Regulation of Hsf1 and the Heat Shock Response

Allosteric Activation of Protein Phosphatase 5 with Small Molecules

The activation of PP5 is essential for a variety of cellular processes, as it participates in a variety of biological pathways by dephosphorylating substrates. However, activation of PP5 by small molecules has been a challenge due to its native "self-inhibition" mechanism, which is controlled by the N-terminal TPR domain and the C-terminal αJ helix. Here, we reported the discovery of DDO-3733, a well-identified TPR-independent PP5 allosteric activator, which facilitates the dephosphorylation process of downstream substrates. Considering the negative regulatory effect of PP5 on heat shock transcription factor HSF1, pharmacologic activation of PP5 by DDO-3733 was found to reduce the HSP90 inhibitor-induced heat shock response. These results provide a chemical tool to advance the exploration of PP5 as a potential therapeutic target and highlight the value of pharmacological activation of PP5 to reduce heat shock toxicity of HSP90 inhibitors.

Structural and functional characterization of Hdh-HSBP1 and its involvement in heat stress and early development in Pacific abalone, Haliotis discus hannai

Heat shock factor binding protein 1 (HSBP1) is known to regulate the activity of heat shock factor 1 (HSF1) and the early development of organisms. To understand the involvement of HSBP1 in the heat shock response and embryonic and larval development of Pacific abalone (Haliotis discus hannai), the Hdh-HSBP1 gene was sequenced from the digestive gland (DG) tissue. The full-length sequence of Hdh-HSBP1 encompassed 738 nucleotides, encoding an 8.42 kDa protein consisting of 75 deduced amino acids. The protein contains an HSBP1 domain and a coiled-coil domain, which are conserved features in the HSBP1 protein family. Protein-protein molecular docking revealed that the coiled-coil region of Hdh-HSBP1 binds to the coiled-coil region of Hdh-HSF1. Tissue expression analysis demonstrated that the highest Hdh-HSBP1 expression occurred in the DG, whereas seasonal expression analysis revealed that this gene was most highly expressed in summer. In heat-stressed abalone, the highest expression of Hdh-HSBP1 occurred at 30 °C. Moreover, time-series analysis revealed that the expression of this gene began to increase significantly at 6 h post-heat stress, with higher expression observed at 12 h and 24 h post-heat stress. Furthermore, Hdh-HSBP1 mRNA expression showed a link to ROS production. Additionally, the expression of Hdh-HSBP1 showed significantly higher expression in the early stages of embryonic development in Pacific abalone. These results suggest that Hdh-HSBP1 plays a crucial role in the stress physiology of Pacific abalone by interacting with Hdh-HSF1, as well as its embryonic development.

The Protective Role of Heat Shock Proteins against Stresses in Animal Breeding

Heat shock proteins (HSPs) play an important role in all living organisms under stress conditions by acting as molecular chaperones. The expression of different HSPs during stress varies depending on their protective functions and anti-apoptotic activities. The application of HSPs improves the efficiency and decreases the economic cost of animal breeding. By upregulating the expression of HSPs, feed supplements can improve stress tolerance in farm animals. In addition, high expression of HSPs is often a feature of tumor cells, and inhibiting the expression of HSPs is a promising novel method for killing these cells and treating cancers. In the present review, the findings of previous research on the application of HSPs in animal breeding and veterinary medicine are summarized, and the knowledge of the actions of HSPs in animals is briefly discussed.

An HSF1-JMJD6-HSP feedback circuit promotes cell adaptation to proteotoxic stress

Heat Shock Factor 1 (HSF1) is best known as the master transcriptional regulator of the heat-shock response (HSR), a conserved adaptive mechanism critical for protein homeostasis (proteostasis). Combining a genome-wide RNAi library with an HSR reporter, we identified Jumonji domain-containing protein 6 (JMJD6) as an essential mediator of HSF1 activity. In follow-up studies, we found that JMJD6 is itself a noncanonical transcriptional target of HSF1 which acts as a critical regulator of proteostasis. In a positive feedback circuit, HSF1 binds and promotes JMJD6 expression, which in turn reduces heat shock protein 70 (HSP70) R469 monomethylation to disrupt HSP70-HSF1 repressive complexes resulting in enhanced HSF1 activation. Thus, JMJD6 is intricately wired into the proteostasis network where it plays a critical role in cellular adaptation to proteotoxic stress.

Interplay of Proteostasis Capacity and Protein Aggregation: Implications for Cellular Function and Disease

Eukaryotic cells are equipped with an intricate proteostasis network (PN), comprising nearly 3,000 components dedicated to preserving proteome integrity and sustaining protein homeostasis. This protective system is particularly important under conditions of external and intrinsic cell stress, where inherently dynamic proteins may unfold and lose functionality. A decline in proteostasis capacity is associated with the aging process, resulting in a reduced folding efficiency of newly synthesized proteins and a deficit in the cellular capacity to degrade misfolded proteins. A critical consequence of PN insufficiency is the accumulation of cytotoxic protein aggregates that underlie various age-related neurodegenerative conditions and other pathologies. By interfering with specific proteostasis components, toxic aggregates place an excessive burden on the PN's ability to maintain proteome integrity. This initiates a feed-forward loop, wherein the generation of misfolded and aggregated proteins ultimately leads to proteostasis collapse and cellular demise.

The Heat Shock Response as a Condensate Cascade

The heat shock response (HSR) is a gene regulatory program controlling expression of molecular chaperones implicated in aging, cancer, and neurodegenerative disease. Long presumed to be activated by toxic protein aggregates, recent work suggests a new functional paradigm for the HSR in yeast. Rather than toxic aggregates, adaptive biomolecular condensates comprised of orphan ribosomal proteins (oRP) and stress granule components have been shown to be physiological chaperone clients. By titrating away the chaperones Sis1 and Hsp70 from the transcription factor Hsf1, these condensates activate the HSR. Upon release from Hsp70, Hsf1 forms spatially distinct transcriptional condensates that drive high expression of HSR genes. In this manner, the negative feedback loop controlling HSR activity - in which Hsf1 induces Hsp70 expression and Hsp70 represses Hsf1 activity - is embedded in the biophysics of the system. By analogy to phosphorylation cascades that transmit information via the dynamic activity of kinases, we propose that the HSR is organized as a condensate cascade that transmits information via the localized activity of molecular chaperones.

pH Dependence of HSF1 trimerization is shaped by intramolecular interactions

Heat shock factor 1 (HSF1) primarily regulates various cellular stress responses. Previous studies have shown that low pH within the physiological range directly activates HSF1 function in vitro. However, the detailed molecular mechanisms remain unclear. This study proposes a molecular mechanism based on the trimerization behavior of HSF1 at different pH values. Extensive mutagenesis of human and goldfish HSF1 revealed that the optimal pH for trimerization depended on the identity of residue 103. In particular, when residue 103 was occupied by tyrosine, a significant increase in the optimal pH was observed, regardless of the rest of the sequence. This behavior can be explained by the protonation state of the neighboring histidine residues, His101 and His110. Residue 103 plays a key role in trimerization by forming disulfide or non-covalent bonds with Cys36. If tyrosine resides at residue 103 in an acidic environment, its electrostatic interactions with positively charged histidine residues prevent effective trimerization. His101 and His110 are neutralized at a higher pH, which releases Tyr103 to interact with Cys36 and drives the effective trimerization of HSF1. This study showed that the protonation state of a histidine residue can regulate the intramolecular interactions, which consequently leads to a drastic change in the oligomerization behavior of the entire protein.

Comprehensive multi-omics analysis reveals WEE1 as a synergistic lethal target with hyperthermia through CDK1 super-activation

Hyperthermic intraperitoneal chemotherapy's role in ovarian cancer remains controversial, hindered by limited understanding of hyperthermia-induced tumor cellular changes. This limits developing potent combinatory strategies anchored in hyperthermic intraperitoneal therapy (HIPET). Here, we perform a comprehensive multi-omics study on ovarian cancer cells under hyperthermia, unveiling a distinct molecular panorama, primarily characterized by rapid protein phosphorylation changes. Based on the phospho-signature, we pinpoint CDK1 kinase is hyperactivated during hyperthermia, influencing the global signaling landscape. We observe dynamic, reversible CDK1 activity, causing replication arrest and early mitotic entry post-hyperthermia. Subsequent drug screening shows WEE1 inhibition synergistically destroys cancer cells with hyperthermia. An in-house developed miniaturized device confirms hyperthermia and WEE1 inhibitor combination significantly reduces tumors in vivo. These findings offer additional insights into HIPET, detailing molecular mechanisms of hyperthermia and identifying precise drug combinations for targeted treatment. This research propels the concept of precise hyperthermic intraperitoneal therapy, highlighting its potential against ovarian cancer.

Feedback control of the heat shock response by spatiotemporal regulation of Hsp70

Cells maintain homeostasis via dynamic regulation of stress response pathways. Stress pathways transiently induce response regulons via negative feedback loops, but the extent to which individual genes provide feedback has not been comprehensively measured for any pathway. Here, we disrupted induction of each gene in the Saccharomyces cerevisiae heat shock response (HSR) and quantified cell growth and HSR dynamics following heat shock. The screen revealed a core feedback loop governing expression of the chaperone Hsp70 reinforced by an auxiliary feedback loop controlling Hsp70 subcellular localization. Mathematical modeling and live imaging demonstrated that multiple HSR targets converge to promote Hsp70 nuclear localization via its release from cytosolic condensates. Following ethanol stress, a distinct set of factors similarly converged on Hsp70, suggesting that nonredundant subsets of the HSR regulon confer feedback under different conditions. Flexible spatiotemporal feedback loops may broadly organize stress response regulons and expand their adaptive capacity.

Adaptive preservation of orphan ribosomal proteins in chaperone-dispersed condensates

Ribosome biogenesis is among the most resource-intensive cellular processes, with ribosomal proteins accounting for up to half of all newly synthesized proteins in eukaryotic cells. During stress, cells shut down ribosome biogenesis in part by halting rRNA synthesis, potentially leading to massive accumulation of aggregation-prone 'orphan' ribosomal proteins (oRPs). Here we show that, during heat shock in yeast and human cells, oRPs accumulate as reversible peri-nucleolar condensates recognized by the Hsp70 co-chaperone Sis1/DnaJB6. oRP condensates are liquid-like in cell-free lysate but solidify upon depletion of Sis1 or inhibition of Hsp70. When cells recover from heat shock, oRP condensates disperse in a Sis1- and Hsp70-dependent manner, and the oRP constituents are incorporated into functional ribosomes in the cytosol, enabling cells to efficiently resume growth. Preserving biomolecules in reversible condensates-like mRNAs in cytosolic stress granules and oRPs at the nucleolar periphery-may be a primary function of the Hsp70 chaperone system.

Kainic Acid-Induced Excitotoxicity Leads to the Activation of Heat Shock Response

Heat shock response (HSR) which is regulated by heat shock factor 1 (HSF1) is the most important mechanism and the major regulator that prevents protein aggregation in neurodegenerative diseases. Excitotoxicity, which is the accumulation of excess glutamate in synaptic cleft, is observed in age-dependent neurodegenerative diseases and also in stroke, epilepsy, and brain trauma. Only a few studies in the literature show the link between excitotoxicity and HSR. In this study, we aimed to show the molecular mechanism underlying this link. We applied heat shock (HS) treatment and induced excitotoxicity with kainic acid (KA) in neuroblastoma (SHSY-5Y) and glia (immortalized human astrocytes (IHA)) cells. We observed that, only in SHSY-5Y cells, heat shock preconditioning increases cell survival after KA treatment. GLT-1 mRNA expression is increased as a result of KA treatment and HS due to the elevation of HSF1 binding to GLT-1 promoter which was induced by HSF1 phosphorylation and sumolation in SHSY-5Y cells. Additionally, glutamine synthetase and glutaminase expressions are increased after HS preconditioning in SHSY-5Y cells indicating that HS activates glutamate metabolism modulators and accelerates the glutamate cycle. In glia cells, we did not observe the effect of HS preconditioning. In summary, heat shock preconditioning might be protective against excitotoxicity-related cell death and degeneration.

Heat Shock Factor 1 Inhibition: A Novel Anti-Cancer Strategy with Promise for Precision Oncology

Heat shock factor 1 (HSF1) is a transcription factor crucial for regulating heat shock response (HSR), one of the significant cellular protective mechanisms. When cells are exposed to proteotoxic stress, HSF1 induces the expression of heat shock proteins (HSPs) to act as chaperones, correcting the protein-folding process and maintaining proteostasis. In addition to its role in HSR, HSF1 is overexpressed in multiple cancer cells, where its activation promotes malignancy and leads to poor prognosis. The mechanisms of HSF1-induced tumorigenesis are complex and involve diverse signaling pathways, dependent on cancer type. With its important roles in tumorigenesis and tumor progression, targeting HSF1 offers a novel cancer treatment strategy. In this article, we examine the basic function of HSF1 and its regulatory mechanisms, focus on the mechanisms involved in HSF1's roles in different cancer types, and examine current HSF1 inhibitors as novel therapeutics to treat cancers.

Serum HSF1 is upregulated in endometriosis patients and serves as a potential diagnostic biomarker

Endometriosis (EMS) is a prevalent gynecological condition lacking reliable diagnostic biomarkers. This prospective study aimed to analyze the potential of serum heat shock transcription factor 1 (HSF1) as a diagnostic marker for EMS. Clinical features of 92 EMS patients and 52 controls were recorded, revealing significant differences in dysmenorrhea, dyspareunia, pelvic pain, nulliparity, and CA125 levels. Serum HSF1 was upregulated in EMS patients, with higher levels in American Society for Reproductive Medicine (ASRM) III/IV than ASRM I/II. Receiver operating characteristic curve analysis demonstrated good diagnostic function for serum HSF1 (AUC: 0.857, sensitivity: 91.30%, specificity: 63.46%). Serum HSF1, dysmenorrhea, dyspareunia, and nulliparity were independent risk factors for EMS, while dysmenorrhea and serum HSF1 were independent risk factors for EMS severity. Additionally, the GSE25628 dataset was downloaded from the GEO database for differential analysis of gene expression. The HSF1 downstream target genes PTGES3, HSP90AA1, and HSPB1 showed significant differential expression in EMS, suggesting their involvement in the regulatory mechanism of HSF1 in EMS.

A Zpr1 co-chaperone mediates folding of eukaryotic translation elongation factor 1A via a GTPase cycle

General protein folding is mediated by chaperones that utilize ATP hydrolysis to regulate client binding and release. Zinc-finger protein 1 (Zpr1) is an essential ATP-independent chaperone dedicated to the biogenesis of eukaryotic translation elongation factor 1A (eEF1A), a highly abundant GTP-binding protein. How Zpr1-mediated folding is regulated to ensure rapid Zpr1 recycling remains an unanswered question. Here, we use yeast genetics and microscopy analysis, biochemical reconstitution, and structural modeling to reveal that folding of eEF1A by Zpr1 requires GTP hydrolysis. Furthermore, we identify the highly conserved altered inheritance of mitochondria 29 (Aim29) protein as a Zpr1 co-chaperone that recognizes eEF1A in the GTP-bound, pre-hydrolysis conformation. This interaction dampens Zpr1⋅eEF1A GTPase activity and facilitates client exit from the folding cycle. Our work reveals that a bespoke ATP-independent chaperone system has mechanistic similarity to ATPase chaperones but unexpectedly relies on client GTP hydrolysis to regulate the chaperone-client interaction.

The unfolded protein response of the endoplasmic reticulum supports mitochondrial biogenesis by buffering nonimported proteins

Almost all mitochondrial proteins are synthesized in the cytosol and subsequently targeted to mitochondria. The accumulation of nonimported precursor proteins occurring upon mitochondrial dysfunction can challenge cellular protein homeostasis. Here we show that blocking protein translocation into mitochondria results in the accumulation of mitochondrial membrane proteins at the endoplasmic reticulum, thereby triggering the unfolded protein response (UPRER). Moreover, we find that mitochondrial membrane proteins are also routed to the ER under physiological conditions. The level of ER-resident mitochondrial precursors is enhanced by import defects as well as metabolic stimuli that increase the expression of mitochondrial proteins. Under such conditions, the UPRER is crucial to maintain protein homeostasis and cellular fitness. We propose the ER serves as a physiological buffer zone for those mitochondrial precursors that cannot be immediately imported into mitochondria while engaging the UPRER to adjust the ER proteostasis capacity to the extent of precursor accumulation.

Neurodegenerative Proteinopathies Induced by Environmental Pollutants: Heat Shock Proteins and Proteasome as Promising Therapeutic Tools

Environmental pollutants' (EPs) amount and diversity have increased in recent years due to anthropogenic activity. Several neurodegenerative diseases (NDs) are theorized to be related to EPs, as their incidence has increased in a similar way to human EPs exposure and they reproduce the main ND hallmarks. EPs induce several neurotoxic effects, including accumulation and gradual deposition of misfolded toxic proteins, producing neuronal malfunction and cell death. Cells possess different mechanisms to eliminate these toxic proteins, including heat shock proteins (HSPs) and the proteasome system. The accumulation and deleterious effects of toxic proteins are induced through HSPs and disruption of proteasome proteins' homeostatic function by exposure to EPs. A therapeutic approach has been proposed to reduce accumulation of toxic proteins through treatment with recombinant HSPs/proteasome or the use of compounds that increase their expression or activity. Our aim is to review the current literature on NDs related to EP exposure and their relationship with the disruption of the proteasome system and HSPs, as well as to discuss the toxic effects of dysfunction of HSPs and proteasome and the contradictory effects described in the literature. Lastly, we cover the therapeutic use of developed drugs and recombinant proteasome/HSPs to eliminate toxic proteins and prevent/treat EP-induced neurodegeneration.

Impact of Non-Invasive Physical Plasma on Heat Shock Protein Functionality in Eukaryotic Cells

Recently, biomedical research has increasingly investigated physical plasma as an innovative therapeutic approach with a number of therapeutic biomedical effects. It is known from radiation and chemotherapy that these applications can lead to the induction and activation of primarily cytoprotective heat shock proteins (HSP). HSP protect cells and tissues from physical, (bio)chemical, and physiological stress and, ultimately, along with other mechanisms, govern resistance and treatment failure. These mechanisms are well known and comparatively well studied in drug therapy. For therapies in the field of physical plasma medicine, however, extremely little data are available to date. In this review article, we provide an overview of the current studies on the interaction of physical plasma with the cellular HSP system.

An Undefined Interaction between Polyamines and Heat Shock Proteins Leads to Cellular Protection in Plasmodium falciparum and Proliferating Cells in Various Organisms

Environmental stimuli can distress the internal reaction of cells and their normal function. To react promptly to sudden environmental changes, a cascade of heat shock proteins (Hsps) functions to protect and act as housekeepers inside the cells. In parallel to the heat shock response, the metabolic polyamine (PA) status changes. Here, we discuss possible ways of putative interactions between Hsps and polyamines in a wide lineage of eukaryotic model organisms with a particular focus on parasitic protozoa such as Plasmodium falciparum (P. falciparum). The supposed interaction between polyamines and Hsps may protect the parasite from the sudden change in temperature during transmission from the female Anopheles mosquito to a human host. Recent experiments performed with the spermidine mimetic inhibitor 15-deoxyspergualine in Plasmodium in vitro cultures show that the drug binds to the C-terminal EEVD motif of Hsp70. This leads to inhibition of protein biosynthesis caused by prevention of eIF5A2 phosphorylation and eukaryotic initiation factor 5A (eIF5A) modification. These observations provide further evidence that PAs are involved in the regulation of protein biosynthesis of Hsps to achieve a protective effect for the parasite during transmission.

Transcellular chaperone signaling is an intercellular stress-response distinct from the HSF-1-mediated heat shock response

Organismal proteostasis is maintained by intercellular signaling processes including cell nonautonomous stress responses such as transcellular chaperone signaling (TCS). When TCS is activated upon tissue-specific knockdown of hsp-90 in the Caenorhabditis elegans intestine, heat-inducible hsp-70 is induced in muscle cells at the permissive temperature resulting in increased heat stress resistance and lifespan extension. However, our understanding of the molecular mechanism and signaling factors mediating transcellular activation of hsp-70 expression from one tissue to another is still in its infancy. Here, we conducted a combinatorial approach using transcriptome RNA-Seq profiling and a forward genetic mutagenesis screen to elucidate how stress signaling from the intestine to the muscle is regulated. We find that the TCS-mediated "gut-to-muscle" induction of hsp-70 expression is suppressed by HSF-1 and instead relies on transcellular-X-cross-tissue (txt) genes. We identify a key role for the PDZ-domain guanylate cyclase txt-1 and the homeobox transcription factor ceh-58 as signaling hubs in the stress receiving muscle cells to initiate hsp-70 expression and facilitate TCS-mediated heat stress resistance and lifespan extension. Our results provide a new view on cell-nonautonomous regulation of "inter-tissue" stress responses in an organism that highlight a key role for the gut. Our data suggest that the HSF-1-mediated heat shock response is switched off upon TCS activation, in favor of an intercellular stress-signaling route to safeguard survival.

Native Size-Exclusion Chromatography-Based Mass Spectrometry Reveals New Components of the Early Heat Shock Protein 90 Inhibition Response Among Limited Global Changes

The molecular chaperone heat shock protein 90 (HSP90) works in concert with co-chaperones to stabilize its client proteins, which include multiple drivers of oncogenesis and malignant progression. Pharmacologic inhibitors of HSP90 have been observed to exert a wide range of effects on the proteome, including depletion of client proteins, induction of heat shock proteins, dissociation of co-chaperones from HSP90, disruption of client protein signaling networks, and recruitment of the protein ubiquitylation and degradation machinery-suggesting widespread remodeling of cellular protein complexes. However, proteomics studies to date have focused on inhibitor-induced changes in total protein levels, often overlooking protein complex alterations. Here, we use size-exclusion chromatography in combination with mass spectrometry (SEC-MS) to characterize the early changes in native protein complexes following treatment with the HSP90 inhibitor tanespimycin (17-AAG) for 8 h in the HT29 colon adenocarcinoma cell line. After confirming the signature cellular response to HSP90 inhibition (e.g., induction of heat shock proteins, decreased total levels of client proteins), we were surprised to find only modest perturbations to the global distribution of protein elution profiles in inhibitor-treated HT29 cells at this relatively early time-point. Similarly, co-chaperones that co-eluted with HSP90 displayed no clear difference between control and treated conditions. However, two distinct analysis strategies identified multiple inhibitor-induced changes, including known and unknown components of the HSP90-dependent proteome. We validate two of these-the actin-binding protein Anillin and the mitochondrial isocitrate dehydrogenase 3 complex-as novel HSP90 inhibitor-modulated proteins. We present this dataset as a resource for the HSP90, proteostasis, and cancer communities (https://www.bioinformatics.babraham.ac.uk/shiny/HSP90/SEC-MS/), laying the groundwork for future mechanistic and therapeutic studies related to HSP90 pharmacology. Data are available via ProteomeXchange with identifier PXD033459.

Comparative Proteomic Analysis Provides New Insights into the Molecular Basis of Thermal-Induced Parthenogenesis in Silkworm (Bombyx mori)

Artificial parthenogenetic induction via thermal stimuli in silkworm is an important technique that has been used in sericultural production. However, the molecular mechanism underlying it remains largely unknown. We have created a fully parthenogenetic line (PL) with more than 85% occurrence and 80% hatching rate via hot water treatment and genetic selection, while the parent amphigenetic line (AL) has less than 30% pigmentation rate and less than 1% hatching rate when undergoing the same treatment. Here, isobaric tags for relative and absolute quantitation (iTRAQ)-based analysis were used to investigate the key proteins and pathways associated with silkworm parthenogenesis. We uncovered the unique proteomic features of unfertilized eggs in PL. In total, 274 increased abundance proteins and 211 decreased abundance proteins were identified relative to AL before thermal induction. Function analysis displayed an increased level of translation and metabolism in PL. After thermal induction, 97 increased abundance proteins and 187 decreased abundance proteins were identified. An increase in stress response-related proteins and decrease in energy metabolism suggested that PL has a more effective response to buffer the thermal stress than AL. Cell cycle-related proteins, including histones, and spindle-related proteins were decreased in PL, indicating an important role of this decrease in the process of ameiotic parthenogenesis.

Transperons: RNA operons as effectors of coordinated gene expression in eukaryotes

Coordinated gene expression allows spatiotemporal control of cellular processes and is achieved by the cotranscription/translation of functionally related genes/proteins. Prokaryotes evolved polycistronic messages (operons) to confer expression from a single promoter to efficiently cotranslate proteins functioning on the same pathway. Yet, despite having far greater diversity (e.g., gene number, distribution, modes of expression), eukaryotic cells employ individual promoters and monocistronic messages. Although gene expression is modular, it does not account for how eukaryotes achieve coordinated localized translation. The RNA operon theory states that mRNAs derived from different chromosomes assemble into ribonucleoprotein particles (RNPs) that act as functional operons to generate protein cohorts upon cotranslation. Work in yeast has now validated this theory and shown that intergenic associations and noncanonical histone functions create pathway-specific RNA operons (transperons) that regulate cell physiology. Herein the involvement of chromatin organization in transperon formation and programmed gene coexpression is discussed.

Metabolic and Transcriptomic Profiling Reveals Etiolated Mechanism in Huangyu Tea (Camellia sinensis) Leaves

Leaf color is one of the key factors involved in determining the processing suitability of tea. It relates to differential accumulation of flavor compounds due to the different metabolic mechanisms. In recent years, photosensitive etiolation or albefaction is an interesting direction in tea research field. However, the molecular mechanism of color formation remains unclear since albino or etiolated mutants have different genetic backgrounds. In this study, wide-target metabolomic and transcriptomic analyses were used to reveal the biological mechanism of leaf etiolation for 'Huangyu', a bud mutant of 'Yinghong 9'. The results indicated that the reduction in the content of chlorophyll and the ratio of chlorophyll to carotenoids might be the biochemical reasons for the etiolation of 'Huangyu' tea leaves, while the content of zeaxanthin was significantly higher. The differentially expressed genes (DEGs) involved in chlorophyll and chloroplast biogenesis were the biomolecular reasons for the formation of green or yellow color in tea leaves. In addition, our results also revealed that the changes of DEGs involved in light-induced proteins and circadian rhythm promoted the adaptation of etiolated tea leaves to light stress. Variant colors of tea leaves indicated different directions in metabolic flux and accumulation of flavor compounds.

The Crucial Role of AR-V7 in Enzalutamide-Resistance of Castration-Resistant Prostate Cancer

Simple Summary

Androgen receptor splice variant 7 (AR-V7) has always been considered a key driver for triggering enzalutamide resistance of castration-resistant prostate cancer (CRPC). In recent years, both the homeostasis of AR-V7 protein and AR-V7’s relationship with LncRNAs have gained great attention with in-depth studies. Starting from protein stability and LncRNA, the paper discusses and summarizes the mechanisms and drugs that affect the CRPC patients’ sensitivity to enzalutamide by regulating the protein or transcriptional stability of AR-V7, hoping to provide therapeutic ideas for subsequent research to break through the CRPC therapeutic bottleneck.

Abstract

Prostate cancer (PCa) has the second highest incidence of malignancies occurring in men worldwide. The first-line therapy of PCa is androgen deprivation therapy (ADT). Nonetheless, most patients progress to castration-resistant prostate cancer (CRPC) after being treated by ADT. As a second-generation androgen receptor (AR) antagonist, enzalutamide (ENZ) is the current mainstay of new endocrine therapies for CRPC in clinical use. However, almost all patients develop resistance during AR antagonist therapy due to various mechanisms. At present, ENZ resistance (ENZR) has become challenging in the clinical treatment of CRPC. AR splice variant 7 (AR-V7) refers to a ligand-independent and constitutively active variant of the AR and is considered a key driver of ENZR in CRPC. In this review, we summarize the mechanisms and biological behaviors of AR-V7 in ENZR of CRPC to contribute novel insights for CRPC therapy.

Aberrant HSF1 signaling activation underlies metformin amelioration of myocardial infarction in mice

Myocardial infarction (MI) is a cardiovascular disease with high morbidity and mortality. Clinically, rehabilitation after massive MI often has a poor prognosis. Therefore, it is necessary to explore the therapeutic methods of myocardial protection after MI. As a first-line treatment for type 2 diabetes, metformin has been found to have a certain protective effect on myocardial tissue. However, its pharmacological mechanism remains unclear. In this study, we investigated key factors that reduced MI with metformin. Through in vivo, in vitro, and in silico analyses, we identified HSF1 as a key target for metformin. HSF1 could up-regulate the transcriptional level of AMPKα2 through transcriptional activation and stimulate the activity of the downstream AMPK/mTOR signaling pathway. Metformin stimulated cardiomyocytes to form stress granules (SGs), and knockdown of HSF1 reversed this process. Furthermore, HSF1 exhibited better in vitro affinity for metformin than AMPK, suggesting that HSF1 may be a more sensitive target for metformin.

HSF1 Can Prevent Inflammation following Heat Shock by Inhibiting the Excessive Activation of the ATF3 and JUN&FOS Genes

Heat Shock Factor 1 (HSF1), a transcription factor frequently overexpressed in cancer, is activated by proteotoxic agents and participates in the regulation of cellular stress response. To investigate how HSF1 level affects the response to proteotoxic stress, we integrated data from functional genomics analyses performed in MCF7 breast adenocarcinoma cells. Although the general transcriptional response to heat shock was impaired due to HSF1 deficiency (mainly chaperone expression was inhibited), a set of genes was identified, including ATF3 and certain FOS and JUN family members, whose stress-induced activation was stronger and persisted longer than in cells with normal HSF1 levels. These genes were direct HSF1 targets, suggesting a dual (activatory/suppressory) role for HSF1. Moreover, we found that heat shock-induced inflammatory response could be stronger in HSF1-deficient cells. Analyses of The Cancer Genome Atlas data indicated that higher ATF3, FOS, and FOSB expression levels correlated with low HSF1 levels in estrogen receptor-positive breast cancer, reflecting higher heat shock-induced expression of these genes in HSF1-deficient MCF7 cells observed in vitro. However, differences between the analyzed cancer types were noted in the regulation of HSF1-dependent genes, indicating the presence of cell-type-specific mechanisms. Nevertheless, our data indicate the existence of the heat shock-induced network of transcription factors (associated with the activation of TNFα signaling) which includes HSF1. Independent of its chaperone-mediated cytoprotective function, HSF1 may be involved in the regulation of this network but prevents its overactivation in some cells during stress.

Effect of Heat Shock Preconditioning on Pressure Injury Prevention via Hsp27 Upregulation in Rat Models

Pressure injury (PI) prevention is a huge industry and involves various interventions. Temperature and moisture are important factors for wound healing; however, the active mechanism by which “moist heat” affects PI prevention has not yet been clarified. Thus, we explored the protective and therapeutic effects of hydrotherapy on PI based on the preconditioning (PC) principle, which might be useful for clinical practice. This study aimed to investigate the preventive mechanisms of heat shock preconditioning on PIs in rat models. The experiment was performed in the basic medical laboratory of Nagano College of Nursing in Japan. Ten rats were divided into two groups, with five rats in each group. Rats in the control group were not bathed. Rats in the preconditioning group (PC group) were bathed with hot tap-water. Bathing was conducted thrice a week. After bathing for 4 weeks, the PI model was constructed on the rats’ dorsal skin. The skin temperature, skin moisture, and area of ulcers were compared between the two groups. In vitro, we investigated the expression of heat shock protein 27 (Hsp27) in 6, 12, and 24 h after the PI model was constructed through Western blot analysis. Ulcers occurred in the control group 24 h after the PI model constructed, wheras the PC group exhibited ulcers after 36 h. The ulcer area was larger in the control group than that in the PC group after 24 h (all p < 0.05). The temperatures of PI wounds in the control group decreased and were lower than those in the PC group after 1, 6, 12, 36, and 48 h (all p < 0.05). However, the skin moisture levels of PI wounds increased in the control group and were higher than those in the PC group at the same time (all p < 0.05). Using Western blot analysis, hydrotherapy preconditioning showed the potential to increase Hsp27 expression after pressure was released (p < 0.05). We determine that heat shock preconditioning had a preventive effect on PIs in rat models, a result that may be associated with their actions in the upregulation of Hsp27.

The peroxisomal exportomer directly inhibits phosphoactivation of the pexophagy receptor Atg36 to suppress pexophagy in yeast

Autophagy receptor (or adaptor) proteins facilitate lysosomal destruction of various organelles in response to cellular stress, including nutrient deprivation. To what extent membrane-resident autophagy receptors also respond to organelle-restricted cues to induce selective autophagy remains poorly understood. We find that latent activation of the yeast pexophagy receptor Atg36 by the casein kinase Hrr25 in rich media is repressed by the ATPase activity of Pex1/6, the catalytic subunits of the exportomer AAA+ transmembrane complex enabling protein import into peroxisomes. Quantitative proteomics of purified Pex3, an obligate Atg36 coreceptor, support a model in which the exportomer tail anchored to the peroxisome membrane represses Atg36 phosphorylation on Pex3 without assistance from additional membrane factors. Indeed, we reconstitute inhibition of Atg36 phosphorylation in vitro using soluble Pex1/6 and define an N-terminal unstructured region of Atg36 that enables regulation by binding to Pex1. Our findings uncover a mechanism by which a compartment-specific AAA+ complex mediating organelle biogenesis and protein quality control staves off induction of selective autophagy.

HSF2 cooperates with HSF1 to drive a transcriptional program critical for the malignant state

Heat shock factor 1 (HSF1) is well known for its role in the heat shock response (HSR), where it drives a transcriptional program comprising heat shock protein (HSP) genes, and in tumorigenesis, where it drives a program comprising HSPs and many noncanonical target genes that support malignancy. Here, we find that HSF2, an HSF1 paralog with no substantial role in the HSR, physically and functionally interacts with HSF1 across diverse types of cancer. HSF1 and HSF2 have notably similar chromatin occupancy and regulate a common set of genes that include both HSPs and noncanonical transcriptional targets with roles critical in supporting malignancy. Loss of either HSF1 or HSF2 results in a dysregulated response to nutrient stresses in vitro and reduced tumor progression in cancer cell line xenografts. Together, these findings establish HSF2 as a critical cofactor of HSF1 in driving a cancer cell transcriptional program to support the anabolic malignant state.

Malaria parasites do respond to heat

The capacity of malaria parasites to respond to changes in their environment at the transcriptional level has been the subject of debate, but recent evidence has unambiguously demonstrated that Plasmodium spp. can produce adaptive transcriptional responses when exposed to some specific types of stress. These include metabolic conditions and febrile temperature. The Plasmodium falciparum protective response to thermal stress is similar to the response in other organisms, but it is regulated by a transcription factor evolutionarily unrelated to the conserved transcription factor that drives the heat shock (HS) response in most eukaryotes. Of the many genes that change expression during HS, only a subset constitutes an authentic response that contributes to parasite survival.

Proteasome regulators in pancreatic cancer

Pancreatic adenocarcinoma is one of the most lethal cancers with rising incidence. Despite progress in its treatment, with the introduction of more effective chemotherapy regimens in the last decade, prognosis of metastatic disease remains inferior to other cancers with long term survival being the exception. Molecular characterization of pancreatic cancer has elucidated the landscape of the disease and has revealed common lesions that contribute to pancreatic carcinogenesis. Regulation of proteostasis is critical in cancers due to increased protein turnover required to support the intense metabolism of cancer cells. The proteasome is an integral part of this regulation and is regulated, in its turn, by key transcription factors, which induce transcription of proteasome structural units. These include FOXO family transcription factors, NFE2L2, hHSF1 and hHSF2, and NF-Y. Networks that encompass proteasome regulators and transduction pathways dysregulated in pancreatic cancer such as the KRAS/ BRAF/MAPK and the Transforming growth factor beta/SMAD pathway contribute to pancreatic cancer progression. This review discusses the proteasome and its transcription factors within the pancreatic cancer cellular micro-environment. We also consider the role of stemness in carcinogenesis and the use of proteasome inhibitors as therapeutic agents.

Essentiality of Sis1, a J-domain protein Hsp70 cochaperone, can be overcome by Tti1, a specialized PIKK chaperone

J-domain protein cochaperones drive much of the functional diversity of Hsp70-based chaperone systems. Sis1 is the only essential J-domain protein of the cytosol/nucleus of Saccharomyces cerevisiae. Why it is required for cell growth is not understood, nor how critical its role is in regulation of heat shock transcription factor 1 (Hsf1). We report that single-residue substitutions in Tti1, a component of the heterotrimeric TTT complex, a specialized chaperone system for phosphatidylinositol 3-kinase-related kinase (PIKK) proteins, allow growth of cells lacking Sis1. Upon depletion of Sis1, cells become hypersensitive to rapamycin, a specific inhibitor of TORC1 kinase. In addition, levels of the three essential PIKKs (Mec1, Tra1, and Tor2), as well as Tor1, decrease upon Sis1 depletion. Overexpression of Tti1 allows growth without an increase in the other subunits of the TTT complex, Tel2 and Tti2, suggesting that it can function independent of the complex. Cells lacking Sis1, with viability supported by Tti1 suppressor, substantially up-regulate some, but not all, heat shock elements activated by Hsf1. Together, our results suggest that Sis1 is required as a cochaperone of Hsp70 for the folding/maintenance of PIKKs, making Sis1 an essential gene, and its requirement for Hsf1 regulation is more nuanced than generally appreciated.

The heat shock response and small molecule regulators

The heat shock response (HSR) is a highly conserved cellular pathway that is responsible for stress relief and the refolding of denatured proteins [1]. When a host cell is exposed to conditions such as heat shock, ischemia, or toxic substances, heat shock factor-1 (HSF-1), a transcription factor, activates the genes that encode for the heat shock proteins (Hsps), which are a family of proteins that work alongside other chaperones to relieve stress and refold proteins that have been denatured (Burdon, 1986) [2]. Along with the refolding of denatured proteins, Hsps facilitate the removal of misfolded proteins by escorting them to degradation pathways, thereby preventing the accumulation of misfolded proteins [3]. Research has indicated that many pathological conditions, such as diabetes, cancer, neuropathy, cardiovascular disease, and aging have a negative impact on HSR function and are commonly associated with misfolded protein aggregation [4,5]. Studies indicate an interplay between mitochondrial homeostasis and HSF-1 levels can impact stress resistance, proteostasis, and malignant cell growth, which further support the role of Hsps in pathological and metabolic functions [6]. On the other hand, Hsp activation by specific small molecules can induce the heat shock response, which can afford neuroprotection and other benefits [7]. This review will focus on the modulation of Hsps and the HSR as therapeutic options to treat these conditions.

HSP70s in Breast Cancer: Promoters of Tumorigenesis and Potential Targets/Tools for Therapy

The high frequency of breast cancer worldwide and the high mortality among women with this malignancy are a serious challenge for modern medicine. A deeper understanding of the mechanisms of carcinogenesis and emergence of metastatic, therapy-resistant breast cancers would help development of novel approaches to better treatment of this disease. The review is dedicated to the role of members of the heat shock protein 70 subfamily (HSP70s or HSPA), mainly inducible HSP70, glucose-regulated protein 78 (GRP78 or HSPA5) and GRP75 (HSPA9 or mortalin), in the development and pathogenesis of breast cancer. Various HSP70-mediated cellular mechanisms and pathways which contribute to the oncogenic transformation of mammary gland epithelium are reviewed, as well as their role in the development of human breast carcinomas with invasive, metastatic traits along with the resistance to host immunity and conventional therapeutics. Additionally, intracellular and cell surface HSP70s are considered as potential targets for therapy or sensitization of breast cancer. We also discuss a clinical implication of Hsp70s and approaches to targeting breast cancer with gene vectors or nanoparticles downregulating HSP70s, natural or synthetic (small molecule) inhibitors of HSP70s, HSP70-binding antibodies, HSP70-derived peptides, and HSP70-based vaccines.

Construction of a Highly Sensitive Thiol-Reactive AIEgen-Peptide Conjugate for Monitoring Protein Unfolding and Aggregation in Cells

Impairment of the protein quality control network leads to the accumulation of unfolded and aggregated proteins. Direct detection of unfolded protein accumulation in the cells may provide the possibility for early diagnosis of neurodegenerative diseases. Here a new platform based on a peptide-conjugated thiol-reactive aggregation-induced emission fluorogen (AIEgen), named MI-BTD-P (or D1), for labeling and tracking unfolded proteins in cells is reported. In vitro experiments with model proteins show that the non-fluorescent D1 only becomes highly fluorescent when reacted with the thiol group of free cysteine (Cys) residues on unfolded proteins but not glutathione or folded proteins with buried or surface exposed Cys. When the labeled unfolded proteins form aggregates, D1 fluorescence intensity is further increased, and fluorescence lifetime is prolonged. D1 is then used to measure unfolded protein loads in cells by flow cytometry and track the aggregate formation of the D1 labeled unfolded proteins using confocal microscopy. In combination with fluorescence lifetime imaging technique, the proteome at different folding statuses can be better differentiated, demonstrating the versatility of this new platform. The rational design of D1 demonstrates the outlook of incorporation of diverse functional groups to achieve maximal sensitivity and selectivity in biological samples.

Identification of a novel compound that simultaneously impairs the ubiquitin-proteasome system and autophagy

The ubiquitin-proteasome system (UPS) and macroautophagy/autophagy are the main proteolytic systems in eukaryotic cells for preserving protein homeostasis, i.e., proteostasis. By facilitating the timely destruction of aberrant proteins, these complementary pathways keep the intracellular environment free of inherently toxic protein aggregates. Chemical interference with the UPS or autophagy has emerged as a viable strategy for therapeutically targeting malignant cells which, owing to their hyperactive state, heavily rely on the sanitizing activity of these proteolytic systems. Here, we report on the discovery of CBK79, a novel compound that impairs both protein degradation by the UPS and autophagy. While CBK79 was identified in a high-content screen for drug-like molecules that inhibit the UPS, subsequent analysis revealed that this compound also compromises autophagic degradation of long-lived proteins. We show that CBK79 induces non-canonical lipidation of MAP1LC3B/LC3B (microtubule-associated protein 1 light chain 3 beta) that requires ATG16L1 but is independent of the ULK1 (unc-51 like autophagy activating kinase 1) and class III phosphatidylinositol 3-kinase (PtdIns3K) complexes. Thermal preconditioning of cells prevented CBK79-induced UPS impairment but failed to restore autophagy, indicating that activation of stress responses does not allow cells to bypass the inhibitory effect of CBK79 on autophagy. The identification of a small molecule that simultaneously impairs the two main proteolytic systems for protein quality control provides a starting point for the development of a novel class of proteostasis-targeting drugs.

Primordial super-enhancers: heat shock-induced chromatin organization in yeast

Specialized mechanisms ensure proper expression of critically important genes such as those specifying cell identity or conferring protection from environmental stress. Investigations of the heat shock response have been critical in elucidating basic concepts of transcriptional control. Recent studies demonstrate that in response to thermal stress, heat shock-responsive genes associate with high levels of transcriptional activators and coactivators and those in yeast intensely interact across and between chromosomes, coalescing into condensates. In mammalian cells, cell identity genes that are regulated by super-enhancers (SEs) are also densely occupied by transcriptional machinery that form phase-separated condensates. We suggest that the stress-remodeled yeast nucleome bears functional and structural resemblance to mammalian SEs, and will reveal fundamental mechanisms of gene control by transcriptional condensates.

The Mitochondrial Hsp90 TRAP1 and Alzheimer's Disease

Alzheimer’s Disease (AD) is the most common form of dementia, characterised by intra- and extracellular protein aggregation. In AD, the cellular protein quality control (PQC) system is derailed and fails to prevent the formation of these aggregates. Especially the mitochondrial paralogue of the conserved Hsp90 chaperone class, tumour necrosis factor receptor-associated protein 1 (TRAP1), is strongly downregulated in AD, more than other major PQC factors. Here, we review molecular mechanism and cellular function of TRAP1 and subsequently discuss possible links to AD. TRAP1 is an interesting paradigm for the Hsp90 family, as it chaperones proteins with vital cellular function, despite not being regulated by any of the co-chaperones that drive its cytosolic paralogues. TRAP1 encloses late folding intermediates in a non-active state. Thereby, it is involved in the assembly of the electron transport chain, and it favours the switch from oxidative phosphorylation to glycolysis. Another key function is that it ensures mitochondrial integrity by regulating the mitochondrial pore opening through Cyclophilin D. While it is still unclear whether TRAP1 itself is a driver or a passenger in AD, it might be a guide to identify key factors initiating neurodegeneration.

Hsp70-mediated quality control: should I stay or should I go?

Chaperones of the 70 kDa heat shock protein (Hsp70) superfamily are key components of the cellular proteostasis system. Together with its co-chaperones, Hsp70 forms proteostasis subsystems that antagonize protein damage during physiological and stress conditions. This function stems from highly regulated binding and release cycles of protein substrates, which results in a flow of unfolded, partially folded and misfolded species through the Hsp70 subsystem. Specific factors control how Hsp70 makes decisions regarding folding and degradation fates of the substrate proteins. In this review, we summarize how the flow of Hsp70 substrates is controlled in the cell with special emphasis on recent advances regarding substrate release mechanisms.

HSF1 promotes endometriosis development and glycolysis by up-regulating PFKFB3 expression

BACKGROUND

Endometriosis is a chronic hormonal inflammatory disease characterized by the presence of endometrial tissue outside the uterus. Endometriosis often causes infertility, which brings physical and mental pain to patients and their families.

METHODS

We examined the functions of heat shock factor 1 (HSF1) in endometriosis development through cell count assay, cell-scratch assay and clone formation experiments. We used quantitative real-time PCR (qRT-PCR) and Western blot (WB) to detect HSF1 expression. Glucose and lactate levels were determined using a glucose (GO) assay kit and a lactate assay kit. Furthermore, we used a HSF1 inhibitor-KRIBB11 to establish a mouse model of endometriosis.

RESULTS

Our data demonstrated that HSF1 promoted endometriosis development. Interestingly, HSF1 enhanced glycolysis via up-regulating PFKFB3 expression in endometriosis cells, which was a key glycolysis enzyme. Consistently, the HSF1 inhibitor KRIBB11 could abrogate endometriosis progression in vivo and in vitro.

CONCLUSIONS

Findings indicate that HSF1 plays an important role in endometriosis development, which might become a new target for the treatment of endometriosis.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary data are available.

Subcellular localization of the J-protein Sis1 regulates the heat shock response

Cells exposed to heat shock induce a conserved gene expression program, the heat shock response (HSR), encoding protein homeostasis (proteostasis) factors. Heat shock also triggers proteostasis factors to form subcellular quality control bodies, but the relationship between these spatial structures and the HSR is unclear. Here we show that localization of the J-protein Sis1, a cofactor for the chaperone Hsp70, controls HSR activation in yeast. Under nonstress conditions, Sis1 is concentrated in the nucleoplasm, where it promotes Hsp70 binding to the transcription factor Hsf1, repressing the HSR. Upon heat shock, Sis1 forms an interconnected network with other proteostasis factors that spans the nucleolus and the surface of the endoplasmic reticulum. We propose that localization of Sis1 to this network directs Hsp70 activity away from Hsf1 in the nucleoplasm, leaving Hsf1 free to induce the HSR. In this manner, Sis1 couples HSR activation to the spatial organization of the proteostasis network.

Augmentation of the heat shock axis during exceptional longevity in Ames dwarf mice

How the heat shock axis, repair pathways, and proteostasis impact the rate of aging is not fully understood. Recent reports indicate that normal aging leads to a 50% change in several regulatory elements of the heat shock axis. Most notably is the age-dependent enhancement of inhibitory signals associated with accumulated heat shock proteins and hyper-acetylation associated with marked attenuation of heat shock factor 1 (HSF1)–DNA binding activity. Because exceptional longevity is associated with increased resistance to stress, this study evaluated regulatory check points of the heat shock axis in liver extracts from 12 months and 24 months long-lived Ames dwarf mice and compared these findings with aging wild-type mice. This analysis showed that 12M dwarf and wild-type mice have comparable stress responses, whereas old dwarf mice, unlike old wild-type mice, preserve and enhance activating elements of the heat shock axis. Old dwarf mice thwart negative regulation of the heat shock axis typically observed in usual aging such as noted in HSF1 phosphorylation at Ser307 residue, acetylation within its DNA binding domain, and reduction in proteins that attenuate HSF1–DNA binding. Unlike usual aging, dwarf HSF1 protein and mRNA levels increase with age and further enhance by stress. Together these observations suggest that exceptional longevity is associated with compensatory and enhanced HSF1 regulation as an adaptation to age-dependent forces that otherwise downregulate the heat shock axis.

Sis1 potentiates the stress response to protein aggregation and elevated temperature

Cells adapt to conditions that compromise protein conformational stability by activating various stress response pathways, but the mechanisms used in sensing misfolded proteins remain unclear. Moreover, aggregates of disease proteins often fail to induce a productive stress response. Here, using a yeast model of polyQ protein aggregation, we identified Sis1, an essential Hsp40 co-chaperone of Hsp70, as a critical sensor of proteotoxic stress. At elevated levels, Sis1 prevented the formation of dense polyQ inclusions and directed soluble polyQ oligomers towards the formation of permeable condensates. Hsp70 accumulated in a liquid-like state within this polyQ meshwork, resulting in a potent activation of the HSF1 dependent stress response. Sis1, and the homologous DnaJB6 in mammalian cells, also regulated the magnitude of the cellular heat stress response, suggesting a general role in sensing protein misfolding. Sis1/DnaJB6 functions as a limiting regulator to enable a dynamic stress response and avoid hypersensitivity to environmental changes.

CDK5RAP3, a Novel Nucleoplasmic Shuttle, Deeply Regulates HSF1-Mediated Heat Stress Response and Protects Mammary Epithelial Cells from Heat Injury

CDK5RAP3 was regarded as the most significant regulator of cellular responses against heat stress, which is associated with dysfunctions of the immune system and animal susceptibility to disease. Despite this, little known about how CDK5RAP3 regulates heat stress response. In this study, CDK5RAP3 conditional Knockout (CKO) mice, CDK5RAP3-/- mouse embryo fibroblasts (MEFs) and bovine mammary epithelial cells (BMECs) were used as an in vitro and in vivo model, respectively to reveal the role of CDK5RAP3 in regulating the heat stress response. The deletion of CDK5RAP3 unexpectedly caused animal lethality after 1.5-h heat stimulations. Furthermore, BMECs were re-cultured for eight hours after heat stress and was found that the expression of CDK5RAP3 and HSPs showed a similar fluctuating pattern of increase (0-2, 4-6 h) and decrease (2-4, 6-8 h). In addition to the remarkably enhanced expression of heat shock protein, apoptosis rate and endoplasmic reticulum stress, the deletion of CDK5RAP3 also affected nucleoplasmic translocation and trimer formation of heat shock factor 1 (HSF1). These programs were further confirmed in the mammary gland of CDK5RAP3 CKO mice and CDK5RAP3-/- MEFs as well. Interestingly, genetic silencing of HSF1 downregulated CDK5RAP3 expression in BMECs. Immunostaining and immunoprecipitation studies suggested a physical interaction between CDK5RAP3 and HSF1 being co-localized in the cytoplasm and nucleus. Besides, CDK5RAP3 also interacted with HSP90, suggesting an operative machinery at both transcriptional level and protein functionality of HSP90 per se. Together, our findings suggested that CDK5RAP3 works like a novel nucleoplasmic shuttle or molecular chaperone, deeply participating in HSF1-mediated heat stress response and protecting cells from heat injury.