Swe1Wee1-dependent tyrosine phosphorylation of Hsp90 regulates distinct facets of chaperone function

Symmetric stimulation of Hsp90 catalyzed ATP hydrolysis through enhanced active site gate dynamics

Heat shock protein 90 (Hsp90) is a vital molecular chaperone that is essential for activating a diverse array of regulatory proteins through an ATP-dependent clamping cycle. The Hsp90 clamping cycle is driven by large-amplitude conformational changes within the N-terminal ATPase domain, including the release of an autoinhibitory N-terminal β-strap followed by a less well-characterized ATP gate rearrangement involving N-terminal helix 1. Here, we employed a combination of 19F nuclear magnetic resonance (NMR) spectroscopy, molecular dynamics (MD) simulations, and ATPase assays to examine the effects of targeted β-strap and helix 1 mutations. Our findings reveal that targeted disruption of helix 1 packing against the ATPase domain accelerates clamp closure, symmetrically enhancing ATP hydrolysis for both subunits of the Hsp90 dimer, whereas activation by the Aha1 cochaperone is disrupted. Decreasing the energy barrier associated with helix 1 release is a key step in modulating the energy landscape that governs the dynamics of the Hsp90 clamping cycle.

Ordered ATP hydrolysis in the Hsp90 chaperone is regulated by Aha1 and a conserved post-translational modification

Hsp90 is a dimeric molecular chaperone that is important for the folding, stabilization, activation, and maturation of hundreds of protein substrates called "clients" in cells. Dozens of co-chaperones and hundreds of post-translational modifications (PTMs) regulate the ATP-dependent client activation cycle. The Aha1 co-chaperone is the most potent stimulator of the ATPase cycle of Hsp90 and phosphorylation of threonine 22 in Hsp90 can regulate the recruitment of Aha1 in cells. We report here that phosphorylation of threonine 22 regulates specific aspects of Aha1 function after recruitment occurs. The phosphomimetic substitution, T22E, neutralizes the action of the Aha1 NxNNWHW motif. Moreover, this substitution can exert this effect from only one protomer of the Hsp90 dimer. This work sheds light on how asymmetric modifications in the Hsp90 dimer can functionalize individual protomers and fine-tune the Hsp90 cycle.

The known unknowns of the Hsp90 chaperone

Molecular chaperones are vital proteins that maintain protein homeostasis by assisting in protein folding, activation, degradation, and stress protection. Among them, heat-shock protein 90 (Hsp90) stands out as an essential proteostasis hub in eukaryotes, chaperoning hundreds of 'clients' (substrates). After decades of research, several 'known unknowns' about the molecular function of Hsp90 remain unanswered, hampering rational drug design for the treatment of cancers, neurodegenerative, and other diseases. We highlight three fundamental open questions, reviewing the current state of the field for each, and discuss new opportunities, including single-molecule technologies, to answer the known unknowns of the Hsp90 chaperone.

Flow cytometry FRET reveals post-translational modifications drive Protein Phosphatase-5 conformational changes in mammalian cells

The serine/threonine Protein Phosphatase-5 (PP5) plays an essential role in regulating hormone and stress-induced signaling networks as well as extrinsic apoptotic pathways in cells. Unlike other Protein Phosphatases, PP5 possesses both regulatory and catalytic domains, and its function is further modulated through post-translational modifications (PTMs). PP5 contains a tetratricopeptide repeat (TPR) domain, which usually inhibits its phosphatase activity by blocking the active site (closed conformation). Certain activators bind to the PP5-TPR domain, alleviating this inhibition and allowing the catalytic domain to adopt an active (open) conformation. While this mechanism has been proposed based on structural and biophysical studies, PP5 conformational changes and activity have yet to be observed in cells. Here, we designed and developed a flow cytometry-based fluorescence resonance energy transfer (FC-FRET) method, enabling real-time observation of PP5 autoinhibition and activation within live mammalian cells. By quantifying FRET efficiency using sensitized emission, we established a standardized and adaptable data acquisition workflow. Our findings revealed that, in a cellular context, PP5 exists in multiple conformational states, none of which alone fully predicts its activity. Additionally, we have demonstrated that PTMs such as phosphorylation and SUMOylation impact PP5 conformational changes, representing a significant advancement in our understanding of its regulatory mechanisms.

Modification of Regulatory Tyrosine Residues Biases Human Hsp90α in its Interactions with Cochaperones and Clients

The highly conserved Hsp90 chaperones control stability and activity of many essential signaling and regulatory proteins including many protein kinases, E3 ligases and transcription factors. Thereby, Hsp90s couple cellular homeostasis of the proteome to cell fate decisions. High-throughput mass spectrometry revealed 178 and 169 posttranslational modifications (PTMs) for human cytosolic Hsp90α and Hsp90β, but for only a few of the modifications the physiological consequences are investigated in some detail. In this study, we explored the suitability of the yeast model system for the identification of key regulatory residues in human Hsp90α. Replacement of three tyrosine residues known to be phosphorylated by phosphomimetic glutamate and by non-phosphorylatable phenylalanine individually and in combination influenced yeast growth and the maturation of 7 different Hsp90 clients in distinct ways. Furthermore, wild-type and mutant Hsp90 differed in their ability to stabilize known clients when expressed in HepG2 HSP90AA1-/- cells. The purified mutant proteins differed in their interaction with the cochaperones Aha1, Cdc37, Hop and p23 and in their support of the maturation of glucocorticoid receptor ligand binding domain in vitro. In vivo and in vitro data correspond well to each other confirming that the yeast system is suitable for the identification of key regulatory sites in human Hsp90s. Our findings indicate that even closely related clients are affected differently by the amino acid replacements in the investigated positions, suggesting that PTMs could bias Hsp90s client specificity.

SUMOylation of protein phosphatase 5 regulates phosphatase activity and substrate release

The serine/threonine protein phosphatase 5 (PP5) regulates hormone and stress-induced signaling networks. Unlike other phosphoprotein phosphatases, PP5 contains both regulatory and catalytic domains and is further regulated through post-translational modifications (PTMs). Here we identify that SUMOylation of K430 in the catalytic domain of PP5 regulates phosphatase activity. Additionally, phosphorylation of PP5-T362 is pre-requisite for SUMOylation, suggesting the ordered addition of PTMs regulates PP5 function in cells. Using the glucocorticoid receptor, a well known substrate for PP5, we demonstrate that SUMOylation results in substrate release from PP5. We harness this information to create a non-SUMOylatable K430R mutant as a 'substrate trap' and globally identified novel PP5 substrate candidates. Lastly, we generated a consensus dephosphorylation motif using known substrates, and verified its presence in the new candidate substrates. This study unravels the impact of cross talk of SUMOylation and phosphorylation on PP5 phosphatase activity and substrate release in cells.

Phosphorylation-driven epichaperome assembly is a regulator of cellular adaptability and proliferation

The intricate network of protein-chaperone interactions is crucial for maintaining cellular function. Recent discoveries have unveiled the existence of specialized chaperone assemblies, known as epichaperomes, which serve as scaffolding platforms that orchestrate the reconfiguration of protein-protein interaction networks, thereby enhancing cellular adaptability and proliferation. This study explores the structural and regulatory aspects of epichaperomes, with a particular focus on the role of post-translational modifications (PTMs) in their formation and function. A key finding is the identification of specific PTMs on HSP90, particularly at residues Ser226 and Ser255 within an intrinsically disordered region, as critical determinants of epichaperome assembly. Our data demonstrate that phosphorylation of these serine residues enhances HSP90's interactions with other chaperones and co-chaperones, creating a microenvironment conducive to epichaperome formation. Moreover, we establish a direct link between epichaperome function and cellular physiology, particularly in contexts where robust proliferation and adaptive behavior are essential, such as in cancer and pluripotent stem cell maintenance. These findings not only provide mechanistic insights but also hold promise for the development of novel therapeutic strategies targeting chaperone assemblies in diseases characterized by epichaperome dysregulation, thereby bridging the gap between fundamental research and precision medicine.

Asymmetric Dynamics Drive Catalytic Activation of the Hsp90 Chaperone

The Hsp90 chaperone is an ATPase enzyme composed of two copies of a three-domain subunit. Hsp90 stabilizes and activates a diverse array of regulatory proteins. Substrates are bound and released by the middle domain through a clamping cycle involving conformational transitions between a dynamic open state and a compact conformationally restricted closed state. Intriguingly, the overall ATPase activity of dimeric Hsp90 can be asymmetrically enhanced through a single subunit when Hsp90 is bound to a cochaperone or when Hsp90 is composed of one active and one catalytically defunct subunit as a heterodimer. To explore the mechanism of asymmetric Hsp90 activation, we designed a subunit bearing N-terminal ATPase mutations that demonstrate increased intra- and interdomain dynamics. Using intact Hsp90 and various N-terminal and middle domain constructs, we blended 19F NMR spectroscopy, molecular dynamics (MD) simulations, and ATPase assays to show that within the context of heterodimeric Hsp90, the conformationally dynamic subunit stimulates the ATPase activity of the normal subunit. The contrasting dynamic properties of the subunits within heterodimeric Hsp90 provide a mechanistic framework to understand the molecular basis for asymmetric Hsp90 activation and its importance for the biological function of Hsp90.

Recruitment of Ahsa1 to Hsp90 is regulated by a conserved peptide that inhibits ATPase stimulation

Hsp90 is a molecular chaperone that acts on its clients through an ATP-dependent and conformationally dynamic functional cycle. The cochaperone Accelerator of Hsp90 ATPase, or Ahsa1, is the most potent stimulator of Hsp90 ATPase activity. Ahsa1 stimulates the rate of Hsp90 ATPase activity through a conserved motif, NxNNWHW. Metazoan Ahsa1, but not yeast, possesses an additional 20 amino acid peptide preceding the NxNNWHW motif that we have called the intrinsic chaperone domain (ICD). The ICD of Ahsa1 diminishes Hsp90 ATPase stimulation by interfering with the function of the NxNNWHW motif. Furthermore, the NxNNWHW modulates Hsp90's apparent affinity to Ahsa1 and ATP. Lastly, the ICD controls the regulated recruitment of Hsp90 in cells and its deletion results in the loss of interaction with Hsp90 and the glucocorticoid receptor. This work provides clues to how Ahsa1 conserved regions modulate Hsp90 kinetics and how they may be coupled to client folding status.

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.

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.

Catalytic inhibitor of Protein Phosphatase 5 activates the extrinsic apoptotic pathway by disrupting complex II in kidney cancer

Serine/threonine protein phosphatase-5 (PP5) is involved in tumor progression and survival, making it an attractive therapeutic target. Specific inhibition of protein phosphatases has remained challenging because of their conserved catalytic sites. PP5 contains its regulatory domains within a single polypeptide chain, making it a more desirable target. Here we used an in silico approach to screen and develop a selective inhibitor of PP5. Compound P053 is a competitive inhibitor of PP5 that binds to its catalytic domain and causes apoptosis in renal cancer. We further demonstrated that PP5 interacts with FADD, RIPK1, and caspase 8, components of the extrinsic apoptotic pathway complex II. Specifically, PP5 dephosphorylates and inactivates the death effector protein FADD, preserving complex II integrity and regulating extrinsic apoptosis. Our data suggests that PP5 promotes renal cancer survival by suppressing the extrinsic apoptotic pathway. Pharmacologic inhibition of PP5 activates this pathway, presenting a viable therapeutic strategy for renal cancer.

Saccharomyces cerevisiae as a tool for deciphering Hsp90 molecular chaperone function

Yeast is a valuable model organism for their ease of genetic manipulation, rapid growth rate, and relative similarity to higher eukaryotes. Historically, Saccharomyces cerevisiae has played a major role in discovering the function of complex proteins and pathways that are important for human health and disease. Heat shock protein 90 (Hsp90) is a molecular chaperone responsible for the stabilization and activation of hundreds of integral members of the cellular signaling network. Much important structural and functional work, including many seminal discoveries in Hsp90 biology are the direct result of work carried out in S. cerevisiae. Here, we have provided a brief overview of the S. cerevisiae model system and described how this eukaryotic model organism has been successfully applied to the study of Hsp90 chaperone function.

Activation of autophagy depends on Atg1/Ulk1-mediated phosphorylation and inhibition of the Hsp90 chaperone machinery

Cellular homeostasis relies on both the chaperoning of proteins and the intracellular degradation system that delivers cytoplasmic constituents to the lysosome, a process known as autophagy. The crosstalk between these processes and their underlying regulatory mechanisms is poorly understood. Here, we show that the molecular chaperone heat shock protein 90 (Hsp90) forms a complex with the autophagy-initiating kinase Atg1 (yeast)/Ulk1 (mammalian), which suppresses its kinase activity. Conversely, environmental cues lead to Atg1/Ulk1-mediated phosphorylation of a conserved serine in the amino domain of Hsp90, inhibiting its ATPase activity and altering the chaperone dynamics. These events impact a conformotypic peptide adjacent to the activation and catalytic loop of Atg1/Ulk1. Finally, Atg1/Ulk1-mediated phosphorylation of Hsp90 leads to dissociation of the Hsp90:Atg1/Ulk1 complex and activation of Atg1/Ulk1, which is essential for initiation of autophagy. Our work indicates a reciprocal regulatory mechanism between the chaperone Hsp90 and the autophagy kinase Atg1/Ulk1 and consequent maintenance of cellular proteostasis.

Potential use of heat shock protein 90 as a biomarker for the diagnosis of human diseases

INTRODUCTION

The heat shock protein 90 (Hsp90) is a protein involved in many different biological processes and especially in cell survival. Some of these functions require the participation of other biological molecules, so Hsp90 is a chaperone that takes part in many protein-protein interactions working as a critical signaling hub protein. As a member of the heat shock protein family, Hsp90 expression is regulated under certain environmental and/or stressful situations, therefore Hsp90 concentration can be monitored and linked to these effects.

AREAS COVERED

This review discusses the Hsp90 expression in samples from individuals affected by different diseases (from infectious to cancer origin), and the biological consequences of these disorders, including the potential use of Hsp90 as a biomarker for the diagnosis of human diseases.

EXPERT OPINION

The potential of Hsp90 as a biomarker disease has been demonstrated in several studies in relation to infectious diseases and especially cancer. However, further research in this field is still needed, mainly to validate in statistically significant clinical studies that the detection of Hsp90 protein allows the diagnosis of some cancers at an early stage and also that it can act as a biomarker for monitoring the efficacy of their therapies.

Synthetic and Medicinal Chemistry Approaches Toward WEE1 Kinase Inhibitors and Its Degraders

WEE1 is a checkpoint kinase critical for mitotic events, especially in cell maturation and DNA repair. Most cancer cells' progression and survival are linked with elevated levels of WEE1 kinase. Thus, WEE1 kinase has become a new promising druggable target. A few classes of WEE1 inhibitors are designed by rationale or structure-based techniques and optimization approaches to identify selective acting anticancer agents. The discovery of the WEE1 inhibitor AZD1775 further emphasized WEE1 as a promising anticancer target. Therefore, the current review provides a comprehensive data on medicinal chemistry, synthetic approaches, optimization methods, and the interaction profile of WEE1 kinase inhibitors. In addition, WEE1 PROTAC degraders and their synthetic procedures, including a list of noncoding RNAs necessary for regulation of WEE1, are also highlighted. From the standpoint of medicinal chemistry, the contents of this compilation serve as an exemplar for the further design, synthesis, and optimization of promising WEE1-targeted anticancer agents.

RIPK1 inhibition contributes to lysosomal membrane stabilization in ischemic astrocytes via a lysosomal Hsp70.1B-dependent mechanism

Receptor-interacting protein kinase 1 (RIPK1) contributes to necroptosis. Our previous study showed that pharmacological or genetic inhibition of RIPK1 protects against ischemic stroke-induced astrocyte injury. In this study, we investigated the molecular mechanisms underlying RIPK1-mediated astrocyte injury in vitro and in vivo. Primary cultured astrocytes were transfected with lentiviruses and then subjected to oxygen and glucose deprivation (OGD). In a rat model of permanent middle cerebral artery occlusion (pMCAO), lentiviruses carrying shRNA targeting RIPK1 or shRNA targeting heat shock protein 70.1B (Hsp70.1B) were injected into the lateral ventricles 5 days before pMCAO was established. We showed that RIPK1 knockdown protected against OGD-induced astrocyte damage, blocked the OGD-mediated increase in lysosomal membrane permeability in astrocytes, and inhibited the pMCAO-induced increase in astrocyte lysosome numbers in the ischemic cerebral cortex; these results suggested that RIPK1 contributed to the lysosomal injury in ischemic astrocytes. We revealed that RIPK1 knockdown upregulated the protein levels of Hsp70.1B and increased the colocalization of Lamp1 and Hsp70.1B in ischemic astrocytes. Hsp70.1B knockdown exacerbated pMCAO-induced brain injury, decreased lysosomal membrane integrity and blocked the protective effects of the RIPK1-specific inhibitor necrostatin-1 on lysosomal membranes. On the other hand, RIPK1 knockdown further exacerbated the pMCAO- or OGD-induced decreases in the levels of Hsp90 and the binding of Hsp90 to heat shock transcription factor-1 (Hsf1) in the cytoplasm, and RIPK1 knockdown promoted the nuclear translocation of Hsf1 in ischemic astrocytes, resulting in increased Hsp70.1B mRNA expression. These results suggest that inhibition of RIPK1 protects ischemic astrocytes by stabilizing lysosomal membranes via the upregulation of lysosomal Hsp70.1B; the mechanism underlying these effects involves decreased Hsp90 protein levels, increased Hsf1 nuclear translocation and increased Hsp70.1B mRNA expression.

Association of Hsp90 with p53 and Fizzy related homolog (Fzr) synchronizing Anaphase Promoting Complex (APC/C): An unexplored ally towards oncogenic pathway

The intricate molecular interactions leading to the oncogenic pathway are the consequence of cell cycle modification controlled by a bunch of cell cycle regulatory proteins. The tumor suppressor and cell cycle regulatory proteins work in coordination to maintain a healthy cellular environment. The integrity of this cellular protein pool is perpetuated by heat shock proteins/chaperones, which assist in proper protein folding during normal and cellular stress conditions. Among these versatile groups of chaperone proteins, Hsp90 is one of the significant ATP-dependent chaperones that aid in stabilizing many tumor suppressors and cell cycle regulator protein targets. Recently, studies have revealed that in cancerous cell lines, Hsp90 stabilizes mutant p53, 'the guardian of the genome.' Hsp90 also has a significant impact on Fzr, an essential regulator of the cell cycle having an important role in the developmental process of various organisms, including Drosophila, yeast, Caenorhabditis elegans, and plants. During cell cycle progression, p53 and Fzr coordinately regulate the Anaphase Promoting Complex (APC/C) from metaphase to anaphase transition up to cell cycle exit. APC/C mediates proper centrosome function in the dividing cell. The centrosome acts as the microtubule organizing center for the correct segregation of the sister chromatids to ensure perfect cell division. This review examines the structure of Hsp90 and its co-chaperones, which work in synergy to stabilize proteins such as p53 and Fizzy-related homolog (Fzr) to synchronize the Anaphase Promoting Complex (APC/C). Dysfunction of this process activates the oncogenic pathway leading to the development of cancer. Additionally, an overview of current drugs targeting Hsp90 at various phases of clinical trials has been included.

p23 and Aha1: Distinct Functions Promote Client Maturation

Hsp90 is a conserved molecular chaperone regulating the folding and activation of a diverse array of several hundreds of client proteins. The function of Hsp90 in client processing is fine-tuned by a cohort of co-chaperones that modulate client activation in a client-specific manner. They affect the Hsp90 ATPase activity and the recruitment of client proteins and can in addition affect chaperoning in an Hsp90-independent way. p23 and Aha1 are central Hsp90 co-chaperones that regulate Hsp90 in opposing ways. While p23 inhibits the Hsp90 ATPase and stabilizes a client-bound Hsp90 state, Aha1 accelerates ATP hydrolysis and competes with client binding to Hsp90. Even though both proteins have been intensively studied for decades, research of the last few years has revealed intriguing new aspects of these co-chaperones that expanded our perception of how they regulate client activation. Here, we review the progress in understanding p23 and Aha1 as promoters of client processing. We highlight the structures of Aha1 and p23, their interaction with Hsp90, and how their association with Hsp90 affects the conformational cycle of Hsp90 in the context of client maturation.

Impact of Co-chaperones and Posttranslational Modifications Toward Hsp90 Drug Sensitivity

Posttranslational modifications (PTMs) regulate myriad cellular processes by modulating protein function and protein-protein interaction. Heat shock protein 90 (Hsp90) is an ATP-dependent molecular chaperone whose activity is responsible for the stabilization and maturation of more than 300 client proteins. Hsp90 is a substrate for numerous PTMs, which have diverse effects on Hsp90 function. Interestingly, many Hsp90 clients are enzymes that catalyze PTM, demonstrating one of the several modes of regulation of Hsp90 activity. Approximately 25 co-chaperone regulatory proteins of Hsp90 impact structural rearrangements, ATP hydrolysis, and client interaction, representing a second layer of influence on Hsp90 activity. A growing body of literature has also established that PTM of these co-chaperones fine-tune their activity toward Hsp90; however, many of the identified PTMs remain uncharacterized. Given the critical role of Hsp90 in supporting signaling in cancer, clinical evaluation of Hsp90 inhibitors is an area of great interest. Interestingly, differential PTM and co-chaperone interaction have been shown to impact Hsp90 binding to its inhibitors. Therefore, understanding these layers of Hsp90 regulation will provide a more complete understanding of the chaperone code, facilitating the development of new biomarkers and combination therapies.

HSP90-CDC37-PP5 forms a structural platform for kinase dephosphorylation

Activation of client protein kinases by the HSP90 molecular chaperone system is affected by phosphorylation at multiple sites on HSP90, the kinase-specific co-chaperone CDC37, and the kinase client itself. Removal of regulatory phosphorylation from client kinases and their release from the HSP90-CDC37 system depends on the Ser/Thr phosphatase PP5, which associates with HSP90 via its N-terminal TPR domain. Here, we present the cryoEM structure of the oncogenic protein kinase client BRAFV600E bound to HSP90-CDC37, showing how the V600E mutation favours BRAF association with HSP90-CDC37. Structures of HSP90-CDC37-BRAFV600E complexes with PP5 in autoinhibited and activated conformations, together with proteomic analysis of its phosphatase activity on BRAFV600E and CRAF, reveal how PP5 is activated by recruitment to HSP90 complexes. PP5 comprehensively dephosphorylates client proteins, removing interaction sites for regulatory partners such as 14-3-3 proteins and thus performing a 'factory reset' of the kinase prior to release.

O-GlcNAcylation suppresses TRAP1 activity and promotes mitochondrial respiration

The molecular chaperone TNF-receptor-associated protein-1 (TRAP1) controls mitochondrial respiration through regulation of Krebs cycle and electron transport chain activity. Post-translational modification (PTM) of TRAP1 regulates its activity, thereby controlling global metabolic flux. O-GlcNAcylation is one PTM that is known to impact mitochondrial metabolism, however the major effectors of this regulatory PTM remain inadequately resolved. Here we demonstrate that TRAP1-O-GlcNAcylation decreases TRAP1 ATPase activity, leading to increased mitochondrial metabolism. O-GlcNAcylation of TRAP1 occurs following mitochondrial import and provides critical regulatory feedback, as the impact of O-GlcNAcylation on mitochondrial metabolism shows TRAP1-dependence. Mechanistically, loss of TRAP1-O-GlcNAcylation decreased TRAP1 binding to ATP, and interaction with its client protein succinate dehydrogenase (SDHB). Taken together, TRAP1-O-GlcNAcylation serves to regulate mitochondrial metabolism by the reversible attenuation of TRAP1 chaperone activity.

Conformational Dynamics and Mechanisms of Client Protein Integration into the Hsp90 Chaperone Controlled by Allosteric Interactions of Regulatory Switches: Perturbation-Based Network Approach for Mutational Profiling of the Hsp90 Binding and Allostery

Understanding the allosteric mechanisms of the Hsp90 chaperone interactions with cochaperones and client protein clientele is fundamental to dissect activation and regulation of many proteins. In this work, atomistic simulations are combined with perturbation-based approaches and dynamic network modeling for a comparative mutational profiling of the Hsp90 binding and allosteric interaction networks in the three Hsp90 maturation complexes with FKBP51 and P23 cochaperones and the glucocorticoid receptor (GR) client. The conformational dynamics signatures of the Hsp90 complexes and dynamics fluctuation analysis revealed how the intrinsic plasticity of the Hsp90 dimer can be modulated by cochaperones and client proteins to stabilize the closed dimer state required at the maturation stage of the ATPase cycle. In silico deep mutational scanning of the protein residues characterized the hot spots of protein stability and binding affinity in the Hsp90 complexes, showing that binding hot spots may often coincide with the regulatory centers that modulate dynamic allostery in the Hsp90 dimer. We introduce a perturbation-based network approach for mutational scanning of allosteric residue potentials and characterize allosteric switch clusters that control mechanism of cochaperone-dependent client recognition and remodeling by the Hsp90 chaperone. The results revealed a conserved network of allosteric switches in the Hsp90 complexes that allow cochaperones and GR protein to become integrated into the Hsp90 system by anchoring to the conformational switch points in the functional Hsp90 regions. This study suggests that the Hsp90 binding and allostery may operate under a regulatory mechanism in which activation or repression of the Hsp90 activity can be pre-encoded in the allosterically regulated Hsp90 dimer motions. By binding directly to the conformational switch centers on the Hsp90, cochaperones and interacting proteins can efficiently modulate the allosteric interactions and long-range communications required for client remodeling and activation.

A specialized Hsp90 co-chaperone network regulates steroid hormone receptor response to ligand

Heat shock protein-90 (Hsp90) chaperone machinery is involved in the stability and activity of its client proteins. The chaperone function of Hsp90 is regulated by co-chaperones and post-translational modifications. Although structural evidence exists for Hsp90 interaction with clients, our understanding of the impact of Hsp90 chaperone function toward client activity in cells remains elusive. Here, we dissect the impact of recently identified higher eukaryotic co-chaperones, FNIP1/2 (FNIPs) and Tsc1, toward Hsp90 client activity. Our data show that Tsc1 and FNIP2 form mutually exclusive complexes with FNIP1, and that unlike Tsc1, FNIP1/2 interact with the catalytic residue of Hsp90. Functionally, these co-chaperone complexes increase the affinity of the steroid hormone receptors glucocorticoid receptor and estrogen receptor to their ligands in vivo. We provide a model for the responsiveness of the steroid hormone receptor activation upon ligand binding as a consequence of their association with specific Hsp90:co-chaperone subpopulations.

Integrin subunit beta 8 contributes to lenvatinib resistance in HCC

Lenvatinib is a multikinase inhibitor approved as a first-line therapy for advanced hepatocellular carcinoma (HCC). However, the development of drug resistance is common, and the underlying mechanisms governing this resistance are largely unknown. In this study, we established two lenvatinib-resistant (LR) HCC cell lines and identified integrin subunit beta 8 (ITGB8) as a critical contributor to lenvatinib resistance in HCC. The elevated expression of ITGB8 was observed in LR HCC cells. Furthermore, silencing of ITGB8 reversed lenvatinib resistance in vitro and in vivo, whereas ectopic expression of ITGB8 in lenvatinib-sensitive parental HCC cells exhibited increased resistance to lenvatinib. Mechanistically, ITGB8 regulated lenvatinib resistance through an HSP90-mediated stabilization of AKT and enhanced AKT signaling. In support of this model, either an AKT inhibitor MK-2206 or an HSP90 inhibitor 17-AAG resensitized LR HCC cells to lenvatinib treatment. Conclusion: Collectively, our results establish a crucial role of ITGB8 in lenvatinib resistance, and suggest that targeting the ITGB8/HSP90/AKT axis is a promising therapeutic strategy in patients with HCC exhibiting lenvatinib resistance.

Therapeutic potential of CDK4/6 inhibitors in renal cell carcinoma

The treatment of advanced and metastatic kidney cancer has entered a golden era with the addition of more therapeutic options, improved survival and new targeted therapies. Tyrosine kinase inhibitors, mammalian target of rapamycin (mTOR) inhibitors and immune checkpoint blockade have all been shown to be promising strategies in the treatment of renal cell carcinoma (RCC). However, little is known about the best therapeutic approach for individual patients with RCC and how to combat therapeutic resistance. Cancers, including RCC, rely on sustained replicative potential. The cyclin-dependent kinases CDK4 and CDK6 are involved in cell-cycle regulation with additional roles in metabolism, immunogenicity and antitumour immune response. Inhibitors of CDK4 and CDK6 are now commonly used as approved and investigative treatments in breast cancer, as well as several other tumours. Furthermore, CDK4/6 inhibitors have been shown to work synergistically with other kinase inhibitors, including mTOR inhibitors, as well as with immune checkpoint inhibitors in preclinical cancer models. The effect of CDK4/6 inhibitors in kidney cancer is relatively understudied compared with other cancers, but the preclinical studies available are promising. Collectively, growing evidence suggests that targeting CDK4 and CDK6 in kidney cancer, alone and in combination with current therapeutics including mTOR and immune checkpoint inhibitors, might have therapeutic benefit and should be further explored.

Hsp90 S-nitrosylation at Cys521, as a conformational switch, modulates cycling of Hsp90-AHA1-CDC37 chaperone machine to aggravate atherosclerosis

Endothelial dysfunction is the initial process of atherosclerosis. Heat shock protein 90 (Hsp90), as a molecular chaperone, plays a crucial role in various cardiovascular diseases. Hsp90 function is regulated by S-nitrosylation (SNO). However, the precise role of SNO-Hsp90 in endothelial dysfunction during atherosclerosis remains unclear. We here identified Hsp90 as a highly S-nitrosylated target in endothelial cells (ECs) by biotin switch assay combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS). The elevation of SNO-Hsp90 was observed in atherosclerotic human and rodent aortas as well as in oxidized LDL (oxLDL)-treated ECs. Inhibition of inducible nitric oxide synthase (iNOS) or transfection with Hsp90 cysteine 521 (Cys521) mutation plasmid decreased the level of SNO-Hsp90 in oxLDL-cultured ECs. Coimmunoprecipitation and proximity ligation assay demonstrated that SNO-Hsp90 at Cys521 suppressed the interaction between Hsp90 and activator of Hsp90 ATPase activity 1 (AHA1), but promoted the association of Hsp90 and cell division cycle 37 (CDC37). Hsp90 Cys521 mutation increased endothelial nitric oxide synthase (eNOS) activity and inhibited nuclear factor kappa-B (NF-κB) signaling, thereby increasing nitric oxide (NO) bioavailability and alleviating endothelial adhesion, inflammation and oxidative stress in oxLDL-treated ECs. Also, administration of endothelial-specific adeno-associated viruses of Cys521-mutated Hsp90 significantly mitigated vascular oxidative stress, macrophage infiltration and atherosclerosis lesion areas in high fat diet-fed ApoE^-/- mice. In conclusion, SNO-Hsp90 at Cys521, that serves as a conformational switch, disrupts Hsp90/AHA1 interaction but promotes recruitment of CDC37 to exacerbate atherosclerosis.

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Hsp90 S-nitrosylation at Cys521 acts as a conformational switch to modulate Hsp90/AHA1 and Hsp90/CDC37 interaction.

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SNO-Hsp90 induces endothelial adhesion, inflammation and oxidative stress.

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SNO-Hsp90 mediates endothelial dysfunction to exacerbate atherosclerosis.

Wee1 Kinase: A Potential Target to Overcome Tumor Resistance to Therapy

During the cell cycle, DNA suffers several lesions that need to be repaired prior to entry into mitosis to preserve genome integrity in daughter cells. Toward this aim, cells have developed complex enzymatic machinery, the so-called DNA damage response (DDR), which is able to repair DNA, temporarily stopping the cell cycle to provide more time to repair, or if the damage is too severe, inducing apoptosis. This DDR mechanism is considered the main source of resistance to DNA-damaging therapeutic treatments in oncology. Recently, cancer stem cells (CSCs), which are a small subset of tumor cells, were identified as tumor-initiating cells. CSCs possess self-renewal potential and persistent tumorigenic capacity, allowing for tumor re-growth and relapse. Compared with cancer cells, CSCs are more resistant to therapeutic treatments. Wee1 is the principal gatekeeper for both G2/M and S-phase checkpoints, where it plays a key role in cell cycle regulation and DNA damage repair. From this perspective, Wee1 inhibition might increase the effectiveness of DNA-damaging treatments, such as radiotherapy, forcing tumor cells and CSCs to enter into mitosis, even with damaged DNA, leading to mitotic catastrophe and subsequent cell death.

Exploring absent protein function in yeast: assaying post translational modification and human genetic variation

Yeast is a valuable eukaryotic model organism that has evolved many processes conserved up to humans, yet many protein functions, including certain DNA and protein modifications, are absent. It is this absence of protein function that is fundamental to approaches using yeast as an in vivo test system to investigate human proteins. Functionality of the heterologous expressed proteins is connected to a quantitative, selectable phenotype, enabling the systematic analyses of mechanisms and specificity of DNA modification, post-translational protein modifications as well as the impact of annotated cancer mutations and coding variation on protein activity and interaction. Through continuous improvements of yeast screening systems, this is increasingly carried out on a global scale using deep mutational scanning approaches. Here we discuss the applicability of yeast systems to investigate absent human protein function with a specific focus on the impact of protein variation on protein-protein interaction modulation.

Antifungal Effect of All-trans Retinoic Acid against Aspergillus fumigatus In Vitro and in a Pulmonary Aspergillosis In Vivo Model

Aspergillus fumigatus is the most common opportunistic fungal pathogen and causes invasive pulmonary aspergillosis (IPA), with high mortality among immunosuppressed patients. The fungistatic activity of all-trans retinoic acid (ATRA) has been recently described in vitro.

Aspergillus fumigatus is the most common opportunistic fungal pathogen and causes invasive pulmonary aspergillosis (IPA), with high mortality among immunosuppressed patients. The fungistatic activity of all-trans retinoic acid (ATRA) has been recently described in vitro. We evaluated the efficacy of ATRA in vivo and its potential synergistic interaction with other antifungal drugs. A rat model of IPA and in vitro experiments were performed to assess the efficacy of ATRA against Aspergillus in association with classical antifungal drugs and in silico studies used to clarify its mechanism of action. ATRA (0.5 and 1 mM) displayed a strong fungistatic activity in Aspergillus cultures, while at lower concentrations, synergistically potentiated fungistatic efficacy of subinhibitory concentration of amphotericin B (AmB) and posaconazole (POS). ATRA also enhanced macrophagic phagocytosis of conidia. In a rat model of IPA, ATRA reduced mortality similarly to posaconazole. Fungistatic efficacy of ATRA alone and synergistically with other antifungal drugs was documented in vitro, likely by inhibiting fungal heat shock protein 90 (Hsp90) expression and Hsp90-related genes. ATRA treatment reduced mortality in a model of IPA in vivo. Those findings suggest ATRA as a suitable fungistatic agent that can also reduce dosage and adverse reactions of classical antifungal drugs and add to the development of new therapeutic strategies against IPA and systemic fungal infections.

Functional connections between cell cycle and proteostasis in the regulation of Candida albicans morphogenesis

Morphological plasticity is a key virulence trait for many fungal pathogens. For the opportunistic fungal pathogen Candida albicans, transitions among yeast, pseudohyphal, and hyphal forms are critical for virulence, because the morphotypes play distinct roles in the infection process. C. albicans morphogenesis is induced in response to many host-relevant conditions and is regulated by complex signaling pathways and cellular processes. Perturbation of either cell-cycle progression or protein homeostasis induces C. albicans filamentation, demonstrating that these processes play a key role in morphogenetic control. Regulators such as cyclin-dependent kinases, checkpoint proteins, the proteasome, the heat shock protein Hsp90, and the heat shock transcription factor Hsf1 all influence morphogenesis, often through interconnected effects on the cell cycle and proteostasis. This review highlights the major cell-cycle and proteostasis regulators that modulate morphogenesis and discusses how these two processes intersect to regulate this key virulence trait.

Systematic Analysis of the Lysine Crotonylome and Multiple Posttranslational Modification Analysis (Acetylation, Succinylation, and Crotonylation) in Candida albicans

Candida albicans is an opportunistic pathogen that causes lethal fungal infections in immunocompromised patients. Lysine crotonylation is a newly discovered PTM (posttranslational modification) epigenetic type that may play a critical role in regulating gene expression. In this study, we used an antibody-enrichment approach along with LC-MS/MS to carry out a quantitative crotonylome analysis in C. albicans We found a total of 5,242 crotonylation sites and 1,584 crotonylated proteins among 9,038 proteins in this organism. Of these crotonylated proteins, a few unique crotonylated motifs are noted such as D and E in positions +1, +2, or +3 or K and R in positions +5 or +6, while A, E, F, G, P, W, and Y are in the -1 position or A, K, and R are found in positions -5, -6, -7, or -8. Functional analysis has shown that a majority of the crotonylated proteins are related to biosynthetic events and carbon metabolism. When combined with previously collected data on acetylation and succinylation, PPI (protein-protein interaction network) analysis reveals that proteins with functions in ribosomal biogenesis, oxidative phosphorylation, nucleus activity, and proteasome formation are heavily modified by these three PTM types. To the best of our knowledge, this is the first crotonylome study carried out in C. albicans and is an important step to a better understanding of the biological and pathogenic impact of PTM in C. albicans IMPORTANCE C. albicans is a kind of pathogen of fungal infections that is found worldwide. Lysine crotonylation of proteins as a recently discovered PTM (posttranslational modification) may have a critical role in regulating cells. We first carried out large-scale analysis of crotonylated proteome and multiple PTM analysis (acetylation, succinylation, and crotonylation), then drew a diagram to show multiple PTM sites on histones in C. albicans of our study. This study about crotonylome in human pathogenic fungi is a milestone that first and deeply investigates the functional analysis of crotonylated proteins in C. albicans, which marks an important start for further research.

Signalling mechanisms involved in stress response to antifungal drugs

The emergence of antifungal resistance is a serious threat in the treatment of mycoses. The primary susceptible fungal cells may evolve a resistance after longer exposure to antifungal agents. The exposure itself causes stress condition, to which the fungus needs to adapt. This review provides detailed description of evolutionary conserved molecular mechanisms contributing to the adaptation response to stress caused by antifungal agents as well as their interconnection. The knowledge may help us to find new ways to delay the emergence of drug resistance as the same mechanisms are used regardless of what antifungal compound causes stress.

Dynamically Shaping Chaperones. Allosteric Modulators of HSP90 Family as Regulatory Tools of Cell Metabolism in Neoplastic Progression

Molecular chaperones have recently emerged as fundamental regulators of salient biological routines, including metabolic adaptations to environmental changes. Yet, many of the molecular mechanisms at the basis of their functions are still unknown or at least uncertain. This is in part due to the lack of chemical tools that can interact with the chaperones to induce measurable functional perturbations. In this context, the use of small molecules as modulators of protein functions has proven relevant for the investigation of a number of biomolecular systems. Herein, we focus on the functions, interactions and signaling pathways of the HSP90 family of molecular chaperones as possible targets for the discovery of new molecular entities aimed at tuning their activity and interactions. HSP90 and its mitochondrial paralog, TRAP1, regulate the activity of crucial metabolic circuitries, making cells capable of efficiently using available energy sources, with relevant implications both in healthy conditions and in a variety of disease states and especially cancer. The design of small-molecules targeting the chaperone cycle of HSP90 and able to inhibit or stimulate the activity of the protein can provide opportunities to finely dissect their biochemical activities and to obtain lead compounds to develop novel, mechanism-based drugs.

Exploring Mechanisms of Communication Switching in the Hsp90-Cdc37 Regulatory Complexes with Client Kinases through Allosteric Coupling of Phosphorylation Sites: Perturbation-Based Modeling and Hierarchical Community Analysis of Residue Interaction Networks

Understanding molecular principles underlying chaperone-based modulation of kinase client activity is critically important to dissect functions and activation mechanisms of many oncogenic proteins. The recent experimental studies have suggested that phosphorylation sites in the Hsp90 and Cdc37 proteins can serve as conformational communication switches of chaperone regulation and kinase interactions. However, a mechanism of allosteric coupling between phosphorylation sites in the Hsp90 and Cdc37 during client binding is poorly understood, and the molecular signatures underpinning specific roles of phosphorylation sites in the Hsp90 regulation remain unknown. In this work, we employed a combination of evolutionary analysis, coarse-grained molecular simulations together with perturbation-based network modeling and scanning of the unbound and bound Hsp90 and Cdc37 structures to quantify allosteric effects of phosphorylation sites and identify unique signatures that are characteristic for communication switches of kinase-specific client binding. By using network-based metrics of the dynamic intercommunity bridgeness and community centrality, we characterize specific signatures of phosphorylation switches involved in allosteric regulation. Through perturbation-based analysis of the dynamic residue interaction networks, we show that mutations of kinase-specific phosphorylation switches can induce long-range effects and lead to a global rewiring of the allosteric network and signal transmission in the Hsp90-Cdc37-kinase complex. We determine a specific group of phosphorylation sites in the Hsp90 where mutations may have a strong detrimental effect on allosteric interaction network, providing insight into the mechanism of phosphorylation-induced communication switching. The results demonstrate that kinase-specific phosphorylation switches of communications in the Hsp90 may be partly predisposed for their regulatory role based on preexisting allosteric propensities.

Post-translational modifications of Hsp90 and translating the chaperone code

Cells have a remarkable ability to synthesize large amounts of protein in a very short period of time. Under these conditions, many hydrophobic surfaces on proteins may be transiently exposed, and the likelihood of deleterious interactions is quite high. To counter this threat to cell viability, molecular chaperones have evolved to help nascent polypeptides fold correctly and multimeric protein complexes assemble productively, while minimizing the danger of protein aggregation. Heat shock protein 90 (Hsp90) is an evolutionarily conserved molecular chaperone that is involved in the stability and activation of at least 300 proteins, also known as clients, under normal cellular conditions. The Hsp90 clients participate in the full breadth of cellular processes, including cell growth and cell cycle control, signal transduction, DNA repair, transcription, and many others. Hsp90 chaperone function is coupled to its ability to bind and hydrolyze ATP, which is tightly regulated both by co-chaperone proteins and post-translational modifications (PTMs). Many reported PTMs of Hsp90 alter chaperone function and consequently affect myriad cellular processes. Here, we review the contributions of PTMs, such as phosphorylation, acetylation, SUMOylation, methylation, O-GlcNAcylation, ubiquitination, and others, toward regulation of Hsp90 function. We also discuss how the Hsp90 modification state affects cellular sensitivity to Hsp90-targeted therapeutics that specifically bind and inhibit its chaperone activity. The ultimate challenge is to decipher the comprehensive and combinatorial array of PTMs that modulate Hsp90 chaperone function, a phenomenon termed the "chaperone code."

Aha-type co-chaperones: the alpha or the omega of the Hsp90 ATPase cycle?

Heat shock protein 90 (Hsp90) is a dimeric molecular chaperone that plays an essential role in cellular homeostasis. It functions in the context of a structurally dynamic ATP-dependent cycle to promote conformational changes in its clientele to aid stability, maturation, and activation. The client activation cycle is tightly regulated by a cohort of co-chaperone proteins that display specific binding preferences for certain conformations of Hsp90, guiding Hsp90 through its functional ATPase cycle. Aha-type co-chaperones are well-known to robustly stimulate the ATPase activity of Hsp90 but other roles in regulating the functional cycle are being revealed. In this review, we summarize the work done on the Aha-type co-chaperones since the 1990s and highlight recent discoveries with respect to the complexity of Hsp90 cycle regulation.

A methylated lysine is a switch point for conformational communication in the chaperone Hsp90

Methylation of a conserved lysine in C-terminal domain of the molecular chaperone Hsp90 was shown previously to affect its in vivo function. However, the underlying mechanism remained elusive. Through a combined experimental and computational approach, this study shows that this site is very sensitive to sidechain modifications and crucial for Hsp90 activity in vitro and in vivo. Our results demonstrate that this particular lysine serves as a switch point for the regulation of Hsp90 functions by influencing its conformational cycle, ATPase activity, co-chaperone regulation, and client activation of yeast and human Hsp90. Incorporation of the methylated lysine via genetic code expansion specifically shows that upon modification, the conformational cycle of Hsp90 is altered. Molecular dynamics simulations including the methylated lysine suggest specific conformational changes that are propagated through Hsp90. Thus, methylation of the C-terminal lysine allows a precise allosteric tuning of Hsp90 activity via long distances.

Methylation of a lysine residue in Hsp90 is a recently discovered post-translational modification but the mechanistic effects of this modification have remained unknown so far. Here the authors combine biochemical and biophysical approaches, molecular dynamics (MD) simulations and functional experiments with yeast and show that this lysine is a switch point, which specifically modulates conserved Hsp90 functions including co-chaperone regulation and client activation.

WEE1 kinase limits CDK activities to safeguard DNA replication and mitotic entry

Precise execution of the cell division cycle is vital for all organisms. The Cyclin dependent kinases (CDKs) are the main cell cycle drivers, however, their activities must be precisely fine-tuned to ensure orderly cell cycle progression. A major regulatory axis is guarded by WEE1 kinase, which directly phosphorylates and inhibits CDK1 and CDK2. The role of WEE1 in the G2/M cell-cycle phase has been thoroughly investigated, and it is a focal point of multiple clinical trials targeting a variety of cancers in combination with DNA-damaging chemotherapeutic agents. However, the emerging role of WEE1 in S phase has so far largely been neglected. Here, we review how WEE1 regulates cell-cycle progression highlighting the importance of this kinase for proper S phase. We discuss how its function is modulated throughout different cell-cycle stages and provide an overview of how WEE1 levels are regulated. Furthermore, we outline recent clinical trials targeting WEE1 and elaborate on the mechanisms behind the anticancer efficacy of WEE1 inhibition. Finally, we consider novel biomarkers that may benefit WEE1-inhibition approaches in the clinic.

A novel method for site-specific chemical SUMOylation: SUMOylation of Hsp90 modulates co-chaperone binding in vitro

SUMO is covalently attached to lysine side chains in target proteins by the action of a cascade of E1, E2, and E3 ligases. Unlike ubiquitin, SUMO does not target proteins for degradation but rather plays a regulatory role in activating target proteins or directing them to multiprotein complexes. Isolating SUMOylated proteins from native sources is challenging because of the low stoichiometry of SUMOylation that occurs for any given target protein in cells. Here we report a novel strategy to couple SUMO to the site of a target lysine for the purpose of in vitro study. Introduction of a single cysteine after the C terminal diglycine motif and a cysteine in place of a target lysine in a substrate protein allows for efficient and specific crosslinking of SUMO using a homo-bifunctional maleimide crosslinker. We demonstrate that SUMO can be crosslinked in this manner to amino acid position 178 in the dimeric molecular chaperone, Hsp90. Chemically SUMOylated Hsp90 has very similar ATPase activity compared to unmodified Hsp90 but displays preferential co-chaperone binding in vivo. Our novel strategy can easily be applied to other SUMOylated or ubiquitinated target protein in vitro.

CgSTE11 mediates cross tolerance to multiple environmental stressors in Candida glabrata

Candida glabrata is a human commensal and an opportunistic human fungal pathogen. It is more closely related to the model yeast Saccharomyces cerevisiae than other Candida spp. Compared with S. cerevisiae, C. glabrata exhibits higher innate tolerance to various environmental stressors, including hyperthermal stress. Here we investigate the molecular mechanisms of C. glabrata adaptation to heat stress via adaptive laboratory evolution. We show that all parallel evolved populations readily adapt to hyperthermal challenge (from 47 °C to 50 °C) and exhibit convergence in evolved phenotypes with extensive cross-tolerance to various other environmental stressors such as oxidants, acids, and alcohols. Genome resequencing identified fixation of mutations in CgSTE11 in all parallel evolved populations. The CgSTE11 homolog in S. cerevisiae plays crucial roles in various mitogen-activated protein kinase (MAPK) signaling pathways, but its role is less understood in C. glabrata. Subsequent verification confirmed that CgSTE11 is important in hyperthermal tolerance and the observed extensive cross-tolerance to other environmental stressors. These results support the hypothesis that CgSTE11 mediates cross-talks between MAPK signaling pathways in C. glabrata in response to environmental challenges.

Mutation of the co-chaperone Tsc1 in bladder cancer diminishes Hsp90 acetylation and reduces drug sensitivity and selectivity

The molecular chaperone Heat shock protein 90 (Hsp90) is essential for the folding, stability, and activity of several drivers of oncogenesis. Hsp90 inhibitors are currently under clinical evaluation for cancer treatment, however their efficacy is limited by lack of biomarkers to optimize patient selection. We have recently identified the tumor suppressor tuberous sclerosis complex 1 (Tsc1) as a new co-chaperone of Hsp90 that affects Hsp90 binding to its inhibitors. Highly variable mutations of TSC1 have been previously identified in bladder cancer and correlate with sensitivity to the Hsp90 inhibitors. Here we showed loss of TSC1 leads to hypoacetylation of Hsp90-K407/K419 and subsequent decreased binding to the Hsp90 inhibitor ganetespib. Pharmacologic inhibition of histone deacetylases (HDACs) restores acetylation of Hsp90 and sensitizes Tsc1-mutant bladder cancer cells to ganetespib, resulting in apoptosis. Our findings suggest that TSC1 status may predict response to Hsp90 inhibitors in patients with bladder cancer, and co-targeting HDACs can sensitize tumors with Tsc1 mutations to Hsp90 inhibitors.

Triggering mitosis

Entry into mitosis is triggered by the activation of cyclin-dependent kinase 1 (Cdk1). This simple reaction rapidly and irreversibly sets the cell up for division. Even though the core step in triggering mitosis is so simple, the regulation of this cellular switch is highly complex, involving a large number of interconnected signalling cascades. We do have a detailed knowledge of most of the components of this network, but only a poor understanding of how they work together to create a precise and robust system that ensures that mitosis is triggered at the right time and in an orderly fashion. In this review, we will give an overview of the literature that describes the Cdk1 activation network and then address questions relating to the systems biology of this switch. How is the timing of the trigger controlled? How is mitosis insulated from interphase? What determines the sequence of events, following the initial trigger of Cdk1 activation? Which elements ensure robustness in the timing and execution of the switch? How has this system been adapted to the high levels of replication stress in cancer cells?

The Multiple Roles and Therapeutic Potential of Molecular Chaperones in Prostate Cancer

Prostate cancer (PCa) is one of the most common cancer types in men worldwide. Heat shock proteins (HSPs) are molecular chaperones that are widely implicated in the pathogenesis, diagnosis, prognosis, and treatment of many cancers. The role of HSPs in PCa is complex and their expression has been linked to the progression and aggressiveness of the tumor. Prominent chaperones, including HSP90 and HSP70, are involved in the folding and trafficking of critical cancer-related proteins. Other members of HSPs, including HSP27 and HSP60, have been considered as promising biomarkers, similar to prostate-specific membrane antigen (PSMA), for PCa screening in order to evaluate and monitor the progression or recurrence of the disease. Moreover, expression level of chaperones like clusterin has been shown to correlate directly with the prostate tumor grade. Hence, targeting HSPs in PCa has been suggested as a promising strategy for cancer therapy. In the current review, we discuss the functions as well as the role of HSPs in PCa progression and further evaluate the approach of inhibiting HSPs as a cancer treatment strategy.

A novel pan-cancer biomarker plasma heat shock protein 90alpha and its diagnosis determinants in clinic

A sensitive and specific diagnosis biomarker, in principle scalable to most cancer types, is needed to reduce the prevalent cancer mortality. Meanwhile, the investigation of diagnosis determinants of a biomarker will facilitate the interpretation of its screening results in clinic. Here we design a large-scale (1558 enrollments), multicenter (multiple hospitals), and cross-validation (two datasets) clinic study to validate plasma Hsp90α quantified by ELISA as a pan-cancer biomarker. ROC curve shows the optimum diagnostic cutoff is 69.19 ng/mL in discriminating various cancer patients from all controls (AUC 0.895, sensitivity 81.33% and specificity 81.65% in test cohort; AUC 0.893, sensitivity 81.72% and specificity 81.03% in validation cohort). Similar results are noted in detecting early-stage cancer patients. Plasma Hsp90α maintains also broad-spectrum for cancer subtypes, especially with 91.78% sensitivity and 91.96% specificity in patients with AFP-limited liver cancer. In addition, we demonstrate levels of plasma Hsp90α are determined by ADAM10 expression, which will affect Hsp90α content in exosomes. Furthermore, Western blotting and PRM-based quantitative proteomics identify that partial false ELISA-negative patients secret high levels of plasma Hsp90α. Mechanism analysis reveal that TGFβ-PKCγ gene signature defines a distinct pool of hyperphosphorylated Hsp90α at Theronine residue. In clinic, a mechanistically relevant population of false ELISA-negative patients express also higher levels of PKCγ. In sum, plasma Hsp90α is a novel pan-cancer diagnosis biomarker, and cancer diagnosis with plasma Hsp90α is particularly effective in those patients with high expression of ADAM10, but may be insufficient to detect the patients with low ADAM10 and those with hyperphosphorylated Hsp90α.

Ligand-independent activation of the P2X7 receptor by Hsp90 inhibition stimulates motor neuron apoptosis

Activation of the extracellular ATP ionotropic receptor P2X7 stimulates motor neuron apoptosis, whereas its inhibition in cell and animal models of amyotrophic lateral sclerosis can be protective. These observations suggest that P2X7 receptor activation is relevant to motor neuron disease and that it could be targeted for therapeutic development. Heat shock protein 90 (Hsp90) is an integral regulatory component of the P2X7 receptor complex, antagonizing ligand-induced receptor activation. Here, we show that the repressive activity of Hsp90 on P2X7 receptor activation in primary motor neurons is highly sensitive to inhibition. Primary motor neurons in culture are 100-fold more sensitive to Hsp90 inhibition by geldanamycin than other neuronal populations. Pharmacological inhibition and down-regulation of the P2X7 receptor prevented motor neuron apoptosis triggered by Hsp90 inhibition, which occurred in the absence of extracellular ATP. These observations suggest that inhibition of a seemingly motor neuron specific pool of Hsp90 leads to ligand independent activation of P2X7 receptor and motor neuron death. Downstream of Hsp90 inhibition, P2X7 receptor activated the phosphatase and tensin homolog (TPEN), which in turn suppressed the pro-survival phosphatidyl inositol 3 kinase (PI3K)/Akt pathway, leading to Fas-dependent motor neuron apoptosis. Conditions altering the interaction between P2X7 receptor and Hsp90, such as recruitment of Hsp90 to other subcellular compartments under stress conditions, or nitration following oxidative stress can induce motor neuron death. These findings may have broad implications in neurodegenerative disorders, including amyotrophic lateral sclerosis, in which activation of P2X7 receptor may be involved in both autonomous and non-autonomous motor neurons death.