28-kDa mammalian heat shock protein, a novel substrate of a growth regulatory protease involved in differentiation of human leukemia cells

MS4A3-HSP27 target pathway reveals potential for haematopoietic disorder treatment in alimentary toxic aleukia

Alimentary toxic aleukia (ATA) is correlated with consuming grains contaminated by Fusarium species, particularly T-2 toxin, which causes serious hurt to human and animal health, chiefly in disorders of the haematopoietic system. However, the mechanism of haematopoietic dysfunction induced by T-2 toxin and the possible target pathway for the treatment of T-2 toxin-induced haematopoietic disorder of ATA remains unclear. In this study, genomes and proteomics were used for the first time to investigate the key differential genes and proteins that inhibit erythroid differentiation of K562 cells caused by T-2 toxin, and it was found that heat shock protein 27 (HSP27) and membrane-spanning 4-domains, subfamily A, member 3 (MS4A3) may play an important role in erythroid differentiation. Meanwhile, MS4A3 interference can inhibit the occurrence of erythroid differentiation of K562 cells and promote the phosphorylation of HSP27. Moreover, the binding of HSP27 to MS4A3 in natural state can activate the phosphorylation site of HSP27 (Ser-83), while T-2 toxin can abolish the activation of phosphorylation site by inhibiting the expression of MS4A3. These findings for the first time demonstrated that the MS4A3-HSP27 pathway may function an efficient therapeutic target pathway for treating T-2 toxin elicited haematopoietic disorders of ATA.

Stress proteins: the biological functions in virus infection, present and challenges for target-based antiviral drug development

Stress proteins (SPs) including heat-shock proteins (HSPs), RNA chaperones, and ER associated stress proteins are molecular chaperones essential for cellular homeostasis. The major functions of HSPs include chaperoning misfolded or unfolded polypeptides, protecting cells from toxic stress, and presenting immune and inflammatory cytokines. Regarded as a double-edged sword, HSPs also cooperate with numerous viruses and cancer cells to promote their survival. RNA chaperones are a group of heterogeneous nuclear ribonucleoproteins (hnRNPs), which are essential factors for manipulating both the functions and metabolisms of pre-mRNAs/hnRNAs transcribed by RNA polymerase II. hnRNPs involve in a large number of cellular processes, including chromatin remodelling, transcription regulation, RNP assembly and stabilization, RNA export, virus replication, histone-like nucleoid structuring, and even intracellular immunity. Dysregulation of stress proteins is associated with many human diseases including human cancer, cardiovascular diseases, neurodegenerative diseases (e.g., Parkinson’s diseases, Alzheimer disease), stroke and infectious diseases. In this review, we summarized the biologic function of stress proteins, and current progress on their mechanisms related to virus reproduction and diseases caused by virus infections. As SPs also attract a great interest as potential antiviral targets (e.g., COVID-19), we also discuss the present progress and challenges in this area of HSP-based drug development, as well as with compounds already under clinical evaluation.

Mammalian HspB1 (Hsp27) is a molecular sensor linked to the physiology and environment of the cell

Constitutively expressed small heat shock protein HspB1 regulates many fundamental cellular processes and plays major roles in many human pathological diseases. In that regard, this chaperone has a huge number of apparently unrelated functions that appear linked to its ability to recognize many client polypeptides that are subsequently modified in their activity and/or half-life. A major parameter to understand how HspB1 is dedicated to interact with particular clients in defined cellular conditions relates to its complex oligomerization and phosphorylation properties. Indeed, HspB1 structural organization displays dynamic and complex rearrangements in response to changes in the cellular environment or when the cell physiology is modified. These structural modifications probably reflect the formation of structural platforms aimed at recognizing specific client polypeptides. Here, I have reviewed data from the literature and re-analyzed my own studies to describe and discuss these fascinating changes in HspB1 structural organization.

Gene expression of Hsps in normal and abnormal embryonic development of mouse hindlimbs

Heat shock proteins (Hsps), which have important biological functions, are a class of highly conserved genetic molecules with the capacity of protecting and promoting cells to repair themselves from damage caused by various stimuli. Our previous studies found that Hsp25, HspB2, HspB3, HspB7, Hsp20, HspB9, HspB10, and Hsp40 may be related to all-trans retinoic acid (atRA)-induced phocomelic and other abnormalities, while HspA12B, HspA14, Trap1, and Hsp105 may be forelimb development-related genes; Grp78 may play an important role in forelimb development. In this study, the embryonic phocomelic, oligodactylic model of both forelimbs and hindlimbs was developed by atRA administered per os to the pregnant mice on gestational day 11, and the expression of 36 members of Hsps family in normal and abnormal development of embryonic hindlimbs was measured by real-time fluorescent quantitative polymerase chain reaction (qRT-PCR). It is found that HspA1L, Hsp22, Hsp10, Hsp60, Hsp47, HspB2, HspB10, HspA12A, Apg1, HspB4, Grp78, and HspB9 probably performs a major function in limb development, and HspA13, Grp94 and Hsp110 may be hindlimb development-related genes.

Heat shock protein 27 mediated signaling in viral infection

Heat shock proteins (HSPs) play a critical role in many intracellular processes, including apoptosis and delivery of other proteins to intracellular compartments. Small HSPs have been shown previously to participate in many cellular functions, including IL-8 induction. Human adenovirus infection activates intracellular signaling, involving particularly the c-Src and mitogen-activated protein kinases [Natarajan, K., et al. (2003) J. Immunol. 170, 6234-6243]. HSP27 and MK2 are also phosphorylated, and c-Src, and its downstream targets, p38, ERK1/2, and c-Jun-terminal kinase (JNK), differentially mediate IL-8 and MCP-1 expression. Specifically, activation and translocation of transcription factor NFκB-p65 occurs in a p38-dependent fashion [Rajaiya, J., et al. (2009) Mol. Vision 15, 2879-2889]. Herein, we report a novel role for HSP27 in an association of p38 with NFκB-p65. Immunoprecipitation assays of virus-infected but not mock-infected cells revealed a signaling complex including p38 and NFκB-p65. Transfection with HSP27 short interfering RNA (siRNA) but not scrambled RNA disrupted this association and reduced the level of IL-8 expression. Transfection with HSP27 siRNA also reduced the level of nuclear localization of NFκB-p65 and p38. By use of tagged p38 mutants, we found that amino acids 279-347 of p38 are necessary for the association of p38 with NFκB-p65. These studies strongly suggest that HSP27, p38, and NFκB-p65 form a signalosome in virus-infected cells and influence downstream expression of pro-inflammatory mediators.

Differential proteome analysis of bone marrow mesenchymal stem cells from adolescent idiopathic scoliosis patients

Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional deformity of the spine. The cause and pathogenesis of scoliosis and the accompanying generalized osteopenia remain unclear despite decades of extensive research. In this study, we utilized two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) coupled with mass spectrometry (MS) to analyze the differential proteome of bone marrow mesenchymal stem cells (BM-MSCs) from AIS patients. In total, 41 significantly altered protein spots were detected, of which 34 spots were identified by MALDI-TOF/TOF analysis and found to represent 25 distinct gene products. Among these proteins, five related to bone growth and development, including pyruvate kinase M2, annexin A2, heat shock 27 kDa protein, γ-actin, and β-actin, were found to be dysregulated and therefore selected for further validation by Western blot analysis. At the protein level, our results supported the previous hypothesis that decreased osteogenic differentiation ability of MSCs is one of the mechanisms leading to osteopenia in AIS. In summary, we analyzed the differential BM-MSCs proteome of AIS patients for the first time, which may help to elucidate the underlying molecular mechanisms of bone loss in AIS and also increase understanding of the etiology and pathogenesis of AIS.

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).

Hsp27 regulates pro-inflammatory mediator release in keratinocytes by modulating NF-kappaB signaling

Heat-shock protein 27 (Hsp27) is a member of the small Hsp family that functions as molecular chaperones and protects cells against environmental stress. Hsp27 is expressed in the upper epidermal layers of normal human skin and has been reported to play a role in keratinocyte differentiation and apoptosis. In this investigation, we show an additional role of Hsp27 in the regulation of inflammatory pathways in keratinocytes. Downregulation of Hsp27 using Hsp27-specific small interfering RNA increased prostaglandin E(2) (PGE(2)) production in both unstimulated and tumor necrosis factor-alpha (TNF-alpha)-stimulated keratinocytes. Moreover, downregulation of Hsp27 increased the release of the pro-inflammatory cytokine IL-8 from TNF-alpha-stimulated and UV-irradiated keratinocytes, and this increase was inhibited by pretreatment with the NF-kappaB inhibitor BAY11-7082. Further studies showed that downregulation of Hsp27 resulted in induction of NF-kappaB reporter activity in keratinocytes. This correlated with enhanced degradation of IkappaB-alpha protein and accumulation of phosphorylated IkappaB-alpha in Hsp27 knockdown cells. Moreover, Hsp27 associated with the IkappaB kinase (IKK) complex. As synthesis of the pro-inflammatory cytokine IL-8 and the prostanoid PGE(2) are regulated by NF-kappaB, this could be a probable mechanism by which Hsp27 modulates the production of these inflammatory cytokines. Thus, Hsp27 plays a protective role in regulating inflammatory responses in skin.

Impact of cyclins E, neutrophil elastase and proteinase 3 expression levels on clinical outcome in primary breast cancer patients

Uncontrolled cell proliferation is one of the hallmarks of cancer and the transition from the G1 to S phase is the most commonly reported cell cycle abnormality in tumors. It has been shown that the oncogenic activity of G1 cyclin E (CCNE) can be amplified by generating hyperactive low molecular weight forms (LMW) through elastase-mediated proteolytic processing. Neutrophil elastase (NE) and proteinase 3 (PR3) are 2 proteases that are aberrantly expressed in breast cancer cells and seem to be involved in cell proliferation. In this study, we evaluated the effect of the expression of these 2 proteases in addition to 2 potential intracellular targets of NE (CCNE1 and CCNE2) on clinical outcome in a population of 205 primary breast cancer patients. By univariate analysis, CCNE1, CCNE2, estrogen receptor and grade significantly predicted relapse free interval (RFI). NE and PR3 did not achieve statistical significance. In a multivariate analysis, elevated CCNE2 [hazard ratio (HR) 2.10, p = 0.008] predicted shorter RFI. In subgroup analyses of the tamoxifen-only treated patients, high CCNE1 levels predicted treatment resistance, while high levels of CCNE2 were associated with poor RFI in untreated patients. Investigation of the relationship between CCNE1, CCNE2 and NE did not show any impact on RFI. To conclude, this study was the first to evaluate these markers at the mRNA level by RT-PCR in a series of primary breast cancer patients, and our results confirmed the impact of high CCNE levels on clinical outcome in systemically untreated and of CCNE1 in tamoxifen-only treated early breast cancer patients.

Cleavage of p21/WAF1/CIP1 by Proteinase 3 Modulates Differentiation of a Monocytic Cell Line

Proteinase 3 (PR3), also called myeloblastin, is involved in the control of myeloid cell growth, but the underlying molecular mechanisms have not been elucidated. In U937/PR3, stably transfected with PRCRSV/PR3 to overexpress PR3, PMA-induced p21 expression was significantly decreased as compared with control U937, and this phenomenon was reversed in the presence of the serine proteinase inhibitor, pefabloc. Conversely, when PR3 was inactivated by small interfering RNA, p21 protein was increased, and PMA-induced monocytic differentiation was potentiated. Mass spectrometry analysis identified Ala45 as the primary cleavage site on p21, and the recombinant mutated p21A45R, generated by site-directed mutagenesis and expressed in Escherichia coli, was resistant to in vitro PR3 cleavage. The U937 cells were then stably transfected with either PRCRSV/p21 or PRCRSV/p21A45R, to ectopically express wild type p21 or PR3-resistant p21, respectively. In U937/p21A45R treated with PS-341, a selective proteasome inhibitor, a significant decrease in the S phase and a blockade in the G0-G1 phase of cell cycle were observed when compared with U937/p21 or control U937. This suggested that both PR3 and the proteasome are efficiently involved in the proteolytic regulation of p21 expression in myeloid cells. Moreover, PMA-induced p21 expression was more pronounced in U937/p21A45R compared with U937/p21 and was concomitant with the morphological features of early differentiation. Our data demonstrated that p21 is one specific target of PR3 and that PR3-mediated p21 cleavage prevents monocytic differentiation.

In search of the molecular mechanism by which small stress proteins counteract apoptosis during cellular differentiation

Many differentiation programs are accompanied by an increase in small heat shock proteins (sHsps) level. Most of the time transient, this accumulation takes place during the early phase of the process and is correlated with the growth arrest that precedes the differentiation. Important biochemical modifications of sHsps occur, such as changes in phosphorylation and oligomerization. The fact that these proteins are induced independently of the signal that triggers differentiation, of the differentiation type, and of the cell type strongly suggests their involvement in fundamental mechanisms of cellular differentiation. Moreover, impairment of sHsps accumulation leads to abortion of the differentiation program and, subsequently, to a massive commitment to cell death. Recent advances in this field of research are presented as well as the hypothesis that should be tested to unravel the mode of action of these proteins during cellular differentiation.

Stat6-protease but not Stat5-protease is inhibited by an elastase inhibitor ONO-5046

A short isoform of Stat6 (65-kDa Stat6), a product of proteolytic processing by an undefined protease (Stat6-protease) in the nucleus, downregulates Stat6-mediated signaling in mast cells. Similarly, Stat5-mediated signaling is downregulated by Stat5-protease in myeloid progenitors. These proteases share a number of characteristics, including their nuclear localization and susceptibility to protease inhibitors. Here, we further investigated these Stat proteases. Interestingly, the activity of Stat6-protease but not of Stat5-protease was inhibited by ONO-5046, an elastase inhibitor that inhibits the activity of neutrophil elastase (NE) and NE-related protease proteinase 3 (PR3). Although both NE and PR3 were able to cleave Stat6 in vitro, the cleavage sites of Stat6 by NE or PR3 differed from that by Stat6-protease in mast cells. In addition, both NE and PR3 could also cleave Stat5, but they differed from Stat5-protease in myeloid progenitors. These results suggest that Stat6-protease may belong to the elastase family but differs from NE or PR3.

Lineage-specific negative regulation of STAT-mediated signaling by proteolytic processing

Accumulating evidence suggests that STAT-mediated signaling plays critical roles in cell differentiation and/or cell expansion and that in turn, STAT-mediated signaling is regulated strictly by many mechanisms. In murine mast cells, when Stat6 is activated by IL-4 and translocated to the nucleus, Stat6 is cleaved by a nucleus-associated protease (namely Stat6-protease). Similarly, the activated Stat5 is cleaved by a protease (Stat5-protease) in the nucleus of myeloid progenitors. These STAT proteases cleave the corresponding STAT proteins at the carboxyl-terminus and the resultant STAT proteins function as dominant negative molecules. Functionally, Stat6-protease protects mast cells from Stat6-dependent growth inhibition while Stat5-protease maintains the immature state of myeloid progenitors. In addition, it has been shown that the activated Stat3 is cleaved in mature neutrophils. These findings indicate that the proteolytic processing of STAT proteins by the nucleus-associated protease functions as a lineage-specific negative-regulator of STAT-mediated signaling.

Concurrent exposure to heat shock and H7 synergizes to trigger breast cancer cell apoptosis while sparing normal cells

Most cancer therapies, including chemotherapy, kill tumor cells by inducing apoptosis. Consequently, the propensity of tumor cells to evade apoptotic signals contributes to therapeutic resistance. Here we show that breast cancer cells exhibiting a highly resistant phenotype undergo apoptosis when exposed to concurrent heat shock and H7, a potent serine/threonine kinase inhibitor. The anti-tumor effects of this combination are synergistic as neither treatment alone adversely affects breast cancer cell growth/survival. In contrast, non-malignant breast epithelial and hematopoietic progenitor cells are resistant to this combination therapy, thereby excluding non-specific cytotoxicity as the cause of tumor cell apoptosis. Heat or other cell stresses, including chemotherapy, preferentially enhance heat shock protein (hsp) synthesis, which serves to protect cells from potentially lethal consequences of heat shock stimuli. Ectopic overexpression of hsps in breast cancer cells protects against chemotherapy-induced apoptosis. Furthermore, increased hsps in primary breast cancers correlates with resistance to therapy and decreased survival. Stress-induced hsp synthesis is mediated by heat shock transcription factor 1 (HSF1). To simulate hsp overexpressing primary breast cancers, a number of breast cancer cell lines were transfected with HSF1d202-316, a constitutively activated form of HSF1 that leads to baseline overexpression of hsps in the absence of stress. Importantly, HSF1d202-316 transfected breast cancer cells undergo apoptosis following concurrent heat shock and H7. In light of its tumor selective activity against breast cancer cells that exhibit a highly resistant phenotype, concurrent H7 and heat shock warrants further investigation as a potential cancer therapy.

Overexpression of Hsp27 in a human melanoma cell line: regulation of E-cadherin, MUC18/MCAM, and plasminogen activator (PA) system

Hsp27 is considered a potential marker for cell differentiation in diverse tissues. Several aspects linked to the differentiation process and to the transition from high to low metastatic potential were analyzed in melanoma cells transfected with Hsp27. E-cadherin plays a central role in cell differentiation, migration, and normal development. Loss of expression or function of E-cadherin has been documented in a variety of human malignancies. We observed by fluorescence-activated cell sorter (FACS) as well as immunofluorescence (IF) analysis a pronounced expression of E-cadherin in Hsp27-transfected A375 melanoma cells compared with control melanoma cells. The expression of the adhesion molecule MUC18/MCAM correlates directly with the metastatic potential of melanoma cells. In contrast to wild-type and neotransfected melanoma cells, in Hsp27-transfected cells the expression of MUC18/MCAM could not be detected by FACS and IF analysis. The plasminogen activator (PA) system plays a central role in mediating extracellular proteolysis and also in nonproteolytic events such as cell adhesion, migration, and transmembrane signaling. Hsp27 transfectants revealed elevated messenger ribonucleic acid expression of the urokinase-type PA (uPA) and its inhibitor, PA inhibitor type 1, which might indicate a neutralization effect of the proteolytic activity of uPA. Control cells failed to express both these molecules. The influence of Hsp27 expression on uPA activity and the involvement of E-cadherin could be demonstrated by use of anti-E-cadherin-blocking antibody. Our data provide evidence for an inhibitory-regulatory role of Hsp27 in tumor progression as found in our system.

Proteinase-3, a serine protease which mediates doxorubicin-induced apoptosis in the HL-60 leukemia cell line, is downregulated in its doxorubicin-resistant variant

We report here that expression of proteinase 3 (PR3), a serine protease, is down-regulated in the HL60/ADR multidrug resistant variant of the human myelogenous leukemia cell line HL-60, and that down-regulation of PR3 is associated with doxorubicin (DOX) resistance in these cells. To determine whether PR3 is involved in DOX-induced apoptosis in HL-60 cells, and whether its loss causes resistance to DOX, we inhibited PR3 expression by an anti-sense PR3 oligodeoxynucleotide and showed that inhibition of PR3 expression results in a significant reduction in DOX-induced DNA fragmentation and increased resistance to DOX-induced apoptosis. Our results revealed that PR3-mediated DOX-induced apoptosis in HL-60 cells is independent of the loss of mitochondrial membrane potential (deltapsi(m)) and activation of the caspase-8 and -9 pathways. Moreover, while PR3 is involved in the cleavage of caspase-3, PR3-mediated DOX-induced DNA fragmentation and apoptosis were not prevented by a specific inhibitor of caspase-3. These data suggest that activation of caspase-3 alone is not sufficient to trigger PR3-mediated DOX-induced apoptosis. Treatment with an anti-PR3 oligomer significantly decreased reactive oxygen species (ROS) generation in cells treated with low concentrations of DOX, revealing a role for PR3 in enhancing production of DOX-induced ROS. Moreover, DOX-induced apoptosis at 0.001-0.01 microM was only inhibited in HL-60 cells pre-treated with the antioxidant N-acetyl-cysteine in the absence of anti-PR3, revealing that DOX-induced apoptosis in these cells is PR3- and ROS-dependent. Our results show that PR3 is involved in DOX-induced ROS-dependent apoptosis and that its loss is associated with resistance to DOX in HL-60 cells.

Overexpression of Hsp27 affects the metastatic phenotype of human melanoma cells in vitro

Overexpression of the small heat shock protein Hsp27 has been shown by us to inhibit the in vitro proliferation rate and to delay tumor development of a human melanoma cell line (A375) in nude mice. We hypothesized that Hsp27 may influence the neoplastic phenotype. In the present study Hsp27 transfectants from this cell line were analyzed for various cellular aspects associated with the metastatic process. We found that Hsp27-overexpressing clones exhibited an altered cellular morphology as compared with control transfected cells. The Hsp27-positive cells tended to develop an epithelial-like phenotype growing in clusters and were characterized by a loss of transcytoplasmic stressfibers. In parallel, Hsp27-expressing cells lost the ability to form colonies in soft agar. The invasive potential was studied in vitro by the use of a reconstituted extracellular matrix-coated filter (Matrigel). Compared with controls, Hsp27-overexpressing cells showed decreased cell invasiveness through Matrigel. A correlation between invasion and activation of matrix metalloproteinases (MMPs) has been shown in several cell models. Secretion of MMPs (MMP-2 and MMP-9) was studied by gelatin-substrate zymogram analysis, as well as by a sensitive gelatinase activity assay. The Hsp27-transfected A375 melanoma cell line showed decreased secretion of MMP-2 and MMP-9 as compared with the control transfected cells. Integrins are adhesion receptors and function in cell invasion by mediating cell movement on matrix molecules and by regulating the expression of MMPs. Both fluorescence-activated cell sorter analysis and immunofluorescence analysis revealed a loss of alpha(v)beta3 integrin in Hsp27-transfected cell colonies. Our results demonstrate that Hsp27 overexpression has a profound impact on several parameters regulating the invasive and metastatic potential of melanoma cells in vitro.

MCF-7 mammary tumour cells express the myeloid cell differentiation controlling factor, serine protease 3/myeloblastin

Our previous data indicated that HSP27 plays a role in MCF-7 cell differentiation similar to that it has in HL-60 cells. In the latter case, this involves a control of its levels by proteinase 3/myeloblastin (PR3/Mbn), a serine proteinase hitherto considered specific of the myeloid lineage. Having observed that the treatment of MCF-7 cells with the serine protease inhibitor N-tosyl-l-phenylalanine-chloromethyl ketone (TPCK) increased their content in HSP27 and induced them to acquire a secretory phenotype, we undertook this work to test the assumption that an enzyme similar or identical to PR3/Mbn might be expressed in this cell line. The data show that MCF-7 cells exhibited specific immunopositivity for a monoclonal antibody against PR3/Mbn. Western blot analysis of immunoprecipitates from MCF-7 cell extracts, obtained and checked with PR3/Mbn monoclonal antibodies, confirmed the presence of the 35 kDa glycosylated and 29 kDa mature forms of the protein. Finally, Northern blot analysis confirmed the expression of the corresponding mRNA. Together with our data with TPCK, this substantiates our hypothesis that, as in HL-60 cells, regulation of MCF-7 cells differentiation might involve a postranslation control on HSP27 levels by a serine protease.

Overexpression of murine small heat shock protein HSP25 interferes with chondrocyte differentiation and decreases cell adhesion

Although multiple functions for the small heat shock protein HSP25 have been proposed, its specific role during developmental and differentiation processes is not known. Cartilage is one of the tissues in which HSP25 is specifically and highly expressed during development. C1 cells, able to form aggregates in vitro, can be induced to differentiate into chondrocytes. In this study, we generated two stable transfected clones overexpressing HSP25 at two different levels. Cell morphology and growth rate were modified in both clones, although the actin content and distribution did not seem to be altered. Overexpressing clones had more difficulties in coalescing, leading to smaller aggregates and they did not differentiate into chondrocytes. Subsequently, these aggregates tended to dissociate into loose masses of dying cells. The strength of all these effects was directly correlated to the level of HSP25 overexpression. These data suggest that overexpressing HSP25 decreases cellular adhesion and interferes with chondrocyte differentiation.

Anthracycline-induced erythroid differentiation of K562 cells is inhibited by p28, a novel mammalian glutathione-binding stress protein

When exposed to the anthracycline doxorubicin, K562 cells undergo differentiation which is characterized by arrested cell division, an increased mean cell diameter, and the production of hemoglobin. The influence of expression of p28, a low-molecular weight stress protein, on the differentiation of K562 cells was examined. Expression of p28 was modulated by transfection of K562 cells with expression vectors containing the murine p28 cDNA in either the sense or antisense orientation, or without the p28 cDNA. In K562 cells where p28 expression was either unaltered or downregulated, exposure to 40 nM Doxorubicin resulted in an arrest of cell division, the production of hemoglobin, and an increased cell diameter consistent with cells undergoing differentiation. K562 cells that overexpressed p28 continued to divide, had fewer hemoglobin-producing cells, had a smaller mean cell diameter and had a 5.5-fold increase in cell survival. Consistent with an inhibition of doxorubicin-induced erythroid differentiation, p28 may act by changes in redox regulation via the glutathione-binding activity of p28 and suggests a general role for p28 in cellular differentiation. Furthermore, p28 expression may be useful in predicting resistance to chemo- or radiation therapy in the treatment of leukemia and lymphoma.

Internalization of proteinase 3 is concomitant with endothelial cell apoptosis and internalization of myeloperoxidase with generation of intracellular oxidants

The important issue addressed by the studies presented here is the mechanism of neutrophil-mediated damage to endothelial and epithelial cells during inflammation. Binding of neutrophil-released granule proteins to endothelial cells may be involved in vascular damage in patients with inflammatory vascular diseases. We have determined whether granule proteins proteinase 3(PR3) and/or myeloperoxidase (MPO) are internalized into endothelial cells, as examined by UV light, confocal, and electron microscopy. Coincident induction of apoptosis and/or the generation of intracellular oxidants were monitored. The results indicate that human endothelial cells (human umbilical vein endothelial cells, human umbilical arterial endothelial cells, human lung microvascular endothelial cells) internalize both PR3 and MPO, which are detected on the cell surface, in the cytoplasm, and possibly nuclear. Epithelial cells (small airway epithelial cells) internalized MPO but not PR3, implying that the mechanism of PR3 internalization may be cell-type specific and different from that of MPO. Internalization of PR3, but not MPO, correlated with activation of apoptosis. Internalization of MPO correlated with an increase in intracellular oxidant radicals. The requirement for the proteolytic activity of PR3 for the induction of apoptosis was examined by generating PR3-truncated fragments that did not contain the components of the catalytic triad. An apoptotic function was localized to the C-terminal portion of PR3. These studies reveal novel mechanisms by which the neutrophil granule proteins PR3 and MPO contribute to tissue injury at sites of inflammation.

Annexin I is a stress protein induced by heat, oxidative stress and a sulfhydryl-reactive agent

Annexin I (also called lipocortin 1) is a 37-kDa member of the annexin family of proteins. It has been proposed to be involved in the regulation of cell growth and differentiation, apoptosis, and inflammation. Previously, we have reported that annexin I displays a chaperone-like function (Kim, G.Y., Lee, H.B., Lee, S.O., Rhee, H.J. & Na, D.S. (1997) Biochem. Mol. Biol. Int. 43, 521-528). To determine the possibility that annexin I is a stress protein, we examined whether expression of annexin I and annexin I mRNA increases in response to stresses in A549 and HeLa cells. Treatments of cells with heat, hydrogen peroxide or sodium arsenite resulted in (a) an increase in annexin I and annexin I mRNA and (b) translocation of annexin I from the cytoplasm to the nucleus and perinuclear region. The annexin I gene promoter region, cloned upstream of a reporter gene, was inducible in response to heat, hydrogen peroxide, and sodium arsenite. These results indicate that annexin I serves as a stress protein and annexins may constitute a new class of stress proteins.

Hsp25 and the p38 MAPK pathway are involved in differentiation of cardiomyocytes

The small heat-shock protein HSP25 is expressed in the heart early during development, and although multiple roles for HSP25 have been proposed, its specific role during development and differentiation is not known. P19 is an embryonal carcinoma cell line which can be induced to differentiate in vitro into either cardiomyocytes or neurons. We have used P19 to examine the role of HSP25 in differentiation. We found that HSP25 expression is strongly increased in P19 cardiomyocytes. Antisense HSP25 expression reduced the extent of cardiomyocyte differentiation and resulted in reduced expression of cardiac actin and the intermediate filament desmin and reduced level of cardiac mRNAs. Thus, HSP25 is necessary for differentiation of P19 into cardiomyocytes. In contrast, P19 neurons did not express HSP25 and antisense HSP25 expression had no effect on neuronal differentiation. The phosphorylation of HSP25 by the p38/SAPK2 pathway is known to be important for certain of its functions. Inhibition of this pathway by the specific inhibitor SB203580 prevented cardiomyocyte differentiation of P19 cells. In contrast, PD90589, which inhibits the ERK1/2 pathway, had no effect. Surprisingly, cardiogenesis was only sensitive to SB203580 during the first 2 days of differentiation, before HSP25 expression increases. In contrast to the effect of antisense HSP25, SB203580 reduced the level of expression of the mesodermal marker Brachyury-T during differentiation. Therefore, we propose that the p38 pathway acts on an essential target during early cardiogenesis. Once this initial step is complete, HSP25 is necessary for the functional differentiation of P19 cardiomyocytes, but its phosphorylation by p38/SAPK2 is not required.

Anti-sense inhibition of small-heat-shock-protein (HSP27) expression in MCF-7 mammary-carcinoma cells induces their spontaneous acquisition of a secretory phenotype

This work was aimed at testing the hypothesis (hitherto supported only by indirect evidence) that, besides contributing to resistance to stress, the small heat-shock-protein HSP27 might be involved in the control of growth and differentiation in mammary-tumour cells, where it is known to be oestrogen-regulated. Therefore, MCF-7 cells were transfected with a modulatable human hsp27 anti-sense cDNA. Clones of transfectants (designated alphahsp27) were selected which, upon expression of the anti-sense, exhibited a decline in HSP27 accumulation, associated with a decrease in resistance to heat shock and in proliferation rate, the degree of the latter reflecting their respective reduction in HSP27 content. The effects of anti-sense inhibition of HSP27 production were similar to those exerted on parental cells by phorbol myristate (TPA). Both resulted in growth inhibition, accumulation of lipid droplets in the cytoplasm, formation of secretory microvesicles with internal microvilli and increased release of several proteins, including the isoforms of a 52-kDa protein, which we identified as the oestrogen-regulated protein cathepsin D, all this without noticeable change in actin organization. These data constitute the first direct support for the hypothesis that, at least in some cell types, HSP27 might play a modulatory role in cell differentiation and (perhaps by this) in proliferation. While allowing dissociation of this role from the known action of HSP27 on actin polymerization, they suggest similar modulation of the function of some protein(s) implicated in the acquisition of the secretory phenotype by MCF-7 cells, with HSP27 also exerting an inhibitory action that can be alleviated either by its phosphorylation (as occurs with TPA) or by inhibition of its production.

Truncation of Sp1 transcription factor by myeloblastin in undifferentiated HL60 cells

When HL60 cells are exposed to 1,25-dihydroxyvitamin D3 (1,25D3), they undergo changes approximating the phenotype of the monocyte. Little is known, however, about the regulation and the mechanisms of this transition. It was previously noted that DNA binding by the Sp1 transcription factor in nuclear extracts of HL60 cells is profoundly altered when these cells are induced to differentiate by 1,25D3. In the present study, we show that in untreated HL60 cells only a truncated, approximately 30-kDa Sp1 fragment, encompassing the C-terminal region, binds to the GC element-containing DNA. Full-length 105-kDa Sp1 protein cannot be detected in these cells, although reverse transriptase-polymerase chain reaction reveals the presence of both 5' and 3' ends of Sp1 mRNA. Following treatment with 10(7) M 1,25D3 for 96 hr or in cells made resistant to 1,25D3 or to 1-beta-D-arabinocytosine, the Sp1 protein can be demonstrated. After an exposure to purified myeloblastin, a serine protease, purified recombinant Sp1 protein and extracts of 1,25D3-treated cells show a pattern of DNA binding similar to the pattern seen using extracts of untreated HL60 cells, indicating that the Sp1 protein is a target for myeloblastin. Because myeloblastin is present in naive HL60 cells and is downregulated during their differentiation, inhibition of proteolysis of these transcription factors seems to provide a mechanism through which differentiating HL60 cells can acquire a new repertoire of gene expression, perhaps for the maintenance of the differentiated phenotype.

Chromosomal fragility may be indicative of altered higher-order DNA organization as the underlying genetic diathesis in complex neurobehavioral disorders

Preliminary observations concerning increased chromosomal fragility in association with behavioural disorders in humans allow an opportunity to suggest a cohesive theory regarding the possible importance of higher-order DNA modifications in the coordination of gene function in brain evolution and during development. Visible or submicroscopic acentric chromosomal fragments are formed as an accompaniment to chromosomal breakage and are associated with sequence amplification. During genomic reintegration of extrachromosomally amplified repeat sequence elements, functional consequences could include unequal crossing over with gain-of-function, and/or deletion with loss-of-function. This process could result in regulatory changes in gene function in association with normal coding regions, since fragile sites appear to be located at or near upstream DNaseI-hypersensitive areas. Earlier research on chromosomal breakage in relation to transposon behaviour in maize has set a precedent by which many elements in a network could be coordinately controlled, a principle which may allow transcriptional control over multiple areas in the genome simultaneously. The hypothesis proposed in this paper implies that a small number of fundamental higher-order changes may be responsible for influencing a wide range of genetic alterations leading to complex phenotypes, sometimes segregating as distinct entities within pedigrees, or alternatively, and perhaps more commonly, presenting with several overlapping phenotypes in some other families. Studying only pure multiplex families in psychiatric genetics may not be sufficient for an understanding of the underlying genetic diathesis in this group of disorders. Validation of the fragile site hypothesis for complex neurobehavioural disorders may offer additional avenues for gene therapy based either on preferential integration of exogenous DNA at fragile sites, or utilizing the acentric fragments to modify sequence amplification extrachromosomally.

Capture-ELISA based on recombinant PR3 is sensitive for PR3-ANCA testing and allows detection of PR3 and PR3-ANCA/PR3 immunecomplexes

Proteinase 3 (PR3), a constituent of azurophil granules of neutrophils (polymorphonuclear cells, PMNs), is the target antigen for most anti-neutrophil cytoplasmic antibodies (c-ANCA) in Wegener's granulomatosis (WG). We have recently developed an expression system for recombinant PR3 (rPR3) that is recognized by c-ANCA. Here, we report on the development and characterization of two monoclonal antibodies (moABs) and a rabbit polyclonal antiserum generated against this rPR3. Epitope competition analysis indicates that the moABs MCPR3-1 and MCPR3-2 recognize overlapping epitopes on the PR3 molecule that are distinct from the ones recognized by moABs 4A5 and 6A6 developed by others. Since MCPR3-2 does not appear to compete for epitopes recognized by a sizable proportion of PR3-ANCA, we used it to develop a sensitive capture enzyme linked immunosorbent assay (ELISA) for clinical PR3-ANCA testing. Both purified PMN PR3 and crude human mast cell line (HMC-1)/PR3-S176A cell lysates were used as sources of PR3 target antigen in this assay with equal analytical sensitivity and specificity. Of 109 patients with ANCA-associated disease, 91 (83.5%) and 90 (82.6%) were PR3-ANCA positive by capture ELISA when PMN-PR3 and HMC-1/PR3-S176A cell lysates were used as antigen, respectively. When HMC-1/PR3 and HMC-1/PR3-S176A cells were used as indirect immunofluorescence (IIF) substrate, 88 (80.7%) and 92 (84.4%) were PR3-ANCA positive, respectively. These differences were not statistically significant. Only 1 of 151 controls without defined ANCA-associated disease tested positive by capture ELISA with either target antigen (both negative by PR3-ANCA specific IIF). The capture ELISA can also be used to detect of PR3-ANCA immunecomplexes and, in combination with the rabbit antiserum, for the quantitative measurement of PR3 in biological fluids.

Molecular chaperones in the etiology and therapy of cancer

Molecular chaperones are ubiquitous, well-conserved proteins that account for 2-5 % of all cellular proteins in most cells. The present review summarizes our current knowledge about their involvement in the etiology and therapy of cancer with special emphasis on the expression of chaperones in malignant cells, their role in folding of (proto)oncogene products, cell cycle regulation, cell differentiation and apoptosis, development of metastasis, and their participation in the recognition of malignant cells. We also overview the importance of chaperones in hyperthermia, drug resistance, and recent approaches in chaperone-immunotherapy.

hsp27 as a switch between differentiation and apoptosis in murine embryonic stem cells

Small stress proteins are developmentally regulated and linked to cell growth and differentiation. The early phase of murine embryonic stem (ES) cell differentiation, characterized by a gradual growth arrest, is accompanied with hsp27 transient accumulation. This differentiation process also correlated with changes in hsp27 phosphorylation and oligomerization. The role of hsp27 was investigated in ES clones stably transfected with murine or human hsp27 genes, placed in sense or antisense orientation. Several clones were obtained that either underexpressed endogenous murine hsp27 or overexpressed murine or human hsp27. Maintained undifferentiated, these clones showed similar growth rates. We report here that hsp27 constitutive overexpression enhanced the differentiation-mediated decreased rate of ES cell proliferation but did not alter morphological changes. In contrast, hsp27 underexpression, which attenuated cell growth arrest, induced differentiation abortion because of an overall cell death by apoptosis. Recently, we showed that hsp27 interfered with cell death probably because of its ability to modulate intracellular glutathione. hsp27 accumulation during ES cell differentiation was also correlated with an increase in glutathione, which was attenuated by hsp27 down-expression. Hence, hsp27 transient expression seems essential for preventing differentiating ES cells from undergoing apoptosis, a switch that may be redox regulated.

Human proteinase-3 expression is regulated by PU.1 in conjunction with a cytidine-rich element

Human proteinase-3 is one of three serine proteinases present in the azurophil granules of polymorphonuclear leukocytes along with elastase and cathepsin G. Proteinase-3 gene expression is confined to the promyelocytic stage of polymorphonuclear leukocyte maturation. The present investigation identifies elements responsible for this highly controlled tissue- and developmental-specific expression of proteinase-3. Within the first 200 base pairs of the proteinase-3 promoter, two elements were identified as important for expression, these elements at -101 and -190 confer the majority of the activity. The element at -101 has a PU.1 consensus. It binds a myeloid nuclear protein of approximately 45 kDa that "supershifts" with PU.1 antibody and is competed by the CD11b PU.1 element. The element at -190 has a core sequence of CCCCGCCC (CG element). The cytidines but not the guanidine are essential for promoter activity. The CG element binds a second nuclear protein with a molecular mass of approximately 40 kDa that is found in cells of myeloid lineage as well as non-myeloid HeLa cells. However, the proteinase-3 promoter is not active in HeLa cells which suggests that the CG element alone is not sufficient for proteinase-3 gene expression. Maturation of promyelocytic cells results in an inhibition of proteinase-3 gene expression and a reduction in nuclear protein binding to the PU.1 and CG elements. Similar elements occur in the elastase and cathepsin G promoters. Using the elastase and cathepsin G PU.1 and CG-like elements as probes results in identical band-shift patterns to that obtained with proteinase-3 PU.1 and CG elements. These data suggest that there is cooperative interaction between a PU.1 and a CG element with a consensus of CCCCXCCC and that they are important control elements for tissue- and developmental-specific expression of azurophil serine proteinases of polymorphonuclear leukocytes.

Heat-shock protein expression in cisplatin-sensitive and -resistant human tumor cells

It has been suggested that the expression of certain heat-shock proteins (HSPs) may be prognostic markers in several tumor types. Since HSPs may be involved in determining cellular sensitivity to chemotherapeutic drugs, the possible relation between HSP expression and cisplatin (cDDP) sensitivity was studied. Three human germ-cell tumor cell lines, 1 human small-cell lung carcinoma (SCLC) cell line and 3 human colon carcinoma cell lines were used as a model for differences in intrinsic cDDP sensitivity. The constitutive expression of a panel of HSPs was studied by immunoblotting. No correlation was found between expression of HSP90, HSP73, HSP72, HSP60 and HSP27 and the extent of intrinsic cDDP sensitivity when all cell lines studied were considered. However, for the 3 cell lines derived from germ-cell carcinomas, HSP27 expression was inversely related to cDDP sensitivity; ie. decreased HSP27 levels were associated with decreased sensitivity. Constitutive HSP expression was also studied in 2 sets of human cell lines with in vitro acquired cDDP resistance. In both resistant cell lines, decreased expression of HSP27 (as determined by Western blotting) was found as compared to the sensitive parent cell lines. Thus, acquired resistance to cDDP was also accompanied by decreased HSP27 expression. Interestingly, when basal HSP27 mRNA levels were measured in the SCLC cell line (GLC4) and its subline with acquired resistance (GLC4-cDDP), no significant differences were detected. Continuous cDDP incubation increased HSP27 levels and induced HSP27 phosphorylation in GLC4 cells, but not in the resistant subline. Thus, although no general relationships between HSP expression and cDDP sensitivity are apparent, high HSP27 expression in vitro relates to high sensitivity to cDDP treatment in some tumor types. This is in accordance with reported clinical data on high HSP27 levels in tumors correlating with good prognosis.

Recombinant human proteinase 3, the Wegener's autoantigen, expressed in HMC-1 cells is enzymatically active and recognized by c-ANCA

We developed a stable expression system for conformationally intact recombinant human PR3 (rPR3) using the human mast cell line HMC-1. Like in U937 cells, the rPR3 is processed from a 34 kDa precursor to the 29 kDa mature form, primarily as the result of oligosaccharide trimming. The rPR3 binds [3H]DFP and hydrolyzes the substrate N-methoxysuccinyl-Ala-Ala-Pro-Val-pNA. The enzymatic activity is inhibited by greater than 95% by alpha 1-PI. The rPR3 and the enzymatically inactive mutant rPR3-S176A are both packaged in granules. Thus, proteolytic autoprocessing is not required for PR3's targeting to granules. This rPR3 is the first to be recognized by most c-ANCA from WG patients and all anti-PR3 ANCA that were detected by standard anti-PR3 specific ELISA. This expression system for rPR3 represents a versatile tool for the analysis of its intracellular processing, structure-function relationships and interaction with autoantibodies.

Biosynthesis and processing of proteinase 3 in U937 cells. Processing pathways are distinct from those of cathepsin G

Proteinase 3 is a human polymorphonuclear leukocyte serine proteinase that degrades elastin in vitro and causes emphysema when administered by intratracheal insufflation into hamsters. Proteinase 3, stored in the azurophilic granules, is expressed in progenitor cells of myeloid origin. In the present study, the biosynthesis, processing, and intracellular transport of the enzyme was investigated in the human myelomonocytic cell line U937. Proteinase 3 is initially identified as a 35-kDa precursor and converted into the 29-kDa mature form within 3 h. By using a combination of techniques including amino-terminal sequencing, we identified the 35-kDa form as a zymogen containing an activation dipeptide but lacking the amino-terminal 25 residues, presumably the result of cleavage by a signal peptidase. Tunicamycin treatment and alkalinization of acidic cell compartments with NH4Cl did not prevent the processing of the proteinase 3 zymogen into the mature form, suggesting that the enzyme is targeted to the cytoplasmic granules by a mechanism other than the mannose 6-phosphate receptor. Brefeldin A inhibited the zymogen processing, suggesting that the dipeptide cleavage occurred in a post-Golgi organelle. The enzyme responsible for the removal of the dipeptide is a cysteine proteinase since E-64d, a class-specific inhibitor, prevented processing. However, treatment of cells with a dipeptidyl peptidase I inhibitor, Gly-Phe-diazomethyl ketone and with the lysosomotropic agents, NH4Cl and chloroquine, did not prevent dipeptide cleavage, indicating that the processing enzyme for proteinase 3 is not dipeptidyl peptidase I. In contrast, Gly-Phe-diazomethyl ketone inhibited cleavage of the dipeptide from cathepsin G. This indicates that processing of proteinase 3 is distinct from that of cathepsin G. Proteinase 3 is also processed at the COOH-terminal extension. Cleavage takes place next to Arg-222, suggesting that a trypsin-like proteinase is involved in the COOH-terminal processing.