Intracellular distribution of mammalian stress proteins. Effects of cytoskeletal-specific agents

Molecular cloning and characterization of gene encoding for cytoplasmic Hsc70 from Pennisetum glaucum may play a protective role against abiotic stresses

Molecular chaperones (Hsps) have been shown to facilitate protein folding or assembly under various developmental and adverse environmental conditions. The aim of this study was to unravel a possible role of heat-shock proteins in conferring abiotic stress tolerance to plants. We isolated a cDNA encoding a cytoplasmic Hsp70 (PgHsc70) from Pennisetum glaucum by screening heat-stress cDNA library. PgHsc70 cDNA encoding 649 amino acids represents all conserved signature motifs characteristic of Hsp70s. The predicted molecular model of PgHsc70 protein suggests that the N-terminus ATP-binding region is evolutionarily conserved, in comparison to C-terminus peptide-binding domains. A single intron in ATPase domain coding region of PgHsc70 exhibited a high degree of conservation with respect to its position and phasing among other plant Hsp70 genes. Recombinant PgHsc70 protein purified from E. coli possessed in vitro chaperone activity and protected PgHsc70 expressing bacteria from damage caused by heat and salinity stress. Nucleotide sequence analysis of 5' flanking promoter region of PgHsc70 gene revealed a potential heat-shock element (HSE) and other putative stress-responsive transcription factor binding sites. Positive correlation existed between differentially up-regulated PgHsc70 transcript levels and the duration and intensity of different environmental stresses. Molecular and biochemical analyses revealed that PgHsc70 gene was a member of the Hsp70 family and suggested that its origin was from duplication of a common ancestral gene. Transcript induction data, presence of several putative stress-responsive transcription factor-binding sites in the promoter region of PgHsc70 and the presence of a protective in vitro chaperone activity of this protein against damage caused by heat and salinity, when expressed in E. coli, suggest its probable role in conferring abiotic stress tolerance to this plant.

Bioreactor for mammalian cell culture

Purpose of this article is to review the current status of bioreactor design for mammalian cell culture. Morphological and biochemical features of two major mammalian cell groups, anchorage-dependent and independent cells are proposed as a basis for different behavior at their cultivation. Different bioreactor configurations are systematically discussed through enumerating elementary physical phenomena and through stressing their physiological significance. Special considerations are given to those areas which are inherent to mammalian cell bioreactor.

Starvation-induced lysosomal degradation of aldolase B requires glutamine 111 in a signal sequence for chaperone-mediated transport

Aldolase B is an abundant cytosolic protein found in all eukaryotic cells. Like many glycolytic enzymes, this protein was sequestered into lysosomes for degradation during nutrient starvation. We report here that the degradation of recombinant aldolase B was enhanced two-fold when rat and human hepatoma cells were starved for amino acid and serum. In addition, starvation-induced degradation of aldolase B was inhibited by chloroquine, an inhibitor of lysosomal proteinases and by 3-methyladenine, an inhibitor of autophagy. Aldolase B has three lysosomal targeting motifs (Q(12)KKEL, Q(58)FREL, and IKLDQ(111)) that have been proposed to interact with hsc73 thereby initiating its transport into lysosomes. In this study, we have mutated the essential glutamine residues in each of these hsc73-binding motifs in order to evaluate their roles in the lysosomal degradation of aldolase B during starvation. We have found that when glutamines 12 or 58 are mutated to asparagines enhanced degradation of aldolase B proceeded normally. However, when glutamine 111 was mutated to an asparagine or a threonine, starvation-induced degradation was completely suppressed. These mutations did not appear to alter the tertiary structure of aldolase B since enzymatic activity was not affected. Our results suggest that starvation-induced lysosomal degradation of aldolase B requires both autophagy and glutamine 111. We discuss the possible roles for autophagy and hsc73-mediated transport in the lysosomal sequestration of aldolase B.

Intracellular distribution of stress glycoproteins in a heat-resistant cell model expressing human HSP70

Heat stress results in the cellular accumulation of heat-shock proteins (HSP) and increased protein glycosylation. Among known stress glycoproteins, GP50 and GP62 are associated with the expression of thermotolerance. In the present study, we characterized subcellular localization and redistribution of GP62 and GP50 in a rodent cell line, M21, before and after cellular heat-stress. M21 cells are heat-resistant cells that overexpress human HSP70 and also have concomitantly high GP62 levels. Cellular fractionation by differential centrifugation showed that GP62 and GP50 was present in each subcellular fraction. However, each stress glycoprotein exhibited a characteristic kinetic pattern of redistribution during cellular recovery after heat stress. For example, glycosylated GP62 was seen predominantly in the mitochondria before heat-stress. Immediately after heat-stress, its presence in the mitochondrial fraction was dramatically reduced, while it increased in lysosomes, microsomes and cytosol. By 1 h after heat stress, it had largely disappeared from microsomal and cytosolic fractions. After 24 h, all subcellular fractions showed only trace amounts of residual GP62. By comparison, GP50 was also highest in the mitochondrial fraction before heat-stress, redistributed like GP62 immediately after heat stress, but remained relatively unchanged thereafter. In contrast to GP62, GP50 showed little redistribution during 24 h after heat-stress and remained at high concentrations in all cell fractions, including microsomes. Distribution of GP50 and GP62 before and after heat stress, based on differential centrifugation, was consistent with immunolocalization data. Following heat stress, both GP50 and GP62 showed a partial overlap in distribution with HSP70. The above results indicate that each stress glycoprotein has a specific subcellular location, both before and after heat stress. The presence of GP62 in virtually all cell fractions is consistent with a multifunctional role for GP62 in the cellular stress response.

Integrity of intermediate filaments is associated with the development of acquired thermotolerance in 9L rat brain tumor cells

Withangulatin A (WA), a newly discovered withanolide isolated from an antitumor Chinese herb, has been shown to be a vimentin intermediate filament-targeting drug by using immunofluorescence microscopy. Together with cytochalasin D and colchicine, these drugs were employed to investigate the importance of vimentin intermediate filaments, actin filaments, and microtubules in the development of acquired thermotolerance in 9L rat brain tumor cells treated at 45 degrees C for 15 min (priming heat-shock). Acquired thermotolerance was abrogated in cells incubated with WA before the priming heat-shock but it could be detected in cells treated with WA after the priming heat-shock. In contrast, cytochalasin D and colchicine do not interfere with the development of thermotolerance at all. The intracellular localizations of vimentin and the constitutive heat-shock protein70 (HSC70) in treated cells were examined by using immunofluorescence microscopy and detergent-extractability studies. In cells treated with WA before the priming heat-shock, vimentin IFs were tightly aggregated around the nucleus and unable to return to their normal organization after a recovery under normal growing conditions. In contrast, the IF network in cells treated with WA after the priming heat-shock was able to reorganize into filamentous form after a recovery period, a behavior similar to that of the cells treated with heat-shock only. HSC70 was found to be co-localized with vimentin during these changes. It is suggested that the integrity of intermediate filaments is important for the development of thermotolerance and that HSC70 may be involved in this process by stabilizing the intermediate filaments through direct or indirect binding.

Heat-shock proteins maintain the viability of ATP-deprived cells: what is the mechanism?

ATP depletion causes necrosis in mammalian cells. However, a previous heat shock can protect cells from the effects of energy deprivation, probably as a result of the synthesis and accumulation of heat-shock proteins (hsps). We propose that hsps protect ATP-depleted cells from rapid necrotic death by inhibiting the aggregation of cytoskeletal proteins that occurs when ATP synthesis is blocked.

Transient increase in vimentin phosphorylation and vimentin-HSC70 association in 9L rat brain tumor cells experiencing heat-shock

Characteristic changes in vimentin were studied in 9L rat brain tumor cells treated at 45 degrees C. During heat-shock treatment, vimentin molecules were rapidly phosphorylated and reorganized from a filamentous form into a perinuclear higher-order structure that was less extractable by nonionic detergent. These effects were found to be highly transient, peaked at 30 min after the onset of heat-shock treatment, and subsided thereafter. Simultaneously, the solubility of the constitutively expressed heat-shock protein 70 (HSC70) was also temporarily decreased and the kinetics was identical to that of vimentin. The results indicated that HSC70 and vimentin were co-insolubilized during the heat-shock treatment. We propose that the reorganization of the intermediate filaments resulted from enhanced phosphorylation of vimentin leads to the concurrent association of HSC70 to the intermediate filaments. This process may play an essential role in regulating heat-shock genes.

Induction of vimentin modification and vimentin-HSP72 association by withangulatin A in 9L rat brain tumor cells

Withangulatin A induced cell rounding up and the morphological alteration resulted from the reorganization of all of the major cytoskeletal components, i.e., vimentin, tubulin, and actin, as revealed by immunofluorescence techniques. When the withangulatin A-treated cells changed to a round-up morphology, vimentin intermediate filaments were found to be collapsed and clustered around the nucleus. The alteration was accompanied by characteristic changes of vimentin molecules, including augmentation of phosphorylation, retardation of electrophoretic mobility, and decrease in detergent extractability. The levels of vimentin phosphorylation were augmented by 2.5- and 1.8-fold in cells incubated with 50 microM withangulatin A for 1 and 3 h, respectively. The electrophoretic mobility of vimentin was partially retarded in cells treated with withangulatin A for 1 h at 10 microM and a completely upshift mobility was observed after 5 h treatment at 50 microM. In addition, vimentin molecules became less extractable by nonident P-40 after the cells were treated with withangulatin A and this effect was dose dependent. The decrease in solubility of vimentin was accompanied by the redistribution of HSP72 into the detergent nonextractable fraction and these two events were well correlated. Our results suggest that withangulatin A induced the modification of vimentin, which resulted in the alteration of cell morphology and redistribution of intracellular HSP72, an event that may play an important role in the induction of heat-shock response.

Adenovirus capsid proteins interact with HSP70 proteins after penetration in human or rodent cells

Soon after penetration of adenovirus serotype 2 in BHK-21 and HeLa cells, HSP70 and HSC70 proteins become associated with the viral capsid. By analysis with a polyclonal antibody derived from a fusion protein containing the C-terminal domain, 290 amino acids of HSP70, and using both immunological methods and infected cells fractionation we observed that a significant amount of HSP70 proteins moved to the nucleus and colocalized with the adenovirus particles. HSP70 proteins of infected cells were isolated as a complex cross-linked with intracytoplasmic adenovirus type 2. By coprecipitation, using a polyclonal-specific antiserum derived from the fusion protein, or two different monoclonal-specific antisera, we showed that HSP70 and HSC70 proteins were associated with hexon, the major adenovirus capsid protein.

Effects of hyperthermia on microtubule organization and cytolytic activity of murine cytotoxic T lymphocytes

When murine cytotoxic T lymphocytes (CTL) are heated at 42 degrees C for 30 min their ability to lyse their target cells (TC) is severely impaired. When the CTL are allowed to recover at 37 degrees C, a partial recovery of cytolytic activity that peaks within 6 h is observed. A dye exclusion assay demonstrated that such a heat shock does not affect the viability of the CTL and direct microscopic observations established that their ability to bind to TC is not impaired. Therefore, the step or steps inhibited by hyperthermia are subsequent to TC recognition and binding. Kupfer et al. ((1983) Proc. Natl. Acad. Sci. USA 80, 7224-7228) demonstrated that upon binding to an appropriate TC, a rapid orientation of the Golgi apparatus and the microtubule organizing center (MTOC) occurred within the CTL so that the two organelles face the TC. This orientation is a prerequisite for efficient TC lysis. We have shown by immunofluorescence and confocal microscopy, using a monoclonal antibody to tubulin and a rabbit autoimmune serum that binds a centriole-associated protein, that the organization of the MTOC-microtubule array is disrupted by hyperthermia. EM suggests that this disorganization of the microtubules may result from an aggregation of the pericentriolar material. The recovery of cytolytic activity is coincident with the reorganization of the microtubules about the MTOC. These findings suggest that the initial inhibitory effect of hyperthermia on CTL function results from the disruption of microtubule organization.

Axonal transport of two major components of the ubiquitin system: free ubiquitin and ubiquitin carboxyl-terminal hydrolase PGP 9.5

Ubiquitin (Ub), a stress protein thought to target abnormal proteins for degradation, is present in abnormal structures that occur in neuronal perikarya and axons of degenerative diseases including Alzheimer disease. To begin to assess the role of the Ub system in the axon, we studied expression and axonal transport of Ub and other stress proteins, as well as of Ub carboxyl-terminal hydrolase PGP 9.5, in the rat visual system in normal conditions and following heat-shock (HS). In the retina, both the constitutive and inducible forms of HSPs 70 were expressed under normal conditions, while in the superior colliculus the inducible form was detected only following HS. Ub, PGP 9.5 and HSPs 70 were transported in the axon exclusively with the slow component b (SCb), known to carry cytoskeletal and cytoplasmic proteins. The exceedingly long time needed for stress proteins to reach distant axonal locales at the rate of SCb (approximately 3 mm/day) makes it unlikely that they could contribute significantly to the stress response at those sites.

Hypergravity signal transduction in HeLa cells with concomitant phosphorylation of proteins immunoprecipitated with anti-microtubule-associated protein antibodies

We have shown that hypergravity (35g) stimulates production of inositol 1,4,5-trisphosphate (IP3) and decreases adenosine 3',5'-cyclic monophosphate (cAMP) levels in HeLa cells. IP3 production rapidly increased 1.5- and 2.1-fold greater (P less than 0.05) than the control after 2- and 5-min exposures to 35g, respectively. The intracellular cAMP levels, determined in the presence of isobutylmethylxanthine, were decreased by 11% (P less than 0.05) and 16% (P less than 0.01) relative to the control after 10- and 20-min exposures to 35g, respectively. The phosphorylation of proteins which were immunoprecipitated by antibodies recognizing microtubule-associated proteins (ipMAPs) was also apparent after exposure of these cells to hypergravity. In the detergent-insoluble fraction, phosphorylation of a 115-kDa protein was significantly enhanced compared to the control after a 5-min exposure to 35g. In the detergent-soluble fraction, phosphorylation of a 200-kDa protein was observed served after a 20-min exposure to 35g. Our study suggests that IP3 and cAMP may act as second messengers in hypergravity signal transduction. Phosphorylation of ipMAPs in both the detergent-soluble and -insoluble fractions suggests that cytoskeletal structures may be influenced by gravity.

Membrane skeleton-bilayer interaction is not the major determinant of membrane phospholipid asymmetry in human erythrocytes

Transbilayer phospholipid distribution, membrane skeleton dissociation/association, and spectrin structure have been analysed in human erythrocytes after subjecting them to heating at 50 degrees C for 15 min. The membrane skeleton dissociation/association was determined by measuring the Tris-induced dissociation of Triton-insoluble membrane skeletons (Triton shells), the spectrin-actin extractability under low ionic conditions, and the binding of spectrin-actin with normal erythrocyte membrane inside-out vesicles (IOVs). The spectrin structure was ascertained by measuring the spectrin dimer-to-tetramer ratio as well as the spectrin tryptophan fluorescence. Both the Tris-induced Triton shell dissociation and the spectrin-actin extractability under low ionic conditions were considerably reduced by the heat treatment. Also, the binding of heated erythrocyte spectrin-actin to IOVs was significantly smaller than that observed with the normal cell spectrin-actin. Further, the quantity of spectrin dimers was appreciably increased in heat-treated erythrocytes as compared to the normal cells. This change in the spectrin dimer-to-tetramer ratio was accompanied by marked changes in the spectrin tryptophan fluorescence. In spite of these heat-induced alterations in structure and bilayer interactions of the membrane skeleton, the inside-outside glycerophospholipid distribution remained virtually unaffected in the heat-treated cells, as judged by employing bee venom and pancreatic phospholipase A2, fluorescamine and Merocyanine 540 as the external membrane probes. These results strongly indicate that membrane bilayer-skeleton interaction is not the major factor in determining the transbilayer phospholipid asymmetry in human erythrocyte membrane.

A role for a 70-kilodalton heat shock protein in lysosomal degradation of intracellular proteins

A 73-kilodalton (kD) intracellular protein was found to bind to peptide regions that target intracellular proteins for lysosomal degradation in response to serum withdrawal. This protein cross-reacted with a monoclonal antibody raised to a member of the 70-kD heat shock protein (hsp70) family, and sequences of two internal peptides of the 73-kD protein confirm that it is a member of this family. In response to serum withdrawal, the intracellular concentration of the 73-kD protein increased severalfold. In the presence of adenosine 5'-triphosphate (ATP) and MgCl2, the 73-kD protein enhanced protein degradation in two different cell-free assays for lysosomal proteolysis.

Expression of different members of heat shock protein 70 gene family in liver and hepatomas

The levels of expression of some genes of the HSP 70 family have been assessed in rat liver and in a series of transplantable hepatomas with different growth rates, subjected to heat shock in vivo. For this purpose, the mRNAs for the constitutive cognate HSC 73, the heat-inducible HSP 70 and the glucose-regulated GRP 78 have been analyzed by: (i) translation in reticulocyte lysates; (ii) hybrid-selected translation, and (iii) Northern blot analysis. In comparison with the liver, the fast-growing 3924A hepatoma has an increased constitutive amount of HSC 73 mRNA and a lower induction of HSP 70 mRNA after heat shock. The behavior of the 9618A slow-growing hepatoma is more similar to that of the liver, indicating that the changes detected in the fast-growing hepatoma are correlated to the high growth rate of the tumor rather than to carcinogenesis. This conclusion is reinforced by the results obtained with Yoshida AH-130 cells, growing at two different rates imposed by the environment in which they develop. When the Yoshida hepatoma grows rapidly in the peritoneal cavity, constitutive expression of HSC 73 mRNA is high and the inducibility of HSP 70 mRNA is poor: the opposite occurs when the tumor grows slowly in the subcutaneous compartment. The amount of GRP 78 mRNA increases progressively from the liver to the fast-growing hepatoma. The level of HSC 73 mRNA seems to correlate with the methylation state of the corresponding gene.

Selective release from cultured mammalian cells of heat-shock (stress) proteins that resemble glia-axon transfer proteins

Cultured rat embryo cells were stimulated to rapidly release a small group of proteins that included several heat-shock proteins (hsp110, hsp71, hscp73) and nonmuscle actin. The extracellular proteins were analyzed by two-dimensional polyacrylamide gel electrophoresis. Heat-shocked cells released the same set of proteins as control cells with the addition of the stress-inducible hsp110 and hsp71. Release of these proteins was not blocked by either monensin or colchicine, inhibitors of the common secretory pathway. A small amount of the glucose-regulated protein grp78 was externalized by this pathway. The extracellular accumulation of these proteins was inhibited after they were synthesized in the presence of the lysine analogue aminoethyl cysteine. It is likely that the analogue-substituted proteins were misfolded and could not be released from cells, supporting our conclusion that a selective release mechanism is involved. Remarkably, actin and the squid heat-shock proteins homologous to rat hsp71 and hsp110 are also among a select group of proteins transferred from glial cells to the squid giant axon, where they have been implicated in neuronal stress responses (Tytell et al.: Brain Res., 363:161-164, 1986). Based in part on the similarities between these two sets of proteins, we hypothesized that these proteins were released from labile cortical regions of animal cells in response to perturbations of homeostasis in cells as evolutionarily distinct as cultured rat embryo cells and squid glial cells.

Induction of the stress response by isolation of rabbit type II pneumocytes

Protein synthesis by isolated rabbit type II pneumocytes was evaluated by incorporation of labeled amino acids, gel electrophoresis, and fluorography. Type II alveolar epithelial cells preferentially synthesize a small number of proteins immediately following isolation and simultaneously exhibit a depression of all other protein synthesis. Examination of the time course of the appearance and decline of these proteins showed them to be actively synthesized during the first 14 h after isolation. Decline in their production was accompanied by a gradual enhancement in the synthesis of other proteins. Actin synthesis was not measurable 1 h after isolation, but increased to 9% of total label incorporated by 14 h. This recovery was independent of attachment to an extracellular matrix. Treatment with actinomycin D immediately following cell isolation abolished the synthesis of these proteins, suggesting a requirement for active mRNA production. A subset of these proteins are induced by heat treatment of cultured type II cells. The half-life, intracellular localization, isoelectric points, apparent molecular weights, and heat inducibility of this group of proteins are similar to stress proteins found in other mammalian systems. These stress proteins are unique in that their synthesis is induced by the cell isolation process. Possible mechanisms by which cell isolation may induce the stress response are discussed.

Heat transfer analysis of frictional heat dissipation during articulation of femoral implants

Previous studies have shown the tendency for frictional heating to occur during articulation of total hip systems in vitro under simulated hip loading conditions. The magnitude of this heating is sufficient to accelerate wear, creep, and oxidation degradation of the UHMWPE bearing surface. It was shown that ceramic articulating systems generate less frictional heating than polished cobalt alloy against UHMWPE. This frictional heating is expected to occur primarily for younger, heavier, and more active patients. Thus, long-term performance of the articulating hip system in these patients may not be that predicted from current, body-temperature wear, creep, and degradation studies. Although the tendency to generate frictional heat has been observed only during in vitro simulated hip loading, a heat transfer analysis of this phenomenon is presented to evaluate the ability of the hip joint to dissipate such heating in vivo. Additional experiments were performed using controlled resistance heaters inside a cobalt femoral head to verify the calculated levels of frictional heat and to assess the heat dissipation under simulated in vivo conditions. The effect of blood perfusion on the effective thermal conductivity of the joint capsule is also discussed. The present study describes and analyzes the various heat dissipation mechanisms present both in vitro and in vivo during articulation of metal and ceramic hip systems. From these tests and analyses, it is concluded that frictional heating in the reconstructed hip cannot be effectively removed, and that degredative elevated temperature processes can be expected to occur in vivo to both the UHMWPE and adjacent tissue under extended periods of excessive patient activity. This is particularly true for metal cobalt alloy femoral heads articulating on UHMWPE versus ceramic heads which generate significantly lower levels of heat.

Progestin regulation of protein synthesis in endometrial cancer

Protein synthesis in cancerous and normal human endometrium was investigated by the incorporation of [35S]methionine and analysis of products by two-dimensional polyacrylamide gel electrophoresis. Comparison of the cellular products from organ cultures of endometrial carcinoma, obtained from each subject before and after in vivo administration of medroxyprogesterone acetate (MPA) for 10-14 days revealed: (i) a decrease in the synthesis of tubulin and of a protein of molecular weight (mol. wt) 68 kDa, isoelectric point (pI) 6.0, and (ii) an increase in the synthesis of creatine kinase (CK) and of protein of mol. wt 36 kDa, pI 4, following MPA therapy. The 68 kDa protein was expressed at relatively reduced levels in organ cultures of normal human endometrium throughout the menstrual cycle. In primary cultures of normal human endometrium throughout the menstrual cycle. In primary cultures from cancerous endometrium endometrium established for several weeks the 68 kDa protein was not expressed but could be induced by heatshock. Primary cultures were also used to investigate the early events following progesterone stimulation which revealed a decrease in synthesis of a protein mol. wt 36 kDa, pI 8 at 8 h following administration.