Inhibition of Daxx-mediated apoptosis by heat shock protein 27

Functional promoter -1271G>C variant of HSPB1 predicts lung cancer risk and survival

PURPOSE Heat-shock protein 27 (Hsp27), encoded by HSPB1, plays crucial roles in tumorigenesis and cell survival and is reported to be an independent prognosis marker for cancer. We hypothesized that genetic variants of the HSPB1 gene may be associated with lung cancer susceptibility and survival. PATIENTS AND METHODS We first resequenced the full-length HSPB1 gene and then genotyped three selected tag single nucleotide polymorphisms (SNPs) in 1,152 paired Chinese lung cancer patient cases and controls. Another 500 paired patient cases and controls were used for replication. We also evaluated the roles of these tagSNPs in the overall survival of 248 patients with advanced non-small-cell lung cancer (NSCLC), and validated the results in another 335 patients with advanced NSCLC. The genotype-phenotype correlation was assessed in 309 workers with occupational exposure to polycyclic-aromatic hydrocarbons (PAHs) as well as by luciferase reporter assay and Western blotting analysis. RESULTS The -1271C allele was associated with a significantly increased lung cancer risk in the two independent patient case-control studies (P < .05 for both), but it conferred a favorable survival for patients with advanced NSCLC in two independent cohorts (adjusted hazard ratio, 0.66 and 0.75, respectively). The occupational PAH-exposed workers carrying the -1271C allele showed higher DNA damage levels than those with the -1271G allele (P = .027). Furthermore, the -1271C allele significantly decreased luciferase activity in four cell lines and resulted in lower Hsp27 expression levels in normal lung tissues when compared with -1271G allele (P < .05). CONCLUSION The functional HSPB1 promoter -1271G>C variant may affect lung cancer susceptibility and survival by modulating endogenous Hsp27 synthesis levels.

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.

Increased monomerization of mutant HSPB1 leads to protein hyperactivity in Charcot-Marie-Tooth neuropathy

Small heat shock proteins are molecular chaperones capable of maintaining denatured proteins in a folding-competent state. We have previously shown that missense mutations in the small heat shock protein HSPB1 (HSP27) cause distal hereditary motor neuropathy and axonal Charcot-Marie-Tooth disease. Here we investigated the biochemical consequences of HSPB1 mutations that are known to cause peripheral neuropathy. In contrast to other chaperonopathies, our results revealed that particular HSPB1 mutations presented higher chaperone activity compared with wild type. Hyperactivation of HSPB1 was accompanied by a change from its wild-type dimeric state to a monomer without dissociation of the 24-meric state. Purification of protein complexes from wild-type and HSPB1 mutants showed that the hyperactive isoforms also presented enhanced binding to client proteins. Furthermore, we show that the wild-type HSPB1 protein undergoes monomerization during heat-shock activation, strongly suggesting that the monomer is the active form of the HSPB1 protein.

The mechanism whereby heat shock induces apoptosis depends on the innate sensitivity of cells to stress

The cellular response to heat shock (HS) is a paradigm for many human diseases collectively known as "protein conformation diseases" in which the accumulation of misfolded proteins induces cell death. Here, we analyzed how cells having a different apoptotic threshold die subsequent to a treatment with HS. Cells with a low apoptotic threshold mainly induced apoptosis through activation of conventional stress kinase signaling pathways. By contrast, cells with a high apoptotic threshold also died by apoptosis but likely after the accumulation of heat-aggregated proteins as revealed by the formation of aggresomes in these cells, which were associated with the generation of atypical nuclear deformations. Inhibition of the proteasome or expression of an aggregation prone protein produced similar nuclear alterations. Furthermore, elevated levels of chaperones markedly suppressed both HS-induced nuclear deformations and apoptosis induced upon protein aggregation whereas they had little effect on stress kinase-mediated apoptosis. We conclude that the relative contribution of stress signaling pathways and the accumulation of protein aggregates to cell death by apoptosis is related to the innate sensitivity of cells to deadly insults.

Hsp-27 expression at diagnosis predicts poor clinical outcome in prostate cancer independent of ETS-gene rearrangement

BACKGROUND

This study was performed to test the hypothesis that expression of small heat shock protein Hsp-27 is, at diagnosis, a reliable predictive biomarker of clinically aggressive prostate cancer.

METHODS

A panel of tissue microarrays constructed from a well-characterised cohort of 553 men with conservatively managed prostate cancer was stained immunohistochemically to detect Hsp-27 protein. Hsp-27 expression was compared with a series of pathological and clinical parameters, including outcome.

RESULTS

Hsp-27 staining was indicative of higher Gleason score (P<0.001). In tissue cores having a Gleason score >7, the presence of Hsp-27 retained its power to independently predict poor clinical outcome (P<0.002). Higher levels of Hsp-27 staining were almost entirely restricted to cancers lacking ERG rearrangements (chi2 trend=31.4, P<0.001), although this distribution did not have prognostic significance.

INTERPRETATION

This study has confirmed that, in prostate cancers managed conservatively over a period of more than 15 years, expression of Hsp-27 is an accurate and independent predictive biomarker of aggressive disease with poor clinical outcome (P<0.001). These findings suggest that apoptotic and cell-migration pathways modulated by Hsp-27 may contain targets susceptible to the development of biologically appropriate chemotherapeutic agents that are likely to prove effective in treating aggressive prostate cancers.

Heat shock protein 27 phosphorylation: kinases, phosphatases, functions and pathology

The small heat shock protein Hsp27 or its murine homologue Hsp25 acts as an ATP-independent chaperone in protein folding, but is also implicated in architecture of the cytoskeleton, cell migration, metabolism, cell survival, growth/differentiation, mRNA stabilization, and tumor progression. A variety of stimuli induce phosphorylation of serine residues 15, 78, and 82 in Hsp27 and serines 15 and 86 in Hsp25. This post-translational modification affects some of the cellular functions of Hsp25/27. As a consequence of the functional importance of Hsp25/27 phosphorylation, aberrant Hsp27 phosphorylation has been linked to several clinical conditions. This review focuses on the different Hsp25/27 kinases and phosphatases that regulate the phosphorylation pattern of Hsp25/27, and discusses the recent findings of the biological implications of these phosphorylation events in physiological and pathological processes. Novel therapeutic strategies aimed at restoring anomalous Hsp27 phosphorylation in human diseases will be presented.

Mutant p53 disrupts the stress MAPK activation circuit induced by ASK1-dependent stabilization of Daxx

Daxx is a regulatory protein for apoptosis signal-regulating kinase 1 (ASK1) which activates c-Jun NH2-terminal kinase (JNK) and p38 pathways in response to stressors such as tumor necrosis factor-alpha (TNFalpha). Here, we show that TNFalpha treatment induces the accumulation of Daxx protein through ASK1 activation by preventing its proteasome-dependent degradation. ASK1 directly phosphorylates Daxx at Ser(176) and Ser(184) and Daxx is required for the sustained activation of JNK. Tumorigenic mutant p53, which binds to Daxx and inhibits Daxx-dependent activation of ASK1, prevents Daxx phosphorylation and stabilization. When mutant p53 was depleted in cancer cells, Daxx was accumulated and the cell-killing effect of TNFalpha was restored. Our results indicate that Daxx not only activates ASK1 but also is a downstream target of ASK1 and that accumulated Daxx further activates ASK1. Thus, the Daxx-ASK1 positive feedback loop amplifying JNK/p38 signaling plays an important role in the cell-killing effects of stressors, such as TNFalpha. Tumorigenic mutant p53 disrupts this circuit and makes cells more tolerable to stresses, as its gain-of-function mechanism.

Modification and reorganization of the cytoprotective cellular chaperone Hsp27 during herpes simplex virus type 1 infection

Chaperone-enriched domains are formed in the nuclei of cells lytically infected with herpes simplex virus type 1 (HSV-1). These domains, called VICE, for virus induced chaperone enriched, contain Hsc70, Hsp70, Hsp40, Hsp90, polyubiquitinated proteins, and components of the proteasome machinery. Accumulating evidence indicates that these sites may be utilized during infection to sequester misfolded, modified, or otherwise unwanted proteins away from viral replication compartments, sites of robust transcription, DNA synthesis, and capsid maturation. To further explore the role of cellular chaperones and VICE domains during HSV-1 infection, we have analyzed the cytoprotective chaperone Hsp27. Here we present evidence that Hsp27, which is known to possess several antioxidant functions, is rapidly reorganized and modified at early stages in response to HSV-1 infection and signaling from the mitogen-activated protein kinase p38. Immunofluorescence analysis and fractionation experiments reveal disparate subcellular localizations of nonphosphorylated and phosphorylated forms of Hsp27 during wild-type HSV-1 infection. Unmodified forms of Hsp27 are localized in nuclear foci that are outside of replication compartments, adjacent to VICE domains, and in the cytoplasm. Conversely, we find that phosphorylated forms of Hsp27 are localized exclusively in the cytoplasm. Last, in cells depleted of all forms of Hsp27, virus replication is significantly reduced.

Hsp27 is persistently expressed in zebrafish skeletal and cardiac muscle tissues but dispensable for their morphogenesis

Constitutive expression of Hsp27 has been demonstrated in vertebrate embryos, especially in developing skeletal and cardiac muscle. Results of several previous studies have indicated that Hsp27 could play a role in the development of these tissues. For example, inhibition of Hsp27 expression has been reported to cause defective development of mammalian myoblasts in vitro and frog embryos in vivo. In contrast, transgenic mice lacking Hsp27 develop normally. Here, we examined the distribution of Hsp27 protein in developing and adult zebrafish and effects of suppressing Hsp27 expression using phosphorodiamidate morpholino oligonucleotides (PMO) on zebrafish development. Consistent with our previous analysis of hsp27 messenger RNA expression, we detected the protein Hsp27 in cardiac, smooth, and skeletal muscle of both embryonic and adult zebrafish. However, embryos lacking detectable Hsp27 after injection of antisense hsp27 PMO exhibited comparable heart beat rates to that of control embryos and cardiac morphology was indistinguishable in the presence or absence of Hsp27. Loss of Hsp27 also had no effect on the structure of the skeletal muscle myotomes in the developing embryo. Finally, embryos injected with antisense hsp27 and scrambled control PMO displayed equal motility. We conclude that Hsp27 is dispensable for zebrafish morphogenesis but could play a role in long-term maintenance of heart and muscle tissues.

Saliva: an emerging biofluid for early detection of diseases

The capability to assess physiological states, detect morbidity initiation and progression, and monitor posttreatment therapeutic outcomes through a noninvasive approach is one of the most desirable goals for healthcare research and delivery. Saliva, a multi-constituent oral fluid, has high potential for the surveillance of general health and disease. To reach the above goal through saliva-based diagnostics, two prerequisites must be fulfilled: (1) discovering biomarker(s) for different diseases among the complicated components of saliva, and (2) advancing sensitivity and specificity of biomarker(s) through persistent development of technologies. Under the support and research blueprint initiated by the National Institute of Dental and Craniofacial Research (NIDCR), salivary diagnostics has not only steadily progressed with respect to accuracy and availability, but has also bridged up-to-date nanotechnology to expand the areas of application. With collective efforts over several years, saliva has been demonstrated to be a promising bodily fluid for early detection of diseases, and salivary diagnostics has exhibited tremendous potential in clinical applications. This review presents an overview of the value of saliva as a credible diagnostic tool, the discovery of salivary biomarkers, and the development of salivary diagnostics now and in the future.

HSP27 phosphorylation increases after 45°C or 41°C heat shocks but not after non-thermal TDMA or GSM exposures

PURPOSE

Experiments with cultured HeLa, S3 and E.A. Hy296 cells were performed to determine if exposure to acute (30 min at 45 degrees C) or chronic (2 h at 41 degrees C) heat shocks or to non-thermal exposures of radiofrequency radiation (RF) induce changes in HSP27 phosphorylation.

MATERIALS AND METHODS

The radiofrequency (RF) exposures used in this study were 847 MHz time division multiple access modulated (TDMA) at a specific absorption rate (SAR) of 5 W kg-1 for 1, 2 or 24 h or 900 MHz GSM modulated (GSM) at a SAR of 3.7 W kg-1 for 1, 2 or 5 h. HSP27 phosphorylation was evaluated by resolving the various phosphorylation forms using two-dimensional gel electrophoresis measuring the relative amount of each by densitometry. Alternatively, an antibody specific for phosphorylated HSP27 was used to detect changes in HSP27 phosphorylation levels. All heat shock and RF exposure conditions were analysed simultaneously along with a matched incubator control sample. Each experiment was repeated three times.

RESULTS

Following heat shock, the degree of phosphorylation of HSP27 varied with the heat dose, with acute hyperthermia (45 degrees C) having an increased proportion of higher phosphorylated forms. Exposure of HeLa S3 cells to 5 W kg-1 TDMA for 1, 2 or 24 h did not induce significant differences in the levels of HSP27 phosphorylation compared to incubator control or sham. Exposure of E.A. Hy926 cells to 3.7 W kg-1 900 MHz GSM for 1, 2 or 5 h did not induce significant differences in the levels of HSP27 phosphorylation compared to sham exposed.

CONCLUSIONS

Acute and moderate hyperthermia significantly increase HSP27 phosphorylation, but there was no significant change in the levels of HSP27 following non-thermal exposure to TDMA and GSM modulated RF radiations.

HSP27 and cell survival in neurones

Although the majority of studies on the protective effect of individual hsps have concentrated on the major inducible heat shock protein Hsp70, a variety of evidence suggests that the small heat shock protein Hsp27 may have a more potent protective effect in the nervous system. Thus, for example, in cultured neurones over-expression of Hsp70 can protect against subsequent exposure to thermal or ischaemic stress but not against exposure to some other stressful stimuli, whereas over-expression of Hsp27 protects against a variety of stresses. Similarly, although transgenic animals over-expressing Hsp70 are protected against cardiac ischaemia, more equivocal results have been obtained in terms of their protection against cerebral ischaemia and other stresses to the nervous system. In contrast, transgenic animals over-expressing Hsp27 have recently been shown to show neuroprotection as well as being protected against cardiac ischaemia. Recent findings have also implicated Hsp27 and related proteins in human disease. Thus, it has been demonstrated that mutation of either Hsp27 or the related protein hsp22 can be observed in specific families with hereditary motor neuropathy caused by premature axonal loss, possibly due to neuronal death and subsequent degeneration. Moreover, the mutations are associated with a reduced ability to promote neuronal survival compared to the wild type protein. Hence, Hsp27 appears to be a potent protective factor for neuronal cells whose mutation results in neuronal cell death and disease, whilst enhanced expression of the wild type protein may be a therapeutic option for human diseases involving excessive neuronal cell death.

Heat shock protein 27 overexpression mitigates cytokine-induced islet apoptosis and streptozotocin-induced diabetes

Beta-cell apoptosis occurs in diabetes mellitus (DM). Heat shock protein (HSP) 27 (human homolog of rodent HSP25) mitigates stress-induced apoptosis but has not been studied in beta-cells. We tested whether HSP27 overexpression attenuates streptozotocin (SZ)-induced DM in vivo and cytokine-induced islet apoptosis in vitro. DM was ascertained by ip glucose tolerance testing, and fasting serum insulin/glucose was measured. Pancreas was stained for insulin, HSP27, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling, and insulin content was measured. HSP25/27 was measured by immunoblotting, isoelectric focusing, and RT-PCR. Islet HSP25/27 oligomerization and inhibitory kappaB protein kinase gamma (nuclear factor kappaB essential modulator) binding were assessed by coimmunoprecipitation. HSP27 transgene (TG) in pancreas localized predominantly in beta-cells. Baseline pancreatic insulin levels in wild-type (WT) and HSP27TG mice were similar, but lower in WT than HSP27TG after SZ (P < 0.01). Intraperitoneal glucose tolerance testing confirmed protection from SZ-DM in HSP27TG. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling and inducible nitric oxide synthase staining were increased in WT vs. HSP27TG islets (P < 0.05) after SZ. Caspase-3 activity was lower in islets from HSP27TG vs. WT mice after cytokine stress in vitro (P < 0.05). There was more HSP25 plus 27 protein from HSP27TG islets than HSP25 from WT (P < 0.01). HSP25 protein but not mRNA was increased in HSP27TG mice. Isoelectric focusing showed similar relative HSP phosphorylation in HSP27TG and WT (P > 0.05). HSP27 bound native HSP25 in TG islets; both bound to inhibitory kappaB protein kinase gamma (nuclear factor kappaB essential modulator). These data show islet protection by HSP27 by mitigation of apoptosis, possibly through nuclear factor kappaB regulation.

The heat shock protein 27 (Hsp27) operates predominantly by blocking the mitochondrial-independent/extrinsic pathway of cellular apoptosis

Heat shock protein 27 (Hsp27) is a molecular chaperone protein which regulates cell apoptosis by interacting directly with the caspase activation components in the apoptotic pathways. With the assistance of the Tat protein transduction domain we directly delivered the Hsp27 into the myocardial cell line, H9c2 and demonstrate that this protein can reverse hypoxia-induced apoptosis of cells. In order to characterize the contribution of Hsp27 in blocking the two major apoptotic pathways operational within cells, we exposed H9c2 cells to staurosporine and cobalt chloride, agents that induce mitochondria-dependent (intrinsic) and -independent (extrinsic) pathways of apoptosis in cells respectively. The Tat-Hsp27 fusion protein showed a greater propensity to inhibit the effect induced by the cobalt chloride treatment. These data suggest that the Hsp27 predominantly exerts its protective effect by interfering with the components of the extrinsic pathway of apoptosis.

Heat shock protein 27 as a new therapeutic target for radiation sensitization of head and neck squamous cell carcinoma

In a wide range of human cancers, increased levels of heat shock protein 27 (Hsp27) are closely associated with tumorigenesis, metastasis, resistance to anticancer therapeutics, and thus poor prognosis. In this study, we evaluate the radiosensitizing effects of Hsp27 gene silencing using OGX-427, a second-generation antisense oligonucleotide (ASO), on the radioresistant head and neck squamous cell carcinoma (HNSCC) SQ20B cells. In vitro, the downregulation of Hsp27 significantly enhanced radiation-induced apoptotic and clonogenic death, and promoted Akt inactivation. In vivo, combining OGX-427 with local tumor irradiation (5 x 2 Gy) led to a significant regression of SQ20B tumors related to a high rate of apoptosis and decreased levels of glutathione antioxidant defenses. Increasing the total radiation dose (15 x 2 Gy) significantly amplified the radiosensitizing effect of OGX-427. Treatment of tumors with OGX-427 plus radiation resulted in a decrease in angiogenesis associated with a reduced activation of the Akt pathway. Furthermore, the combined treatment enhanced the survival of SQ20B-bearing mice and showed no signs of acute and delayed toxicity. Our findings demonstrate for the first time that Hsp27 knockdown enhances the cytotoxic effects of radiotherapy in vivo and provide preclinical proof of principle for clinical trials using Hsp27 antisense technology in the treatment of patients with HNSCC radioresistant cancers.

Serum heat shock protein 27 is increased in chronic pancreatitis and pancreatic carcinoma

OBJECTIVES

A prior study suggested serum heat shock protein 27 (HSP27) as a potential marker for pancreatic carcinoma, but its accuracy in differentiating cancer from chronic pancreatitis was not evaluated. We aimed to analyze HSP27 levels in pancreatic carcinoma, chronic pancreatitis, and healthy subjects and assess its diagnostic efficacy.

METHODS

Pretreatment serums from 58 pancreatic carcinoma, 44 chronic pancreatitis, and 102 control subjects were collected. Serum HSP27 and carbohydrate antigen 19-9 (CA19-9) levels were analyzed using an enzyme-linked immunosorbent assay and radioimmunoassay, respectively.

RESULTS

Heat shock protein 27 levels were significantly higher in cancer and pancreatitis compared with control (P < 0.001 for both), but no significant difference was noted between cancer and pancreatitis (P = 0.978). By logistic regression, HSP27 was a significant predictor of differentiation between cancer and control (P < 0.0001) but not between cancer and pancreatitis (P = 0.885). At a cutoff of 1650 ng/L, the sensitivity and specificity for differentiating cancer from healthy control were 62.1% and 95.1%, respectively. Receiver operating characteristic analyses showed a greater area under curve for CA19-9 compared with HSP27 in differentiating between cancer and control (0.92 and 0.84, respectively, P = 0.014).

CONCLUSIONS

Serum HSP27 is increased in both chronic pancreatitis and pancreatic carcinoma. It should not be recommended as a diagnostic marker for pancreatic carcinoma.

The 27-kDa heat shock protein confers cytoprotective effects through a beta 2-adrenergic receptor agonist-initiated complex with beta-arrestin

Heat shock proteins represent an emerging model for the coordinated, multistep regulation of apoptotic signaling events. Although certain aspects of the biochemistry associated with heat shock protein cytoprotective effects are known, little information is found describing the regulation of heat shock protein responses to harmful stimuli. During screening for noncanonical beta adrenergic receptor signaling pathways in human urothelial cells, using mass spectroscopy techniques, an agonist-dependent interaction with beta-arrestin and the 27-kDa heat shock protein was observed in vitro. Formation of this beta-arrestin/Hsp27 complex in response to the selective beta adrenergic receptor agonist isoproterenol, was subsequently confirmed in situ by immunofluorescent colocalization studies. Radioligand binding techniques characterized a homogeneous population of the beta2 adrenergic receptor subtype expressed on these cells. Using terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling, immunoblot analysis and quantitation of caspase-3 activity to detect apoptosis, preincubation of these cells with isoproterenol was found to be sufficient for protection against programmed cell death initiated by staurosporine. RNA interference strategies confirmed the necessity for Hsp27 as well as both beta-arrestin isoforms to confer this cytoprotective consequence of beta adrenergic receptor activation in this cell model. As a result, these studies represent the first description of an agonist-dependent relationship between a small heat shock protein and beta-arrestin to form a previously unknown antiapoptotic "signalosome."

Dysregulation of CD8+ lymphocyte apoptosis, chronic disease, and immune regulation

Expansion of CD8+ lymphocyte subsets are found in many states with chronic antigenic exposure including HIV, multiple myeloma, rheumatoid arthritis, CMV infection, transplantation and even normal aging. These expansions are characterized by the expression of CD57 antigen and the loss of CD28-. These lymphocytes are thought to represent clonally expanded cytotoxic T lymphocytes (CTL) that have become senescent and lack proliferative ability. These cells also demonstrate suppressive properties and have been linked with immunodeficiency raising the question of the function of these cells in relationship to immunoregulation. Alterations in the CD95/Fas apoptotic pathway and changes in pro-survival factors such as Hsp27 likely contribute to this lymphocyte subset expansion. Further understanding of the normal CD8+ lymphocyte response to antigen and the factors that lead to abnormal continued expansion in certain disease states will be crucial to understanding the pathogenesis of chronic antigenic stimulation.

Hsp27 protects against ischemic brain injury via attenuation of a novel stress-response cascade upstream of mitochondrial cell death signaling

Heat shock protein 27 (Hsp27), a recently discovered member of the heat shock protein family, is markedly induced in the brain after cerebral ischemia and other injury states. In non-neuronal systems, Hsp27 has potent cell death-suppressing functions. However, the mechanism of Hsp27-mediated neuroprotection has not yet been elucidated. Using transgenic and viral overexpression of Hsp27, we investigated the molecular mechanism by which Hsp27 exerts its neuroprotective effect. Overexpression of Hsp27 conferred long-lasting tissue preservation and neurobehavioral recovery, as measured by infarct volume, sensorimotor function, and cognitive tasks up to 3 weeks following focal cerebral ischemia. Examination of signaling pathways critical to neuronal death demonstrated that Hsp27 overexpression led to the suppression of the MKK4/JNK kinase cascade. While Hsp27 overexpression did not suppress activation of an upstream regulatory kinase of the MKK/JNK cascade, ASK1, Hsp27 effectively inhibited ASK1 activity via a physical association through its N-terminal domain and the kinase domain of ASK1. The N-terminal region of Hsp27 was required for neuroprotective function against in vitro ischemia. Moreover, knockdown of ASK1 or inhibition of the ASK1/MKK4 cascade effectively inhibited cell death following neuronal ischemia. This underscores the importance of this kinase cascade in the progression of ischemic neuronal death. Inhibition of PI3K had no effect on Hsp27-mediated neuroprotection, suggesting that Hsp27 does not promote cell survival via activation of PI3K/Akt. Based on these findings, we conclude that overexpression of Hsp27 confers long-lasting neuroprotection against ischemic brain injury via a previously unexplored association and inhibition of ASK1 kinase signaling.

Mass spectrometry in systems biology: an overview

As an emerging field, systems biology is currently the talk of the town, which challenges our philosophy in comprehending biology. Instead of the reduction approach advocated in molecular biology, systems biology aims at systems-level understanding of correlations among molecular components. Such comprehensive investigation requires massive information from the "omics" cascade demanding high-throughput screening techniques. Being one of the most versatile analytical methods, mass spectrometry has already been playing a significant role at this early stage of systems biology. In this review, we documented the advances in modern mass spectrometry technologies as well as nascent inventions. Recent applications of mass spectrometry-based techniques and methodologies in genomics, proteomics, transcriptomics and metabolomics will be further elaborated individually. Undoubtedly, more applications of mass spectrometry in systems biology can be expected in the near future.

Differentially expressed proteins of mesenchymal stem cells derived from human cord blood (hUCB) during osteogenic differentiation

Multipotent mesenchymal stem cells (MSCs) derived from human umbilical cord blood (hUCB) represent promising candidates for the development of future cellular therapy strategies. MSCs have been found to be able to differentiate into various tissues. One of the primary limitations in our understanding of the biology of human MSCs is the absence of prospective markers required for the monitoring of lineage-specific differentiation. hUCB-derived MSCs have been found to have significantly greater osteogenic potential. In this study, we focused on proteins that were differentially expressed during osteogenic differentiation of hUCB-MSCs. And we analyzed the protein expression inherent to osteogenic differentiation by two-dimensional gel electrophoresis, ESI-Q-TOF, and Western blotting. Eleven differentially expressed spots were observed between the two groups (before and after differentiation) on the 2-DE map. These might also be proved as useful cytosolic biomarker proteins for osteogenesis, and might be employed in quality control of osteoblasts in cell-therapy applications.

Long-term exposure to low lithium concentrations stimulates proliferation, modifies stress protein expression pattern and enhances resistance to oxidative stress in SH-SY5Y cells

SH-SY5Y cells, derived from a human neuroblastoma, were submitted to short- or long-term exposures to lithium carbonate concentrations ranging from 0.5 to 8 mM. Short-term exposures (4 days) to concentrations higher than 6 mM were found to reduce cell growth rate while exposure to 8 mM resulted in significant cell mortality. These ranges of concentrations induced an overexpression of (1) the HSP27 stress protein, (2) a 108 kDa protein (P108) recognized by an anti-phospho-HSP27(Ser78) antibody, and probably corresponding to a phosphorylated HSP27 tetramer, (3) a 105 kDa protein (P105), possible glycosylated or phosphorylated form of the GRP94 stress protein and (4) a phosphorylated (inactivated) form of glycogen synthase kinase (GSK3alpha/beta) SH-SY5Y cells, when cultured in the presence of 0.5 mM lithium for 25 weeks, displayed interesting features as compared to controls: (1) higher cell growth rate, (2) increased resistance toward the inhibitory effects of high lithium concentrations on cell proliferation, (3) lower basal level of lipid peroxidation (TBARS) and improved tolerance to oxidative stress induced by high lithium concentrations, (5) reduced expression of monomeric HSP27 versus an increase of corresponding tetrameric protein (P108) and (6) overexpression of a 105 kDa protein (P105). In conclusion, our study suggests that chronic treatment (over several months) by therapeutic relevant lithium concentrations could favour neurogenesis, decrease the vulnerability of neuronal cells to oxidative stress and induce posttranslational changes of molecular chaperones.

HSP27 is involved in the pathogenesis of kidney tubulointerstitial fibrosis

We hypothesized that heat shock protein 27 (HSP27), a small heat shock protein with actin-remodeling properties, is involved in the pathogenesis of kidney tubulointerstitial fibrosis. We first examined its expression in the rat unilateral ureteral obstruction (UUO) model of kidney fibrosis and epithelial-to-mesenchymal transition (EMT). Immunoblot analyses showed that UUO resulted in significant upregulation of TGF-beta1, alpha-smooth muscle actin (alpha-SMA), total and phosphorylated HSP27, and phosphorylated p38MAPK. Immunofluorescence studies showed that HSP27 costained with TGF-beta1, alpha-SMA, and E-cadherin in areas of tubulointerstitial injury. We next attempted to translate these studies in an in vitro model of EMT using rat proximal tubular epithelial cells (NRK52E). TGF-beta1 (20 ng/ml) treatment resulted in EMT (upregulation of alpha-SMA and downregulation of E-cadherin) and significant upregulation of total and phosphorylated HSP27 and p38MAPK after 3 days. Real-time PCR analyses showed that HSP27, vimentin, and fibronectin increased whereas E-cadherin mRNA levels decreased. Double-staining immunofluorescence studies showed intracytoplasmic colocalization of HSP27 with both F-actin and E-cadherin in cells undergoing EMT. HSP27 overexpression by transient transfection significantly increased E-cadherin while decreasing E-cadherin repressor Snail levels. In aggregate, these studies show that HSP27 is involved in the pathogenesis of TGF-beta1-induced EMT and chronic tubulointerstitial fibrosis. HSP27 overexpression may delay injury by upregulating E-cadherin through downregulation of Snail.

Irradiation leads to apoptosis of Kupffer cells by a Hsp27-dependant pathway followed by release of TNF-alpha

In a previous publication, we were able to show that irradiation of Kupffer cells, the liver resident macrophages, leads to an increased TNF-alpha concentration in the culture medium. The pathomechanisms underlying this phenomenon, however, remained to be elucidated. Here, we show that following irradiation of Kupffer cells, the apoptosis rate increased drastically within 48 h. At the same time, the total TNF-alpha concentration in cell lysates of Kupffer cells attached to the culture plate decreased. However, normalization of the TNF-alpha concentration with respect to cell number revealed that TNF-alpha concentration per attached cell remained constant during the observation period. Western blot analysis showed that heat shock protein 27 (Hsp27) is strongly downregulated and bax is upregulated in irradiated Kupffer cells as compared to sham-irradiated cells. Overexpression of Hsp27 in Kupffer cells was shown to prevent the effect of irradiation on bax expression, apoptosis and, at the same time, on increase of TNF-alpha concentration in the Kupffer cell medium. We conclude that irradiation of Kupffer cells leads to apoptosis because of downregulation of Hsp27 and consecutive upregulation of bax expression. Furthermore, we suggest that apoptosis of Kupffer cells leads to an increase of TNF-alpha concentration in the culture medium which may be due to cell death rather than active release or synthesis.

Antibody titres to heat shock protein 27 are elevated in patients with acute coronary syndrome

IgG antibody titres to heat shock protein 27 (anti-Hsp27) were measured to determine whether these titres were affected in patients admitted with acute coronary syndrome. Blood samples were taken from 94 patients admitted with acute coronary syndrome. Anti-Hsp27 IgG titres were determined using an in-house enzyme-linked immunosorbent assay (ELISA) in the first and second 12 h after the onset of symptoms and compared with values for 81 age- and sex-matched control subjects. Median antibody titres to Hsp27 in the first sample from patients whose diagnosis was a myocardial infarction (n = 42) was 0.41 absorbancy units (range 0.28-0.57) and for those with unstable angina (n = 52) was 0.31 (range 0.20-0.42), both being significantly higher than for controls (n = 81), which was 0.08 (range 0.05-0.15) (P < 0.05). However, titres fell in the second samples collected in the coronary syndrome patients and were then no longer significantly different from controls (P > 0.05). Myocardial infarction patients also had significantly higher anti-Hsp27 titres in the first 12 h than patients with unstable angina (P < 0.05), but again the difference in the second sample did not reach statistical significance (P > 0.05). Serum antibody titres to Hsp27 rise and fall rapidly after the onset of acute coronary syndrome, and may be an early marker of myocardial ischaemia as patients with myocardial infarction or unstable angina both had high titres.

Forced, not voluntary, exercise effectively induces neuroprotection in stroke

Previous treadmill exercise studies showing neuroprotective effects have raised questions as to whether exercise or the stress related to it may be key etiologic factors. In this study, we examined different exercise regimens (forced and voluntary exercise) and compared them with the effect of stress-only on stroke protection. Adult male Sprague-Dawley rats (n = 65) were randomly assigned to treatment groups for 3 weeks. These groups included control, treadmill exercise, voluntary running wheel exercise, restraint, and electric shock. Levels of the stress hormone, corticosterone, were measured in the different groups using ELISA. Animals from each group were then subjected to stroke induced by a 2-h middle cerebral artery (MCA) occlusion followed by 48-h reperfusion. Infarct volume was determined in each group, while changes in gene expression of stress-induced heat shock proteins (Hsp) 27 and 70 were compared using real-time PCR between voluntary and treadmill exercise groups. The level of corticosterone was significantly higher in both stress (P < 0.05) and treadmill exercise (P < 0.05) groups, but not in the voluntary exercise group. Infarct volume was significantly reduced (P < 0.01) following stroke in rats exercised on a treadmill. However, the amelioration of damage was not duplicated in voluntary exercise, even though running distance in the voluntary exercise group was significantly (P < 0.01) longer than that of the forced exercise group (4,828 vs. 900 m). Furthermore, rats in the electric shock group displayed a significantly increased (P < 0.01) infarct volume. Expression of both Hsp 27 and Hsp 70 mRNA was significantly increased (P < 0.01) in the treadmill exercise group as compared with that in the voluntary exercise group. These results suggest that exercise with a stressful component, rather than either voluntary exercise or stress alone, is better able to reduce infarct volume. This exercise-induced neuroprotection may be attributable to up-regulation of stress-induced heat shock proteins 27 and 70.

Integrated activation of MAP3Ks balances cell fate in response to stress

In vivo, tissues and organs are exposed to numerous stressors that require cells to respond appropriately for viability and homeostasis. Cells respond to these stressors, which range from UV irradiation, heat shock, chemicals, and changes in osmolality, to oxidative stress and inflammatory cytokines, by activating pathways that protect cells from damage. If the stress is too great, cells commit to undergo apoptosis. Such cell fate decisions involve the stress-mediated activation of mitogen-activated protein kinase (MAPK) networks, ultimately under the control of MAPK kinase kinases, or MAP3Ks. It is the MAP3Ks that coordinate the localization, duration and magnitude of MAPK activation in response to cell stress. A single stressor may activate several MAP3Ks, each of which impacts the balance between survival and apoptotic signaling. In this prospect article, we review the specific MAP3Ks that integrate the physiological response to cell stressors. The interrelationships among different stressors are discussed, with an emphasis on how the balance of signaling through MAP3Ks controls the MAPK response to determine cell fate.

Heat shock proteins: essential proteins for apoptosis regulation

Many different external and intrinsic apoptotic stimuli induce the accumulation in the cells of a set of proteins known as stress or heat shock proteins (HSPs). HSPs are conserved proteins present in both prokaryotes and eukaryotes. These proteins play an essential role as molecular chaperones by assisting the correct folding of nascent and stress-accumulated misfolded proteins, and by preventing their aggregation. HSPs have a protective function, that is they allow the cells to survive to otherwise lethal conditions. Various mechanisms have been proposed to account for the cytoprotective functions of HSPs. Several of these proteins have demonstrated to directly interact with components of the cell signalling pathways, for example those of the tightly regulated caspasedependent programmed cell death machinery, upstream, downstream and at the mitochondrial level. HSPs can also affect caspase-independent apoptosis-like process by interacting with apoptogenic factors such as apoptosis-inducing factor (AIF) or by acting at the lysosome level. This review will describe the different key apoptotic proteins interacting with HSPs and the consequences of these interactions in cell survival, proliferation and apoptotic processes. Our purpose will be illustrated by emerging strategies in targeting these protective proteins to treat haematological malignancies.

Daxx contains two nuclear localization signals and interacts with importin alpha3

Daxx plays a major role in several important signaling pathways including transcription and cell death. It has been postulated that Daxx regulates both events from the nucleus; however, the mechanism by which Daxx is localized in the nucleus remains obscure. Here we show that nuclear localization of Daxx is controlled by two independent signals and importin 3. Domain analysis reveals that Daxx contains two separate nuclear localizing domains. Site-directed mutagenesis reveals that the basic aa sequence RLKRK at residues 227-231 (NLS1) is responsible for nuclear localization of N-terminal domain, while aa sequence KKSRKEKK at residues 630-637 (NLS2) is responsible for nuclear localization of the C-terminal domain. Mutations of a NLS consensus sequence RKKRR at residues 391-395 and several other basic aa clusters have no effect on Daxx nuclear localization. In full-length Daxx, NLS1 contributes partially to nuclear localization, while NLS2 plays a major role. Markedly, it is essential to disrupt both NLS1 and NLS2 in order to completely block nuclear localization of the full-length protein and to prevent its association with PML nuclear bodies. Furthermore, Daxx interacts selectively with importin alpha3 through its NLS1 and NLS2 sequences. Conversely, importin alpha3 utilizes two NLS-binding sites for Daxx interaction, suggesting that the importin/mediates nuclear import of Daxx. Finally, we show that nuclear localization of Daxx is essential for its transcriptional effects on GR and p53. Together, these data unveil a molecular mechanism that controls nuclear localization of Daxx and support a nuclear role of Daxx in transcriptional regulation.

Insulin-induced myocardial protection in isolated ischemic rat hearts requires p38 MAPK phosphorylation of Hsp27

Six hours after insulin treatment, hearts express heat shock protein 70 (Hsp70) and have improved contractile function after ischemia-reperfusion injury. In this study we examined hearts 1 h after insulin treatment for contractile function and for expression of Hsp70 and Hsp27. Adult, male Sprague-Dawley rats were assigned to groups: 1) sham, 2) control, 3) insulin injected (200 μU/g body wt), 4) heat shock treated (core body temperature, 42°C for 15 min), and 5) heat shock and insulin treated. At 1 h after these treatments, hearts were isolated, equilibrated to Langendorff perfusion for 30 min, and then subjected for 30 min no-flow global ischemia (37°C) followed by 2 h of reperfusion. Insulin-treated hearts had significantly increased contractile function compared with control hearts. At 1 h after insulin treatment, a minimal change in Hsp70 and Hsp27 content were detected. By 3 h after insulin treatment, a significant increase in Hsp70, but not Hsp27, was detected by Western blot analysis. By immunofluorescence, minimal Hsp70 was detected in insulin-treated hearts, whereas Hsp27 was detected in all hearts, indicative of its constitutive expression. Phosphospecific isoforms of Hsp27 were detected in insulin-, heat shock-, and heat shock and insulin-treated hearts. After ischemia and reperfusion, the insulin-treated hearts had significantly elevated levels of phosphorylated Hsp27. Inhibition of p38 MAPK with SB-203580 blocked the insulin-induced phosphorylation of Hsp27 and the improved functional recovery. In conclusion, insulin induces an apparent rapid phosphorylation of Hsp27 that is associated with improved functional recovery after ischemia-reperfusion injury.

Proteomic identification of heat shock protein 27 as a differentiation and prognostic marker in neuroblastoma but not in Ewing's sarcoma

Neuroblastoma (NB) and Ewing's sarcoma (ES) cell lines were analysed by two-dimensional gel electrophoresis (2-DE) searching for new diagnostic/prognostic markers. Protein expression profiles displayed a high degree of similarity with the exception of marked heat shock protein (HSP) 27 and less marked HSP60 and HSP70 family up-modulations in NB cells. HSP27, which showed peculiar variability in different NB cell preparations, responded to all trans-retinoic acid treatment in NB cells but not in ES cells at gene and protein expression levels. Immunohistochemistry studies showed different behaviours of HSP27 and HSP70 expression in NB and ES biopsies. HSP27 was less expressed, whereas HSP70 was more expressed in the immature areas of NB. HSP27 expression showed positive and statistically significant correlation with favourable prognosis, and HSP27 expression also negatively correlated with increasing aggressiveness of histological type. In ES, both chaperones were expressed without characteristic patterns. Our results suggest that HSP27, after further clinical validations, could be used as a marker of neuronal differentiation in vivo for the assessment of the biological behaviour of NB and for the risk stratification of patients.

Protective role of Hsp27 protein against gamma radiation-induced apoptosis and radiosensitization effects of Hsp27 gene silencing in different human tumor cells

PURPOSE

The ability of heat shock protein 27 (Hsp27) to protect cells from stressful stimuli and its increased levels in tumors resistant to anticancer therapeutics suggest that it may represent a target for sensitization to radiotherapy. In this study, we investigate the protective role of Hsp27 against radiation-induced apoptosis and the effect of its attenuation in highly expressing radioresistant cancer cell lines.

METHODS AND MATERIALS

We examined clonogenic death and the kinetics of apoptotic events in different tumor cell lines overexpressing or underexpressing Hsp27 protein irradiated with photons. The radiosensitive Jurkat cell line, which does not express Hsp27 constitutively or in response to gamma-rays, was stably transfected with Hsp27 complementary DNA. Attenuation of Hsp27 expression was accomplished by antisense or RNAi (interfering RNA) strategies in SQ20B head-and-neck squamous carcinoma, PC3 prostate cancer, and U87 glioblastoma radioresistant cells.

RESULTS

We measured concentration-dependent protection against the cytotoxic effects of radiation in Jurkat-Hsp27 cells, which led to a 50% decrease in apoptotic cells at 48 hours in the highest expressing cells. Underlying mechanisms leading to radiation resistance involved a significant increase in glutathione levels associated with detoxification of reactive oxygen species, a delay in mitochondrial collapse, and caspase activation. Conversely, attenuation of Hsp27 in SQ20B cells, characterized by their resistance to apoptosis, sensitizes cells to irradiation. This was emphasized by increased apoptosis, decreased glutathione basal level, and clonogenic cell death. Sensitization to irradiation was confirmed in PC3 and U87 radioresistant cells.

CONCLUSION

Hsp27 gene therapy offers a potential adjuvant to radiation-based therapy of resistant tumors.

Heat shock genes - integrating cell survival and death

Heat shock induced gene expression and other cellular responses help limit the damage caused by stress and thus facilitate cellular recovery. Cellular damage also triggers apoptotic cell death through several pathways. This paper briefly reviews interactions of the major heat shock proteins with components of the apoptotic pathways. Hsp90, which acts as a chaperone for unstable signal transducers to keep them poised for activation, interacts with RIP and Akt and promotes NF-kappa B mediated inhibition of apoptosis; in addition it also blocks some steps in the apoptotic pathways. Hsp70 is mostly anti-apoptotic and acts at several levels like inhibition of translocation of Bax into mitochondria, release of cytochrome c from mitochondria,formation of apoptosome and inhibition of activation of initiator caspases. Hsp70 also modulates JNK,NF-kappa B and Akt signaling pathways in the apoptotic cascade. In contrast, Hsp60 has both anti-and pro-apoptotic roles. Cytosolic Hsp60 prevents translocation of the pro-apoptotic protein Bax into mitochondria and thus promotes cell survival but it also promotes maturation of procaspase-3,essential for caspase mediated cell death. Our recent in vivo studies show that RNAi for the Hsp60D in Drosophila melanogaster prevents induced apoptosis. Hsp27 exerts its anti-apoptotic influence by inhibiting cytochrome c and TNF-mediated cell death. alpha beta crystallin suppresses caspase-8 and cytochrome c mediated activation of caspase-3. Studies in our laboratory also reveal that absence or reduced levels of the developmentally active as well as stress induced non-coding hsr omega transcripts, which are known to sequester diverse hnRNPs and related nuclear RNA-binding proteins,block induced apoptosis in Drosophila. Modulation of the apoptotic pathways by Hsps reflects their roles as "weak links" between various "hubs" in cellular networks. On the other hand, non-coding RNAs, by virtue of their potential to bind with multiple proteins,can act as "hubs" in these networks. In view of the integrative nature of living systems, it is not surprising that stress-induced genes,generally believed to primarily function in cell survival pathways, inhibit or even promote cell death pathways at multiple levels to ensure homeostasis at cell and/or organism level. The heat shock genes obviously do much more than merely help cells survive stress.

Oncoproteomics of hepatocellular carcinoma: from cancer markers' discovery to functional pathways

Hepatocellular carcinoma (HCC) is a heterogeneous cancer with no promising treatment and remains one of the most prevailing and lethal malignancies in the world. Researchers in many biological areas now routinely identify and characterize protein markers by a mass spectrometry-based proteomic approach, a method that has been commonly used to discover diagnostic biomarkers for cancer detection. The proteomic research platforms span from the classical two-dimensional polyacrylamide gel electrophoresis (2-DE) to the latest Protein Chip or array technology, which are often integrated with the MALDI (matrix-assisted laser-desorption ionization), SELDI (surface-enhanced laser desorption/ionization) or tandem mass spectrometry (MS/MS). New advances on quantitative proteomic analysis (e.g. SILAC, ICAT, and ITRAQ) and multidimensional protein identification technology (MudPIT) have greatly enhanced the capability of proteomic methods to study the expressions, modifications and functions of protein markers. The present article reviews the latest proteomic development and discovery of biomarkers in HCC that may provide insights into the underlying mechanisms of hepatocarcinogenesis and the readiness of biomarkers for clinical uses.

Phosphorylation of Ser78 of Hsp27 correlated with HER-2/neu status and lymph node positivity in breast cancer

Background

Abnormal amplification/expression of HER-2/neu oncogene has been causally linked with tumorigenesis and metastasis in breast cancer and associated with shortened overall survival of patients. Recently, heat shock protein 27 (Hsp27) was reported to be highly expressed in HER-2/neu positive tumors and cell lines. However, putative functional links between phosphorylation of Hsp27 with HER-2/neu status and other clinicopathological features remain to be elucidated.

Results

Comparative phosphoproteomic studies of HER-2/neu positive and -negative breast tumors revealed that Hsp27, one of the identified phosphoproteins, was highly phosphorylated in HER-2/neu positive tumors. The extent of Hsp27 phosphorylation at its Ser¹⁵, Ser⁷⁸ and Ser⁸² residues were further evaluated with site-specific antibodies in tumor samples by tissue lysate array- and tissue microarray-based analyses, and in the BT474 breast cancer cell line treated with heregulin α1 (HRG α1) or the p38 MAPK inhibitor, SB203580. The tissue lysate array study indicated that only the level of pSer⁷⁸ in HER-2/neu positive tumors was more than 2-fold that in HER-2/neu negative tumors. Treatment of BT474 cells with HRG α1 and SB203580 indicated that Ser⁷⁸ phosphorylation was mainly regulated by the HER-2/neu-p38 MAPK pathway. Immunohistochemical staining of sections from a tissue microarray with 97 breast tumors showed that positive staining of pSer⁷⁸ significantly correlated with HER-2/neu (p = 0.004) and lymph node positivity (p = 0.026).

Conclusion

This investigation demonstrated the significant correlation of enhanced phosphorylation of the Ser⁷⁸ residue of Hsp27 with HER-2/neu and lymph node positivity in breast cancer.

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.

Binding of caspase-3 prodomain to heat shock protein 27 regulates monocyte apoptosis by inhibiting caspase-3 proteolytic activation

Caspase-3 is an essential executioner of apoptosis responsible for regulating many important cellular processes, among them the number of circulating monocytes, central players in the innate immune response. The activation of caspase-3 requires its processing from an inactive precursor. Here we show that the small heat shock protein 27 (Hsp27) associates with caspase-3 and protein-protein interaction experiments in vivo and with purified proteins demonstrate a direct interaction between Hsp27 and the amino-terminal prodomain of caspase-3. Using an in vitro caspase-3 activation assay, our results further establish that the interaction of Hsp27 with the caspase-3 prodomain inhibits the second proteolytic cleavage necessary for caspase-3 activation, revealing a novel mechanism for the regulation of this effector caspase. Hsp27 expression in monocytes is constitutive. Consistent with a central role of Hsp27 in blocking caspase-3 activation, Hsp27 down-regulation by double-stranded RNA interference induces apoptosis of macrophages, whereas Hsp27 overexpression increases the life span of monocytes by inhibiting apoptosis. Highlighting the importance of cell partitioning in the regulation of apoptosis, immunofluorescence, and subcellular fractionation studies revealed that whereas both caspase-3 and Hsp27 are cytoplasmic in fresh monocytes (i.e. not undergoing apoptosis), Hsp27 moves to the nucleus during apoptosis, a relocalization that can be blocked by promoting the differentiation of monocytes to macrophages or by inhibiting cell death. These results reveal a novel mechanism of caspase-3 regulation and underscore a novel and fundamental role of Hsp27 in the regulation of monocyte life span.

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 regulates Akt activation and polymorphonuclear leukocyte apoptosis by scaffolding MK2 to Akt signal complex

We have shown previously that Akt exists in a signal complex with p38 MAPK, MAPK-activated protein kinase-2 (MK2), and heat shock protein 27 (Hsp27) and MK2 phosphorylates Akt on Ser-473. Additionally, dissociation of Hsp27 from Akt, prior to Akt activation, induced polymorphonuclear leukocyte (PMN) apoptosis. However, the role of Hsp27 in regulating Akt activation was not examined. This study tested the hypothesis that Hsp27 regulates Akt activation and promotes cell survival by scaffolding MK2 to the Akt signal complex. Here we show that loss of Akt/Hsp27 interaction by anti-Hsp27 antibody treatment resulted in loss of Akt/MK2 interaction, loss of Akt-Ser-473 phosphorylation, and induced PMN apoptosis. Transfection of myristoylated Akt (AktCA) in HK-11 cells induced Akt-Ser-473 phosphorylation, activation, and Hsp27-Ser-82 phosphorylation. Cotransfection of AktCA with Hsp27 short interfering RNA, but not scrambled short interfering RNA, silenced Hsp27 expression, without altering Akt expression in HK-11 cells. Silencing Hsp27 expression inhibited Akt/MK2 interaction, inhibited Akt phosphorylation and Akt activation, and induced HK-11 cell death. Deletion mutagenesis studies identified acidic linker region (amino acids 117-128) on Akt as an Hsp27 binding region. Deletion of amino acids 117-128 on Akt resulted in loss of its interaction with Hsp27 and MK2 but not with Hsp90 as demonstrated by immunoprecipitation and glutathione S-transferase pulldown studies. Co-transfection studies demonstrated that constitutively active MK2 (MK2EE) phosphorylated Aktwt (wild type) on Ser-473 but failed to phosphorylate Akt(Delta117-128) mutant in transfixed cells. These studies collectively define a novel role of Hsp27 in regulating Akt activation and cellular apoptosis by mediating interaction between Akt and its upstream activator MK2.

Heat Shock Protein 27 Protects L929 Cells from Cisplatin-Induced Apoptosis by Enhancing Akt Activation and Abating Suppression of Thioredoxin Reductase Activity

PURPOSE

Heat shock protein 27 (Hsp27) is up-regulated in multiple malignancies and implicated in cisplatin resistance. It is attempted to know how Hsp27 endues cell with cisplatin resistance by interfering with upstream of both apoptosis signal-regulating kinase 1 (ASK1)/p38 mitogen-activated protein kinase-activated apoptotic signaling and serine/threonine kinase Akt-dependent survival signaling.

EXPERIMENTAL DESIGN

The mouse L929 cells stably transfected with human Hsp27 or its dominant-negative mutant and the human cervical cancer HeLa cells transfected with Hsp27 siRNA were used. The cisplatin-induced apoptosis and activation of ASK1, p38, and Akt were compared in control cells, cells overexpressing Hsp27, and cells with their endogenous Hsp27 knocked down.

RESULTS

Hsp27 effectively protected the cells from cisplatin-induced DNA fragmentation. The p38 inhibitors obviously decreased whereas Akt inhibitors markedly increased the apoptotic fraction in cisplatin-treated cells. Overexpression of Hsp27 doubly enhanced the drug-induced Akt activation while substantially depressing the drug-induced activation of ASK1 and p38. Knockdown of the endogenous Hsp27 in HeLa cells resulted in the effects opposite to that observed in the Hsp27-overexpressing cells. Enhancement of Akt activation is associated with complex formation between Akt and Hsp27, whereas depression of ASK1/p38 activation is attributed to a reversion of the drug-induced inhibition of thioredoxin reductase activity and subsequent oxidation of thioredoxin.

CONCLUSIONS

Hsp27 endues cells with cisplatin resistance via depression of the drug-induced ASK1/p38 activation and enhancement of the drug-induced Akt activation. This study revealed the intervention of Hsp27 in upstream of both ASK1/p38 apoptotic signaling and phosphatidylinositol 3-kinase/Akt survival signaling. Therefore, the inhibition of Hsp27 may be a novel strategy of cancer chemotherapy.

Characterization of HSP27 phosphorylation induced by microtubule interfering agents: Implication of p38 signalling pathway

Vincristine and paclitaxel are widely used antitumoral drugs that interfere with microtubule dynamics. We have previously demonstrated that vincristine induces phosphorylation of HSP27 at serine 82 in MCF-7 cells. In this report, we show that vincristine also causes phosphorylation of serines 78 and 15. Moreover, we demonstrate that phosphorylation of this chaperone is induced by the p38 signalling pathway while the JNK pathway is not implicated. Differences between vincristine and paclitaxel treatments are also appreciated. Thus, while vincristine induces a strong phosphorylation of the three serines, paclitaxel induces a weak phosphorylation of serine 78 and has no effect over serines 82 and 15 phosphorylation. Interestingly, pre-treatment of cells with a ten-fold excess of paclitaxel abolishes vincristine-induced phosphorylation of HSP27.

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.

Apoptosis versus cell differentiation: role of heat shock proteins HSP90, HSP70 and HSP27

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

Interaction of mammalian Hsp22 with lipid membranes

Hsp22/HspB8 is a member of the small heat-shock protein family, whose function is not yet completely understood. Our immunolocalization studies in a human neuroblastoma cell line, SK-N-SH, using confocal microscopy show that a significant fraction of Hsp22 is localized to the plasma membrane. We therefore investigated its interactions with lipid vesicles in vitro. Intrinsic tryptophan fluorescence is quenched in the presence of lipid vesicles derived from either bovine brain lipid extract or purified lipids. Time-resolved fluorescence studies show a decrease in the lifetimes of the tryptophan residues. Both of these results indicate burial of some tryptophan residues of Hsp22 upon interaction with lipid vesicles. Membrane interactions also lead to increase in fluorescence polarization of Hsp22. Gel-filtration chromatography shows that Hsp22 binds stably with lipid vesicles; the extent of binding depends on the nature of the lipid. Hsp22 binds more strongly to vesicles made of lipids containing a phosphatidic acid, phosphatidylinositol or phosphatidylserine headgroup (known to be present in the inner leaflet of plasma membrane) compared with lipid vesicles made of a phosphatidylcholine head-group alone. Far-UV CD spectra reveal conformational changes upon binding to the lipid vesicles or in membrane-mimetic solvent, trifluoroethanol. Thus our fluorescence, CD and gel-filtration studies show that Hsp22 interacts with membrane and this interaction leads to stable binding and conformational changes. The present study therefore clearly demonstrates that Hsp22 exhibits potential membrane interaction that may play an important role in its cellular functions.