlights the importance of developing selective inhibitors targeting the interaction between Hsp90 alpha and VP16 to reduce toxicity, a major challenge in the clinical use of Hsp90 inhibitors.