On the role of Hsp27 in regulating apoptosis

Heat shock proteins (Hsps) comprise several different families of proteins that are induced in response to a wide variety of physiological and environmental insults. One such protein which is highly induced during the stress response is a 27-kDa protein, termed Hsp27 whose expression is seen to correlate with increased survival in response to cytotoxic stimuli. It has been shown to prevent cell death by a wide variety of agents that cause apoptosis. Hsp27 is a molecular chaperone with an ability to interact with a large number of proteins. Recent evidence has shown that Hsp27 regulates apoptosis through an ability to interact with key components of the apoptotic signalling pathway, in particular, those involved in caspase activation and apoptosis. This article will review recent advances in the field and will address some of the potential mechanisms by which Hsp27 functions as an anti-apoptotic molecule.     

hMLH1、P27、P53的表达及其在宫颈癌发病中的意义

目的 了解宫颈癌中hMLH1、P27、P53表达情况及其与宫颈癌发生和发展的关系.方法 采用免疫组织化学技术SP法检测临床资料较完整的72例子宫颈鳞癌和31例慢性宫颈炎组织hMLH1、P27、P53蛋白表达.结果 （1）hMLH1在宫颈炎及宫颈癌组的表达率分别为61.3%和58.3%,差异无显著性（P＞0.05）;hM-LH1在宫颈癌各期中表达率分别为Ⅰ期60.0%,Ⅱ期52.6%,Ⅲ期33.3%,差异无显著性（P＞0.05）;hMLH1表达率与宫颈癌分级无关（P＞0.05）;（2）P27在宫颈炎及宫颈癌组的表达率分别为74.2%%和76.4%,差异无显著性（P＞0.05）;P27的表达率与宫颈癌分级和分期无关（P＞0.05）;（3）P53在宫颈炎及宫颈癌组的表达率分别为32.3%和65.3%,差异有显著性（P＜0.05）;P53在宫颈癌各级中的表达率分别为Ⅰ级36.4%,Ⅱ级73.0%,Ⅲ级67.9%,Ⅰ级与Ⅱ、Ⅲ级的表达率差异有显著性（P＜0.05）;P53表达率与宫颈癌分期无关（P＜0.05）;（4）hMLH1表达阳性与阴性的宫颈癌中P27的表达率为94.6%和60.0%,差异有显著性（P＜0.05）;P53的表达率为62.8%和62.1%,差异无显著性（P＞0.05）.结论 P53基因突变与宫颈癌的发生和组织分化程度有关;hMLH1与P27表达缺失和宫颈癌发生的关系尚不确切.hMLH1可能使宫颈癌中P27表达上调,而对p53基因突变累积无明显抑制作用.     

Hsp27 silencing coordinately inhibits proliferation and promotes Fas-induced apoptosis by regulating the PEA-15 molecular switch

Heat shock protein 27 (Hsp27) is emerging as a promising therapeutic target for treatment of various cancers. Although the role of Hsp27 in protection from stress-induced intrinsic cell death has been relatively well studied, its role in Fas (death domain containing member of the tumor necrosis factor receptor superfamily)-induced apoptosis and cell proliferation remains underappreciated. Here, we show that Hsp27 silencing induces dual coordinated effects, resulting in inhibition of cell proliferation and sensitization of cells to Fas-induced apoptosis through regulation of PEA-15 (15-kDa phospho-enriched protein in astrocytes). We demonstrate that Hsp27 silencing suppresses proliferation by causing PEA-15 to bind and sequester extracellular signal-regulated kinase (ERK), resulting in reduced translocation of ERK to the nucleus. Concurrently, Hsp27 silencing promotes Fas-induced apoptosis by inducing PEA-15 to release Fas-associating protein with a novel death domain (FADD), thus allowing FADD to participate in death receptor signaling. Conversely, Hsp27 overexpression promotes cell proliferation and suppresses Fas-induced apoptosis. Furthermore, we show that Hsp27 regulation of PEA-15 activity occurs in an Akt-dependent manner. Significantly, Hsp27 silencing in a panel of phosphatase and tensin homolog on chromosome 10 (PTEN) wild-type or null cell lines, and in LNCaP cells that inducibly express PTEN, resulted in selective growth inhibition of PTEN-deficient cancer cells. These data identify a dual coordinated role of Hsp27 in cell proliferation and Fas-induced apoptosis via Akt and PEA-15, and indicate that improved clinical responses to Hsp27-targeted therapy may be achieved by stratifying patient populations based on tumor PTEN expression.     

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. These authors contributed equally to this work.     

The role of the cysteine residue in the chaperone and anti‐apoptotic functions of human Hsp27

The small heat shock protein Hsp27 is a molecular chaperone and an anti‐apoptotic protein. Human Hsp27 has one cysteine residue at position 137. We investigated the role of this cysteine residue in the chaperone and anti‐apoptotic functions of Hsp27 by mutating the cysteine residue to an alanine (Hsp27_C137A) and comparing it to wild‐type protein (Hsp27_WT). Both proteins were multi‐subunit oligomers, but subunits of Hsp27_WT were disulfide‐linked unlike those of Hsp27_C137A, which were monomeric. Hsp27_C137A was indistinguishable from Hsp27_WT with regard to its secondary structure, surface hydrophobicity, oligomeric size and chaperone function. S‐thiolation and reductive methylation of the cysteine residue had no apparent effect on the chaperone function of Hsp27_WT. The anti‐apoptotic function of Hsp27_C137A and Hsp27_WT was studied by overexpressing them in CHO cells. No difference in the caspase‐3 or ‐9 activity was observed in staurosporine‐treated cells. The rate of apoptosis between Hsp27_C137A and Hsp27_WT overexpressing cells was similar whether the cells were treated with staurosporine or etoposide. However, the mutant protein was less protective relative to the wild‐type protein in preventing caspase‐3 and caspase‐9 activation and apoptosis induced by 1 mM H₂O₂ in CHO and HeLa cells. These data demonstrate that in human Hsp27, disulfide formation by the lone cysteine does not affect its chaperone function and anti‐apoptotic function against chemical toxicants. However, oxidation of the lone cysteine in Hsp27 might at least partially affect the anti‐apoptotic function against oxidative stress. J. Cell. Biochem. 110: 408–419, 2010. © 2010 Wiley‐Liss, Inc.     

Inhibition of heat shock protein (Hsp) 27 potentiates the suppressive effect of Hsp90 inhibitors in targeting breast cancer stem-like cells

Heat shock protein (Hsp) 90 is an ATP-dependent chaperone and its expression has been reported to be associated with poor prognosis of breast cancer. Cancer stem cells (CSCs) are particular subtypes of cells in cancer which have been demonstrated to be important to tumor initiation, drug resistance and metastasis. In breast cancer, breast CSCs (BCSCs) are identified as CD24-CD44 + cells or cells with high intracellular aldehyde dehydrogenase activity (ALDH+). Although the clinical trials of Hsp90 inhibitors in breast cancer therapy are ongoing, the BCSC targeting effect of them remains unclear. In the present study, we discovered that the expression of Hsp90α was increased in ALDH + human breast cancer cells. Geldanamycin (GA), a Hsp90 inhibitor, could suppress ALDH + breast cancer cells in a dose dependent manner. We are interesting in the insufficiently inhibitory effect of low dose GA treatment. It was correlated with the upregulation of Hsp27 and Hsp70. By co-treatment with HSP inhibitors, quercetin or KNK437 potentiated BCSCs, which determined with ALDH+ population or mammosphere cells, toward GA inhibition, as well as anti-proliferation and anti-migration effects of GA. With siRNA mediated gene silencing, we found that knockdown of Hsp27 could mimic the effect of HSP inhibitors to potentiate the BCSC targeting effect of GA. In conclusion, combination of HSP inhibitors with Hsp90 inhibitors could serve as a potential solution to prevent the drug resistance and avoid the toxicity of high dose of Hsp90 inhibitors in clinical application. Furthermore, Hsp27 may play a role in chemoresistant character of BCSCs.     

Heat-shock protein 27 (Hsp27) as a target of methylglyoxal in gastrointestinal cancer

The molecular mechanisms underlying the posttranslational modification of proteins in gastrointestinal cancer are still unknown. Here, we investigated the role of methylglyoxal modifications in gastrointestinal tumors. Methylglyoxal is a reactive dicarbonyl compound produced from cellular glycolytic intermediates that reacts non-enzymatically with proteins. By using a monoclonal antibody to methylglyoxal-modified proteins, we found that murine heat-shock protein 25 and human heat-shock protein 27 were the major adducted proteins in rat gastric carcinoma mucosal cell line and human colon cancer cell line, respectively. Furthermore, we found that heat-shock protein 27 was modified by methylglyoxal in ascending colon and rectum of patients with cancer. However, methylglyoxal-modified heat-shock protein 25/heat-shock protein 27 was not detected in non cancerous cell lines or in normal subject. Matrix-associated laser desorption/ionization mass spectrometry/mass spectrometry analysis of peptide fragments identified Arg-75, Arg-79, Arg-89, Arg-94, Arg-127, Arg-136, Arg-140, Arg-188, and Lys-123 as methylglyoxal modification sites in heat-shock protein 27 and in phosphorylated heat-shock protein 27. The transfer of methylglyoxal-modified heat-shock protein 27 into rat intestinal epithelial cell line RIE was even more effective in preventing apoptotic cell death than that of native control heat-shock protein 27. Furthermore, methylglyoxal modification of heat-shock protein 27 protected the cells against both the hydrogen peroxide- and cytochrome c-mediated caspase activation, and the hydrogen peroxide-induced production of intracellular reactive oxygen species. The levels of lactate converted from methylglyoxal were increased in carcinoma mucosal cell lines. Our results suggest that posttranslational modification of heat-shock protein 27 by methylglyoxal may have important implications for epithelial cell injury in gastrointestinal cancer.     

Over-expression of ERp29 attenuates doxorubicin-induced cell apoptosis through up-regulation of Hsp27 in breast cancer cells

The endoplasmic reticulum protein 29 (ERp29) has a critical role in regulating protein folding, maturation and secretion. However, its role in carcinogenesis remains elusive. Recently, we reported that ERp29 is a novel tumor suppressor and regulates mesenchymal-epithelial transition in MDA-MB-231 breast cancer cells. Here, we investigated whether ERp29 plays a role in the response of breast cancer cells to chemotherapeutic agents. We found that expression of ERp29 increased the resistance to doxorubicin, but not cisplatin and paclitaxel, and decreased the doxorubicin-induced cell apoptosis in MDA-MB-231 cells, whereas knockdown of ERp29 in MCF-7 cells increased the doxorubicin cytotoxicity. A proteomics study identified up-regulation of Hsp27 and down-regulation of stathmin-1, galectin and prohibitin in the doxorubicin-resistant, ERp29 over-expressing MDA-MB-231 cells. Further, we demonstrated that ERp29 up-regulated expression of Hsp27 by down-regulating eukaryotic translational initiation factor 2α (eIF2α). When Hsp27 was knocked down by siRNA in the doxorubicin-resistant, ERp29 over-expressing MDA-MB-231 cells and parental MCF-7 cells, cell viability was significantly decreased and doxorubicin-induced cell apoptosis was enhanced. These results indicate that Hsp27 is involved in the ERp29-mediated resistance to doxorubicin. Therefore, targeting of Hsp27, with a combination of other chemotherapeutic agents, is a rational strategy in treating doxorubicin-resistant cancer cells.     

Hsp27 inhibits 6-hydroxydopamine-induced cytochrome c release and apoptosis in PC12 cells

Cellular stress may stimulate cell survival pathways or cell death depending on its severity. 6-Hydroxydopamine (6-OHDA) is a neurotoxin that targets dopaminergic neurons that is often used to induce neuronal cell death in models of Parkinson's disease. Here we present evidence that 6-OHDA induces apoptosis in rat PC12 cells that involves release of cytochrome c and Smac/Diablo from mitochondria, caspase-3 activation, cleavage of PARP, and nuclear condensation. 6-OHDA also induced the heat shock response, leading to increased levels of Hsp25 and Hsp70. Increased Hsp25 expression was associated with cell survival. Prior heat shock or overexpression of Hsp27 (human homologue of Hsp25) delayed cytochrome c release, caspase activation, and reduced the level of apoptosis caused by 6-OHDA. We conclude that 6-OHDA induces a variety of responses in cultured PC12 cells ranging from cell survival to apoptosis, and that induction of stress proteins such as Hsp25 may protect cells from undergoing 6-OHDA-induced apoptosis.     

Thiolutin inhibits endothelial cell adhesion by perturbing Hsp27 interactions with components of the actin and intermediate filament cytoskeleton

Thiolutin is a dithiole synthesized by Streptomyces sp. that inhibits endothelial cell adhesion and tumor growth. We show here that thiolutin potently inhibits developmental angiogenesis in zebrafish and vascular outgrowth from tissue explants in 3D cultures. Thiolutin is a potent and selective inhibitor of endothelial cell adhesion accompanied by rapid induction of HSPB1 (Hsp27) phosphorylation. The inhibitory effects of thiolutin on endothelial cell adhesion are transient, potentially due to a compensatory increase in Hsp27 protein levels. Accordingly, heat shock induction of Hsp27 limits the anti-adhesive activity of thiolutin. Thiolutin treatment results in loss of actin stress fibers, increased cortical actin as cells retract, and decreased cellular F-actin. Mass spectrometric analysis of Hsp27 binding partners following immunoaffinity purification identified several regulatory components of the actin cytoskeleton that associate with Hsp27 in a thiolutin-sensitive manner including several components of the Arp2/3 complex. Among these, ArpC1a is a direct binding partner of Hsp27. Thiolutin treatment induces peripheral localization of phosphorylated Hsp27 and Arp2/3. Hsp27 also associates with the intermediate filament components vimentin and nestin. Thiolutin treatment specifically ablates Hsp27 interaction with nestin and collapses nestin filaments. These results provide new mechanistic insights into regulation of cell adhesion and cytoskeletal dynamics by Hsp27.     

In vitro maintenance and sperm development in the testis of the house cricket (Acheta domesticus)

Summary

Whole testes of Acheta domesticus were maintained in vitro for up to 48 h. Development of sperm could not be induced in the penultimate stage testis irrespective of hormone influence. A partial stimulation of spermatogenesis in the ultimate stage testis was achieved using 10^?6 M 20-hydroxyecdysone but completion of spermiogenesis was not seen.     

Repression of apurinic/apyrimidinic endonuclease by p53-dependent apoptosis in hydronephrosis-induced rat kidney

Abstract

p53 plays a major role in apoptosis through activation of pro-apoptotic gene Bax. It also regulates apurinic/apyrimidinic endonuclease (APE) expression in the base excision repair pathway against oxidative DNA damages. This study investigated whether p53-dependent apoptosis is correlated with APE using an experimental rat model of hydronephrosis. Hydronephrosis was induced by partial ligation of the right ureter. Animals were sacrificed on scheduled time after unilateral ureteral obstruction and the expression of 8-OHdG, γ-H2AX, apoptotic proteins and APE was determined. The accumulated p53 activated Bax and caspase-3 7 days after hydronephrosis induction and the resulting high levels of p53-dependent apoptotic proteins and γ-H2AX tended to decrease APE. The intensities of 8-OHdG and caspase-3 immunolocalization significantly increased in obstructed kidneys than in sham-operated kidneys, although APE immunoreactivity increased after hydronephrosis induction. These results suggest that oxidative DNA damages in obstructed kidneys may trigger p53-dependent apoptosis through repression of APE.     

P21(Cip1/WAF1) expression in the mouse testis before and after X irradiation

During spermatogenesis, the radiosensitivity of testicular cells changes considerably. To investigate the molecular mechanism underlying these radiosensitivity differences, p21^(Cip1/WAF1) expression was studied before and after irradiation in the adult mouse testis. P21^(Cip1/WAF1) is a cyclin-dependent kinase inhibitor (CDI) and has a role in the G1/S checkpoint and differentiation. P21^(Cip1/WAF1) expression was observed in the normal testis, using Western blotting analysis. After a dose of 4 Gy, but not after 0.3 Gy, an increase in p21^(Cip1/WAF1) expression could be determined in whole testis lysates. To investigate which germ cells are involved in p21^(Cip1/WAF1) protein expression, immunohistochemical analysis was performed on irradiated testis. In the normal testis a weak staining for p21^(Cip1/WAF1) was found in pachytene spermatocytes in epithelial stage V up to step 5 spermatids. A dose of 4 Gy of X-irradiation resulted in a transient increase of p21^(Cip1/WAF1) staining in these cells with a maximum at 6 hr post irradiation, despite the fact that the irradiation did not induce an increase in the number of apoptotic spermatocytes. When a dose of 0.3 Gy was given, no increase in p21^(Cip1/WAF1) staining was observed. Using the TUNEL technique, a 10-fold increase in apoptotic spermatogonia was found after a dose of 4 Gy. However, no staining for p21^(Cip1/WAF1) was observed in spermatogonia, suggesting that these cells do not undergo a p21^(Cip1/WAF1)-induced G1 arrest prior to DNA repair or apoptosis. These data imply that p21^(Cip1/WAF1) is a factor which could be important during the meiotic prophase in spermatocytes and repair mechanisms in these cells, but not in spermatogonial cell cycle delay or apoptosis induction. Mol. Reprod. Dev. 47:240–247, 1997. © 1997 Wiley-Liss, Inc.     

Induction of heat shock proteins (HSPs) by sodium arsenite in cultured astrocytes and reduction of hydrogen peroxide-induced cell death

Induction of heat shock proteins (HSPs) protects cells from oxidative injury. Here Hsp72, Hsp27 and heme oxygenase-1 (HO-1) were induced in cultured rat astrocytes, and protection against oxidative stress was investigated. Astrocytes were treated with sodium arsenite (20-50 micro m) for 1 h, which was non-toxic to cells, 24 h later they were exposed to 400 micro m H2O2 for 1 h, and cell death was evaluated at different time points. Arsenite triggered strong induction of HSPs, which was prevented by 1 micro g/mL cycloheximide (CXH). H2O2 caused cell loss and increased cell death with features of apoptosis, i.e. TdT-mediated dUTP nick-end labelling (TUNEL) reaction and caspase-3 activation. These features were abrogated by pre-treatment with arsenite, which prevented cell loss and significantly reduced the number of dead cells. The protective effect of arsenite was not detected in the presence of CHX. Pre-treatment with arsenite increased protein kinase B (Akt) and extracellular signal regulated kinase 1/2 (ERK1/2) phosphorylation after H2O2. However, while Akt phosphorylation was prevented by CHX, Erk1/2 phosphorylation was further enhanced by CHX. The results show that transient arsenite pre-treatment induces Hsp72, HO-1 and, to a lesser extent, Hsp27; it reduces H2O2-induced astrocyte death; and it causes selective activation of Akt following H2O2. It is suggested that HSP expression at the time of H2O2 exposure protects astrocytes from oxidative injury and apoptotic cell death by means of pro-survival Akt.     

P27 knockout mice: reduced myostatin in muscle and altered adipogenesis

Knockout of the P27(kip) gene, which encodes a cyclin-dependent kinase inhibitor involved in cell proliferation regulation, results in growth enhancement in mice. To investigate how p27 deficiency affected adipogenesis and myogenesis, levels of PPARgamma, C/EBPalpha, and the myogenesis inhibitor, myostatin, were measured in p27(-/-) (n=14), p27(+/-) (n=18), and p27(+/+) mice (n=11). Body weight and gastrocnemius muscle (GC) mass were increased in p27(-/-) mice (P<0.05), but there were no differences in fat depot weights, percent body fat or serum leptin concentrations among genotypes. PPARgamma, but not C/EBPalpha, was markedly increased in p27(-/-) mice (P<0.05). There was also a higher incidence of inguinal fat apoptosis (P<0.01) in p27(-/-) mice. Myostatin levels were reduced in GC muscle of p27(-/-) mice (P<0.05). These findings suggest that in p27 deficient mice, increased skeletal muscle mass is mediated in part through decreased myostatin. Although total adiposity was not changed, increased PPARgamma levels suggest an alteration in adipogenesis.     

Functional role of GKAP1 in the regulation of male germ cell spontaneous apoptosis and sperm number

G kinase‐anchoring protein 1 (GKAP1) is a G kinase‐associated protein that is conserved in many eutherians and is mainly expressed in the testis, especially in spermatocytes and round spermatids. The function of GKAP1 in the testis is largely unknown. Here, we revealed that deletion of GKAP1 led to an increase in sperm production with swollen epididymis, and germ cell apoptosis was found to decrease in GKAP1 knock‐out mice. Further investigations showed that a deficiency of GKAP1 could partly change the cellular location of cGK‐Iα and increase the amount of active cAMP response element‐binding protein (CREB) in the nucleus. Therefore, the expression of a particular inhibitor of apoptosis proteins (IAPs) was upregulated because of the activation of CREB, and this increase in IAPs was associated with a decrease in the level of activated caspase‐3. These results suggest that a deficiency of GKAP1 in mouse testis could increase sperm production through a reduction of the spontaneous apoptosis of germ cells in the testis, possibly because of a change in the activity of the cGK‐Iα pathway.     

Radiosensitization of wildtype p53 cancer cells by the MDM2-inhibitor PXN727 is associated with altered heat shock protein 70 (Hsp70) levels

The oncoprotein MDM2 (murine double minute 2) is often overexpressed in human tumors and thereby attenuates the function of the tumor suppressor p53. In this study, we investigated the effects of the novel MDM2-inhibitor PXN727 on p53 activation, cell proliferation, cell cycle distribution and radiosensitivity. Since the localization of heat shock protein 70 (Hsp70) exerts different effects on radioresistance of tumor cells, we investigated the impact of PXN727 on intracellular, membrane, and secreted Hsp70 levels. We could show that PXN727 exerts its effects on wildtype p53 (HCT116 p53^+/+, A549) but not p53 depleted (HCT116 p53^−/−) or mutated (FaDu) tumor cells. PXN727 activates p53, induces the expression of p21, reduces the proportion of cells in the radioresistant S-phase and induces senescence. Radiosensitivity was significantly increased by PXN727 in HCT116 p53^+/+ tumor cells. Furthermore, PXN727 causes a downregulation of Hsp70 membrane expression and an upregulated secretion of Hsp70 in wildtype p53 tumor cells. Our data suggest that re-activation of p53 by MDM2-inhibition modulates Hsp70 membrane expression and secretion which might contribute to the radiosensitizing effect of the MDM2-inhibitor PXN727.