Dissociation as a result of phosphorylation of an aggregated form of the small stress protein, hsp27

Protective effect of phosphorylated Hsp27 in coronary arteries through actin stabilization

There is evidence for an inverse association between cellular expression of Hsp27 and vascular disease with carotid plaques, endarterectomy specimens, and cardiac biopsies investigated to date. Here we compare non-diseased coronary arteries from human heart transplant donors and patients with dilated cardiomyopathy (DCM) with no evidence of coronary artery disease, to coronary arteries from patients with ischemic heart disease (IHD) in order to determine abundance of phosphorylated Hsp27 (phospho-Hsp27) in plaque-free diseased vessels and elucidate how this protective effect is brought about through protein regulation. Western blotting identified phospho-Hsp27, phosphorylated on Ser82, Ser78, and Ser15, to be specifically decreased in IHD, but not DCM, compared to non-diseased vessels. Immunohistochemistry confirmed these results and revealed phospho-Hsp27 was located within both smooth muscle and endothelial cells. Disease-free coronary arteries and from patients with IHD were then subjected to 2-Dimensional Difference Gel Electrophoresis (2D-DIGE) analysis to detect proteins with altered abundance, which were subsequently identified by mass spectrometry. Hsp27 showed decreased abundance in ischemic vessels as expected. The expression of cytoskeletal proteins, namely vimentin was significantly reduced, while transgelin and tropomyosin showed significantly increased abundance in vessels with IHD. Immunohistochemistry studies suggested an increase in G-actin abundance to be present within IHD vessels. The results are consistent with the hypothesis that phospho-Hsp27 protects against vascular disease possibly by stabilizing the actin cytoskeleton within endothelial and/or smooth muscle cells.

Dynamic processes that reflect anti-apoptotic strategies set up by HspB1 (Hsp27)

Human HspB1 (also denoted Hsp27) is an oligomeric anti-apoptotic protein that has tumorigenic and metastatic roles. To approach the structural organizations of HspB1 that are active in response to apoptosis inducers acting through different pathways, we have analyzed the relative protective efficiency induced by this protein as well its localization, oligomerization and phosphorylation. HeLa cells, that constitutively express high levels of HspB1 were treated with either etoposide, Fas agonist antibody, staurosporine or cytochalasin D. Variability in HspB1 efficiency to interfere with the different apoptotic transduction pathways induced by these agents were detected. Moreover, inducer-specific dynamic changes in HspB1 localization, native size and phosphorylation were observed, that differed from those observed after heat shock. Etoposide and Fas treatments gradually shifted HspB1 towards large but differently phosphorylated oligomeric structures. In contrast, staurosporine and cytochalasin D induced the rapid but transient formation of small oligomers before large structures were formed. These events correlated with inducer-specific phosphorylations of HspB1. Of interest, the formation of small oligomers in response to staurosporine and cytochalasin D was time correlated with the rapid disruption of F-actin. The subsequent, or gradual in the case of etoposide and Fas, formation of large oligomeric structures was a later event concomitant with the early phase of caspase activation. These observations support the hypothesis that HspB1 has the ability, through specific changes in its structural organization, to adapt and interfere at several levels with challenges triggered by different signal transduction pathways upstream of the execution phase of apoptosis.

The small heat shock protein, HSPB6, in muscle function and disease

The small heat shock protein, HSPB6, is a 17-kDa protein that belongs to the small heat shock protein family. HSPB6 was identified in the mid-1990s when it was recognized as a by-product of the purification of HSPB1 and HSPB5. HSPB6 is highly and constitutively expressed in smooth, cardiac, and skeletal muscle and plays a role in muscle function. This review will focus on the physiologic and biochemical properties of HSPB6 in smooth, cardiac, and skeletal muscle; the putative mechanisms of action; and therapeutic implications.

The small heat shock protein HSP25 protects astrocytes against stress induced by proteasomal inhibition

Proteasomal dysfunction has been implicated in neurodegenerative diseases, and molecular chaperones may provide a first line of defence against protein aggregate formation. We have shown before that oligodendrocytes respond to proteasomal inhibition by the onset of apoptotic cell death, whereas astrocytes have a higher capability to cope with stressful conditions that might be causally related to their high constitutive level of HSP25. This study was undertaken to investigate the effects of the proteasomal inhibitor MG-132 on aggregate formation in astrocytes, and to test if HSP25 exerts a protective means. Our data show that upon proteasomal inhibition aggresomes are formed in astrocytes that contain the small HSPs, HSP25 and alpha B-crystallin, and ubiquitinated proteins. HSP expression is induced and HSP25, alpha B-crystallin and ubiquitinated proteins are translocated from the soluble to the detergent-insoluble fraction. Simultaneously, the cytoskeletal organization is disturbed, microfilaments are fragmented, GFAP intermediate filaments and microtubules surround the aggresome, and mitochondria are assembled in these structures. Mitochondria membrane potential, however, stays intact. Aggresome formation and apoptotic cell death do not correlate. After the removal of MG-132, the observed effects are reversible. MG-132 promotes the formation of small oligomers of HSP25, which have been connected to the protection of the microfilament system. Downregulation of HSP25 by siRNA approach causes actin filament breakdown in control cells in the absence of stress stimuli, and sensitizes astrocytes against stress induced by proteasomal inhibition. Hence, HSP25 enables astrocytes to prevent irreversible damage and to recover after removal of the proteasomal inhibitor MG-132.

The role of Hsp27 and actin in the regulation of movement in human cancer cells responding to heat shock

Human heat shock 27-kDa protein 1 (HSPB1)/heat shock protein (Hsp) 27 is a small heat shock protein which is thought to have several roles within the cell. One of these roles includes regulating actin filament dynamics in cell movement, since Hsp27 has previously been found to inhibit actin polymerization in vitro. In this study, the role of Hsp27 in regulating actin filament dynamics is further investigated. Hsp27 protein levels were reduced using siRNA in SW480 cells, a human colon cancer cell line. An in vitro wound closure assay showed that cells with knocked down Hsp27 levels were unable to close wounds, indicating that this protein is involved in regulating cell motility. Immunoprecipitation pull down assays were done, to observe if and when Hsp27 and actin are in the same complex within the cell, before and after heat shock. At all time points tested, Hsp27 and actin were present in the same cell lysate fraction. Lastly, indirect immunostaining was done before and after heat shock to evaluate Hsp27 and actin interaction in cells. Hsp27 and actin showed colocalization before heat shock, little association 3 h after heat shock, and increased association 24 h after heat shock. Cytoprotection was observed as early as 3 h after heat shock, yet cells were still able to move. These results show that Hsp27 and actin are in the same complex in cells and that Hsp27 is important for cell motility.

MAPKAPK-2 modulates p38-MAPK localization and small heat shock protein phosphorylation but does not mediate the injury associated with p38-MAPK activation during myocardial ischemia

MAPKAPK-2 (MK2) is a protein kinase activated downstream of p38-MAPK which phosphorylates the small heat shock proteins HSP27 and alphaB crystallin and modulates p38-MAPK cellular distribution. p38-MAPK activation is thought to contribute to myocardial ischemic injury; therefore, we investigated MK2 effects on ischemic injury and p38 cellular localization using MK2-deficient mice (KO). Immunoblotting of extracts from Langendorff-perfused hearts subjected to aerobic perfusion or global ischemia or reperfusion showed that the total and phosphorylated p38 levels were significantly lower in MK2(-/-) compared to MK2(+/+) hearts at baseline, but the ratio of phosphorylated/total p38 was similar. These results were confirmed by cellular fractionation and immunoblotting for both cytosolic and nuclear compartments. Furthermore, HSP27 and alphaB crsytallin phosphorylation were reduced to baseline in MK2(-/-) hearts. On semiquantitative immunofluorescence laser confocal microscopy of hearts during aerobic perfusion, the mean total p38 fluorescence was significantly higher in the nuclear compared to extranuclear (cytoplasmic, sarcomeric, and sarcolemmal compartments) in MK2(+/+) hearts. However, although the increase in phosphorylated p38 fluorescence intensity in all compartments following ischemia in MK2(+/+) hearts was lost in MK2(-/-) hearts, it was basally elevated in nuclei of MK2(-/-) hearts and was similar to that seen during ischemia in MK2(+/+) hearts. Despite these differences, similar infarct volumes were recorded in wild-type MK2(+/+) and MK2(-/-) hearts, which were decreased by the p38 inhibitor SB203580 (1 microM) in both genotypes. In conclusion, p38 MAPK-induced myocardial ischemic injury is not modulated by MK2. However, the absence of MK2 perturbs the cellular distribution of p38. The preserved nuclear distribution of active p38 MAPK in MK2(-/-) hearts and the conserved response to SB203580 suggests that activation of p38 MAPK may contribute to injury independently of MK2.

Posttranslational modulation on the biological activities of molecular chaperones

Molecular chaperones are a family of proteins that were first noticed to exist about 45 years ago from their increased transcription under heat shock conditions. As a result, the regulation of their encoding genes has been subject to extensive studies. Recent studies revealed that the biological activities of molecular chaperones can also be effectively modulated at the protein level. The ways of modulation so far elucidated include allosteric effect, covalent modification, protein-protein interaction, and conformational alteration induced by such macro-environmental conditions as temperature and pH. These latter aspects were reviewed here. Emphasized here is the importance of such immediate structural alterations that lead to an immediate activity increase, providing the immediate protection needed for the cells to survive the stress conditions.

alphaB-crystallin extracellularly suppresses ADP-induced granule secretion from human platelets

alphaB-crystallin, a low-molecular-weight heat shock protein (HSP), has binding sites on platelets. However, the exact role of alphaB-crystallin is not clarified. In this study, we investigated the effect of alphaB-crystallin on platelet granule secretion. alphaB-crystallin attenuated the adenosine diphosphate (ADP)-induced phosphorylation of p44/p42 mitogen-activated protein kinase (MAPK) and p38 MAPK. The ADP-stimulated HSP27 phosphorylation was markedly reduced by alphaB-crystallin. alphaB-crystallin significantly suppressed the ADP-induced secretions of both platelet-derived growth factor (PDGF)-AB and serotonin. Therefore, our results strongly suggest that alphaB-crystallin extracellularly suppresses platelet granule secretion by inhibition of HSP27 phosphorylation via p44/p42 MAPK and p38 MAPK.

Phosphorylation dependence of hsp27 multimeric size and molecular chaperone function

The molecular chaperone Hsp27 exists as a distribution of large oligomers that are disassembled by phosphorylation at Ser-15, -78, and -82. It is controversial whether the unphosphorylated Hsp27 or the widely used triple Ser-to-Asp phospho-mimic mutant is the more active molecular chaperone in vitro. This question was investigated here by correlating chaperone activity, as measured by the aggregation of reduced insulin or alpha-lactalbumin, with Hsp27 self-association as monitored by analytical ultracentrifugation. Furthermore, because the phospho-mimic is generally assumed to reproduce the phosphorylated molecule, the size and chaperone activity of phosphorylated Hsp27 were compared with that of the phospho-mimic. Hsp27 was triply phosphorylated by MAPKAP-2 kinase, and phosphorylation was tracked by urea-PAGE. An increasing degree of suppression of insulin or alpha-lactalbumin aggregation correlated with a decreasing Hsp27 self-association, which was the least for phosphorylated Hsp27 followed by the mimic followed by the unphosphorylated protein. It was also found that Hsp27 added to pre-aggregated insulin did not reverse aggregation but did inhibit these aggregates from assembling into even larger aggregates. This chaperone activity appears to be independent of Hsp27 phosphorylation. In conclusion, the most active chaperone of insulin and alpha-lactalbumin was the Hsp27 (elongated) dimer, the smallest Hsp27 subunit observed under physiological conditions. Next, the Hsp27 phospho-mimic is only a partial mimic of phosphorylated Hsp27, both in self-association and in chaperone function. Finally, the efficient inhibition of insulin aggregation by Hsp27 dimer led to the proposal of two models for this chaperone activity.

Regulation of HSP27 on NF-kappaB pathway activation may be involved in metastatic hepatocellular carcinoma cells apoptosis

Background

During the process of metastasis, cells are subjected to various apoptotic stimuli. Aberrant expression of apoptotic regulators often contribute to cell metastasis. Heat shock protein 27(HSP27) is confirmed as an apoptosis regulator, but its antiapoptotic mechanism in metastatic hepatocellular carcinoma (HCC) cells remains unclear.

Methods

Levels of HSP27 protein and its phosphorylation in Hep3B, MHCC97L to MHCC97H cells with different metastatic potentials were determined by western blot analysis. MHCC97H cells were transfected with specific small interference RNA (siRNA) against HSP27. The in vitro migration and invasion potentials of cells were evaluated by Transwell assay. The apoptosis ratio of MHCC97H cells was analyzed by TUNEL staining and Flow Cytometry. Alteration of signal transduction pathway after HSP27 knockdown in MHCC97H cells was evaluated through a Human Q Series Signal Transduction in Cancer Gene Array analysis. Nuclear NF-κB contentration and endogenous IKK activity were demonstrated by ELISA assay. The association of IKKα, IKKβ, IκBα with HSP27 and the association between IKKβ and IKKα in MHCC97H cells were determined by co-immunoprecipitation assay followed by western blot analysis.

Results

HSP27 protein and its phosphorylation increased in parallel with enhanced metastatic potentials of HCC cells. siRNA-mediated HSP27 knockdown in MHCC97H significantly suppressed cells migration and invasion in vitro and induced cell apoptosis; the prominently altered signal transduction pathway was NF-κB pathway after HSP27 knockdown in MHCC97H cells. Furthermore, inhibition of HSP27 expression led to a significant decrease of nuclear NF-κB contentration and endogenous IKK activity. In addition, HSP27 was associated with IKKα, IKKβ, IκBα in three HCC cells above. ELISA assay and western blot analysis also showed a decrease of the association between IKKβ and IKKα, the association between phosphor-HSP27 and IKK complex, and an increase of total IκBα but reducing tendency of phosphor-IκBα when HSP27 expression was efficiently knocked down in MHCC97H cells.

Conclusion

Altogether, these findings revealed a possible effect of HSP27 on apoptosis in metastatic HCC cells, in which HSP27 may regulate NF-kB pathway activation.

VIP induces PKA-mediated rapid and sustained phosphorylation of HSP20

The small molecular weight heat shock protein HSP20 has been proposed to regulate smooth muscle relaxation in a manner dependent on its phosphorylated state. We present the first evidence of HSP20 phosphorylation in response to a naturally occurring neurotransmitter. HSP20 was rapidly phosphorylated in colonic circular smooth muscle cells exposed to the physiologically relevant relaxant neuropeptide, Vasoactive Intestinal Peptide (VIP). HSP20 phosphorylation was significantly and substantially increased by 30s following VIP treatment and remained elevated for 30 min. VIP-induced HSP20 phosphorylation was dose dependent. Both basal and VIP-induced HSP20 phosphorylations were solely mediated by Protein Kinase A. Maximal phosphorylation of HSP20 was induced by the same VIP concentration range which induces maximal relaxation. Increased phosphorylation of HSP20 occurred in both cytosolic and particulate cell fractions. Our findings represent evidence for neurogenic modulation of the cyclic molecular regulation of relaxation required for peristalsis via a VIP-PKA-HSP20 pathway.

PKD, PKD2, and p38 MAPK mediate Hsp27 serine-82 phosphorylation induced by neurotensin in pancreatic cancer PANC-1 cells

It is widely recognized that Hsp27 is a downstream substrate of the p38 MAPK cascade whereas the role of PKD family members in mediating receptor-stimulated Hsp27 Ser-82 phosphorylation has not been evaluated. Here, we show that neurotensin induced a rapid and striking increase in Hsp27 Ser-82 phosphorylation in PANC-1 cells, which was closely correlated with stimulation of activation loop phosphorylation of PKDs and p38 MAPK Thr180/Tyr182 phosphorylation. Treatment of PANC-1 cells with either the selective PKC inhibitor GF-I or the p38 MAPK inhibitor SB202190 partially reduced neurotensin-induced Hsp27 Ser-82 phosphorylation. However, treatment of the cells with a combination of GF-I and SB202190 virtually abolished neurotensin-induced Hsp27 Ser-82 phosphorylation. Overexpression of PKD in stably transfected PANC-1 cells increased the magnitude and prolonged the duration of Hsp27 Ser-82 phosphorylation in response to neurotensin. Either PKD or PKD2 gene silencing utilizing siRNAs targeting distinct PKD or PKD2 sequences reduced neurotensin-stimulated Hsp27 Ser-82 phosphorylation, but cotransfection of siRNAs targeting both, PKD and PKD2, markedly decreased neurotensin-induced Hsp27 Ser-82 phosphorylation. Knockdown of PKD and PKD2 abolished Hsp27 phosphorylation in cells treated with SB202190. Thus, neurotensin induces Hsp27 Ser-82 phosphorylation through p38 MAPK- and PKC/PKD-dependent pathways in PANC-1 cells. Our results demonstrate, for the first time, that neurotensin induces a striking increase in Hsp27 phosphorylation on Ser-82 in PANC-1 cells through convergent p38 MAPK, PKD, and PKD2 signaling.

HSP27 phosphorylation is correlated with ADP-induced platelet granule secretion

Adenosine diphosphate (ADP) plays a crucial role in hemostasis and thrombosis by activating platelets. ADP has been reported to induce heat-shock protein (HSP) 27 phosphorylation in human platelets. However, the exact role of HSP27 phosphorylation in human platelets has not yet been clarified. In the present study, we investigated the mechanisms and the roles of ADP-induced HSP27 phosphorylation in human platelets. We showed for the first time that both of decreased phosphorylation levels of HSP27 by PD98059, a MEK1/2 inhibitor and SB203580, a p38 MAPK inhibitor were correlated with the suppressed levels of platelet granule secretion but not with platelet aggregation. Furthermore, the inhibition of either the p44/p42 MAPK or p38 MAPK pathways had no effect on ADP-induced platelet aggregation. These results strongly suggest that the ADP-induced phosphorylation of HSP27 via p44/p42 MAPK and/or p38 MAPK is therefore sufficient for platelet granule secretion but not for platelet aggregation in humans.

Cyclic strain-induced HSP27 phosphorylation modulates actin filaments in airway smooth muscle cells

Mechanical stress (cyclic deformational strain) increases proteins of cytoskeletal and contractile domains in airway smooth muscle (ASM) cells in a manner that increases cell contractility. Here we studied the role of HSP27 in strain-induced microfilament formation and stability. Cultured ASM cells showed rapid phosphorylation of HSP27 upon cyclic strain within a few minutes that continued for 30 to 40 minutes. Such increases in HSP27 phosphorylation were abolished with SB 202190, a specific inhibitor of p38 mitogen-activated protein kinase (MAPK), but not by PD 98059 (an inhibitor of extracellular regulated kinase), GF109203X (an inhibitor of protein kinase C), or Y27632 (an inhibitor of Rho kinase). Direct activation of RhoA by GTPgammaS did not alter the level of HSP27 phosphorylation. Confocal microscopy revealed that cells pre-incubated with SB 202190, and/or Y27632 resulted in disorganization of stress fibers upon strain, unlike PD 98059 and GF 1092030X, suggesting that both p38 MAPK and Rho kinase were necessary for strain-induced microfilament formation. To determine the relationship between HSP27 and RhoA in strain-induced microfilament formation, cells were transfected with various isoforms of HSP27 and RhoA before strain. Co-expression of inactive HSP27 (3A-HSP27) with constitutively active EGF-RhoA (RhoV14) caused diminution of microfilaments compared with constitutive active EGFP-RhoA (RhoV14) alone, suggesting that HSP27 is necessary for microfilament stability. Similarly, expression of phosphomimicking HSP27 (3D-HSP27) was sufficient for retaining microfilament formation even when co-expressed with the dominant-negative RhoA (EGFP-RhoN17). Thus, HSP27 activation is necessary for microfilament stability independently of RhoA activation.

Structure, function, property, and role in neurologic diseases and other diseases of the sHsp22

Small heat shock proteins are members of the heat shock proteins family. They share important identical features: 1) they form the conserved structure 'alpha-crystallin domain' with about 80-100 residues in the C-terminal part of the proteins; 2) they have monomeric molecular masses ranging in 12-43 kDa; 3) they associate into large oligomers consisting in many cases of subunits; 4) they increase expression under stress conditions; 5) they exhibit a highly dynamic structure; and 6) they play a chaperone-like role. Hsp22 (also known as HspB8, H11, and E2IG1) retains the structural motif of the 'alpha-crystallin' family of Hsps and is a member of the superfamily of sHsps. Hsp22 displays chaperone activity, autokinase activity, and trigger or block apoptosis activity. It differs from canonical family members existing as a monomer. A decrease in the HspB8 activity may contribute to the development of some neurologic diseases and others.

Regulation of stress-induced intracellular sorting and chaperone function of Hsp27 (HspB1) in mammalian cells

In vitro, small Hsps (heat-shock proteins) have been shown to have chaperone function capable of keeping unfolded proteins in a form competent for Hsp70-dependent refolding. However, this has never been confirmed in living mammalian cells. In the present study, we show that Hsp27 (HspB1) translocates into the nucleus upon heat shock, where it forms granules that co-localize with IGCs (interchromatin granule clusters). Although heat-induced changes in the oligomerization status of Hsp27 correlate with its phosphorylation and nuclear translocation, Hsp27 phosphorylation alone is not sufficient for effective nuclear translocation of HspB1. Using firefly luciferase as a heat-sensitive reporter protein, we demonstrate that HspB1 expression in HspB1-deficient fibroblasts enhances protein refolding after heat shock. The positive effect of HspB1 on refolding is completely diminished by overexpression of Bag-1 (Bcl-2-associated athanogene), the negative regulator of Hsp70, consistent with the idea of HspB1 being the substrate holder for Hsp70. Although HspB1 and luciferase both accumulate in nuclear granules after heat shock, our results suggest that this is not related to the refolding activity of HspB1. Rather, granular accumulation may reflect a situation of failed refolding where the substrate is stored for subsequent degradation. Consistently, we found 20S proteasomes concentrated in nuclear granules of HspB1 after heat shock. We conclude that HspB1 contributes to an increased chaperone capacity of cells by binding unfolded proteins that are hereby kept competent for refolding by Hsp70 or that are sorted to nuclear granules if such refolding fails.

(-)-epigallocatechin gallate inhibits prostaglandin D2-stimulated HSP27 induction via suppression of the p44/p42 MAP kinase pathway in osteoblasts

We previously reported that prostaglandin D2 (PGD2) stimulates heat shock protein 27 (HSP27) induction through p38 mitogen-activated protein (MAP) kinase, stress-activated protein kinase (SAPK)/c-Jun N-terminal kinase (JNK) and p44/p42 MAP kinase in osteoblast-like MC3T3-E1 cells. In the present study, we investigated whether (-)-epigallocatechin gallate (EGCG), the major polyphenol found in green tea, affects the induction of HSP27 in these cells and the mechanism. EGCG significantly reduced the HSP27 induction stimulated by PGD2 without affecting the levels of HSP70. The PGD2-induced phosphorylation of p38 MAP kinase or SAPK/JNK was not affected by EGCG. On the contrary, EGCG markedly suppressed the PGD2-induced phosphorylation of p44/p42 MAP kinase and MEK1/2. However, the PGD2-induced phosphorylation of Raf-1 was not inhibited by EGCG. These results strongly suggest that EGCG suppresses the PGD2-stimulated induction of HSP27 at the point between Raf-1 and MEK1/2 in osteoblasts.

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.

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.

Mobile phone base station-emitted radiation does not induce phosphorylation of Hsp27

An in vitro study focusing on the effects of low-level radiofrequency (RF) fields from mobile radio base stations employing the International Mobile Telecommunication 2000 (IMT-2000) cellular system was conducted to test the hypothesis that modulated RF fields act to induce phosphorylation and overexpression of heat shock protein hsp27. First, we evaluated the responses of human cells to microwave exposure at a specific absorption rate (SAR) of 80 mW/kg, which corresponds to the limit of the average whole-body SAR for general public exposure defined as a basic restriction in the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. Second, we investigated whether continuous wave (CW) and Wideband Code Division Multiple Access (W-CDMA) modulated signal RF fields at 2.1425 GHz induced activation or gene expression of hsp27 and other heat shock proteins (hsps). Human glioblastoma A172 cells were exposed to W-CDMA radiation at SARs of 80 and 800 mW/kg for 2-48 h, and CW radiation at 80 mW/kg for 24 h. Human IMR-90 fibroblasts from fetal lungs were exposed to W-CDMA at 80 and 800 mW/kg for 2 or 28 h, and CW at 80 mW/kg for 28 h. Under the RF field exposure conditions described above, no significant differences in the expression levels of phosphorylated hsp27 at serine 82 (hsp27[pS82]) were observed between the test groups exposed to W-CDMA or CW signal and the sham-exposed negative controls, as evaluated immediately after the exposure periods by bead-based multiplex assays. Moreover, no noticeable differences in the gene expression of hsps were observed between the test groups and the negative controls by DNA Chip analysis. Our results confirm that exposure to low-level RF field up to 800 mW/kg does not induce phosphorylation of hsp27 or expression of hsp gene family.

TNF-α decreases hsp 27 in human blood mononuclear cells: Involvement of protein kinase c

Treatment of PBMCs with TNF-alpha decreased the levels of heat shock protein (HSP) 27, but had little effect on the level of HSP70. Parallel to the decrease of HSP27, TNF-alpha increased the level of HSP27 in the incubation medium of the cells. The decrease of HSP27 induced by TNF-alpha was suppressed by the pretreatment of PBMCs with the specific protein kinase C (PKC) inhibitor, GF109203X. Furthermore, phorbol myristate acetate (PMA), a PKC stimulant, but not dibutyryl cyclic AMP, a protein kinase A stimulant, decreased the levels of HSP27. To investigate the effect of TNF-alpha on the oligomerization state of HSP27 in PBMCs, we performed sucrose density gradient centrifugation with subsequent fractionation and immunoassay. Extract of vehicle-treated PBMCs contained mainly dissociated forms of HSP27. The amounts of dissociated forms of HSP27 in PBMCs was decreased by TNF-alpha, while the amounts of aggregated form of HSP27 was little changed. In intact PBMCs, HSP27 is constitutively phosphorylated at Ser78, but not at Ser15 or at Ser82. The amount of phosphorylated HSP27 at Ser78 was decreased by TNF-alpha. These results indicate that TNF-alpha reduces HSP27 in PBMCs through PKC activation. This decrease may be due to efflux of dissociated form of HSP27, phosphorylated HSP27 at Ser78, from the cells.

Cell signaling pathways to αB-crystallin following stresses of the cytoskeleton

Small heat shock proteins (sHSPs) act as chaperone, but also in protecting the different cytoskeletal components. Recent results suggest that alphaB-crystallin, a member of sHSPs family, might regulate actin filament dynamics, stabilize them in a phosphorylation dependent manner, and protect the integrity of intermediate filaments (IF) against extracellular stress. We demonstrate that vinblastin and cytochalasin D, which respectively disorganize microtubules and actin microfilaments, trigger the activation of the p38/MAPKAP2 kinase pathway and lead to the specific alphaB-crystallin phosphorylation at serine 59. Upstream of p38, we found that RhoK, PKC and PKA are selectively involved in the activation of p38 and phosphorylation of alphaB-crystallin, depending on the cytoskeletal network disorganized. Moreover, we demonstrate that chronic perturbations of IF network result in the same activation of p38 MAPK and alphaB-crystallin phosphorylation, as with severe disorganization of other cytoskeletal networks. Finally, we also show that Ser 59 phosphorylated alphaB-crystallin colocalizes with cytoskeletal components. Thus, disturbance of cytoskeleton leads by converging signaling pathways to the phosphorylation of alphaB-crystallin, which probably acts as a protective effector of the cytoskeleton.

Analysis of Properties of Small Heat Shock Protein Hsp25 in MAPK-activated Protein Kinase 2 (MK2)-deficient Cells

Small heat shock proteins (sHsps) exist in dynamic oligomeric complexes and display diverse biological functions ranging from chaperone properties to modulator of apoptosis. So far, the role of stress-dependent phosphorylation of mammalian sHsps for its structure and function has been analyzed by using various phosphorylation site mutants overexpressed in different cell types as well as by non-exclusive inhibitors of the p38 MAPK cascade. Here we investigate the role of phosphorylation of endogenous sHsp in a genetic model lacking the major Hsp25 kinase, the MAP kinase-activated protein kinase MK2. We demonstrate that in MK2-deficient fibroblasts, where no stress-dependent phosphorylation of Hsp25 at Ser86 and no in vitro binding to 14-3-3 was detectable, stress-dependent disaggregation of endogenous Hsp25 complexes is impared and kinetics of arsenite-dependent, H2O2-dependent, and sublethal heat shock-induced insolubilization of Hsp25 is delayed. Similarly, green fluorescent protein-tagged Hsp25 shows retarded subcellular accumulation into stress granules in MK2-deficient cells after arsenite treatment. Decreased insolubilization of Hsp25 in MK2-deficient cells correlates with increased resistance against arsenite, H2O2, and sublethal heat shock treatment and with decreased apoptosis. In contrast, after severe, lethal heat shock MK2-deficient embryonic fibroblasts cells show fast and complete insolubilization of Hsp25 independent of MK2 and no increased stress resistance. Hence, MK2-dependent formation of insoluble stress granules and irreversible cell damage by oxidative stresses and sublethal heat shock correlate and only upon severe, lethal heat shock MK2-independent processes could determine insolubilization of Hsp25 and are more relevant for cellular stress damage.

Short-chain fatty acids induce acute phosphorylation of the p38 mitogen-activated protein kinase/heat shock protein 27 pathway via GPR43 in the MCF-7 human breast cancer cell line

The expression of GPR41 and 43, which have recently been identified as G-protein-coupled cell-surface receptors for short-chain fatty acids (SCFAs), was detected in a human breast cancer cell line (MCF-7) by RT-PCR. Acetate, propionate and butyrate induced an increase in intracellular Ca2+ in these cells that was not blocked by treatment with pertussis toxin (PTX). SCFAs significantly reduced forskolin-induced cAMP levels in these cells. The phosphorylation of mitogen-activated protein kinase (MAPK) p38 was selectively increased by SCFAs. The downstream substrate heat shock protein 27 (HSP27) was also phosphorylated by SCFAs at Ser-78 and-82, but not-15. Propionate induced elevations in intracellular Ca2+ and the phosphorylation of p38 were inhibited by the silencing of GPR43 using a specific siRNA. These results suggest that GPR41 and 43 mediate SCFA signaling in mammary epithelial cells and thereby play an important role in their stress management.

Heat shock protein 27: its potential role in vascular disease

Heat shock proteins are molecular chaperones that have an ability to protect proteins from damage induced by environmental factors such as free radicals, heat, ischaemia and toxins, allowing denatured proteins to adopt their native configuration. Heat shock protein-27 (Hsp27) is a member of the small Hsp (sHsp) family of proteins, and has a molecular weight of approximately 27 KDa. In addition to its role as a chaperone, it has also been reported to have many additional functions. These include effects on the apoptotic pathway, cell movement and embryogenesis. In this review, we have focused on its possible role in vascular disease.

Prostaglandin D2 induces the phosphorylation of HSP27 in osteoblasts: function of the MAP kinase superfamily

We previously reported that prostaglandin D(2) (PGD(2)) stimulates the induction of heat shock protein 27 (HSP27) in osteoblast-like MC3T3-E1 cells. In the present study, we investigated whether PGD(2) stimulates the phosphorylation of HSP27 in MC3T3-E1 cells exposed to heat shock. In the cultured MC3T3-E1 cells, PGD(2) markedly stimulated the phosphorylation of HSP27 at Ser-15 and Ser-85 in a time-dependent manner. Among the mitogen-activated protein (MAP) kinase superfamily, p44/p42 MAP kinase and p38 MAP kinase were phosphorylated by PGD(2) which had little effect on the phosphorylation of stress-activated protein kinase (SAPK)/c-Jun N-terminal kinase (JNK). The PGD(2)-induced phosphorylation of HSP27 was attenuated by PD169316, an inhibitor of p38 MAP kinase or PD98059, a MEK inhibitor. SP600125, a SAPK/JNK inhibitor did not affect the HSP27 phosphorylation. In addition, PD169316 suppressed the PGD(2)-induced phosphorylation of MAPKAP kinase 2. These results strongly suggest that PGD(2) stimulates HSP27 phosphorylation via p44/p42 MAP kinase and p38 MAP kinase but not SAPK/JNK in osteoblasts.

Vincristine regulates the phosphorylation of the antiapoptotic protein HSP27 in breast cancer cells

Vincristine is an antitumor drug that inhibits microtubule polymerization, causes G2/M arrest and induces apoptosis. 2D-PAGE and MALDI-TOF-MS analysis of vincristine effects on MCF7 cells, revealed a vincristine upregulated form and a vincristine downregulated form of the antiapoptotic protein HSP27. These findings linked to the lack of vincristine effect over HSP27 mRNA, suggest a protein post-translational modification. Further assays indicated the presence of a phosphorylated peptide, containing serine 82, only in the vincristine upregulated form. Serine 82 phosphorylation was confirmed using specific antibodies. Thus, phosphorylation of HSP27 may play a role in the cellular response to vincristine.

In vivo resolution of oligomers with fluorescence photobleaching recovery histograms

Simple independent enzyme-catalyzed reactions distributed homogeneously throughout an aqueous environment cannot adequately explain the regulation of metabolic and other cellular processes in vivo. Such an unstructured system results in unacceptably slow substrate turnover rates and consumes inordinate amounts of cellular energy. Current approaches to resolving compartmentalization in living cells requires the partitioning of the molecular species in question such that its localization can be resolved with fluorescence microscopy. Standard imaging approaches will not resolve localization of protein activity for proteins that are ubiquitously distributed, but whose function requires a change in state of the protein. The small heat shock protein sHSP27 exists as both dimers and large multimers and is distributed homogeneously throughout the cytoplasm. A fusion of the green fluorescent protein variant S65T and sHSP27 is used to assess the ability of diffusion rate histograms to resolve compartmentalization of the 2 dominant oligomeric species of sHSP27. Diffusion rates were measured by multiphoton fluorescence photobleaching recovery. Under physiologic conditions, diffusion rate histograms resolved at least 2 diffusive transport rates within a living cell potentially corresponding to the large and small oligomers of sHSP27. Given that oligomerization is often a means of regulation, compartmentalization of different oligomer species could provide a means for efficient regulation and localization of sHsp27 activity.

Expression and distribution of HSP27 in response to G418 in different human breast cancer cell lines

Heat shock proteins (HSPs) play an important role in folding, intracellular localization and degradation of cellular proteins. However, the cellular role of HSP27 is not completely understood. The conflicting results have been reported regarding stress-induced nuclear translocation of HSP27. In this study, human breast cancer cells transiently and stably expressing HSP27-EGFP chimera were utilized to observe the intracellular localization of HSP27. The data show that the transient and stable expression of HSP27-EGFP displayed distinguishingly cellular localization. The nuclear translocalization of HSP27-EGFP was correlated with the presence of G418. Experiments carried out with different human breast cancer cell lines revealed clearly different distribution patterns of endogenous HSP27. The subcellular distribution of endogenous HSP27 appeared diffuse throughout the cytoplasm in MDA435 cells. In MCF-7 and SKBR3 cells, the accumulation of the protein was distinctly seen along the cell membrane and around nucleus. Moreover, the nuclear translocation of endogenous HSP27 was stimulated by G418 only in MDA435 cells, but not in MCF-7 and SKBR3 cells. Overexpression of HSP27 has been associated with resistance to cisplatin and doxorubicin. The correlation of the expression pattern of HSP27 with the drug resistance may need to be investigated. Further studies on the intracellular function of HSP27 may take into account its interaction proteins in the cells. It may provide useful information for the identification of sensitivity of carcinoma cells to the chemotherapeutic drugs and development of more specific agents to circumvent HSP27.

Self-association and chaperone activity of Hsp27 are thermally activated

The small heat shock protein 27 (Hsp27) is an oligomeric, molecular chaperone in vitro. This chaperone activity and other physiological roles attributed to Hsp27 have been reported to depend on the state of self-association. In the present work, we have used sedimentation velocity experiments to demonstrate that the self-association of Hsp27 is independent of pH and ionic strength but increases significantly as the temperature is increased from 10 to 40 degrees C. The largest oligomers formed at 10 degrees C are approximately 8-12 mer, whereas at 40 degrees C oligomers as large as 22-30 mer are observed. Similarly, the chaperone activity of Hsp27 as indicated by its ability to inhibit dithiothreitol-induced insulin aggregation also increases with increased temperature, with a particularly sharp increase in activity as temperature is increased from 34 to 43 degrees C. Similar studies of an Hsp27 triple variant that mimics the behavior of the phosphorylated protein establish that this protein has greatly diminished chaperone activity that responds minimally to increased temperature. We conclude that Hsp27 can exploit a large number of oligomerization states and that the range of oligomer size and the magnitude of chaperone activity increase significantly as temperature is increased over the range that is relevant to the physiological heat shock response.

Phosphatidylinositol 3-kinase/Akt plays a role in sphingosine 1-phosphate-stimulated HSP27 induction in osteoblasts

We previously reported that p38 mitogen-activated protein (MAP) kinase plays a part in sphingosine 1-phosphate-stimulated heat shock protein 27 (HSP27) induction in osteoblast-like MC3T3-E1 cells. In the present study, we investigated whether phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) is involved in the induction of HSP27 in these cells. Sphingosine 1-phosphate time dependently induced the phosphorylation of Akt. Akt inhibitor, 1L-6-hydroxymethyl-chiro-inositol 2-(R)-2-O-methyl-3-O-octadecylcarbonate, reduced the HSP27 induction stimulated by sphingosine 1-phosphate. The sphingosine 1-phosphate-induced phosphorylation of GSK-3beta was suppressed by Akt inhibitor. The sphingosine 1-phosphate-induced HSP27 levels were attenuated by LY294002 or wortmannin, PI3K inhibitors. Furthermore, LY294002 or Akt inhibitor did not affect the sphingosine 1-phosphate-induced phosphorylation of p38 MAP kinase and SB203580, a p38 MAP kinase inhibitor, had little effect on the phosphorylation of Akt. These results suggest that PI3K/Akt plays a part in the sphingosine 1-phosphate-stimulated induction of HSP27, maybe independently of p38 MAP kinase, in osteoblasts.

Effect of methylglyoxal modification and phosphorylation on the chaperone and anti-apoptotic properties of heat shock protein 27

Heat shock protein 27 (Hsp27) is a stress-inducible protein in cells that functions as a molecular chaperone and also as an anti-apoptotic protein. Methylglyoxal (MGO) is a reactive dicarbonyl compound produced from cellular glycolytic intermediates that reacts non-enzymatically with proteins to form products such as argpyrimidine. We found considerable amount of Hsp27 in phosphorylated form (pHsp27) in human cataractous lenses. pHsp27 was the major argpyrimidine-modified protein in brunescent cataractous lenses. Modification by MGO enhanced the chaperone function of both pHsp27 and native Hsp27, but the effect on Hsp27 was at least three-times greater than on pHsp27. Phosphorylation of Hsp27 abolished its chaperone function. Transfer of Hsp27 using a cationic lipid inhibited staurosporine (SP)-induced apoptotic cell death by 53% in a human lens epithelial cell line (HLE B-3). MGO-modified Hsp27 had an even greater effect (62% inhibition). SP-induced reactive oxygen species in HLE-B3 cells was significantly lower in cells transferred with MGO-modified Hsp27 when compared to native Hsp27. In vitro incubation experiments showed that MGO-modified Hsp27 reduced the activity of caspase-9, and MGO-modified pHsp27 reduced activities of both caspase-9 and caspase-3. Based on these results, we propose that Hsp27 becomes a better anti-apoptotic protein after modification by MGO, which may be due to multiple mechanisms that include enhancement of chaperone function, reduction in oxidative stress, and inhibition of activity of caspases. Our results suggest that MGO modification and phosphorylation of Hsp27 may have important consequences for lens transparency and cataract development.

Mild hyperthermia plus adenoviral p53 over-expression additively inhibits the viability of human malignant glioma cells

Adenoviral replacement of the p53 gene has already been proved effective for the treatment of various tumours, including malignant gliomas. However, it is difficult to treat malignant glioma with p53 gene therapy alone because of problems with resistance or a less-than-satisfactory response to the treatment. This study investigated whether heat shock at 43 degrees C (mild hyperthermia) augments the cytotoxic effect of p53 gene transfer on malignant glioma cells expressing wild-type p53 (D54) or mutant p53 (U373-MG and U251-MG). The combination of mild hyperthermia and adenoviral p53 over-expression had an additive inhibitory effect on cellular proliferation in all three cell lines studied. Further, both cell cycle analysis and a DNA fragmentation assay showed that apoptosis was induced by p53 over-expression alone but not by heat shock at 43 degrees C alone. However, p53 over-expression followed by mild hyperthermia additively increased the proportion of cells in which apoptosis was induced, regardless of the endogenous p53 status of the tumour cells. Interestingly, a caspase-independent mechanism was observed to be involved in the p53-induced apoptosis in U251-MG and D54 cells. Taken together, the findings showed that combining adenoviral p53 transfer with mild hyperthermia inhibits the proliferation of malignant glioma cells in an additive manner, irrespective of their endogenous p53 status, suggesting a novel treatment strategy for this malignancy.

Attenuated phosphorylation of heat shock protein 27 correlates with tumor progression in patients with hepatocellular carcinoma

Heat shock protein 27 (HSP27) is expressed at high levels in human hepatocellular carcinoma (HCC). We examined correlations of total HSP27 and serine phosphorylated (Ser-15, Ser-78, and Ser-82) HSP27 levels in HCC tissues with clinical and pathologic characteristics in 48 resected HCC specimens. The levels of total and Ser-phosphorylated HSP27 were evaluated by Western blot analysis. Immunohistochemical analysis of HSP27 expression was also performed on some samples. Phosphorylation of HSP27 was detected in all 48 HCC tissues. Levels of phosphorylated HSP27 were correlated inversely with tumor size, microvascular invasion of HCC, and tumor stage by TNM classification. In contrast, only microvascular invasion showed an inverse correlation with total HSP27 levels. The decrease in phosphorylated HSP27 in progressed HCC was also observed by immunohistochemistry. Levels of phosphorylated HSP27 gradually decreased in parallel with HCC progression. Our findings suggest that phosphorylated HSP27 may have a suppressive role in progression of human HCC.

Adenylyl cyclase-cAMP system inhibits thrombin-induced HSP27 in vascular smooth muscle cells

We previously reported that thrombin stimulates the induction of heat shock protein (HSP) 27 via p38 mitogen-activated protein (MAP) kinase activation in aortic smooth muscle A10 cells. In the present study, we investigated the effect of the adenylyl cyclase-cAMP system on the thrombin-stimulated induction of HSP27 in A10 cells. Forskolin, a direct activator of adenylyl cyclase, reduced the thrombin-induced p38 MAP kinase phosphorylation, and significantly suppressed the thrombin-stimulated accumulation of HSP27. However, dideoxyforskolin, a forskolin derivative that does not activate cAMP, failed to suppress the HSP27 accumulation. Furthermore, dibutyryl-cAMP (DBcAMP), a permeable analog of cAMP, significantly suppressed the accumulation of HSP27. On the other hand, calphostin C, an inhibitor of protein kinase C (PKC), reduced the thrombin-induced p38 MAP kinase phosphorylation, and significantly suppressed the thrombin-stimulated accumulation of HSP27. Moreover, forskolin reduced the p38 MAP kinase phosphorylation induced by the 12-O-tetradecanoylphorbol-13-acetate (TPA), a PKC-activating phorbol ester, and significantly suppressed the TPA-stimulated accumulation of HSP27. These results indicate that adenylyl cyclase-cAMP system has an inhibitory role in thrombin-stimulated HSP27 induction in aortic smooth muscle cells, and the effect seems to be exerted on the thrombin-induced PKC- p38 MAP kinase signaling pathway.

Akt regulates thrombin-induced HSP27 phosphorylation in aortic smooth muscle cells: function at a point downstream from p38 MAP kinase

We previously reported that p38 MAP kinase takes part in thrombin-induced HSP27 phosphorylation in aortic smooth muscle A10 cells. In the present study, we investigated whether Akt is involved in the phosphorylation of HSP27 and the role of adenylyl cyclase-cAMP system. Thrombin time-dependently induced the phosphorylation of heat shock protein 27 (HSP27) and Akt in aortic smooth muscle A10 cells. SB203580, a p38 MAP kinase inhibitor, significantly suppressed the thrombin-induced phosphorylation of Akt and the Akt inhibitor suppressed the phosphorylation of HSP27. Furthermore, the thrombin-induced phosphorylation of HSP27, p38 MAP kinase and Akt were decreased by dibutyryl-cAMP (DBcAMP). These results strongly suggest that Akt functions the thrombin-induced phosphorylation of HSP27 at a point downstream from p38 MAP kinase in aortic smooth muscle cells and the adenylyl cyclase-cAMP system is upstream regulator of the HSP27 phosphorylation in these cells.

Possible involvement of phosphatidylinositol 3-kinase/Akt signal pathway in vasopressin-induced HSP27 phosphorylation in aortic smooth muscle A10 cells

We previously reported that p38 mitogen-activated protein (MAP) kinase takes a part in arginine vasopressin (AVP)-induced heat shock protein 27 (HSP27) phosphorylation in aortic smooth muscle A10 cells. In the present study, we investigated whether phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) is involved in the phosphorylation of HSP27 in these cells. AVP time-dependently induced the phosphorylation of PI3K and Akt. Akt inhibitor, 1l-6-hydroxymethyl-chiro-inositol 2-(R)-2-O-methyl-3-O-octadecylcarbonate, partially suppressed the phosphorylation of HSP27. The AVP-induced HSP27 phosphorylation was attenuated by LY294002, a PI3K inhibitor. The combination of Akt inhibitor and SB203580, a p38 MAP kinase inhibitor, completely suppressed the AVP-induced phosphorylation of HSP27. Furthermore, LY294002 or Akt inhibitor did not affect the AVP-induced phosphorylation of p38 MAP kinase and SB203580 did not affect the phosphorylation of PI3K or Akt. These results suggest that PI3K/Akt plays a part in the AVP-induced phosphorylation of HSP27, maybe independently of p38 MAP kinase, in aortic smooth muscle A10 cells.

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.

Small heat shock proteins HSP27 and alphaB-crystallin: cytoprotective and oncogenic functions

Heat shock protein-27 (HSP27) and alphaB-crystallin are ubiquitous small heat shock proteins whose expression is induced in response to a wide variety of physiological and environmental insults. They allow the cells to survive in otherwise lethal conditions. Various mechanisms have been proposed to account for the cytoprotective functions of these small heat shock proteins. First, these proteins are powerful molecular chaperones whose main function is to prevent the aggregation of nascent and stress-accumulated misfolded proteins. Second, they interact directly with various components of the tightly regulated programmed cell death machinery, upstream and downstream of the mitochondrial events. Third, they appear to play a role in the proteasome-mediated degradation of selected proteins. Both HSP27 and alphaB-crystallin were also proposed to participate in the development of neurodegenerative diseases and malignant tumors in which their overexpression could induce drug resistance. Altogether, these properties suggest that these small heat shock proteins are appropriate targets for modulating cell death pathways.

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.

Midazolam suppresses thrombin-induced heat shock protein 27 phosphorylation through inhibition of p38 mitogen-activated protein kinase in cardiac myocytes

It has been shown that anesthetics have effects of cardiac preconditioning. Heat shock proteins (HSPs) function as molecular chaperone. Among them, HSP27, a low-molecular-weight HSP, abundantly exist in heart. However, the relationship between anesthetics and HSP27 in heart is not yet clarified. We investigated whether thrombin induces or phosphorylates HSP27 in primary cultured mouse myocytes and the effect of midazolam on the thrombin-stimulated HSP27 phosphorylation and the mechanism behind it. Thrombin time dependently phosphorylated HSP27 at Ser-15 and Ser-85 while having no effect on the levels of HSP27. Midazolam markedly suppressed the thrombin-induced phosphorylation of HSP27 at both Ser-15 and Ser-85. Thrombin induced the phosphorylation of p44/p42 MAP kinase and p38 MAP kinase without affecting stress-activated protein kinase/c-Jun N-terminal kinase. In addition, midazolam attenuated the phosphorylation of thrombin-induced p38 MAP kinase but not that of p44/p42 MAP kinase. SB203580 and PD169316, inhibitors of p38 MAP kinase, suppressed the thrombin-induced phosphorylation of HSP27 at both Ser-15 and Ser-85. These results strongly suggest that thrombin induces the HSP27 phosphorylation at least through the p38 MAP kinase activation in cardiac myocytes and that midazolam inhibits the thrombin-induced HSP27 phosphorylation via suppression of p38 MAP kinase activation.

Self-association of a Small Heat Shock Protein

Human Hsp27 oligomerizes in vivo in a phosphorylation-dependent manner that regulates the functional activity of the protein. We have studied the self-association of wild-type Hsp27 by both sedimentation velocity and sedimentation equilibrium analysis and established that the protein forms an equilibrium mixture of monomers/dimers, tetramers, 12-mers and 16-mers (20 mM Tris-HCl (pH 8.4), 100 mM NaCl, 20 degrees C). Corresponding analysis of the S15D/S78D/S82D triple variant, which is believed to mimic the behavior of phosphorylated Hsp27, establishes that this form of the protein forms primarily monomers and dimers but also forms a small fraction of very large oligomers. Variants in which critical N-terminal sequences have been deleted exhibit oligomerization behavior that is intermediate between that of the triple variant and the wild-type protein. On the other hand a C-terminal sequence deletion variant forms larger oligomers than does the wild-type protein, but also exhibits a greater fraction of smaller oligomers. Notably, the presence of an N-terminal His6-tag induces formation of much larger oligomers than observed for any other form of the protein. The results of this work establish that the wild-type protein forms smaller oligomers than previously believed, define the roles played by various structural domains in Hsp27 oligomerization, and provide improved molecular probes with better-defined properties for the design of future experiments.

Effects of a heat shock protein inhibitor KNK437 on heat sensitivity and heat tolerance in human squamous cell carcinoma cell lines differing in p53 status

PURPOSE

The effects of a heat shock protein (hsp) inhibitor KNK437 (N-formyl-3,4-methylenedioxy-benzylidene-gamma-butyrolactam) were examined on the heat sensitivity and heat tolerance of human cancer cells with special reference to p53 status.

MATERIALS AND METHODS

Human squamous cell carcinoma (SAS) and glioblastoma cell lines (A-172) transfected with mutant p53 (mp53) or control neo genes were used. KNK437 was added in culture medium at a final concentration of 50, 100 or 300 microM 1 h before heating (42 degrees C). Surviving fractions of cells were measured by use of a clonogenic assay. Effects of KNK437 on the accumulation of heat shock proteins and DNA binding activity of heat shock factor 1 were examined with Western blot analysis and gel mobility-shift assay, respectively. Heat-induced apoptotic bodies were detected by Hoechst 33342 staining.

RESULTS

The mp53-transfected SAS (SAS/mp53) and A-172 (A-172/mp53) cells were more resistant to heat than the neomycin (neo)-transfected SAS (SAS/neo) and A-172 (A-172/neo) cells. The constitutive amount of hsp27 was larger in SAS/mp53 than in SAS/neo cells. Clear differences in the constitutive amounts of hsp40, hsp72 and hsp90 were not observed between SAS/mp53 and SAS/neo cells. KNK437 enhanced the heat sensitivity in SAS/mp53 and A-172/mp53 cells more effectively than in neo control cells. Heat tolerance was suppressed by KNK437 in SAS/mp53 and SAS/neo cells and also in A-172/mp53 and A-172/neo cells. Along with suppression of heat tolerance, KNK437 suppressed heat-induced accumulation of both hsp27 and hsp72. Heat-induced apoptotic bodies were enhanced by KNK437 in SAS/mp53 and SAS/neo cells.

CONCLUSION

The results suggest a possible mechanism for the heat sensitivity of SAS cells. Heat sensitivity depends on p53 status regulating the amount of hsp27. Heat tolerance is suppressed by KNK437 through the suppression of heat-induced accumulations of hsp27 and hsp72 and the induction of p53-independent apoptosis.

Autophosphorylation of the 16 kDa and 70 kDa antigens (Hsp 16.3 and Hsp 70) of Mycobacterium tuberculosis

Several antigens of Mycobacterium tuberculosis, identified by monoclonal antibodies, have been previously cloned and are being exploited in the development of improved vaccines and diagnostic reagents. In this study, the molecular characteristics of two of these antigens, the immunodominant proteins Hsp 16.3 and Hsp 70, were analysed in further detail by assessing their capacity to undergo protein phosphorylation, a chemical modification frequently used by organisms to adjust to environmental variations. Hsp 16.3 was overproduced in an Escherichia coli expression system and purified to homogeneity. Upon incubation in the presence of radioactive ATP, it was shown to possess autophosphorylation activity. Two-dimensional analysis of its phosphoamino acid content revealed that it was modified exclusively at serine residues. In addition, cross-linking experiments demonstrated that it could tightly bind to ATP. Purified Hsp 70 was also shown to autophosphorylate but phosphorylation occurred exclusively at threonine residues. This reaction was found to be strongly stimulated by calcium ions. These data indicate that both structural and functional similarities exist between Hsp 16.3 (Acr) and alpha-crystallin, a eukaryotic protein which plays an important role in maintaining the transparency of the vertebrate eye, and that the functional properties of Hsp 70 from M. tuberculosis are similar to those of other bacterial members of the Hsp 70 family, particularly the E. coli homologue DnaK.