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

Large potentials of small heat shock proteins

Modern classification of the family of human small heat shock proteins (the so-called HSPB) is presented, and the structure and properties of three members of this family are analyzed in detail. Ubiquitously expressed HSPB1 (HSP27) is involved in the control of protein folding and, when mutated, plays a significant role in the development of certain neurodegenerative disorders. HSPB1 directly or indirectly participates in the regulation of apoptosis, protects the cell against oxidative stress, and is involved in the regulation of the cytoskeleton. HSPB6 (HSP20) also possesses chaperone-like activity, is involved in regulation of smooth muscle contraction, has pronounced cardioprotective activity, and seems to participate in insulin-dependent regulation of muscle metabolism. HSPB8 (HSP22) prevents accumulation of aggregated proteins in the cell and participates in the regulation of proteolysis of unfolded proteins. HSPB8 also seems to be directly or indirectly involved in regulation of apoptosis and carcinogenesis, contributes to cardiac cell hypertrophy and survival and, when mutated, might be involved in development of neurodegenerative diseases. All small heat shock proteins play important "housekeeping" roles and regulate many vital processes; therefore, they are considered as attractive therapeutic targets.

Absence of caveolin-1 alters heat shock protein expression in spontaneous mammary tumors driven by Her-2/neu expression

In a previous study, we measured caveolin-1 protein levels, both in the normal breast and in breast cancer. The study revealed no association between caveolin-1 expression in the epithelial compartment and clinical disease outcome. However, high levels of caveolin-1 in the stromal tissue surrounding the tumor associated strongly with reduced metastasis and improved survival. Using an animal model, we found that the onset of mammary tumors driven by Her-2/neu expression was accelerated in mice lacking caveolin-1. We have analysed the heat shock protein (Hsp) response in the tumors of mice lacking caveolin-1. In all cases, the mammary tumors were estrogen and progesterone receptor negative, and the levels of Her-2/neu (evaluated by immunohistochemistry) were not different between the caveolin-1 +/+ (n = 8) and the caveolin-1 -/- (n = 7) tumors. However, a significant reduction in the extent of apoptosis was observed in mammary tumors from animals lacking caveolin-1. While Bcl-2, Bax, and survivin levels in the tumors were not different, the amount of HSPA (Hsp70) was almost double in the caveolin-1 -/- tumors. In contrast, HSPB1 (Hsp27/Hsp25) levels were significantly lower in the caveolin-1 -/- tumors. The mammary tumors from caveolin-1 null mice expressed more HSPC4 (gp96 or grp94), but HSPC1 (Hsp90), HSPA5 (grp78), HSPD1 (Hsp60), and CHOP were not altered. No significant changes in these proteins were found in the stroma surrounding these tumors. These results demonstrate that the disruption of the Cav-1 gene can cause alterations of specific Hsps as well as tumor development.

Expression, purification and some properties of fluorescent chimeras of human small heat shock proteins

Small heat shock proteins (sHsp) are ubiquitously expressed in all human tissues and have an important housekeeping role in preventing the accumulation of aggregates of improperly folded or denatured proteins. They also participate in the regulation of the cytoskeleton, proliferation, apoptosis and many other vital processes. Fluorescent chimeras composed of sHsp and enhanced fluorescent proteins have been used to determine the intracellular locations of small heat shock proteins and to analyse the hetero-oligomeric complexes formed by different sHsp. However, the biochemical properties and chaperone-like activities of these chimeras have not been investigated. To determine the properties of these chimeras, we fused enhanced yellow and cyan fluorescent proteins (EYFP and ECFP) to the N-termini of four ubiquitously expressed human small heat shock proteins: HspB1, HspB5, HspB6, and HspB8. The eight fluorescent chimeras of small heat shock proteins and isolated fluorescent proteins were expressed in Escherichia coli. The chimeric proteins were isolated and purified via ammonium sulphate fractionation, ion exchange and size-exclusion chromatography. This method provided 20-100 mg of fluorescent chimeras from 1L of bacterial culture. The spectral properties of the chimeras were similar to those of the isolated fluorescent proteins. The fusion of fluorescent proteins to HspB6 and HspB8, which typically form dimers, did not affect their quaternary structures. Oligomers of the fluorescent chimeras of HspB1 and HspB5 were less stable and contained fewer subunits than oligomers formed by the wild-type proteins. Fusion with EYFP decreased the chaperone-like activity of HspB5 and HspB6 whereas fusion with ECFP increased chaperone-like activity. All fluorescent chimeras of HspB1 and HspB8 had higher chaperone-like activity than the wild-type proteins. Thus, although fluorescent chimeras are useful for many purposes, the fluorescent proteins used to form these chimeras may affect certain important properties of sHsp.

PRKC-ζ Expression Promotes the Aggressive Phenotype of Human Prostate Cancer Cells and Is a Novel Target for Therapeutic Intervention

We show protein kinase C-zeta (PKC-ζ) to be a novel predictive biomarker for survival from prostate cancer (P < 0.001). We also confirm that transcription of the PRKC-ζ gene is crucial to the malignant phenotype of human prostate cancer. Following siRNA silencing of PRKC-ζ in PC3-M prostate cancer cells, stable transfectant cell line si-PRKC-ζ-PC3-M(T1-6) is phenotypically nonmalignant in vitro and in vivo. Genome-wide expression analysis identified 373 genes to be differentially expressed in the knockdown cells and 4 key gene networks to be significantly perturbed during phenotype modulation. Functional interconnection between some of the modulated genes is revealed, although these may be within different regulatory pathways, emphasizing the complexity of their mutual interdependence. Genes with altered expression following PRKC-ζ knockdown include HSPB1, RAD51, and ID1 that we have previously described to be critical in prostatic malignancy. Because expression of PRKC-ζ is functionally involved in promoting the malignant phenotype, we propose PKC-ζ as a novel and biologically relevant target for therapeutic intervention in prostate cancer.

Hsp27-actin interaction

Hsp27 oligomer is reported to interact with F-actin as a barbed-end-capping protein. The present study determined the binding strength and stoichiometry of the interaction using fluorescence of probes attached to Hsp27 cysteine-137. The fluorescence of acrylodan attached to Hsp27 increased 4-5-fold upon interaction with F-actin. Titration of the fluorescence with F-actin yielded a weak binding constant (K_D^app = 5.3 μM) with an actin/Hsp27 stoichiometry between < 1 and 6. This stoichiometry is inconsistent with an F-actin end-capping protein. Pyrene attached to Hsp27 exhibited a large excimer fluorescence, in agreement with the known proximity of the cysteine-137's in the Hsp27 oligomer. Upon interaction with F-actin the pyrene-Hsp27 excimer fluorescence was largely lost, suggesting that Hsp27 interacts with F-actin as a monomer, consistent with the acrylodan-Hsp27 results. EM images of F-actin-Hsp27 demonstrated that Hsp27 is not a strong G-actin sequester. Thus, Hsp27, in vitro, is a weak F-actin side-binding protein.

Heat shock protein as molecular targets for breast cancer therapeutics

Recent advances in the understanding of the molecular mechanisms involved in the breast cancer development and progression have led to the identification of numerous novel molecular targets. Among these, heat shock proteins (HSPs) are being emerging molecular target due to its diverse function in cancer cells. HSPs are highly conserved molecular chaperone that are synthesized by cell in response to various stress conditions. Mammalian HSPs have been classified into several families according to their molecular weight: HSP100, HSP90, HSP72, and small molecular HSPs (including HSP27). They are essential proteins that play a key role in cell survival through the cytoprotective mechanisms. In addition, HSPs are often overexpressed in a rage of cancers including breast cancer, and its overexpression seems to be associated with poor clinical outcomes. Also, HSP90 play a role in facilitating transformation by stabilizing the mutated and overexpressed oncoproteins found in breast cancer cell. Pharmacological targeting of HSP is therefore indicated and in the case of HSP90, numerous inhibitory drugs are undergoing clinical trial for treatment of breast cancer and other cancers. In this review, we describe the roles of HSPs in cancer cell and introduce the HSPs inhibitor as molecular target in cancer therapy and its recent clinical trials in breast cancer.

Lipid rafts: signaling and sorting platforms of cells and their roles in cancer

Lipid rafts are defined as microdomains within the lipid bilayer of cellular membranes that assemble subsets of transmembrane or glycosylphosphatidylinisotol-anchored proteins and lipids (cholesterol and sphingolipids) and experimentally resist extraction in cold detergent (detergent-resistant membrane). These highly dynamic raft domains are essential in signaling processes and also form sorting platforms for targeted protein traffic. Lipid rafts are involved in protein endocytosis that occurs via caveolae or flotillin-dependent pathways. Non-constitutive protein components of rafts fluctuate dramatically in cancer with impacts on cell proliferation, signaling, protein trafficking, adhesion and apoptosis. This article focuses on the identification of candidate cancer-associated biomarkers in carcinoma cells using state-of-the-art proteomics.

The potential role of heat shock protein 27 in cardiovascular disease

Heat shock proteins (Hsps) comprise several families of proteins expressed by a number of cell types following exposure to stressful environmental conditions that include heat, free radicals, toxins and ischemia, and are particularly involved in the recognition and renaturation of mis-folded proteins. Heat shock protein-27 (Hsp27) is a member of the small Hsp (sHsp) family with a molecular weight of approximately 27 KDa. In addition to its chaperoning functions, Hsp27 also appears to be involved in a diverse range of cellular functions, promoting cell survival through effects on the apoptotic pathway and plays important roles in cytoskeleton dynamics, cell differentiation and embryogenesis. Over the past two decades there has been an increasing interest in the relationship between Hsp27 and cardiovascular disease. Hsp27 is thought to exert an important role in the atherosclerotic process. Serum Hsp27 concentrations appear to be a biomarker of myocardial ischemia. In this review, we will focus on the possible protective and immuno-modulatory roles of Hsp27 in atherogenesis with special emphasis on their changes following acute coronary events and their potential as diagnostic and therapeutic targets.

Effects of a 1.5 T time-varying magnetic field on cell volume regulation of bovine adrenal chromaffin cells in hyposmotic media

Effects of a time-varying magnetic field on cell volume regulation by hyposmotic stress in cultured bovine adrenal chromaffin cells were examined. Through regulatory volume decrease (RVD), cell volume of chromaffin cells that were incubated in a hypotonic medium initially increased, reached a peak and finally recovered to the initial value. Two hour exposure to a magnetic field and addition of cytochalasin D increased peak value and delayed return to initial value. Intracellular F-actin contents initially decreased but returned to normal levels after 10 sec. Two hour exposure to the magnetic field and addition of cytochalasin D continuously reduced the F-actin content. Results suggest that exposure to the magnetic field stimulated disruption of the actin cytoskeleton and that the disruption delayed the recovery to the volume prior to osmotic stress.

HSPB1, actin filament dynamics, and aging cells

Investigations into the possible roles of human HSPB1 in aging have focused on its role as a molecular chaperone protecting partially folded or unfolded proteins, particularly during oxidative stress. A thorough analysis of potential roles of HSPB1 in aging cells has been hampered by a limited knowledge of its functions in living cells. Most studies have employed cell-free extracts and purified proteins. For example, HSPB1 is known to bind actin in vitro, and this observation led to the hypothesis that HSPB1 regulates actin filament dynamics. In the study summarized herein, the role of HSPB1 in regulating actin filament dynamics was further investigated by using cultured human cells. These results show that HSPB1 and actin form a complex in vivo and that HSPB1 is important for cell motility. A model for HSPB1 as a regulator of actin filament dynamics is presented, and evidence from the literature on cytoskeletal alterations in aging cells is discussed.

Proteasome inhibition induces hsp30 and hsp70 gene expression as well as the acquisition of thermotolerance in Xenopus laevis A6 cells

Previous studies have shown that inhibiting the activity of the proteasome leads to the accumulation of damaged or unfolded proteins within the cell. In this study, we report that proteasome inhibitors, lactacystin and carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG132), induced the accumulation of ubiquitinated proteins as well as a dose- and time-dependent increase in the relative levels of heat shock protein (HSP)30 and HSP70 and their respective mRNAs in Xenopus laevis A6 kidney epithelial cells. In A6 cells recovering from MG132 exposure, HSP30 and HSP70 levels were still elevated after 24 h but decreased substantially after 48 h. The activation of heat shock factor 1 (HSF1) may be involved in MG132-induced hsp gene expression in A6 cells since KNK437, a HSF1 inhibitor, repressed the accumulation of HSP30 and HSP70. Exposing A6 cells to simultaneous MG132 and mild heat shock enhanced the accumulation of HSP30 and HSP70 to a much greater extent than with each stressor alone. Immunocytochemical studies determined that HSP30 was localized primarily in the cytoplasm of lactacystin- or MG132-treated cells. In some cells treated with higher concentrations of MG132 or lactacystin, we observed in the cortical cytoplasm (1) relatively large HSP30 staining structures, (2) colocalization of actin and HSP30, and (3) cytoplasmic areas that were devoid of HSP30. Lastly, MG132 treatment of A6 cells conferred a state of thermotolerance such that they were able to survive a subsequent thermal challenge.

Heat shock protein 27: a potential biomarker for colorectal carcinoma

AIM: To find specific biomarkers for colorectal carcinoma using a proteomic method to provide clues to early diagnosis, prognosis and therapy of colorectal carcinoma as well as to understanding the molecular mechanisms governing cancer progression.

METHODS: Six colorectal carcinoma patients were included in the study. High-resolution two-dimensional gel electrophoresis (2-DE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) were utilized for the identification of proteins differentially expressed between cancer and adjacent non-cancerous tissue. The differential expression of heat shock protein 27 (HSP27) was further verified by Western blot and immunohistochemistry.

RESULTS: Comparative analysis of 2-DE maps revealed 42 differentially expressed proteins between the two groups. Ten differential proteins were further identified by mass spectrometry, including HSP27, disulfide isomerase (DI), heterogeneous nuclear ribonucleoprotein A2/B1 (HnRNP A2/B1), triosephosphate isomerase (TIM), pyruvate kinase, etc. Western blot and immunohistochemistry analyses confirmed the overexpression of HSP27 in colorectal carcinoma. These results indicate that HSP27 may be a potential biomarker for colorectal cancer.

CONCLUSION: Many differential proteins are identified between cancer and adjacent non-cancerous tissue in patients with colorectal carcinoma. HSP27 might be a potential biomarker for early diagnosis, therapy and prognosis of colorectal carcinoma.

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.

Identification of HSP27 as a potential tumor marker for colorectal cancer by the two-dimensional polyacrylamide gel electrophoresis

The identification of specific biomarkers for colorectal cancer would provide the basis for early diagnosis, prognosis, therapy, as well as clues for understanding the molecular mechanisms governing cancer progression. This study was designed to use comparative proteomics technology to find the differentially expressed proteins between human colorectal carcinoma and the corresponding normal tumor-adjacent colorectal tissues. We have used the highly sensitive two-dimensional gel electrophoresis (2-DE) coupled with matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) for the identification of proteins differentially expressed in tumoral and neighboring normal mucosa. We have detected differences in abundance of 42 proteins with statistical variance of the tumor versus normal spot volume ratio within the 95th confidence level (Student's t-test; P < 0.05). 10 out of 42 analyzed proteins were unambiguously identified by MS coupled with database interrogation as being differentially expressed in colorectal cancer. Of the 10 newly implicated proteins, HSP27 was chosen for detailed analysis. Preliminary studies demonstrated that the differentially expressed proteins found by 2-DE could be confirmed and validated by western blotting and immunohistochemistry analyses in those few cases. The results suggest that HSP27 might be a potential biomarker for early diagnosis, prognosis, monitoring in the therapy of colorectal carcinoma.

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.

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.