Actin cytoskeleton and small heat shock proteins: how do they interact?

Analysis of the alphaB-crystallin domain responsible for inhibiting tubulin aggregation

The cytoskeleton has a unique property such that changes of conformation result in polymerization into a filamentous form. alphaB-Crystallin, a small heat shock protein (sHsp), has chaperone activities for various substrates, including proteins constituting the cytoskeleton, such as actin; intermediate filament; and tubulin. However, it is not clear whether the "alpha-crystallin domain" common to sHsps also has chaperone activity for the protein cytoskeleton. To investigate the possibility that the C-terminal alpha-crystallin domain of alpha-crystallin has the aggregation-preventing ability for tubulin, we constructed an N-terminal domain deletion mutant of alphaB-crystallin. We characterized its structural properties and chaperone activities. Far-ultraviolet (UV) circular dichroism measurements showed that secondary structure in the alpha-crystallin domain of the deletion mutant is maintained. Ultracentrifuge analysis of molecular masses indicated that the deletion mutant formed smaller oligomers than did the full-length protein. Chaperone activity assays demonstrated that the N-terminal domain deletion mutant suppressed heat-induced aggregation of tubulin well. Comparison of chaperone activities for 2 other substrates (citrate synthase and alcohol dehydrogenase) showed that it was less effective in the suppression of their aggregation. These results show that alphaB-crystallin recognizes a variety of substrates and especially that alpha-crystallin domain binds free cytoskeletal proteins. We suggest that this feature would be advantageous in its functional role of holding or folding multiple proteins denatured simultaneously under stress conditions.

Genome-wide analysis and expression profiling of the small heat shock proteins in zebrafish

Small Heat Shock Proteins (sHSPs) have important roles in preventing disease and promoting resistance to environmental stressors. Mutations in any one of a number of sHSPs, including HSP27 (HSPB1), HSP22 (HSPB8), alphaA-crystallin (HSPB4), or alphaB-crystallin (HSPB5) can result in neuronal degeneration, myopathy, and/or cataract in humans. Ten sHSPs are known in humans, and thirteen have been identified in teleost fish. Here we report the identification of thirteen zebrafish sHSPs. Using a combination of phylogenetic analysis and analysis of synteny, we have determined that ten are likely orthologs of human sHSPs. We have used quantitative RT-PCR to determine the relative expression levels of all thirteen sHSPs during development and in response to heat shock. Our findings indicate that most of the zebrafish sHSPs are expressed during development, and five of these genes are transcriptionally upregulated by heat shock at one or more stages of development.

The cellular "networking" of mammalian Hsp27 and its functions in the control of protein folding, redox state and apoptosis

Cells possess effective mechanisms to cope with chronic or acute disturbance of homeostasis. Key roles in maintaining or restoring homeostasis are played by the various heat shock or stress proteins (Hsps). Among the Hsps, the group of proteins characterized by low molecular masses (between 20 to 30 kDa) and homology to alpha-crystallin are called small stress proteins (denoted sHsps). The present chapter summarizes the actual knowledge of the protective mechanisms generated by the expression of mammalian Hsp27 (also denoted HspB1 in human) against the cytotoxicity induced by heat shock and oxidative stress. It also describes the anti-apoptotic properties of Hsp27 and their putative consequences in different pathological conditions.

The interaction and cellular localization of HSP27 and ERbeta are modulated by 17beta-estradiol and HSP27 phosphorylation

Recently, we identified heat shock protein 27 (HSP27) as an estrogen receptor-beta (ERbeta) associated protein that acts as a co-repressor of estrogen signaling and serves as a biomarker of atherosclerosis. In this study, we sought to further characterize the subcellular interaction of HSP27 and ERbeta, as well as explore the factors that may modulate this interaction. In vitro we determined that phosphorylated HSP27 is retained in the cytoplasm after treatment with 17beta-estradiol and to a lesser extent with heat shock. Under all experimental conditions ERbeta was found to be slightly more abundant in the cytoplasm compared to the nucleus. HSP27 and ERbeta associate in both the cytoplasm and nucleus, however, co-localization studies reveal that in the presence of 17beta-estradiol, a significant portion of this interaction occurs outside of the nucleus. These data highlight an extranuclear interaction between ERbeta and HSP27 that may be of potential importance in modulating estrogen signaling.

Maximal eccentric exercise induces a rapid accumulation of small heat shock proteins on myofibrils and a delayed HSP70 response in humans

In this study the stress protein response to unaccustomed maximal eccentric exercise in humans was investigated. Eleven healthy males performed 300 maximal eccentric actions with the quadriceps muscle. Biopsies from vastus lateralis were collected at 30 min and 4, 8, 24, 96, and 168 h after exercise. Cellular regulation and localization of heat shock protein (HSP) 27, alpha B-crystallin, and HSP70 were analyzed by immunohistochemistry, ELISA technique, and Western blotting. Additionally, mRNA levels of HSP27, alpha B-crystallin, and HSP70 were quantified by Northern blotting. After exercise (30 min), 81 +/- 8% of the myofibers showed strong HSP27 staining (P < 0.01) that gradually decreased during the following week. alpha B-Crystallin mimicked the changes observed in HSP27. After exercise (30 min), the ELISA analysis showed a 49 +/- 13% reduction of the HSP27 level in the cytosolic fraction (P < 0.01), whereas Western blotting revealed a 15-fold increase of the HSP27 level in the myofibrillar fraction (P < 0.01). The cytosolic HSP70 level increased to 203 +/- 37% of the control level 24 h after exercise (P < 0.05). After 4 days, myofibrillar-bound HSP70 had increased approximately 10-fold (P < 0.01) and was accompanied by strong staining on cross sections. mRNA levels of HSP27, alpha B-crystallin, and HSP70 were all elevated the first day after exercise (P < 0.01); HSP70 mRNA showed the largest increase (20-fold at 8 h). HSP27 and alpha B-crystallin seemed to respond immediately to maximal eccentric exercise by binding to cytoskeletal/myofibrillar proteins, probably to function as stabilizers of disrupted myofibrillar structures. Later, mRNA and total HSP protein levels, especially HSP70, increased, indicating that HSPs play a role in skeletal muscle recovery and remodeling/adaptation processes to high-force exercise.

Diazoxide, as a postconditioning and delayed preconditioning trigger, increases HSP25 and HSP70 in the central nervous system following combined cerebral stroke and hemorrhagic shock

Combined hemorrhagic shock (Shock) and unilateral common carotid artery occlusion (Stroke) results in a decrease of oxygen availability to peripheral tissues and organs and the central nervous system (CNS). A variety of biochemical processes ensue, including organ failure, cellular apoptosis, and necrosis. The present study used male, Sprague-Dawley rats to assess the impact of cerebral insult. Using heat-shock protein 25 and 70 (HSP25, HSP70) as biomarkers, measured 24 h after injury, we tested the hypothesis that pharmacological induction of preconditioning can offer cytoprotection from combined Stroke and Shock. The compound, diazoxide (DZ), is known to induce preconditioning through its effect as a mitochondrial potassium ATP (mK(ATP)) channel opener and succinate dehydrogenase inhibitor. When administered 24 h prior to Stroke and Shock (delayed preconditioning), DZ increased cerebral cortical and hippocampal levels of HSP25 and HSP70. A more clinically relevant treatment paradigm was tested, where DZ was administered after the induction of Stroke and Shock (postconditioning). When administered 60 min (but not 10 min) after the induction of Stroke and Shock, DZ significantly increased HSP25 and HSP70 expression in the ipsilateral cerebral cortex and hippocampus. Taken together, these results suggest that DZ treatment may be efficacious for CNS injury resulting from blood loss and anoxia from combined cerebral ischemia and hemorrhagic shock. "Postconditioning" triggered by DZ, immediately before resuscitation, is a potentially effective treatment for ischemia-reperfusion injury from combined Stroke and Shock.

Interactive sequences in the stress protein and molecular chaperone human alphaB crystallin recognize and modulate the assembly of filaments

Molecular chaperones including the small heat shock proteins, alphaB crystallin and sHSP27 participate in the assembly, disassembly, and reorganization of the cytoskeleton during cell development and differentiation. While alphaB crystallin and sHSP27 stabilize and modulate filament assembly and re-organization, the sequences and structural domains mediating interactions between these proteins and filaments are unknown. It is important to define these interactive domains in order to understand differential interactions between chaperones and stable or unfolding filaments and their function in the cellular stress response. Protein pin arrays identified sequences in human alphaB crystallin that selectively interacted with native or partially unfolded filament proteins desmin, glial-fibrillary acidic protein, and actin. Circular dichroism spectroscopy determined differences in the structure of these filaments at 23 and 45 degrees C. Seven alphaB crystallin sequences had stronger interactions with desmin and six sequences had stronger interactions with glial-fibrillary acidic protein at 23 degrees C than at 45 degrees C. The alphaB crystallin sequences (33)LESDLFPTSTSLSPFYLRPPSFLR(56) and (129)DPLTITSSLSSDGV(145) had the strongest interactions with actin at 23 degrees C, while (57)APSWFDTG(64), (111)HGFISREF(118), (145)VNGPRKQVSG(154), and (155)PERTIPITREEK(165) had the strongest interactions with actin at 45 degrees C. The actin interactive sequences of alphaB crystallin overlapped with previously identified alphaB crystallin chaperone sequences and were synthesized to evaluate their effect on the assembly and aggregation of actin. Full-length alphaB crystallin and the core domain chaperone sequence (131)LTITSSLSSDGV(143) promoted actin polymerization at 37 degrees C and inhibited depolymerization and aggregation at 50 degrees C. The results support the hypothesis that interactive domains in alphaB crystallin have multiple functions in stabilizing the cytoskeleton and protecting cytosolic proteins from unfolding.

Age-Related Increase of Insoluble, Phosphorylated Small Heat Shock Proteins in Human Skeletal Muscle

Among mammalian heat shock proteins (Hsps), small Hsps (sHsps) are constitutively expressed in skeletal muscles. We investigated age-related changes of phosphorylation and cellular distribution of representative sHsps (Hsp27 and alphaB-crystallin) in human vastus lateralis muscle under resting conditions. We also examined upstream kinases which may be responsible for phosphorylation of sHsps, namely p38 mitogen-activated protein kinase (MAPK), MAPK-activated protein kinase-2, and extracellular signal-regulated kinase-1/2. The study groups consisted of nine young (15-38 years old) and nine aged (51-79 years old) patients who underwent orthopedic surgery. sHsps protein levels were higher in the insoluble fraction of aged muscles. The phosphorylated states of sHsps were enhanced in both the soluble and insoluble fraction of aged patients. The phosphorylated form of each upstream kinase was elevated in aged patients. Ubiquitinated proteins accumulated in the insoluble fractions of aged muscles. Aging mechanisms may affect the activation process of MAPKs, and the phosphorylation and accumulation of sHsps.

Hsp27 (HspB1) and alphaB-crystallin (HspB5) as therapeutic targets

Hsp27 and alphaB-crystallin are molecular chaperones that are constitutively expressed in several mammalian cells, particularly in pathological conditions. These proteins share functions as diverse as protection against toxicity mediated by aberrantly folded proteins or oxidative-inflammation conditions. In addition, these proteins share anti-apoptotic properties and are tumorigenic when expressed in cancer cells. This review summarizes the current knowledge about Hsp27 and alphaB-crystallin and the implications, either positive or deleterious, of these proteins in pathologies such as neurodegenerative diseases, myopathies, asthma, cataracts and cancers. Approaches towards therapeutic strategies aimed at modulating the expression and/or the activities of Hsp27 and alphaB-crystallin are presented.

Anthrax lethal toxin paralyzes actin-based motility by blocking Hsp27 phosphorylation

Inhalation of anthrax causes fatal bacteremia, indicating a meager host immune response. We previously showed that anthrax lethal toxin (LT) paralyzes neutrophils, a major component of innate immunity. Here, we have found that LT also inhibits actin-based motility of the intracellular pathogen Listeria monocytogenes. LT inhibition of actin assembly is mediated by blockade of Hsp27 phosphorylation, and can be reproduced by treating cells with the p38 mitogen-activated protein (MAP) kinase inhibitor SB203580. Nonphosphorylated Hsp27 inhibits Listeria actin-based motility in cell extracts, and binds to and sequesters purified actin monomers. Phosphorylation of Hsp27 reverses these effects. RNA interference knockdown of Hsp27 blocks LT inhibition of Listeria actin-based motility. Rescue with wild-type Hsp27 accelerates Listeria speed in knockdown cells, whereas introduction of Hsp27 mutants incapable of phosphorylation or dephosphorylation causes slowing down. We propose that Hsp27 facilitates actin-based motility through a phosphorylation cycle that shuttles actin monomers to regions of new actin filament assembly. Our findings provide a previously unappreciated mechanism for LT virulence, and emphasize a central role for p38 MAP kinase-mediated phosphorylation of Hsp27 in actin-based motility and innate immunity.

Modulation of HSP25 and TNF-alpha during the early stages of functional overload of a rat slow and fast muscle

Early events in response to abrupt increases in activation and loading with muscle functional overload (FO) are associated with increased damage and inflammation. Heat shock protein 25 (HSP25) may protect against these stressors, and its expression can be regulated by muscle loading and activation. The purpose of this study was to investigate the responses of HSP25, phosphorylated HSP25 (pHSP25), and tumor necrosis factor-alpha (TNF-alpha) during FO of the slow soleus and fast plantaris. We compared the HSP25 mRNA, HSP25 protein, pHSP25, and TNF-alpha responses in the soleus and plantaris after 0.5, 1, 2, 3, and 7 days of FO. HSP25 and pHSP25 were quantified in soluble and insoluble fractions. HSP25 mRNA increased immediately in both muscles and decreased with continued FO. However, HSP25 mRNA levels were consistently higher in the muscles of FO than control rats. In the soluble fraction, HSP25 increased in the plantaris after 2-7 days of FO with the greatest response at 3 and 7 days. The pHSP25 response to FO was greater in the plantaris than soleus at all points in the soluble fraction and at 0.5 days in the insoluble fraction. TNF-alpha levels in the plantaris, but not soleus, were higher than control at 0.5-2 days of FO. This may have contributed to the greater FO response in pHSP25 in the plantaris than soleus as TNF-alpha increased pHSP25 in C2C12 myotubes. These results suggest that the initial responses of pHSP25 and TNF-alpha to mechanical stress and inflammation associated with FO are greater in a fast than slow extensor muscle.

Cytoskeletal stability and heat shock-mediated thermoprotection of central pattern generation in Locusta migratoria

Prior exposure to extreme temperatures can induce thermoprotection in migratory locusts, which is important for survival in their natural environment. An important motor activity that needs to be protected is ventilation. The mechanism underlying heat shock is not fully understood, and our goal was to test the idea that cytoskeletal stability is critical for such thermoprotection. Cytoskeletal stabilizers (concanavalin A) and destabilizers (colchicine) were bath-applied in semi-intact locust preparations in both control (C) and pre-treated heat-shocked (3 h, 45 degrees C) animals. We measured parameters of the ventilatory motor pattern during maintained high temperature (43 degrees C) and recorded the times taken for motor pattern generation to fail and then recover on returning to room temperature. We found that concanavalin A mimicked the effects of a prior heat stress in control animals by increasing time to failure and decreasing time to recovery of motor pattern generation. However, colchicine destroyed protection in heat-shocked animals by decreasing time to failure and increasing time to recovery. Our findings confirm that the cytoskeleton has a mechanistic role in preserving neural function at high temperatures, possibly through stabilizing ion channels and other integral membrane proteins (e.g. Na(+)/K(+) ATPase) and their interactions with heat shock proteins.

Thermally induced and developmentally regulated expression of a small heat shock protein in Trichinella spiralis

A cDNA encoding a small heat shock protein of Trichinella spiralis, Ts-sHsp, was cloned and expressed and is herein characterized. This cDNA encoded a predicted protein of 165 amino acids, which had a high sequence identity in alpha crystallin domain with various small heat shock proteins of other organisms. A Western blot analysis indicated that anti-Ts-sHsp recombinant antibody recognized the protein of adults and larvae migrating at about 19 kDa. An in situ localization study showed the protein to be abundantly present in the body wall muscle cells, hypodermis, stichocytes, and esophagus of muscle larvae. The Ts-sHsp recombinant protein possessed chaperone activity to suppress the thermally-induced aggregation of citrate synthase. This sHsp was expressed at various developmental stages of T. spiralis, but at different levels. A high level was observed in mature muscle larvae (infective larvae), which was much higher than the levels seen in adults, newborn larvae, or immature muscle larvae. The expression of the sHsp gene was thermal inducible, thus responding to both cold (0 degrees C) and heat shock (43 degrees C) stress; however, at different patterns. The expression of Ts-sHsp increased gradually from 3 to 72 h after cold stress, while the expression was elevated to its highest after 3 h heat stress and then decreased. These results suggest that this small heat shock protein likely plays a role in the tolerance to both chemical and physical stresses, thereby enhancing the survival ability of Trichinella muscle larvae.

Plasminogen and angiostatin interact with heat shock proteins

Previous studies from this laboratory have demonstrated that plasminogen and angiostatin bind to endothelial cell (EC) surface-associated actin via their kringles in a specific manner. Heat shock proteins (hsps) like hsp 27 are constitutively expressed by vascular ECs and regulate actin polymerization, cell growth, and migration. Since many hsps have also been found to be highly abundant on cell surfaces and there is evidence that bacterial surface hsps may interact with human plasminogen, the purpose of this study was to determine whether human plasminogen and angiostatin would interact with human hsps. ELISAs were developed in our laboratory to assess these interactions. It was observed that plasminogen bound to hsps 27, 60, and 70. In all cases, binding was inhibited (85-90%) by excess (50 mM) lysine indicating kringle involvement. Angiostatin predominantly bound to hsp 27 and to hsp 70 in a concentration- and kringle-dependent manner. As observed previously for actin, there was concentration-dependent inhibition of angiostatin's interaction with hsp 27 by plasminogen. In addition, 30-fold molar excess actin inhibited (up to 50%), the interaction of plasminogen with all hsps. However, 30-fold molar excess actin could only inhibit the interaction of angiostatin with hsp 27 by 15-20%. Collectively, these data indicate that (i) while plasminogen interacts specifically with hsp 27, 60, and 70, angiostatin interacts predominantly with hsp 27 and to some extent with hsp 70; (ii) plasminogen only partially displaces angiostatin's binding to hsp 27 and (iii) actin only partially displaces plasminogen/angiostatin binding to hsps. It is conceivable therefore that surface-associated hsps could mediate the binding of these ligands to cells like ECs.

Heat shock protein 27 is involved in neurite extension and branching of dorsal root ganglion neurons in vitro

Alteration of the cytoskeleton in response to growth factors and extracellular matrix proteins is necessary for neurite growth. The cytoskeletal components, such as actin and tubulin, can be modified through interaction with other cellular proteins, including the small heat shock protein Hsp27. Our previous work suggested that Hsp27 influences neurite growth, potentially via its phosphorylation state interactions with actin. To investigate further the role of Hsp27 in neurite outgrowth of adult dorsal root ganglion (DRG) neurons, we have both down-regulated endogenous Hsp27 and expressed exogenous Hsp27. Down-regulation of Hsp27 with Hsp27 siRNA resulted in a decrease of neuritic tree length and complexity. In contrast, expression of exogenous Hsp27 in these neurons resulted in an increase in neuritic tree length and branching. Collectively, these results demonstrate that Hsp27 may play a role in neuritic growth via modulation of the actin cytoskeleton.

Recruitment of phosphorylated small heat shock protein Hsp27 to nuclear speckles without stress

During stress, the mammalian small heat shock protein Hsp27 enters cell nuclei. The present study examines the requirements for entry of Hsp27 into nuclei of normal rat kidney (NRK) renal epithelial cells, and for its interactions with specific nuclear structures. We find that phosphorylation of Hsp27 is necessary for the efficient entry into nuclei during heat shock but not sufficient for efficient nuclear entry under control conditions. We further report that Hsp27 is recruited to an RNAse sensitive fraction of SC35 positive nuclear speckles, but not other intranuclear structures, in response to heat shock. Intriguingly, Hsp27 phosphorylation, in the absence of stress, is sufficient for recruitment to speckles found in post-anaphase stage mitotic cells. Additionally, pseudophosphorylated Hsp27 fused to a nuclear localization peptide (NLS) is recruited to nuclear speckles in unstressed interphase cells, but wildtype and nonphosphorylatable Hsp27 NLS fusion proteins are not. The expression of NLS-Hsp27 mutants does not enhance colony forming abilities of cells subjected to severe heat shock, but does regulate nuclear speckle morphology. These data demonstrate that phosphorylation, but not stress, mediates Hsp27 recruitment to an RNAse soluble fraction of nuclear speckles and support a site-specific role for Hsp27 within the nucleus.

Phosphorylation of HSP27 and synthesis of 14-3-3ε are parallel responses to hyperosmotic stress in the hippocampus

A stress-responsive, mitogen-activated protein kinase, p38, is activated by phosphorylation in response to adverse environmental insults. In the present study, the effects of hyperosmolarity on p38 activation and protein synthesis in the brain were examined. Hyperosmotic stress of rat brain slices, produced by addition of sorbitol to the incubation buffer, produced prolonged phosphorylation and activation of p38, most prominently in the hippocampus as compared to the cortex or cerebellum. In comparison, the prototypic mitogen-activated protein kinase, extracellular signal-regulated kinase, was transiently phosphorylated and another stress-activated protein kinase, c-Jun NH(2)-terminal kinase, was not phosphorylated above basal levels. Examination of downstream p38 signaling events revealed phosphorylation of the small heat shock protein 27 (HSP27) that was abolished by incubation with SB202190 [4-(4-Fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)1H-imidazole], a p38 inhibitor. Concomitantly, hyperosmolarity diminished total levels of protein synthesis within hippocampal slices, as determined by incorporation of (35)S-labeled methionine/cysteine into protein during tissue incubation. However, synthesis of a 30-kDa protein, identified as 14-3-3epsilon with mass spectrometry, increased in response to hyperosmolarity. The synthesis of 14-3-3epsilon was dose-dependently induced by increasingly hyperosmotic conditions in a p38-independent manner. We conclude from these results that 14-3-3epsilon synthesis and p38-mediated HSP27 phosphorylation in the hippocampus are parallel responses to the hyperosmotic environment.

Heat shock protein expression in canine malignant mammary tumours

Background

Abnormal levels of Heat Shock Proteins (HSPs) have been observed in many human neoplasms including breast cancer and it has been demonstrated that they have both prognostic and therapeutic implications. In this study, we evaluated immunohistochemical expression of HSPs in normal and neoplastic canine mammary glands and confronted these results with overall survival (OS), in order to understand the role of HSPs in carcinogenesis and to establish their potential prognostic and/or therapeutic value.

Methods

Immunohistochemical expression of Hsp27, Hsp72, Hsp73 and Hsp90 was evaluated in 3 normal canine mammary glands and 30 malignant mammary tumours (10 in situ carcinomas, 10 invasive carcinomas limited to local structures without identifiable invasion of blood or lymphatic vessels, 10 carcinomas with invasion of blood or lymphatic vessels and/or metastases to regional lymph nodes). A semi-quantitative method was used for the analysis of the results.

Results

Widespread constitutive expression of Hsp73 and Hsp90 was detected in normal tissue, Hsp72 appeared to be focally distributed and Hsp27 showed a negative to rare weak immunostaining. In mammary tumours, a significant increase in Hsp27 (P < 0.01), Hsp72 (P < 0.05) and Hsp90 (P < 0.01) expression was observed as well as a significant reduction in Hsp73 (P < 0.01) immunoreactivity compared to normal mammary gland tissue. Hsp27 demonstrated a strong positivity in infiltrating tumour cells and metaplastic squamous elements of invasive groups. High Hsp27 expression also appeared to be significantly correlated to a shorter OS (P = 0.00087). Intense immunolabelling of Hsp72 and Hsp73 was frequently detected in infiltrative or inflammatory tumour areas. Hsp90 expression was high in all tumours and, like Hsp73, it also showed an intense positivity in lymphatic emboli.

Conclusion

These results suggest that Hsp27, Hsp72 and Hsp90 are involved in canine mammary gland carcinogenesis. In addition, Hsp27 appears to be implicated in tumour invasiveness and its high immunodetection in invasive tumours is indicative of a poorer clinical outcome.

Proteomic analysis reveals a novel role for the actin cytoskeleton in vincristine resistant childhood leukemia--an in vivo study

Intrinsic or acquired resistance to vincristine (VCR), an antimicrotubule agent used in the treatment of childhood acute lymphoblastic leukemia (ALL), is a major clinical problem. Using a clinically relevant NOD/SCID mouse xenograft model of ALL, we established that alterations in the actin and tubulin cytoskeleton are involved in in vivo VCR resistance. Altered protein expression between VCR-sensitive ALL xenografts, and xenografts with intrinsic or acquired VCR resistance, was identified using 2-D DIGE coupled with MS. Of the 19 proteins displaying altered expression, 11 are associated with the actin cytoskeleton. Altered expression of the actin- and/or tubulin-binding proteins gelsolin, moesin, ezrin, tropomyosin, CAP-G, HSP27, HSP70, TCP-1, and stathmin were associated with in vivo VCR resistance. The actin-regulating protein gelsolin was increased in both acquired and resistant leukemia as confirmed by immunoblotting and gene expression. The major cytoskeletal protein, gamma-actin, was down-regulated in the VCR-resistant leukemia xenografts; in contrast, there was no significant change in beta-actin expression. This study provides the first evidence for a role of the actin cytoskeleton in intrinsic and acquired in vivo antimicrotubule drug resistance in childhood leukemia and highlights the power of 2-D DIGE for the discovery of resistance markers, pharmacoproteomics, and signaling pathways in cancer.

Differences in the chaperone-like activities of the four main small heat shock proteins of Drosophila melanogaster

The Drosophila melanogaster family of small heat shock proteins (sHsps) is composed of 4 main members (Hsp22, Hsp23, Hsp26, and Hsp27) that display distinct intracellular localization and specific developmental patterns of expression in the absence of stress. In an attempt to determine their function, we have examined whether these 4 proteins have chaperone-like activity using various chaperone assays. Heat-induced aggregation of citrate synthase was decreased from 100 to 17 arbitrary units in the presence of Hsp22 and Hsp27 at a 1:1 molar ratio of sHsp to citrate synthase. A 5 M excess of Hsp23 and Hsp26 was required to obtain the same efficiency with either citrate synthase or luciferase as substrate. In an in vitro refolding assay with reticulocyte lysate, more than 50% of luciferase activity was recovered when heat denaturation was performed in the presence of Hsp22, 40% with Hsp27, and 30% with Hsp23 or Hsp26. These differences in luciferase reactivation efficiency seemed related to the ability of sHsps to bind their substrate at 42 degrees C, as revealed by sedimentation analysis of sHsp and luciferase on sucrose gradients. Therefore, the 4 main sHsps of Drosophila share the ability to prevent heat-induced protein aggregation and are able to maintain proteins in a refoldable state, although with different efficiencies. The functional reasons for their distinctive cell-specific pattern of expression could reflect the existence of defined substrates for each sHsp within the different intracellular compartments.

αB-Crystallin Maintains Skeletal Muscle Myosin Enzymatic Activity and Prevents its Aggregation under Heat-shock Stress

Here, we provide functional and direct structural evidence that alphaB-crystallin, a member of the small heat-shock protein family, suppresses thermal unfolding and aggregation of the myosin II molecular motor. Chicken skeletal muscle myosin was thermally unfolded at heat-shock temperature (43 degrees C) in the absence and in the presence of alphaB-crystallin. The ATPase activity of myosin at 25 degrees C was used as a parameter to monitor its unfolding. Myosin retained only 65% and 8% of its ATPase activity when incubated at heat-shock temperature for 15 min and 30 min, respectively. However, 84% and 58% of the myosin ATPase activity was maintained when it was incubated with alphaB-crystallin under the same conditions. Furthermore, actin-stimulated ATPase activity of myosin was reduced by approximately 90%, when myosin was thermally unfolded at 43 degrees C for 30 min, but was reduced by only approximately 42% when it was incubated with alphaB-crystallin under the same conditions. Light-scattering assays and bound thioflavin T fluorescence indicated that myosin aggregates when incubated at 43 degrees C for 30 min, while alphaB-crystallin suppressed this thermal aggregation. Photo-labeled bis-ANS alphaB-crystallin fluorescence studies confirmed the transient interaction of alphaB-crystallin with myosin. These findings were further supported by electron microscopy of rotary shadowed molecules. This revealed that approximately 94% of myosin molecules formed inter and intra-molecular aggregates when incubated at 43 degrees C for 30 min. alphaB-Crystallin, however, protected approximately 48% of the myosin molecules from thermal aggregation, with protected myosin appearing identical to unheated molecules. These results are the first to show that alphaB-crystallin maintains myosin enzymatic activity and prevents the aggregation of the motor under heat-shock conditions. Thus, alphaB-crystallin may be critical for nascent myosin folding, promoting myofibrillogenesis, maintaining cytoskeletal integrity and sustaining muscle performance, since heat-shock temperatures can be produced during multiple stress conditions or vigorous exercise.

Biological significance of decreased HSP27 in human atherosclerosis

OBJECTIVE

Because culprit atherosclerotic plaques contain proteases, we hypothesized that the diminished heat shock protein 27 (HSP27) released by atherosclerotic plaques could be due to proteolysis. We assessed the role of HSP27 in human vascular smooth muscle cells (VSMCs) under proteolytic injury.

METHODS AND RESULTS

Active plasmin is present in culprit atherosclerotic plaques. Recombinant HSP27 was cleaved by plasmin and this effect was prevented by different inhibitors. Fragments and aggregated forms of HSP27 appeared after incubation of mammary control endarteries with plasmin. Coincubation of atherosclerotic plaques with recombinant HSP27 or mammary endarteries led to HSP27 proteolysis. After incubation of VSMCs with plasmin, HSP27 was overexpressed, phosphorylated, aggregated, and redistributed from the cytoskeleton to the cytosol, nucleus, and cell membrane. Plasmin-induced VSMC apoptosis was significantly higher in VSMCs treated by HSP27 siRNA. Immunohistochemical analysis of atherosclerotic plaques showed that plasmin(ogen) and apoptotic cells are localized in the core/shoulder whereas HSP27 and VSMCs are mainly expressed in the cap/media.

CONCLUSIONS

Extracellular HSP27 can be degraded by enzymes released from atherosclerotic plaques and may reflect a proteolytic imbalance. Intracellular HSP27 downregulation decreases VSMCs resistance to proteolytically-induced apoptosis. HSP27 might play a pivotal role in the prevention of plaque instability and rupture.

Time course and differential responses of the major heat shock protein families in human skeletal muscle following acute nondamaging treadmill exercise

The exercise-induced expression of heat shock proteins (HSPs) in rodent models is relatively well defined. In contrast, comparable data from human studies are limited and the exercise-induced stress response of human skeletal muscle is far from understood. This study has characterized the time course and magnitude of the HSP response in the skeletal muscles of a healthy active, but untrained, young male population following a running exercise protocol. Eight subjects performed 45 min of treadmill running at a speed corresponding to their lactate threshold (11.7 +/- 0.5 km/h; 69.8 +/- 4.8% maximum O2 uptake). Muscle biopsies were obtained from the vastus lateralis muscle immediately before and at 24 h, 48 h, 72 h, and 7 days postexercise. Exercise induced a significant (P < 0.05) but variable increase in HSP70, heat shock cognate (HSC) 70, and HSP60 expression with peak increases (typically occurring at 48 h postexercise) to 210, 170, and 139% of preexercise levels, respectively. In contrast, exercise did not induce a significant increase in either HSP27, alphaB-crystallin, SOD 2 (MnSOD) protein content, or the activity of SOD and catalase. When examining baseline protein levels, HSC70, HSP27, and alphaB-crystallin appeared consistently expressed between subjects, whereas HSP70 and MnSOD displayed marked individual variation of up to 3- and 1.5-fold, respectively. These data are the first to define the time course and extent of HSP production in human skeletal muscle following a moderately demanding and nondamaging running exercise protocol. Data demonstrate a differential effect of aerobic exercise on specific HSPs.

Hepatocyte cytoskeleton during ischemia and reperfusion--influence of ANP-mediated p38 MAPK activation

AIM

To determine functional consequences of this activation, whereby we focused on a potential regulation of the hepatocyte cytoskeleton during ischemia and reperfusion.

METHODS

For in vivo experiments, animals received ANP (5 microg/kg) intravenously. In a different experimental setting, isolated rat livers were perfused with KH-buffer+/-ANP (200 nmol/L) +/-SB203580 (2 micromol/L). Livers were then kept under ischemic conditions for 24 h, and either transplanted or reperfused. Actin, Hsp27, and phosphorylated Hsp27 were determined by Western blotting, p38 MAPK activity by in vitro phosphorylation assay. F-actin distribution was determined by confocal microscopy.

RESULTS

We first confirmed that ANP preconditioning leads to an activation of p38 MAPK and observed alterations of the cytoskeleton in hepatocytes of ANP-preconditioned organs. ANP induced an increase of hepatic F-actin after ischemia, which could be prevented by the p38 MAPK inhibitor SB203580 but had no effect on bile flow. After ischemia untreated livers showed a translocation of Hsp27 towards the cytoskeleton and an increase in total Hsp27, whereas ANP preconditioning prohibited translocation but caused an augmentation of Hsp27 phosphorylation. This effect is also mediated via p38 MAPK, since it was abrogated by the p38 MAPK inhibitor SB203580.

CONCLUSION

This study reveals that ANP-mediated p38 MAPK activation leads to changes in hepatocyte cytoskeleton involving an elevation of phosphorylated Hsp27 and thereby for the first time shows functional consequences of ANP-induced hepatic p38 MAPK activation.

Differential subcellular localization of members of the Toxoplasma gondii small heat shock protein family

The results of this study describe the identification and characterization of the Toxoplasma gondii alpha-crystallin/small heat shock protein (sHsp) family. By database (www.toxodb.org) search, five parasite sHsps (Hsp20, Hsp21, Hsp28, Hsp29, and the previously characterized Hsp30/Bag1) were identified. As expected, they share the homologous alpha-crystallin domain, which is the key characteristic of sHsps. However, the N-terminal segment of each protein contains unique characteristics in size and sequence. Most T. gondii sHsps are constitutively expressed in tachyzoites and fully differentiated bradyzoites, with the exception of Hsp30/Bag1. Interestingly, by subcellular localization we observed that T. gondii sHsps are located in different compartments. Hsp20 is located at the apical end of the cell, Hsp28 is located inside the mitochondrion, Hsp29 showed a membrane-associated labeling, and Hsp21 appeared throughout the cytosol of the parasites. These particular differences in the immunostaining patterns suggest that their targets and functions might be different.

Purinergic receptor antagonists inhibit odorant-induced heat shock protein 25 induction in mouse olfactory epithelium

Heat shock proteins (HSPs) accumulate in cells exposed to a variety of physiological and environmental factors, such as heat shock, oxidative stress, toxicants, and odorants. Ischemic, stressed, and injured cells release ATP in large amounts. Our hypothesis is that noxious stimulation (in this case, strong odorant) evokes the release of ATP in the olfactory epithelium (OE). Extracellular ATP, a signal of cellular stress, induces the expression of HSPs via purinergic receptors. In the present study, in vivo odorant exposure (heptanal or R-carvone) led to a selective induction of HSP25 in glia-like sustentacular cells in the Swiss Webster mouse OE, as previously shown in rats (Carr et al., 2001). Furthermore, in vitro and in vivo administration of purinergic receptor antagonists suramin and pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) blocked the expression of HSP25 immunoreactivity in sustentacular cells. ATP released by acutely injured cells could act as an early signal of cell and tissue damage, causing HSP expression and initiating a stress signaling cascade to protect against further damage. Sustentacular cells have a high capacity to detoxify xenobiotics and thereby protect the olfactory epithelium from airborne pollutants. Thus, the robust, rapid induction of HSPs in sustentacular cells may help maintain the integrity of the OE during exposure to toxicants.

Inhibition of apoptosis by p26: implications for small heat shock protein function during Artemia development

p26, an abundantly expressed small heat shock protein, is thought to establish stress resistance in oviparously developing embryos of the crustacean Artemia franciscana by preventing irreversible protein denaturation, but it might also promote survival by inhibiting apoptosis. To test this possibility, stably transfected mammalian cells producing p26 were generated and their ability to resist apoptosis induction determined. Examination of immunofluorescently stained transfected 293H cells by confocal microscopy demonstrated p26 is diffusely distributed in the cytoplasm with a minor amount of the protein in nuclei. As shown by immunoprobing of Western blots, p26 constituted approximately 0.6% of soluble cell protein. p26 localization and quantity were unchanged during prolonged culture, and the protein had no apparent ill effects on transfected cells. Molecular sieve chromatography in Sepharose 6B revealed p26 oligomers of about 20 monomers, with a second fraction occurring as larger aggregates. A similar pattern was observed in sucrose gradients, but overall oligomer size was smaller. Mammalian cells containing p26 were more thermotolerant than cells transfected with the expression vector only, and as measured by annexin V labeling, Hoescht 33342 nuclear staining and procaspase-3 activation, transfected cells effectively resisted apoptosis induction by heat and staurosporine. The ability to confer thermotolerance and limit heat-induced apoptosis is important because Artemia embryos are frequently exposed to high temperature in their natural habitat. p26 also blocked apoptosis in transfected cells during drying and rehydration, findings with direct relevance to Artemia life history characteristics because desiccation terminates cyst diapause. Thus, in addition to functioning as a molecular chaperone, p26 inhibits apoptosis, an activity shared by other small heat shock proteins and with the potential to play an important role during Artemia embryo development.

Soluble factors from Lactobacillus GG activate MAPKs and induce cytoprotective heat shock proteins in intestinal epithelial cells

Conditioned media from the probiotic Lactobacillus GG (LGG-CM) induce heat shock protein (Hsp) expression in intestinal epithelial cells. LGG-CM induces both Hsp25 and Hsp72 in a time- and concentration-dependent manner. These effects are mediated by a low-molecular-weight peptide that is acid and heat stable. DNA microarray experiments demonstrate that Hsp72 is one of the most highly upregulated genes in response to LGG-CM treatment. Real-time PCR and electrophoretic mobility shift assay confirm that regulation of Hsp induction is at least in part transcriptional in nature, involving heat shock factor-1. Although Hsps are not induced for hours after exposure, transient exposure to LGG-CM is sufficient to initiate the signal for Hsp induction, suggesting that signal transduction pathways may be involved. Experiments confirm that LGG-CM modulates the activity of certain signaling pathways in intestinal epithelial cells by activating MAP kinases. Inhibitors of p38 and JNK block the expression of Hsp72 normally induced by LGG-CM. Functional studies indicate that LGG-CM treatment of gut epithelial cells protects them from oxidant stress, perhaps by preserving cytoskeletal integrity. By inducing the expression of cytoprotective Hsps in gut epithelial cells, and by activating signal transduction pathways, the peptide product(s) secreted by LGG may contribute to the beneficial clinical effects attributed to this probiotic.

Wrapping the α-Crystallin Domain Fold in a Chaperone Assembly

Small heat shock proteins (sHsps) are oligomers that perform a protective function by binding denatured proteins. Although ubiquitous, they are of variable sequence except for a C-terminal approximately 90-residue "alpha-crystallin domain". Unlike larger stress response chaperones, sHsps are ATP-independent and generally form polydisperse assemblies. One proposed mechanism of action involves these assemblies breaking into smaller subunits in response to stress, before binding unfolding substrate and reforming into larger complexes. Two previously solved non-metazoan sHsp multimers are built from dimers formed by domain swapping between the alpha-crystallin domains, adding to evidence that the smaller subunits are dimers. Here, the 2.5A resolution structure of an sHsp from the parasitic flatworm Taenia saginata Tsp36, the first metazoan crystal structure, shows a new mode of dimerization involving N-terminal regions, which differs from that seen for non-metazoan sHsps. Sequence differences in the alpha-crystallin domains between metazoans and non-metazoans are critical to the different mechanism of dimerization, suggesting that some structural features seen for Tsp36 may be generalized to other metazoan sHsps. The structure also indicates scope for flexible assembly of subunits, supporting the proposed process of oligomer breakdown, substrate binding and reassembly as the chaperone mechanism. It further shows how sHsps can bind coil and secondary structural elements by wrapping them around the alpha-crystallin domain. The structure also illustrates possible roles for conserved residues associated with disease, and suggests a mechanism for the sHsp-related pathogenicity of some flatworm infections. Tsp36, like other flatworm sHsps, possesses two divergent sHsp repeats per monomer. Together with the two previously solved structures, a total of four alpha-crystallin domain structures are now available, giving a better definition of domain boundaries for sHsps.

Oscillatory Pressurization of an Animal Cell as a Poroelastic Spherical Body

The analytical solution of a spherical poroelastic body under an oscillatory hydrostatic pressurization is obtained. This solution is then parameterized and interpreted in terms of a spherical animal cell with the cytoskeleton serving as the solid phase. It is found that for a cell with free or nearly free membrane leakage (such as in the case of an osteocytic cell body), the induced pore fluid pressure amplitude near the center of the cell exceeds the amplitude of the applied pressure by 50% if the loading frequency falls near that of normal human gait (1 Hz). A parametric analysis shows that the leakage coefficient is proportional to the intrinsic permeability ratio between the boundary and the bulk matrix. The physiological implication of the solution is further interpreted and discussed through an anatomical analysis of two representative cellular entities under compression: a chondrocyte and an osteocytic cell body. Finally, through a comparison between the characteristic time of gait and the characteristic pore fluid pressure relaxation times of various fluid-saturated entities in the body (such as a tumor, the brain, the cortical bone, the trabecular bone, and the cartilage, etc.), it is found that the gait-induced pore fluid transport seems to be important only in deeply buried cells and the mineralized cartilage.

Cyclosporine A induces vascular fibrosis and heat shock protein expression in rat

The immunosuppressive drug Cyclosporine A (CsA) has been successfully used in several diseases with immunological basis and in transplant patients. However, the therapeutic treatment induces several side effects, which include the development of severe hypertension, renal failure and cardiotoxicity in the majority of the patients. Since the mechanism by which CsA induces hypertension is not well defined, the aim of this study is to evaluate the morphological changes and the expression of heat shock proteins (HSPs) in the thoracic aorta of CsA-treated rats. The study was carried out on 40 male Wistar rats with an average weight of 200-250 g. The animals were divided into four groups. Groups I and II were injected subcutaneously (sc) daily with castor oil for 15 or 30 days and used as control; group III and IV were injected sc daily with CsA (15 mg/Kg/day) for 15 or 30 days. After the end of the treatment, the thoracic aortae were removed and treated for morphological (Sirius Red) and immunohistochemical evaluation (HSP 25, alphaB-crystallin and HSP 47). The results indicate that CsA induces (1) time-dependent vascular damage visible as fibrosis mainly in intima-media tunica of aorta, and (2) a clear increase in HSP expression. In fact, after 30 days of treatment, HSP and alphaB-crystallin are increased in all tunicas, whereas HSP47 only in tunica media and adventitia. These findings could suggest that these proteins are up-regulated after CsA treatment in order to play a defensive role in vascular damage.

Effects of small heat shock proteins on the thermal denaturation and aggregation of F-actin

Effect of recombinant chicken small heat shock protein with molecular mass 24 kDa (Hsp24) and recombinant human small heat shock protein with molecular mass 27 kDa (Hsp27) on the heat-induced denaturation and aggregation of skeletal F-actin was analyzed by means of differential scanning calorimetry and light scattering. All small heat shock proteins did not affect thermal unfolding of F-actin measured by differential scanning calorimetry, but effectively prevented aggregation of thermally denatured actin. Small heat shock protein formed stable complexes with denatured (but not with intact) F-actin. The size of these highly soluble complexes was smaller than the size of intact F-actin filaments. It is supposed that protective effect of small heat shock proteins on the cytoskeleton is at least partly due to prevention of aggregation of denatured actin.

Regulation and function of small heat shock protein genes during amphibian development

Small heat shock proteins (shsps) are molecular chaperones that are inducible by environmental stress such as elevated temperature or exposure to heavy metals or arsenate. Recent interest in shsps has been propelled by the finding that shsp synthesis or mutations are associated with various human diseases. While much is known about shsps in cultured cells, less is known about their expression and function during early animal development. In amphibian model systems, shsp genes are developmentally regulated under both normal and environmental stress conditions. For example, in Xenopus, the shsp gene family, hsp30, is repressed and not heat-inducible until the late neurula/early tailbud stage whereas other hsps are inducible at the onset of zygotic genome activation at the midblastula stage. Furthermore, these shsp genes are preferentially induced in selected tissues. Recent studies suggest that the developmental regulation of these shsp genes is controlled, in part, at the level of chromatin structure. Some shsps including Xenopus and Rana hsp30 are synthesized constitutively in selected tissues where they may function in the prevention of apoptosis. During environmental stress, amphibian multimeric shsps bind to denatured target protein, inhibittheir aggregation and maintain them in a folding-competent state until reactivated by other cellular chaperones. Phosphorylation of shsps appears to play a major role in the regulation of their function.

Heat Shock Protein 27 in Chronic Allograft Nephropathy: A Local Stress Response

BACKGROUND

Heat shock protein (HSP) 27 plays a cytoprotective role through its antioxidant, antiapoptotic, and actin-stabilizing properties during cell stress. The authors hypothesized that HSP27 is involved in chronic allograft nephropathy (CAN), a chronic state of inflammation and stress.

METHODS

The authors used the Fisher 344-to-Lewis model of CAN. Transplants were performed in 3-month-old recipient rats. HSP27 mRNA and protein levels were determined using semiquantitative polymerase chain reaction, microarray (stress-toxicity, GEArray) analyses, gene sequencing, immunoblotting, and immunohistochemical analyses at 10 days and 6 months posttransplant. P38 mitogen-activated protein kinase (MAPK), manganese (Mn) superoxide dismutase (SOD), copper-zinc (CuZn) SOD, FasL, Bax, hypoxia-inducible factor (HIF)-1alpha, and CD3 lymphocytes were studied in parallel as selective biomarkers of oxidative stress (OS), apoptosis, hypoxia, and graft-infiltrating immune cells.

RESULTS

Six months after transplantation, kidney allografts displayed histologic and functional features of CAN, including tubular atrophy, interstitial fibrosis, glomerulosclerosis, and increased proteinuria and serum creatinine levels. HSP27 mRNA and protein levels in CAN were reduced by 50% and 85%, respectively (P=0.04). Immunohistochemical analyses revealed a "shift" in HSP27 from the medulla to the cortex in allografts with CAN. Bax, phosphorylated p38-MAPK, HIF-1alpha, and MnSOD followed a parallel relocation pattern. CD3 lymphocyte density and tubular FasL expression were also greater in the cortex of allografts with CAN. Time-course analyses revealed that most of these changes were present as early as 10 days posttransplant.

CONCLUSIONS

The shift of HSP27 from the medulla to the cortex, combined with greater CD3, p38-MAPK, Bax, FasL, HIF-1alpha, and MnSOD immunoreactivity in this area of the kidney, likely represents an allograft-level response to CAN-related OS-hypoxia.

p38 MAPK/HSP25 signaling mediates cadmium-induced contraction of mesangial cells and renal glomeruli

The environmental pollutant cadmium affects human health, with the kidney being a primary target. In addition to proximal tubules, glomeruli and their contractile mesangial cells have also been identified as targets of cadmium nephrotoxicity. Glomerular contraction is thought to contribute to reduced glomerular filtration, a characteristic of cadmium nephrotoxicity. Because p38 MAPK/HSP25 signaling has been implicated in smooth muscle contraction, we examined its role in cadmium-induced contraction of mesangial cells. We report that exposure of mesangial cells to cadmium resulted in 1) cell contraction, 2) activation of MAP kinases, 3) increased HSP25 phosphorylation coincident with p38 MAP kinase activation, 4) sequential phosphorylation of the two phosphorylation sites of mouse HSP25 with Ser15 being phosphorylated before Ser86, 5) reduction of oligomeric size of HSP25, and 6) association of HSP25 with microfilaments. Exposure of isolated rat glomeruli to cadmium also resulted in contraction and increased HSP25 phosphorylation. The cadmium-induced responses were inhibited by the specific p38 MAP kinase inhibitor SB-203580, and cadmium-induced phosphorylation of HSP25 was inhibited by expression of a dominant-negative p38 MAP kinase mutant. These findings tentatively suggest that cadmium-induced nephrotoxicity results, in part, from glomerular contraction due to p38 MAP kinase/HSP25 signaling-dependent contraction of mesangial cells. With regard to the cellular action of HSP25, these data support a change in paradigm: in addition to its well-established cytoprotective function, HSP25 may also be involved in processes that ultimately lead to adverse effects, as is observed in the response of mesangial cells to cadmium.

The role of atrial natriuretic peptide in the immune system

Atrial natriuretic peptide (ANP) is a hormone predominately produced by the heart atria which regulates the water and salt balance as well as blood pressure homeostasis. Being expressed in various parts of the immune system a link of the peptide to the immune system has been proposed. In fact, this review focus on effects of ANP in the immune system and reports about the role of the peptide in innate immune functions as well as in the adaptive immune response.

The decrease of the cytoskeleton tubulin follows the decrease of the associating molecular chaperone alphaB-crystallin in unloaded soleus muscle atrophy without stretch

The cytoskeletal component tubulin/microtubule commonly allows the cell to respond mechanically to the environment. The concentration of free tubulin dimer is autoregulated in the balance of free dimer and polymeric forms of microtubule (MT) protein, having an intrinsic property of "dynamic instability", and through cotranslational beta-tubulin mRNA degradation. Recently, we have demonstrated that alphaB-crystallin is a key molecule of muscle atrophy, since alphaB-crystallin has a chaperone-like-activity that suppresses tubulin aggregation and protects the MT disassembly against both Ca2+ and depolymelizing alkaloid in vitro. Most of the small heat-shock proteins (sHsps), including alphaB-crystallin, are expressed in skeletal muscle. However, no report to date has studied the changes of tubulin/MT during muscle adaptation. Here, we examined changes in tubulin content in rat soleus muscles after hindlimb suspension (HS) with/without passive stretch and the recovery. HS induced rapid decreases of soleus muscle mass, most Hsps (alphaB-crystallin, Hsp90, Hsp70, Hsp27, and p20) and tubulin contents in soleus muscle, while heat-shock cognate 70-kDa protein (Hsc70) did not decrease. Soleus muscle mass, most Hsps, and tubulin were maintained with passive stretch. After 5 days' recovery, the levels of tubulin and Hsps, but not Hsc70, were restored to control levels. The interactions of alphaB-crystallin and tubulin/MT were observed with immunoprecipitation with an anti-alpha-tubulin antibody and taxol-dependent MT assembly. Other sHsps were also associated with alphaB-crystallin and MT, whereas Hsp90 and Hsp70 did not co-precipitate with them. These data imply an interaction and close relationship between alphaB-crystallin and tubulin/MTs in muscle tissues. The amount of mRNA of alphaB-crystallin decreased with the muscle atrophy level, whereas the gene expression level of betaI-tubulin was maintained during HS. This means a significant role of post-transcriptional regulation in tubulin/MT system in muscle adaptation, whereas alphaB-crystallin and most sHsps are regulated at the transcriptional level. Additional functional contribution of alphaB-crystallin to tubulin/MTs during myotube formation was examined using C2C12 myoblast cultured cells, the alphaB-crystallin expression of which was decreased or increased. It indicated the necessity of alphaB-crystallin during microtubule reorganization. In conclusion, tubulin/MTs were revealed to be one of the substrates of alphaB-crystallin, and also serial decreases of alphaB-crystallin and tubulin/MT in early soleus muscle atrophy suggest that the chaperone effect of alphaB-crystallin on the cytoskeleton, which may be also dynamically regulated in the muscle cell, is a key mechanism for muscle adaptation and protection of the atrophy and also muscle differentiation.

Cloning, characterization, and heat stress-induced redistribution of a protein homologous to human hsp27 in the zebrafish Danio rerio

Hsp27 is a small heat shock protein (shsp) regulating stress tolerance and increasingly thought to play roles in tissue homeostasis and differentiation. The zebrafish Danio rerio is an important model for the study of developmental processes, but little is known regarding shsps in this animal. Here, we report the sequence, expression, regulation, and function of a zebrafish protein (zfHsp27) homologous to human Hsp27. zfHsp27 contains three conserved phosphorylatable serines and a cysteine important for regulation of apoptosis, but it lacks much of a C-terminal tail domain and shows low homology in two putative actin interacting domains that are features of mammalian Hsp27. zfHsp27 mRNA is most abundant in adult skeletal muscle and heart and is upregulated during early embryogenesis. zfHsp27 expressed in mammalian fibroblasts was phosphorylated in response to heat stress and anisomycin, and this phosphorylation was prevented by treatment with SB202190, an inhibitor of p38 MAPK. Expression of zfHsp27 and human Hsp27 in mammalian fibroblasts promoted a similar degree of tolerance to heat stress. zfHsp27 fusion proteins entered the nucleus and associated with the cytoskeleton of heat stressed cells in vitro and in zebrafish embryos. These results reveal conservation in regulation and function of mammalian and teleost Hsp27 proteins and define zebrafish as a new model for the study of Hsp27 function.

Heat shock treatment protects osmotic stress-induced dysfunction of the blood-brain barrier through preservation of tight junction proteins

The blood-brain barrier (BBB) is a specialized structure in the central nervous system (CNS), which participates in maintenance of a state of cerebrospinal fluid homeostasis. The endothelial cells of the cerebral capillaries and the tight junctions between them form the basis of the BBB. Research has shown that destruction of the BBB is associated with diseases of the CNS. However, there is little research on how the BBB might be protected. In this study, we used a high osmotic solution (1.6 M D-mannitol) to open the BBB of rats and Evans blue dye as a macromolecular marker. The effect of heat shock treatment was evaluated. The results show that increased synthesis of heat shock protein 72 (Hsp72) was induced in the heated group only. BBB permeability was significantly less in the heat shock-treated group after hyperosmotic shock. The major tight junction proteins, occludin and zonula occludens (ZO)-1, were significantly decreased after D-mannitol treatment in the nonheated group, whereas they were preserved in the heated group. The coimmunoprecipitation studies demonstrated that Hsp72 could be detected in the precipitates of brain extract interacting with anti-ZO-1 antibodies as well as those interacting with anti-occludin antibodies in the heated group. We conclude that the integrity of tight junctions could be maintained by previous heat shock treatment, which might be associated with the increased production of Hsp72.

Small heat shock protein 27 (Hsp27) expression is highly induced in rat myometrium during late pregnancy and labour

The underlying mechanisms that regulate uterine contractions during labour are still poorly understood. A candidate regulatory protein is heat shock protein 27 (Hsp27). It belongs to the small heat shock protein family and can regulate actin cytoskeleton dynamics, act as a chaperone, and may regulate contractile protein activation. As a result, we hypothesized that Hsp27 expression would be highly induced during late pregnancy and labour. Hsp27 mRNA expression was significantly elevated (P <0.05) on days 17 to 22 of gestation. In addition, immunoblot analysis demonstrated that detection of total Hsp27 increased (P <0.05) between day 21 and 1 day post-partum (PP) inclusive. Since phosphorylation of Hsp27 has been reported to be a prerequisite for smooth muscle contraction, we examined the temporal and spatial expression of Ser-15 phosphorylated Hsp27. Immunoblot analysis showed that the detection of Ser-15 phosphorylated Hsp27 significantly increased (P <0.05) between days 19 and 23 (active labour) inclusive, in parallel with detection of total Hsp27. Immunocytochemical analysis of Ser-15 phosphorylated Hsp27 expression in situ demonstrated that phosphorylated Hsp27 in circular muscle became detectable in peri-nuclear and membrane regions on days 19 to 22, but was primarily restricted to the cytoplasm on days 23 to PP. In contrast, phosphorylated Hsp27 in longitudinal muscle was primarily detected in myocyte membranes on days 15 to 22, and then also became detectable in the cytoplasm of myocytes on days 23 and PP. Our results demonstrate that Hsp27 expression is highly upregulated during late pregnancy and labour and suggest that Hsp27 is a potential candidate contraction-associated protein.

Hsp27 and axonal growth in adult sensory neurons in vitro

Background

Neurite growth can be elicited by growth factors and interactions with extracellular matrix molecules like laminin. Among the targets of the signalling pathways activated by these stimuli are cytoskeletal elements, such as actin, tubulin and neurofilaments. The cytoskeleton can also be modulated by other proteins, such as the small heat shock protein Hsp27. Hsp27 interacts with actin and tubulin in non-neuronal cells and while it has been suggested to play a role in the response of some neurons to injury, there have been no direct studies of its contribution to axonal regeneration.

Results

We have investigated neurite initiation and process extension using cultures of adult dorsal root ganglion (DRG) sensory neurons and a laminin stimulation paradigm. Employing confocal microscopy and biochemical analyses we have examined localization of Hsp27 at early and later stages of neurite growth. Our results show that Hsp27 is colocalized with actin and tubulin in lamellopodia, filopodia, focal contacts and mature neurites and growth cones. Disruption of the actin cytoskeleton with cytochalasin D results in aberrant neurite initiation and extension, effects which may be attributable to alterations in actin polymerization states. Inhibition of Hsp27 phosphorylation in our cultures results in an atypical growth pattern that may be attributable to an effect of pHsp27 on the stability of the actin cytoskeleton.

Conclusion

We observed colocalization of the phosphorylated and non-phosphorylated forms of Hsp27 with actin and tubulin in both very early and later stages of neurite growth from cultured adult DRG neurons. The colocalization of Hsp27 and pHsp27 with actin in lamellopodia and focal contacts at early stages of neurite growth, and in processes, branch points and growth cones at later stages, suggests that Hsp27 may play a role in neuritogenesis and subsequent neurite extension, and potentially in the patterning of this growth. Hsp27 has been reported to play a key role in modulating actin cytoskeletal dynamics as an actin-capping protein in non-neuronal cells. Our results suggest that this may also be the case in neurons and support a role for Hsp27 in neurite outgrowth via its phosphorylation state-dependent interactions with actin.

Hsp27 consolidates intracellular redox homeostasis by upholding glutathione in its reduced form and by decreasing iron intracellular levels

Small stress proteins [small heat shock proteins (sHsps)] are molecular chaperones that modulate the ability of cells to respond to oxidative stress. The current knowledge concerning the protective mechanism generated by the expression of mammalian heat shock protein-27 (Hsp27) that allows cells to increase their resistance to oxidative stress is presented. We describe the effects mediated by Hsp27 expression toward crucial enzymes such as glucose-6-phosphate dehydrogenase and glutathione reductase that uphold glutathione in its reduced form. New data are presented showing that the expression of sHsps correlates with a drastic decrease in the intracellular level of iron, a catalyzer of hydroxyl radical (OH( . )) generation. A decreased ability of sHsps expressing cells to concentrate iron will therefore end up in a decreased level of oxidized proteins. In addition, we propose a role of Hsp27 in the presentation of oxidized proteins to the proteasome degradation machinery. We also present an analysis of several Hsp27 mutants that suggests that the C-terminal part of this stress protein is essential for its protective activity against oxidative stress.

Epithelial-to-mesenchymal transition and oxidative stress in chronic allograft nephropathy

Epithelial-to-mesenchymal transition (EMT) and oxidative stress contribute to kidney tissue fibrosis in various forms of native kidney disease. However, their role in chronic allograft nephropathy (CAN) remains somewhat uncertain. To address this question, kidney transplants were performed in 3-month-old rats, using the Fisher 344 --> Lewis model of CAN. Six-month posttransplant, kidney allografts displayed significant tubular atrophy, interstitial fibrosis and vascular wall thickening. Allograft recipients had significantly higher levels of serum creatinine (4.7 +/- 1.3 versus 0.59 +/- 0.08 mg/dL, p = 0.03) and proteinuria (380 +/- 102 versus 30.2 +/- 8 mg/dL, p = 0.04) compared to syngeneic grafts. Semiquantitative PCR, immunoblot and immunohistochemical analyses demonstrated increased alpha-smooth muscle actin (alpha-SMA) mRNA and protein levels coupled with reduced E-cadherin mRNA and protein immunoreactivity, confirming the presence of CAN-associated EMT. Allograft alpha-SMA levels were increased as early as 1-2 weeks posttransplant. Immunohistochemical studies for collagen type I and III, superoxide anion (O(2) (-)), inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) confirmed that tubular O(2) (-), eNOS and iNOS, and interstitial collagen I, III and O(2) (-) levels were significantly increased in CAN-associated EMT. In conclusion, these observations suggest that CAN-associated EMT may be a link between oxidative stress and allograft fibrosis.

Stimulation of Fas agonistic antibody-mediated apoptosis by heparin-like agents suppresses Hsp27 but not Bcl-2 protective activity

We report that in Jurkat T cells or freshly isolated T lymphocytes, physiological concentrations of high-molecular weight sulfated polysaccharides such as heparin, heparan sulfate, and dextran sulfate significantly increased the percentage of cell death induced by Fas IgM agonistic antibody. The phenomenon was caspase dependent and P53 independent and correlated with an increased accessibility of cell surface Fas receptors. We also observed that the Fas IgM agonistic antibody-dependent formation of sodium dodecyl sulfate (SDS)-resistant large structures containing Fas receptor was decreased in the presence of heparin-like agents. In contrast, the different agents had no effect when cell death was triggered by FasL, the natural ligand of Fas that does not generate SDS-resistant forms of Fas. Interestingly, the synergistic effect of heparin-like agents toward Fas IgM agonistic antibody-mediated cell death abolished Hsp27 antiapoptotic activity but did not alter much the protection generated by Bcl-2 expression.

Hsp27 anti-sense oligonucleotides sensitize the microtubular cytoskeleton of Chinese hamster ovary cells grown at low pH to 42 degrees C-induced reorganization

Chinese hamster ovary (CHO) cells maintained in vitro at pH 6.7 were used to model cells in the acidic environment of tumours. CHO cells grown at pH 6.7 develop thermotolerance during 42 degrees C heating at pH 6.7 and their cytoskeletal systems are resistant to 42 degrees C-induced perinuclear collapse. Hsp27 levels are elevated in cells grown at pH 6.7 and are further induced during 42 degrees C heating, while Hsp70 levels remain low or undetectable, suggesting that Hsp27 is responsible for some of the novel characteristics of these cells. An anti-sense oligonucleotide strategy was used to test the importance of Hsp27 by lowering heat-induced levels of the protein. The response of the microtubular cytoskeleton to heat was used as an endpoint to assess the effectiveness of the anti-sense strategy. Treatment with anti-sense oligonucleotides prevented the heat-induced increase of Hsp27 levels measured immediately following heat. Treatment with anti-sense oligonucleotides also sensitized the cytoskeleton of cells grown at low pH to heat-induced perinuclear collapse. However, cytoskeletal collapse was not evident in cells grown at pH 6.7 and treated with 4-nt mismatch oligonucleotides or in control cells maintained and heated at pH 6.7. The cytoskeleton collapsed around the nucleus in cells cultured and heated at pH 7.3. These results confirm that over-expression of Hsp27 confers heat protection to the microtubular cytoskeleton in CHO cells grown at low pH.

Small heat shock proteins in inherited peripheral neuropathies

Small heat shock proteins (small HSPs) are molecular chaperones that protect cells against stress by assisting in the correct folding of denatured proteins and thus prevent aggregation of misfolded proteins. Small HSPs also modulate apoptotic pathways by interacting with components of programmed cell death. Furthermore, some small HSPs interact with the cytoskeleton to assist in spatial organization and dynamics of its structural elements. The role of small HSPs has been studied in many disorders, including neurodegenerative disease. Recently, mutations in HSPB1 (HSP27) and HSPB8 (HSP22), two members of the small HSP superfamily, have been associated with inherited peripheral neuropathies. In this review, we will summarize the current knowledge of small HSPs, in particular HSPB1 and HSPB8, and discuss their role in health and disease.

In search of the molecular mechanism by which small stress proteins counteract apoptosis during cellular differentiation

Many differentiation programs are accompanied by an increase in small heat shock proteins (sHsps) level. Most of the time transient, this accumulation takes place during the early phase of the process and is correlated with the growth arrest that precedes the differentiation. Important biochemical modifications of sHsps occur, such as changes in phosphorylation and oligomerization. The fact that these proteins are induced independently of the signal that triggers differentiation, of the differentiation type, and of the cell type strongly suggests their involvement in fundamental mechanisms of cellular differentiation. Moreover, impairment of sHsps accumulation leads to abortion of the differentiation program and, subsequently, to a massive commitment to cell death. Recent advances in this field of research are presented as well as the hypothesis that should be tested to unravel the mode of action of these proteins during cellular differentiation.

Grp78 is essential for 11-deoxy-16,16-dimethyl PGE2-mediated cytoprotection in renal epithelial cells

11-Deoxy-16,16-dimethyl PGE2(DDM-PGE2) protects renal proximal tubule epithelial cells (LLC-PK1) against the toxicity induced by 2,3,5- tris(glutathion- S-yl)hydroquinone (TGHQ), a potent nephrotoxic and nephrocarcinogenic metabolite of hydroquinone. We have now determined the ability of DDM-PGE2to protect against other renal toxicants and report that DDM-PGE2only protects against oncotic cell death, induced by H2O2, iodoacetamide, and TGHQ, but not against apoptotic cell death induced by cisplatin, mercuric chloride, or tumor necrosis factor-α. DDM-PGE2-mediated cytoprotection is associated with the upregulation of at least five proteins, including the major endoplasmic reticulum (ER) chaperone glucose-regulated protein 78 (Grp78). To elucidate the role of Grp78 in oncotic cell death, we used LLC-PK1cells in which induction of grp78 expression was disrupted by stable expression of an antisense grp78 RNA (pkASgrp78). As anticipated, DDM-PGE2failed to induce Grp78 in pkASgrp78 cells, with a concomitant inability to provide cytoprotection. In contrast, DDM-PGE2induced Grp78 and afforded cytoprotection against H2O2, iodoacetamide, and TGHQ in empty vector transfected cells (pkNEO). These data suggest that Grp78 plays an essential role in DDM-PGE2-mediated cytoprotection. Moreover, TGHQ-induced p38 MAPK activation is disrupted under conditions of a compromised ER stress response in pkASgrp78 cells, which likely contributes to the loss of cytoprotection. Finally, using two-dimensional gel electrophoresis coupled to matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy, we found that DDM-PGE2induced several proteins in pkNEO cells, but not in pkASgrp78 cells, including retinol-binding protein, myosin light chain, and heat shock protein 27. The findings suggest that additional proteins may act in concert with Grp78 during DDM-PGE2-mediated cytoprotection against oncotic cell death.

pH-induced changes of the structure of small heat shock proteins with molecular mass 24/27kDa (HspB1)

The effect of pH on the structure of recombinant chicken Hsp24, human Hsp27 and their 3D mutants mimicking phosphorylation at Ser15, Ser77/78, and Ser81/82 was analyzed. Circular dichroism and fluorescent spectroscopy indicate that changes of pH in the range 6.0-7.5 weakly affected the secondary and tertiary structure of the wild type proteins, but induced noticeable changes in the structure of their 3D mutants. According to size-exclusion chromatography and analytical ultracentrifugation variation of pH-induced pronounced changes in the quaternary structure of small heat shock proteins and acidification resulted in accumulation of large oligomers of Hsp24/27. It is concluded that small changes of pH strongly affect the quaternary structure of small heat shock proteins and by this means can influence their functioning in the cell.