Requirement for Hsp90 and a CyP-40-type Cyclophilin in Negative Regulation of the Heat Shock Response

Abstract

The heat shock response is a highly conserved mechanism that allows cells to withstand a variety of stress conditions. Activation of this response is characterized by increased synthesis of heat shock proteins (HSPs), which protect cellular proteins from stress-induced denaturation. Heat shock transcription factors (HSFs) are required for increased expression of HSPs during stress conditions and can be found in complexes containing components of the Hsp90 molecular chaperone machinery, raising the possibility that Hsp90 is involved in regulation of the heat shock response. To test this, we have assessed the effects of mutations that impair activity of the Hsp90 machinery on heat shock related events in Saccharomyces cerevisiae. Mutations that either reduce the level of Hsp90 protein or eliminate Cpr7, a CyP-40-type cyclophilin required for full Hsp90 function, resulted in increased HSF-dependent activities. Genetic tests also revealed that Hsp90 and Cpr7 function synergistically to repress gene expression from HSFdependent promoters. Conditional loss of Hsp90 activity resulted in both increased HSF-dependent gene expression and acquisition of a thermotolerant phenotype. Our results reveal that Hsp90 and Cpr7 are required for negative regulation of the heat shock response under both stress and nonstress conditions and establish a specific endogenous role for the Hsp90 machinery in S. cerevisiae.All cells possess a defense mechanism known as the heat shock response, which allows them to survive exposure to otherwise lethal doses of certain stresses (1-3). These stresses include environmental challenges, such as elevated temperatures, and pathophysiological states, such as viral infections (4). The heat shock response is characterized by increased synthesis of a set of proteins collectively referred to as heat shock proteins (HSPs) 1 whose principal role is to assist target substrates in their synthesis, transport, and proper folding (5-7). The requirement for chaperoning activities increases as cells are exposed to elevated temperatures or to other conditions that promote protein denaturation and aggregation. Because chaperoning activity is also crucial for the function of proteins not exposed to stress, HSPs play important roles for life under normal conditions as well.Expression of HSPs is under the control of heat shock transcription factors (HSFs) (4,8,9). In most eukaryotic systems, HSF is maintained as a monomer unable to bind DNA until activated by stress (4,8). Activated HSF forms homotrimers capable of binding to heat shock elements (HSEs) present at promoters of genes encoding HSPs, ultimately leading to transcriptional activation (4,8). The monomer to trimer transition is believed to be negatively regulated, at least in part, by Hsp70 (4,8). The acquisition of transcriptional activity by HSF is correlated with increased phosphorylation (10); however, the functional relationship between phosphorylation and regulation of the heat shock response is still not fully understood. In contrast to most eukaryoti...

Cns1 Is an Activator of the Ssa1 ATPase Activity

“…For Cpr6 and Cpr7, PPIase activity has been demonstrated previously (26,35,46). Since Cns1 is a suppressor of the cellular defects observed upon deletion of the TPR-containing peptidyl-prolyl isomerase Cpr7, the formal possibility existed that Cns1 also may exhibit prolyl isomerase activity.…”

Hyperthermia in the febrile range induces HSP72 expression proportional to exposure temperature but not to HSF-1 DNA-binding activity in human lung epithelial A549 cells

“…HSF-1 is activated through a stepwise process comprising trimerization, nuclear translocation, and phosphorylation of serines in the transactivation domains (Cotto and Morimoto 1999). Regulation of this process is incompletely understood, but involves phosphorylation and dephosphorylation of certain serine residues (Chu et al 1996;Guettouche et al 2005;Holmberg et al 2001;Park and Liu 2001;Xavier et al 2000;Xia et al 1998;Xia and Voellmy 1997) and heterologous oligomerization of HSF-1 (Ali et al 1998;Bharadwaj et al 1999;Duina et al 1998). We have previously demonstrated in the mouse RAW 264.7 macrophage cell line that HSF-1 is activated to a hypophosphorylated DNA-binding form without transactivating activity by exposure to 39.5°C for 1 h .…”

Chaperoning the Chaperone: A Role for the Co-chaperone Cpr7 in Modulating Hsp90 Function in Saccharomyces cerevisiae

“…Loss of CPR7 resulted in slow growth and defects in activity of clients such as the glucocorticoid receptor and the heatshock transcription factor Hsf1 (Duina et al 1996(Duina et al , 1998a. These defects were rescued by the overexpression of CNS1, which encodes an essential TPR-containing co-chaperone Figure 3 Expression and function of Cpr6/ Cpr7 chimeras.…”