In response to stress, heat shock factor 1 (HSF1) acquires rapid DNA binding and transient transcriptional activity while undergoing conformational transition from an inert non-DNA-binding monomer to active functional trimers. Attenuation of the inducible transcriptional response occurs during heat shock or upon recovery at non-stress conditions and involves dissociation of the HSF1 trimer and loss of activity. We have used the hydrophobic repeats of the HSF1 trimerization domain in the yeast two-hybrid protein interaction assay to identify heat shock factor binding protein 1 (HSBP1), a novel, conserved, 76-amino-acid protein that contains two extended arrays of hydrophobic repeats that interact with the HSF1 heptad repeats. HSBP1 is nuclear-localized and interacts in vivo with the active trimeric state of HSF1 that appears during heat shock. During attenuation of HSF1 to the inert monomer, HSBP1 associates with Hsp70. HSBP1 negatively affects HSF1 DNA-binding activity, and overexpression of HSBP1 in mammalian cells represses the transactivation activity of HSF1. To establish a biological role for HSBP1, the homologous Caenorhabditis elegans protein was overexpressed in body wall muscle cells and was shown to block activation of the heat shock response from a heat shock promoter-reporter construct. Alteration in the level of HSBP1 expression in C. elegans has severe effects on survival of the animals after thermal and chemical stress, consistent with a role for HSBP1 as a negative regulator of the heat shock response.

A hallmark of diseases of protein conformation and aging is the appearance of protein aggregates associated with cellular toxicity. We posit that the functional properties of the proteostasis network (PN) protect the proteome from misfolding and combat the proteotoxic events leading to cellular pathology. In this study, we have identified new components of the proteostasis network that can suppress aggregation and proteotoxicity, by performing RNA interference (RNAi) genetic screens for multiple unrelated conformationally challenged cytoplasmic proteins expressed in Caenorhabditis elegans. We identified 88 suppressors of polyglutamine (polyQ) aggregation, of which 63 modifiers also suppressed aggregation of mutant SOD1G93A. Of these, only 23 gene-modifiers suppressed aggregation and restored animal motility, revealing that aggregation and toxicity can be genetically uncoupled. Nine of these modifiers were shown to be effective in restoring the folding and function of multiple endogenous temperature-sensitive (TS) mutant proteins, of which five improved folding in a HSF-1–dependent manner, by inducing cytoplasmic chaperones. This triage screening strategy also identified a novel set of PN regulatory components that, by altering metabolic and RNA processing functions, establish alternate cellular environments not generally dependent on stress response activation and that are broadly protective against misfolded and aggregation-prone proteins.

Vertebrate cells express a family of heat shock transcription factors (HSF1 to HSF4) that coordinate the inducible regulation of heat shock genes in response to diverse signals. HSF1 is potent and activated rapidly though transiently by heat shock, whereas HSF2 is a less active transcriptional regulator but can retain its DNA binding properties for extended periods. Consequently, the differential activation of HSF1 and HSF2 by various stresses may be critical for cells to survive repeated and diverse stress challenges and to provide a mechanism for more precise regulation of heat shock gene expression. Here we show, using a novel DNA binding and detection assay, that HSF1 and HSF2 are coactivated to different levels in response to a range of conditions that cause cell stress. Above a low basal activity of both HSFs, heat shock preferentially activates HSF1, whereas the amino acid analogue azetidine or the proteasome inhibitor MG132 coactivates both HSFs to different levels and hemin preferentially induces HSF2. Unexpectedly, we also found that heat shock has dramatic adverse effects on HSF2 that lead to its reversible inactivation coincident with relocalization from the nucleus. The reversible inactivation of HSF2 is specific to heat shock and does not occur with other stressors or in cells expressing high levels of heat shock proteins. These results reveal that HSF2 activity is negatively regulated by heat and suggest a role for heat shock proteins in the positive regulation of HSF2.The heat shock response is a cellular defense against the deleterious effects of physiological and environmental stress that is mediated by heat shock transcription factors (HSFs). In vertebrates, four members of the HSF family have been identified (27,28,38,40,46), and of these, HSF1 and HSF2 are ubiquitously expressed and conserved (27,40). HSF1 and HSF2 are expressed as inert monomers and dimers, respectively, in unstressed cells. Upon activation, these HSFs trimerize and function as transcriptional activators that bind with similar, but not identical, specificities to the heat shock element (HSE), thus regulating heat shock gene transcription and hence the expression of diverse heat shock proteins and molecular chaperones (2,40,49,62).HSF1 and HSF2 differ in their pathways of activation and the nature of their transcriptional responses. Whereas HSF1 is activated upon exposure to a multitude of physiological and environmental stresses (41, 62), HSF2 activity appears to be more selective, being induced upon down-regulation of the ubiquitin-proteasome pathway (22), during differentiation (36,37,42,49), and in early development (9, 23, 37). Comparison of the HSF1 and HSF2 transactivation domains as chimeric proteins with a minimal heterologous DNA binding domain reveals that HSF1 is a more potent transcriptional activator than HSF2 (47, 59, 60). These observations are also supported by studies comparing hsp70 and hsp90 gene transcription rates in K562 cells in which endogenous HSF1 or HSF2 was activated (49). In those studies, HSF1 ...

Amyotrophic lateral sclerosis (ALS) is a progressive and ultimately fatal neurodegenerative disease. Pyrazolone containing small molecules have shown significant disease attenuating efficacy in cellular and murine models of ALS. Pyrazolone based affinity probes were synthesized to identify high affinity binding partners and ascertain a potential biological mode of action. Probes were confirmed to be neuroprotective in PC12-SOD1G93A cells. PC12-SOD1G93A cell lysates were used for protein pull-down, affinity purification, and subsequent proteomic analysis using LC-MS/MS. Proteomics identified the 26S proteasome regulatory subunit 4 (PSMC1), 26S proteasome regulatory subunit 6B (PSMC4), and T-complex protein 1 (TCP-1) as putative protein targets. Coincubation with appropriate competitors confirmed the authenticity of the proteomics results. Activation of the proteasome by pyrazolones was demonstrated in the absence of exogenous proteasome inhibitor and by restoration of cellular protein degradation of a fluorogenic proteasome substrate in PC12-SOD1G93A cells. Importantly, supplementary studies indicated that these molecules do not induce a heat shock response. We propose that pyrazolones represent a rare class of molecules that enhance proteasomal activation in the absence of a heat shock response and may have therapeutic potential in ALS.

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Heat shock factor 1 (HSF1) is the ubiquitous stress-responsive transcriptional activator which is essential for the inducible transcription of genes encoding heat shock proteins and molecular chaperones. HSF1 localizes within the nucleus of cells exposed to heat shock, heavy metals, and amino acid analogues, to form large, irregularly shaped, brightly staining granules which are not detected during attenuation of the heat shock response or when cells are returned to their normal growth conditions. The kinetics of detection of HSF1 granules parallels the transient induction of heat shock gene transcription. HSF1 granules are also detected using an HSF1-Flag epitope tagged protein or a chimeric HSF1-green fluorescent protein which reveals that these nuclear structures are stress-induced and can be detected in living cells. The spatial organization of HSF1 granules in nuclei of stressed cells reveals that they are novel nuclear structures which are stress-dependent and provides evidence that the nucleus undergoes dynamic reorganization in response to stress.

Pyrazolone derivatives have previously been found to be inhibitors of Cu/Zn superoxide dismutase 1 (SOD1)-dependent protein aggregation, which extended survival of an amyotrophic lateral sclerosis (ALS) mouse model. On the basis of ADME analysis, we describe herein a new series of tertiary amine-containing pyrazolones and their structure-activity relationships. Further conversion to the conjugate salts greatly improved their solubility. Phosphate compound 17 exhibited numerous benefits both to cellular activity and to CNS-related drug-like properties in vitro and in vivo, including microsomal stability, tolerated toxicity, and blood-brain barrier permeation. These results indicate that tertiary amine pyrazolones comprise a valuable class of ALS drug candidates.

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