Mice lacking HSP90beta fail to develop a placental labyrinth

The Hsp90β Isoform: An Attractive Target for Drug Development

The beta isoform of 90 kDa heat shock protein (Hsp90β) plays a critical role in maintaining cellular proteostasis by assisting in the folding and refolding of proteins, which is essential for both normal cellular function and stress response. It is constitutively expressed in mammalian cells, differentiating it from the inducible Hsp90α isoform. Hsp90β's involvement in diverse cellular processes, such as signal transduction, cell cycle control, and apoptosis, underscores its significant role in various diseases, including cancer and neurodegenerative disorders. The isoform-specific functions of Hsp90β and its interaction with unique client proteins make it a promising target for therapeutic intervention, particularly in the development of selective inhibitors that avoid the adverse effects observed with pan-Hsp90 inhibitors. This review delves into the structural and functional intricacies of Hsp90β, its role in disease, and the potential for selective drug development.

The Zika virus NS5 protein binds HSP90 to suppress EGF-induced Akt signaling and trophoblast cell migration

Zika virus (ZIKV) infection during pregnancy can cause congenital Zika virus syndrome (CZV), including fetal growth restriction and death. In the developing placenta, trophoblast cells respond to epidermal growth factor (EGF) to migrate into the decidua to facilitate implantation and fetal development. EGF activates the Akt protein kinase, a master regulator of trophoblast cell migration. Akt signaling and stability are dependent on heat shock protein 90 (HSP90), which mediates the maturation of proteins necessary for EGF/Akt signaling. Here we show that ZIKV infection inhibits EGF-mediated Akt activation and downstream signaling to suppress trophoblast migration. The ZIKV non-structural protein 5 (NS5) is sufficient to inhibit trophoblast migration through its binding interaction with HSP90, leading to suppression of Akt phosphorylation and inhibition of EGF-induced trophoblast migration. Thus, ZIKV NS5/HSP90 interactions play a key role in disruption of trophoblast function, revealing an underlying cause of improper placental development and fetal disease.

Off to a good start: The importance of the placental exchange surface - Lessons from the mouse

The role of the chorio-allantoic placenta as the critical nutrient- and oxygen-supplying organ to nourish the demands of the fetus has been well recognized. This function relies on the successful establishment of the placental feto-maternal exchange unit, or interhaemal barrier, across which all nutrients as well as waste products must pass to cross from the maternal to the fetal blood circulation, or vice versa, respectively. As a consequence, defects in the establishment of this elaborate interface lead to fetal growth retardation or even embryonic lethality, depending on the severity of the defect. Beyond this essential role, however, it has also emerged that the functionality of the feto-maternal interface dictates the proper development of specific embryonic organs, with tightest links observed to the formation of the heart. In this article, we build on the foundational strength of the mouse as experimental model in which the placental causality of embryonic defects can be genetically proven. We discuss in detail the formation of the interhaemal barrier that makes up the labyrinth layer of the murine placenta, including insights into drivers of its formation and the interdependence of the cell types that make up this essential interface, from in vivo and in vitro data using mouse trophoblast stem cells. We highlight mouse genetic tools that enable the elucidation of cause-effect relationships between defects driven by either the trophoblast cells of the placenta or by embryonic cell types. We specifically emphasize gene knockouts for which a placental causality of embryonic heart defects has been demonstrated. This in-depth perspective provides much-needed insights while highlighting remaining gaps in knowledge that are essential for gaining a better understanding of the multi-facetted roles of the placenta in setting us up for a healthy start in life well beyond nutritional support alone.

Characterization and expression analysis of heat shock proteins HfHspc1 and HfHspc4 in Haemaphysalis flava ticks

In this study, the cDNAs of heat shock cognate 90 protein 1 (HfHspc1) and heat shock cognate 90 protein 4 (HfHspc4) from Haemaphysalis flava (Acari: Ixodidae) were obtained using the rapid amplification of cDNA ends (RACE) approach, and the expression patterns of HfHspc1 and HfHspc4 in different developmental stages, engorgement stages and tick organs were analyzed by qPCR. The full length of HfHspc1 was 2411 bp, and its open reading frame (ORF) was 2196 bp, encoding a protein of 732 aa, containing five HSPC family signatures, with MEEVD motif at its extreme C-terminal. The full length of HfHspc4 was 2800 bp, and its ORF was 2364 bp, encoding a protein of 789 aa, containing a signal peptide and five family signatures, with HEEL motif at its extreme C-terminal. The expression of HfHspc1 and HfHspc4 was the highest in males, while it was significantly the highest in the ovaries of fully engorged females, potentially implying the roles of these proteins in the successful digestion of blood and development of eggs.

N6-methyladenosine dynamics in placental development and trophoblast functions, and its potential role in placental diseases

N6-methyladenosine (m6A) is the most abundant modification controlling RNA metabolism and cellular functions, but its roles in placental development are still poorly understood. Here, we characterized the synchronization of m6A modifications and placental functions by mapping the m6A methylome in human placentas (n = 3, each trimester), revealing that the dynamic patterns of m6A were associated with gene expression homeostasis and different biological pathways in placental development. Then, we generated trophoblast-specific knockout mice of Wtap, a critical component of methyltransferase complex, and demonstrated that Wtap was essential for trophoblast proliferation, placentation and perinatal growth. Further in vitro experiments which includes cell viability assays and series molecular binding assays demonstrated that WTAP-m6A-IGF2BP3 axis regulated the RNA stability and translation of Anillin (ANLN) and VEGFA, promoting trophoblast proliferation and secretion. Dysregulation of this regulatory axis was observed in placentas from pregnancies with fetal growth restriction (FGR) or preeclampsia, revealing the pathogenic effects of imbalanced m6A modifications. Therefore, our findings provide novel insights into the functions and regulatory mechanisms of m6A modifications in placental development and placental-related gestational diseases.

Previously unrecognized and potentially consequential challenges facing Hsp90 inhibitors in cancer clinical trials

Targeting the heat shock protein-90 (Hsp90) chaperone machinery in various cancers with 200 monotherapy or combined-therapy clinical trials since 1999 has not yielded any success of food and drug administration approval. Blames for the failures were unanimously directed at the Hsp90 inhibitors or tumors or both. However, analyses of recent cellular and genetic studies together with the Hsp90 data from the Human Protein Atlas database suggest that the vast variations in Hsp90 expression among different organs in patients might have been the actual cause. It is evident now that Hsp90β is the root of dose-limiting toxicity (DLT), whereas Hsp90α is a buffer of penetrated Hsp90 inhibitors. The more Hsp90α, the safer Hsp90β, and the lower DLT are for the host. Unfortunately, the dramatic variations of Hsp90, from total absence in the eye, muscle, pancreas, and heart to abundance in reproduction organs, lung, liver, and gastrointestinal track, would cause the selection of any fair toxicity biomarker and an effective maximum tolerable dose (MTD) of Hsp90 inhibitor extremely challenging. In theory, a safe MTD for the organs with high Hsp90 could harm the organs with low Hsp90. In reverse, a safe MTD for organs with low or undetectable Hsp90 would have little impact on the tumors, whose cells exhibit average 3-7% Hsp90 over the average 2-3% Hsp90 in normal cells. Moreover, not all tumor cell lines tested follow the "inhibitor binding-client protein degradation" paradigm. It is likely why the oral Hsp90 inhibitor TAS-116 (Pimitespib), which bypasses blood circulation and other organs, showed some beneficiary efficacy by conveniently hitting tumors along the gastrointestinal track. The critical question is what the next step will be for the Hsp90 chaperone as a cancer therapeutic target.

Discovery of Cell Number-Interstitial Fluid Volume (CIF) Ratio Reveals Secretory Autophagy Pathway to Supply eHsp90α for Wound Healing

Cell secretion repairs tissue damage and restores homeostasis throughout adult life. The extracellular heat shock protein-90alpha (eHsp90α) has been reported as an exosome cargo and a potential driver of wound healing. However, neither the mechanism of secretion nor the genetic evidence for eHsp90α in wound healing has been substantiated. Herein, we show that tissue injury causes massive deposition of eHsp90α in tissues and secretion of eHsp90α by cells. Sequential centrifugations of conditioned medium from relevant cell lines revealed the relative distributions of eHsp90α in microvesicle, exosome and trypsin-sensitive supernatant fractions to be approximately <2%, <4% and >95%, respectively. Establishing the cell-number-to-interstitial-fluid-volume (CIF) ratio for the microenvironment of human tissues as 1 × 109 cells: 1 mL interstitial fluid enabled us to predict the corresponding tissue concentrations of eHsp90α in these fractions as 3.74 μg/mL, 5.61 μg/mL and 178 μg/mL. Remarkably, the 178 μg/mL eHsp90α matches the previously reported 100-300 μg/mL of recombinant eHsp90α whose topical application promotes maximum wound healing in animal models. More importantly, we demonstrate that two parallel secretory autophagy-regulating gene families, the autophagy-regulating (AR) genes and the Golgi reassembly-stacking protein (GRASP) genes work together to mediate the secretion of the physiological concentration of eHsp90α to promote wound healing. Thus, utilization of the CIF ratio-based extrapolation method may enable investigators to rapidly predict biomarker targets from cell-conditioned-medium data.

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.

HSP70-mediated mitochondrial dynamics and autophagy represent a novel vulnerability in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC), the most prevalent type of pancreatic cancer, is one of the deadliest forms of cancer with limited therapy options. Overexpression of the heat shock protein 70 (HSP70) is a hallmark of cancer that is strongly associated with aggressive disease and worse clinical outcomes. However, the underlying mechanisms by which HSP70 allows tumor cells to thrive under conditions of continuous stress have not been fully described. Here, we report that PDAC has the highest expression of HSP70 relative to normal tissue across all cancers analyzed. Furthermore, HSP70 expression is associated with tumor grade and is further enhanced in metastatic PDAC. We show that genetic or therapeutic ablation of HSP70 alters mitochondrial subcellular localization, impairs mitochondrial dynamics, and promotes mitochondrial swelling to induce apoptosis. Mechanistically, we find that targeting HSP70 suppresses the PTEN-induced kinase 1 (PINK1) mediated phosphorylation of dynamin-related protein 1 (DRP1). Treatment with the HSP70 inhibitor AP-4-139B was efficacious as a single agent in primary and metastatic mouse models of PDAC. In addition, we demonstrate that HSP70 inhibition promotes the AMP-activated protein kinase (AMPK) mediated phosphorylation of Beclin-1, a key regulator of autophagic flux. Accordingly, we find that the autophagy inhibitor hydroxychloroquine (HCQ) enhances the ability of AP-4-139B to mediate anti-tumor activity in vivo. Collectively, our results suggest that HSP70 is a multi-functional driver of tumorigenesis that orchestrates mitochondrial dynamics and autophagy. Moreover, these findings support the rationale for concurrent inhibition of HSP70 and autophagy as a novel therapeutic approach for HSP70-driven PDAC.

Co-targeting HSP90 alpha and CDK7 overcomes resistance against HSP90 inhibitors in BCR-ABL1+ leukemia cells

HSP90 has emerged as an appealing anti-cancer target. However, HSP90 inhibitors (HSP90i) are characterized by limited clinical utility, primarily due to the resistance acquisition via heat shock response (HSR) induction. Understanding the roles of abundantly expressed cytosolic HSP90 isoforms (α and β) in sustaining malignant cells' growth and the mechanisms of resistance to HSP90i is crucial for exploiting their clinical potential. Utilizing multi-omics approaches, we identified that ablation of the HSP90β isoform induces the overexpression of HSP90α and extracellular-secreted HSP90α (eHSP90α). Notably, we found that the absence of HSP90α causes downregulation of PTPRC (or CD45) expression and restricts in vivo growth of BCR-ABL1+ leukemia cells. Subsequently, chronic long-term exposure to the clinically advanced HSP90i PU-H71 (Zelavespib) led to copy number gain and mutation (p.S164F) of the HSP90AA1 gene, and HSP90α overexpression. In contrast, acquired resistance toward other tested HSP90i (Tanespimycin and Coumermycin A1) was attained by MDR1 efflux pump overexpression. Remarkably, combined CDK7 and HSP90 inhibition display synergistic activity against therapy-resistant BCR-ABL1+ patient leukemia cells via blocking pro-survival HSR and HSP90α overexpression, providing a novel strategy to avoid the emergence of resistance against treatment with HSP90i alone.

Timing and duration of nutrient restriction and its impacts on placental development and umbilical blood flow in adolescent sheep

We hypothesized that nutrient restriction from day 50-90 of gestation decreases umbilical blood flow and that umbilical blood flow would recover to control values upon realimentation during late gestation (d 90 to 130) or remain reduced in ewes that continued to be nutrient restricted. On d 50 of gestation, young nulliparous whiteface ewes (6-8 mo; n = 41) carrying singletons were randomly assigned to two dietary treatments: 100% of NRC recommendations (CON) or 60% of CON (RES). On d 90 of gestation, ewes either remained on CON or RES until d 130, or CON ewes were RES from d 90 to 130, or RES ewes were realimented to CON from d 90 to 130. This resulted in 4 treatment groups on day 130: CON-CON, CON-RES, RES-RES, RES-CON. Umbilical blood flow and fetal and placental measurements were obtained via ultrasonography every 10 days from day 50-110. Non-survival surgeries were performed on days 50, 90, and 130 (n = 6-7 ewes/group) where uterine artery and umbilical blood flows were measured during surgery via ultrasonography. Conceptus weights were recorded and placentomes collected to determine binucleate cell numbers. The study was conducted as a completely randomized design arrangement with repeated measures. Data were analyzed using the MIXED procedure of SAS. There was a nutritional treatment by day interaction (P < 0.01) with CON ewes having greater umbilical blood flow compared with RES by d 90. Fetal biparietal distance, abdominal width, and kidney area increased (P < 0.05) in CON-RES with all these measurements increasing during late gestation. We partially accept our hypothesis as nutrient restriction during mid gestation decreased umbilical blood flow. However, blood flow did not return to control levels upon realimentation. By d 130, fetal and placental weights were similar between RES-RES and CON-CON. Binucleate cell numbers in the fetal trophoblast were not influenced by nutritional treatments. Our findings suggest that refeeding previously nutrient restricted pregnant adolescent ewes to control levels does not reestablish umbilical blood flow. Adequate placental development during mid gestation could protect the fetus from a decreased umbilical blood flow later in gestation when nutrients were limited by 40%.

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.

PRM-based quantitative proteomics analysis of altered HSP abundance in villi and decidua of patients with early missed abortion

OBJECTIVE

In this study, we aimed to identify differentially expressed heat shock protein (HSP) profiles in the villi and decidua from patients with early missed abortion (EMA).

METHODS

By using high-throughput and high-precision parallel reaction monitoring (PRM)-based targeted proteomics techniques, this study examined the abundance of HSPs in the villi and decidua of 10 patients with EMA and 10 controls. Moreover, the abundance of 3 HSPs in the villi of another 22 patients with EMA and 22 controls was verified with Western blotting and immunohistochemistry (IHC).

RESULTS

There were potential differences in the abundance of 16 HSPs and 42 polypeptides in human villi and decidua compared with those of the control group. Among them, HSP90AB1, HSPD1 and HSPA13 were downregulated in abundance in villi of patients with EMA, with a statistically significant difference, which was consistent with the verification results of Western blots and IHC.

CONCLUSION

Using a PRM-based targeted proteomics technique, this study is the first to screen and quantitatively analyze the expression profile of HSPs in the villi and decidua of patients with EMA. The significant downregulation of HSP90AB1, HSPD1 and HSPA13 was found to have a potentially intimate association with the occurrence of EMA. The findings in our study may provide novel potential research targets related to HSPs for the pathogenesis, prevention and treatment of EMA.

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.

HSP90β promotes osteoclastogenesis by dual-activation of cholesterol synthesis and NF-κB signaling

Heat shock protein 90β (Hsp90β, encoded by Hsp90ab1 gene) is the most abundant proteins in the cells and contributes to variety of biological processes including metabolism, cell growth and neural functions. However, genetic evidences showing Hsp90β in vivo functions using tissue specific knockout mice are still lacking. Here, we showed that Hsp90β exerted paralogue-specific role in osteoclastogenesis. Using myeloid-specific Hsp90ab1 knockout mice, we provided the first genetic evidence showing the in vivo function of Hsp90β. Hsp90β binds to Ikkβ and reduces its ubiquitylation and proteasomal degradation, thus leading to activated NF-κB signaling. Meanwhile, Hsp90β increases cholesterol biosynthesis by activating Srebp2. Both pathways promote osteoclastogenic genes expression. Genetic deletion of Hsp90ab1 in osteoclast or pharmacological inhibition of Hsp90β alleviates bone loss in ovariectomy-induced mice. Therefore, Hsp90β is a promising druggable target for the treatment of osteoporosis.

Extracellular HSP90 promotes differentiation of lens epithelial cells to fiber cells by activating LRP1-YAP-PROX1 axis

Capsular residual lens epithelial cells (CRLEC) undergo differentiation to fiber cells for lens regeneration or tansdifferentiation to myofibroblasts leading to posterior capsular opacification (PCO) after cataract surgery. The underlying regulatory mechanism remains unclear. Using human lens epithelial cell lines and the ex vivo cultured rat lens capsular bag model, we found that the lens epithelial cells secrete HSP90α extracellularly (eHSP90) through an autophagy-associated pathway. Administration of recombinant GST-HSP90α protein or its M-domain induces the elongation of rat CRLEC cells with concomitant upregulation of the crucial fiber cell transcriptional factor PROX1and its downstream targets, β- and γ-crystallins and structure proteins. This regulation is abolished by PROX1 siRNA. GST-HSP90α upregulates PROX1 by binding to LRP1 and activating LRP1-AKT mediated YAP degradation. The upregulation of GST-HSP90α on PROX1 expression and CRLEC cell elongation is inhibited by LRP1 and AKT inhibitors, but activated by YAP-1 inhibitor (VP). These data demonstrated that the capsular residue epithelial cells upregulate and secrete eHSP90α, which in turn drive the differentiation of lens epithelial cell to fiber cells. The recombinant HSP90α protein is a potential novel differentiation regulator during lens regeneration.

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.

The Distinct Assignments for Hsp90α and Hsp90β: More Than Skin Deep

For decades, the undisputable definition of the cytosolic Hsp90α and hsp90β proteins being evolutionarily conserved, ATP-driven chaperones has ruled basic research and clinical trials. The results of recent studies, however, have fundamentally challenged this paradigm, not to mention the spectacular failures of the paradigm-based clinical trials in cancer and beyond. We now know that Hsp90α and Hsp90β are both ubiquitously expressed in all cell types but assigned for distinct and irreplaceable functions. Hsp90β is essential during mouse development and Hsp90α only maintains male reproductivity in adult mice. Neither Hsp90β nor Hsp90α could substitute each other under these biological processes. Hsp90β alone maintains cell survival in culture and Hsp90α cannot substitute it. Hsp90α also has extracellular functions under stress and Hsp90β does not. The dramatic difference in the steady-state expression of Hsp90 in different mouse organs is due to the variable expressions of Hsp90α. The lowest expression of Hsp90 is less than 2% and the highest expression of Hsp90 is 9% among non-transformed cell lines. The two linker regions only take up less than 5% of the Hsp90 proteins, but harbor 21% of the total amino acid substitutions, i.e., 40% in comparison to the 86% overall amino acid homology. A full understanding of the distinctions between Hsp90α and Hsp90β could lead to new, safe and effective therapeutics targeting Hsp90 in human disorders such as cancer. This is the first comprehensive review of a comparison between the two cytosolic Hsp90 isoforms.

Structure, Function, and Inhibitors of the Mitochondrial Chaperone TRAP1

Tumor necrosis factor receptor-associated protein 1 (TRAP1) is a mitochondrial molecular chaperone modulating cellular metabolism and signaling pathways by altering the conformation, activity, and stability of numerous substrate proteins called clients. It exerts its chaperone function as an adaptive response to counter cellular stresses instead of maintaining housekeeping protein homeostasis. However, the stress-adaptive machinery becomes dysregulated to support the progression and maintenance of human diseases, such as cancers; therefore, TRAP1 has been proposed as a promising target protein for anticancer drug development. In this review, by collating recent reports on high-resolution TRAP1 structures and structure-activity relationships of inhibitors, we aimed to provide better insights into the chaperoning mechanism of the emerging drug target and to suggest an efficient strategy for the development of potent TRAP1 inhibitors.

The ribosomal chaperone NACA recruits PHD2 to cotranslationally modify HIF-α

Prolyl hydroxylase domain protein 2 (PHD2)-catalyzed modification of hypoxia-inducible factor (HIF)-α is a key event in oxygen sensing. We previously showed that the zinc finger of PHD2 binds to a Pro-Xaa-Leu-Glu (PXLE) motif. Here, we show that the zinc finger binds to this motif in the ribosomal chaperone nascent polypeptide complex-α (NACA). This recruits PHD2 to the translation machinery to cotranslationally modify HIF-α. Importantly, this cotranslational modification is enhanced by a translational pause sequence in HIF-α. Mice with a knock-in Naca gene mutation that abolishes the PXLE motif display erythrocytosis, a reflection of HIF pathway dysregulation. In addition, human erythrocytosis-associated mutations in the zinc finger of PHD2 ablate interaction with NACA. Tibetans, who have adapted to the hypoxia of high altitude, harbor a PHD2 variant that we previously showed displays a defect in zinc finger binding to p23, a PXLE-containing HSP90 cochaperone. We show here that Tibetan PHD2 maintains interaction with NACA, thereby showing differential interactions with PXLE-containing proteins and providing an explanation for why Tibetans are not predisposed to erythrocytosis.

Translational reprogramming in response to accumulating stressors ensures critical threshold levels of Hsp90 for mammalian life

The cytosolic molecular chaperone Hsp90 is essential for eukaryotic life. Although reduced Hsp90 levels correlate with aging, it was unknown whether eukaryotic cells and organisms can tune the basal Hsp90 levels to alleviate physiologically accumulated stress. We have investigated whether and how mice adapt to the deletion of three out of four alleles of the two genes encoding cytosolic Hsp90, with one Hsp90β allele being the only remaining one. While the vast majority of such mouse embryos die during gestation, survivors apparently manage to increase their Hsp90β protein to at least wild-type levels. Our studies reveal an internal ribosome entry site in the 5' untranslated region of the Hsp90β mRNA allowing translational reprogramming to compensate for the genetic loss of Hsp90 alleles and in response to stress. We find that the minimum amount of total Hsp90 required to support viability of mammalian cells and organisms is 50-70% of what is normally there. Those that fail to maintain a threshold level are subject to accelerated senescence, proteostatic collapse, and ultimately death. Therefore, considering that Hsp90 levels can be reduced ≥100-fold in the unicellular budding yeast, critical threshold levels of Hsp90 have markedly increased during eukaryotic evolution.

Hsp90β inhibition upregulates interferon response and enhances immune checkpoint blockade therapy in murine tumors

Response resistance to the immune checkpoint blockade (ICB) immunotherapy remains a major clinical challenge that may be overcome through the rational combination of ICB and specific targeted therapeutics. One emerging combination strategy is based on sensitizing ICB-refractory tumors with antagonists of 90kD heat shock protein (Hsp90) that target all four isoforms. However, pan-Hsp90 inhibitors are limited by the modest efficacy, on-target and off-tumor toxicities, and induction of the heat shock response (HSR) that overrides the effect of Hsp90 inhibition. Recently, we developed Hsp90β-selective inhibitors that were cytotoxic to cancer cells but did not induce HSR in vitro. Here, we report that the Hsp90β inhibitor NDNB1182 downregulated CDK4 (an Hsp90β-dependent client protein) and induced the expression of endogenous retroviral elements and interferon-stimulated genes. In syngeneic mouse models of prostate cancer and breast cancer, NDNB1182 significantly augmented the efficacy of ICB therapy. Furthermore, NDNB1182 showed superior tolerability to the pan-Hsp90 inhibitor Ganetespib in mice. Our findings provide evidence that Hsp90β inhibition is a potentially effective and safe regimen to combine with ICB to treat immunotherapy-refractory solid tumors.

Origination of LTR Retroelement-Derived NYNRIN Coincides with Therian Placental Emergence

The emergence of the placenta is a revolutionary event in the evolution of therian mammals, to which some LTR retroelement-derived genes, such as PEG10, RTL1, and syncytin, are known to contribute. However, therian genomes contain many more LTR retroelement-derived genes that may also have contributed to placental evolution. We conducted large-scale evolutionary genomic and transcriptomic analyses to comprehensively search for LTR retroelement-derived genes whose origination coincided with therian placental emergence and that became consistently expressed in therian placentae. We identified NYNRIN as another Ty3/Gypsy LTR retroelement-derived gene likely to contribute to placental emergence in the therian stem lineage. NYNRIN knockdown inhibited the invasion of HTR8/SVneo invasive-type trophoblasts, whereas the knockdown of its nonretroelement-derived homolog KHNYN did not. Functional enrichment analyses suggested that NYNRIN modulates trophoblast invasion by regulating epithelial-mesenchymal transition and extracellular matrix remodeling and that the ubiquitin-proteasome system is responsible for the functional differences between NYNRIN and KHNYN. These findings extend our knowledge of the roles of LTR retroelement-derived genes in the evolution of therian mammals.

Cytosolic Hsp90 Isoform-Specific Functions and Clinical Significance

The heat shock protein 90 (Hsp90) is a molecular chaperone and a key regulator of proteostasis under both physiological and stress conditions. In mammals, there are two cytosolic Hsp90 isoforms: Hsp90α and Hsp90β. These two isoforms are 85% identical and encoded by two different genes. Hsp90β is constitutively expressed and essential for early mouse development, while Hsp90α is stress-inducible and not necessary for survivability. These two isoforms are known to have largely overlapping functions and to interact with a large fraction of the proteome. To what extent there are isoform-specific functions at the protein level has only relatively recently begun to emerge. There are studies indicating that one isoform is more involved in the functionality of a specific tissue or cell type. Moreover, in many diseases, functionally altered cells appear to be more dependent on one particular isoform. This leaves space for designing therapeutic strategies in an isoform-specific way, which may overcome the unfavorable outcome of pan-Hsp90 inhibition encountered in previous clinical trials. For this to succeed, isoform-specific functions must be understood in more detail. In this review, we summarize the available information on isoform-specific functions of mammalian Hsp90 and connect it to possible clinical applications.

Hsp90 and Associated Co-Chaperones of the Malaria Parasite

Heat shock protein 90 (Hsp90) is one of the major guardians of cellular protein homeostasis, through its specialized molecular chaperone properties. While Hsp90 has been extensively studied in many prokaryotic and higher eukaryotic model organisms, its structural, functional, and biological properties in parasitic protozoans are less well defined. Hsp90 collaborates with a wide range of co-chaperones that fine-tune its protein folding pathway. Co-chaperones play many roles in the regulation of Hsp90, including selective targeting of client proteins, and the modulation of its ATPase activity, conformational changes, and post-translational modifications. Plasmodium falciparum is responsible for the most lethal form of human malaria. The survival of the malaria parasite inside the host and the vector depends on the action of molecular chaperones. The major cytosolic P. falciparum Hsp90 (PfHsp90) is known to play an essential role in the development of the parasite, particularly during the intra-erythrocytic stage in the human host. Although PfHsp90 shares significant sequence and structural similarity with human Hsp90, it has several major structural and functional differences. Furthermore, its co-chaperone network appears to be substantially different to that of the human host, with the potential absence of a key homolog. Indeed, PfHsp90 and its interface with co-chaperones represent potential drug targets for antimalarial drug discovery. In this review, we critically summarize the current understanding of the properties of Hsp90, and the associated co-chaperones of the malaria parasite.

Gene expression and functional analysis of Aha1a and Aha1b in stress response in zebrafish

Activator of heat shock protein 90 (hsp90) ATPase (Aha1) is a Hsp90 co-chaperone required for Hsp90 ATPase activation. Aha1 is essential for yeast survival and muscle development in C. elegans under elevated temperature and hsp90-deficeiency induced stress conditions. The roles of Aha1 in vertebrates are poorly understood. Here, we characterized the expression and function of Aha1 in zebrafish. We showed that zebrafish genome contains two aha1 genes, aha1a and aha1b, that show distinct patterns of expression during development. Under the normal physiological conditions, aha1a is primarily expressed in skeletal muscle cells of zebrafish embryos, while aha1b is strongly expressed in the head region. aha1a and aha1b expression increased dramatically in response to heat shock induced stress. In addition, Aha1a-GFP fusion protein exhibited a dynamic translocation in muscle cells in response to heat shock. Moreover, upregulation of aha1 expression was also observed in hsp90a1 knockdown embryos that showed a muscle defect. Genetic studies demonstrated that knockout of aha1a, aha1b or both had no detectable effect on embryonic development, survival, and growth in zebrafish. The aha1a and aha1b mutant embryos showed normal muscle development and stress response in response to heat shock. Single or double aha1a and aha1b mutants could grow into normal reproductive adults with normal skeletal muscle structure and morphology compared with wild type control. Together, data from these studies indicate that Aha1a and Aha1b are involved in stress response. However, they are dispensable in zebrafish embryonic development, growth, and survival.

Extracellular Heat Shock Protein-90 (eHsp90): Everything You Need to Know

“Extracellular” Heat Shock Protein-90 (Hsp90) was initially reported in the 1970s but was not formally recognized until 2008 at the 4th International Conference on The Hsp90 Chaperone Machine (Monastery Seeon, Germany). Studies presented under the topic of “extracellular Hsp90 (eHsp90)” at the conference provided direct evidence for eHsp90’s involvement in cancer invasion and skin wound healing. Over the past 15 years, studies have focused on the secretion, action, biological function, therapeutic targeting, preclinical evaluations, and clinical utility of eHsp90 using wound healing, tissue fibrosis, and tumour models both in vitro and in vivo. eHsp90 has emerged as a critical stress-responding molecule targeting each of the pathophysiological conditions. Despite the studies, our current understanding of several fundamental questions remains little beyond speculation. Does eHsp90 indeed originate from purposeful live cell secretion or rather from accidental dead cell leakage? Why did evolution create an intracellular chaperone that also functions as a secreted factor with reported extracellular duties that might be (easily) fulfilled by conventional secreted molecules? Is eHsp90 a safer and more optimal drug target than intracellular Hsp90 chaperone? In this review, we summarize how much we have learned about eHsp90, provide our conceptual views of the findings, and make recommendations on the future studies of eHsp90 for clinical relevance.

Hyperthermia increases HSP production in human PDMCs by stimulating ROS formation, p38 MAPK and Akt signaling, and increasing HSF1 activity

Background

Human placenta-derived multipotent cells (hPDMCs) are isolated from a source uncomplicated by ethical issues and are ideal for therapeutic applications because of their capacity for multilineage differentiation and proven immunosuppressive properties. It is known that heat shock preconditioning induces the upregulation of heat shock proteins (HSPs), which enhance survival and engraftment of embryonic stem cells (ESCs) during transplantation in live animal models, although whether heat shock preconditioning has the same effects in hPDMCs is unclear.

Methods

The hPDMCs were isolated from placenta of healthy donors. The cells were treated with heat shock (43 °C, 15 min), followed by evaluation of cell viability. Furthermore, the HSPs expression was assessed by Western blot, qPCR. The reactive oxygen species (ROS) production and signal pathway activation were determined by flow cytometry and Western blot, respectively. The regulatory pathways involved in HSPs expression were examined by pretreatment with chemical inhibitors, and siRNAs of MAPK, Akt, and heat shock factor 1 (HSF1), followed by determination of HSPs expression.

Results

This study demonstrates that heat shock treatment induced ROS generation and HPSs expression in hPDMCs. Heat shock stimulation also increased p38 MAPK and Akt phosphorylation. These effects were reduced by inhibitors of ROS, p38 MAPK and Akt. Moreover, we found that heat shock treatment enhanced nuclear translocation of the HSF1 in hPDMCs, representing activation of HSF1. Pretreatment of hPDMCs with ROS scavengers, SB203580 and Akt inhibitors also reduced the translocation of HSF1 induced by heat shock.

Conclusions

Our data indicate that heat shock acts via ROS to activate p38 MAPK and Akt signaling, which subsequently activates HSF1, leading to HSP activation and contributing to the protective role of hPDMCs.

HSP90 as a regulator of extracellular matrix dynamics

The extracellular matrix (ECM) is a dynamic and organised extracellular network assembled from proteins and carbohydrates exported from the cell. The ECM is critical for multicellular life, providing spatial and temporal cellular cues to maintain tissue homeostasis. Consequently, ECM production must be carefully balanced with turnover to ensure homeostasis; ECM dysfunction culminates in disease. Hsp90 is a molecular chaperone central to protein homeostasis, including in the ECM. Intracellular and extracellular Hsp90 isoforms collaborate to regulate the levels and status of proteins in the ECM via multiple mechanisms. In so doing, Hsp90 regulates ECM dynamics, and changes in Hsp90 levels or activity support the development of ECM-related diseases, like cancer and fibrosis. Consequently, Hsp90 levels may have prognostic value, while inhibition of Hsp90 may have therapeutic potential in conditions characterised by ECM dysfunction.

Histology Atlas of the Developing Mouse Placenta

The use of the mouse as a model organism is common in translational research. This mouse-human similarity holds true for placental development as well. Proper formation of the placenta is vital for development and survival of the maturing embryo. Placentation involves sequential steps with both embryonic and maternal cell lineages playing important roles. The first step in placental development is formation of the blastocyst wall (approximate embryonic days [E] 3.0-3.5). After implantation (∼E4.5), extraembryonic endoderm progressively lines the inner surface of the blastocyst wall (∼E4.5-5.0), forming the yolk sac that provides histiotrophic support to the embryo; subsequently, formation of the umbilical vessels (∼E8.5) supports transition to the chorioallantoic placenta and hemotrophic nutrition. The fully mature ("definitive") placenta is established by ∼E12.5. Abnormal placental development often leads to embryonic mortality, with the timing of death depending on when placental insufficiency takes place and which cells are involved. This comprehensive macroscopic and microscopic atlas highlights the key features of normal and abnormal mouse placental development from E4.5 to E18.5. This in-depth overview of a transient (and thus seldom-analyzed) developmental tissue should serve as a useful reference to aid researchers in identifying and describing mouse placental changes in engineered, induced, and spontaneous disease models.

Heterogeneous Responses and Isoform Compensation Dim Therapeutic Window of Hsp90 ATP-Binding Inhibitors in Cancer

The rare capacity for heat shock protein-90 (Hsp90) chaperones to support almost the entire cellular signaling networks was viewed as a potential breakthrough point to combat tumor resistance to single oncogene-based therapeutics. Over two decades, several generations of Hsp90 ATP-binding inhibitors have entered numerous cancer clinical trials, but few have advanced to FDA approval for treatment of human cancers. Herein, we report that Hsp90 expression dramatically vary especially among different types of non-cancer cells and organs. The highly variable levels of Hsp90 from as low as 1.7% to as high as 9% of their total cellular proteins were responsible for either an extreme sensitivity or an extreme resistance to a classical Hsp90 ATP-binding inhibitor. Among randomly selected cancer cell lines, the same client proteins for regulation of cell growth exhibited unexpectedly heterogenous reactions in response to Hsp90 ATP-binding inhibitor, inconsistent with the current understanding. Finally, a minimum amount (<10%) of Hsp90β was still required for client protein stability and cell survival even in the presence of full Hsp90α. These new findings of Hsp90 expression in host and isoform compensation in tumor cells could complicate biomarker selection, toxicity readout and clinical efficacy of Hsp90-ATP-binding inhibitors in cancer clinical trials.

Heat shock protein-90alpha (Hsp90α) stabilizes hypoxia-inducible factor-1α (HIF-1α) in support of spermatogenesis and tumorigenesis

Hypoxia-inducible factor-1 (HIF-1), a master transcriptional factor for protecting cells from hypoxia, plays a critical role in spermatogenesis and tumorigenesis. For the past two decades, numerous small molecule inhibitors that block mRNA synthesis, protein translation, or DNA binding of HIF-1α have entered clinical trials. To date, few have advanced to FDA approval for clinical applications due to limited efficacy at their toxicity-tolerable dosages. New windows for developing effective and safe therapeutics require better understanding of the specific mechanism of action. The finding that a chaperone-defective mutant heat shock protein-90-alpha (Hsp90α) blocks spermatogenesis, a known hypoxia-driven process in mouse testis prompted us to focus on the role of Hsp90α in HIF-1α. Here we demonstrate that Hsp90α gene knockout causes a dramatic reduction of the high steady-state level of HIF-1α in the testis, blocking sperm production and causing infertility of the mice. In HIF-1α-dependent tumor cells, we found that Hsp90α forms protein complexes with hypoxia-elevated HIF-1α and Hsp90α knockout prevents hypoxia-induced HIF-1α accumulation. In contrast, downregulation of Hsp90β had little effect on hypoxia-induced accumulation of HIF-1α. Instead, Hsp90β protects signaling molecules responsible for cellular homeostasis from assault by 17-AAG (17-N-allylamino-17-demethoxygeldanamycin), a general ATPase inhibitor of both Hsp90α and Hsp90β. Since targeting Hsp90β gene is lethal in both cultured cells and in mice, our new finding explains the toxicity of the previous inhibitor trials and identifies the specific binding of Hsp90α to HIF-1α as a new therapeutic window for developing safer and more effective treatment of male infertility and cancer.

Genomic organization and hypoxia inducible factor responsive regulation of teleost hsp90β gene during hypoxia stress

BACKGROUND

The physiological significance of a large family of heat-shock proteins (HSPs), comprised of the cytosolic HSP90A and the endoplasmic reticulum component of HSPB, is evident in prokaryotes and eukaryotes. The HSP90A is believed to play critical roles in diverse physiological functions of cell viability and chromosomal stability including stress management. Heightened abundance of hsp90β transcript was documented in Channa striatus, a freshwater fish, which is capable of surviving within an extremely hypoxic environment.

METHODS AND RESULTS

To better understand the mechanism of hsp90β gene expression, we investigated its genomic organization. Eleven exons were identified, including a long upstream intron with a remarkable similarity with human, but not with chicken counterpart. Dual-luciferase assays identified promoter activity in a 1366 bp 5'-flanking segment beyond the transcription initiation site. Examination detected a minimal promoter of 754 bp containing a TATA-box, CAAT-enhancer in addition to providing clues regarding other enhancer and repressor elements. The driving capability of this minimal promoter was further validated by its binding ability with TATA-box binding protein and the generation of GFP expressing transgenic zebrafish (F₂). Further, deletion of an inverted HIF (hypoxia inducible factor) motif RCGTG (upstream of the TATA-box) dramatically reduced luciferase expression in a hypoxic environment (CoCl₂ treated cultivable cells) and was identified as a cis-acting HIF responsive element, necessary for the hypoxia-induced expression.

CONCLUSIONS

The results obtained herein provide an insight regarding how hsp90β gene expression is controlled by HIF responsive element in teleost both during hypoxia stress management and normal physiological functions, and suggested that the hsp90β gene promoter could be used as a potential candidate for generating ornamental and food-fish transgenics.

The HSP90/R2TP assembly chaperone promotes cell proliferation in the intestinal epithelium

The R2TP chaperone cooperates with HSP90 to integrate newly synthesized proteins into multi-subunit complexes, yet its role in tissue homeostasis is unknown. Here, we generated conditional, inducible knock-out mice for Rpap3 to inactivate this core component of R2TP in the intestinal epithelium. In adult mice, Rpap3 invalidation caused destruction of the small intestinal epithelium and death within 10 days. Levels of R2TP substrates decreased, with strong effects on mTOR, ATM and ATR. Proliferative stem cells and progenitors deficient for Rpap3 failed to import RNA polymerase II into the nucleus and they induced p53, cell cycle arrest and apoptosis. Post-mitotic, differentiated cells did not display these alterations, suggesting that R2TP clients are preferentially built in actively proliferating cells. In addition, high RPAP3 levels in colorectal tumors from patients correlate with bad prognosis. Here, we show that, in the intestine, the R2TP chaperone plays essential roles in normal and tumoral proliferation.

The Role of HSP90α in Methamphetamine/Hyperthermia-Induced Necroptosis in Rat Striatal Neurons

Methamphetamine (METH) is one of the most widely abused synthetic drugs in the world. The users generally present hyperthermia (HT) and psychiatric symptoms. However, the mechanisms involved in METH/HT-induced neurotoxicity remain elusive. Here, we investigated the role of heat shock protein 90 alpha (HSP90α) in METH/HT (39.5°C)-induced necroptosis in rat striatal neurons and an in vivo rat model. METH treatment increased core body temperature and up-regulated LDH activity and the molecular expression of canonical necroptotic factors in the striatum of rats. METH and HT can induce necroptosis in primary cultures of striatal neurons. The expression of HSP90α increased following METH/HT injuries. The specific inhibitor of HSP90α, geldanamycin (GA), and HSP90α shRNA attenuated the METH/HT-induced upregulation of receptor-interacting protein 3 (RIP3), phosphorylated RIP3, mixed lineage kinase domain-like protein (MLKL), and phosphorylated MLKL. The inhibition of HSP90α protected the primary cultures of striatal neurons from METH/HT-induced necroptosis. In conclusion, HSP90α plays an important role in METH/HT-induced neuronal necroptosis and the HSP90α-RIP3 pathway is a promising therapeutic target for METH/HT-induced neurotoxicity in the striatum.

Selective Inhibition of the Hsp90α Isoform

The 90 kDa heat shock protein (Hsp90) is a molecular chaperone that processes nascent polypeptides into their biologically active conformations. Many of these proteins contribute to the progression of cancer, and consequently, inhibition of the Hsp90 protein folding machinery represents an innovative approach toward cancer chemotherapy. However, clinical trials with Hsp90 N-terminal inhibitors have encountered deleterious side effects and toxicities, which appear to result from the pan-inhibition of all four Hsp90 isoforms. Therefore, the development of isoform-selective Hsp90 inhibitors is sought to delineate the pathological role played by each isoform. Herein, we describe a structure-based approach that was used to design the first Hsp90α-selective inhibitors, which exhibit >50-fold selectivity versus other Hsp90 isoforms.

The molecular chaperone Hsp90α deficiency causes retinal degeneration by disrupting Golgi organization and vesicle transportation in photoreceptors

Heat shock protein 90 (Hsp90) is an abundant molecular chaperone with two isoforms, Hsp90α and Hsp90β. Hsp90β deficiency causes embryonic lethality, whereas Hsp90α deficiency causes few abnormities except male sterility. In this paper, we reported that Hsp90α was exclusively expressed in the retina, testis, and brain. Its deficiency caused retinitis pigmentosa (RP), a disease leading to blindness. In Hsp90α-deficient mice, the retina was deteriorated and the outer segment of photoreceptor was deformed. Immunofluorescence staining and electron microscopic analysis revealed disintegrated Golgi and aberrant intersegmental vesicle transportation in Hsp90α-deficient photoreceptors. Proteomic analysis identified microtubule-associated protein 1B (MAP1B) as an Hsp90α-associated protein in photoreceptors. Hspα deficiency increased degradation of MAP1B by inducing its ubiquitination, causing α-tubulin deacetylation and microtubule destabilization. Furthermore, the treatment of wild-type mice with 17-DMAG, an Hsp90 inhibitor of geldanamycin derivative, induced the same retinal degeneration as Hsp90α deficiency. Taken together, the microtubule destabilization could be the underlying reason for Hsp90α deficiency-induced RP.

General Structural and Functional Features of Molecular Chaperones

Molecular chaperones are a group of structurally diverse and highly conserved ubiquitous proteins. They play crucial roles in facilitating the correct folding of proteins in vivo by preventing protein aggregation or facilitating the appropriate folding and assembly of proteins. Heat shock proteins form the major class of molecular chaperones that are responsible for protein folding events in the cell. This is achieved by ATP-dependent (folding machines) or ATP-independent mechanisms (holders). Heat shock proteins are induced by a variety of stresses, besides heat shock. The large and varied heat shock protein class is categorised into several subfamilies based on their sizes in kDa namely, small Hsps (HSPB), J domain proteins (Hsp40/DNAJ), Hsp60 (HSPD/E; Chaperonins), Hsp70 (HSPA), Hsp90 (HSPC), and Hsp100. Heat shock proteins are localised to different compartments in the cell to carry out tasks specific to their environment. Most heat shock proteins form large oligomeric structures, and their functions are usually regulated by a variety of cochaperones and cofactors. Heat shock proteins do not function in isolation but are rather part of the chaperone network in the cell. The general structural and functional features of the major heat shock protein families are discussed, including their roles in human disease. Their function is particularly important in disease due to increased stress in the cell. Vector-borne parasites affecting human health encounter stress during transmission between invertebrate vectors and mammalian hosts. Members of the main classes of heat shock proteins are all represented in Plasmodium falciparum, the causative agent of cerebral malaria, and they play specific functions in differentiation, cytoprotection, signal transduction, and virulence.

Protein quality control of cell stemness

Protein quality control (PQC) systems play essential roles in the recognition, refolding and clearance of aberrant proteins, thus ensuring cellular protein homeostasis, or proteostasis. Especially, continued proliferation and differentiation of stem cells require a high rate of translation; therefore, accurate PQC systems are essential to maintain stem cell function. Growing evidence suggested crucial roles of PQC systems in regulating the stemness and differentiation of stem cells. This review focuses on current knowledge regarding the components of the proteostasis network in stem cells, and the importance of proteostasis in maintaining stem cell identity and regenerative functions. A complete understanding of this process might uncover potential applications in aging intervention and aging-related diseases.

The Yeast Hsp70 Cochaperone Ydj1 Regulates Functional Distinction of Ssa Hsp70s in the Hsp90 Chaperoning Pathway

Heat-shock protein (Hsp) 90 assists in the folding of diverse sets of client proteins including kinases and growth hormone receptors. Hsp70 plays a major role in many Hsp90 functions by interacting and modulating conformation of its substrates before being transferred to Hsp90s for final maturation. Each eukaryote contains multiple members of the Hsp70 family. However, the role of different Hsp70 isoforms in Hsp90 chaperoning actions remains unknown. Using v-Src as an Hsp90 substrate, we examined the role of each of the four yeast cytosolic Ssa Hsp70s in regulating Hsp90 functions. We show that the strain expressing stress-inducible Ssa3 or Ssa4, and the not constitutively expressed Ssa1 or Ssa2, as the sole Ssa Hsp70 isoform reduces v-Src-mediated growth defects. The study shows that although different Hsp70 isoforms interact similarly with Hsp90s, v-Src maturation is less efficient in strains expressing Ssa4 as the sole Hsp70. We further show that the functional distinction between Ssa2 and Ssa4 is regulated by its C-terminal domain. Further studies reveal that Ydj1, which is known to assist substrate transfer to Hsp70s, interacts relatively weakly with Ssa4 compared with Ssa2, which could be the basis for poor maturation of the Hsp90 client in cells expressing stress-inducible Ssa4 as the sole Ssa Hsp70. The study thus reveals a novel role of Ydj1 in determining the functional distinction among Hsp70 isoforms with respect to the Hsp90 chaperoning action.

Modulation of hippocampal neuronal resilience during aging by the Hsp70/Hsp90 co-chaperone STI1

Chaperone networks are dysregulated with aging, but whether compromised Hsp70/Hsp90 chaperone function disturbs neuronal resilience is unknown. Stress-inducible phosphoprotein 1 (STI1; STIP1; HOP) is a co-chaperone that simultaneously interacts with Hsp70 and Hsp90, but whose function in vivo remains poorly understood. We combined in-depth analysis of chaperone genes in human datasets, analysis of a neuronal cell line lacking STI1 and of a mouse line with a hypomorphic Stip1 allele to investigate the requirement for STI1 in aging. Our experiments revealed that dysfunctional STI1 activity compromised Hsp70/Hsp90 chaperone network and neuronal resilience. The levels of a set of Hsp90 co-chaperones and client proteins were selectively affected by reduced levels of STI1, suggesting that their stability depends on functional Hsp70/Hsp90 machinery. Analysis of human databases revealed a subset of co-chaperones, including STI1, whose loss of function is incompatible with life in mammals, albeit they are not essential in yeast. Importantly, mice expressing a hypomorphic STI1 allele presented spontaneous age-dependent hippocampal neurodegeneration and reduced hippocampal volume, with consequent spatial memory deficit. We suggest that impaired STI1 function compromises Hsp70/Hsp90 chaperone activity in mammals and can by itself cause age-dependent hippocampal neurodegeneration in mice. Cover Image for this issue: doi: 10.1111/jnc.14749.

After Conventional Wisdom Has Failed, What Drives Wound Healing?

Between 2006 and 2015, the U.S. Food and Drug Administration’s (FDA) overall likelihood of approval (LOA) from Phase I clinical trials for all therapeutic candidates was 9.6%, with the highest LOA in haematology (26.1%) and the lowest in oncology (5.1%). Two critical features attributed to the success of advancing trials were i) targeting driver genes responsible for disease, and ii) use of human disease-relevant animal models during preclinical studies. For decades, conventional wisdom has been that growth factors are the drivers of wound healing, but few have either advanced to clinical applications or proven effective. The purpose of this paper is to explore heat shock protein 90-alpha (Hsp90α)’s role as a potential driver of wound healing and as a possible future therapeutic entity through a review of recent literature, including studies with human disease-relevant animal models. Of the approximately 7,000 gene products generated by a given mammalian cell type, the Hsp90 family of proteins (Hsp90α and Hsp90β) accounts for 2–3% of them. Hsp90β fulfils the role of an intracellular chaperone, but Hsp90α’s intracellular function is surprisingly dispensable. Instead, the abundancy of Hsp90α appears to have been prepared for extracellular purposes. When secreted via exosomes by cells under environmental stress, such as injury, Hsp90α protects cells from hypoxia-induced cell death, reduces local inflammation, and subsequently promotes cell migration to repair the injured tissue. Unlike conventional growth factors, secreted Hsp90α stimulates all major cell types involved in wound healing equally, resists microenvironmental inhibitors like TGFβ and hyperglycaemia, and is highly stable. Inhibition of exosome-mediated Hsp90α secretion, neutralisation of Hsp90α’s ATPase-independent extracellular functions, or interruption of Hsp90α-LRP-1 signalling blocks wound closure in vivo. Topical application of Hsp90α’s therapeutic entity, F-5 (a 115-amino acid peptide), has shown great promise for healing acute burn and diabetic wounds in mice and pigs.

HSP90 inhibitor geldanamycin reverts IL-13- and IL-17-induced airway goblet cell metaplasia

Goblet cell metaplasia, a disabling hallmark of chronic lung disease, lacks curative treatments at present. To identify novel therapeutic targets for goblet cell metaplasia, we studied the transcriptional response profile of IL-13-exposed primary human airway epithelia in vitro and asthmatic airway epithelia in vivo. A perturbation-response profile connectivity approach identified geldanamycin, an inhibitor of heat shock protein 90 (HSP90) as a candidate therapeutic target. Our experiments confirmed that geldanamycin and other HSP90 inhibitors prevented IL-13-induced goblet cell metaplasia in vitro and in vivo. Geldanamycin also reverted established goblet cell metaplasia. Geldanamycin did not induce goblet cell death, nor did it solely block mucin synthesis or IL-13 receptor-proximal signaling. Geldanamycin affected the transcriptome of airway cells when exposed to IL-13, but not when exposed to vehicle. We hypothesized that the mechanism of action probably involves TGF-β, ERBB, or EHF, which would predict that geldanamycin would also revert IL-17-induced goblet cell metaplasia, a prediction confirmed by our experiments. Our findings suggest that persistent airway goblet cell metaplasia requires HSP90 activity and that HSP90 inhibitors will revert goblet cell metaplasia, despite active upstream inflammatory signaling. Moreover, HSP90 inhibitors may be a therapeutic option for airway diseases with goblet cell metaplasia of unknown mechanism.

The effect of mesenchymal stem cell-secreted factors on airway epithelial repair

Aim: This study was aimed to investigate the effect of mesenchymal stem cell (MSC)-secreted factors on airway repair. Materials & methods: An indirect in vitro coculture model of injured airway epithelium explant with MSCs was developed. LC–MS/MS analysis was performed to determine factors secreted by MSCs and their involvement in epithelium repair was evaluated by histopathological assessment. Results: The identification of 54 of MSC proteins of which 44 of them were secretory/extracellular proteins. 43 of the secreted proteins were found to be involved in accelerating airway epithelium repair by stimulating the migratory, proliferative and differentiation abilities of the endogenous repair mechanisms. MSC-secreted proteins also initiated epithelial–mesenchymal transition process during early repair. Conclusion: MSC-secreted factors accelerated airway epithelial repair by stimulating the endogenous reparative and regenerative ability of lung cells.

Heat Shock Protein 90 as a Prognostic Marker and Therapeutic Target for Adrenocortical Carcinoma

Background: Adrenocortical carcinoma (ACC) is a rare tumor entity with restricted therapeutic opportunities. HSP90 (Heat Shock Protein 90) chaperone activity is fundamental for cell survival and contributes to different oncogenic signaling pathways. Indeed, agents targeting HSP90 function have shown therapeutic efficacy in several cancer types. We have examined the expression of HSP90 in different adrenal tumors and evaluated the use of HSP90 inhibitors in vitro as possible therapy for ACC. Methods: Immunohistochemical expression of HSP90 isoforms was investigated in different adrenocortical tumors and associated with clinical features. Additionally, a panel of N-terminal (17-allylamino-17-demethoxygeldanamycin (17-AAG), luminespib, and ganetespib) and C-terminal (novobiocin and silibinin) HSP90 inhibitors were tested on various ACC cell lines. Results: Within adrenocortical tumors, ACC samples exhibited the highest expression of HSP90β. Within a cohort of ACC patients, HSP90β expression levels were inversely correlated with recurrence-free and overall survival. In functional assays, among five different compounds tested luminespib and ganetespib induced a significant decrease in cell viability in single as well as in combined treatments with compounds of the clinically used EDP-M scheme (etoposide, doxorubicin, cisplatin, mitotane). Inhibition of cell viability correlated furthermore with a decrease in proliferation, in cell migration and an increase in apoptosis. Moreover, analysis of cancer pathways indicated a modulation of the ERK1/2-and AKT-pathways by luminespib and ganetespib treatment. Conclusions: Our findings emphasize HSP90 as a marker with prognostic impact and promising target with N-terminal HSP90 inhibitors as drugs with potential therapeutic efficacy toward ACC.

Heat-shock protein 90α is involved in maintaining the stability of VP16 and VP16-mediated transactivation of α genes from herpes simplex virus-1

Background

Numerous host cellular factors are exploited by viruses to facilitate infection. Our previous studies and those of others have shown heat-shock protein 90 (Hsp90), a cellular molecular chaperone, is involved in herpes simplex virus (HSV)-1 infection. However, the function of the dominant Hsp90 isoform and the relationship between Hsp90 and HSV-1 α genes remain unclear.

Methods and results

Hsp90α knockdown or inhibition significantly inhibited the promoter activity of HSV-1 α genes and downregulated virion protein 16(VP16) expression from virus and plasmids. The Hsp90α knockdown-induced suppression of α genes promoter activity and downregulation of α genes was reversed by VP16 overexpression, indicating that Hsp90α is involved in VP16-mediated transcription of HSV-1 α genes. Co-immunoprecipitation experiments indicated that VP16 interacted with Hsp90α through the conserved core domain within VP16. Based on using autophagy inhibitors and the presence of Hsp90 inhibitors in ATG7^−/− (autophagy-deficient) cells, Hsp90 inhibition-induced degradation of VP16 is dependent on macroautophagy-mediated degradation but not chaperone-mediated autophagy (CMA) pathway. In vivo studies demonstrated that treatment with gels containing Hsp90 inhibitor effectively reduced the level of VP16 and α genes, which may contribute to the amelioration of the skin lesions in an HSV-1 infection mediated zosteriform model.

Conclusion

Our study provides new insights into the mechanisms by which Hsp90α facilitates the transactivation of HSV-1 α genes and viral infection, and highlights the importance of developing selective inhibitors targeting the interaction between Hsp90α and VP16 to reduce toxicity, a major challenge in the clinical use of Hsp90 inhibitors.

Electronic supplementary material

The online version of this article (10.1186/s10020-018-0066-x) contains supplementary material, which is available to authorized users.