Cytosolic Hsp90 Isoform-Specific Functions and Clinical Significance

Comprehensive analysis of resorcinyl-imidazole Hsp90 inhibitor design

Human Hsp90 chaperones are implicated in various aspects of cancer. Due to this, Hsp90 has been explored as potential target in cancer treatment. Initial attempts to use Hsp90 inhibitors in drug trials failed due to toxicity and inefficacy. The next generation of drugs were less toxic but still insufficiently effective in a clinical setting. Recently, a lot of effort is being put into understanding the consequences of Hsp90 isoform selective inhibition, expecting that this might hold the key in targeting Hsp90 for disease treatment. Here we investigate a series of compounds containing the aryl-resorcinol scaffold with a 5-membered ring as a promising class of new human Hsp90 inhibitors, reaching nanomolar affinity. We compare how the replacement of 5-membered ring, from thiadiazole to imidazole, as well as a variety of their substituents, influences the potency of these inhibitors for Hsp90 alpha and beta isoforms. To further elucidate the dissimilarity in ligand selectivity between the isoforms, a mutant protein was constructed and tested against the ligand library. In addition, we performed a series of molecular dynamics (MD) and docking simulations to further explain our experimental findings as well as evaluated key compounds in cell assays. Our results deepen the understanding of Hsp90 isoform ligand selectivity and serve as an informative base for further Hsp90 inhibitor optimization.

Mesenchymal stem cell-derived exosomes ameliorate hypoxic pulmonary hypertension by inhibiting the Hsp90aa1/ERK/pERK pathway

Hypoxic pulmonary hypertension (HPH) is a serious and life-threatening chronic cardiopulmonary disease characterized by progressive elevation of pulmonary artery pressure and pulmonary vascular remodeling. Mesenchymal stem cell- derived exosomes (MSC-Exos) can relieve HPH by reversing pulmonary vascular remodeling. The HPH model was established in healthy male Sprague-Dawley (SD) rats aged 6 to 8 weeks. The rats were placed in a room with oxygen concentration of (10 ± 1) % for 8 h a day over 28 days, were then injected intravenously with MSC-Exos (100 ug protein/kg) or equal-volume phosphate buffer saline (PBS) once a day over 1 week. Right ventricular systolic pressure (RVSP), right ventricular hypertrophy index (RVHI) and pulmonary vascular remodeling were observed after anesthesia. In addition, platelet-derived growth factor BB (PDGF-BB) were used to stimulate rat pulmonary artery smooth muscle cells (PASMCs) to construct HPH pathological cell models. The results showed that MSC-Exos could not only reduce the elevation of RVSP, right ventricular hypertrophy and the degree of pulmonary vascular remodeling in HPH rats, but also reduce the proliferation, migration and apoptosis resistance of PASMCs. Finally, GSE53408 and GSE113439 datasets were analyzed and showed that the expression of Hsp90aa1 and pERK/ERK were significantly increased in HPH, also could be inhibited by MSC-Exos. Meanwhile, inhibition of Hsp90aa1 also reduced PASMCs migration and pERK/ERK protein level. In conclusion, MSC-Exos alleviated HPH by suppressing PASMCs proliferation, migration and apoptosis resistance through inhibiting the Hsp90aa1/ERK/pERK pathway.

The Role of HSP90 Molecular Chaperones in Depression: Potential Mechanisms

Major depressive disorder (MDD) is characterized by high rates of disability and death and has become a public health problem that threatens human life and health worldwide. HPA axis disorder and neuroinflammation are two common biological abnormalities in MDD patients. Hsp90 is an important molecular chaperone that is widely distributed in the organism. Hsp90 binds to the co-chaperone and goes through a molecular chaperone cycle to complete its regulation of the client protein. Numerous studies have demonstrated that Hsp90 regulates how the HPA axis reacts to stress and how GR, the HPA axis' responsive substrate, matures. In addition, Hsp90 exhibits pro-inflammatory effects that are closely related to neuroinflammation in MDD. Currently, Hsp90 inhibitors have made some progress in the treatment of a variety of human diseases, but they still need to be improved. Further insight into the role of Hsp90 in MDD provides new ideas for the development of new antidepressant drugs targeting Hsp90.

Hsp90 Promotes Gastric Cancer Cell Metastasis and Stemness by Regulating the Regional Distribution of Glycolysis-Related Metabolic Enzymes in the Cytoplasm

Heat-shock protein 90 (Hsp90) plays a crucial role in tumorigenesis and tumor progression; however, its mechanism of action in gastric cancer (GC) remains unclear. Here, the role of Hsp90 in GC metabolism is the focus of this research. High expression of Hsp90 in GC tissues can interact with glycolysis, collectively affecting prognosis in clinical samples. Both in vitro and in vivo experiments demonstrate that Hsp90 is able to regulate the migration and stemness properties of GC cells. Metabolic phenotype analyses indicate that Hsp90 influences glycolytic metabolism. Mechanistically, Hsp90 interacts with glycolysis-related enzymes, forming multienzyme complexes to enhance glycolysis efficiency and yield. Additionally, Hsp90 binds to cytoskeleton-related proteins, regulating the regional distribution of glycolytic enzymes at the cell margin and lamellar pseudopods. This effect could lead to a local increase in efficient energy supply from glycolysis, further promoting epithelial-mesenchymal transition (EMT) and metastasis. In summary, Hsp90, through its interaction with metabolic enzymes related to glycolysis, forms multi-enzyme complexes and regulates regional distribution of glycolysis by dynamic cytoskeletal adjustments, thereby promoting the migration and stemness of GC cells. These conclusions also support the potential for a combined targeted approach involving Hsp90, glycolysis, and the cytoskeleton in clinical therapy.

Hsp90α and cell death in cancers: a review

Heat shock protein 90α (Hsp90α), an important molecular chaperone, plays a crucial role in regulating the activity of various intracellular signaling pathways and maintaining the stability of various signaling transduction proteins. In cancer, the expression level of Hsp90α is often significantly upregulated and is recognized as one of the key factors in cancer cell survival and proliferation. Cell death can help achieve numerous purposes, such as preventing aging, removing damaged or infected cells, facilitating embryonic development and tissue repair, and modulating immune response. The expression of Hsp90α is closely associated with specific modes of cell death including apoptosis, necrotic apoptosis, and autophagy-dependent cell death, etc. This review discusses the new results on the relationship between expression of Hsp90α and cell death in cancer. Hsp90α is frequently overexpressed in cancer and promotes cancer cell growth, survival, and resistance to treatment by regulating cell death, rendering it a promising target for cancer therapy.

Sleep fragmentation exacerbates myocardial ischemia‒reperfusion injury by promoting copper overload in cardiomyocytes

Sleep disorders increase the risk and mortality of heart disease, but the brain-heart interaction has not yet been fully elucidated. Cuproptosis is a copper-dependent type of cell death activated by the excessive accumulation of intracellular copper. Here, we showed that 16 weeks of sleep fragmentation (SF) resulted in elevated copper levels in the male mouse heart and exacerbated myocardial ischemia-reperfusion injury with increased myocardial cuproptosis and apoptosis. Mechanistically, we found that SF promotes sympathetic overactivity, increases the germination of myocardial sympathetic nerve terminals, and increases the level of norepinephrine in cardiac tissue, thereby inhibits VPS35 expression and leads to impaired ATP7A related copper transport and copper overload in cardiomyocytes. Copper overload further leads to exacerbated cuproptosis and apoptosis, and these effects can be rescued by excision of the sympathetic nerve or administration of copper chelating agent. Our study elucidates one of the molecular mechanisms by which sleep disorders aggravate myocardial injury and suggests possible targets for intervention.

Phosphorylation-Driven Epichaperome Assembly: A Critical Regulator of Cellular Adaptability and Proliferation

The intricate protein-chaperone network is vital for cellular function. Recent discoveries have unveiled the existence of specialized chaperone complexes called epichaperomes, protein assemblies orchestrating the reconfiguration of protein-protein interaction networks, enhancing cellular adaptability and proliferation. This study delves into the structural and regulatory aspects of epichaperomes, with a particular emphasis on the significance of post-translational modifications in shaping their formation and function. A central finding of this investigation is the identification of specific PTMs on HSP90, particularly at residues Ser226 and Ser255 situated within an intrinsically disordered region, as critical determinants in epichaperome assembly. Our data demonstrate that the phosphorylation of these serine residues enhances HSP90's interaction with other chaperones and co-chaperones, creating a microenvironment conducive to epichaperome formation. Furthermore, this study establishes a direct link between epichaperome function and cellular physiology, especially in contexts where robust proliferation and adaptive behavior are essential, such as cancer and stem cell maintenance. These findings not only provide mechanistic insights but also hold promise for the development of novel therapeutic strategies targeting chaperone complexes in diseases characterized by epichaperome dysregulation, bridging the gap between fundamental research and precision medicine.

A novel PET probe to selectively image heat shock protein 90α/β isoforms in the brain

BACKGROUND

Heat shock proteins (HSPs) are present throughout the brain. They function as molecular chaperones, meaning they help with the folding and unfolding of large protein complexes. These chaperones are vital in the development of neuropathological conditions such as Alzheimer's disease and Lewy body disease, with HSP90, a specific subtype of HSP, playing a key role. Many studies have shown that drugs that inhibit HSP90 activity have beneficial effects in the neurodegenerative diseases. Therefore, HSP90 PET imaging ligand can be used effectively to study HSP90 in neurodegenerative diseases. Among four HSP90 isoforms, two cytosolic isoforms (HSP90α and HSP90β) thought to be involved in the structural homeostasis of the proteins related to the neurodegenerative diseases. Currently, no useful PET imaging ligands selectively targeting the two cytosolic isoforms of HSP90 have been available yet.

RESULTS

In this study, we developed a novel positron emission tomography (PET) imaging ligand, [11C]BIIB021, by 11C-radiolabeling (a positron emitter with a half-life of 20.4 min) 6-Chloro-9-[(4-methoxy-3,5-dimethylpyridin-2-yl)methyl]-9H-purin-2-amine (BIIB021), an inhibitor with a high affinity for and selectivity to HSP90α and HSP90β. [11C]BIIB021 was synthesized with a high yield, molar activity and radiochemical purity. [11C]BIIB021 showed a high binding affinity for rat brain homogenate as well as human recombinant HSP90α and HSP90β proteins. Radioactivity was well detected in the rat brain (SUV 1.4). It showed clear specific binding in PET imaging of healthy rats and autoradiography of healthy rat and human brain sections. Radiometabolite was detected in the brain, however, total distribution volume was well quantified using dual-input graphical model. Inhibition of p-glycoprotein increased brain radioactivity concentrations. However, total distribution volume values with and without p-glycoprotein inhibition were nearly the same.

CONCLUSIONS

We have developed a new PET imaging agent, [11C]BIIB021, specifically targeting HSP90α/β. We have been successful in synthesizing [11C]BIIB021 and in vitro and in vivo imaging HSP90α/β. However, the quantification of HSP90α/β is complicated by the presence of radiometabolites in the brain and the potential to be a substrate for p-glycoprotein. Further efforts are needed to develop radioligand suitable for imaging of HSP90α/β.

HSP90β controls NLRP3 autoactivation

Gain-of-function mutations in NLRP3 are linked to cryopyrin-associated periodic syndromes (CAPS). Although NLRP3 autoinflammasome assembly triggers inflammatory cytokine release, its activation mechanisms are not fully understood. Our study used a functional genetic approach to identify regulators of NLRP3 inflammasome formation. We identified the HSP90β-SGT1 chaperone complex as crucial for autoinflammasome activation in CAPS. A deficiency in HSP90β, but not in HSP90α, impaired the formation of ASC specks without affecting the priming and expression of inflammasome components. Conversely, activating NLRP3 with stimuli such as nigericin or alum bypassed the need for SGT1 and HSP90β, suggesting the existence of alternative inflammasome assembly pathways. The role of HSP90β was further demonstrated in PBMCs derived from CAPS patients. In these samples, the pathological constitutive secretion of IL-1β could be suppressed using a pharmacological inhibitor of HSP90β. This finding underscores the potential of SGT1-HSP90β modulation as a therapeutic strategy in CAPS while preserving NLRP3's physiological functions.

Insights into Hsp90 mechanism and in vivo functions learned from studies in the yeast, Saccharomyces cerevisiae

The molecular chaperone Hsp90 (Heat shock protein, 90 kDa) is an abundant and essential cytosolic protein required for the stability and/or folding of hundreds of client proteins. Hsp90, along with helper cochaperone proteins, assists client protein folding in an ATP-dependent pathway. The laboratory of Susan Lindquist, in collaboration with other researchers, was the first to establish the yeast Saccharomyces cerevisiae as a model organism to study the functional interaction between Hsp90 and clients. Important insights from studies in her lab were that Hsp90 is essential, and that Hsp90 functions and cochaperone interactions are highly conserved between yeast and mammalian cells. Here, we describe key mechanistic insights into the Hsp90 folding cycle that were obtained using the yeast system. We highlight the early contributions of the laboratory of Susan Lindquist and extend our analysis into the broader use of the yeast system to analyze the understanding of the conformational cycle of Hsp90 and the impact of altered Hsp90 function on the proteome.

Heat shock protein 90: biological functions, diseases, and therapeutic targets

Heat shock protein 90 (Hsp90) is a predominant member among Heat shock proteins (HSPs), playing a central role in cellular protection and maintenance by aiding in the folding, stabilization, and modification of diverse protein substrates. It collaborates with various co-chaperones to manage ATPase-driven conformational changes in its dimer during client protein processing. Hsp90 is critical in cellular function, supporting the proper operation of numerous proteins, many of which are linked to diseases such as cancer, Alzheimer's, neurodegenerative conditions, and infectious diseases. Recognizing the significance of these client proteins across diverse diseases, there is a growing interest in targeting Hsp90 and its co-chaperones for potential therapeutic strategies. This review described biological background of HSPs and the structural characteristics of HSP90. Additionally, it discusses the regulatory role of heat shock factor-1 (HSF-1) in modulating HSP90 and sheds light on the dynamic chaperone cycle of HSP90. Furthermore, the review discusses the specific contributions of HSP90 in various disease contexts, especially in cancer. It also summarizes HSP90 inhibitors for cancer treatment, offering a thoughtful analysis of their strengths and limitations. These advancements in research expand our understanding of HSP90 and open up new avenues for considering HSP90 as a promising target for therapeutic intervention in a range of diseases.

Molecular Investigation and Preliminary Validation of Candidate Genes Associated with Neurological Damage in Heat Stroke

Heat stroke (HS) is a severe medical condition characterized by a systemic inflammatory response that may precipitate multi-organ dysfunction, with a particular predilection for inducing profound central nervous system impairments. We aim to employ bioinformatics techniques for the retrieval and analysis of genes associated with heat stroke-induced neurological damage. We performed a comprehensive analysis of the GSE64778 dataset from the Sequence Read Archive, resulting in the identification of 1178 significantly differentially expressed genes (DEGs). We retrieved 2914 genes associated with heat stroke from the GeneCards database and 2377 genes associated with heat stroke from the Comparative Toxicogenomics Database (CTD). The intersection of the top 300 DEGs in the GSE64778 dataset intersected with the search results of GeneCards and CTD, yielding 25 final candidates for DEGs associated with heat stroke. Gene Ontology functional annotation results indicated that the target genes were mainly involved in apoptosis, stress response, and negative regulation of cellular processes and function in processes such as protein dimerization and protein binding. The Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed a predominant enrichment of candidate target genes within the PI3K-AKT signaling pathway. Subsequent protein-protein interaction network analysis highlighted HSP90aa1 as a central gene, indicating its pivotal role by possessing the highest number of edges among the genes enriched in the PI3K-AKT signaling pathway. Quantitative reverse transcription-polymerase chain reaction analysis performed on blood samples from patients validated the expression of Hsp90aa1 in individuals exhibiting early neurological damage in HS, consistent with the findings from the mRNA bioinformatics analysis. Additionally, the bioinformatics analysis of the upstream microRNAs (miRNAs) regulating HSP90aa1 and the target miRNAs associated with candidate long non-coding RNAs (lncRNAs) identified three lncRNAs, eight miRNAs, and one mRNA in the regulatory network. The DIANA Tools database and algorithms were employed for pathway enrichment and correlation analysis, revealing a significant association between LOC102547734 and MIR-206-3p, with the latter being identified as a target binding site Moreover, the analysis unveiled a correlation between MIR-206-3p and HSP90aa1, implicating the latter as a potential target binding site within the regulatory network.

Establishing Order Through Disorder by the Hsp90 Molecular Chaperone

The Heat Shock Protein 90 (Hsp90) molecular chaperone is a key driver of protein homeostasis (proteostasis) under physiologically normal and stress conditions. In eukaryotes, Hsp90 is essential and is one of the most abundant proteins in a cell where the chaperone shuttles between the cytoplasm and nucleus to fold, stabilize, and regulate client proteins and protein complexes. Numerous high-throughput screens have mapped the Hsp90 interactome, building a vast network comprising ∼25% of the proteome in budding yeast. How Hsp90 is able to associate with this diverse and large cadre of targets is critical to comprehending how the proteostatic process works. Here, we review recent progress on our understanding of the molecular underpinnings driving Hsp90-client interactions from both the perspective of the targets and Hsp90. In addition to considering the available Hsp90-client structures, we also assessed recently identified Hsp90-client peptide complexes to build a model that justifies how Hsp90 might recognize a wide spectrum of target proteins. In brief, Hsp90 either directly recognizes a site within an intrinsically disordered region (IDR) of a client protein to transiently regulate that client or it associates with an unstructured polypeptide section created by the concerted efforts of multiple chaperones and cochaperones to stably associate with a client. Overall, Hsp90 exploits a common recognition property (i.e., IDR) within diverse clients to support chaperone-actionthereby enabling its central role in proteostasis.

Targeting HSP70 chaperones by rhein sensitizes liver cancer to artemisinin derivatives

BACKGROUND

Liver cancer is one of common types of cancer with poor prognosis and limited therapies. Heat shock proteins (HSP) are molecular chaperones that have important roles in tumorigenesis, and emerging as therapeutic targets. Artemisinin and rhein are natural agents from Artemisia annua L. and Rheum undulatum L., respectively. Both rhein and artemisinin have anticancer effects; however, the molecular targets of rhein remain to be identified. It is also unclear whether rhein can synergize with artemisinin derivatives to inhibit liver cancer.

PURPOSE

We aim to identify the targets of rhein in the treatment of hepatocarcinoma and determine the effects of combining rhein and artemisinin derivatives on liver cancer cells.

METHODS

The targets of rhein were detected by mass spectrometry and validated by rhein-proteins interaction assays. The effects of rhein on the chaperone activity of HSP72/HSC70/GRP78 were determined by luciferase refolding assays. Cell viability and apoptosis were determined by CCK8 and flow cytometry assays. For in vivo study, xenograft tumor models were established and treated with rhein and artesunate. Tumor growth was monitored regularly.

RESULTS

Mass spectrometry analysis of rhein-binding proteins in HepG2 cells revealed that HSP72, HSC70 and GRP78 were more profoundly pulled down by rhein-crosslinked sepharose 4B beads compared to the control beads. Further experiments demonstrated that rhein directly interacted with HSP72/HSC70/GRP78 proteins, and inhibit their activity of refolding denatured luciferase. Meanwhile, rhein induced proteasomal degradation of HIF1α and β-catenin. Artesunate or dihydroartemisinin in combination with knockdown of both HSP72 and HSC70 significantly inhibited cell viability. The HSP70/HSC70/GRP78 inhibitors VER-155,008 and rhein phenocopied HSP72/HSC70 knockdown, synergizing with artesunate or dihydroartemisinin to inhibit hepatocarcinoma cell viability. Combinatorial treatment with rhein and artemisinin derivatives significantly induced hepatocarcinoma cell apoptosis, and inhibited tumor growth in vivo.

CONCLUSIONS

The current study demonstrates that rhein is a novel HSP72/HSC70/GRP78 inhibitor that suppresses the chaperone activity of HSP70s. Dual inhibition of HSP72 and HSC70 can enhance the sensitivity of hepatocarcinoma cells to artemisinin derivatives. Combined treatment with artemisinin derivative and rhein significantly inhibits hepatocarcinoma. Artemisinin derivatives in combination with dual inhibition of HSP72 and HSC70 represents a new approach to improve cancer therapy.

Hsf1 and the molecular chaperone Hsp90 support a 'rewiring stress response' leading to an adaptive cell size increase in chronic stress

Cells are exposed to a wide variety of internal and external stresses. Although many studies have focused on cellular responses to acute and severe stresses, little is known about how cellular systems adapt to sublethal chronic stresses. Using mammalian cells in culture, we discovered that they adapt to chronic mild stresses of up to two weeks, notably proteotoxic stresses such as heat, by increasing their size and translation, thereby scaling the amount of total protein. These adaptations render them more resilient to persistent and subsequent stresses. We demonstrate that Hsf1, well known for its role in acute stress responses, is required for the cell size increase, and that the molecular chaperone Hsp90 is essential for coupling the cell size increase to augmented translation. We term this translational reprogramming the 'rewiring stress response', and propose that this protective process of chronic stress adaptation contributes to the increase in size as cells get older, and that its failure promotes aging.

Structural and functional complexity of HSP90 in cellular homeostasis and disease

Heat shock protein 90 (HSP90) is a chaperone with vital roles in regulating proteostasis, long recognized for its function in protein folding and maturation. A view is emerging that identifies HSP90 not as one protein that is structurally and functionally homogeneous but, rather, as a protein that is shaped by its environment. In this Review, we discuss evidence of multiple structural forms of HSP90 in health and disease, including homo-oligomers and hetero-oligomers, also termed epichaperomes, and examine the impact of stress, post-translational modifications and co-chaperones on their formation. We describe how these variations influence context-dependent functions of HSP90 as well as its interaction with other chaperones, co-chaperones and proteins, and how this structural complexity of HSP90 impacts and is impacted by its interaction with small molecule modulators. We close by discussing recent developments regarding the use of HSP90 inhibitors in cancer and how our new appreciation of the structural and functional heterogeneity of HSP90 invites a re-evaluation of how we discover and implement HSP90 therapeutics for disease treatment.

Proliferation, migration, and resistance to oxidative and thermal stresses of HT1080 cells with knocked out genes encoding Hsp90α and Hsp90β

Heat shock protein 90 (Hsp90) fulfils essential housekeeping functions in the cell associated with the folding, stabilization, and turnover of various proteins. In mammals, there exist two Hsp90 isoforms, stress-inducible Hsp90α and constitutively expressed Hsp90β. In an attempt to identify cellular processes dependent on Hsp90α and Hsp90β, we generated a panel of clones of human fibrosarcoma HT1080 cells with the knocked out HSP90AA1 or HSP90AB1 genes encoding, respectively, Hsp90α and Hsp90β. The knockout of the HSP90AA1 and HSP90AB1 genes practically did not affect cell proliferation and resistance to thermal shock and oxidative stress. The loss of Hsp90α in Hsp90α-null cell clones also did not impair cell migration, while the migration of the Hsp90β-null cell clones was prominently reduced as compared to parent HT1080 cells. This indicated the necessity of Hsp90β for efficient basal migration of HT1080 cells whereas Hsp90α seems to be dispensable for this process. The knockout of one Hsp90 isoform was invariably accompanied by an increase in the level of the other Hsp90 isoform by 30-50%, which partly or fully compensated for a decrease in the total level of Hsp90. Thus, we demonstrated the dispensability of Hsp90α and Hsp90β for HT1080 cells in several cellular processes under normal and stress conditions, which suggested the participation of the two Hsp90 isoforms in the same biological processes and full or at least partial functional substitution of one Hsp90 isoform by the other.

HSP90α is needed for the survival of rod photoreceptors and regulates the expression of rod PDE6 subunits

Heat shock protein 90 (HSP90) is an abundant molecular chaperone that regulates the stability of a small set of proteins essential in various cellular pathways. Cytosolic HSP90 has two closely related paralogs: HSP90α and HSP90β. Due to the structural and sequence similarities of cytosolic HSP90 paralogs, identifying the unique functions and substrates in the cell remains challenging. In this article, we assessed the role of HSP90α in the retina using a novel HSP90α murine knockout model. Our findings show that HSP90α is essential for rod photoreceptor function but was dispensable in cone photoreceptors. In the absence of HSP90α, photoreceptors developed normally. We observed rod dysfunction in HSP90α knockout at 2 months with the accumulation of vacuolar structures, apoptotic nuclei, and abnormalities in the outer segments. The decline in rod function was accompanied by progressive degeneration of rod photoreceptors that was complete at 6 months. The deterioration in cone function and health was a "bystander effect" that followed the degeneration of rods. Tandem mass tag proteomics showed that HSP90α regulates the expression levels of <1% of the retinal proteome. More importantly, HSP90α was vital in maintaining rod PDE6 and AIPL1 cochaperone levels in rod photoreceptor cells. Interestingly, cone PDE6 levels were unaffected. The robust expression of HSP90β paralog in cones likely compensates for the loss of HSP90α. Overall, our study demonstrated the critical need for HSP90α chaperone in the maintenance of rod photoreceptors and showed potential substrates regulated by HSP90α in the retina.

Despite their structural similarities, the cytosolic isoforms of human Hsp90 show different behaviour in thermal unfolding due to their conformation: An FTIR study

Heat shock proteins 90 (Hsp90) are chaperones that promote the proper folding of other proteins under high temperature stress situations. Hsp90s are highly conserved and ubiquitous proteins, and in mammalian cells, they are localized in the cytoplasm, endoplasmic reticulum, and mitochondria. Cytoplasmic Hsp90 are named Hsp90α and Hsp90β and differ mainly in their expression pattern: Hsp90α is expressed under stress conditions, while Hsp90β is a constitutive protein. Structurally, both share the same characteristics by presenting three well-conserved domains, one of which, the N-terminal domain, has a binding site for ATP to which various drugs targeting this protein, including radicicol, can bind. The protein is mainly found in dimeric form and adopts different conformations depending on the presence of ligands, co-chaperones and client proteins. In this study, some aspects of structure and thermal unfolding of cytoplasmic human Hsp90 were analysed by infrared spectroscopy. The effect on Hsp90β of binding with a non-hydrolysable ATP analogue and radicicol was also examined. The results obtained showed that despite the high similarity in secondary structure the two isoforms exhibit substantial differences in their behaviour during thermal unfolding, as Hsp90α exhibits higher thermal stability, slower denaturation process and different event sequence during unfolding. Ligand binding strongly stabilizes Hsp90β and slightly modifies the secondary structure of the protein as well. Most likely, these structural and thermostability characteristics are closely related to the conformational cycling of the chaperone and its propensity to exist in monomer or dimer form.

An Editorial on the Special Issue ‘Hsp90 Structure, Mechanism and Disease’

Hsp90 is known for its role in the activation of an eclectic set of regulatory and signal transduction proteins [...]

Organismal Roles of Hsp90

Heat shock protein 90 (Hsp90) is a highly conserved molecular chaperone that assists in the maturation of many client proteins involved in cellular signal transduction. As a regulator of cellular signaling processes, it is vital for the maintenance of cellular proteostasis and adaptation to environmental stresses. Emerging research shows that Hsp90 function in an organism goes well beyond intracellular proteostasis. In metazoans, Hsp90, as an environmentally responsive chaperone, is involved in inter-tissue stress signaling responses that coordinate and safeguard cell nonautonomous proteostasis and organismal health. In this way, Hsp90 has the capacity to influence evolution and aging, and effect behavioral responses to facilitate tissue-defense systems that ensure organismal survival. In this review, I summarize the literature on the organismal roles of Hsp90 uncovered in multicellular organisms, from plants to invertebrates and mammals.