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SUMMARY Chaperones are central to the proteostasis network (PN) and safeguard the proteome from misfolding, aggregation and proteotoxicity. We categorized the human chaperome of 332 genes into network communities using function, localization, interactome, and expression datasets. During human brain aging, expression of 32% of the chaperome corresponding to ATP-dependent chaperone machines is repressed, whereas 19.5% corresponding to ATP-independent chaperones and co-chaperones are induced. These repression and induction clusters are enhanced in Alzheimer's, Huntington's, and Parkinson's brains. Functional properties of the chaperome were assessed by perturbation in C. elegans and human cell models expressing Aβ, polyglutamine and Huntingtin. Of 219 C. elegans orthologs, knockdown of sixteen enhanced both Aβ and polyQ-associated toxicity. These correspond to 28 human orthologs, of which 52% and 41% are repressed, respectively, in brain aging and disease, and 37.5% affected Huntingtin aggregation in human cells. These results identify a critical chaperome sub-network that functions in aging and disease.

Molecular chaperones, inducible by heat shock and a variety of other stresses, have critical roles in protein homeostasis, balancing cell stress with adaptation, survival, and cell death mechanisms. In transformed cells and tumors, chaperones are frequently overexpressed, with constitutive activation of the heat shock transcription factor HSF1 implicated in tumor formation. Here, we describe the activity of triptolide, a diterpene triepoxide from the plant Triptergium wilfordii, as an inhibitor of the human heat shock response. Triptolide treatment of human tissue culture cells prevented the inducible expression of heat shock genes, shown by suppression of an HSP70 promoter-reporter construct and by suppression of endogenous HSP70 gene expression. Upon examining the steps in the HSF1 activation pathway, we found that triptolide abrogates the transactivation function of HSF1 without interfering in the early events of trimer formation, hyperphosphorylation, and DNA binding. The ability of triptolide to inhibit the heat shock response renders these cells sensitive to stress-induced cell death, which may be of great relevance to cancer treatments.Elevated levels of heat shock protein expression have been identified as a biomarker for many cancers and are correlated with poor prognosis (reviewed in Ref. 1). Molecular chaperones have diverse roles in the regulation of signal transduction and in numerous aspects of cell growth and cell death. At the level of specific chaperones, HSP90, HSP70, and HSP27 have each been implicated in promoting cancer. HSP90 regulates the activities of many signaling molecules and kinases important in cancer, including NF-B, p53, Raf1, Akt, and steroid aporeceptors (reviewed in Ref. 2). In addition, HSP90, HSP70, and HSP27 have been shown to be anti-apoptotic (reviewed in Ref.3). Although they serve to prevent stressed primary cells from initiating cell death, in transformed cells the elevated levels of these chaperones may interfere with the proper regulation of caspase activities.Several cancer strategies have focused on the inhibition of individual chaperones. For instance, inhibition of HSP90 by the fungal antibiotic radicicol, the benzoquinone ansamycin geldanamycin, and the geldanamycin-related analog 17-allylamino-17-demethoxygeldanamycin (17-AAG), which has been shown to potently reduce tumor growth, is currently in clinical trials (4). Depletion of HSP70 levels by antisense RNAs causes cell death in transformed cell lines, but not in nontransformed cells, and inhibits tumorigenesis in xenograft models (5, 6). Similar anticancer effects have also been observed with antisense RNA against HSP27 (7).The regulation of heat shock gene expression is complex and involves a multitude of promoter elements that confer responses to specific signals and growth factors (8 -12). Common to all heat shock-induced genes are heat shock elements, promoter sites that have high affinity for binding to a family of heat shock transcription factors (HSFs).4 HSF1 is well characterized and is essential for ...