GRP75 Regulates Mitochondrial-Supercomplex Turnover to Modulate Insulin Sensitivity.

GRP75 (75-kDA glucose-regulated protein), defined as a major component of both the mitochondrial quality control system and mitochondria-associated membrane, plays a key role in mitochondrial homeostasis. In this study, we assessed the roles of GRP75, other than as a component, in insulin action in both in vitro and in vivo models with insulin resistance. We found that GRP75 was downregulated in mice fed a high-fat diet (HFD) and that induction of Grp75 in mice could prevent HFD-induced obesity and insulin resistance. Mechanistically, GRP75 influenced insulin sensitivity by regulating mitochondrial function through its modulation of mitochondrial-supercomplex turnover rather than mitochondria-associated membrane communication: GRP75 was negatively associated with respiratory chain complex activity and was essential for mitochondrial-supercomplex assembly and stabilization. Moreover, mitochondrial dysfunction in Grp75-knockdown cells might further increase mitochondrial fragmentation, thus triggering cytosolic mtDNA release and activating the cGAS/STING-dependent proinflammatory response. Therefore, GRP75 can serve as a potential therapeutic target of insulin resistant-related diabetes or other metabolic diseases.

GRP75 mediates endoplasmic reticulum-mitochondria coupling during palmitate-induced pancreatic ß-cell apoptosis.

The endoplasmic reticulum (ER) and mitochondria are structurally connected with each other at specific sites termed mitochondria-associated membranes (MAMs). These physical links are composed of several tethering proteins and are important during varied cellular processes, such as calcium homeostasis, lipid metabolism and transport, membrane biogenesis, and organelle remodeling. However, the attributes of specific tethering proteins in these cellular functions remain debatable. Here, we present data to show that one such tether protein, glucose regulated protein 75 (GRP75), is essential in increasing ER-mitochondria contact during palmitate-induced apoptosis in pancreatic insulinoma cells. We demonstrate that palmitate increased GRP75 levels in mouse and rat pancreatic insulinoma cells as well as in mouse primary islet cells. This was associated with increased mitochondrial Ca2+ transfer, impaired mitochondrial membrane potential, increased ROS production, and enhanced physical coupling between the ER and mitochondria. Interestingly, GRP75 inhibition prevented these palmitate-induced cellular aberrations. Additionally, GRP75 overexpression alone was sufficient to impair mitochondrial membrane potential, increase mitochondrial Ca2+ levels and ROS generation, augment ER-mitochondria contact, and induce apoptosis in these cells. In vivo injection of palmitate induced hyperglycemia and hypertriglyceridemia, as well as impaired glucose and insulin tolerance in mice. These animals also exhibited elevated GRP75 levels accompanied by enhanced apoptosis within the pancreatic islets. Our findings suggest that GRP75 is critical in mediating palmitate-induced ER-mitochondrial interaction leading to apoptosis in pancreatic islet cells.

Circular RNA 0025984 Ameliorates Ischemic Stroke Injury and Protects Astrocytes Through miR-143-3p/TET1/ORP150 Pathway.

MiR-143-3p is aberrantly expressed in patients with ischemic stroke and associated with ischemic brain injury. However, the underlying mechanisms are largely unknown. Here, we confirmed circ_0025984 and TET1 as a sponge and target of miR-143-3p, respectively, by luciferase reporter assay. In astrocytes, OGD significantly decreased circ_0025984 and TET1 levels but increased miR-143-3p levels, which was also observed in brains of mice with MCAO. Treatment with miR-143-3p inhibitor or circ_0025984 significantly decreased astrocyte apoptosis and autophagy, as well as cerebral injury and neuron loss in mice with MCAO. Notably, TET1 overexpression decreased astrocyte apoptosis and autophagy and induced promoter hypomethylation and expression of ORP150. Our results demonstrated for the first time that circ_0025984 protects astrocytes from ischemia-induced autophagy and apoptosis by targeting the miR-143-3p/TET1 pathway and might inhibit cerebral injury induced by ischemic stroke. Furthermore, our data revealed the important positive regulation of ORP150 by TET1, which could be associated with its neuroprotective role. Graphical abstract Model for signaling pathway of circ_0025984/miR-143-3p/TET1 inastrocytes cultured under OGD. In astrocytes, circ_0025984 acts as a sponge of miR-143-3p, which directly targets TET1 and decreases its expression (A). After translocatinginto the nucleus, TET1 binds to the promoter of ORP150, converts 5mC into 5hmC,leading to DNA demethylation and increased expression of ORP150 (B). In astrocytescultured under OGD, ER stress is induced and eventually leads to apoptosis andautophagy mediated by ATG7, which is regulated by circ_0025984 via ORP150 andGRP78 (C).

Heat shock protein A12B gene therapy improves perfusion, promotes neovascularization, and decreases fibrosis in a murine model of hind limb ischemia.

BACKGROUND: Heat shock protein A12B expressed in endothelial cells is important and required for angiogenesis to form functional vessels in ischemic tissue. We have previously shown the cardioprotective effects of heat shock protein A12B overexpression in a rat model of diabetic myocardial infarction. In this study, we aim to explore the role of heat shock protein A12B in a surgically-induced murine hind-limb ischemia model. MATERIALS AND METHODS: Adult 8- to 12-week-old C57BL/6J mice were divided into 2 groups: treated with Adeno.LacZ (control group) and with Adeno.HSPA12B (experimental group) and, with both groups subjected to right femoral artery ligation. Immediately after surgery, mice in both groups received either Adeno.HSPA12B or Adeno.LacZ (1 × 109 plaque forming units) in both the semimembranosus and gastrocnemius muscles of the right limb. The left limb served as the internal control. Both groups underwent serial laser Doppler imaging preoperatively, and again postoperatively until 28 days. Immunohistochemical analysis was performed 3 and 28 days post-surgery. RESULTS: Mice in the Adeno.HSPA12B gene therapy group showed improved motor function and a significantly higher blood perfusion ratio on postoperative days 21 and 28, along with better motor function. Immunohistochemical analysis showed increased expression of vascular endothelial growth factor, thioredoxin-1, heme oxygenase, and hypoxia-inducible factor 1α, along with a decreased expression of A-kinase-anchoring protein 12 and thioredoxin-interacting protein levels. The Adeno.HSPA12B-treated group also showed increased capillary and arteriolar density and an increased capillary-myocyte ratio, along with reduced fibrosis compared to the Adeno.LacZ group. CONCLUSION: Our study demonstrates that targeted Adeno.HSPA12B gene delivery into ischemic muscle enhances perfusion and angiogenic protein expression. This molecule shows promise for the management of peripheral vascular disease as a potential target for clinical trials and subsequent drug therapy.

Effects of mancozeb on heat Shock protein 70 (HSP70) and its relationship with the thermal physiology of Physalaemus henselii (Peters, 1872) tadpoles (Anura: Leptodactylidae).

Negative impacts on amphibians have been reported due to contamination by agrochemicals. However, until now, no study has tested the effect of the fungicide mancozeb (MZ) on thermal tolerance and its relationship with the expression of heat shock proteins (HSPs). MZ is the best-selling broad-spectrum fungicide in the world, which negatively affects non-target organisms. Here, we tested for the first time the effects of MZ on critical thermal maximum (CTmax) and its relationship to the expression of heat shock protein 70 (HSP70) in tadpoles of Physalameus henselii, a colder-adapted species in southernmost of the Neotropical region. A sublethal concentration of 2 mg/L was used. We found that the CTmax of the MZ-treated group was lower than that of the control group. In addition, there was an increase in HSP70 expression in tadpoles exposed to MZ and in tadpoles that underwent heat treatment. However, tadpoles subjected to MZ and heat treatment showed no induced HSP70 protein expression. Our results demonstrated that sublethal doses of the fungicide MZ negatively affected the thermal physiology and heat shock protein expression in tadpoles of P. henselii by inducing an increase in HSP70 concentration and by reducing the critical CTmax supported by tadpoles. It is important to understand the relationship between environmental contamination and physiological thermal limits in our current scenario of high rates of habitat conversion associated with unrestricted use of agrochemicals, as well as the challenging environmental changes induced by global warming.

Comprehensive interactome profiling of the human Hsp70 network highlights functional differentiation of J domains.

Hsp70s comprise a deeply conserved chaperone family that has a central role in maintaining protein homeostasis. In humans, Hsp70 client specificity is provided by 49 different co-factors known as J domain proteins (JDPs). However, the cellular function and client specificity of JDPs have largely remained elusive. We have combined affinity purification-mass spectrometry (AP-MS) and proximity-dependent biotinylation (BioID) to characterize the interactome of all human JDPs and Hsp70s. The resulting network suggests specific functions for many uncharacterized JDPs, and we establish a role of conserved JDPs DNAJC9 and DNAJC27 in histone chaperoning and ciliogenesis, respectively. Unexpectedly, we find that the J domain of DNAJC27 but not of other JDPs can fully replace the function of endogenous DNAJC27, suggesting a previously unappreciated role for J domains themselves in JDP specificity. More broadly, our work expands the role of the Hsp70-regulated proteostasis network and provides a platform for further discovery of JDP-dependent functions.

Transcriptional Enhancer Factor Domain Family member 4 Exerts an Oncogenic Role in Hepatocellular Carcinoma by Hippo-Independent Regulation of Heat Shock Protein 70 Family Members.

Transcriptional enhancer factor domain family member 4 (TEAD4) is a downstream effector of the conserved Hippo signaling pathway, regulating the expression of genes involved in cell proliferation and differentiation. It is up-regulated in several cancer types and is associated with metastasis and poor prognosis. However, its role in hepatocellular carcinoma (HCC) remains largely unexplored. Using data from The Cancer Genome Atlas, we found that TEAD4 was overexpressed in HCC and was associated with aggressive HCC features and worse outcome. Overexpression of TEAD4 significantly increased proliferation and migration rates in HCC cells in vitro as well as tumor growth in vivo. Additionally, RNA sequencing analysis of TEAD4-overexpressing HCC cells demonstrated that TEAD4 overexpression was associated with the up-regulation of genes involved in epithelial-to-mesenchymal transition, proliferation, and protein-folding pathways. Among the most up-regulated genes following TEAD4 overexpression were the 70-kDa heat shock protein (HSP70) family members HSPA6 and HSPA1A. Chromatin immunoprecipitation-quantitative real-time polymerase chain reaction experiments demonstrated that TEAD4 regulates HSPA6 and HSPA1A expression by directly binding to their promoter and enhancer regions. The pharmacologic inhibition of HSP70 expression in TEAD4-overexpressing cells reduced the effect of TEAD4 on cell proliferation. Finally, by overexpressing TEAD4 in yes-associated protein (YAP)/transcriptional coactivator with PDZ binding motif (TAZ)-knockdown HCC cells, we showed that the effect of TEAD4 on cell proliferation and its regulation of HSP70 expression does not require YAP and TAZ, the main effectors of the Hippo signaling pathway. Conclusion: A novel Hippo-independent mechanism for TEAD4 promotes cell proliferation and tumor growth in HCC by directly regulating HSP70 family members.

Hsp70 acts as a fine-switch that controls E3 ligase CHIP-mediated TAp63 and ΔNp63 ubiquitination and degradation.

The major clinical problem in human cancer is metastasis. Metastases are the cause of 90% of human cancer deaths. TAp63 is a critical suppressor of tumorigenesis and metastasis. ΔNp63 acts as a dominant-negative inhibitor to block the function of p53 and TAp63. Although several ubiquitin E3 ligases have been reported to regulate p63 stability, the mechanism of p63 regulation remains partially understood. Herein, we show that CHIP, an E3 ligase with a U-box domain, physically interacts with p63 and promotes p63 degradation. Notably, Hsp70 depletion by siRNA stabilizes TAp63 in H1299 cells and destabilizes ΔNp63 in SCC9 cells. Loss of Hsp70 results in a reduction in the TAp63-CHIP interaction in H1299 cells and an increase in the interaction between ΔNp63 and CHIP in SCC9 cells. Our results reveal that Hsp70 acts as a molecular switch to control CHIP-mediated ubiquitination and degradation of p63 isoforms. Furthermore, regulation of p63 by the Hsp70-CHIP axis contributes to the migration and invasion of tumor cells. Hence, our findings demonstrate that Hsp70 is a crucial regulator of CHIP-mediated ubiquitination and degradation of p63 isoforms and identify a new pathway for maintaining TAp63 or ΔNp63 stability in cancers.

Mutation of the BAG-1 domain decreases its protective effect against hypoxia/reoxygenation by regulating HSP70 and the PI3K/AKT signalling pathway in SY-SH5Y cells.

BCL-2-associated athanogene-1 (BAG-1) is a multifunctional protein that was first identified as a binding partner of BCL-2. Our previous results indicated that BAG-1 large (BAG-1L) overexpression significantly increases cell viability and decreases apoptosis by upregulating HSP70 and p-AKT in response to hypoxia/reoxygenation in SY-SH5Y cells. However, the functional domain of BAG-1L that exerts these protective effects against hypoxic damage has not been identified. In this study, we examined changes in HSP70 and p-AKT protein levels in SH-SY5Y cells with or without BAG-1L domain mutation after six hours of hypoxia/reoxygenation treatment. The BAG-1 domain mutant (BAG-1MUT) attenuated neuronal viability and proliferation while enhancing apoptosis after hypoxia/reoxygenation, which was achieved in part by inhibiting the HSP70 and p-AKT signalling pathways. This evidence illustrates that the BAG-1 domain plays a key role in protecting cells from hypoxia/reoxygenation injury.

HSP70 regulates Eg5 distribution within the mitotic spindle and modulates the cytotoxicity of Eg5 inhibitors.

The heat shock protein 70 (HSP70) is a conserved molecular chaperone and proteostasis regulator that protects cells from pharmacological stress and promotes drug resistance in cancer cells. In this study, we found that HSP70 may promote resistance to anticancer drugs that target the mitotic kinesin, Eg5, which is essential for assembly and maintenance of the mitotic spindle and cell proliferation. Our data show that loss of HSP70 activity enhances Eg5 inhibitor-induced cytotoxicity and spindle abnormalities. Furthermore, HSP70 colocalizes with Eg5 in the mitotic spindle, and inhibition of HSP70 disrupts this colocalization. Inhibition or depletion of HSP70 also causes Eg5 to accumulate at the spindle pole, altering microtubule dynamics and leading to chromosome misalignment. Using ground state depletion microscopy followed by individual molecule return (GSDIM), we found that HSP70 inhibition reduces the size of Eg5 ensembles and prevents their localization to the inter-polar region of the spindle. In addition, bis(maleimido)hexane-mediated protein-protein crosslinking and proximity ligation assays revealed that HSP70 inhibition deregulates the interaction between Eg5 tetramers and TPX2 at the spindle pole, leading to their accumulation in high-molecular-weight complexes. Finally, we showed that the passive substrate-binding activity of HSP70 is required for appropriate Eg5 distribution and function. Together, our results show that HSP70 substrate-binding activity may regulate proper assembly of Eg5 ensembles and Eg5-TPX2 complexes to modulate mitotic distribution/function of Eg5. Thus, HSP70 inhibition may sensitize cancer cells to Eg5 inhibitor-induced cytotoxicity.

Inhibition of orf virus replication in goat skin fibroblast cells by the HSPA1B protein, as demonstrated by iTRAQ-based quantitative proteome analysis.

Orf virus (ORFV) infects sheep and goat tissues, resulting in severe proliferative lesions. To analyze cellular protein expression in ORFV-infected goat skin fibroblast (GSF) cells, we used two-dimensional liquid chromatography-tandem mass spectrometry coupled with isobaric tags for relative and absolute quantification (iTRAQ). The proteomics approach was used along with quantitative reverse transcription polymerase chain reaction (RT-qPCR) to detect differentially expressed proteins in ORFV-infected GSF cells and mock-infected GSF cells. A total of 282 differentially expressed proteins were identified. It was found that 222 host proteins were upregulated and 60 were downregulated following viral infection. We confirmed that these proteins were differentially expressed and found that heat shock 70-kDa protein 1B (HSPA1B) was differentially expressed and localized in the cytoplasm. It was also noted that HSPA1B caused inhibition of viral proliferation, in the middle and late stages of viral infection. The differentially expressed proteins were associated with the biological processes of viral binding, cell structure, signal transduction, cell adhesion, and cell proliferation.

Endothelial cell HSPA12B and yes-associated protein cooperatively regulate angiogenesis following myocardial infarction.

Angiogenesis is essential for cardiac functional recovery after myocardial infarction (MI). HSPA12B is predominately expressed in endothelial cells and required for angiogenesis. Yes-associated protein (YAP) plays an important role in tumor angiogenesis. This study investigated the cooperative role of HSPA12B and YAP in angiogenesis after MI. Silencing of either HSPA12B or YAP impaired hypoxia-promoted endothelial cell proliferation and angiogenesis. Deficiency of HSPA12B suppressed YAP expression and nuclear translocation after hypoxia. Knockdown of YAP attenuated hypoxia-stimulated HSPA12B nuclear translocation and abrogated HSPA12B-promoted endothelial cell angiogenesis. Mechanistically, hypoxia induced an interaction between endothelial HSPA12B and YAP. ChIP assay showed that HSPA12B is a target gene of YAP/transcriptional enhanced associated domain 4 (TEAD4) and a coactivator in YAP-associated angiogenesis. In vivo studies using the MI model showed that endothelial cell-specific deficiency of HSPA12B (eHspa12b-/-) or YAP (eYap-/-) impaired angiogenesis and exacerbated cardiac dysfunction compared with WT mice. MI increased YAP expression and nuclear translocation in WT hearts but not eHspa12b-/- hearts. HSPA12B expression and nuclear translocation were upregulated in WT MI hearts but not eYap-/- MI myocardium. Our data demonstrate that endothelial HSPA12B is a target and coactivator for YAP/TEAD4 and cooperates with YAP to regulate endothelial angiogenesis after MI.

Two-step mechanism of J-domain action in driving Hsp70 function.

J-domain proteins (JDPs), obligatory Hsp70 cochaperones, play critical roles in protein homeostasis. They promote key allosteric transitions that stabilize Hsp70 interaction with substrate polypeptides upon hydrolysis of its bound ATP. Although a recent crystal structure revealed the physical mode of interaction between a J-domain and an Hsp70, the structural and dynamic consequences of J-domain action once bound and how Hsp70s discriminate among its multiple JDP partners remain enigmatic. We combined free energy simulations, biochemical assays and evolutionary analyses to address these issues. Our results indicate that the invariant aspartate of the J-domain perturbs a conserved intramolecular Hsp70 network of contacts that crosses domains. This perturbation leads to destabilization of the domain-domain interface-thereby promoting the allosteric transition that triggers ATP hydrolysis. While this mechanistic step is driven by conserved residues, evolutionarily variable residues are key to initial JDP/Hsp70 recognition-via electrostatic interactions between oppositely charged surfaces. We speculate that these variable residues allow an Hsp70 to discriminate amongst JDP partners, as many of them have coevolved. Together, our data points to a two-step mode of J-domain action, a recognition stage followed by a mechanistic stage.

An additional physiological role for HSP70: Assistance of vascular reactivity.

AIMS: HSP70, a molecular chaperone, helps to maintain proteostasis. In muscle biology, however, evidence suggests HSP70 to have a more versatile range of functions, as genetic deletion of its inducible genes impairs Ca2+ handling, and consequently, cardiac and skeletal muscle contractility. Still, it is unknown whether HSP70 is involved in vascular reactivity, an intrinsic physiological mechanism of blood vessels. Therefore, we designed this study to test the hypothesis that proper vascular reactivity requires the assistance of HSP70. MAIN METHODS: We performed functional studies in a wire-myograph using thoracic aorta isolated from male Sprague Dawley rats. Experiments were conducted with and without an HSP70 inhibitor as well as in heat-stressed vessels. The expression levels of HSP70 were evaluated with Western blotting. NO and ROS levels were assessed with fluorescence microscopy. KEY FINDINGS: We report that blockade of HSP70 weakens contraction in response to phenylephrine (dose-response) in the aorta. Additionally, we demonstrated that inhibition of HSP70 affects the amplitude of the fast and of the slow components of the time-force curve. Corroborating these findings, we found that inhibition of HSP70, in vessels over-expressing this protein, partly rescues the contractile phenotype of aortic rings. Furthermore, we show that blockade of HSP70 facilitates relaxation in response to acetylcholine and clonidine without affecting the basal levels of NO and ROS. SIGNIFICANCE: Our work introduces an additional physiological role for HSP70, the assistance of vascular reactivity, which highlights this protein as a new player in vascular physiology, and therefore, uncovers a promising research avenue for vascular diseases.

Autophagy and Hsp70 activation alleviate oral epithelial cell death induced by food-derived hypertonicity.

Stable intracellular and intercellular osmolarity is vital for all physiological processes. Although it is the first organ that receives food, the osmolarity around the mouth epithelium has never been systematically investigated. We found that oral epithelial cells are a population of ignored cells routinely exposed to hypertonic environments mainly composed of saline, glucose, etc. in vivo after chewing food. By using cultured oral epithelial cells as an in vitro model, we found that the hypotonic environments caused by both high NaCl and high glucose induced cell death in a dose- and time-dependent manner. Transcriptomics revealed similar expression profiles after high NaCl and high glucose stimulation. Most of the common differentially expressed genes were enriched in "mitophagy" and "autophagy" according to KEGG pathway enrichment analysis. Hypertonic stimulation for 1 to 6 h resulted in autophagosome formation. The activation of autophagy protected cells from high osmolarity-induced cell death. The activation of Hsp70 by the pharmacological activator handelin significantly improved the cell survival rate after hypertonic stimulation. The protective role of Hsp70 activation was partially dependent on autophagy activation, indicating a crosstalk between Hsp70 and autophagy in hypertonic stress response. The extract of the handelin-containing herb Chrysanthemum indicum significantly protected oral epithelial cells from hypertonic-induced death, providing an inexpensive way to protect against hypertonic-induced oral epithelial damage. In conclusion, the present study emphasized the importance of changes in osmolarity in oral health for the first time. The identification of novel compounds or herbal plant extracts that can activate autophagy or HSPs may contribute to oral health and the food industry.

Heat shock protein signaling in brain ischemia and injury.

Heat shock proteins (HSPs) are chaperones that catalyze the refolding of denatured proteins. In addition to their ability to prevent protein denaturation and aggregation, the HSPs have also been shown to modulate many signaling pathways. Among HSPs, the inducible 70 kDa HSP (HSP70) has especially been shown to improve neurological outcome in experimental models of brain ischemia and injury. HSP70 can modulate various aspects of the programmed cell death pathways and inflammation. This review will focus on potential mechanisms of the neuroprotective effects of HSP70 in stroke and brain trauma models. We also comment on potential ways in which HSP70 could be translated into clinical therapies.

The molecular chaperone Hsp70 from the thermotolerant Diptera species differs from the Drosophila paralog in its thermostability and higher refolding capacity at extreme temperatures.

Previously, we demonstrated that species of the Stratiomyidae family exhibit higher tolerance to thermal stress in comparison with that of many representatives of Diptera, including Drosophila species. We hypothesized that species of this group inherited the specific structures of their chaperones from an ancestor of the Stratiomyidae family, and this enabled the descendants to colonize various extreme habitats. To explore this possibility, we cloned and expressed in Escherichia coli copies of the Hsp70 genes from Stratiomys singularior, a typical eurythermal species, and Drosophila melanogaster, for comparison. To investigate the thermal sensitivity of the chaperone function of the inducible 70-kDa heat shock proteins from these species, we used an in vitro refolding luciferase assay. We demonstrated that under conditions of elevated temperature, S. singularior Hsp70 exhibited higher reactivation activity in comparison with D. melanogaster Hsp70 and even human Hsp70. Similarly, S. singularior Hsp70 was significantly more thermostable and showed in vitro refolding activity after preheatment at higher temperatures than D. melanogaster paralog. Thermally induced unfolding experiments using differential scanning calorimetry indicated that Hsp70 from both Diptera species is formed by two domains with different thermal stabilities and that the ATP-binding domain of S. singularior is stable at temperatures 4 degrees higher than that of the D. melanogaster paralog. To the best of our knowledge, this study represents the first report that provides direct experimental data indicating that the evolutionary history of a species may result in adaptive changes in the structures of chaperones to enable them to elicit protective functions at extreme environments.

MAPKAP kinase 2-mediated phosphorylation of HspA1L protects male germ cells from heat stress-induced apoptosis.

Developing male germ cells are extremely sensitive to heat stress; consequently, anatomic and physiologic adaptations have evolved to maintain proper thermoregulation during mammalian spermatogenesis. At the cellular level, increased expression and activity of HSP70 family members occur in response to heat stress in order to refold partially denatured proteins and restore function. In addition, several kinase-mediated signaling pathways are activated in the testis upon hyperthermia. The p38 MAP kinase (MAPK) pathway plays an important role in mitigating heat stress, and recent findings have implicated the downstream p38 substrate, MAPKAP kinase 2 (MK2), in this process. However, the precise function that this kinase plays in spermatogenesis is not completely understood. Using a proteomics-based screen, we identified and subsequently validated that the testis-enriched HSP70 family member, HspA1L, is a novel substrate of MK2. We demonstrate that MK2 phosphorylates HspA1L solely on Ser241, a residue within the N-terminal nucleotide-binding domain of the enzyme. This phosphorylation event enhances the chaperone activity of HspA1L in vitro and renders male germ cells more resistant to heat stress-induced apoptosis. Taken together, these findings illustrate a novel stress-induced signaling cascade that promotes the chaperone activity of HspA1L with implications for understanding male reproductive biology.

Differential expression of HSF1 and HSPA6 genes and physiological responses in Angus and Simmental cattle breeds.

The aim of this study was to identify whether more and less adapted Angus and Simmental cattle differed in physiological responses and expression of the heat shock factor 1 (HSF1) and the heat shock 70 kDa protein 6 (HSPA6), when subjected to heat stress. Thirty bulls (n = 15 ANG; n = 15 SIM), extremes "more adapted" and "less adapted" within each breed were selected to the heat tolerance test. They were selected according to an index based on the average of the respiratory rate obtained on two hot summer days from one hundred bulls. Before the heat tolerance test day, animals were taken to a paddock with water, grass and shade until 7 a.m. of the following day for morning measurements. They were kept in the barn without access to water and shade until 1 p.m. for the afternoon measurements. Respiratory rate in the morning (MRR) and afternoon (ARR), hair coat surface temperature in the morning (MST) and afternoon (AST), rectal temperature in the morning (MRT) and afternoon (ART) were measured and blood samples were collected for expression analysis of the HSF1 and HSPA6 genes. The MIXED procedure of SAS was used for all statistical analysis. The more adapted Simmental group had lesser values of MRR (P = 0.023) and MRT (P = 0.095), but there was no difference within Angus breed. The ARR was greater (P = 0.004) in less adapted animals for both breeds. The ART was lower in the Simmental breed (P < 0.001). Less adapted had greater levels of mRNA of HSF1 (P = 0.06) and HSPA6 (P = 0.09). In conclusion, respiratory rate, rectal temperature and expression of the HSF1 and HSPA6 genes can be indicators of thermotolerance in taurine cattle. Both breeds show physiologically similar responses under heat stress conditions.

Prion disease is accelerated in mice lacking stress-induced heat shock protein 70 (HSP70).

Prion diseases are a group of incurable neurodegenerative disorders that affect humans and animals via infection with proteinaceous particles called prions. Prions are composed of PrPSc, a misfolded version of the cellular prion protein (PrPC). During disease progression, PrPSc replicates by interacting with PrPC and inducing its conversion to PrPSc As PrPSc accumulates, cellular stress mechanisms are activated to maintain cellular proteostasis, including increased protein chaperone levels. However, the exact roles of several of these chaperones remain unclear. Here, using various methodologies to monitor prion replication (i.e. protein misfolding cyclic amplification and cellular and animal infectivity bioassays), we studied the potential role of the molecular chaperone heat shock protein 70 (HSP70) in prion replication in vitro and in vivo Our results indicated that pharmacological induction of the heat shock response in cells chronically infected with prions significantly decreased PrPSc accumulation. We also found that HSP70 alters prion replication in vitro More importantly, prion infection of mice lacking the genes encoding stress-induced HSP70 exhibited accelerated prion disease progression compared with WT mice. In parallel with HSP70 being known to respond to endogenous and exogenous stressors such as heat, infection, toxicants, and ischemia, our results indicate that HSP70 may also play an important role in suppressing or delaying prion disease progression, opening opportunities for therapeutic intervention.