Gambogic acid and gambogenic acid induce a thiol-dependent heat shock response and disrupt the interaction between HSP90 and HSF1 or HSF2

Linda Pesonen,Aurélie De Thonel,Valérie Mezger,Délara Sabéran-Djoneidi,Pia Roos-Mattjus,Viktor Bäck,Sally Svartsjö

doi:10.1007/s12192-021-01222-4

Abstract

Cancer cells rely on heat shock proteins (HSPs) for growth and survival. Especially HSP90 has multiple client proteins and plays a critical role in malignant transformation, and therefore different types of HSP90 inhibitors are being developed. The bioactive natural compound gambogic acid (GB) is a prenylated xanthone with antitumor activity, and it has been proposed to function as an HSP90 inhibitor. However, there are contradicting reports whether GB induces a heat shock response (HSR), which is cytoprotective for cancer cells and therefore a potentially problematic feature for an anticancer drug. In this study, we show that GB and a structurally related compound, called gambogenic acid (GBA), induce a robust HSR, in a thiol-dependent manner. Using heat shock factor 1 (HSF1) or HSF2 knockout cells, we show that the GB or GBA-induced HSR is HSF1-dependent. Intriguingly, using closed form ATP-bound HSP90 mutants that can be co-precipitated with HSF1, a known facilitator of cancer, we show that also endogenous HSF2 co-precipitates with HSP90. GB and GBA treatment disrupt the interaction between HSP90 and HSF1 and HSP90 and HSF2. Our study implies that these compounds should be used cautiously if developed for cancer therapies, since GB and its derivative GBA are strong inducers of the HSR, in multiple cell types, by involving the dissociation of a HSP90-HSF1/HSF2 complex.

Highlights

HSP90 is an essential ATP-dependent molecular chaperone that is one of the most abundant proteins in eukaryotic cells
There was no induction of HSPA1A or HSPH1 mRNA in response to Gambogic acid (GB) treatment in cells lacking heat shock factor 1 (HSF1). These results show that 17-AAG, GB, and the GB-analog gambogenic acid (GBA) induce a heat shock response (HSR) that is strictly dependent on HSF1 but not on HSF2
We show that acute treatments with either GB or its structural analog GBA induce a thiol-dependent HSR in multiple cell lines derived from different cellular

Summary

Introduction

HSP90 is an essential ATP-dependent molecular chaperone that is one of the most abundant proteins in eukaryotic cells. HSP90 has a vast repertoire of client proteins consisting of kinases and phosphatases, nuclear hormone receptors, actin and tubulin, and the proteasome subunits, and its activity and client specificity rely on different co-chaperones (Csermely et al 1998; Pearl 2016). The heat shock response (HSR) is a universal stressprotective pathway that is induced in response to proteotoxic stress, e.g., exposure to heat, proteasome inhibitors, and infections (Richter et al 2010). The HSR is characterized by a fast and massive increase in the expression of molecular chaperones, such as the heat shock proteins (HSPs), which refold damaged proteins and prevent protein aggregation. The transcription of HSP genes is mediated by heat shock factors (HSFs). HSFs oligomerize and accumulate into the nucleus and bind to specific heat shock elements (HSEs). HSF2 has, been shown to form heterocomplexes with HSF1 and modulate the expression of HSR genes, suggesting a role in the HSR (Östling et al 2007; Sandqvist et al 2009)

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Conclusion