Effect of continuous heat stress on cell growth and protein synthesis in Aedes albopictus

Aedes albopictus (clone C6/36) cells, which normally grow at 28 degrees C, were maintained at a supraoptimal temperature of 37 degrees C. The effect of continuous heat stress (37 degrees C) on cell growth was analyzed as were the modifications occurring with protein synthesis during short- and long-term heat stress. We observed that cells in lag or exponential growth phase, present inhibition of cell growth, and cells in the lag phase showed more sensitivity to death than cells growing exponentially. During the first hour of exposing the cells to 37 degrees C, they synthesized two heat shock proteins (hsps) of 82 kd and 70 kd, respectively, concomitant with inhibition of normally produced proteins at control temperature (28 degrees C). However, for incubations longer than 2 hr at 37 degrees C, a shift to the normal pattern of protein synthesis occurred. During these transitions, two other hsps of 76 kd and 90 kd were synthesized. Pulse chase experiments showed that the 70-kd hsp is stable at least for 18 hr, when the cells are returned to 28 degrees C. However, if cells were incubated at 37 degrees C, the 70-kd hsp is stable for at least 48 hr. The 70-kd hsp was localized in the cytoplasmic and in the nuclear compartment. Our results indicate a possible role of hsp 70-kd protein in the regulation of cell proliferation.     

Effects of cycloheximide on thermotolerance expression, heat shock protein synthesis, and heat shock protein mRNA accumulation in rat fibroblasts.

A single hyperthermic exposure can render cells transiently resistant to subsequent high temperature stresses. Treatment of rat embryonic fibroblasts with cycloheximide for 6 h after a 20-min interval at 45 degrees C inhibits protein synthesis, including heat shock protein (hsp) synthesis, and results in an accumulation of hsp 70 mRNA, but has no effect on subsequent survival responses to 45 degrees C hyperthermia. hsp 70 mRNA levels decreased within 1 h after removal of cycloheximide but then appeared to stabilize during the next 2 h (3 h after drug removal and 9 h after heat shock). hsp 70 mRNA accumulation could be further increased by a second heat shock at 45 degrees C for 20 min 6 h after the first hyperthermic exposure in cycloheximide-treated cells. Both normal protein and hsp synthesis appeared increased during the 6-h interval after hyperthermia in cultures which received two exposures to 45 degrees C for 20 min compared with those which received only one treatment. No increased hsp synthesis was observed in cultures treated with cycloheximide, even though hsp 70 mRNA levels appeared elevated. These data indicate that, although heat shock induces the accumulation of hsp 70 mRNA in both normal and thermotolerant cells, neither general protein synthesis nor hsp synthesis is required during the interval between two hyperthermic stresses for Rat-1 cells to express either thermotolerance (survival resistance) or resistance to heat shock-induced inhibition of protein synthesis.     

Heat induced expression of CD95 and its correlation with the activation of apoptosis upon heat shock in rat histiocytic tumor cells

The heat shock response is a universal phenomenon and is among the most highly conserved cellular responses. However, BC-8, a rat histiocytoma, fails to mount a heat shock response unlike all other eukaryotic cells. In the absence of induction of heat shock proteins, apoptotic cell death is activated in BC-8 tumor cells upon heat shock. We demonstrate here that stable transformants of BC-8 tumor cells transfected with hsp70 cDNA constitutively express hsp70 protein and are transiently protected from heat induced apoptosis for 6-8 h. In addition heat stress induces CD95 gene expression in these tumor cells. There is a delay in CD95 expression in hsp70 transfected cells suggesting a correlation between the cell surface expression of CD95 and the time of induction of apoptosis in this tumor cell line. Also expression of CD95 antigen appears to inhibit the interaction between heat shock factors and heat shock elements in these cells resulting in the lack of heat shock response.     

Effect of Sindbis virus infection on induction of heat shock proteins in Aedes albopictus cells.

When Aedes albopictus cells (clone C7) were infected with Sindbis virus, the production of cytopathic effect CPE depended largely on the conditions under which the cells were cultured. We observed marked inhibition of cellular RNA and protein synthesis, as well as a loss of the ability to induce heat shock proteins, e.g., hsp70, under conditions which led to cytopathic effect. Infected cells in which heat shock proteins could no longer be induced contained much lower amounts of hsp70 mRNA after heat shock than did mock-infected cells which were similarly treated. It is suggested that this decreased level of hsp70 mRNA is due to a failure of these cells to synthesize hsp70 mRNA after heat shock.     

Immunological evidence for the association of p53 with a heat shock protein, hsc70, in p53-plus-ras-transformed cell lines.

A rabbit antiserum was prepared against the C-terminal peptide of 21 amino acids from the human heat shock protein hsp70. These antibodies were shown to be specific for this highly inducible heat shock protein (72 kilodaltons [kDa] in rat cells), and for a moderately inducible, constitutively expressed heat shock protein, hsc70 (74 kDa). In six independently derived rat cell lines transformed by a murine cDNA-genomic hybrid clone of p53 plus an activated Ha-ras gene, elevated levels of p53 were detected by immunoprecipitation by using murine-specific anti-p53 monoclonal antibodies. In all cases, the hsc70, but not the hsp70, protein was coimmunoprecipitated with the murine p53 protein. Similarly, antiserum to heat shock protein coimmunoprecipitated p53. Western blot (immunoblot) analysis demonstrated that the hsc70 and p53 proteins did not share detectable antigenic epitopes. The results provide clear immunological evidence for the specific association of a single heat shock protein, hsc70, with p53 in p53-plus-ras-transformed cell lines. A p53 cDNA clone, p11-4, failed to produce clonable cell lines from foci of primary rat cells transfected with p11-4 plus Ha-ras. A mutant p53 cDNA clone derived from p11-4, SVKH215, yielded a 2- to 35-fold increase in the number of foci produced after transfection of rat cells with SVKH215 plus Ha-ras. When cloned, 87.5% of these foci produced transformed cell lines. SVKH215 encodes a mutant p53 protein that binds preferentially to the heat shock proteins of 70 kDa compared with binding by the parental p11-4 p53 gene product. These data suggest that the p53-hsc70 protein complex could have functional significance in these transformed cells.     

Two developmental stages of Neurospora crassa utilize similar mechanisms for responding to heat shock but contrasting mechanisms for recovery.

At the heat shock temperature of 45 degrees C, there is a transient induction of the synthesis of heat shock proteins and repression of normal protein synthesis in cells of Neurospora crassa. Both conidiospores and mycelial cells resume normal protein synthesis after 60 min at high temperature. At the RNA level, however, these two developmental stages responded with different kinetics to elevated temperature. Heat shock RNAs (for hsp30 and hsp83) accumulated and declined more rapidly in spores than in mycelia, and during recovery spores accumulated mRNA that encoded a normal protein (the proteolipid subunit of the mitochondrial ATPase), whereas mycelia showed no increase in this normal RNA (for at least 120 min). Therefore, the resumption of normal protein synthesis in spores may depend upon accumulation of new mRNAs. In contrast, mycelial cells appeared to change their translational preference during continued incubation at elevated temperature, from a discrimination against normal mRNAs to a resumption of their translation into normal cellular proteins, exemplified by the ATPase proteolipid subunit whose synthesis was measured in the heat-shocked cells.     

Constitutively expressed rat mRNA encoding a 70-kilodalton heat-shock-like protein.

A nearly full-length cDNA clone isolated from the rat pheochromocytoma cell line, PC12, revealed extensive nucleotide sequence similarity between the rat cDNA and the Drosophila melanogaster hsp70 gene. The rat recombinant clone encodes a 71,000-dalton protein that is 70% identical with the dipteran hsp70 protein. Remarkably, a truncated segment of this cDNA clone was originally isolated by immunoreactivity with antisera raised to catecholamine-synthesizing enzymes, suggesting that this heat shock protein and these catecholamine enzymes shared antigenic determinants. The rat hsp70-related mRNA is responsible for the production of a constitutive hsp70 protein, because it is present in abundant amounts in various tissues at normal growth temperatures and is only minimally induced by hyperthermia. The rat hsp70-related sequence is part of a multigene family that extends across species to mice and humans.     

An Hsp70-like protein in the ER: identity with the 78 kd glucose-regulated protein and immunoglobulin heavy chain binding protein

We have characterized a cDNA clone that encodes a protein related to the 70 kd heat shock protein, but is expressed in normal rat liver. This protein has a hydrophobic leader and is secreted into the endoplasmic reticulum. We show that it is identical with two previously described proteins: GRP78, whose synthesis is induced by glucose starvation, and BiP, which is found bound to immunoglobulin heavy chains in pre-B cells. This protein, which is abundant in antibody-secreting cells, can be released from heavy chains by ATP, a reaction analogous to the release of hsp70 from heat shocked nuclear structures. We propose a specific role for this protein in the assembly of secreted and membrane-bound proteins.     

The expression of heat shock protein hsp27 and a complexed 22-kilodalton protein is inversely correlated with oncogenicity of adenovirus-transformed cells.

We isolated a monoclonal antibody that immunoprecipitated two proteins of 22 and 27 kilodaltons (kDa) from nononcogenic adenovirus type 5 early region 1 (E1)-transformed rat cells but not from oncogenic adenovirus type 12 E1-transformed rat cells. In a variety of adenovirus-transformed cells including cells transformed by E1A and the c-H-ras oncogene, we found a perfect, inverse correlation between the presence of these two proteins and the oncogenicity of these cells in syngeneic immunocompetent rats. Characterization of the two proteins revealed that they occur in a large (700-kDa) complex and that the 27-kDa protein is identical to the already known 27-kDa (28-kDa) heat shock protein hsp27. The suppression of the hsp27 protein in oncogenic cells is further demonstrated by the fact that its mRNA is absent even after heat-shock induction.     

Lack of heat shock response triggers programmed cell death in a rat histiocytic cell line.

Stress response is a universal phenomenon. However, a rat histiocytic cell line, BC-8, showed no heat shock response and failed to synthesize heat shock protein 70 (hsp70) upon heat shock at 42 degrees C for 30 min. BC-8 is a clone of AK-5, a rat macrophage tumor line that is adapted to grow in culture and has the same chromosome number and tumorigenic potential as AK-5. An increase in either the incubation temperature or time or both to BC-8 cells leads to loss of cell viability. In addition, heat shock conditions activated apoptotic cell death in these cells as observed by cell fragmentation, formation of nuclear comets, apoptotic bodies, DNA fragmentation and activation of ICE-like cysteine proteases. Results presented here demonstrate that BC-8 cells cannot mount a typical heat shock response unlike all other eukaryotic cells and that in the absence of induction of hsps upon stress, these cells undergo apoptosis at 42 degrees C.     

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

Following a brief period of heat stress, the two highly conserved mammalian stress proteins, hsp68 and 70, were examined with respect to their intracellular locations. In four independent cell lines, hsp68 and 70 were found to partition into both Triton X-100-soluble and insoluble fractions as assessed by two-dimensional gel analysis of newly synthesized polypeptides, whereas a fifth cell line showed these proteins only in the Triton X-100-insoluble fraction. In addition, a previously described cell fractionation technique was utilized to gain information regarding the segregation of the two major mammalian stress proteins, hsp68 and 70, into distinct biochemically and morphologically characterized subcellular compartments of PtK2-epithelial cells. Two cytoskeletal-specific agents, taxol and colchicine, were also probed for their effects on the disposition of these polypeptides. Under our conditions of acute heat exposure, hsp68, 70 and their isoforms were globally distributed in all subcellular fractions examined, with a few notable exceptions in drug-treated cells. Colchicine, a microtubule-depolymerizing drug, inhibited the association of hsp68 and its variants with the double-detergent-extractable labile "cytoskeleton," whereas taxol, a microtubule-stabilizing agent, in some manner, facilitated the transit of hsp68 and its isovariants from a cytoplasmic to nuclear domain. Degree of cell density is a factor which influences the synthesis of various cytoskeletal proteins; therefore, we studied the effect of cell confluency on the disposition of mammalian stress proteins hsp68 and 70 in human FS-4 fibroblasts. In confluent cultures, where cell-cell contact was maximal, we observed the appearance of a previously undetected polypeptide which was not found in sparsely populated cultures. This protein may represent a post-translationally modified isoform of a preexisting heat shock protein, or perhaps, a novel stress protein.     

The constitutive and stress inducible forms of hsp 70 exhibit functional similarities and interact with one another in an ATP- dependent fashion

Mammalian cells constitutively express a cytosolic and nuclear form of heat shock protein (hsp) 70, referred to here as hsp 73. In response to heat shock or other metabolic insults, increased expression of another cytosolic and nuclear form of hsp 70, hsp 72, is observed. The constitutively expressed hsp 73, and stress-inducible hsp 72, are highly related proteins. Still unclear, however, is exactly why most eukaryotic cells, in contrast to prokaryotic cells, express a novel form of hsp 70 (i.e., hsp 72) after experiencing stress. To address this question, we prepared antibodies specific to either hsp 72 or hsp 73 and have compared a number of biological properties of the two proteins, both in vivo and in vitro. Using metabolic pulse-chase labeling and immunoprecipitation analysis, both the hsp 72 and hsp 73 specific antibodies were found to coprecipitate a significant number of newly synthesized proteins. Such interactions appeared transient and sensitive to ATP. Consequently, we suspect that both hsp 72 and hsp 73 function as molecular chaperones, interacting transiently with nascent polypeptides. During the course of these studies, we routinely observed that antibodies specific to hsp 73 resulted in the coprecipitation of hsp 72. Similarly, antibodies specific to hsp 72 were capable of coprecipitating hsp 73. Using a number of different approaches, we show that the constitutively expressed, pre-existing hsp 73 rapidly forms a stable complex with the newly synthesized stress inducible hsp 72. As is demonstrated by double-label indirect immunofluorescence, both proteins exhibit a coincident locale within the cell. Moreover, injection of antibodies specific to hsp 73 into living cells effectively blocks the ability of both hsp 73 and hsp 72 to redistribute from the cytoplasm into the nucleus and nucleolus after heat shock. These results are discussed as they relate to the possible structure and function of the constitutive (hsp 73) and highly stress inducible (hsp 72) forms of hsp 70, both within the normal cell as well as in the cell experiencing stress.     

Patterns of protein synthesis in various cells after extreme heat shock

The analysis of proteins synthesized in rat thymocytes and mouse teratocarcinoma PCC-4 Aza 1 and myeloma Sp2/0 cells after 1 h of treatment at 42 or 44 degrees C was carried out. Shock at 42 degrees C reduced the total synthetic rate of proteins in all three cell lines and induced "classical" heat-shock protein with a mass of 70 kDa (hsp 70). Heat shock at 44 degrees C resulted in almost complete inhibition of protein synthesis; only a small amount of hsp 70 was synthesized. Meanwhile a new 48-kDa polypeptide (pI = 7.5) was found in the cells exposed to severe heat shock. This protein was compared by peptide mapping with other known polypeptides of the same size: heat-shock protein from chicken embryo cells and mitogen-stimulated polypeptide from human lymphoid cells. The peptide maps were not identical. It was also shown that after a shock at 44 degrees C teratocarcinoma cells were able to accumulate anomalous amounts of hsp 70 despite hsp 70 synthesis inhibition. The data show that reaction of various cells to extreme heat shock depends heavily on cell type.     

Analysis of the state of differentiation of two rat colon carcinoma clones with distinct tumorigenic properties.

The presence of some characteristics of normal rat intestinal epithelial cells was studied on two clones originating from a single rat colon carcinoma. These clones differed by their tumorigenic properties in the syngeneic host. However, they grow similarly in vitro and in immuno-deprived animals. The PROb clone which had the ability to form progressive tumors in the syngeneic host appeared to possess more features of differentiated cells than the REGb clone which was immunologically rejected by syngeneic hosts. Indeed, the morphology of the cells was different, the REBb cells having a more fibroblastic appearance while the PROb cells had the capacity to form domes characterizing the functional polarization of the cell layer. The two clones could also be distinguished by their expression of proteins of intermediate filaments. Both expressed cytokeratins showing their epithelial origin, but only REGb cells displayed vimentin which is characteristic of mesenchymal or poorly differentiated epithelial cells. Furthermore, analysis of the expression of a series of glycoconjugate tissue antigens and an unknown protein (p120) showed that the PROb cells resembled more the normal adult digestive epithelium than the REGb cells did. In conclusion, it appears that in this model, the most aggressive cells, those resisting to the constraints imposed by the immune system, are also the more differentiated ones.     

A novel hsp70-like protein (P70) is present in mouse spermatogenic cells.

Mouse spermatogenic cells contain relatively large amounts of a 70-kilodalton protein (P70) that is closely related to hsp70, the major inducible heat shock protein. When hsp70 from spermatogenic cells is heat induced, it migrates to the same location as does P70 on two-dimensional polyacrylamide gels, indicating that it has an apparently identical mass and isoelectric point. P70 reacts strongly and specifically with an anti-Drosophila hsp70 monoclonal antibody that is specific for products of the hsp70 gene family. Both P70 and hsp70 are also ATP-binding proteins and are purified by using ATP-affinity chromatography. However, P70 and hsp70 are unique proteins on the basis of peptide map analysis and are regulated differently in germ cells. P70 appears to be a novel heat shock protein of spermatogenic cells which is synthesized in association with germ cell differentiation.     

Synthesis of heat shock proteins in Cf124 cells: Effect of virus infection

The transient synthesis of a class of proteins known as heat shock or stress response proteins was induced when Cf124 cells were incubated at high temperature. When cells were infected with Chilo iridescent virus and simultaneously heat shocked, heat shock protein (hsp) synthesis was delayed, and the shut-off of hsp synthesis was suppressed. In previously heat shocked cells, inhibition of hsp synthesis was dependent upon the multiplicity of infection, however, when infection preceded heat shock, the synthesis of hsp started immediately after heat shock. In all cases, hsp synthesis was dependent upon newly synthesized messenger RNA.     

Different induction of 70,000-Da heat shock protein and metallothionein in HeLa cells by copper.

To clarify the physiological roles of heat shock proteins induced by copper, we studied the synthesis of these proteins and metallothionein, as well as the level and nature of copper incorporated into HeLa cells. Incubation in medium containing 200 microM cupric sulfate and above induced the synthesis of 70,000-Da heat shock protein (hsp70) in these cells. However, the synthesis of hsp70 did not increase in the presence of less than 200 microM cupric sulfate. On the other hand, the synthesis of metallothionein increased due to 100 microM cupric sulfate. The uptake of copper into the cells depended on the cupric sulfate concentration in the medium. To analyze the nature of the intracellular copper, cell extracts were separated by gel filtration chromatography into three fractions: the high molecular weight, metallothionein, and low molecular weight fractions. No copper was found in the low molecular weight fraction of control cells, but appeared distinctly at 200 microM cupric sulfate and above. Copper in the high molecular weight fraction also began to increase at 200 microM cupric sulfate and above, whereas in the metallothionein fraction it began to increase even at 50 to 100 microM cupric sulfate. Furthermore, inhibition of cell growth was also observed at 200 microM cupric sulfate and above but not at 100 microM and below.(ABSTRACT TRUNCATED AT 250 WORDS)     

A comprehensive analysis of heat shock protein synthesis in human peripheral lymphocytes: the effect of penicillin/streptomycin.

A reliable experimental procedure is described for the simultaneous characterisation of a comprehensive range of heat shock proteins (hsps) in human peripheral lymphocytes. In this system, a mild heat shock from 37 to 42 degrees C for 1 h induced the synthesis of hsps 105, 90, 70, 60, 57, 47, 40, 27 and 16. Densitometric analyses of 35[S]-methionine labelled protein gels indicated that levels of these hsps peaked at 3 to 4 h, following post-heat shock recovery at 37 degrees C. The presence of penicillin and streptomycin in the cell culture medium, appeared to have little effect on the kinetics of hsp synthesis. The present method can be used for relatively small blood samples and its relative ease of application and reproducibility make it appropriate for screening the expression of hsps in human lymphocytes from a range of individuals.