Hsp70 and the Cochaperone StiA (Hop) Orchestrate Hsp90-Mediated Caspofungin Tolerance in Aspergillus fumigatus

Antimicrob Agents Chemother. 2015 Aug;59(8):4727-33. doi: 10.1128/AAC.00946-15. Epub 2015 May 26.


Aspergillus fumigatus is the primary etiologic agent of invasive aspergillosis (IA), a major cause of death among immunosuppressed patients. Echinocandins (e.g., caspofungin) are increasingly used as second-line therapy for IA, but their activity is only fungistatic. Heat shock protein 90 (Hsp90) was previously shown to trigger tolerance to caspofungin and the paradoxical effect (i.e., decreased efficacy of caspofungin at higher concentrations). Here, we demonstrate the key role of another molecular chaperone, Hsp70, in governing the stress response to caspofungin via Hsp90 and their cochaperone Hop/Sti1 (StiA in A. fumigatus). Mutation of the StiA-interacting domain of Hsp70 (C-terminal EELD motif) impaired thermal adaptation and caspofungin tolerance with loss of the caspofungin paradoxical effect. Impaired Hsp90 function and increased susceptibility to caspofungin were also observed following pharmacologic inhibition of the C-terminal domain of Hsp70 by pifithrin-μ or after stiA deletion, further supporting the links among Hsp70, StiA, and Hsp90 in governing caspofungin tolerance. StiA was not required for the physical interaction between Hsp70 and Hsp90 but had distinct roles in the regulation of their function in caspofungin and heat stress responses. In conclusion, this study deciphering the physical and functional interactions of the Hsp70-StiA-Hsp90 complex provided new insights into the mechanisms of tolerance to caspofungin in A. fumigatus and revealed a key C-terminal motif of Hsp70, which can be targeted by specific inhibitors, such as pifithrin-μ, to enhance the antifungal activity of caspofungin against A. fumigatus.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Antifungal Agents / pharmacology*
  • Aspergillus fumigatus / drug effects
  • Aspergillus fumigatus / metabolism*
  • Caspofungin
  • Echinocandins / pharmacology*
  • Fungal Proteins / metabolism*
  • HSP70 Heat-Shock Proteins / metabolism*
  • HSP90 Heat-Shock Proteins / metabolism*
  • Heat-Shock Response / drug effects
  • Humans
  • Lipopeptides
  • Molecular Chaperones / metabolism*
  • Protein Binding
  • Protein Structure, Tertiary


  • Antifungal Agents
  • Echinocandins
  • Fungal Proteins
  • HSP70 Heat-Shock Proteins
  • HSP90 Heat-Shock Proteins
  • Lipopeptides
  • Molecular Chaperones
  • Caspofungin