Hsp90: a specialized but essential protein-folding tool

Overexpression of SlHSP90.2 leads to altered root biomass and architecture in tomato (Solanum lycopersicum)

The Heat shock proteins 90 family plays pivotal roles in root growth and plant development. Its isoforms have been identified in several plant species with transcripts presents in almost all stages of plant growth. However, its functional relevance has not been completely established. Therefore, in this study, we provide evidence about the role of SlHSP90.2 in tomato (Solanum lycopersicum) root development. Using tomato cultivars with differing root phenotypes, we have shown that SlHSP90.2 transcripts are in accordance with root architecture, i.e. high rooting cultivars had more expression of SlHSP90.2 as compared to low rooting cultivars. Moreover, overexpression of SlHSP90.2 gene in transgenic tomato plants showed significant increase in root biomass and architecture, as evident from the analysis of fresh and dry weights of root and shoot samples, primary root length and length and number of lateral roots. The transgenic lines are also more tolerant to salinity and drought stresses. The results of the present study suggest that genetic manipulation of HSP90.2 homologs in other crops can offer promising leads to develop plant with better root biomass and architecture and improved agronomics traits, like better water and mineral absorption, salinity and drought tolerance potential.

Clinical Significance of Monitoring Circulating Free DNA and Plasma Heat Shock Protein 90alpha in Patients with Esophageal Squamous Cell Carcinoma

Background

Esophageal squamous cell carcinoma (ESCC) is the predominant histological type of esophageal cancer in China and has an extremely poor prognosis. Circulating free DNA (cfDNA) and plasma heat shock protein 90alpha (Hsp90a) are two novel noninvasive biomarkers for diagnosis and prognostic prediction of several types of cancer. However, to the best of our knowledge, the roles of the two biomarkers in ESCC are still unknown.

Methods

Here, we recruited 93 primary ESCC patients and detected plasma concentrations of the two markers at different time points, including 1-3 days pre-chemotherapy, 1-7 days pre-surgery and 7-14 days post-surgery. Baseline concentrations of the two markers were associated with main characteristics of ESCC patients which were collected at first diagnosis. Correlation between the two markers and traditional serum biomarkers at baseline was also examined. Furthermore, dynamic changes of the cfDNA and Hsp90α concentrations among different time points and the potential clinical significance were assessed.

Results

Consequently, there was no significant association between baseline concentrations of the two markers and clinical features. Especially, cfDNA demonstrated stronger correlation with other circulating biomarkers than Hsp90α at baseline level. Importantly, both cfDNA and Hsp90α concentrations were significantly increased after surgery. Kaplan-Meier survival analysis showed that a change in concentration of cfDNA (ΔcfDNA) but not Hsp90α (ΔHSP90ɑ) between pre-surgery and post-surgery had significant effect on the overall survival of surgical patients with ESCC.

Conclusion

Thus, ΔcfDNA evaluation could be a promising prognostic marker for surgical ESCC patients. Our findings may improve the understanding of the function of cfDNA and Hsp90α in ESCC.

Genome-Wide Characterization of HSP90 Gene Family in Cucumber and Their Potential Roles in Response to Abiotic and Biotic Stresses

Heat shock protein 90 (HSP90) possesses critical functions in plant developmental control and defense reactions. The HSP90 gene family has been studied in various plant species. However, the HSP90 gene family in cucumber has not been characterized in detail. In this study, a total of six HSP90 genes were identified from the cucumber genome, which were distributed to five chromosomes. Phylogenetic analysis divided the cucumber HSP90 genes into two groups. The structural characteristics of cucumber HSP90 members in the same group were similar but varied among different groups. Synteny analysis showed that only one cucumber HSP90 gene, Csa1G569290, was conservative, which was not collinear with any HSP90 gene in Arabidopsis and rice. The other five cucumber HSP90 genes were collinear with five Arabidopsis HSP90 genes and six rice HSP90 genes. Only one pair of paralogous genes in the cucumber HSP90 gene family, namely one pair of tandem duplication genes (Csa1G569270/Csa1G569290), was detected. The promoter analysis showed that the promoters of cucumber HSP90 genes contained hormone, stress, and development-related cis-elements. Tissue-specific expression analysis revealed that only one cucumber HSP90 gene Csa3G183950 was highly expressed in tendril but low or not expressed in other tissues, while the other five HSP90 genes were expressed in all tissues. Furthermore, the expression levels of cucumber HSP90 genes were differentially induced by temperature and photoperiod, gibberellin (GA), downy mildew, and powdery mildew stimuli. Two cucumber HSP90 genes, Csa1G569270 and Csa1G569290, were both differentially expressed in response to abiotic and biotic stresses, which means that these two HSP90 genes play important roles in the process of cucumber growth and development. These findings improve our understanding of cucumber HSP90 family genes and provide preliminary information for further studies of cucumber HSP90 gene functions in plant growth and development.

A Novel Mechanism of 17-AAG Therapeutic Efficacy on HSP90 Inhibition in MYCN-Amplified Neuroblastoma Cells

Background

Neuroblastoma is the most common pediatric extra-cranial nervous system tumor, originating from neural crest elements and giving rise to tumors in the adrenal medulla and sympathetic chain ganglia. Amplification of MYCN confers increased malignancy and poorer prognosis in high-risk neuroblastoma. Our SILAC proteomics analysis revealed over-expression of HSP90 in MYCN-amplified IMR-32 compared to the non-MYCN amplified SK-N-SH human neuroblastoma cells, rendering them highly resistant to therapeutic intervention.

Methods

We used cellular bio-functional (proliferation, migration/invasion, apoptosis, viability and stem-cell self-renewal) assays and Western blot analysis to elucidate the therapeutic efficacy of HSP90 inhibition with 17-AAG.

Results

17-AAG treatment significantly inhibited cellular proliferation, viability and migration/invasion and increased apoptosis in both cell lines. Moreover, drug treatment significantly abrogated stem-cell self-renewal potential in the MYCN-amplified IMR-32 cells. Differential tumorigenic protein expression revealed a novel mechanism of therapeutic efficacy after 17-AAG treatment with a significant downregulation of HMGA1, FABP5, Oct4, MYCN, prohibitin and p-L1CAM in SK-N-SH cells. However, we observed a significant up-regulation of p-L1CAM, MYCN and prohibitin, and significant down-regulation of Oct4, FABP5, HMGA1, p-ERK, cleaved/total caspase-3 and PARP1 in IMR-32 cells.

Conclusions

HSP90 inhibition revealed a novel therapeutic mechanism of antitumor activity in MYCN-amplified neuroblastoma cells that may enhance therapeutic sensitivity.

Full-Length Transcriptome Analysis of Four Different Tissues of Cephalotaxus oliveri

Cephalotaxus oliveri is a tertiary relict conifer endemic to China, regarded as a national second-level protected plant in China. This species has experienced severe changes in temperature and precipitation in the past millions of years, adapting well to harsh environments. In view of global climate change and its endangered conditions, it is crucial to study how it responds to changes in temperature and precipitation for its conservation work. In this study, single-molecule real-time (SMRT) sequencing and Illumina RNA sequencing were combined to generate the complete transcriptome of C. oliveri. Using the RNA-seq data to correct the SMRT sequencing data, the four tissues obtained 63,831 (root), 58,108 (stem), 33,013 (leaf) and 62,436 (male cone) full-length unigenes, with a N50 length of 2523, 3480, 3181, and 3267 bp, respectively. Additionally, 35,887, 11,306, 36,422, and 25,439 SSRs were detected for the male cone, leaf, root, and stem, respectively. The number of long non-coding RNAs predicted from the root was the largest (11,113), and the other tissues were 3408 (stem), 3193 (leaf), and 3107 (male cone), respectively. Functional annotation and enrichment analysis of tissue-specific expressed genes revealed the special roles in response to environmental stress and adaptability in the different four tissues. We also characterized the gene families and pathways related to abiotic factors. This work provides a comprehensive transcriptome resource for C. oliveri, and this resource will facilitate further studies on the functional genomics and adaptive evolution of C. oliveri.

Characterization of the interactome of c-Src within the mitochondrial matrix by proximity-dependent biotin identification

C-Src kinase is localized in several subcellular compartments, including mitochondria where it is involved in the regulation of organelle functions and overall metabolism. Surprisingly, the characterization of the intramitochondrial Src interactome has never been fully determined. Using in vitro proximity-dependent biotin identification (BioID) coupled to mass spectrometry, we identified 51 candidate proteins that may interact directly or indirectly with c-Src within the mitochondrial matrix. Pathway analysis suggests that these proteins are involved in a large array of mitochondrial functions such as protein folding and import, mitochondrial organization and transport, oxidative phosphorylation, tricarboxylic acid cycle and metabolism of amino and fatty acids. Among these proteins, we identified 24 tyrosine phosphorylation sites in 17 mitochondrial proteins (AKAP1, VDAC1, VDAC2, VDAC3, LonP1, Hsp90, SLP2, PHB2, MIC60, UBA1, EF-Tu, LRPPRC, ACO2, OAT, ACAT1, ETFβ and ATP5β) as potential substrates for intramitochondrial Src using in silico prediction of tyrosine phospho-sites. Interaction of c-Src with SLP2 and ATP5β was confirmed using coimmunoprecipitation. This study suggests that the intramitochondrial Src could target several proteins and regulate different mitochondrial functions.

Chronic exposure to environmental cadmium affects growth and survival, cellular stress, and glucose metabolism in juvenile channel catfish (Ictalurus punctatus)

Anthropogenic activities have led to the enrichment of cadmium in freshwater systems where it is a contaminant of concern for fisheries and aquaculture as it has no known biological function and is toxic at trace concentrations. Yet, knowledge gaps remain regarding effects of chronic exposure to environmentally relevant concentrations on freshwater fish. Thus, the objectives of the current study were to assess chronic impacts of cadmium on channel catfish (Ictalurus punctatus) including how tissue-specific bioaccumulation patterns relate to functions of those tissues over time. We focused on liver and kidneys, and expression of genes related to cellular stress, glucose metabolism, and steroidogenesis. Catfish were exposed to concentrations of 0.5 (control), 2 (low), and 6 (high) μg L^-1 Cd from fertilization to six months. Cadmium exposure negatively impacted channel catfish growth and was linked to bioaccumulation of tissue Cd, which followed a dose-related response, where concentrations in trunk kidney > liver = head kidney >> muscle. Differences in tissue Ca, Cu, Fe, and Zn concentrations were also observed between treatments. Following 3 months of exposure, expression of metallothionein (MT) and heat shock proteins (HSP) 70 & 90 increased relative to controls; however, no differences were detected at 6 months, suggesting compensation. Conversely, there were no differences in expression patterns for key genes in steroidogenesis, steroidogenic factor 1 (SF1), steroidogenic acute regulatory protein (StAR), and cytochrome P450scc (P450), which supports the observation that Cd did not affect the secondary stress response, evaluated via plasma cortisol and glucose concentrations following a low water stress event. As a function of length and weight, the high Cd treatment yielded fish that were significantly smaller than controls. In addition to the cellular responses in MT and HSPs noted, reduced growth in the high Cd treatment was likely due, at least in part, to elevated energetic demands. This is supported by observations of the upregulation of genes necessary for glucose metabolism. Hexokinase (HK), glucose-6-phosphatase (G6P), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were significantly elevated in the high treatment relative to controls at 3 months of exposure. Over the study period, exposure also reduced survival of channel catfish from 3 to 6 months. Reduced fitness, as a consequence of cadmium exposure, could be visible at the population level through altered life histories and growth patterns.

Grapevine Responses to Heat Stress and Global Warming

The potential effects of the forthcoming climate change include the rising of the average annual temperature and the accumulation of extreme weather events, like frequent and severe heatwaves, a phenomenon known as global warming. Temperature is an important environmental factor affecting almost all aspects of growth and development in plants. The grapevine (Vitis spp.) is quite sensitive to extreme temperatures. Over the current century, temperatures are projected to continue rising with negative impacts on viticulture. These consequences range from short-term effects on wine quality to long-term issues such as the suitability of certain varieties and the sustainability of viticulture in traditional wine regions. Many viticultural zones, particularly in Mediterranean climate regions, may not be suitable for growing winegrapes in the near future unless we develop heat-stress-adapted genotypes or identify and exploit stress-tolerant germplasm. Grapevines, like other plants, have developed strategies to maintain homeostasis and cope with high-temperature stress. These mechanisms include physiological adaptations and activation of signaling pathways and gene regulatory networks governing heat stress response and acquisition of thermotolerance. Here, we review the major impacts of global warming on grape phenology and viticulture and focus on the physiological and molecular responses of the grapevine to heat stress.

Genome-wide analysis of HSP90 gene family in the Mediterranean olive (Olea europaea subsp. europaea) provides insight into structural patterns, evolution and functional diversity

Plants regularly experience multiple abiotic and biotic pressures affecting their normal development. The 90-kDa heat shock protein (HSP90) plays a dynamic role in countering abiotic and biotic stresses via a plethora of functional mechanisms. The HSP90 has been investigated in many plant species. However, there is little information available about this gene family in the cultivated Mediterranean olive tree, Olea europaea subsp. europaea var. europaea. In the current study, we systematically performed genome-wide identification and characterization of the HSP90 gene family in O. europaea var. europaea (OeHSP90s). Twelve regular OeHSP90s were identified, which were phylogenetically grouped into two major clusters and four sub-clusters, showing five paralogous gene pairs evolving under purifying selection. All of the 12 proteins contained a Histidine kinase-like ATPase (HATPase_c) domain, justifying the role played by HSP90 proteins in ATP binding and hydrolysis. The predicted 3D structure of OeHSP90 proteins provided information to understand their functions at the biochemical level. Consistent with their phylogenetic relationships, OeHSP90 members were predicted to be localized in different cellular compartments, suggesting their involvement in various subcellular processes. In consonance with their spatial organization, olive HSP90 family members were found to share similar motif arrangements and similar number of exons. We found that OeHSP90 promoters contained various cis-acting elements associated with light responsiveness, hormone signaling pathways and reaction to various stress conditions. In addition, expression sequence tags (ESTs) analysis offered a view of OeHSP90 tissue- and developmental stage specific pattern of expression. Proteins interacting with OeHSP90s were predicted and their potential roles were discussed. Overall, our results offer premises for further investigation of the implication of HSP90 genes in the physiological processes of the olive and its adaptation to stresses.

Genome Wide Analysis of Citrus sinensis Heat Shock Proteins

Background

Plant and animal cells possess a ubiquitous protein known as heat shock proteins (HSPs). Hsps were originally described in relation to heat shock and against abiotic and biotic stresses. Heat shock protein was classified in other crops on the bases of single classes or all classes but in Citrus sinensis Hsps groups, classes, subfamilies and members were not classified and characterized up to our knowledge.

Objectives

Present study was focused on the identification and grouping of C. sinensis Hsps (CsHsps) classes, members among classes, their phylogenetic relationship, gene structure, conserved motifs and identification of proteins by using bioinformatics tools and analyses.

Materials and Methods

Genomic, Peptide and CDS sequences of CsHsps were downloaded from phytozome. MEGA 7 used for the phylogenetic analysis, GSDS for gene structure, UGENE for the multiple sequence alignment and MEME suite for the conserved motif analysis.

Results

The genome size of C. sinensis was 367 Mb, Chromosome number (2n)18, having 151 Hsps with six groups CsHsp10, 20, 40, 60,70 and 90. CsHsp20 was the largest group having 54 members, followed by CsHsp60 and CsHsp70 both having 30 members respectively.

Conclusion

CsHsps members within a class shared more similar gene and protein structure. CsHsp 60, CsHsp 70 and CsHsp90 shared more conserved and similar amino acid pattern. Each class had some important proteins such as Cpn in CsHsp10, Hypothetical proteins in CsHsp20 and 40, Dnak in CsHsp60, Molecular chaperone in CsHsp70 and Hsp90 in CsHsp90. These proteins are produced by cells in response to stresses in citrus. Chaperonins and some hypothetical proteins identified in CsHsps, help in ATP synthesis and protein degradation. This is genome wide analysis and classification sets the groundwork for future investigations to fully characterize functionally the Citrus Hsps families and underscores the relevance of Hsps response to abiotic and biotic stresses in Citrus.

Betaine Supplementation May Improve Heat Tolerance: Potential Mechanisms in Humans

Betaine has been demonstrated to increase tolerance to hypertonic and thermal stressors. At the cellular level, intracellular betaine functions similar to molecular chaperones, thereby reducing the need for inducible heat shock protein expression. In addition to stabilizing protein conformations, betaine has been demonstrated to reduce oxidative damage. For the enterocyte, during periods of reduced perfusion as well as greater oxidative, thermal, and hypertonic stress (i.e., prolonged exercise in hot-humid conditions), betaine results in greater villi length and evidence for greater membrane integrity. Collectively, this reduces exercise-induced gut permeability, protecting against bacterial translocation and endotoxemia. At the systemic level, chronic betaine intake has been shown to reduce core temperature, all-cause mortality, markers of inflammation, and change blood chemistry in several animal models when exposed to heat stress. Despite convincing research in cell culture and animal models, only one published study exists exploring betaine's thermoregulatory function in humans. If the same premise holds true for humans, chronic betaine consumption may increase heat tolerance and provide another avenue of supplementation for those who find that heat stress is a major factor in their work, or training for exercise and sport. Yet, this remains speculative until data demonstrate such effects in humans.

Immune Responses of Asian Seabass Lates calcarifer to Dietary Glycyrrhiza uralensis

To understand the impacts of dietary Glycyrrhiza uralensis on the immune responses of Lates calcarifer, the expression of immune-related genes including crp, c-3, c-4, mtor, mlst-8, eif4e, hsp-70, hsp-90, il-8il-8, il-10, tgfβ1, tnf, ifn-γ1, and mxf in L. calcarifer juveniles was evaluated in this study. Fish were fed experimental diets with G. uralensis levels of 0%, 1%, 3%, and 5% for 56 days. The results showed that dietary G. uralensis could improve the growth and survival of L. calcarifer and regulate the immune-related genes' expression in L. calcarifer. Dietary G. uralensis significantly upregulated the expression level of crp, mtor, hsp-90, c-3, and c-4 genes in the liver of L. calcarifer, while hsp-70 gene expression was nearly downregulated. It did not upregulate the expression of elf4e and mlst-8 in the 1% and 3% inclusion groups, but it was the exact opposite in the 5% inclusion group. G. uralensis significantly affected the expression of il-8, il-10, tnf, ifn-γ1, mxf, and tgfβ1 in the head kidney of L. calcarifer. G. uralensis upregulated the expression of tnf and tgfβ1 consistently, but ifn-γ1 was at a low expression level. The expression of il-8 and il-10 was upregulated in the 1% group, while it was downregulated in the 5% group. The results from the present study indicate that dietary G. uralensis appeared to improve the immune function of L. calcarifer, and the optimum inclusion level should be between 1-3%.

Evolutionary history of the heat shock protein 90 (Hsp90) family of 43 plants and characterization of Hsp90s in Solanum tuberosum

Heat shock protein 90 genes/proteins (Hsp90s) are related to the stress resistance found in various plant species. These proteins affect the growth and development of plants and have important effects on the plants under various stresses (cold, drought and salt) in the environment. In this study, we identified 334 Hsp90s from 43 plant species, and Hsp90s were found in all species. Phylogenetic tree and conserved domain database analysis of all Hsp90s showed three independent clades. The analysis of motifs, gene duplication events, and the expression data from PGSC website revealed the gene structures, evolution relationships, and expression patterns of the Hsp90s. In addition, analysis of the transcript levels of the 7 Hsp90s in potato (Solanum tuberosum) under low temperature and high temperature stresses showed that these genes were related to the temperature stresses. Especially StHsp90.2 and StHsp90.4, under high or low temperature conditions, the expression levels in leaves, stems, or roots were significantly up-regulated. Our findings revealed the evolution of the Hsp90s, which had guiding significance for further researching the precise functions of the Hsp90s.

Genome-wide association studies of Ca and Mn in the seeds of the common bean (Phaseolus vulgaris L.)

SNP markers linked to genes controlling Ca and Mn uptake were identified in the common bean seeds using DArT-based association mapping (AM). The Ca concentration in the seeds varied between 475 and 3,100 mg kg^-1 with an average of 1,280.9 mg kg^-1 and the Mn concentration ranged from 4.87 to 27.54 mg kg^-1 with a mean of 11.76 mg kg^-1. A total of 19,204 SNP markers were distributed across 11 chromosomes that correspond to the haploid genome number of the common bean. The highest value of ΔK was determined as K = 2, and 173 common bean genotypes were split into two main subclusters as POP1 (Mesoamerican) and POP2 (Andean). The results of the UPGMA dendrogram and PCA confirmed those of STRUCTURE analysis. MLM based on the Q + K model identified a large number of markers-trait associations. Of the 19,204 SNPs, five (on Pv2, 3, 8, 10 and 11) and four (on Pv2, 3, 8 and 11) SNPs were detected to be significantly related to the Ca content of the beans grown in Bornova and Menemen, respectively in 2015. In 2016, six SNPs (on Pv1-4, 8 and 10) were identified to be significantly associated with the Ca content of the seeds obtained from Bornova and six SNPs (on Pv1-4, 8 and 10) from Menemen. Eight (on Pv3, 5 and 11) and four (on Pv2, 5 and 11) SNPs had a significant association with Mn content in Bornova in 2015 and 2016, respectively. In Menemen, eight (on Pv3, 5, 8 and 11) and 11 (on Pv1, 2, 5, 10 and 11) SNPs had a significant correlation with Mn content in 2015 and 2016, respectively.

Dynamic proteomic analysis of Phanerochaete chrysosporium under copper stress

The model white rot fungus Phanerochaete chrysosporium is frequently preferred for heavy metal accumulation studies due to its high resistance to heavy metals, including copper (Cu). Here, the response of P. chrysosporium under Cu stress at different time points was investigated for the first time by a detailed proteomic analysis using 2DE MALDI-TOF/MS and nanoLC-MS/MS techniques. A total of 123 Cu-responsive protein spots were determined using 2DE approach, and 104 of them were corresponded to 73 distinct open reading frames (ORFs). Of identified ones, 88 spots were over-, and 16 spots were underrepresented. The majority of these proteins showed to the strongest response at 8th h of Cu exposure. Using nanoLC-MS/MS analysis, a total of 167 differentially produced proteins were identified from Cu-exposed cultures after enrichment of the membrane proteins followed by SILAC. Seventy four, 66, and 69 overrepresented, and 56, 71, and 64 underrepresented proteins were identified at 2 h, 4 h, and 8 h of Cu exposure, respectively. The bioinformatic analysis of these proteins revealed that intracellular trafficking proteins such as Ran GTPase and a p24 family protein, and certain proteins involved in posttranslational modification, protein turnover and folding were Cu-responsive. Three important transcription factors (TFs), NAC, BTF3, and homeobox TFs, 40S and 60S ribosomal proteins, chaperones such as Hsp26/Hsp42 and mortalin, as well as 20S proteasome, 14-3-3 proteins and Hsp90 involve in Cu-stress response of P. chrysosporium. Moreover, certain elements of translation machinery, the proteins related with aspartate, methionine, and pyruvate metabolisms, transketolase, and trehalase related with carbohydrate metabolism, citrate synthase, fumarase, V-ATPase, and F0F1-type ATPase playing role in energy production and conversion, transport proteins such as multidrug resistance and p24 family proteins as well as actin-related proteins involved in cytoskeleton remodeling were determined to be Cu-responsive. The present proteome analysis revealed that P. chrysosporium mainly regulates translational and posttranslational processes, certain transport processes, many metabolic pathways and cytoskeleton to overcome the Cu-induced oxidative stress.

The molecular chaperone Hsp90 regulates heterochromatin assembly through stabilizing multiple complexes in fission yeast

In the fission yeast Schizosaccharomyces pombe, both RNAi machinery and RNAi-independent factors mediate transcriptional and posttranscriptional silencing and heterochromatin formation. Here, we show that the silencing of reporter genes at major native heterochromatic loci (centromeres, telomeres, mating-type locus and rDNA regions) and an artificially induced heterochromatin locus is alleviated in a fission yeast hsp90 mutant, hsp90-G84C Also, H3K9me2 enrichment at heterochromatin regions, especially at the mating-type locus and subtelomeres, is compromised, suggesting heterochromatin assembly defects. We further discovered that Hsp90 is required for stabilization or assembly of the RNA-induced transcriptional silencing (RITS) and Argonaute siRNA chaperone (ARC) RNAi effector complexes, the RNAi-independent factor Fft3, the shelterin complex subunit Poz1 and the Snf2/HDAC-containing repressor complex (SHREC). Our ChIP data suggest that Hsp90 regulates the efficient recruitment of the methyltransferase/ubiquitin ligase complex CLRC by shelterin to chromosome ends and targeting of the SHREC and Fft3 to mating type locus and/or rDNA region. Finally, our genetic analyses demonstrated that increased heterochromatin spreading restores silencing at subtelomeres in the hsp90-G84C mutant. Thus, this work uncovers a conserved factor critical for promoting RNAi-dependent and -independent heterochromatin assembly and gene silencing through stabilizing multiple effectors and effector complexes.

Multifaceted roles of HEAT SHOCK PROTEIN 90 molecular chaperones in plant development

HEAT SHOCK PROTEINS 90 (HSP90s) are molecular chaperones that mediate correct folding and stability of many client proteins. These chaperones act as master molecular hubs involved in multiple aspects of cellular and developmental signalling in diverse organisms. Moreover, environmental and genetic perturbations affect both HSP90s and their clients, leading to alterations of molecular networks determining respectively plant phenotypes and genotypes and contributing to a broad phenotypic plasticity. Although HSP90 interaction networks affecting the genetic basis of phenotypic variation and diversity have been thoroughly studied in animals, such studies are just starting to emerge in plants. Here, we summarize current knowledge and discuss HSP90 network functions in plant development and cellular homeostasis.

S100A6 is a critical regulator of hematopoietic stem cells

The fate options of hematopoietic stem cells (HSCs) include self-renewal, differentiation, migration, and apoptosis. HSCs self-renewal divisions in stem cells are required for rapid regeneration during tissue damage and stress, but how precisely intracellular calcium signals are regulated to maintain fate options in normal hematopoiesis is unclear. S100A6 knockout (KO) HSCs have reduced total cell numbers in the HSC compartment, decreased myeloid output, and increased apoptotic HSC numbers in steady state. S100A6KO HSCs had impaired self-renewal and regenerative capacity, not responding to 5-Fluorouracil. Our transcriptomic and proteomic profiling suggested that S100A6 is a critical HSC regulator. Intriguingly, S100A6KO HSCs showed decreased levels of phosphorylated Akt (p-Akt) and Hsp90, with an impairment of mitochondrial respiratory capacity and a reduction of mitochondrial calcium levels. We showed that S100A6 regulates intracellular and mitochondria calcium buffering of HSC upon cytokine stimulation and have demonstrated that Akt activator SC79 reverts the levels of intracellular and mitochondrial calcium in HSC. Hematopoietic colony-forming activity and the Hsp90 activity of S100A6KO are restored through activation of the Akt pathway. We show that p-Akt is the prime downstream mechanism of S100A6 in the regulation of HSC self-renewal by specifically governing mitochondrial metabolic function and Hsp90 protein quality.

Selective Autophagy Maintains the Aryl Hydrocarbon Receptor Levels in HeLa Cells: A Mechanism That Is Dependent on the p23 Co-Chaperone

The aryl hydrocarbon receptor (AHR) is an environmental sensing molecule which impacts diverse cellular functions such as immune responses, cell growth, respiratory function, and hematopoietic stem cell differentiation. It is widely accepted that the degradation of AHR by 26S proteasome occurs after ligand activation. Recently, we discovered that HeLa cells can modulate the AHR levels via protein degradation without exogenous treatment of a ligand, and this degradation is particularly apparent when the p23 content is down-regulated. Inhibition of autophagy by a chemical agent (such as chloroquine, bafilomycin A1, or 3-methyladenine) increases the AHR protein levels in HeLa cells whereas activation of autophagy by short-term nutrition deprivation reduces its levels. Treatment of chloroquine retards the degradation of AHR and triggers physical interaction between AHR and LC3B. Knockdown of LC3B suppresses the chloroquine-mediated increase of AHR. Down-regulation of p23 promotes AHR degradation via autophagy with no change of the autophagy-related gene expression. Although most data in this study were derived from HeLa cells, human lung (A549), liver (Hep3B), and breast (T-47D and MDA-MB-468) cells also exhibit AHR levels sensitive to chloroquine treatment and AHR-p62/LC3 interactions. Here we provide evidence supporting that AHR undergoes the p62/LC3-mediated selective autophagy in HeLa cells.

Antibodies to Heat Shock Proteins 90α and 90β in Psoriasis

One of many hypotheses of psoriasis pathogenesis supposes an overexpression of heat shock proteins (Hsps) in different skin layers and systemic immunologic response to them. Hsp90 is one of the most abundant chaperone in eukaryotic cells. The number of studies concerning the role of Hsp90 and anti-Hsp90 antibodies in etiopathogenesis of various diseases is also constantly expanding. Still, there are not many reports concerning potential involvement of this Hsp family or anti-Hsp90 immunization in pathomechanism of psoriasis. The aim of the study was the estimation of anti-Hsp90α and anti-Hsp90β IgG antibodies in the sera of the psoriatic patients at different phases of disease activity in comparison to the sera of healthy individuals. The study material consisted of sera from psoriasis patients (n = 80) in active phase and in the remission phase and healthy individuals (n = 80). Concentrations of anti-Hsp90α and anti-Hsp90β IgG antibodies were determined using ELISA technique. In the patients with psoriasis (both in the active phase of the disease and in the remission phase) concentrations of anti-Hsp90α antibodies were significantly higher than in healthy individuals and they correlated positively with psoriasis area severity index values. The mean concentrations of anti-Hsp90β antibodies in the psoriatic patients and healthy controls were comparable. The obtained results indicate an existence of increased immunological response to Hsp90α in psoriasis. It may suggest the role of the extracellular form of this chaperone and/or anti-Hsp90α antibodies in etiopathogenesis of this dermatosis. The inhibition of Hsp90α may represent a novel therapeutic approach to treat psoriasis.

Protein Misfolding Diseases and Therapeutic Approaches

Protein folding is the process by which a polypeptide chain acquires its functional, native 3D structure. Protein misfolding, on the other hand, is a process in which protein fails to fold into its native functional conformation. This misfolding of proteins may lead to precipitation of a number of serious diseases such as Cystic Fibrosis (CF), Alzheimer's Disease (AD), Parkinson's Disease (PD), and Amyotrophic Lateral Sclerosis (ALS) etc. Protein Quality-control (PQC) systems, consisting of molecular chaperones, proteases and regulatory factors, help in protein folding and prevent its aggregation. At the same time, PQC systems also do sorting and removal of improperly folded polypeptides. Among the major types of PQC systems involved in protein homeostasis are cytosolic, Endoplasmic Reticulum (ER) and mitochondrial ones. The cytosol PQC system includes a large number of component chaperones, such as Nascent-polypeptide-associated Complex (NAC), Hsp40, Hsp70, prefoldin and T Complex Protein-1 (TCP-1) Ring Complex (TRiC). Protein misfolding diseases caused due to defective cytosolic PQC system include diseases involving keratin/collagen proteins, cardiomyopathies, phenylketonuria, PD and ALS. The components of PQC system of Endoplasmic Reticulum (ER) include Binding immunoglobulin Protein (BiP), Calnexin (CNX), Calreticulin (CRT), Glucose-regulated Protein GRP94, the thiol-disulphide oxidoreductases, Protein Disulphide Isomerase (PDI) and ERp57. ER-linked misfolding diseases include CF and Familial Neurohypophyseal Diabetes Insipidus (FNDI). The components of mitochondrial PQC system include mitochondrial chaperones such as the Hsp70, the Hsp60/Hsp10 and a set of proteases having AAA+ domains similar to the proteasome that are situated in the matrix or the inner membrane. Protein misfolding diseases caused due to defective mitochondrial PQC system include medium-chain acyl-CoA dehydrogenase (MCAD)/Short-chain Acyl-CoA Dehydrogenase (SCAD) deficiency diseases, hereditary spastic paraplegia. Among therapeutic approaches towards the treatment of various protein misfolding diseases, chaperones have been suggested as potential therapeutic molecules for target based treatment. Chaperones have been advantageous because of their efficient entry and distribution inside the cells, including specific cellular compartments, in therapeutic concentrations. Based on the chemical nature of the chaperones used for therapeutic purposes, molecular, chemical and pharmacological classes of chaperones have been discussed.

Identification of Target Associations for Polypharmacology from Analysis of Crystallographic Ligands of the Protein Data Bank

The design of a chemical entity that potently and selectively binds to a biological target of therapeutic relevance has dominated the scene of drug discovery so far. However, recent findings suggest that multitarget ligands may be endowed with superior efficacy and be less prone to drug resistance. The Protein Data Bank (PDB) provides experimentally validated structural information about targets and bound ligands. Therefore, it represents a valuable source of information to help identifying active sites, understanding pharmacophore requirements, designing novel ligands, and inferring structure-activity relationships. In this study, we performed a large-scale analysis of the PDB by integrating different ligand-based and structure-based approaches, with the aim of identifying promising target associations for polypharmacology based on reported crystal structure information. First, the 2D and 3D similarity profiles of the crystallographic ligands were evaluated using different ligand-based methods. Then, activity data of pairs of similar ligands binding to different targets were inspected by comparing structural information with bioactivity annotations reported in the ChEMBL, BindingDB, BindingMOAD, and PDBbind databases. Afterward, extensive docking screenings of ligands in the identified cross-targets were made in order to validate and refine the ligand-based results. Finally, the therapeutic relevance of the identified target combinations for polypharmacology was evaluated from comparison with information on therapeutic targets reported in the Therapeutic Target Database (TTD). The results led to the identification of several target associations with high therapeutic potential for polypharmacology.

Identification of watermelon heat shock protein members and tissue-specific gene expression analysis under combined drought and heat stresses

Heat shock protein (Hsp) gene family members in the watermelon genome were identified and characterized by bioinformatics analysis. In addition, expression profiles of genes under combined drought and heat stress conditions were experimentally analyzed. In the watermelon genome, 39 genes belonging to the sHsp family, 101 genes belonging to the Hsp40 family, 23 genes belonging to the Hsp60 family, 12 genes belonging to the Hsp70 family, 6 genes belonging to the Hsp90 family, and 102 genes belonging to the Hsp100 family were found. It was also observed that the proteins in the same cluster in the phylogenetic trees had similar motif patterns. When the estimated 3-dimensional structures of the Hsp proteins were examined, it was determined that the α-helical structure was dominant in almost all families. The most orthologous relationship appeared to be between watermelon, soybean, and poplar in the ClaHsp gene families. For tissue-specific gene expression analysis under combined stress conditions, expression analysis of one representative Hsp gene each from root, stem, leaf, and shoot tissues was performed by real-time PCR. A significant increase was detected usually at 30 min in almost all tissues. This study provides extensive information for watermelon Hsps, and can enhance our knowledge about the relationships between Hsp genes and combined stresses.

Dietary non-protein energy source regulates antioxidant status and immune response of barramundi (Lates calcarifer)

This study evaluates the effects of different dietary sources of non-protein energy on growth performance, histological structure, antioxidant status and immune response of barramundi Lates calcarifer. Fish were fed with isoenergetic diets (18 kJ/g) with two types of non-protein energy in the experimental groups and a regular diet was used as the control for 56 days. The specific growth rate and survival of fish were not significantly different between experimental diets. Hepatic histology did not reveal significant differences between dietary treatments at cellular level. The activity of most antioxidant enzymes in the lipid group significantly increased, and the antioxidant capacity in the carbohydrate group was significantly higher than that in other treatments. In the TOR pathway, LST8 homolog (mLST8) expression in the high lipid group was downregulated, and the mechanistic target of rapamycin (mTOR) expression in the high carbohydrate group was downregulated and eIF4E expression was upregulated. The C-reactive protein (CRP) expression in the high lipid and high carbohydrate groups was upregulated. The expression levels of heat shock protein genes in the high lipid group and the high carbohydrate group were significantly downregulated. This study indicates that the lipid diet have less effect in fish immunity but is more suitable as a non-protein ingredient for energy supply for barramundi.

Plasmodium falciparum R2TP complex: driver of parasite Hsp90 function

Heat shock protein 90 (Hsp90) is essential for the development of the main malaria agent, Plasmodium falciparum. Inhibitors that target Hsp90 function are known to not only kill the parasite, but also reverse resistance of the parasite to traditional antimalarials such as chloroquine. For this reason, Hsp90 has been tagged as a promising antimalarial drug target. As a molecular chaperone, Hsp90 facilitates folding of proteins such as steroid hormone receptors and kinases implicated in cell cycle and development. Central to Hsp90 function is its regulation by several co-chaperones. Various co-chaperones interact with Hsp90 to modulate its co-operation with other molecular chaperones such as Hsp70 and to regulate its interaction with substrates. The role of Hsp90 in the development of malaria parasites continues to receive research attention, and several Hsp90 co-chaperones have been mapped out. Recently, focus has shifted to P. falciparum R2TP proteins, which are thought to couple Hsp90 to a diverse set of client proteins. R2TP proteins are generally known to form a complex with Hsp90, and this complex drives multiple cellular processes central to signal transduction and cell division. Given the central role that the R2TP complex may play, the current review highlights the structure-function features of Hsp90 relative to R2TPs of P. falciparum.

Medium-Throughput Detection of Hsp90/Cdc37 Protein-Protein Interaction Inhibitors Using a Split Renilla Luciferase-Based Assay

The protein-folding chaperone Hsp90 enables the maturation and stability of various oncogenic signaling proteins and is thus pursued as a cancer drug target. Folding in particular of protein kinases is assisted by the co-chaperone Cdc37. Several inhibitors against the Hsp90 ATP-binding site have been developed. However, they displayed significant toxicity in clinical trials. By contrast, the natural product conglobatin A has an exceptionally low toxicity in mice. It targets the protein-protein interface (PPI) of Hsp90 and Cdc37, suggesting that interface inhibitors have an interesting drug development potential. In order to identify inhibitors of the Hsp90/Cdc37 PPI, we have established a mammalian cell lysate-based, medium-throughput amenable split Renilla luciferase assay. This assay employs N-terminal and C-terminal fragments of Renilla luciferase fused to full-length human Hsp90 and Cdc37, respectively. We expect that our assay will allow for the identification of novel Hsp90/Cdc37 interaction inhibitors. Such tool compounds will help to evaluate whether the toxicity profile of Hsp90/Cdc37 PPI inhibitors is in general more favorable than that of ATP-competitive Hsp90 inhibitors. Further development of such tool compounds may lead to new classes of Hsp90 inhibitors with applications in cancer and other diseases.

Tumour-Secreted Hsp90α on External Surface of Exosomes Mediates Tumour - Stromal Cell Communication via Autocrine and Paracrine Mechanisms

Extracellular heat shock protein-90alpha (eHsp90α) plays an essential role in tumour invasion and metastasis. The plasma eHsp90α levels in patients with various cancers correlate with the stages of the diseases. Nonetheless, the mechanism of action by tumour-secreted eHsp90α remained unclear. Here we show that eHsp90α accounts for approximately 1% of the total cellular Hsp90α and is associated with tumour-secreted exosomes. CRISPR-cas9 knockout of Hsp90α did not affect the overall distribution and quantity of secreted exosomes, but it caused increased exosome-associated CD9 and decreased exosome-associated TSG101, Alix, and CD63. However, Hsp90α-knockout tumour cells have not only lost their own constitutive motility, but also the ability to recruit stromal cells via secreted exosomes. These defects are specifically due to the lack of eHsp90α on tumour cell-secreted exosomes. Anti-Hsp90α antibody nullified the pro-motility activity of tumour-secreted exosomes and human recombinant Hsp90α protein fully rescued the functional defects of eHsp90α-free exosomes. Finally, while current exosome biogenesis models exclusively implicate the luminal location of host cytosolic proteins inside secreted exosomes, we provide evidence for eHsp90α location on the external surface of tumour-secreted exosomes. Taken together, this study elucidates a new mechanism of action by exosome-associated eHsp90α.

Potential role of the heat shock protein 90 (hsp90) in buffering mutations to favour cyclical parthenogenesis in the peach potato aphid Myzus persicae (Aphididae, Hemiptera)

Heat-shock proteins 90 (hsp90s) are a class of molecules able to stabilize a network of 'client' proteins that are involved in several processes. Furthermore, recent studies indicated that mutations in the hsp90-encoding gene induce a wide range of phenotypic abnormalities, which have been interpreted as an increased sensitivity of different developmental pathways to hidden/cryptic mutations. In order to verify the role of hsp90 in aphids, we amplified and sequenced the hsp90 gene in 17 lineages of the peach potato aphid Myzus persicae (Sulzer, 1776) looking for the presence of mutations. In particular, we compared lineages with different reproductive modes (obligate vs. cyclical parthenogenesis), propensity to develop winged females and karyotype stability. Differently from the cyclical parthenogenetic lineages that possessed functional hsp90 genes, the seven analysed asexual lineages showed severe mutations (including frameshift and non-sense mutations). In vivo functional assays with the hsp90-inhibitor geldanamycin showed that some lineages with cyclical parthenogenesis may lose their ability to induce sexuales in the absence of active hsp90 revealing the presence of cryptic mutations in their genomes. As a whole, our data suggest that hsp90 could play in aphids a role in buffering hidden/cryptic mutations that disrupt cyclical parthenogenesis.

Comparative Proteomics and Physiological Analyses Reveal Important Maize Filling-Kernel Drought-Responsive Genes and Metabolic Pathways

Despite recent scientific headway in deciphering maize (Zea mays L.) drought stress responses, the overall picture of key proteins and genes, pathways, and protein-protein interactions regulating maize filling-kernel drought tolerance is still fragmented. Yet, maize filling-kernel drought stress remains devastating and its study is critical for tolerance breeding. Here, through a comprehensive comparative proteomics analysis of filling-kernel proteomes of two contrasting (drought-tolerant YE8112 and drought-sensitive MO17) inbred lines, we report diverse but key molecular actors mediating drought tolerance in maize. Using isobaric tags for relative quantification approach, a total of 5175 differentially abundant proteins (DAPs) were identified from four experimental comparisons. By way of Venn diagram analysis, four critical sets of drought-responsive proteins were mined out and further analyzed by bioinformatics techniques. The YE8112-exclusive DAPs chiefly participated in pathways related to "protein processing in the endoplasmic reticulum" and "tryptophan metabolism", whereas MO17-exclusive DAPs were involved in "starch and sucrose metabolism" and "oxidative phosphorylation" pathways. Most notably, we report that YE8112 kernels were comparatively drought tolerant to MO17 kernels attributable to their redox post translational modifications and epigenetic regulation mechanisms, elevated expression of heat shock proteins, enriched energy metabolism and secondary metabolites biosynthesis, and up-regulated expression of seed storage proteins. Further, comparative physiological analysis and quantitative real time polymerase chain reaction results substantiated the proteomics findings. Our study presents an elaborate understanding of drought-responsive proteins and metabolic pathways mediating maize filling-kernel drought tolerance, and provides important candidate genes for subsequent functional validation.

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.

Genome-wide identification and expression analysis of Hsp70, Hsp90, and Hsp100 heat shock protein genes in barley under stress conditions and reproductive development

Abiotic stress including extreme temperature disturbs the plant cellular homeostasis consequently limiting the yield potential of crop plants. Heat shock proteins (Hsps) are part of major rescue machinery of plants which aid to combat these stressed conditions by re-establishing protein homeostasis. Hsps with their chaperone and co-chaperone mechanisms regulate the activity of their substrate proteins in an ATP-dependent manner. In the present investigation, a genome-wide identification, evolutionary relationship, and comprehensive expression analysis of Hsp70, Hsp90, and Hsp100 gene families have been done in barley. The barley genome possesses 13 members of the Hsp70 gene family, along with 4 members of the Hsp110 subfamily, and 6 members of Hsp90 and 8 members of the Hsp100 gene family. Hsp genes are distributed on all 7 chromosomes of barley, and their encoded protein members are predicted to be localized to cell organelles such as cytosol, mitochondria, chloroplast, and ER. Despite a larger genome size, there are lesser members of these Hsp genes in barley, owing to less duplication events. The variable expression pattern obtained for genes encoding proteins localized to the same subcellular compartment suggests their diverse roles and involvement in different cellular responses. Expression profiling of these genes was performed by qRT-PCR in an array of 32 tissues, which showed a differential and tissue-specific expression of various members of Hsp gene families. We found the upregulation of HvHspc70-4, HvHsp70Mt70-2, HvHspc70-5a, HvHspc70-5b, HvHspc70-N1, HvHspc70-N2, HvHsp110-3, HvHsp90-1, HvHsp100-1, and HvHsp100-2 upon exposure to heat stress during reproductive development. Furthermore, their higher expression during heat stress, heavy metal stress, drought, and salinity stress was also observed in a tissue-specific manner.

Involvement of Hsp90 and cyclophilins in intoxication by AIP56, a metalloprotease toxin from Photobacterium damselae subsp. piscicida

AIP56 (apoptosis inducing protein of 56 kDa) is a key virulence factor secreted by virulent strains of Photobacterium damselae subsp. piscicida (Phdp), a Gram-negative bacterium that causes septicemic infections in several warm water marine fish species. AIP56 is systemically disseminated during infection and induces massive apoptosis of host macrophages and neutrophils, playing a decisive role in the disease outcome. AIP56 is a single-chain AB-type toxin, being composed by a metalloprotease A domain located at the N-terminal region connected to a C-terminal B domain, required for internalization of the toxin into susceptible cells. After binding to a still unidentified surface receptor, AIP56 is internalised through clathrin-mediated endocytosis, reaches early endosomes and translocates into the cytosol through a mechanism requiring endosomal acidification and involving low pH-induced unfolding of the toxin. At the cytosol, the catalytic domain of AIP56 cleaves NF-κB p65, leading to the apoptotic death of the intoxicated cells. It has been reported that host cytosolic factors, including host cell chaperones such as heat shock protein 90 (Hsp90) and peptidyl-prolyl cis/trans isomerases (PPIases), namely cyclophilin A/D (Cyp) and FK506-binding proteins (FKBP) are involved in the uptake of several bacterial AB toxins with ADP-ribosylating activity, but are dispensable for the uptake of other AB toxins with different enzymatic activities, such as Bacillus anthracis lethal toxin (a metalloprotease) or the large glycosylating toxins A and B of Clostridium difficile. Based on these findings, it has been proposed that the requirement for Hsp90/PPIases is a common and specific characteristic of ADP-ribosylating toxins. In the present work, we demonstrate that Hsp90 and the PPIases cyclophilin A/D are required for efficient intoxication by the metalloprotease toxin AIP56. We further show that those host cell factors interact with AIP56 in vitro and that the interactions increase when AIP56 is unfolded. The interaction with Hsp90 was also demonstrated in intact cells, at 30 min post-treatment with AIP56, suggesting that it occurs during or shortly after translocation of the toxin from endosomes into the cytosol. Based on these findings, we propose that the participation of Hsp90 and Cyp in bacterial toxin entry may be more disseminated than initially expected, and may include toxins with different catalytic activities.

HSC70 and HSP90 chaperones perform complementary roles in translocation of the cholera toxin A1 subunit from the endoplasmic reticulum to the cytosol

Cholera toxin (CT) travels by vesicle carriers from the cell surface to the endoplasmic reticulum (ER) where the catalytic A1 subunit of CT (CTA1) dissociates from the rest of the toxin, unfolds, and moves through a membrane-spanning translocon pore to reach the cytosol. Heat shock protein 90 (HSP90) binds to the N-terminal region of CTA1 and facilitates its ER-to-cytosol export by refolding the toxin as it emerges at the cytosolic face of the ER membrane. HSP90 also refolds some endogenous cytosolic proteins as part of a foldosome complex containing heat shock cognate 71-kDa protein (HSC70) and the HSC70/HSP90-organizing protein (HOP) linker that anchors HSP90 to HSC70. We accordingly predicted that HSC70 and HOP also function in CTA1 translocation. Inactivation of HSC70 by drug treatment disrupted CTA1 translocation to the cytosol and generated a toxin-resistant phenotype. In contrast, the depletion of HOP did not disrupt CT activity against cultured cells. HSC70 and HSP90 could bind independently to disordered CTA1, even in the absence of HOP. This indicated HSP90 and HSC70 recognize distinct regions of CTA1, which was confirmed by the identification of a YYIYVI-binding motif for HSC70 that spans residues 83-88 of the 192-amino acid CTA1 polypeptide. Refolding of disordered CTA1 occurred in the presence of HSC70 alone, indicating that HSC70 and HSP90 can each independently refold CTA1. Our work suggests a novel translocation mechanism in which sequential interactions with HSP90 and HSC70 drive the N- to C-terminal extraction of CTA1 from the ER.

Genome-wide analysis of HSP70 family genes in cabbage (Brassica oleracea var. capitata) reveals their involvement in floral development

BACKGROUND

Heat shock proteins have important functions in regulating plant growth and response to abiotic stress. HSP70 family genes have been described in several plant species, but a comprehensive analysis of the HSP70 family genes in cabbage has not been reported to date, especially their roles in floral development.

RESULTS

In this study, we identified 52 BoHSP70 genes in cabbage. The gene structures, motifs, and chromosome locations of the BoHSP70 genes were analyzed. The genes were divided into seven classes using a phylogenetic analysis. An expression analysis showed that the BoHSP70 genes were highly expressed in actively growing tissues, including buds and calluses. In addition, six BoHSP70 genes were highly expressed in the binuclear-pollen-stage buds of a male fertile line compared with its near isogenic sterile line. These results were further verified using qRT-PCR. Subcellular localization analysis of the bud-specific gene BoHSP70-5 showed that it was localized in the cytoplasm.

CONCLUSIONS

Our results help to elucidate the involvement of the BoHSP70 family genes in cabbage floral development and establish the groundwork for future research on the functions of these genes.

Genome-wide identification and expression analysis of HSP90 gene family in Nicotiana tabacum

BACKGROUND

Heat shock proteins 90 (HSP90s) are a highly conserved protein family of cellular chaperones widely found in plants; they play a fundamental role in response to biotic and abiotic stresses. The genome-wide analysis of HSP90 gene family has been completed for some species; however, it has been rarely reported for the tobacco HSP90 genes.

RESULTS

In this study, we systematically conducted genome-wide identification and expression analysis of the tobacco HSP90 gene family, including gene structures, evolutionary relationships, chromosomal locations, conserved domains, and expression patterns. Twenty-one NtHSP90s were identified and classified into eleven categories (NtHSP90-1 to NtHSP90-11) based on phylogenetic analysis. The conserved structures and motifs of NtHSP90 proteins in the same subfamily were highly consistent. Most NtHSP90 proteins contained the ATPase domain, which was closely related to conserved motif 2. Motif 5 was a low complexity sequence and had the function of signal peptide. At least 6 pairs of NtHSP90 genes underwent gene duplication, which arose from segment duplication and tandem duplication events. Phylogenetic analysis showed that most species expanded according to their own species-specific approach during the evolution of HSP90s. Dynamic expression analysis indicated that some NtHSP90 genes may play fundamental roles in regulation of abiotic stress response. The expression of NtHSP90-4, NtHSP90-5, and NtHSP90-9 were up-regulated, while NtHSP90-6, and NtHSP90-7 were not induced by ABA, drought, salt, cold and heat stresses. Among the five treatments, NtHSP90s were most strongly induced by heat stress, and weakly activated by ABA treatment. There was a similar response pattern of NtHSP90s under osmotic stress, or extreme temperature stress.

CONCLUSIONS

This is the first genome-wide analysis of Hsp90 in N. tabacum. These results indicate that each NtHSP90 member fulfilled distinct functions in response to various abiotic stresses.

Label-free quantification of protein expression in the rainbow trout (Oncorhynchus mykiss) in response to short-term exposure to heat stress

Rainbow trout (Oncorhynchus mykiss) are a cold-water salmonid species that is highly susceptible to heat stress. Summer temperature stress is a common issue in trout aquaculture. To better understand the molecular mechanisms of the heat-stress response in the trout, we used label-free quantitative proteome techniques to identify differentially expressed proteins in the livers of rainbow trout exposed to heat stress. We identified 3362 proteins and 152 differentially expressed proteins (p < 0.05; fold-change >2). Of these, 37 were uniquely expressed in the heat-stress group and 35 were uniquely expressed in the control group. In addition, 42 proteins were significantly upregulated (fold-change >2) and 38 proteins were significantly downregulated (fold-change >2). GO (Gene Ontology) analysis indicated that these differentially expressed proteins were primarily expressed in the nucleus, extracellular matrix, and cytoplasm, and were associated with a variety of functions, including protein binding/bridging and enzyme facilitation. KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis of the differentially expressed proteins showed that, during high temperature stress, many biological processes were extensively altered, particularly the estrogen signaling pathway, the complement and coagulation cascades, and the platelet activation pathway. Our study focused on the identification of a systematic approach for the characterization of regulatory networks. Our results provide a framework for further studies of the heat-stress response in fish.

Modulation of Human Hsp90α Conformational Dynamics by Allosteric Ligand Interaction at the C-Terminal Domain

Recent years have seen heat shock protein 90 kDa (Hsp90) attract significant interest as a viable drug target, particularly for cancer. To date, designed inhibitors that target the ATPase domain demonstrate potent anti-proliferative effects, but have failed clinical trials due to high levels of associated toxicity. To circumvent this, the focus has shifted away from the ATPase domain. One option involves modulation of the protein through allosteric activation/inhibition. Here, we propose a novel approach: we use previously obtained information via residue perturbation scanning coupled with dynamic residue network analysis to identify allosteric drug targeting sites for inhibitor docking. We probe the open conformation of human Hsp90α for druggable sites that overlap with these allosteric control elements, and identify three putative natural compound allosteric modulators: Cephalostatin 17, 20(29)-Lupene-3β-isoferulate and 3'-Bromorubrolide F. We assess the allosteric potential of these ligands by examining their effect on the conformational dynamics of the protein. We find evidence for the selective allosteric activation and inhibition of Hsp90's conformational transition toward the closed state in response to ligand binding and shed valuable insight to further the understanding of allosteric drug design and Hsp90's complex allosteric mechanism of action.

Exposure to environmentally relevant cadmium concentrations negatively impacts early life stages of channel catfish (Ictalurus punctatus)

Cadmium is a persistent contaminant of surface waters. The effects of cadmium on early life stages of fish are not well understood, although they are often disproportionately affected by contaminants. The objectives of this study were to examine effects of chronic exposure to environmentally relevant concentrations on growth, development, cellular stress, and glucose metabolism of channel catfish, Ictalurus punctatus. Eggs were wet-fertilized in treatment water at concentrations of 0.4 (control), 2.2 (low), or 8.5 (high) μg L^-1 and monitored through swim-up, black fry stage. Eggs and fry accumulated cadmium dose-dependently. Fertilization rates were unaffected, yet hatch rate was significantly reduced in the high treatment. Survival to black fry and overall size and condition factor were not affected; however, differences in yolk sac size, and presumably energetics of yolk fry, was detected. Physiological pathways were also affected, demonstrated by altered gene expression, most notably in genes related to carbohydrate metabolism. Elevated expression of HK and G6PD, rather than G6P and GADPH, suggests glucose may be shunted towards the pentose-phosphate pathway. Overall, observations indicate cadmium negatively affects development in early life stages of channel catfish, which could lead to shifts in population structure and life history patterns in exposed populations of wild fish.

Heat-shock protein 90 modulates cardiac ventricular hypertrophy via activation of MAPK pathway

The Raf/MAPK/ERK kinase (Mek)/extracellular signal-regulated kinases (Erk) pathway is activated in cardiac hypertrophy after a myocardial infarction. Although heat-shock protein 90 (Hsp90) may regulate the Raf/Mek/Erk signal pathway, the role of Hsp90 in pathophysiological cardiac hypertrophy remains unclear. In this study, we examined the role of Hsp90 in this pathway in cardiac hypertrophy under in vivo and in vitro experimental conditions. Cultured rat cardiomyocytes were treated with the Hsp90 inhibitor 17-(allylamino)-17-dimethoxy-geldanamycin (17-AAG) and proteasome inhibitor MG-132, and then incubated with endothelin-1 (ET) to induce hypertrophy of the cells. The ET-induced increase in the cell size was attenuated by 17-AAG pretreatment. Immunoblot analysis revealed that the c-Raf content of ET-treated cardiomyocytes was decreased in the presence of 17-AAG. An increase in phosphorylation levels of Erk1/2 and GATA4 in ET-treated cardiomyocytes was also attenuated by the 17-AAG pretreatment. Myocardial infarction was produced by ligation of the left ventricular coronary artery in rats, and then 17-AAG was intraperitoneally administered to the animals starting from the 2ndweek after coronary artery ligation (CAL). CAL-induced increases in the heart weight and cross-sectional area were attenuated by 17-AAG treatment. CAL rats showed signs of chronic heart failure with cardiac hypertrophy, whereas cardiac function in CAL rats treated with 17-AAG was not reduced. Treatment of CAL rats with 17-AAG caused a decrease in the c-Raf content and Erk1/2 and GATA4 phosphorylation levels. These findings suggest that Hsp90 is involved in the activation of the Raf/Mek/Erk pathway via stabilization of c-Raf in cardiomyocytes, resulting in the development of cardiac hypertrophy following myocardial infarction.

Novobiocin-ferrocene conjugates possessing anticancer and antiplasmodial activity independent of HSP90 inhibition

A series of tailored novobiocin-ferrocene conjugates was prepared in moderate yields and investigated for in vitro anticancer and antiplasmodial activity against the MDA-MB-231 breast cancer line and Plasmodium falciparum 3D7 strain, respectively. While the target compounds displayed moderate anticancer activity against the breast cancer cell line with IC₅₀ values in the mid-micromolar range, compounds 10a-c displayed promising antiplasmodial activity as low as 0.889 µM. Furthermore, the most promising compounds were tested for inhibitory effects against a postulated target, heat shock protein 90 (Hsp90). A selection of tailored novobiocin derivatives bearing the organometallic ferrocene unit were synthesized and characterized by common spectroscopic techniques. The target compounds were investigated for in vitro anticancer and antimalarial activity against the MDA-MB-231 breast cancer cell line and Plasmodium falciparum 3D7 strain, respectively.

Hsp83/Hsp90 Physically Associates with Insulin Receptor to Promote Neural Stem Cell Reactivation

Neural stem cells (NSCs) have the ability to exit quiescence and reactivate in response to physiological stimuli. In the Drosophila brain, insulin receptor (InR)/phosphatidylinositol 3-kinase (PI3K)/Akt pathway triggers NSC reactivation. However, intrinsic mechanisms that control the InR/PI3K/Akt pathway during reactivation remain unknown. Here, we have identified heat shock protein 83 (Hsp83/Hsp90), a molecular chaperone, as an intrinsic regulator of NSC reactivation. Hsp83 is both necessary and sufficient for NSC reactivation by promoting the activation of InR pathway in larval brains in the presence of dietary amino acids. Both Hsp83 and its co-chaperone Cdc37 physically associate with InR. Finally, reactivation defects observed in brains depleted of hsp83 were rescued by over-activation of the InR/PI3K/Akt pathway, suggesting that Hsp83 functions upstream of the InR/PI3K/Akt pathway during NSC reactivation. Given the conservation of Hsp83 and the InR pathway, our finding may provide insights into the molecular mechanisms underlying mammalian NSC reactivation.

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Hsp83/Hsp90 and its co-chaperone Cdc37 are required for NSC reactivation

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Hsp83 overexpression results in premature NSC reactivation on fed condition

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Hsp83 and Cdc37 physically associate with InR

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Hsp83 and Cdc37 are required for the activation of InR pathway in NSCs

Treatment with crocin improves cardiac dysfunction by normalizing autophagy and inhibiting apoptosis in STZ-induced diabetic cardiomyopathy

BACKGROUND AND AIM

The association of diabetes mellitus (DM) and poor metabolic control with high incidence of cardiovascular diseases is well established. The aim of this study was to investigate the potential cardioprotective effect of crocin (Crocus sativus L. extract) on diabetic heart dysfunction and to elucidate the mediating molecular mechanisms.

METHODS AND RESULTS

Streptozotocin (STZ)-induced diabetic rats were treated with two different concentrations of crocin (10 or 20 mg/kg), while isolated cardiac myocytes exposed to 25 mM glucose, were treated with 1 or 10 μM of crocin. Treatment of STZ-diabetic rats with crocin resulted in normalization of plasma glucose levels, inhibition of cardiac hypertrophy and fibrosis, and improvement of cardiac contractile function. Heat Shock Response was enhanced. Myocardial AMPK phosphorylation was increased after treatment with crocin, resulting in normalization of autophagy marker proteins (LC3BII/LC3BI ratio, SQSTM1/p62 and Beclin-1), while the diabetes-induced myocardial apoptosis was decreased. Similar results regarding the effect of crocin on autophagy and apoptosis pathways were obtained in isolated cardiac myocytes exposed to high concentration of glucose.

CONCLUSION

The results suggest that crocin improves the deteriorated cardiac function in diabetic animals by enhancing the heat shock response, inhibiting apoptosis and normalizing autophagy in cardiac myocytes. Thus, treatment with crocin may represent a novel approach for treating diabetic cardiomyopathy.

Combination of ATO with FLT3 TKIs eliminates FLT3/ITD+ leukemia cells through reduced expression of FLT3

Acute myeloid leukemia (AML) patients with FLT3/ITD mutations have a poor prognosis. Monotherapy with selective FLT3 tyrosine kinase inhibitors (TKIs) have shown transient and limited efficacy due to the development of resistance. Arsenic trioxide (ATO, As₂O₃) has been proven effective in treating acute promyelocytic leukemia (APL) and has shown activity in some cases of refractory and relapsed AML and other hematologic malignances. We explored the feasibility of combining FLT3 TKIs with ATO in the treatment of FLT3/ITD+ leukemias. The combination of FLT3 TKIs with ATO showed synergistic effects in reducing proliferation, viability and colony forming ability, and increased apoptosis in FLT3/ITD+ cells and primary patient samples. In contrast, no cooperativity was observed against wild-type FLT3 leukemia cells. ATO reduced expression of FLT3 RNA and its upstream transcriptional regulators (HOXA9, MEIS1), and induced poly-ubiquitination and degradation of the FLT3 protein, partly through reducing its binding with USP10. ATO also synergizes with FLT3 TKIs to inactivate FLT3 autophosphorylation and phosphorylation of its downstream signaling targets, including STAT5, AKT and ERK. Furthermore, ATO combined with sorafenib, a FLT3 TKI, in vivo reduced growth of FLT3/ITD+ leukemia cells in NSG recipients. In conclusion, these results suggest that ATO is a potential candidate to study in clinical trials in combination with FLT3 TKIs to improve the treatment of FLT3/ITD+ leukemia.

Gene expression and promoter characterization of heat-shock protein 90B gene (HSP90B) in the model unicellular green alga Chlamydomonas reinhardtii

Molecular chaperones or heat shock proteins are a large protein family with important functions in every cellular organism. Among all types of the heat shock proteins, information on the ER-localized HSP90 protein (HSP90B) and its encoding gene is relatively scarce in the literature, especially in photosynthetic organisms. In this study, expression profiles as well as promoter sequence of the HSP90B gene were investigated in the model green alga Chlamydomonas reinhardtii. We have found that HSP90B is strongly induced by heat and ER stresses, while other short-term exposure to abiotic stresses, such as salinity, dark-to-light transition or light stress does not appear to affect the expression. Promoter truncation analysis as well as chromatin immunoprecipitation using the antibodies recognizing histone H3 and acetylated histone H3, revealed a putative core constitutive promoter sequence between -1 to -253 bp from the transcription start site. Our results also suggested that the nucleotides upstream of the core promoter may contain repressive elements such as putative repressor binding site(s).

Identification of genes associated with stress tolerance in moth bean [Vigna aconitifolia (Jacq.) Marechal], a stress hardy crop

Moth bean is the most drought and heat tolerant cultigens among Asian Vigna. We performed comparative transcriptome analysis of moth bean cultivar "Marumoth" under control and stress condition. De novo transcriptome assembly was carried out by using Velvet followed by Oases softwares. Differential expression analyses, SSR identification and validation and mapping of pathways and transcription factors were conducted. A total of 179,979 and 201,888 reads were generated on Roche 454 platform and 48,617,205 and 45,449,053 reads were generated on ABI Solid platform for the control and stressed samples. Combined assembly from Roche and ABI Solid platforms generated 16,090 and 15,096 transcripts for control and stressed samples. We found 1287 SSRs and 5606 transcripts involved in 179 pathways. The 55 transcription factor families represented 19.42% of total mothbean transcripts. In expression profiling, ten transcripts were found to be up-regulated and 41 down-regulated while 490 showed no major change under moisture stress condition. Stress inducible genes like Catalase, Cyt P450 monooxygenase, heat shock proteins (HSP 90 and HSP 70), oxidoreductase, protein kinases, dehydration responsive protein (DRP), universal stress protein and ferridoxin NADH oxidoreductase genes were up-regulated in stressed sample. Genes which might be involved in moisture stress tolerance in moth bean were identified and these might be useful for stress tolerance breeding in moth bean and other related crops.