Modulation of Hsf1 activity by novobiocin and geldanamycin

Abstract

Since Hsp90 is a known modulator of HSF1 activity, we examined the effects of two pharmacological inhibitors of Hsp90, novobiocin and geldanamycin, on HSF1 DNA-binding activity in the Xenopus oocyte model system. Novobiocin exhibits antiproliferative activity in culture cells and interacts with a C-terminal ATP-binding pocket on Hsp90, inhibiting Hsp90 autophosphorylation. Treatment of oocytes with novobiocin followed by heat shock results in a dose-dependent decrease in HSF1 DNA-binding and transcriptional activity. Immunoprecipitation experiments demonstrate novobiocin does not alter HSF1 activity through dissociation of Hsp90 from either monomeric or trimerized HSF1, suggesting that the effect of novobiocin on HSF1 is mediated through alterations in Hsp90 autophosphorylation. Geldanamycin binds the N-terminal ATPase site of Hsp90 and inhibits chaperone activity. Geldanamycin treatment of oocytes resulted in a dose-dependent increase in stability of active HSF1 trimers during submaximal heat shock and a delay in disassembly of trimers during recovery. The results suggest that Hsp90 chaperone activity is required for disassembly of HSF1 trimers. The data obtained with novobiocin suggests the C-terminal ATP-binding activity of Hsp90 is required for the initial steps of HSF1 trimerization, whereas the effects of geldanamycin suggest N-terminal ATPase and chaperone activities are required for disassembly of activated trimers. These data provide important insight into the molecular mechanisms by which pharmacological inhibitors of Hsp90 affect the heat shock response.

Molecular Stress-inducing Compounds Increase Osteoclast Formation in a Heat Shock Factor 1 Protein-dependent Manner

“…Moreover, we have found no clear correlation between the potency of the HSP90 inhibitors and their ability to induce osteoclast formation. It should also be noted that these compounds had a minimal effect on the induction of HSR, consistent with previous observations that novobiocin causes a dose-dependent decrease in Hsf1 DNA-binding and transcriptional activities (61). Combined, these results suggest that HSP90 inhibition per se may not enhance osteoclast formation and is consistent with a role for the involvement of Hsf1 downstream target involvement.…”

Co-targeting AR and HSP90 suppresses prostate cancer cell growth and prevents resistance mechanisms

“…This reveals a key mechanistic advantage for the combination, compared to single-agent treatment with N-terminal Hsp90 inhibitors, that may markedly improve patient responses. Similar to combined 17-AAG and bicalutamide, C-terminal targeted Hsp90 inhibitors do not elicit a heat shock response (Conde et al 2009, Eskew et al 2011, and development of these agents is currently being pursued to take advantage of this characteristic.…”

Biology of the Heat Shock Response and Protein Chaperones: Budding Yeast (Saccharomyces cerevisiae) as a Model System

“…In yeast, a double mutant lacking constitutively expressed Hsp90 and a cyclophilin 40 homolog, hsc82⌬ cpr7⌬, exhibits high levels of Hsf1 activity in the absence of stress and is thermotolerant (113,169). Moreover, studies to identify Hsf1 pharmacological modulators showed that some Hsf1 activators also function as Hsp90-specific inhibitors, such as geldanamycin and radicicol (67,241,403). Recently, celastrol, an active component of Chinese medicine, was found to promote HSP gene expression through Hsf1 activation and to block the maturation of Hsp90-dependent steroid receptors in yeast and human cells (185,465,507).…”