Involvement of molecular chaperones in intracellular protein breakdown

Transcriptional Reprogramming of Candida tropicalis in Response to Isoespintanol Treatment

Candida tropicalis, an opportunistic pathogen, ranks among the primary culprits of invasive candidiasis, a condition notorious for its resistance to conventional antifungal drugs. The urgency to combat these drug-resistant infections has spurred the quest for novel therapeutic compounds, with a particular focus on those of natural origin. In this study, we set out to evaluate the impact of isoespintanol (ISO), a monoterpene derived from Oxandra xylopioides, on the transcriptome of C. tropicalis. Leveraging transcriptomics, our research aimed to unravel the intricate transcriptional changes induced by ISO within this pathogen. Our differential gene expression analysis unveiled 186 differentially expressed genes (DEGs) in response to ISO, with a striking 85% of these genes experiencing upregulation. These findings shed light on the multifaceted nature of ISO's influence on C. tropicalis, spanning a spectrum of physiological, structural, and metabolic adaptations. The upregulated DEGs predominantly pertained to crucial processes, including ergosterol biosynthesis, protein folding, response to DNA damage, cell wall integrity, mitochondrial activity modulation, and cellular responses to organic compounds. Simultaneously, 27 genes were observed to be repressed, affecting functions such as cytoplasmic translation, DNA damage checkpoints, membrane proteins, and metabolic pathways like trans-methylation, trans-sulfuration, and trans-propylamine. These results underscore the complexity of ISO's antifungal mechanism, suggesting that it targets multiple vital pathways within C. tropicalis. Such complexity potentially reduces the likelihood of the pathogen developing rapid resistance to ISO, making it an attractive candidate for further exploration as a therapeutic agent. In conclusion, our study provides a comprehensive overview of the transcriptional responses of C. tropicalis to ISO exposure. The identified molecular targets and pathways offer promising avenues for future research and the development of innovative antifungal therapies to combat infections caused by this pathogenic yeast.

Mechanisms of nucleophosmin (NPM)-mediated regulated cell death elucidated by Hsp70 during renal ischemia

Nucleophosmin (NPM), a nucleolar-based protein chaperone, promotes Bax-mediated mitochondrial injury and regulates cell death during acute kidney injury. However, the steps that transform NPM from an essential to a toxic protein during stress are unknown. To localize NPM-mediated events causing regulated cell death during ischemia, wild type (WT) and Hsp70 mutant proteins with characterized intracellular trafficking defects that restrict movement to either the nucleolar region (M45) or cytosol (985A) were expressed in primary murine proximal tubule epithelial cells (PTEC) harvested from Hsp70 null mice. After ischemia in vitro, PTEC survival was significantly improved and apoptosis reduced in rank order by selectively overexpressing WT > M45 > 985A Hsp70 proteins. Only Hsp70 with nuclear access (WT and M45) inhibited T95 NPM phosphorylation responsible for NPM translocation and also reduced cytosolic NPM accumulation. In contrast, WT or 985A > M45 significantly improved survival in Hsp70 null PTEC that expressed a cytosol-restricted NPM mutant, more effectively bound NPM, and also reduced NPM-Bax complex formation required for mitochondrial injury and cell death. Hsp70 knockout prevented the cytoprotective effect of suppressing NPM in ischemic PTEC and also increased cytosolic NPM accumulation after acute renal ischemia in vivo, emphasizing the inhibitory effect of Hsp70 on NPM-mediated toxicity. Distinct cytoprotective mechanisms by wild type and mutant Hsp70 proteins identify dual nuclear and cytosolic events that mediate NPM toxicity during stress-induced apoptosis and are rational targets for therapeutic AKI interventions. Antagonizing these early events in regulated cell death promotes renal cell survival during experimental AKI.

Increased presence of nuclear DNAJA3 and upregulation of cytosolic STAT1 and of nucleic acid sensors trigger innate immunity in the ClpP-null mouse

Mitochondrial dysfunction may activate innate immunity, e.g. upon abnormal handling of mitochondrial DNA in TFAM mutants or in altered mitophagy. Recent reports showed that also deletion of mitochondrial matrix peptidase ClpP in mice triggers transcriptional upregulation of inflammatory factors. Here, we studied ClpP-null mouse brain at two ages and mouse embryonal fibroblasts, to identify which signaling pathways are responsible, employing mass spectrometry, subcellular fractionation, immunoblots, and reverse transcriptase polymerase chain reaction. Several mitochondrial unfolded protein response factors showed accumulation and altered migration in blue-native gels, prominently the co-chaperone DNAJA3. Its mitochondrial dysregulation increased also its extra-mitochondrial abundance in the nucleus, a relevant observation given that DNAJA3 modulates innate immunity. Similar observations were made for STAT1, a putative DNAJA3 interactor. Elevated expression was observed not only for the transcription factors Stat1/2, but also for two interferon-stimulated genes (Ifi44, Gbp3). Inflammatory responses were strongest for the RLR pattern recognition receptors (Ddx58, Ifih1, Oasl2, Trim25) and several cytosolic nucleic acid sensors (Ifit1, Ifit3, Oas1b, Ifi204, Mnda). The consistent dysregulation of these factors from an early age might influence also human Perrault syndrome, where ClpP loss-of-function leads to early infertility and deafness, with subsequent widespread neurodegeneration.

Bacterial Hsp90 Facilitates the Degradation of Aggregation-Prone Hsp70-Hsp40 Substrates

In eukaryotes, the 90-kDa heat shock proteins (Hsp90s) are profusely studied chaperones that, together with 70-kDa heat shock proteins (Hsp70s), control protein homeostasis. In bacteria, however, the function of Hsp90 (HtpG) and its collaboration with Hsp70 (DnaK) remains poorly characterized. To uncover physiological processes that depend on HtpG and DnaK, we performed comparative quantitative proteomic analyses of insoluble and total protein fractions from unstressed wild-type (WT) Escherichia coli and from knockout mutants ΔdnaKdnaJ (ΔKJ), ΔhtpG (ΔG), and ΔdnaKdnaJΔhtpG (ΔKJG). Whereas the ΔG mutant showed no detectable proteomic differences with wild-type, ΔKJ expressed more chaperones, proteases and ribosomes and expressed dramatically less metabolic and respiratory enzymes. Unexpectedly, we found that the triple mutant ΔKJG showed higher levels of metabolic and respiratory enzymes than ΔKJ, suggesting that bacterial Hsp90 mediates the degradation of aggregation-prone Hsp70-Hsp40 substrates. Further in vivo experiments suggest that such Hsp90-mediated degradation possibly occurs through the HslUV protease.

Bacterial Hsp90 Facilitates the Degradation of Aggregation-Prone Hsp70-Hsp40 Substrates

In eukaryotes, the 90-kDa heat shock proteins (Hsp90s) are profusely studied chaperones that, together with 70-kDa heat shock proteins (Hsp70s), control protein homeostasis. In bacteria, however, the function of Hsp90 (HtpG) and its collaboration with Hsp70 (DnaK) remains poorly characterized. To uncover physiological processes that depend on HtpG and DnaK, we performed comparative quantitative proteomic analyses of insoluble and total protein fractions from unstressed wild-type (WT) Escherichia coli and from knockout mutants ΔdnaKdnaJ (ΔKJ), ΔhtpG (ΔG), and ΔdnaKdnaJΔhtpG (ΔKJG). Whereas the ΔG mutant showed no detectable proteomic differences with wild-type, ΔKJ expressed more chaperones, proteases and ribosomes and expressed dramatically less metabolic and respiratory enzymes. Unexpectedly, we found that the triple mutant ΔKJG showed higher levels of metabolic and respiratory enzymes than ΔKJ, suggesting that bacterial Hsp90 mediates the degradation of aggregation-prone Hsp70-Hsp40 substrates. Further in vivo experiments suggest that such Hsp90-mediated degradation possibly occurs through the HslUV protease.

Proteome analysis of excretory-secretory proteins of Entamoeba histolytica HM1:IMSS via LC-ESI-MS/MS and LC-MALDI-TOF/TOF

BACKGROUND

Excretory-secretory (ES) proteins of E. histolytica are thought to play important roles in the host invasion, metabolism, and defence. Elucidation of the types and functions of E. histolytica ES proteins can further our understanding of the disease pathogenesis. Thus, the aim of this study is to use proteomics approach to better understand the complex ES proteins of the protozoa.

METHODS

E. histolytica ES proteins were prepared by culturing the trophozoites in protein-free medium. The ES proteins were identified using two mass spectrometry tools, namely, LC-ESI-MS/MS and LC-MALDI-TOF/TOF. The identified proteins were then classified according to their biological processes, molecular functions, and cellular components using the Panther classification system (PantherDB).

RESULTS

A complementary list of 219 proteins was identified; this comprised 201 proteins detected by LC-ESI-MS/MS and 107 proteins by LC-MALDI-TOF/TOF. Of the 219 proteins, 89 were identified by both mass-spectrometry systems, while 112 and 18 proteins were detected exclusively by LC-ESI-MS/MS and LC-MALDI-TOF/TOF respectively. Biological protein functional analysis using PantherDB showed that 27% of the proteins were involved in metabolic processes. Using molecular functional and cellular component analyses, 35% of the proteins were found to be involved in catalytic activity, and 21% were associated with the cell parts.

CONCLUSION

This study showed that complementary use of LC-ESI-MS/MS and LC-MALDI-TOF/TOF has improved the identification of ES proteins. The results have increased our understanding of the types of proteins excreted/secreted by the amoeba and provided further evidence of the involvement of ES proteins in intestinal colonisation and evasion of the host immune system, as well as in encystation and excystation of the parasite.

Rehosting of bacterial chaperones for high-quality protein production

Coproduction of DnaK/DnaJ in Escherichia coli enhances solubility but promotes proteolytic degradation of their substrates, minimizing the yield of unstable polypeptides. Higher eukaryotes have orthologs of DnaK/DnaJ but lack the linked bacterial proteolytic system. By coexpression of DnaK and DnaJ in insect cells with inherently misfolding-prone recombinant proteins, we demonstrate simultaneous improvement of soluble protein yield and quality and proteolytic stability. Thus, undesired side effects of bacterial folding modulators can be avoided by appropriate rehosting in heterologous cell expression systems.

Proteome analysis of the Escherichia coli heat shock response under steady-state conditions

In this study a proteomic approach was used to investigate the steady-state response of Escherichia coli to temperature up-shifts in a cascade of two continuously operated bioreactors. The first reactor served as cell source with optimal settings for microbial growth, while in the second chemostat the cells were exposed to elevated temperatures. By using this reactor configuration, which has not been reported to be used for the study of bacterial stress responses so far, it is possible to study temperature stress under well-defined, steady-state conditions. Specifically the effect on the cellular adaption to temperature stress using two-dimensional gel electrophoresis was examined and compared at the cultivation temperatures of 37 degrees C and 47.5 degrees C. As expected, the steady-state study with the double bioreactor configuration delivered a different protein spectrum compared to that obtained with standard batch experiments in shaking flasks and bioreactors. Setting a high cut-out spot-to-spot size ratio of 5, proteins involved in defence against oxygen stress, functional cell envelope proteins, chaperones and proteins involved in protein biosynthesis, the energy metabolism and the amino acid biosynthesis were found to be differently expressed at high cultivation temperatures. The results demonstrate the complexity of the stress response in a steady-state culture not reported elsewhere to date.

Protein isoaspartate methyltransferase is a multicopy suppressor of protein aggregation in Escherichia coli

We used preS2-S'-beta-galactosidase, a three-domain fusion protein that aggregates extensively at 43 degrees C in the cytoplasm of Escherichia coli, to search for multicopy suppressors of protein aggregation and inclusion body formation and took advantage of the known differential solubility of preS2-S'-beta-galactosidase at 37 and 43 degrees C to develop a selection procedure for the gene products that would prevent its aggregation in vivo at 43 degrees C. First, we demonstrate that the differential solubility of preS2-S'-beta-galactosidase results in a lactose-positive phenotype at 37 degrees C as opposed to a lactose-negative phenotype at 43 degrees C. We searched for multicopy suppressors of preS2-S'-beta-galactosidase aggregation by selecting pink lactose-positive colonies on a background of white lactose-negative colonies at 43 degrees C after transformation of bacteria with an E. coli gene bank. We discovered that protein isoaspartate methyltransferase (PIMT) is a multicopy suppressor of preS2-S'-beta-galactosidase aggregation at 43 degrees C. Overexpression of PIMT reduces the amount of preS2-S'-beta-galactosidase found in inclusion bodies at 43 degrees C and increases its amount in soluble fractions. It reduces the level of isoaspartate formation in preS2-S'-beta-galactosidase and increases its thermal stability in E. coli crude extracts without increasing the thermostability of a control protein, citrate synthase, in the same extracts. We could not detect any induction of the heat shock response resulting from PIMT overexpression, as judged from amounts of DnaK and GroEL, which were similar in the PIMT-overproducing and control strains. These results suggest that PIMT might be overburdened in some physiological conditions and that its overproduction may be beneficial in conditions in which protein aggregation occurs, for example, during biotechnological protein overproduction or in protein aggregation diseases.

Interspecific- and acclimation-induced variation in levels of heat-shock proteins 70 (hsp70) and 90 (hsp90) and heat-shock transcription factor-1 (HSF1) in congeneric marine snails (genusTegula): implications for regulation ofhspgene expression

In our previous studies of heat-shock protein (hsp) expression in congeneric marine gastropods of the genus Tegula, we observed interspecific and acclimation-induced variation in the temperatures at which heat-shock gene expression is induced (Ton). To investigate the factors responsible for these inter- and intraspecific differences in Ton, we tested the predictions of the ‘cellular thermometer’ model for the transcriptional regulation of hsp expression. According to this model, hsps not active in chaperoning unfolded proteins bind to a transcription factor, heat-shock factor-1 (HSF1), thereby reducing the levels of free HSF1 that are available to bind to the heat-shock element, a regulatory element upstream of hsp genes. Under stress, hsps bind to denatured proteins, releasing HSF1, which can now activate hsp gene transcription. Thus, elevated levels of heat-shock proteins of the 40, 70 and 90 kDa families (hsp 40, hsp70 and hsp90, respectively) would be predicted to elevate Ton. Conversely, elevated levels of HSF1 would be predicted to decrease Ton. Following laboratory acclimation to 13, 18 and 23°C, we used solid-phase immunochemistry (western analysis) to quantify endogenous levels of two hsp70 isoforms (hsp74 and hsp72), hsp90 and HSF1 in the low- to mid-intertidal species Tegula funebralis and in two subtidal to low-intertidal congeners, T. brunnea and T. montereyi. We found higher endogenous levels of hsp72 (a strongly heat-induced isoform) at 13 and 18°C in T. funebralis in comparison with T. brunnea and T. montereyi. However, T. funebralis also had higher levels of HSF1 than its congeners. The higher levels of HSF1 in T. funebralis cannot, within the framework of the cellular thermometer model, account for the higher Ton observed for this species, although they may explain why T. funebralis is able to induce the heat-shock response more rapidly than T. brunnea. However, the cellular thermometer model does appear to explain the cause of the increases in Ton that occurred during warm acclimation of the two subtidal species, in which warm acclimation was accompanied by increased levels of hsp72, hsp74 and hsp90, whereas levels of HSF1 remained stable. T. funebralis, which experiences greater heat stress than its subtidal congeners, consistently had higher ratios of hsp72 to hsp74 than its congeners, although the sum of levels of the two isoforms was similar for all three species except at the highest acclimation temperature (23°C). The ratio of hsp72 to hsp74 may provide a more accurate estimate of environmental heat stress than the total concentrations of both hsp70 isoforms.

DNA immunization with Trypanosoma cruzi HSP70 fused to the KMP11 protein elicits a cytotoxic and humoral immune response against the antigen and leads to protection

Murine immunization with Trypanosoma cruzi KMP11-HSP70 fused genes but not the KMP11 gene alone elicited both an immunoglobulin G2a long-lasting humoral immune response against KMP11 protein and activation of CD8+ cytotoxic T lymphocytes specific for two KMP11 peptides containing A2 motifs. Moreover, protection against the parasite challenge was observed after immunization with the chimeric gene.

Genomic profiling of short- and long-term caloric restriction effects in the liver of aging mice

We present genome-wide microarray expression analysis of 11,000 genes in an aging potentially mitotic tissue, the liver. This organ has a major impact on health and homeostasis during aging. The effects of life- and health-span-extending caloric restriction (CR) on gene expression among young and old mice and between long-term CR (LT-CR) and short-term CR (ST-CR) were examined. This experimental design allowed us to accurately distinguish the effects of aging from those of CR on gene expression. Aging was accompanied by changes in gene expression associated with increased inflammation, cellular stress, and fibrosis, and reduced capacity for apoptosis, xenobiotic metabolism, normal cell-cycling, and DNA replication. LT-CR and just 4 weeks of ST-CR reversed the majority of these changes. LT-CR produced in young mice a pattern of gene expression that is a subset of the changes found in old LT-CR mice. It is possible that the early changes in gene expression, which extend into old age, are key to the life- and health-span-extending effects of CR. Further, ST-CR substantially shifted the "normo-aging" genomic profile of old control mice toward the "slow-aging" profile associated with LT-CR. Therefore, many of the genomic effects of CR are established rapidly. Thus, expression profiling should prove useful in quickly identifying CR- mimetic drugs and treatments.

CYP2E1 degradation by in vitro reconstituted systems: role of the molecular chaperone hsp90

One major mode of regulation of cytochrome P450 2E1 (CYP2E1) is at the posttranscriptional level, since many low-molecular-weight compounds stabilize the enzyme against proteolysis by the proteasome complex. In an in vitro system containing human liver microsomes, degradation of CYP2E1 in the microsomes required addition of the human liver cytosol fraction in a reaction sensitive to inhibitors of the proteasome complex. It is not clear how CYP2E1 in the microsomal membrane becomes accessible to the cytosolic proteasome. Since molecular chaperones play a role in protein folding and degradation, the possible role of heat shock proteins in CYP2E1 degradation by this reconstituted system was evaluated. Degradation of CYP2E1 required ATP; ATP-gammaS, a nonhydrolyzable analogue of ATP, did not catalyze CYP2E1 degradation by the cytosol fraction, indicating that ATP hydrolysis is required. Geldanamycin, a specific inhibitor of hsp90, inhibited the degradation of microsomal CYP2E1 by the cytosol fraction. Control experiments indicated that geldanamycin was not a substrate/ligand of CYP2E1 nor did it prevent microsomal lipid peroxidation, a process which increases CYP2E1 turnover. Inhibition by geldanamycin was prevented by molybdate. Both of these compounds have been shown to promote alterations in hsp90 structure and to modulate hsp90-protein interactions. The proteasome activity in the cytosol, as assayed by the cleavage of a fluorogenic peptide, was enhanced when ATP was added and inhibited by 30-40% by geldanamycin, effects that are similar, although less pronounced, to the degradation of CYP2E1 by the cytosol. Purified 20S proteasome could catalyze degradation of CYP2E1; however, in an assay using equal peptidase activity, the cytosol fraction was much more effective than the 20S proteasome in promoting CYP2E1 degradation. Immunodepletion of hsp90 from the cytosol resulted in prevention of the degradation of CYP2E1, a reaction that was reversed by the addition of pure hsp90 to this cytosol. These results suggest that in addition to the proteasome, the cytosol fraction contains other factors that modulate the efficiency of CYP2E1 degradation. The sensitivity to geldanamycin and molybdate and the immunodepletion experiments suggest that hsp90 is one of these factors that interact with CYP2E1 and/or with the proteasome to promote the degradation of this microsomal P450.

Recombinant adeno-associated virus expressing human papillomavirus type 16 E7 peptide DNA fused with heat shock protein DNA as a potential vaccine for cervical cancer

In this study, we explore a potential vaccine for human papillomavirus (HPV)-induced tumors, using heat shock protein as an adjuvant, a peptide vaccine for safety, and adeno-associated virus (AAV) as a gene delivery vector. The tumor vaccine was devised by constructing a chimeric gene which contained HPV type 16 E7 cytotoxic T-lymphocyte (CTL) epitope DNA (M. C. Feltkamp, H. L. Smits, M. P. Vierboom, R. P. Minnaar, B. M. de Jongh, J. W. Drijfhout, J. ter Schegget, C. J. Melief, and W. M. Kast, Eur. J. Immunol. 23:2242-2249, 1993) fused with the heat shock protein gene as a tumor vaccine delivered via AAV. Our results demonstrate that this vaccine can eliminate tumor cells in syngeneic animals and induce CD4- and CD8-dependent CTL activity in vitro. Moreover, studies with knockout mice with distinct T-cell deficiencies confirm that CTL-induced tumor protection is CD4 and CD8 dependent. Taken together, the evidence indicates that this chimeric gene delivered by AAV has potential as a cervical cancer vaccine.

Lon and Clp family proteases and chaperones share homologous substrate-recognition domains

Lon protease and members of the Clp family of molecular chaperones and protease regulatory subunits contain homologous regions with properties expected for substrate-binding domains. Fragments corresponding to these sequences are stably and independently folded for Lon, ClpA, and ClpY. The corresponding regions from ClpB and ClpX are unstable. All five fragments exhibit distinct patterns of binding to three proteins that are protease substrates in vivo: the heat shock transcription factor sigma32, the SOS mutagenesis protein UmuD, and Arc repressor bearing the SsrA degradation tag. Recognition of UmuD is mediated through peptide sequences within a 24-residue N-terminal region whereas recognition of both sigma32 and SsrA-tagged Arc requires sequences at the C terminus. These results indicate that the Lon and Clp proteases use the same mechanism of substrate discrimination and suggest that these related ATP-dependent bacterial proteases scrutinize accessible or disordered regions of potential substrates for the presence of specific targeting sequences.

Intracellular amyloidogenesis by human islet amyloid polypeptide induces apoptosis in COS-1 cells

Human islet amyloid polypeptide (hIAPP) is co-secreted with insulin from pancreatic islet beta cells. This peptide spontaneously aggregates in the form of fibrils, and amyloid deposits are associated with dead or degenerating beta cells, a hallmark of noninsulin-dependent diabetes mellitus. We demonstrated that COS-1 cells transfected with vectors expressing hIAPP exhibited intracellular amyloid deposits that were associated with cell death (O'Brien, Butler, Kreutter, Kane, Eberhardt, Am J Pathol 1995, 147:609-616). To establish the mechanism of cell death, we transfected COS-1 cells with vectors expressing amyloidogenic hIAPP or nonamyloidogenic rat IAPP and mutant hIAPP constructs and assayed them for markers characteristic of apoptosis and necrosis by fluorescence-activated cell sorting analysis. Amyloidogenic hIAPP-transfected COS cells contained up to threefold more apoptotic cells present at 96 hours after transfection compared with the nonamyloidogenic vector controls. The hIAPP-induced apoptosis was negligible at 24 and 48 hours after transfection and was maximal at 96 hours which parallels the time course of amyloidogenesis. Immunohistochemical staining and confocal microscopy showed that hIAPP is localized with distinct clustering in the endoplasmic reticulum and Golgi apparatus with no discernable extracellular staining. These experiments provide direct evidence that intracellular hIAPP amyloid causes cell death by triggering apoptotic pathways.

Perturbation of Hsp90 interaction with nascent CFTR prevents its maturation and accelerates its degradation by the proteasome

Maturation of wild-type CFTR nascent chains at the endoplasmic reticulum (ER) occurs inefficiently; many disease-associated mutant forms do not mature but instead are eliminated by proteolysis involving the cytosolic proteasome. Although calnexin binds nascent CFTR via its oligosaccharide chains in the ER lumen and Hsp70 binds CFTR cytoplasmic domains, perturbation of these interactions alone is without major influence on maturation or degradation. We show that the ansamysin drugs, geldanamycin and herbimycin A, which inhibit the assembly of some signaling molecules by binding to specific sites on Hsp90 in the cytosol or Grp94 in the ER lumen, block the maturation of nascent CFTR and accelerate its degradation. The immature CFTR molecule was detected in association with Hsp90 but not with Grp94, and geldanamycin prevented the Hsp90 association. The drug-enhanced degradation was decreased by lactacystin and other proteasome inhibitors. Therefore, consistent with other examples of countervailing effects of Hsp90 and the proteasome, it would seem that this chaperone may normally contribute to CFTR folding and, when this function is interfered with by an ansamycin, there is a further shift to proteolytic degradation. This is the first direct evidence of a role for Hsp90 in the maturation of a newly synthesized integral membrane protein by interaction with its cytoplasmic domains on the ER surface.

Heat shock response and protein degradation: regulation of HSF2 by the ubiquitin-proteasome pathway

Mammalian cells coexpress a family of heat shock factors (HSFs) whose activities are regulated by diverse stress conditions to coordinate the inducible expression of heat shock genes. Distinct from HSF1, which is expressed ubiquitously and activated by heat shock and other stresses that result in the appearance of nonnative proteins, the stress signal for HSF2 has not been identified. HSF2 activity has been associated with development and differentiation, and the activation properties of HSF2 have been characterized in hemin-treated human K562 erythroleukemia cells. Here, we demonstrate that a stress signal for HSF2 activation occurs when the ubiquitin-proteasome pathway is inhibited. HSF2 DNA-binding activity is induced upon exposure of mammalian cells to the proteasome inhibitors hemin, MG132, and lactacystin, and in the mouse ts85 cell line, which carries a temperature sensitivity mutation in the ubiquitin-activating enzyme (E1) upon shift to the nonpermissive temperature. HSF2 is labile, and its activation requires both continued protein synthesis and reduced degradation. The downstream effect of HSF2 activation by proteasome inhibitors is the induction of the same set of heat shock genes that are induced during heat shock by HSF1, thus revealing that HSF2 affords the cell with a novel heat shock gene-regulatory mechanism to respond to changes in the protein-degradative machinery.

Proteasome inhibitors cause induction of heat shock proteins and trehalose, which together confer thermotolerance in Saccharomyces cerevisiae

An accumulation in cells of unfolded proteins is believed to be the common signal triggering the induction of heat shock proteins (hsps). Accordingly, in Saccharomyces cerevisiae, inhibition of protein breakdown at 30 degrees C with the proteasome inhibitor MG132 caused a coordinate induction of many heat shock proteins within 1 to 2 h. Concomitantly, MG132, at concentrations that had little or no effect on growth rate, caused a dramatic increase in the cells' resistance to very high temperature. The magnitude of this effect depended on the extent and duration of the inhibition of proteolysis. A similar induction of hsps and thermotolerance was seen with another proteasome inhibitor, clasto-lactacystin beta-lactone, but not with an inhibitor of vacuolar proteases. Surprisingly, when the reversible inhibitor MG132 was removed, thermotolerance decreased rapidly, while synthesis of hsps continued to increase. In addition, exposure to MG132 and 37 degrees C together had synergistic effects in promoting thermotolerance but did not increase hsp expression beyond that seen with either stimulus alone. Although thermotolerance did not correlate with hsp content, another thermoprotectant trehalose accumulated upon exposure of cells to MG132, and the cellular content of this disaccharide, unlike that of hsps, quickly decreased upon removal of MG132. Also, MG132 and 37 degrees C had additive effects in causing trehalose accumulation. Thus, the resistance to heat induced by proteasome inhibitors is not just due to induction of hsps but also requires a short-lived metabolite, probably trehalose, which accumulates when proteolysis is reduced.

Heat shock fusion proteins as vehicles for antigen delivery into the major histocompatibility complex class I presentation pathway

Mice immunized with heat shock proteins (hsps) isolated from mouse tumor cells (donor cells) produce CD8 cytotoxic T lymphocytes (CTL) that recognize donor cell peptides in association with the major histocompatibility complex (MHC) class I proteins of the responding mouse. The CTL are induced apparently because peptides noncovalently associated with the isolated hsp molecules can enter the MHC class I antigen processing pathway of professional antigen-presenting cells. Using a recombinant heat shock fusion protein with a large fragment of ovalbumin covalently linked to mycobacterial hsp70, we show here that when the soluble fusion protein was injected without adjuvant into H-2b mice, CTL were produced that recognized an ovalbumin-derived peptide, SIINFEKL, in association with Kb. The peptide is known to arise from natural processing of ovalbumin in H-2b mouse cells, and CTL from the ovalbumin-hsp70-immunized mice and a highly effective CTL clone (4G3) raised against ovalbumin-expressing EL4 tumor cells (EG7-OVA) were equally effective in terms of the concentration of SIINFEKL required for half-maximal lysis in a CTL assay. The mice were also protected against lethal challenge with ovalbumin-expressing melanoma tumor cells. Because large protein fragments or whole proteins serving as fusion partners can be cleaved into short peptides in the MHC class I processing pathway, hsp fusion proteins of the type described here are promising candidates for vaccines aimed at eliciting CD8 CTL in populations of MHC-disparate individuals.