Heat stress facilitates stretch-induced hypertrophy of cultured muscle cells

Increased mechanical stress induced by stretch is an important growth stimulus in skeletal muscle. Heat shock proteins (HSPs) are an important family of endogenous, protective proteins. HSP90 and HSP70 families show elevated levels under beat stress. Mechanical stress, such as physical exercise, is known to induce not only muscular hypertrophy but also the elevation of HSPs expression in skeletal muscle. The purpose of this study was to determine whether heat stress facilitates the stretch-induced hypertrophy of skeletal muscle cells. Cultured rat myotubes (L6) were plated on collagenized Silastic membranes and incubated at 41 degrees C for 60 and 75 minutes (heat shock). Following the incubation, the cells were subjected two-second stretching and four-second releasing for 4 days at 37 degrees C. Protein concentrations in the homogenates and pellets of the cultured skeletal muscle cells increased under heat shock and/or mechanical stretching. The protein concentration of cells following mechanical stretching following heat shock was significantly higher than that following either heat shock or mechanical stretching alone. HSP72 in supernatants and HSP90 in pellets increased under heat shock and/or mechanical stretching. HSP90 in supernatants decreased following heat shock and/or mechanical stretching. Changes in HSPs and cellular protein concentrations in stressed cells suggest that the expression of HSPs may be closely related with muscular hypertrophy.     

Heat shock gene expression in Xenopus laevis A6 cells in response to heat shock and sodium arsenite treatments

Continuous exposure of a Xenopus laevis kidney epithelial cell line, A6, to either heat shock (33 degrees C) or sodium arsenite (50 microM) resulted in transient but markedly different temporal patterns of heat-shock protein (HSP) synthesis and HSP 70 and 30 mRNA accumulation. Heat-shock-induced synthesis of HSPs was detectable within 1 h and reached maximum levels by 2-3 h. While sodium arsenite induced the synthesis of some HSPs within 1 h, maximal HSP synthesis did not occur until 12 h. The pattern of HSP 70 and 30 mRNA accumulation was similar to the response observed at the protein level. During recovery from heat shock, a coordinate decline in HSPs and HSP 70 and 30 mRNA was observed. During recovery from sodium arsenite, a similar phenomenon occurred during the initial stages. However, after 6 h of recovery, HSP 70 mRNA levels persisted in contrast to the declining HSP 30 mRNA levels. Two-dimensional polyacrylamide gel electrophoresis revealed the presence of 5 HSPs in the HSP 70 family, of which two were constitutive, and 16 different stress-inducible proteins in the HSP 30 family. In conclusion, heat shock and sodium arsenite induce a similar set of HSPs but maximum synthesis of the HSP is temporally separated by 12-24 h.     

Secretion of the heat shock proteins HSP70 and HSC70 by baby hamster kidney (BHK‐21) cells

The HSPs (heat‐shock proteins) of the 70‐kDa family, the constitutively expressed HSC70 (cognate 70‐kDa heat‐shock protein) and the stress‐inducible HSP70 (stress‐inducible 70‐kDa heat‐shock protein), have been reported to be actively secreted by various cell types. The mechanisms of the release of these HSPs are obscure, since they possess no consensus secretory signal sequence. We showed that baby hamster kidney (BHK‐21) cells released HSP70 and HSC70 in a serum‐free medium and that this process was the result of an active secretion of HSPs rather than the non‐specific release of the proteins due to cell death. It was found that the secretion of HSP70 and HSC70 is independent of de novo protein synthesis. BFA (Brefeldin A) did not inhibit the basal secretion of HSPs, indicating that the secretion of HSP70 and HSC70 from cells occurs by a non‐classical pathway. Exosomes did not contribute to the secretion of HSP70 and HSC70 by cells. MBC (methyl‐β‐cyclodextrin), a substance that disrupts the lipid raft organization, considerably reduced the secretion of both HSPs, indicating that lipid rafts are involved in the secretion of HSP70 and HSC70 by BHK‐21 cells. The results suggest that HSP70 and HSC70 are actively secreted by BHK‐21 cells in a serum‐free medium through a non‐classical pathway in which lipid rafts play an important role.     

Heat shock proteins HSP70 and HSP27 in the cerebral spinal fluid of patients undergoing thoracic aneurysm repair correlate with the probability of postoperative paralysis

An understanding of the time course and correlation with injury of heat shock proteins (HSPs) released during brain and/or spinal cord cellular stress (ischemia) is critical in understanding the role of the HSPs in cellular survival, and may provide a clinically useful biomarker of severe cellular stress. We have analyzed the levels of HSPs in the cerebrospinal fluid (CSF) from patients who are undergoing thoracic aneurysm repair. Blood and CSF samples were collected at regular intervals, and CSF was analyzed by enzyme-linked immunosorbent assay for HSP70 and HSP27. These results were correlated with intraoperative somatosensory-evoked potentials measurements and postoperative paralysis. We find that the levels of these proteins in many patients are elevated and that the degree of elevation correlates with the risk of permanent paralysis. We hypothesize that sequential measurement intraoperatively of the levels of the heat shock proteins HSP70 and HSP27 in the CSF can predict those patients who are at greatest risk for paralysis during thoracic aneurysm surgery and will allow us to develop means of preventing or attenuating this severe and often fatal complication.     

Heat shock protein 60 reactive T cells in juvenile idiopathic arthritis: what is new?

Juvenile idiopathic arthritis (JIA) is a disease characterized by chronic joint inflammation, caused by a deregulated immune response. In patients with JIA, heat shock proteins (HSPs) are highly expressed in the synovial lining tissues of inflamed joints. HSPs are endogenous proteins that are expressed upon cellular stress and are able to modulate immune responses. In this review, we concentrate on the role of HSPs, especially HSP60, in modulating immune responses in both experimental and human arthritis, with a focus on JIA. We will mainly discuss the tolerogenic immune responses induced by HSPs, which could have a beneficial effect in JIA. Overall, we will discuss the immune modulatory capacity of HSPs, and the underlying mechanisms of HSP60-mediated immune regulation in JIA, and how this can be translated into therapy.     

Apoptosis Versus Cell Differentiation: Role of Heat Shock Proteins HSP90, HSP70 and HSP27

Heat shock proteins HSP27, HSP70 and HSP90 are molecular chaperones whose expression is increased after many different types of stress. They have a protective function helping the cell to cope with lethal conditions. The cytoprotective function of HSPs is largely explained by their anti-apoptotic function. HSPs have been shown to interact with different key apoptotic proteins. As a result, HSPs can block essentially all apoptotic pathways, most of them involving the activation of cystein proteases called caspases. Apoptosis and differentiation are physiological processes that share many common features, for instance, chromatin condensation and the activation of caspases are frequently observed. It is, therefore, not surprising that many recent reports imply HSPs in the differentiation process. This review will comment on the role of HSP90, HSP70 and HSP27 in apoptosis and cell differentiation. HSPs may determine de fate of the cells by orchestrating the decision of apoptosis versus differentiation.Key Words: apoptosis, differentiation, heat shock proteins, chaperones, cancer cells, anticancer drugs     

热休克蛋白HSP70和gp96在抗病毒感染中的作用

热休克蛋白(HSP)是一组在进化上高度保守、具有重要生理功能的蛋白质家族,是生物在应激条件下产生的一种非特异性防御产物,在调节免疫应答和抗病毒反应中起重要作用。现简要介绍HSP70、gp96(HSP96,GRP94)这两种HSP与病毒感染的关系及在抗病毒感染中的作用。     

植物热激蛋白的功能及其基因表达的调控

本文介绍了植物热激蛋白的产生、分布和分类。着重论述了热激反应的特点、植物热激蛋白的功能、热激基因表达与调控的研究进展     

植物热激蛋白的功能及其基因表达的调控

本文介绍了植物热激蛋白的产：生、分布和分类。着重论述了热激反应的特点、植物热激蛋白的功能、热激基因表达与调控的研究进展。     

Chaperones in cell cycle regulation and mitogenic signal transduction: a review

Chaperones/heat shock proteins (HSPs) of the HSP90 and HSP70 families show elevated levels in proliferating mammalian cells and a cell cycle-dependent expression. They transiently associate with key molecules of the cell cycle control system such as Cdk4, Wee-1, pRb, p53, p27/Kip1 and are involved in the nuclear localization of regulatory proteins. They also associate with viral oncoproteins such as SV40 super T, large T and small t antigen, polyoma large and middle S antigen and EpsteinBarr virus nuclear antigen. This association is based on a J-domain in the viral proteins and may assist their targeting to the pRb/E2F complex. Small HSPs and their state of phosphorylation and oligomerization also seem to be involved in proliferation and differentiation. Chaperones/HSPs thus play important roles within cell cycle processes. Their exact functioning, however, is still a matter of discussion. HSP90 in particular, but also HSP70 and other chaperones associate with proteins of the mitogen-activated signal cascade, particularly with the Src kinase, with tyrosine receptor kinases, with Raf and the MAP-kinase activating kinase (MEK). This apparently serves the folding and translocation of these proteins, but possibly also the formation of large immobilized complexes of signal transducing molecules (scaffolding function).     

Heat shock protein expression in thermotolerant and thermosensitive lines of cotton

The expression of heat shock proteins (HSPs) was compared between genetically characterized heat tolerant and heat sensitive lines of cotton (Gossypium hirsutum andG. barbadense) using electrophoretic analysis ofin vivo labelled proteins. No differences were observed between the two lines with regard to: the temperature at which HSP synthesis was induced (37°C); the temperature at which HSP synthesis was maximal (45°C); the rates of recovery from HSP synthesis; the duration of HSP synthesis; or the major size classes of HSPs expressed in these two lines. Several HSPs were identified on 2D gels which were expressed uniquely in either the tolerant or sensitive cotton line. However, the HSP pattern displayed in a heat tolerant BC-3 individual was that of the heat sensitive parent.Abbreviations HSPs heat shock proteins - IEF isoelecticfocusing     

Localization of small heat shock proteins to the higher plant endomembrane system.

Three related gene families of low-molecular-weight (LMW) heat shock proteins (HSPs) have been characterized in plants. We describe a fourth LMW HSP family, represented by PsHSP22.7 from Pisum sativum and GmHSP22.0 from Glycine max, and demonstrate that this family of proteins is endomembrane localized. PsHSP22.7 and GmHSP22.0 are 76.7% identical at the amino acid level. Both proteins have amino-terminal signal peptides and carboxyl-terminal sequences characteristic of endoplasmic reticulum (ER) retention signals. The two proteins closely resemble class I cytoplasmic LMW HSPs, suggesting that they evolved from the cytoplasmic proteins through the addition of the signal peptide and ER retention motif. The endomembrane localization of these proteins was confirmed by cell fractionation. The polypeptide product of PsHSP22.7 mRNA was processed to a smaller-M(r) form by canine pancreatic microsomes; in vivo, GmHSP22.0 polysomal mRNA was found to be predominantly membrane bound. In vitro-processed PsHSP22.7 corresponded in mass and pI to one of two proteins detected in ER fractions from heat-stressed plants by using anti-PsHSP22.7 antibodies. Like other LMW HSPs, PsHSP22.7 was observed in higher-molecular-weight structures with apparent masses of between 80 and 240 kDa. The results reported here indicate that members of this new class of LMW HSPs are most likely resident ER proteins and may be similar in function to related LMW HSPs in the cytoplasm. Along with the HSP90 and HSP70 classes of HSPs, this is the third category of HSPs localized to the ER.     

Expression of a Conserved Family of Cytoplasmic Low Molecular Weight Heat Shock Proteins during Heat Stress and Recovery

Plants synthesize several families of low molecular weight (LMW) heat shock proteins (HSPs) in response to elevated temperatures. We have characterized two cDNAs, HSP18.1 and HSP17.9, that encode members of the class I family of LMW HSPs from pea (Pisum sativum). In addition, we investigated the expression of these HSPs at the mRNA and protein levels during heat stress and recovery. HSP18.1 and HSP17.9 are 82.1% identical at the amino acid level and are 80.8 to 92.9% identical to class I LMW HSPs of other angiosperms. Heat stress experiments were performed using intact seedlings subjected to a gradual temperature increase and held at a maximum temperature of 30 to 42 degrees Celsius for 4 hours. HSP18.1 and HSP17.9 mRNA levels peaked at the beginning of the maximum temperature period and declined rapidly after the stress period. Antiserum against a HSP18.1 fusion protein recognized both HSP18.1 and HSP17.9 but not members of other families of LMW HSPs. The accumulation of HSP18.1-immunodetected protein was proportional to the severity of the heat stress, and the protein had a half-life of 37.7 ± 8 hours. The long half-life of these proteins supports the hypothesis that they are involved in establishing thermotolerance.     

Heat shock protein 25 or inducible heat shock protein 70 activates heat shock factor 1: dephosphorylation on serine 307 through inhibition of ERK1/2 phosphorylation

The expression of heat shock proteins (HSPs) is known to be increased via activation of heat shock factor 1 (HSF1), and excess expression of HSPs exerts feedback inhibition of HSF1. However, the molecular mechanism to modulate such relationships between HSPs and HSF1 is not clear. In the present study, we show that stable transfection of either Hsp25 or inducible Hsp70 (Hsp70i) increased expression of endogenous HSPs such as HSP25 and HSP70i through HSF1 activation. However, these phenomena were abolished when the dominant negative Hsf1 mutant was transfected to HSP25 or HSP70i overexpressed cells. Moreover, the increased HSF1 activity by either HSP25 or HSP70i was found to result from dephosphorylation of HSF1 on serine 307 that increased the stability of HSF1. Either HSP25 or HSP70i inhibited ERK1/2 phosphorylation because of increased MKP1 phosphorylation by direct interaction of these HSPs with MKP1. Treatment of HOS and NCI-H358 cells, which showed high expressions of endogenous HSF1, with small interfering RNA (siRNA) of either HSP27 (siHSP27)or HSP70i (siHSP70i) inhibited both HSP27 and HSP70i proteins; this was because of increased ERK1/2 phosphorylation and serine phosphorylation of HSF1. The results, therefore, suggested that when the HSF1 protein level was high in cancer cells, excess expression of HSP27 or HSP70i strongly facilitates the expression of HSP proteins through HSF1 activation, resulting in severe radio- or chemoresistance.     

Myocardial heat shock proteins during the development of heart failure

When cardiomyocytes are exposed to stresses, production of heat shock proteins (HSPs) in the cells is enhanced. Such increase in cellular HSP production is considered to bring about tolerance against stress-induced cell damage. The exact role of the cellular HSPs remains unclear. In the present study, HSPs in the viable left ventricular myocardium were determined during the development of heart failure following coronary artery ligation (CAL). The rats after CAL showed symptoms of chronic heart failure (CHF) at the 8th week, but not at the 1st and 2nd weeks. Myocardial HSP27, which may bind to cytoskeletal protein, at the 1st, 2nd, and 8th weeks after CAL was approximately 180, 160, and 125% of the control, respectively. Myocardial HSP60, one of mitochondrial proteins, at the 8th week increased to 140% of the control, whereas those at the 1st and 2nd weeks did not change. Myocardial HSP72, an inducible form of HSP70 family, at the 1st week after CAL increased to 180% of the control, whereas that at the 2nd or 8th week was similar to control. Myocardial heat shock constitutive protein 73 (HSC73), a constitutively expressed form of HSP70 family, and HSP90, which may bind to steroid hormone receptor and actin fiber, of CAL rats did not alter throughout the experiment. These findings show that diverse changes in the production of myocardial HSPs occur during the development of heart failure. Only the increase in myocardial HSP60 production was associated with the development of CHF.     

Specific protein homeostatic functions of small heat‐shock proteins increase lifespan

During aging, oxidized, misfolded, and aggregated proteins accumulate in cells, while the capacity to deal with protein damage declines severely. To cope with the toxicity of damaged proteins, cells rely on protein quality control networks, in particular proteins belonging to the family of heat‐shock proteins (HSPs). As safeguards of the cellular proteome, HSPs assist in protein folding and prevent accumulation of damaged, misfolded proteins. Here, we compared the capacity of all Drosophila melanogaster small HSP family members for their ability to assist in refolding stress‐denatured substrates and/or to prevent aggregation of disease‐associated misfolded proteins. We identified CG14207 as a novel and potent small HSP member that exclusively assisted in HSP70‐dependent refolding of stress‐denatured proteins. Furthermore, we report that HSP67BC, which has no role in protein refolding, was the most effective small HSP preventing toxic protein aggregation in an HSP70‐independent manner. Importantly, overexpression of both CG14207 and HSP67BC in Drosophila leads to a mild increase in lifespan, demonstrating that increased levels of functionally diverse small HSPs can promote longevity in vivo.     

Nuclear localization and the heat shock proteins

The highly conserved heat shock proteins (HSP) belong to a subset of cellular proteins that localize to the nucleus. HSPs are atypical nuclear proteins in that they localize to the nucleus selectively, rather than invariably. Nuclear localization of HSPs is associated with cell stress and cell growth. This aspect of HSPs is highly conserved with nuclear localization occurring in response to a wide variety of cell stresses. Nuclear localization is likely important for at least some of the heat shock proteins’ protective functions; little is known about the function of the heat shock proteins in the nucleus. Nuclear localization is signalled by the presence of a basic nuclear localization sequence (NLS) within a protein. Though most is known about HSP 72’s nuclear localization, the NLS(s) has not been definitively identified for any of the heat shock proteins. Likely more is involved than presence of a NLS; since the heat shock proteins only localize to the nucleus under selective conditions, nuclear localization must be regulated. HSPs also function as chaperons of nuclear transport, facilitating the movement of other macromolecules across the nuclear membrane. The mechanisms involved in chaperoning of proteins by HSPs into the nucleus are still being identified.     

Heat shock resistance conferred by expression of the human HSP27 gene in rodent cells

Heat shock induces in cells the synthesis of specific proteins called heat shock proteins (HSPs) and a transient state of thermotolerance. The putative role of one of the HSPs, HSP27, as a protective molecule during thermal stress has been directly assessed by measuring the resistance to hyperthermia of Chinese hamster and mouse cells transfected with the human HSP27 gene contained in plasmid pHS2711. One- and two-dimensional gel electrophoresis of [3H]leucine- and [32P]orthophosphate-labeled proteins, coupled with immunological analysis using Ha27Ab and Hu27Ab, two rabbit antisera that specifically recognize the hamster and the human HSP27 protein respectively, were used to monitor expression and inducibility of the transfected and endogenous proteins. The human HSP27 gene cloned in pHS2711 is constitutively expressed in rodent cells, resulting in accumulation of the human HSP27 and all phosphorylated derivatives. No modification of the basal or heat-induced expression of endogenous HSPs is detected. The presence of additional HSP27 protein provides immediate protection against heat shock administered 48 h after transfection and confers a permanent thermoresistant phenotype to stable transfectant Chinese hamster and mouse cell lines. Mild heat treatment of the transfected cells results in an induction of the full complement of the endogenous heat shock proteins and a small increase in thermoresistance, but the level attained did not surpass that of heat-induced thermotolerant control cells. These results indicate that elevated levels of HSP27 is sufficient to give protection from thermal killing. It is concluded that HSP27 plays a major role in the increased thermal resistance acquired by cells after exposure to HSP inducers.