BACKGROUND: Hsp90 is a molecular chaperone essential for cell viability in eukaryotes that is associated with the maturation of proteins involved in important cell functions and implicated in the stabilization of the tumor phenotype of various cancers, making this chaperone a notably interesting therapeutic target. Celastrol is a plant-derived pentacyclic triterpenoid compound with potent antioxidant, anti-inflammatory and anticancer activities; however, celastrol's action mode is still elusive.RESULTS: In this work, we investigated the effect of celastrol on the conformational and functional aspects of Hsp90á. Interestingly, celastrol appeared to target Hsp90á directly as the compound induced the oligomerization of the chaperone via the C-terminal domain as demonstrated by experiments using a deletion mutant. The nature of the oligomers was investigated by biophysical tools demonstrating that a two-fold excess of celastrol induced the formation of a decameric Hsp90á bound throughout the C-terminal domain. When bound, celastrol destabilized the C-terminal domain. Surprisingly, standard chaperone functional investigations demonstrated that neither the in vitro chaperone activity of protecting against aggregation nor the ability to bind a TPR co-chaperone, which binds to the C-terminus of Hsp90á, were affected by celastrol.CONCLUSION: Celastrol interferes with specific biological functions of Hsp90á. Our results suggest a model in which celastrol binds directly to the C-terminal domain of Hsp90á causing oligomerization. However, the ability to protect against protein aggregation (supported by our results) and to bind to TPR co-chaperones are not affected by celastrol. Therefore celastrol may act primarily by inducing specific oligomerization that affects some, but not all, of the functions of Hsp90á.GENERAL SIGNIFICANCE: To the best of our knowledge, this study is the first work to use multiple probes to investigate the effect that celastrol has on the stability and oligomerization of Hsp90á and on the binding of this chaperone to Tom70. This work provides a novel mechanism by which celastrol binds Hsp90á.
Antineoplastic Agents HSP90 Heat-Shock Proteins