Sense and antisense modification of glial alpha B-crystallin production results in alterations of stress fiber formation and thermoresistance

Intermediate filament interactions can be altered by HSP27 and alphaB-crystallin

HSP27 and alphaB-crystallin are both members of the small heat shock protein family. alphaB-crystalllin has been proposed to modulate intermediate filaments and recently a mutation in alphaB-crystallin has been identified as the genetic basis of desmin related myopathy. This disease is characterised in its pathology by aggregates of intermediate filaments associated with alphaB-crystallin. Here we report that HSP27 like alphaB-crystallin is associated with glial fibrillary acidic protein and vimentin intermediate filament networks in unstressed U373MG astrocytoma cells. HSP27 is also associated with keratin filaments in MCF7 cells, indicating that this association is not restricted to a particular intermediate filament type. The association of sHSPs with both the soluble and filamentous intermediate filament fractions of U373 cells was demonstrated biochemically. Heat shock or drug treatments induced a co-collapse of intermediate filaments and associated small heat shock proteins. These data show that the presence of HSP27 or alphaB-crystallin could not prevent filament collapse and suggest that the purpose of this association is more than just filament binding. Indeed, in U373MG cells the intermediate filament association with small heat shock proteins is similar to that observed for another protein chaperone, HSC70. In order to discern the effect of different chaperone classes on intermediate filament network formation and maintenance, several in vitro assays were assessed. Of these, falling ball viscometry revealed a specific activity of small heat shock proteins compared to HSC70 that was apparently inactive in this assay. Intermediate filaments form a gel in the absence of small heat shock proteins. In contrast, inclusion of alphaB-crystallin or HSP27 prevented gel formation but not filament assembly. The transient transfection of GFAP into MCF7 cells was used to show that the induction of a completely separate network of intermediate filaments resulted in the specific association of the endogenous HSP27 with these new GFAP filaments. These data lead us to propose that one of the major functions of the association of small heat shock proteins with intermediate filaments is to help manage the interactions that occur between filaments in their cellular networks. This is achieved by protecting filaments against those non-covalent interactions that result when they come into very close proximity as seen from the viscosity experiments and which have the potential to induce intermediate filament aggregation as seen in some disease pathologies.

Accumulation of class I mutant p53 and apoptosis induced by carboplatin in a human glioma cell line

Following DNA damage, wild-type p53 increases and mediates the multiple cellular responses for the repair of DNA damage or apoptosis. Inactivation of p53 by single-amino-acid substitutions contributes to the malignant phenotype and confers resistance to therapy. Among tumor-derived p53 mutants, class I mutants still retain a native-like three-dimensional structure, whereas class II mutants have unfolded DNA-binding domains. Sequencing analysis demonstrated that a human glioma cell line (U-373MG) had only a class I mutant form of p53 of His273, which targets an Arg273 that contacts DNA but retains the native structure. In this study, we investigated the metabolic alteration of the class I mutant p53 in apoptosis of U-373MG. The cell cycle progression of U-373MG cells was affected by the addition of carboplatin, while the amount of mutant p53 also increased in their nuclei. The treated cells underwent apoptosis 48h after exposure to 50 microg/ml carboplatin. Although the exact mechanism of the class I mutant p53 in the process of apoptosis has not yet been clarified, the fact that accumulation of the activated mutant p53 in the nucleus of U-373MG is concomitant with apoptosis, just as wild-type p53 does, implies that the class I mutant p53 might retain the ability to participate in apoptosis.

Formation of GFAP cytoplasmic inclusions in astrocytes and their disaggregation by alphaB-crystallin

In several neuropathological conditions, alphaB-crystallin and glial fibrillary acidic protein (GFAP) accumulate and form cytoplasmic inclusions in astrocytes. To explore the pathogenesis of the inclusions and the possible functions of the accumulated alphaB-crystallin, GFAP and alphaB-crystallin were overexpressed in cultured astrocytes by transient transfection. Human GFAP formed filamentous, cytoplasmic inclusions in mouse astrocytes, NIH3T3 cells, rat C6 glioma cells, and human U251 glioma cells. These human GFAP inclusions did not contain the endogenous vimentin or beta-tubulin, and the intermediate filament and microtubular networks of the transfected cells appeared normal. alphaB-crystallin and hsp25 were associated with the GFAP inclusions. Increasing intracellular alphaB-crystallin levels using recombinant adenoviruses, either before or after GFAP inclusions were formed, decreased the number of inclusion-bearing astrocytes and converted the human GFAP from an inclusion to a spread, filamentous form. These results suggest that alphaB-crystallin reorganizes abnormal intermediate filament aggregates into the normal filamentous network.

Rat Hsp20 confers thermoresistance in a clonal survival assay, but fails to protect coexpressed luciferase in Chinese hamster ovary cells

Hsp20 is a mammalian small heat shock protein with some deviating in vitro characteristics. We now compare the in vivo cellular thermoprotective abilities of Hsp20 with those of its direct relative, alphaB-crystallin. In a clonal survival assay Chinese hamster ovary (CHO) cells stably overexpressing Hsp20 survive equally well as alphaB-crystallin-expressing cells, after a heat shock. In a transient assay, however, overexpression of Hsp20 did not result in an enhanced recovery of coexpressed firefly luciferase after heat shock, in contrast to alphaB-crystallin. This might indicate that these highly homologous stress proteins are involved in at least partially distinct protective activities in cultured cells.

Effect of mutations of murine lens alphaB crystallin on transfected neural cell viability and cellular translocation in response to stress

We examined the influence of over-expressed native and mutant murine lens alphaB crystallin on the response of a murine neural cell line to heat and ionic strength shock. Native and mutant (F27R and KK174/175LL) murine alphaB crystallin amplicons were subcloned into a Lac-Switch IPTG-inducible RSV promoter eukaryotic vector, and transfected into N1E-115 cells using lipofectin. Expression was induced maximally 8 h after addition of IPTG (optimal final concentration 1 mM) to the medium. Cells grew normally after transfection with native and mutant murine alphaB crystallin. We demonstrated expression of the protein using specific anti-alpha crystallin antibodies. Viability under severe heat and ionic strength stress increased when cells had been transfected with native alphaB crystallin, but not with mutants F27R or KK174/175LL. Heat shock caused translocation of both native and mutant alphaB crystallins into the central region of the cells. These results show that mutations in alphaB crystallin that effect its chaperone-like activity may also influence viability of N1E-115 neural cells under stress, while not influencing the distribution of the protein within the cell.

MKBP, a novel member of the small heat shock protein family, binds and activates the myotonic dystrophy protein kinase

Muscle cells are frequently subjected to severe conditions caused by heat, oxidative, and mechanical stresses. The small heat shock proteins (sHSPs) such as alphaB-crystallin and HSP27, which are highly expressed in muscle cells, have been suggested to play roles in maintaining myofibrillar integrity against such stresses. Here, we identified a novel member of the sHSP family that associates specifically with myotonic dystrophy protein kinase (DMPK). This DMPK-binding protein, MKBP, shows a unique nature compared with other known sHSPs: (a) In muscle cytosol, MKBP exists as an oligomeric complex separate from the complex formed by alphaB-crystallin and HSP27. (b) The expression of MKBP is not induced by heat shock, although it shows the characteristic early response of redistribution to the insoluble fraction like other sHSPs. Immunohistochemical analysis of skeletal muscle cells shows that MKBP localizes to the cross sections of individual myofibrils at the Z-membrane as well as the neuromuscular junction, where DMPK has been suggested to be concentrated. In vitro, MKBP enhances the kinase activity of DMPK and protects it from heat-induced inactivation. These results suggest that MKBP constitutes a novel stress-responsive system independent of other known sHSPs in muscle cells and that DMPK may be involved in this system by being activated by MKBP. Importantly, since the amount of MKBP protein, but not that of other sHSP family member proteins, is selectively upregulated in skeletal muscle from DM patients, an interaction between DMPK and MKBP may be involved in the pathogenesis of DM.

Alpha B-crystallin is associated with intermediate filaments in astrocytoma cells

Alpha B-crystallin, a major protein of the vertebrate lens and a member of the small heat shock protein family, is expressed in non-lenticular tissues, including the central nervous system, where it is found mainly in glia. In Rosenthal fibers (RF), astrocytic inclusions that accumulate in Alexander's Disease, alpha B-crystallin is found with hsp27 and skeins of intermediate filaments (IF) of the GFAP and vimentin types. We have investigated the association between IF and alpha B-crystallin in a human astrocytoma cell line, U-373MG, which expresses alpha B-crystallin. Cytoskeletal preparations contained alpha B-crystallin, and a filamentous pattern in which alpha B-crystallin co-localized with GFAP and vimentin by double label immunofluorescence. Immuno-electronmicroscopy confirmed the localization to IF. GFAP isolated from bovine brain and re-assembled, was associated with alpha B-crystallin. Thus, a proportion of alpha B-crystallin in astroglia is associated with IF, and this association may be critical in the formation of RF.

alpha B-crystallin and hsp25 in neonatal cardiac cells--differences in cellular localization under stress conditions

Two members of the small heat shock protein family, alpha B-crystallin and hsp25, occur at high levels in the mammalian heart. To try and understand any differences in functioning, we compared their properties in cultured rat neonatal cardiac myocytes. Both proteins are stress-inducible, but the level of hsp25 is only slightly increased in cultured cardiac myocytes subjected to hyperthermic stress, while alpha B-crystallin levels even remain unchanged. Phosphorylation of alpha B-crystallin and to a lesser extent also of hsp25 is induced after the heat shock. Directly after heat stress, alpha B-crystallin and hsp25 are partly found in detergent-insoluble fractions, representing cytoskeletal/nuclear structures. Additionally, we show by confocal laser scanning microscopy that alpha B-crystallin and hsp25 become associated with sarcomeric structures directly after the heat shock, indicating a cytoskeletal protective function. Four to six hours after the heat shock, both proteins reoccupy their original positions in the cytoplasm again. In contrast to alpha B-crystallin, hsp25 not only translocates to the cytoskeleton but also migrates to positions inside the nucleus. Despite the fact that both proteins are normally part of the same complex, their behavior in neonatal cardiac myocytes appears to be very different. The sarcomeric association of alpha B-crystallin occurs under milder conditions and persists for a longer period of time in comparison with hsp25. Our findings suggest that alpha B-crystallin and hsp25 are both involved in protection of the cytoskeleton during stress situations in the heart, although in different manners. In addition, hsp25 also plays a role inside the nucleus.

Small heat shock proteins and protection against ischemic injury in cardiac myocytes

BACKGROUND

Overexpression of the inducible hsp70 protects against ischemic cardiac damage. However, it is unclear whether the small heat shock proteins hsp27 and alphaB-crystallin protect against ischemic injury.

METHODS AND RESULTS

Our aim was to examine whether the overexpression of hsp27 and alphaB-crystallin in neonatal and adult rat cardiomyocytes would protect against ischemic injury. Recombinant adenovirus expressing hsp27 or alphaB-crystallin under the control of the cytomegalovirus promoter was used to infect cardiac myocytes at high efficiency as assessed by immunostaining. Overexpression was confirmed by Western blot analysis. Cardiomyocytes were subjected to simulated ischemic stress, and survival was estimated through assessment of lactate dehydrogenase and creatine phosphokinase release. The hsp27 overexpression decreased lactate dehydrogenase release by 45+/-7.5% in adult cardiomyocytes but had no effect in the neonatal cells. In contrast, alphaB-crystallin overexpression was associated with a decrease in cytosolic enzyme release in both adult (29+/-6.6%) and neonatal (32+/-5.4%) cardiomyocytes. Decreased endogenous hsp25 with an antisense adenovirus produced a 29+/-9.9% increase in damage with simulated ischemia. Overexpression of the inducible hsp70 in adult cardiomyocytes was associated with a 34+/-4.6% decrease in lactate dehydrogenase release and is in line with our previous results in neonatal cardiomyocytes.

CONCLUSIONS

The increased expression of hsp27 and alphaB-crystallin through an adenovirus vector system protects against ischemic injury in adult cardiomyocytes. Likewise, the overexpression of alphaB-crystallin protects against ischemic damage in neonatal cardiomyocytes. Decreasing the high levels of endogenous hsp25 present in neonatal cardiomyocytes renders them more susceptible to damage caused by simulated ischemia.

Expression of molecular chaperones and vesicle transport proteins in differentiating oligodendrocytes

The major stages of oligodendrocyte differentiation are defined by the presence or absence of certain myelin-specific proteins. Events leading to the successful processing of these proteins, such as the folding, assembly, and trafficking of these proteins through the biosynthetic pathway, are largely undefined. In the present study, we have examined both cultured primary oligodendrocytes and immortalized oligodendrocyte cell lines for the presence of molecular chaperones and/or vesicle transport proteins. We find that a select set of these proteins are expressed relatively early in oligodendrocyte differentiation, whereas a characteristically different set of proteins are expressed at later stages of oligodendrocyte differentiation. In other systems, these proteins participate in the folding and assembly of protein complexes, in the prevention of protein aggregation, as well as the trafficking of proteins via vesicles to specific subcellular destinations including the plasma membrane. Some of the chaperones and/or vesicle transport proteins investigated in this study may play a pivotal role in the certain aspect of myelin biogenesis.

Subunit exchange of alphaA-crystallin

alpha-Crystallin, the major protein in the mammalian lens, is a molecular chaperone that can bind denaturing proteins and prevent their aggregation. Like other structurally related small heat shock proteins, each alpha-crystallin molecule is composed of an average of 40 subunits that can undergo extensive reorganization. In this study we used fluorescence resonance energy transfer to monitor the rapid exchange of recombinant alpha-crystallin subunits. We labeled alphaA-crystallin with stilbene iodoacetamide (4-acetamido-4'-((iodoacetyl)amino)stilbene-2,2'-disulfonic acid), which serves as an energy donor and with lucifer yellow iodoacetamide, which serves as an energy acceptor. Upon mixing the two populations of labeled alphaA-crystallin, we observed a reversible, time-dependent decrease in stilbene iodoacetamide emission intensity and a concomitant increase in lucifer yellow iodoacetamide fluorescence. This result is indicative of an exchange reaction that brings the fluorescent alphaA-crystallin subunits close to each other. We further showed that the exchange reaction is strongly dependent on temperature, with a rate constant of 0.075 min-1 at 37 degrees C and an activation energy of 60 kcal/mol. The subunit exchange is independent of pH and calcium concentration but decreases at low and high ionic strength, suggesting the involvement of both ionic and hydrophobic interactions. It is also markedly reduced by the binding of large denatured proteins. The degree of inhibition is directly proportional to the molecular mass and the amount of bound polypeptide, suggesting an interaction of several alphaA-crystallin subunits with multiple binding sites of the denaturing protein. Our findings reveal a dynamic organization of alphaA-crystallin subunits, which may be a key factor in preventing protein aggregation during denaturation.

Abundance and location of the small heat shock proteins HSP25 and alphaB-crystallin in rat and human heart

BACKGROUND

In the heart, there are high constitutive levels of the two related small heat shock proteins, HSP25 and alphaB-crystallin. To gain insight into their functional role, we have analyzed abundance and location of both proteins in rat and human hearts at different stages of development and in diseased state.

METHODS AND RESULTS

Immunoblotting analysis of rat ventricular tissue at fetal, neonatal, and adult stages reveals the level of HSP25 to decline strongly during development, whereas the level of alphaB-crystallin remains nearly constant. In parallel, the portion of phosphorylated isoforms of HSP25 decreases as shown by two-dimensional polyacrylamide gel electrophoresis. HSP25 is detected in cardiomyocytes and endothelial and vascular smooth muscle cells, whereas alphaB-crystallin is detected in cardiomyocytes only by immunofluorescence and immunoelectron microscopy. Both proteins colocalize in the I-band and M-line region of myofibrils in cardiomyocytes. In diseased and transplanted adult human hearts, HSP25 and alphaB-crystallin levels are considerably elevated compared with fetal hearts. In failing adult human hearts, phosphorylated isoforms of HSP25 predominate, and cardiomyocytes with a partial dislocation of HSP25 and alphaB-crystallin are observed.

CONCLUSIONS

Differential accumulation and location of HSP25 and alphaB-crystallin in heart tissue during development imply distinct functions of both proteins, which seem to be involved in organization of cytoskeletal structures. As judged by level, phosphorylation state, and location of both small heat shock proteins, diseased adult human hearts share features with fetal hearts.

alpha-crystallin stabilizes actin filaments and prevents cytochalasin-induced depolymerization in a phosphorylation-dependent manner

alpha-crystallin, a major lens protein of approximately 800 kDa with subunits of about 20 kDa has previously been shown to act as a chaperone protecting other proteins from stress-induced damage and to share sequence similarity with small heat-shock proteins, sHsp. It is now demonstrated that this chaperone effect extends to protection of the intracellular matrix component actin. It was found that the powerful depolymerization effect of cytochalasin D could be almost completely blocked by alpha-crystallin, alpha A-crystallin or alpha B-crystallin. However, phosphorylation of alpha-crystallin markedly decreased its protective effect. It is suggested that phosphorylation of alpha-crystallin may contribute to changes in actin structure observed during cellular remodeling that occurs with the terminal differentiation of a lens epithelial cell to a fiber cell and contributes to cellular remodeling in other cell types that contain alpha-crystallin species. This communication presents biochemical evidence clearly demonstrating that alpha-crystallin is involved in actin polymerization-depolymerization dynamics. It is also shown that alpha-crystallin prevented heat-induced aggregation of actin filaments. alpha-crystallin was found to stabilize actin polymers decreasing dilution-induced depolymerization rates up to twofold while slightly decreasing the critical concentration from 0.23 microM to 0.18 microM. Similar results were found with either alpha-crystallin or its purified subunits alpha A-crystallin and alpha B-crystallin. In contrast to the experiments with cytochalasin D, phosphorylation had no effect. There does not appear to be an interaction between alpha-crystallin and actin monomers since the effect of alpha-crystallin in enhancing actin polymerization does not become apparent until some polymerization has occurred. Examination of the stoichiometry of the alpha-crystallin effect indicates that 2-3 alpha-crystallin monomers/actin monomer give maximum actin polymer stabilization.

Effects of site-directed mutations on the chaperone-like activity of alphaB-crystallin

Recombinant alphaB-crystallin has been shown to exhibit chaperone-like activity, suppressing the thermal aggregation of gamma-crystallin and aggregation of the reduced insulin B chain conferring thermotolerance to Escherichia coli BL21(DE3) cells. Mutations were made in three specific areas of the alphaB-crystallin, the N terminus D2G, the conserved phenylalanine-rich region, F24R, F27R, F27A, and the two C-terminal lysines K174L/K175L, K174G/K175G. Biophysical characterization of the mutant alphaB-crystallins using far-UV CD revealed no change in secondary structural elements. Tryptophan fluorescence demonstrated global structural changes. Heat stability of the mutant alphaB-crystallins was not significantly affected as indicated by tryptophan fluorescence of heat-treated proteins. Mutations within the phenylalanine-rich region abolish the chaperone-like activity as measured by both in vivo and in vitro assays. Proteins with mutations at the C terminus demonstrated no significant chaperone-like activity, failing to confer thermotolerance on E. coli and demonstrating no significant inhibition of protein aggregation in either gamma-crystallin or reduced insulin B chain assays. The N-terminal mutation D2G demonstrated a significant reduction in efficiency of the chaperone-like activity although some thermotolerance was conferred in the E. coli assay. In vitro assays showed that complete inhibition of aggregation was only achieved at 10-fold higher concentrations of D2G than that required by the native alphaB-crystallin. Consistent changes in the chaperone-like activity of the site-directed mutants were demonstrated by the three assays. The results suggested that both charge-charge and hydrophobic interactions are important in protein binding by alphaB-crystallin and that the conserved RLFDQFF region is vital for chaperone-like activity.

Growth and differentiation of C2 myogenic cells are dependent on serum response factor

In order to study to what extent and at which stage serum response factor (SRF) is indispensable for myogenesis, we stably transfected C2 myogenic cells with, successively, a glucocorticoid receptor expression vector and a construct allowing for the expression of an SRF antisense RNA under the direction of the mouse mammary tumor virus long terminal repeat. In the clones obtained, SRF synthesis is reversibly down-regulated by induction of SRF antisense RNA expression by dexamethasone, whose effect is antagonized by the anti-hormone RU486. Two kinds of proliferation and differentiation patterns have been obtained in the resulting clones. Some clones with a high level of constitutive SRF antisense RNA expression are unable to differentiate into myotubes; their growth can be blocked by further induction of SRF antisense RNA expression by dexamethasone. Other clones are able to differentiate and are able to synthesize SRF, MyoD, myogenin, and myosin heavy chain at confluency. When SRF antisense RNA expression is induced in proliferating myoblasts by dexamethasone treatment, cell growth is blocked and cyclin A concentration drops. When SRF antisense RNA synthesis is induced in arrested confluent myoblasts cultured in a differentiation medium, cell fusion is blocked and synthesis of not only SRF but also MyoD, myogenin, and myosin heavy chain is inhibited. Our results show, therefore, that SRF synthesis is indispensable for both myoblast proliferation and myogenic differentiation.

Transcription regulation of alpha B-crystallin in astrocytes: analysis of HSF and AP1 activation by different types of physiological stress

The coordinated cellular responses to physiological stress are known to be effected in part by the activation of heat-shock factor 1, a transcriptional activator protein capable of binding to, and inducing transcription from genes containing heat shock elements. Other stress responsive signal transduction pathways also exist including the stress activated protein kinase cascade that regulates the activity of the transcription factor AP1. We have examined the expression of the low molecular stress proteins, heat shock protein 27 and alpha B-crystallin in astrocytes in response to physiological stress of different types and asked what component of this induction is effected at the transcriptional level and whether activation of heat shock factor 1 and AP1 might account for these events. We have found that stress regulated induction of alpha B-crystallin has a strong transcriptional component and that it may be effected by at least two different transcriptional mechanisms. In one set of phenomena, represented here by cadmium exposure, alpha B-crystallin and heat shock protein 27 are coordinately regulated and this occurs in the presence of activated heat shock factor 1. In the second series of phenomena, represented here by hypertonic stress, alpha B-crystallin is induced in the absence of heat shock factor activation and in the absence of any corresponding change in heat shock protein 27 expression. Although hypertonic stress does activate an AP1-like binding activity, the AP1 consensus binding site in the alpha B-crystallin promoter does not appear to be a target for this hypertonic stress inducible activity. These data suggest that the hypertonic stress response is effected through a heat shock factor independent mechanism and that hypertonic stress regulated induction of alpha B-crystallin does not directly depend on the SAPK pathway and AP1 activity.

Distinctive immunohistochemical profiles of small heat shock proteins (heat shock protein 27 and alpha B-crystallin) in human brain tumors

BACKGROUND

Recent studies have described alpha B-crystallin as a member of the small heat shock protein (HSP) family, and the expressions of alpha-crystallin-related small heat shock proteins, namely HSP27 and alpha B-crystallin, in the brain appear to be regulated in a similar way by various stress conditions.

METHODS

A comparative immunohistochemical analysis was performed on 198 human brain tumors to examine the expressions of HSP27 and alpha B-crystallin.

RESULTS

Positive staining with HSP27 was frequently observed in schwannomas, craniopharyngiomas, epidermoid cysts, and metastatic tumors to the brain. The immunopositivity of HSP27 was relatively low in tumors originating from neuroepithelium as well as in meningiomas; however, a statistically significantly higher percentage of HSP27-positive cells was noted in their anaplastic counterparts, such as glioblastomas, anaplastic oligodendrogliomas, anaplastic ependymomas, and anaplastic meningiomas (P < 0.005). Conversely, a positive immunoexpression of alpha B-crystallin was frequently observed among astrocytic tumors, schwannomas, hemangioblastomas, and chordomas.

CONCLUSIONS

The immunohistochemical expression of HSP27 and alpha B-crystallin differed among histologic types of tumors. Furthermore, the immunopositivity of HSP27, which was considered to play a role not only in drug resistance but also in the regulation of cell proliferation, increased in proportion to the anaplasia of the tumors.

Neurodegeneration in the limbic and paralimbic system in progressive supranuclear palsy

Progressive supranuclear palsy is neuropathologically characterized by neuronal degeneration of the basal ganglia, brain stem, and cerebellum. In addition, cortical neuronal degeneration associated with neurofibrillary tangles formation has been identified over wide areas of the brain in patients with progressive supranuclear palsy. We studied the distribution of alpha B-crystallin-positive degenerating neurons in cases with progressive supranuclear palsy, and compared them with those in Pick's disease. Alzheimer's disease, senile dementia of Alzheimer type, and normal aged individuals. A large number of alpha B-crystallin-positive neurons was found in the cerebral cortices of four out of nine patients with progressive supranuclear palsy. In particular, alpha B-crystallin-positive ballooned neurons were frequently observed in deep cortical pyramidal cell layers of the limbic and paralimbic systems in these diseases. The involvement of the limbic and paralimbic systems may thus contribute to personality changes as well as to memory and cognitive impairment in some patients with progressive supranuclear palsy.

Alpha B-crystallin in C6 glioma cells supports their survival in elevated extracellular K+: the implication of a protective role of alpha B-crystallin accumulation in reactive glia

It has been shown by immunohistochemical studies that alpha B-crystallin accumulates in the reactive and neoplastic glial cells in a variety of pathologic situations. However, the molecular mechanism for the induction of alpha B-crystallin in diseased brains is still unknown. Since any destructive brain lesions cause an abnormal elevation in the potassium (K+) concentration of the extracellular space, which disturbs the regulatory mechanism of glial cell volume, we investigated the influence of elevated extracellular K+ on the expression of alpha B-crystallin in glial cells. The treatment of rat C6 glioma cells with augmented K+ in the culture media induced an accumulation of alpha B-crystallin mRNA in a dose-dependent manner and an accumulation of the alpha B-crystallin as well. Furthermore, an overexpression of alpha B-crystallin in the C6 transformant transfected with a rat alpha B-crystallin cDNA conferred a resistant phenotype against the insult of elevated extracellular K+ on the glioma cells. Thus, alpha B-crystallin may contribute to the survival of reactive glia in the presence of a high extracellular K+ concentration.

Alteration of collagen-dependent adhesion, motility, and morphogenesis by the expression of antisense alpha 2 integrin mRNA in mammary cells

Although integrins are known to mediate adhesive binding of cells to the extracellular matrix, their role in mediating cellular growth, morphology, and differentiation is less clear. To determine more directly the role of the alpha 2 beta 1 integrin, a collagen and laminin receptor, in mediating the collagen-dependent differentiation of mammary cells, we reduced expression of the integrin by the well differentiated human breast carcinoma cell line, T47D, by stably expressing alpha 2 integrin antisense mRNA. Flow cytometry demonstrated that the antisense-expressing clones had levels of alpha 2 beta 1 integrin on their surfaces that were decreased by 30–70%. Adhesion of antisense-expressing clones to both collagens I and IV was decreased relative to controls in a manner that correlated with the level of cell surface alpha 2 beta 1 integrin expression. Adhesion to fibronectin and laminin were not affected. Motility across collagen-coated filters in haptotaxis assays was increased for only those clones that exhibited intermediate levels of adhesion to collagen, suggesting that an intermediate density of cell-surface alpha 2 beta 1 integrin optimally supports cell motility. When cultured in three-dimensional collagen gels, T47D cells organized in a manner suggestive of a glandular epithelium. In contrast, antisense-expressing clones with decreased alpha 2 beta 1 integrin were not able to organize in three-dimensional collagen gels. The growth rate of T47D cells was reduced when the cells were cultured in three-dimensional collagen gels. Unlike adhesion, motility, and morphogenesis, growth rates were unaffected by reduction of alpha 2 beta 1 integrin expression. Our results suggest that adhesive interactions mediated by a critical level of surface alpha 2 beta 1 integrin expression are key determinants of the collagen-dependent morphogenetic capacity of mammary epithelial cells.

Modulation of cellular thermoresistance and actin filament stability accompanies phosphorylation-induced changes in the oligomeric structure of heat shock protein 27

Phosphorylation of heat shock protein 27 (HSP27) can modulate actin filament dynamics in response to growth factors. During heat shock, HSP27 is phosphorylated at the same sites and by the same protein kinase as during mitogenic stimulation. This suggests that the same function of the protein may be activated during growth factor stimulation and the stress response. To determine the role of HSP27 phosphorylation in the heat shock response, several stable Chinese hamster cell lines that constitutively express various levels of the wild-type HSP27 (HU27 cells) or a nonphosphorylatable form of human HSP27 (HU27pm3 cells) were developed. In contrast to HU27 cells, which showed increased survival after heat shock, HU27pm3 cells showed only slightly enhanced survival. Evidence is presented that stabilization of microfilaments is a major target of the protective function of HSP27. In the HU27pm3 cells, the microfilaments were thermosensitized compared with those in the control cells, whereas wild-type HSP27 caused an increased stability of these structures in HU27 cells. HU27 but not HU27pm3 cells were highly resistant to cytochalasin D treatment compared with control cells. Moreover, in cells treated with cytochalasin D, wild-type HSP27 but not the phosphorylated form of HSP27 accelerated the reappearance of actin filaments. The mutations in human HSP27 had no effect on heat shock-induced change in solubility and cellular localization of the protein, indicating that phosphorylation was not involved in these processes. However, induction of HSP27 phosphorylation by stressing agents or mitogens caused a reduction in the multimeric size of the wild-type protein, an effect which was not observed with the mutant protein. We propose that early during stress, phosphorylation-induced conformational changes in the HSP27 oligomers regulate the activity of the protein at the level of microfilament dynamics, resulting in both enhanced stability and accelerated recovery of the filaments. The level of protection provided by HSP27 during heat shock may thus represent the contribution of better maintenance of actin filament integrity to overall cell survival.