Aha1 can act as an autonomous chaperone to prevent aggregation of stressed proteins

Stress-inducible phosphoprotein 1 (Sti1/Stip1/Hop) sequesters misfolded proteins during stress

Co-chaperones are key elements of cellular protein quality control. They cooperate with the major heat shock proteins Hsp70 and Hsp90 in folding proteins and preventing the toxic accumulation of misfolded proteins upon exposure to stress. Hsp90 interacts with the co-chaperone stress-inducible phosphoprotein 1 (Sti1/Stip1/Hop) and activator of Hsp90 ATPase protein 1 (Aha1) among many others. Sti1 and Aha1 control the ATPase activity of Hsp90, but Sti1 also facilitates the transfer of client proteins from Hsp70 to Hsp90, thus connecting these two major branches of protein quality control. We find that misbalanced expression of Sti1 and Aha1 in yeast and mammalian cells causes severe growth defects. Also, deletion of STI1 causes an accumulation of soluble misfolded ubiquitinated proteins and a strong activation of the heat shock response. We discover that, during proteostatic stress, Sti1 forms cytoplasmic inclusions in yeast and mammalian cells that overlap with misfolded proteins. Our work indicates a key role of Sti1 in proteostasis independent of its Hsp90 ATPase regulatory functions by sequestering misfolded proteins during stress.

The role of Aha1 in cancer and neurodegeneration

The 90 kDa Heat shock protein (Hsp90) is a family of ubiquitously expressed molecular chaperones responsible for the stabilization and maturation of >400 client proteins. Hsp90 exhibits dramatic conformational changes to accomplish this, which are regulated by partner proteins termed co-chaperones. One of these co-chaperones is called the activator or Hsp90 ATPase activity homolog 1 (Aha1) and is the most potent accelerator of Hsp90 ATPase activity. In conditions where Aha1 levels are dysregulated including cystic fibrosis, cancer and neurodegeneration, Hsp90 mediated client maturation is disrupted. Accumulating evidence has demonstrated that many disease states exhibit large hetero-protein complexes with Hsp90 as the center. Many of these include Aha1, where increased Aha1 levels drive disease states forward. One strategy to block these effects is to design small molecule disruptors of the Hsp90/Aha1 complex. Studies have demonstrated that current Hsp90/Aha1 small molecule disruptors are effective in both models for cancer and neurodegeration.

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.

Human Aha1's N-terminal extension confers it holdase activity in vitro

Molecular chaperones are key components of protein quality control system, which plays an essential role in controlling protein homeostasis. Aha1 has been identified as a co-chaperone of Hsp90 known to strongly accelerate Hsp90's ATPase activity. Meanwhile, it is reported that Aha1 could also act as an autonomous chaperone and protect stressed or disordered proteins from aggregation. Here, in this article, a series of in vitro experiments were conducted to verify whether Aha1 has a non-Hsp90-dependent holdase activity and to elucidate the associated molecular mechanism for substrate recognition. According to the results of the refolding assay, the highly conserved N-terminal extension spanning M1 to R16 in Aha1 from higher eukaryotes is responsible for the holdase activity of the protein. As revealed by the NMR data, Aha1's N-terminal extension mainly adopts a disordered conformation in solution and shows no tight contacts with the core structure of Aha1's N-terminal domain. Based on the intrinsically disordered structure feature and the primary sequence of Aha1's N-terminal extension, the fuzzy-type protein-protein interactions involving this specific region and the unfolded substrate proteins are expected. The following mutation analysis data demonstrated that the Van der Waals contacts potentially involving two tryptophans including W4 and W11 do not play a dominant role in the interaction between Aha1 and unfolded maltose binding protein (MBP). Meanwhile, since the high concentration of NaCl could abolish the holdase activity of Aha1, the electrostatic interactions mediated by those charged residues in Aha1's N-terminal extension are thus indicated to play a crucial role in the substrate recognition.

A Split Renilla Luciferase Complementation Assay for the Evaluation of Hsp90/Aha1 Complex Disruptors and Their Activity at the Aha1 C-Terminal Domain

Disruption of interactions between Hsp90 and the cochaperone protein, Aha1, has emerged as a therapeutic strategy to inhibit Aha1-driven cancer metastasis and tau aggregation in models of tauopathy. A combination of split Renilla luciferase assays was developed to screen and quantify the ability of small molecules to disrupt interactions between Hsp90 and both full length Aha1 protein (Aha1-FL) and the Aha1 C-terminal domain (Aha1-CTD). This luminescence-based approach was used to identify withaferin A and gedunin as disruptors of Hsp90/Aha1 interactions and provided insight into the binding regions for gambogic acid and gedunin on the Hsp90 homodimer. All compounds tested that disrupted Hsp90/Aha1-CTD interactions were found to disrupt interactions between Hsp90 and Aha1-FL, suggesting that interactions between Hsp90 and the Aha1-CTD play a key role in the stability of Hsp90/Aha1 complexes.

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.

AHSA1 Promotes Proliferation and EMT by Regulating ERK/CALD1 Axis in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the major causes of cancer-related death worldwide. AHSA1 as a chaperone of HSP90 promotes the maturation, stability, and degradation of related cancer-promoting proteins. However, the regulatory mechanism and biological function of AHSA1 in HCC are largely unknown. Actually, we found that AHSA1 was significantly upregulated in HCC tissues and cell lines and was notably correlated with the poor clinical characteristics and prognosis of HCC patients in this study. Furthermore, both in vitro and in vivo, gain- and loss-of-function studies demonstrated that AHSA1 promoted the proliferation, invasion, metastasis, and epithelial-mesenchymal transition (EMT) of HCC. Moreover, the mechanistic study indicated that AHSA1 recruited ERK1/2 and promoted the phosphorylation and inactivation of CALD1, while ERK1/2 phosphorylation inhibitor SCH772984 reversed the role of AHSA1 in the proliferation and EMT of HCC. Furthermore, we demonstrated that the knockdown of CALD1 reversed the inhibition of proliferation and EMT by knocking AHSA1 in HCC. We also illustrated a new molecular mechanism associated with AHSA1 in HCC that was independent of HSP90 and MEK1/2. In summary, AHSA1 may play an oncogenic role in HCC by regulating ERK/CALD1 axis and may serve as a novel therapeutic target for HCC.

Aha1 Is an Autonomous Chaperone for SULT1A1

The cochaperone Aha1 activates HSP90 ATPase to promote the folding of its client proteins; however, very few client proteins of Aha1 are known. With the use of an ascorbate peroxidase (APEX)-based proximity labeling method, we identified SULT1A1 as a proximity protein of HSP90 that is modulated by genetic depletion of Aha1. Immunoprecipitation followed by Western blot analysis showed the interaction of SULT1A1 with Aha1, but not HSP90. We also observed a reduced level of SULT1A1 protein upon genetic depletion of Aha1 but not upon pharmacological inhibition of HSP90, suggesting that the SULT1A1 protein level is regulated by Aha1 alone. Maturation-dependent interaction assay results showed that Aha1, but not HSP90, binds preferentially to newly synthesized SULT1A1. Reconstitution of Aha1-depleted cells with wild-type Aha1 and its E67K mutant, which is deficient in interacting with HSP90, restored SULT1A1 protein to the same level. Nonetheless, complementation of Aha1-depleted cells with an Aha1 mutant lacking the first 20 amino acids, which disrupts its autonomous chaperone function, was unable to rescue the SULT1A1 protein level. Together, our study revealed, for the first time, Aha1 as an autonomous chaperone in regulating SULT1A1. SULT1A1 is a phase-II metabolic enzyme, where it adds sulfate groups to hydroxyl functionalities in endogenous hormones and xenobiotic chemicals to improve their solubilities and promote their excretion. Thus, our work suggests the role of Aha1 cochaperone in modulating the detoxification of endogenous and environmental chemicals.

Comprehensive proteomic analysis to elucidate the anti-heat stress effects of nano-selenium in rainbow trout (Oncorhynchus mykiss)

Because of the continuous intensification of global warming, extreme climate fluctuations, and high-density farming, cold-water rainbow trout (Oncorhynchus mykiss) are exposed to conditions of heat stress, which has severely impacted their survival and yield. Nano-selenium (nano-Se) shows higher biological activity and lower toxicity and has emerged as an ideal and ecological Se formulation. Herein rainbow trout were fed either a basal diet (control group) or basal diet plus 5 mg/kg nano-Se (treatment group). Samples were collected before (18 °C for 9 days; CG18, Se18) and after (24 °C for 8 h; CG24, Se24) heat stress. The DIA/SWATH approach was then applied to compare changes at the proteome level. We found 223 and 269 differentially abundant proteins in the CG18-CG24 and Se18-Se24 groups, respectively, which mainly included apoptosis-, heat stress-, and lipid-related proteins. In comparison with the CG18-CG24 group, the Se18-Se24 group showed higher abundance of molecular chaperone, such as Hsp70, Hsp90a.1, Hspa8, Hsp30, DNAJA4, Dnajb1, Bag2 and Ahsa1; on nano-Se supplementation, the heat stress-induced decline in the abundance of the selenoprotein MsrB2 was partially restored. Furthermore, nano-Se supplementation downregulated the abundance of lipid-related (CYP51, EBP, DHCR7, DHCR24, and APOB) and pro-apoptotic (caspase-8 and Bad) proteins. Protein-protein interaction analyses suggested that nano-Se inhibits apoptosis by upregulating the expression of Hsp70, Hsp90a.1, Hspa8, and Dnajb1; further, Hsp70/Hspa8 and MsrB2 appear to play a synergistic role in antioxidant defense under heat stress. Overall, our findings provide novel insights into nano-Se-mediated tolerance of heat stress, demonstrating that nano-Se exerts its anti-heat stress effects in rainbow trout by promoting protein repair, enhancing recovery of antioxidant enzyme activity, and alleviating lipid metabolism and apoptosis.

HSP90 and Aha1 modulate microRNA maturation through promoting the folding of Dicer1

Aha1 is a co-chaperone of heat shock protein 90 (HSP90), and it stimulates the ATPase activity of HSP90 to promote the folding of its client proteins. By employing ascorbate peroxidase (APEX)-based proximity labeling and proteomic analysis, we identified over 30 proteins exhibiting diminished abundances in the proximity proteome of HSP90 in HEK293T cells upon genetic depletion of Aha1. Dicer1 is a top-ranked protein, and we confirmed its interactions with HSP90 and Aha1 by immunoprecipitation followed by western blot analysis. Genetic depletion of Aha1 and pharmacological inhibition of HSP90 both led to reduced levels of Dicer1 protein. Additionally, HSP90 and Aha1 bind preferentially to newly translated Dicer1. Reconstitution of Aha1-depleted cells with wild-type Aha1 substantially rescued Dicer1 protein level, and a lower level of restoration was observed for complementation with the HSP90-binding-defective Aha1-E67K, whereas an Aha1 mutant lacking the first 20 amino acids-which abolishes its chaperone activity-failed to rescue Dicer1 protein level. Moreover, knockdown of Aha1 and inhibition of HSP90 led to diminished levels of mature microRNAs (miRNAs), but not their corresponding primary miRNAs. Together, we uncovered a novel mechanism of HSP90 and Aha1 in regulating the miRNA pathway through promoting the folding of Dicer1 protein, and we also demonstrated that Aha1 modulates this process by acting as an autonomous chaperone and a co-chaperone for HSP90.

Identification of AHSA1 as a Potential Therapeutic Target for Breast Cancer: Bioinformatics Analysis and In Vitro Studies

BACKGROUND

Shenling Baizhu Powder (SBP), a famous Traditional Chinese Medicine (TCM) formulation, has been widely used in the adjuvant treatment of cancers, including breast cancer. This study aims to identify potential new targets for breast cancer treatment based on the network pharmacology of SBP. <P> Methods: By analyzing the relationship between herbs and target proteins, potential targets of multiple herbs in SBP were identified by network pharmacology analysis. Besides, by comparing the data of breast cancer tissue with normal tissue, upregulated genes in two breast cancer expression profiles were found. Thereafter, the expression level and prognosis of activator of heat shock protein 90 (HSP90) ATPase activity 1 (AHSA1) were further analyzed in breast cancer by bioinformatics analysis, and the network module of AHSA1 binding protein was constructed. Furthermore, the effect of knocking down AHSA1 on the proliferation, migration, and invasion of breast cancer cells was verified by MTT, clone formation assay, and transwell assay. <P> Results: Vascular endothelial growth factor A (VEGFA), intercellular adhesion molecule 1 (ICAM1), chemokine (C-X-C motif) ligand 8 (CXCL8), AHSA1, and serpin family E member 1 (SERPINE1) were associated with multiple herbs in SBP. AHSA1 was remarkably upregulated in breast cancer tissues and positively correlated with poor overall survival and disease metastasis-free survival. Furthermore, knockdown of AHSA1 significantly inhibited the migration and invasion in MCF-7 and MDA-MB-231 breast cancer cells but had no obvious effect on proliferation. In addition, among the proteins that bind to AHSAl, the network composed of proteasome, chaperonin, and heat shock proteins is closely connected, and these proteins are associated with poor prognosis in a variety of cancers. <P> Conclusion: AHSA1 is positively correlated with breast cancer progression and might act as a novel therapeutic target for breast cancer.

Orchardgrass ACTIVATOR OF HSP90 ATPASE possesses autonomous chaperone properties and activates Hsp90 transcription to enhance thermotolerance

High temperature stress is an environmental factor that negatively affects the growth and development of crops. Hsp90 (90 kDa heat shock protein) is a major molecular chaperone in eukaryotic cells, contributing to the maintenance of cell homeostasis through interaction with co-chaperones. Aha1 (activator of Hsp90 ATPase) is well known as a co-chaperone that activates ATPase activity of Hsp90 in mammals. However, biochemical and physiological evidence relating to Aha has not yet been identified in plants. In this study, we investigated the heat-tolerance function of orchardgrass (Dactylis glomerata L.) Aha (DgAha). Recombinant DgAha interacted with cytosolic DgHsp90s and efficiently protected substrates from thermal denaturation. Furthermore, heterologous expression of DgAha in yeast (Saccharomyces cerevisiae) cells and Arabidopsis (Arabidopsis thaliana) plants conferred thermotolerance in vivo. Enhanced expression of DgAha in Arabidopsis stimulates the transcription of Hsp90 under heat stress. Our data demonstrate that plant Aha plays a positive role in heat stress tolerance via chaperone properties and/or activation of Hsp90 to protect substrate proteins in plants from thermal injury.

Hsp90 and its co-chaperone Sti1 control TDP-43 misfolding and toxicity

Protein misfolding is a central feature of most neurodegenerative diseases. Molecular chaperones can modulate the toxicity associated with protein misfolding, but it remains elusive which molecular chaperones and co-chaperones interact with specific misfolded proteins. TDP-43 misfolding and inclusion formation are a hallmark of amyotrophic lateral sclerosis (ALS) and other neurodegenerative diseases. Using yeast and mammalian neuronal cells we find that Hsp90 and its co-chaperone Sti1 have the capacity to alter TDP-43 misfolding, inclusion formation, aggregation, and cellular toxicity. Our data also demonstrate that impaired Hsp90 function sensitizes cells to TDP-43 toxicity and that Sti1 specifically interacts with and strongly modulates TDP-43 toxicity in a dose-dependent manner. Our study thus uncovers a previously unrecognized tie between Hsp90, Sti1, TDP-43 misfolding, and cellular toxicity.

Aha1 Exhibits Distinctive Dynamics Behavior and Chaperone-Like Activity

Aha1 is the only co-chaperone known to strongly stimulate the ATPase activity of Hsp90. Meanwhile, besides the well-studied co-chaperone function, human Aha1 has also been demonstrated to exhibit chaperoning activity against stress-denatured proteins. To provide structural insights for a better understanding of Aha1's co-chaperone and chaperone-like activities, nuclear magnetic resonance (NMR) techniques were used to reveal the unique structure and internal dynamics features of full-length human Aha1. We then found that, in solution, both the two domains of Aha1 presented distinctive thermal stabilities and dynamics behaviors defined by their primary sequences and three-dimensional structures. The low thermal stability (melting temperature of Aha1^28-162: 54.45 °C) and the internal dynamics featured with slow motions on the µs-ms time scale were detected for Aha1's N-terminal domain (Aha1N). The aforementioned experimental results suggest that Aha1N is in an energy-unfavorable state, which would therefore thermostatically favor the interaction of Aha1N with its partner proteins such as Hsp90's middle domain. Differently from Aha1N, Aha1C (Aha1's C-terminal domain) exhibited enhanced thermal stability (melting temperature of Aha1^204-335: 72.41 °C) and the internal dynamics featured with intermediate motions on the ps-ns time scale. Aha1C's thermal and structural stabilities make it competent for the stabilization of the exposed hydrophobic groove of dimerized Hsp90's N-terminal domain. Of note, according to the NMR data and the thermal shift results, although the very N-terminal region (M1-W27) and the C-terminal relaxin-like factor (RLF) motif showed no tight contacts with the remaining parts of human Aha1, they were identified to play important roles in the recognition of intrinsically disordered pathological α-synuclein.

AHA1 upregulates IDH1 and metabolic activity to promote growth and metastasis and predicts prognosis in osteosarcoma

Osteosarcoma (OS) is the most common primary malignant bone tumor in children and adolescents. Although activator of HSP90 ATPase activity 1 (AHA1) is reported to be a potential oncogene, its role in osteosarcoma progression remains largely unclear. Since metabolism reprogramming is involved in tumorigenesis and cancer metastasis, the relationship between AHA1 and cancer metabolism is unknown. In this study, we found that AHA1 is significantly overexpressed in osteosarcoma and related to the prognosis of osteosarcoma patients. AHA1 promotes the growth and metastasis of osteosarcoma both in vitro and in vivo. Mechanistically, AHA1 upregulates the metabolic activity to meet cellular bioenergetic needs in osteosarcoma. Notably, we identified that isocitrate dehydrogenase 1 (IDH1) is a novel client protein of Hsp90-AHA1. Furthermore, the IDH1 protein level was positively correlated with AHA1 in osteosarcoma. And IDH1 overexpression could partially reverse the effect of AHA1 knockdown on cell growth and migration of osteosarcoma. Moreover, high IDH1 level was also associated with poor prognosis of osteosarcoma patients. This study demonstrates that AHA1 positively regulates IDH1 and metabolic activity to promote osteosarcoma growth and metastasis, which provides novel prognostic biomarkers and promising therapeutic targets for osteosarcoma patients.

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.

Management of Hsp90-Dependent Protein Folding by Small Molecules Targeting the Aha1 Co-Chaperone

Hsp90 plays an important role in health and is a therapeutic target for managing misfolding disease. Compounds that disrupt co-chaperone delivery of clients to Hsp90 target a subset of Hsp90 activities, thereby minimizing the toxicity of pan-Hsp90 inhibitors. Here, we have identified SEW04784 as a first-in-class inhibitor of the Aha1-stimulated Hsp90 ATPase activity without inhibiting basal Hsp90 ATPase. Nuclear magnetic resonance analysis reveals that SEW84 binds to the C-terminal domain of Aha1 to weaken its asymmetric binding to Hsp90. Consistent with this observation, SEW84 blocks Aha1-dependent Hsp90 chaperoning activities, including the in vitro and in vivo refolding of firefly luciferase, and the transcriptional activity of the androgen receptor in cell-based models of prostate cancer and promotes the clearance of phosphorylated tau in cellular and tissue models of neurodegenerative tauopathy. We propose that SEW84 provides a novel lead scaffold for developing therapeutic approaches to treat proteostatic disease.

Therapeutic Potential of the Hsp90/Cdc37 Interaction in Neurodegenerative Diseases

Alzheimer's, Huntington's, and Parkinson's are devastating neurodegenerative diseases that are prevalent in the aging population. Patient care costs continue to rise each year, because there is currently no cure or disease modifying treatments for these diseases. Numerous efforts have been made to understand the molecular interactions governing the disease development. These efforts have revealed that the phosphorylation of proteins by kinases may play a critical role in the aggregation of disease-associated proteins, which is thought to contribute to neurodegeneration. Interestingly, a molecular chaperone complex consisting of the 90 kDa heat shock protein (Hsp90) and Cell Division Cycle 37 (Cdc37) has been shown to regulate the maturation of many of these kinases as well as regulate some disease-associated proteins directly. Thus, the Hsp90/Cdc37 complex may represent a potential drug target for regulating proteins linked to neurodegenerative diseases, through both direct and indirect interactions. Herein, we discuss the broad understanding of many Hsp90/Cdc37 pathways and how this protein complex may be a useful target to regulate the progression of neurodegenerative disease.

Gradual and Acute Temperature Rise Induces Crossing Endocrine, Metabolic, and Immunological Pathways in Maraena Whitefish (Coregonus maraena)

The complex and still poorly understood nature of thermoregulation in various fish species complicates the determination of the physiological status on the basis of diagnostic marker genes and indicative molecular pathways. The present study aimed to compare the physiological impacts of both gradual and acute temperature rise from 18 to 24°C on maraena whitefish in aquaculture. Microarray-based transcriptome profiles in the liver, spleen and kidney of heat-stressed maraena whitefish revealed the modulation of a significantly higher number of genes in those groups exposed to gradually rising temperatures compared with the acutely stressed groups, which might reflect early adaptation mechanisms. Moreover, we suggest a common set of 11 differentially expressed genes that indicate thermal stress induced by gradual or acute temperature rise in the three selected tissues. Besides the two pathways regulated in both data sets unfolded protein response and aldosterone signaling in epithelial cells, we identified unique tissue- and stress type-specific pathways reflecting the crossroads between signal transduction, metabolic and immunologic pathways to cope with thermal stress. In addition, comparing lists of differentially regulated genes with meta-analyzed published data sets revealed that “acute temperature rise”-responding genes that encode members of the HSP70, HSP90, and HSP40 families; their functional homologs; co-chaperones and stress-signal transducers are well-conserved across different species, tissues and/or cell types and experimental approaches.

Hsp90 inhibitors radicicol and geldanamycin have opposing effects on Leishmania Aha1-dependent proliferation

Hsp90 and its co-chaperones are essential for the medically important parasite Leishmania donovani, facilitating life cycle control and intracellular survival. Activity of Hsp90 is regulated by co-chaperones of the Aha1 and P23 families. In this paper, we studied the expression of L. donovani Aha1 in two life cycle stages, its interaction with Hsp90 and the phenotype of Aha1 null mutants during the insect stage and inside infected macrophages. This study provides a detailed in vitro analysis of the function of Aha1 in Leishmania parasites and the first instance of a reverse genetic analysis of Aha1 in a protozoan parasite. While Aha1 is non-essential under standard growth conditions and at elevated temperature, Aha1 protects against ethanol stress. However, both overexpression and lack of Aha1 affected parasite growth in the presence of the Hsp90 inhibitors radicicol (RAD) and geldanamycin (GA). Under RAD pressure, P23 and Aha1 act in an antagonistic way. By contrast, expression levels of both co-chaperones have similar effects under GA treatment, indicating different inhibition mechanisms by the two compounds. Aha1 is also secreted in virulence-enhancing exosomes. This may explain why the loss of Aha1 reduces the infectivity of L. donovani in ex vivo mouse macrophages, indicating a role during the intracellular mammalian stage.

Identifying Inhibitors of the Hsp90-Aha1 Protein Complex, a Potential Target to Drug Cystic Fibrosis, by Alpha Technology

Deletion of a single phenylalanine residue at position 508 of the protein CFTR (cystic fibrosis transmembrane conductance regulator), a chloride channel in lung epithelium, is the most common cause for cystic fibrosis. As a consequence, folding of the CFTRΔF508 protein and delivery to the cell surface are compromised, resulting in degradation of the polypeptide. Accordingly, decreased surface presence of CFTRΔF508 causes impaired chloride ion conductivity and is associated with mucus accumulation, a hallmark of cystic fibrosis. Molecular chaperones such as Hsp90 and its co-chaperone partner Aha1 are thought to play a key role in targeting folding-deficient CFTRΔF508 for degradation. Thus, pharmacologic manipulation to inhibit Hsp90-Aha1 chaperone complex formation appears beneficial to inhibit proteolysis of CFTRΔF508 and rescue its residual chloride channel activity. Therefore, we have screened a collection of 14,400 druglike chemical compounds for inhibitors of the Hsp90-Aha1 complex by amplified luminescence proximity homogeneous assay (Alpha). We identified two druglike molecules that showed promising results when we tested their ability to restore chloride channel activity in culture cells expressing the mutant CFTRΔF508 protein. The two molecules were most effective in combination with the corrector VX-809 and may therefore serve as a lead compound that can be further developed into a drug to treat cystic fibrosis patients.