Growth factors acting via tyrosine kinase receptors induce HSP90 alpha gene expression

Antibodies to Heat Shock Proteins 90α and 90β in Psoriasis

One of many hypotheses of psoriasis pathogenesis supposes an overexpression of heat shock proteins (Hsps) in different skin layers and systemic immunologic response to them. Hsp90 is one of the most abundant chaperone in eukaryotic cells. The number of studies concerning the role of Hsp90 and anti-Hsp90 antibodies in etiopathogenesis of various diseases is also constantly expanding. Still, there are not many reports concerning potential involvement of this Hsp family or anti-Hsp90 immunization in pathomechanism of psoriasis. The aim of the study was the estimation of anti-Hsp90α and anti-Hsp90β IgG antibodies in the sera of the psoriatic patients at different phases of disease activity in comparison to the sera of healthy individuals. The study material consisted of sera from psoriasis patients (n = 80) in active phase and in the remission phase and healthy individuals (n = 80). Concentrations of anti-Hsp90α and anti-Hsp90β IgG antibodies were determined using ELISA technique. In the patients with psoriasis (both in the active phase of the disease and in the remission phase) concentrations of anti-Hsp90α antibodies were significantly higher than in healthy individuals and they correlated positively with psoriasis area severity index values. The mean concentrations of anti-Hsp90β antibodies in the psoriatic patients and healthy controls were comparable. The obtained results indicate an existence of increased immunological response to Hsp90α in psoriasis. It may suggest the role of the extracellular form of this chaperone and/or anti-Hsp90α antibodies in etiopathogenesis of this dermatosis. The inhibition of Hsp90α may represent a novel therapeutic approach to treat psoriasis.

Mitochondrial active and relaxed state respiration after heat shock mRNA response in the heart

Induction of Heat Shock Proteins results in cytoprotection. Beneficial effect results from transcription and translational cellular components' involvement that defends metabolism and thus induce ischemic protection of the tissue. Mitochondrial respiration is also involved in stress- induced conditions. It is not a uniform process. Cytochrome c Oxidase (CytOx) representing complex IV of the Electron Transfer Chain (ETC) has a regulatory role for mitochondrial respiratory activity, which is tested in our study after hsp induction. Moreover, protein translation for mitochondrial components was probed by the detection of MT-CO1 for Subunit 1 of CytOx neosynthesis. Wistar rats were subjected to whole-body hyperthermia at 42.0-42.5 °C for 15 min followed by a normothermic recovery period. Heat shock response was monitored time dependent from LV biopsies of all control and heat treated animals with PCR-analysis for hsp 32, 60, 70.1, 70.2, 90 and MT-CO1 expression at 15, 30, 45, 60, 120 and 360 min recovery (n = 5 in each group), respectively. Enzymatic activity of CytOx were evaluated polarographically. High energy phosphates were detected by chromatographic analysis. The mRNA expression of MT-CO1 peaked at 60 min and was accompanied by hsp 32 (r = 0.457; p = 0.037) and hsp 70.2 (r = 0.615; p = 0.003) upregulation. With hsp induction, mitochondrial respiration was increased initially. Enzymatic activity reconciled from active into relaxed status wherein CytOx activity was completely inhibited by ATP. Myocardial ATP content increased from stress induced point i.e. < 1 µmol g^-1 protein w/w to finally 1.5 ± 0.53 µmol g^-1 protein w/w at 120 min recovery interval. Hyperthermic, myocardial hsp- induction goes along with increased CytOx activity representing an increased "active" mitochondrial respiration. In parallel, de -novo holoenzyme assembly of CytOx begins as shown by MT-CO1 upregulation at 60 min recovery time crossing with a final return to the physiological "relaxed" state and ATP -inhibited respiration.

Chaperones in cell cycle regulation and mitogenic signal transduction: a review

Chaperones/heat shock proteins (HSPs) of the HSP90 and HSP70 families show elevated levels in proliferating mammalian cells and a cell cycle-dependent expression. They transiently associate with key molecules of the cell cycle control system such as Cdk4, Wee-1, pRb, p53, p27/Kip1 and are involved in the nuclear localization of regulatory proteins. They also associate with viral oncoproteins such as SV40 super T, large T and small t antigen, polyoma large and middle S antigen and EpsteinBarr virus nuclear antigen. This association is based on a J-domain in the viral proteins and may assist their targeting to the pRb/E2F complex. Small HSPs and their state of phosphorylation and oligomerization also seem to be involved in proliferation and differentiation. Chaperones/HSPs thus play important roles within cell cycle processes. Their exact functioning, however, is still a matter of discussion. HSP90 in particular, but also HSP70 and other chaperones associate with proteins of the mitogen-activated signal cascade, particularly with the Src kinase, with tyrosine receptor kinases, with Raf and the MAP-kinase activating kinase (MEK). This apparently serves the folding and translocation of these proteins, but possibly also the formation of large immobilized complexes of signal transducing molecules (scaffolding function).

Mechanisms of disease: the role of heat-shock protein 90 in genitourinary malignancy

Insight into the molecular biology of cancer has allowed the development of novel therapeutic strategies that target specific oncogenic pathways. Molecular therapeutic strategies are now part of the armamentarium available against urologic malignancy. Among the many targets of interest in urologic cancer, heat-shock protein 90 (HSP90) shows great promise. This molecule has a major role in prostate as well as in renal malignancy. In contrast to other targets, where cancer might escape inhibition via alternative pathways, HSP90 operates at multiple checkpoints in a cancer cell. Its inhibition could, therefore, prove more difficult for neoplastic cells to overcome. Inhibitors of HSP90, such as geldanamycin and its derivatives (17-allylamino-17-demethoxygeldanamycin and 17-dimethylaminoethylamino-17-demethoxygeldanamycin, known as 17AAG and 17DMAG, respectively) are available and have shown activity both in vivo and in vitro. 17AAG is currently being tested for efficacy in humans after having completed phase I trials, while 17DMAG is still in phase I evaluation. Phase II trials of HSP90 inhibitors in urologic malignancy are being conducted in kidney and advanced prostate cancer. Beyond monotherapy, HSP90 inhibitors might also prove to be beneficial in combination therapy with other chemotherapeutic agents in advanced disease. Studies being conducted in prostate cancer will hopefully help to define this potential application better.

A proteomic screen identified stress-induced chaperone proteins as targets of Akt phosphorylation in mesangial cells

The serine-threonine kinase Akt regulates mesangial cell apoptosis, proliferation, and hypertrophy. To define Akt signaling pathways in mesangial cells, we performed a functional proteomic screen for rat mesangial cell proteins phosphorylated by Akt. A group of chaperone proteins, heat shock protein (Hsp) 70, Hsp90alpha, Hsp90beta, Glucose-regulated protein (Grp) Grp78, Grp94, and protein disulfide isomerase (PDI) were identified as potential Akt substrates by two techniques: (a) in vitro phosphorylation of mesangial cell lysate by recombinant active Akt followed by protein separation by SDS-PAGE or 2-DE and phosphoprotein identification by peptide mass fingerprinting using MALDI-MS, or (b) immunoblot analysis of proteins from PDGF-stimulated mesangial cells using an anti-Akt phospho-motif antibody. In vitro kinase reactions using recombinant proteins confirmed that Akt phosphorylates Hsp70, Hsp90alpha and beta, Grp94, and PDI. Immunoprecipitation of Akt from mesangial cell lysate coprecipitated Grp78 and Hsp70. PDGF stimulation of mesangial cells caused an acidic shift in the isoelectric point of Hsp70, Hsp90, and PDI that was dependent on PI-3K activity for Hsp70 and Hsp90. The data suggest that Akt-mediated phosphorylation of stress-induced chaperones represents a mechanism for regulation of chaperone function during mesangial cell responses to physiologic and pathologic stimuli.

Differential expression of Hsp90 isoforms in geldanamycin-treated 9L cells

In mammals, two major Hsp90 isoforms (Hsp90alpha and Hsp90beta) have been identified and found to be highly conserved among different species. However, the expression control of Hsp90 isoforms at both transcriptional and translational levels is largely unknown. Herein, we quantitatively investigate the changes in the total mRNA and inductive protein levels of Hsp90alpha and Hsp90beta in rat gliosarcoma cells treated with geldanamycin (GA). The stability of mRNA and protein was estimated. The translational efficiency of Hsp90 isoforms was measured employing in vitro translation techniques. It was found that Hsp90alpha was more inducible than Hsp90beta after GA treatment, whereas the hsp90alpha mRNA level was lower than that of hsp90beta. In addition, higher translational efficiency of hsp90alpha mRNA was observed, suggesting that translational control played an important role. Taken together, our results indicate that differential expression between Hsp90alpha and Hsp90beta is a consequence of both distinct mRNA profiles and differential translation processes.

Synergistic activity of imatinib and 17-AAG in imatinib-resistant CML cells overexpressing BCR-ABL – Inhibition of P-glycoprotein function by 17-AAG

Overexpression of BCR-ABL and P-glycoprotein (Pgp) are two of the known mechanisms of imatinib resistance. As combination therapy may allow to overcome drug resistance, we investigated the effect of combination treatment with imatinib and 17-allylamino-17-demethoxygeldanamycin (17-AAG), a heat-shock protein 90 (Hsp90) inhibitor, on different imatinib-sensitive and imatinib-resistant CML cell lines. In imatinib-sensitive cells, combination index (CI) values obtained using the method of Chou and Talalay indicated additive (CI=1) or marginally antagonistic (CI>1) effects following simultaneous treatment with imatinib and 17-AAG. In imatinib-resistant cells both drugs acted synergistically (CI<1). In primary chronic-phase CML cells additive or synergistic effects of the combination of imatinib plus 17-AAG were discernible. Annexin V/propidium iodide staining showed that the activity of imatinib plus 17-AAG is mediated by apoptosis. Combination treatment with imatinib plus 17-AAG was more effective in reducing the BCR-ABL protein level than 17-AAG alone. Monotherapy with 17-AAG decreased P-glycoprotein activity, which may increase intracellular imatinib levels and contribute to the sensitization of CML cells to imatinib. The results suggest that combination of imatinib and 17-AAG may be useful to overcome imatinib resistance in a clinical setting.

Hsp90 isoforms: functions, expression and clinical importance

The 90 kDa heat shock protein, Hsp90, is a main functional component of an important cytoplasmic chaperone complex, and it is involved in various cellular processes, such as cell proliferation, differentiation and apoptosis. Identification of Hsp90 as a molecular target of various anticancer drugs highlighted its importance from the clinical point of view. Here we summarize the current knowledge of various Hsp90 isoforms regarding their genomic location, molecular evolution, functional differences, differential induction after various environmental stresses and in pathological conditions as well as the growing importance of discriminating between Hsp90 isoforms in clinical practice.

Hsp70 and Hsp90--a relay team for protein folding

Molecular chaperones are a functionally defined set of proteins which assist the structure formation of proteins in vivo. Without certain protective mechanisms, such as binding nascent polypeptide chains by molecular chaperones, cellular protein concentrations would lead to misfolding and aggregation. In the mammalian system, the molecular chaperones Hsp70 and Hsp90 are involved in the folding and maturation of key regulatory proteins, like steroid hormone receptors, transcription factors, and kinases, some of which are involved in cancer progression. Hsp70 and Hsp90 form a multichaperone complex, in which both are connected by a third protein called Hop. The connection of and the interplay between the two chaperone machineries is of crucial importance for cell viability. This review provides a detailed view of the Hsp70 and Hsp90 machineries, their cofactors and their mode of regulation. It summarizes the current knowledge in the field, including the ATP-dependent regulation of the Hsp70/Hsp90 multichaperone cycle and elucidates the complex interplay and their synergistic interaction.

Protection against hypoxia-induced increase in blood-brain barrier permeability: role of tight junction proteins and NFkappaB

Co-culture with glial cells and glia-conditioned media can induce blood-brain barrier properties in microvessel endothelial cells and protect against hypoxia-induced blood-brain barrier breakdown. We examined the effect of two types of glia-conditioned media on brain microvessel endothelial cell permeability and tight junction protein expression, and studied potential mechanisms of action. We found that C6-glioma-conditioned media, but not rat astrocyte-conditioned media, protected against an increase in permeability induced by exposure to 1% oxygen for 24 hours. This hypoxic stress caused an increase in the expression of tight junction proteins claudin-1 and actin, particularly in cells treated with C6-conditioned media. We found that C6-conditioned media has a significantly higher level of both basic fibroblast growth factor and vascular endothelial growth factor. Treatment with C6-conditioned media for 1 or 3 days protects against hypoxia-induced permeability increases, and this protective effect may be mediated by signal transduction pathways terminating at the transcription factor NFkappaB.

Exogenous expression of heat shock protein 90kDa retards the cell cycle and impairs the heat shock response

The 90-kDa heat shock protein, HSP90, is an abundant molecular chaperone which functions in cellular homeostasis in prokaryotes and eukaryotes. It is well known that HSP90 plays a critical and indispensable role in regulating cell growth through modulations of various signal transduction pathways, but its roles in cell cycle control are not so well known. We transferred human HSP90 (wild-type or mutated types) expression vectors into NIH-3T3 cells in order to study certain functions of HSP90 in the cell cycle and cell growth under physiological conditions. We found that the exogenous expression of HSP90 (wild-type) induced a decrease in cell growth via retardation of the G1/S transition. The inhibition of cell growth was caused by reduced expressions of cyclin D3 and cyclin A mRNA and protein. On the other hand, no stable transfectants with the three types of mutated HSP90 were obtained. Unexpectedly, exogenous HSP90 expression impaired the heat shock response by inhibiting both heat shock transcription factor 1(HSF1) activation and transportation of HSF1 into the nucleus. The HSF1 function was disrupted by the direct association between HSF1 and exogenous HSP90, which was present as a monomer. These results reveal important roles of HSP90 in cell cycle control and in the stress response of nontransformed cells.

Preconditioning of 3T3 cells by fresh medium together with genistein enhances prostaglandin E(2) release

Bradykinin induced prostaglandin E(2) release from the Swiss 3T3 fibroblasts, preconditioned with fresh culture medium. Although treatment with genistein for the entire period of preconditioning and incubation with bradykinin attenuated prostaglandin E(2) release, treatment with fresh culture medium and genistein for only the preconditioning period further augmented the prostaglandin E(2) release. In the cells preconditioned with fresh culture medium and genistein, bradykinin caused the phosphorylation of protein tyrosine and mitogen-activated protein kinase/extracellular-regulated kinase (MAPK/ERK), followed by arachidonic acid release. Interestingly, preconditioning with genistein alone also caused phosphorylation and arachidonic acid release, probably reflecting rebound activation after the washout of genistein. However, preconditioning with genistein alone induced neither the augmentation of prostaglandin E(2) release nor the expression of cyclooxygenase-2. The further potentiation of bradykinin-induced prostaglandin E(2) release by combined preconditioning with fresh culture medium and genistein may be due to the activation of the MAPK/ERK-c phospholipase A(2) pathway by preconditioning with genistein.

Proteomic detection of changes in protein synthesis induced by fibroblast growth factor-2 in MCF-7 human breast cancer cells

Fibroblast growth factor-2 (FGF-2) is a potent regulator of breast cancer cell growth through stimulation of tyrosine kinase receptors and activation of the mitogen-activated protein kinase cascade. In the present study, we have investigated changes in protein synthesis induced by FGF-2 stimulation of the prototypic human breast cancer cell line MCF-7. Using high-resolution two-dimensional electrophoresis of (35)S amino acid metabolically labeled proteins and computerized analysis of 2D autoradiograms, we found that four proteins were up-regulated within the first 12 h of FGF-2 stimulation. Mass spectrometry analysis (MALDI-TOF and MS-MS) of tryptic fragments and database searches allowed the identification of these FGF-2-regulated proteins as the heat shock proteins HSP90 and HSP70, the proliferating cell nuclear antigen (PCNA), and the transcriptionaly controlled tumor protein (TCTP). We then analyzed the distribution of these proteins in various cancerous and normal breast epithelial cells. Interestingly, the four FGF-2-regulated proteins were found to be constitutively up-regulated in ras-transfected MCF-7 cells, indicating their relevance to the up-regulation of cellular proliferation. Moreover, HSP90 and PCNA were found at higher levels in cancerous cells than in normal cells. The role of HSP90 was further investigated using the specific inhibitor geldanamycin. We showed that the functionality of HSP90 is strictly required in order to obtain FGF-2 mitogenic stimulation in MCF-7 cells, indicating the crucial role played by this molecular chaperone in the control of breast cancer cell growth. Finally, these results show that proteomic analysis is a valuable method for identifying potential markers or therapeutic targets related to cancer growth.

Function of 90-kDa heat shock protein in cellular differentiation of human embryonal carcinoma cells

Heat shock proteins (HSPs) have been recognized as molecules that maintain cellular homeostasis during changes in the environment. Here we report that HSP90 functions not only in stress responses but also in certain aspects of cellular differentiation. We found that HSP90 showed remarkably high expression in undifferentiated human embryonal carcinoma (EC) cells, which were subsequently dramatically down-regulated during in vitro cellular differentiation, following retinoic acid (RA) treatment, at the protein level. Surprisingly, heat shock treatment also triggered the down-regulation of HSP90 within 48 h at the protein level. Furthermore, the heat treatment induced cellular differentiation into neural cells. This down-regulation of HSP90 by heat treatment was shifted to an up-regulation pattern after cellular differentiation in response to RA treatment. In order to clarify the functions of HSP90 in cellular differentiation, we conducted various experiments, including overexpression of HSP90 via gene transfer. We showed that the RA-induced differentiation of EC cells into a neural cell lineage was inhibited by overexpression of the HSP90alpha or -beta isoform via the gene transfer method. On the other hand, the overexpression of HSP90beta alone impaired cellular differentiation into trophoectoderm. These results show that down-regulation of HSP90 is a physiologically critical event in the differentiation of human EC cells and that specific HSP90 isoforms may be involved in differentiation into specific cell lineages.

Reduction in myocardial infarct size by basic fibroblast growth factor following coronary occlusion in a canine model

In a canine model of permanent coronary occlusion it has been shown that basic fibroblast growth factor (bFGF) reduced infarct size and this was associated with an increase in myocardial capillary density a week after infarction. In a preliminary work from our own laboratory using a model of occlusion followed by prolonged reperfusion we observed a similar reduction in infarct size without evidence of myocardial neovascularization. The aim of the present investigation was to evaluate the effects of bFGF on infarct size and blood flow to the infarct zone in an acute experiment in which myocardial neovascularization would be excluded as a mechanism by the short duration of the study. Seventeen mongrel dogs were anesthetized and the heart was exposed through a left thoracotomy. The left anterior descending (LAD) coronary artery was isolated and occluded for 3 h. Fifteen min after LAD occlusion dogs received bFGF 20 microg of bFGF (n=6) or placebo (n=11) by intracoronary injection infused over 5 min. We measured heart rate, aortic pressure, regional coronary blood flow (CBF), regional shortening fraction (SF) at 1, 30 and 180 min of occlusion, then the LAD was reperfused for 5 min then the dogs were euthanized and infarct size was measured. Regional CBF was similar between the two groups of dogs throughout all the study. The SF was similar between the two groups prior the onset of ischemia and at the beginning of the ischemic period. After 180 min of ischemia SF was 2.7+/-4.1% for bFGF and -3.1+/-4.7 for placebo (P=0.049), and during reperfusion SF was 3.4+/-4.6% for bFGF and 0.4+/-1.0% for placebo treated dogs (P=0.023). The infarct size, normalized for the area at risk was 14.2+/-5.2% in bFGF group vs 25.8+/-8.2% in placebo group (P=0.015). In summary we have demonstrated that bFGF significantly limits myocardial necrosis after acute coronary occlusion, and that this occurred without an increase in regional myocardial perfusion and within a period of time too brief for angiogenesis to have occurred. By exclusion, it appears that the salutary effect of bFGF is likely to be mediated by a cellular mechanism. The mechanism or mechanisms responsible for myocardial salvage by bFGF may have significant potential to be exploited in the clinical arena as the basis for therapies to protect the acutely ischemic myocardium.

Corticotropin-releasing factor induces phosphorylation of phospholipase C-gamma at tyrosine residues via its receptor 2beta in human epidermoid A-431 cells

This laboratory previously reported that corticotropin-releasing factor (CRF) increased intracellular free calcium concentrations, cellular cAMP, inositol 1,4,5-trisphosphate, protein kinase C activity, and protein phosphorylation in human A-431 cells. The increase was blocked by CRF receptor antagonist. In this study, we identified the type of CRF receptors present and investigated whether CRF induced tyrosine phosphorylation of phospholipase C-gamma via CRF receptors. Using novel primers in reverse transcriptase-polymerase chain reaction, we determined the CRF receptor type to be that of 2beta. The levels of the CRF receptor type 2beta were not altered in cells treated with activators of protein kinase C, Ca2+ ionophore, or cells overexpressing heat shock protein 70 kDa. Cells treated with CRF displayed increases in protein tyrosine phosphorylation approximately at 150 kDa as detected by immunoblotting using an antibody against phosphotyrosine. Immunoprecipitation with antibodies directed against phospholipase C-beta3, -gamma1, or -gamma2 isoforms (which have molecular weights around 150 kDa) followed by Western blotting using an anti-phosphotyrosine antibody showed that only phospholipase C-gamma1 and -gamma2 were phosphorylated. The increase in phospholipase C-gamma phosphorylation was concentration-dependent with an EC50 of 4.2+/-0.1 pM. The maximal phosphorylation by CRF at 1 nM occurred by 5 min. The CRF-induced phosphorylation was inhibited by the protein tyrosine kinase inhibitors genistein and herbimycin A, suggesting that CRF activates protein tyrosine kinases. Treatment of cells with CRF receptor antagonist, but not pertussis toxin, prior to treatment with CRF inhibited the CRF-induced phosphorylation, suggesting it is mediated by the CRF receptor type 2beta that is not coupled to pertussis toxin-sensitive G-proteins. Treatment with 1,2-bis(2iminophenoxy)ethane-N,N,N',N'-tetraacetic acid attenuated the phospholipase C-gamma phosphorylation. In summary, CRF induces phospholipase C-gamma phosphorylation at tyrosine residues, which depends on Ca2+ and is mediated by activation of protein tyrosine kinases via the CRF receptor type 2beta.

Expression of heat shock proteins in mouse skin during wound healing

Wound healing conditions generate a stressful environment for the cells involved in the regeneration process and are therefore postulated to influence the expression of heat shock proteins (Hsps). We have examined the expression of four Hsps (Hsp27, Hsp60, Hsp70 and Hsp90) and a keratin (keratin 6) by immunohistochemistry during cutaneous wound repair from Day 1 to Day 21 after wounding in the mouse. Hsps were constitutively expressed in normal mouse epidermis and their patterns of expression were modified during the healing process. The changes were not directly linked to the time course of the healing process but rather were dependent on the location of cells in the regenerating epidermis. In the thickened epidermis, Hsp60 was induced in basal and low suprabasal cells, Hsp70 showed a reduced expression, and Hsp90 and Hsp27 preserved a suprabasal pattern with an induction in basal and low suprabasal cells. All Hsps had a uniform pattern of expression in the migrating epithelial tongue. These observations suggest that the expression of Hsps in the neoepidermis is related to the proliferation, the migration, and the differentiation states of keratinocytes within the wound.

Medium change amplifies mitogen-activated protein kinase-mediated prostaglandin E2 synthesis in Swiss 3T3 fibroblasts

In Swiss 3T3 fibroblasts, changing the culture medium prior to stimulation resulted in an augmentation of bradykinin-induced prostaglandin E2 synthesis. The augmentation depended on the duration of the exposure to the fresh medium, with a maximum effect at 1 h. Fetal calf serum in the fresh medium was essential for augmented prostaglandin E2 synthesis. The medium change slightly augmented the bradykinin-induced increase in intracellular free Ca2+ concentration and phosphoinositide hydrolysis with a different time course from that for prostaglandin E2 synthesis. 4',5,7-Trihydroxyisoflavone (genistein) and 3,4-dihydroxybenzylidene-malononitrile (tyrphostin 23), inhibitors of tyrosine kinases, and 2'-amino-3'-methoxyflavone (PD98059), an inhibitor of mitogen-activated protein kinase (MAPK) kinase, attenuated the increase in prostaglandin E2 synthesis. Bradykinin caused phosphorylation of cytosolic phospholipase A2 and p42/p44 MAPK, which was augmented by the medium change. From the results, it is concluded that activation of MAPK and cytosolic phospholipase A2 is involved in the augmentation of prostaglandin E2 synthesis produced by the medium change.

The 90-kDa molecular chaperone family: structure, function, and clinical applications. A comprehensive review

The 90-kDa molecular chaperone family (which comprises, among other proteins, the 90-kDa heat-shock protein, hsp90 and the 94-kDa glucose-regulated protein, grp94, major molecular chaperones of the cytosol and of the endoplasmic reticulum, respectively) has become an increasingly active subject of research in the past couple of years. These ubiquitous, well-conserved proteins account for 1-2% of all cellular proteins in most cells. However, their precise function is still far from being elucidated. Their involvement in the aetiology of several autoimmune diseases, in various infections, in recognition of malignant cells, and in antigen-presentation already demonstrates the essential role they likely will play in clinical practice of the next decade. The present review summarizes our current knowledge about the cellular functions, expression, and clinical implications of the 90-kDa molecular chaperone family and some approaches for future research.

Glutathione depletion associated with the HIV-1 TAT protein mediates the extracellular appearance of acidic fibroblast growth factor

Primary murine embryonic fibroblasts transfected with HIV-1 TAT demonstrated decreased levels of high energy phosphates (ATP, GTP, UTP/CTP), adenine nucleotides (ATP, ADP, AMP), and both NAD+/NADH redox pairs, resulting in a substantial loss of redox poise. A greater than 50% decrease in intracellular reduced glutathione (GSH) concentration was accompanied by the extracellular appearance of acidic fibroblast growth factor (FGF-1). Addition of either N-acetyl-L-cysteine or glutathione ester (GSE), but not L-2-oxothiazolidine 4-carboxylate, partially restored intracellular GSH levels and resulted in loss of extracellular FGF-1. Treatment of FGF-1-transduced cells with buthionine sulfoximine (BSO) resulted in a time- and dose-dependent decrease in total cellular GSH concentration that was accompanied by the extracellular appearance of FGF-1. Inclusion of GSE during BSO treatment eliminated the extracellular appearance of FGF-1. BSO treatment of cells transfected with a mutant form of FGF-1, in which all three cysteine residues were replaced with serines, also decreased total cellular GSH concentration but failed to induce the extracellular appearance of FGF-1. Collectively, these results suggest that HIV-1 TAT induces a condition of oxidative stress, which mediates cellular secretion of FGF-1, an observation relevant to the pathophysiologic development and progression of AIDS-associated Kaposi's sarcoma.

Serum-starvation induces the extracellular appearance of FGF-1

Autocrine/paracrine stimulation of cell growth by members of the fibroblast growth factor (FGF) family of polypeptides is dependent upon extracellular interactions with specific high affinity receptors at the cell surface. Acidic FGF (FGF-1) lacks a classical signal sequence for secretion, suggesting that intrinsic levels of this mitogen may not stimulate cell growth and utilizes a non-classical pathway to gain access to the extracellular compartment. To evaluate the biological potential of intracellular FGF-1 more rigorously, human cDNA sequences for the growth factor were introduced into primary murine embryonic fibroblasts using retrovirally mediated gene transfer. Heparin affinity, Western analysis, mitogenic assays, in situ immunohistochemical techniques, induction of tyrosine phosphorylation and antibody inhibition studies were used to demonstrate functionality of the FGF-1 transgene in this experimental model. Under normal culture conditions, cells constitutively expressing intracellular FGF-1 exhibited a slight growth advantage. In contrast, when maintained in reduced serum, these cells adopted a transformed phenotype and demonstrated an enhanced growth potential, induction of FGF-specific phosphotyrosyl proteins and the nuclear association of the growth factor. Analysis of the conditioned media from these stressed cells indicated that serum starvation induces the secretion of FGF-1 as latent high molecular mass complexes requiring reducing agents to activate its full biological potential.

The HIV-1 TAT protein induces the expression and extracellular appearance of acidic fibroblast growth factor

Mounting experimental evidence suggests that the TAT protein, released from human immunodeficiency virus-1 (HIV-1)-infected inflammatory cells, may genetically reprogram targeted cells within a localized environment to develop highly vascularized tumors of mesenchymal origin. The fibroblast growth factor (FGF) family of polypeptides has gained general acceptance as initiators of angiogenesis and functions as potent mitogens for mesoderm-derived cells. To evaluate a potential biological relationship between TAT and acidic FGF (FGF-1), primary murine embryonic fibroblasts either were transfected with the viral transactivator or were transduced (retrovirally mediated) with a secreted, chimeric form of the human polypeptide growth factor, human stomach tumor/Kaposi's sarcoma (hst/KS)FGF-1. Reverse transcriptase-polymerase chain reaction, Western blotting, in situ immunohistochemical, heparin affinity, DNA synthesis, and transient transfection techniques were used to confirm expression, localization, and functionality of the transgenes. Both transfected and transduced cells constitutively expressing either TAT or (hst/KS)FGF-1 adopted a transformed phenotype, maintained aggressive growth behavior, and demonstrated both induction of FGF-specific phosphotyrosyl proteins and nuclear association of FGF-1 and FGF-1 receptor. Increased levels of endogenous, murine FGF-1 mRNA (reverse transcriptase-polymerase chain reaction) and protein (immunoblot analysis) were apparent in both (hst/KS)FGF-1- and TAT-transformed cells. Medium conditioned by (hst/KS)FGF-1-transduced cells contained steady-state levels of biologically active FGF-1 which exhibited a representative molecular weight. Limited sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the conditioned medium from TAT-transformed cells demonstrated the appearance of FGF-1 as latent, high molecular weight complexes requiring reducing agents to activate full biological activity. Collectively, these results suggest that TAT induces the expression and secretion of FGF-1, which may be potentially relevant to the pathophysiological development of AIDS-Kaposi's sarcoma.

Regulation of HSP60 mRNA expression in a human ovarian carcinoma cell line

The expression of the 60-kDa heat-shock protein (HSP60) varies markedly among patients with ovarian carcinoma, and high-level expression predicts poor survival in such patients treated with cisplatin (DDP)-containing chemotherapy programs. We investigated the expression of HSP60 in human ovarian carcinoma 2008 cells and an 11-fold DDP-resistant subline 2008/C13*5.25. Heating for 2 h at 44 degrees C produced a 2.7 +/- 0.16-fold increase (mean +/- SD) that was maximal at 4 h after the start of heat exposure. Exposure to an IC50 concentration of DDP for 1 h induced a 1.8 +/- 0.03-fold increase in hsp60 expression. The opposite was true for cadmium and zinc, both of which induced increases in metallothionein IIA but not in the hsp60 message. 2008/C13*5.25 cells constitutively over-expressed hsp60 mRNA by 1.7 +/- 0.16 orders of magnitude and contained a 3.8 +/- 0.45-fold higher level of HSP60 as detected by immunocytochemical staining. 2008/C13*5.25 cells showed 1.2-fold cross-resistance to thermal killing. Expression of hsp60 was markedly reduced in 2008 xenografts as compared with 2008 cells growing in vitro; however, neither serum starvation nor refeeding altered the message level. Exposure to a variety of growth factors and drug treatments known to alter the DDP sensitivity of 2008 cells, including epidermal growth factor, 12-O-tetradecanoylphorbol-13-acetate, buthionine sulfoximine, ouabain, and forskolin, did not alter hsp60 expression. These results suggest a role for HSP60 in mediating resistance to both DDP and hyperthermia but indicate that the hsp60 mRNA levels are not regulated by the factors listed above.