Progress in dodecafluoropentane emulsion as a neuroprotective agent in a rabbit stroke model

Dodecafluoropentane emulsion (DDFPe) in 250 nm nanodroplets seems to swell modestly to accept and carry large amounts of oxygen in the body at >29 °C. Small particle size allows oxygen delivery even into hypoxic tissue unreachable by erythrocytes. Using permanent cerebral embolic occlusion in rabbits, we assessed DDFPe dose response as a neuroprotectant at 7 and 24 h post-embolization without lysis of arterial obstructions and investigated blood pharmacokinetics. New Zealand White rabbits (N = 56) received cerebral angiography and embolic spheres (diameter = 700-900 μm) occluded middle and/or anterior cerebral arteries. Intravenous DDFPe dosing (2 % w/v emulsion) began at 60 min and repeated every 90 min until sacrifice at 7 or 24 h post-embolization. Seven-hour groups: (1) control (embolized without treatment, N = 6), and DDFPe treatment: (2) 0.1 ml/kg (N = 7), (3) 0.3 ml/kg (N = 9), (4) 0.6 ml/kg (N = 8). Twenty-four-hour groups: (5) control (N = 16), and DDFPe treatment: (6) 0.1 ml/kg (N = 10). Infarcts as percent of total brain volume were determined using vital stains on brain sections. Other alert normal rabbits (N = 8) received IV doses followed by rapid arterial blood sampling and GC-MS analysis. Percent infarct volume means significantly decreased for all DDFPe-treated groups compared with controls, p = <0.004 to <0.03. Blood DDFP (gas) half-life was 1.45 ± 0.17 min with R = 0.958. Mean blood clearance was 78.5 ± 24.9 ml/min/kg (mean ± SE). Intravenous DDFPe decreases ischemic stroke infarct volumes. Blood half-life values are very short. The much longer therapeutic effect, >90 min, suggests multiple compartments. Lowest effective dose and maximum effective therapy duration are not yet defined. Rapid development is warranted.

In vivo resolution of oligomers with fluorescence photobleaching recovery histograms

Simple independent enzyme-catalyzed reactions distributed homogeneously throughout an aqueous environment cannot adequately explain the regulation of metabolic and other cellular processes in vivo. Such an unstructured system results in unacceptably slow substrate turnover rates and consumes inordinate amounts of cellular energy. Current approaches to resolving compartmentalization in living cells requires the partitioning of the molecular species in question such that its localization can be resolved with fluorescence microscopy. Standard imaging approaches will not resolve localization of protein activity for proteins that are ubiquitously distributed, but whose function requires a change in state of the protein. The small heat shock protein sHSP27 exists as both dimers and large multimers and is distributed homogeneously throughout the cytoplasm. A fusion of the green fluorescent protein variant S65T and sHSP27 is used to assess the ability of diffusion rate histograms to resolve compartmentalization of the 2 dominant oligomeric species of sHSP27. Diffusion rates were measured by multiphoton fluorescence photobleaching recovery. Under physiologic conditions, diffusion rate histograms resolved at least 2 diffusive transport rates within a living cell potentially corresponding to the large and small oligomers of sHSP27. Given that oligomerization is often a means of regulation, compartmentalization of different oligomer species could provide a means for efficient regulation and localization of sHsp27 activity.

Delaying S-phase progression rescues cells from heat-induced S-phase hypertoxicity

The mechanism by which a cell protects itself from the lethal effects of heat shock and other stress-inducing agents is the subject of much research. We have investigated the relationship between heat-induced damage to DNA replication machinery and the lethal effects of heat shock, in S-phase cells, which are more sensitive to heat shock than either G1 or G2. We found that maintaining cells in aphidicolin, which prevents the passage of cells through S-phase, can rescue S-phase HeLa cells from the lethal effects of heat shock. When S-phase, HeLa cells were held for 5-6 h in 3 microM aphidicolin the measured clonogenic survival was similar to that for exponentially growing cells. It is known, that heat shock induces denaturation or unfolding of proteins, rendering them less soluble and more likely to co-isolate with the nuclear matrix. Here, we show that enhanced binding of proteins involved in DNA replication (PCNA, RPA, and cyclin A), with the nuclear matrix, correlates with lethality of S-phase cells following heat shock under four different experimental conditions. Specifically, the amounts of RPA, PCNA, and cyclin A associated with the nuclear matrix when cells resumed progression through S-phase correlated with cell killing. Heat-induced enhanced binding of nuclear proteins involved with other aspects of DNA metabolism, (Mrell, PDI), do not show this correlation. These results support the hypothesis that heat-induced changes in the binding of proteins associated with DNA replication factories are the potentially lethal lesions, which become fixed to lethal lesions by S-phase progression but are repairable if S-phase progression is delayed.

Heat-activated transgene expression from adenovirus vectors infected into human prostate cancer cells

Replication-deficient adenovirus expression vectors were used to introduce a recombinant DNA construct containing enhanced green fluorescent protein (EGFP) under control of a truncated, human heat shock promoter into human prostate cancer cells growing either exponentially or in plateau phase. This was done to measure controlled, heat shock-induced EGFP expression under conditions relevant to treating human cancers with heat-activated gene therapy. Both the temporal duration and magnitude of EGFP expression increased proportionately with stronger heat shocks (time at temperature) up to maximum values that were induced by 4 h at 41.0 degrees C or 2 h at 42.0 degrees C. Longer heat shocks at either temperature yielded no additional EGFP expression and ultimately reduced it. Maximal EGFP expression was induced in exponential cultures by heat shocks delivered 12-24 h after virus infection. Induction at progressively later postinfection times induced increasingly lower, peak EGFP expression. Maximal EGFP expression could not be induced until 48 h after infection of plateau phase cultures but could still be induced 180 h after virus infection. However, peak EGFP levels in plateau cultures were approximately 25-50% of those observed in identically induced exponential cultures. Ostensibly, the differences in expression from the heat shock promoter observed in exponential and plateau cultures were attributable to cell division diluting the vector within exponential cultures and the lower metabolic activity in serum-starved plateau cultures. For all experimental conditions, EGFP expression induced from the heat shock promoter was comparable with or higher than that from the constitutively active cytomegalovirus promoter over any 24-h period. The experimental results demonstrated that EGFP expression from the heat shock promoter was controllable in both exponential and plateau phase cultures and support the plausibility of using controlled heat shock activation of this promoter as a means of regulating both the spatial and temporal expression of therapeutic DNA constructs within human tissues. The ability to localize and regulate expression from the heat shock promoter may prove particularly advantageous for many cancer applications, especially if the therapeutic products are highly toxic, e.g., proteotoxins or cytokines. However, the results of this study suggest that differential growth conditions within tumors could markedly affect the expression of recombinant DNA under control of both inducible and constitutive promoters. Consequently, inducing schemes may need to be spatially adjusted to obtain the desired therapeutic results in all tumor domains using heat-activated gene therapy.

Inhibition of the 26S proteasome induces expression of GLCLC, the catalytic subunit for gamma-glutamylcysteine synthetase

The majority of short- and long-lived cellular proteins are degraded by the activities of the 26S proteasome, a large multi-catalytic protease. Its unique function places it as a central regulatory activity for many important physiological processes. Lactacystin is a very specific 26S proteasome inhibitor and represents an excellent tool for demonstrating that a pathway exhibits proteasome-dependent biochemical regulation. Exposure of HepG2 cells to lactacystin resulted in robust elevation of GLCLC mRNA levels, followed by an increase in GSH concentrations. GLCLC is the gene that encodes the catalytic subunit for gamma-glutamylcysteine synthetase, the rate-limiting enzyme for the synthesis of glutathione (GSH). Inhibition of non-proteasome, protease activities did not induce GLCLC. Gel mobility shift assays and expression of CAT activity from heterologous reporter vectors identified Nrf2 mediation of the GLCLC antioxidant response element, ARE4, as the mechanism by which lactacystin induced GLCLC. These studies have identified 26S proteasome activity as a central regulatory pathway for glutathione synthesis.

On the path to the heat shock response: destabilization and formation of partially folded protein intermediates, a consequence of protein thiol modification

This review discusses the initial events that occur during oxidative stress that induce the synthesis of heat shock proteins. The focus is on non-native oxidation or modification of protein thiols and the destablization that can result. Proteins that contain non-native modified thiols can become destablized such that they unfold into molten globule-like intermediates at or below 37 degrees C, relieving Hsf-1 negative regulation, and inducing Hsp transcription.

Diamide-induced cytotoxicity and thermotolerance in CHO cells

Treatment with the sulfhydryl oxidant diamide denatures and aggregates cellular proteins, which prior studies have implicated as an oxidative damage that activates the heat shock transcription factor and induces thermotolerance. This study was initiated to further characterize cellular response to diamide-denatured proteins, including their involvement in diamide cytotoxicity. Cytotoxic diamide exposures at 37.0 degrees C denatured and aggregated cellular proteins in a manner that was proportional to cell killing, but this correlation was different than that established for heated cells. Diamide exposures at 24.0 degrees C were orders of magnitude less cytotoxic, with little additional killing occurring after diamide was removed and cells were returned to 37.0 degrees C. Thus, protein denaturation that occurred at 37.0 degrees C, after proteins were chemically destabilized by diamide at 24.0 degrees C [Freeman et al., J. Cell. Physiol., 164:356-366 (1995); Senisterra et al., Biochemistry 36: 11002-11011 (1997)], had little effect on cell killing. Thermotolerance protected cells against diamide cytotoxicity but did not reduce the amount of denatured and aggregated protein observed immediately following diamide exposure. However, denatured/aggregated proteins in thermotolerant cells were disaggregated within 17 h following diamide exposure, while no disaggregation was observed in nontolerant cells. This more rapid disaggregation of proteins may be one mechanism by which thermotolerance protects cells against diamide toxicity, as it has been postulated to do against heat killing. As with heat shock, nontoxic diamide exposures induced maximal tolerance against heat killing; however, there was no detectable, increased synthesis of heat shock proteins. Thus, diamide treatment proved to be a reproducible procedure for inducing a phase of thermotolerance that does not require new heat shock protein (HSP) synthesis, without having to use transcription or translation inhibitors to suppress HSP gene expression. These results complement those from studies with other stresses to establish the importance of protein denaturation/aggregation as a cytotoxic consequence of stress and a trigger for thermotolerance induction. The data also illustrate that differences in how proteins are denatured and aggregated can affect their cytotoxicity and the manner in which thermotolerance is expressed.

Proteins containing non-native disulfide bonds generated by oxidative stress can act as signals for the induction of the heat shock response

While oxidative stress can induce a heat shock response, the primary signals that initiate activation have not been identified. To identify such signals, HepG2 and V 79 cells were exposed to menadione, a compound that redox-cycles to generate superoxide. The oxidative stress generated by menadione resulted in oxidation of protein thiols in a dose-dependent manner. This was followed by protein destabilization and denaturation, as determined by differential scanning calorimetry of whole cells. To directly evaluate the effect of non-native disulfides on protein conformation, Ca2(+)-ATPase, isolated from rabbit sarcoplasmic reticulum, was chemically modified to contain non-native intermolecular or glutathione (GHS)-mixed disulfides. Differential scanning calorimetry profiles and 1-anilinonaphthalene-8-sulfonic acid fluorescence indicated that formation of non-native disulfides produced protein destabilization, denaturation, and exposure of hydrophobic domains. Cellular proteins shown to contain oxidized thiols formed detergent-insoluble aggregates. Cells treated with menadione exhibited activation of HSF-1, accumulated Hsp 70 mRNA, and increased synthesis of Hsp 70. This work demonstrates that formation of physiologically relevant, non-native intermolecular and GSH-mixed disulfides causes proteins to destabilize, unfold such that hydrophobic domains are exposed, and initiate a signal for induction of the heat shock response.

Thermotolerance expression in mitotic CHO cells without increased translation of heat shock proteins

The objective of this study was to unequivocally demonstrate thermotolerance expression in mammalian cells in the absence of stress-induced synthesis of heat shock proteins (HSPs). Mitotic cells were selected as an experimental system since their genome was in the form of condensed chromosomes and ostensibly incapable of being transcribed; thus, obviating stress-induced HSP gene expression. Asynchronous Chinese hamster ovary (CHO) cells were treated with 0.2 microgram/ml nocodazole to accumulate cells in mitosis for harvest by mitotic shakeoff. Cells were maintained in mitosis with nocodazole during thermotolerance induction, thermotolerance development, and all challenge hyperthermia exposures. Although the heat shock transcription factor was activated by the thermotolerance inducing heat shock, as indicated by gel mobility shift assay, no increase in steady-state HSP mRNA levels was detected, as expected. Preferential synthesis of HSPs from extant mRNA was not detected during thermotolerance development and cellular levels of the 27 kDa, 70 kDa, and 90 kDa heat shock proteins remained constant, as determined by Western Blot analyses. The magnitude and induction threshold of expressed thermotolerance was not diminished when cells were incubated with 10.0 micrograms/ml cycloheximide during thermotolerance development confirming that new protein synthesis was not requisite. Parallel experiments were performed using nonmitotic cells in which protein synthesis was inhibited during thermotolerance development with 10.0 micrograms/ml cycloheximide. As with mitotic cells, high levels of thermotolerance were attained without detectable increases in the cellular content of the 27 kDa, 70 kDa, and 90 kDa heat shock proteins. The results of this study demonstrated that high levels of thermotolerance could be expressed in mitotic cells without stress-induced, preferential synthesis of HSPs, and support the contention that a substantial fraction of thermotolerance expressed in nonmitotic cells also occurs independently of induced HSP synthesis.

Excess protein in nuclei isolated from heat-shocked cells results from a reduced extractability of nuclear proteins

An excellent correlation has been established between the quantity of protein associated with nuclei isolated from heat-shocked cells and the level of hyperthermic cell killing. However, controversy remains about whether increases in nuclear-associated protein result from a heat-induced migration of cytoplasmic proteins into the nucleus or because hyperthermia reduces the solubility of nuclear proteins in the detergent buffers commonly used to isolate nuclei. To address this controversy, the nuclear protein content was measured in whole and detergent-extracted cells before and following hyperthermia. It was found that hyperthermia caused no significant change in the nuclear protein content of whole, unextracted cells, and when fluorescently labeled proteins were microinjected into the cytoplasm no gross change in the selective permeability of the nuclear membrane to soluble proteins was observed during or following hyperthermia. Measurements in extracted cells showed that the detergent buffers removed protein from both the nucleus and cytoplasm of control, nonheated cells and that hyperthermia reduced the extractability of both nuclear and cytoplasmic proteins. The amount of protein found in nuclei isolated from heated cells approached that observed in nuclei within nonheated whole cells as the hyperthermic exposure was increased. Thus, the dose-dependent, two- to threefold increase in the protein content of nuclei isolated from heated cells represents a heat-induced reduction in the extractability of proteins normally present within cell nuclei and does not result from a mass migration of cytoplasmic proteins into the nucleus, although some specific proteins (e.g., the 70 KDa heat shock protein) do migrate to the nucleus following heat shock. Differential scanning calorimetry (DSC) measurements of whole cells, isolated nuclei, cytoplasts, and karyoplasts supported these conclusions and suggested that most of the detergent-insoluble proteins remaining in the nuclei and cytoplasm of heated cells are in their native state. Thus, a relatively small amount of denatured protein may be sufficient to initiate and sustain insoluble protein aggregates comprised of mostly native proteins. Analyses of the DSC data also implied that the previously identified critical target proteins, predicted to have a Tm of 46.0 degrees C, are present in both the nucleus and cytoplasm.

Characterization of a signal generated by oxidation of protein thiols that activates the heat shock transcription factor

The diazenecarbonyl derivative, diamide, was used to produce nonnative protein disulfides in Chinese hamster ovary cells in order to characterize the events that occur during thiol oxidation-induced denaturation that trigger induction of Hsp 70. We limit the term protein denaturation to a process involving a conformational rearrangement by which the ordered native structure of a protein changes to a more disordered structure. Protein thiol oxidation resulted in immediate destabilization of proteins, as assessed by differential scanning calorimetry (DSC). The DSC profile indicated both a decrease in the onset temperature for detection of denaturation and destabilization of a class of proteins with an average transition temperature (Tm) of 60 degrees C. Concomitant with destabilization was an increase in proteins associated with isolated nuclei. Thiol oxidation also induced heat shock transcription factor (HSF) binding activity, however, this was nearly undetectable immediately following diamide treatment: maximum activation occurred 3 hr following exposure. In contrast, heat shock denatured thermolabile proteins which exhibited a Tm of < or = 48 degrees C. Heat shock also resulted in a rapid increase in proteins associated with isolated nuclei and produced immediate and maximum activation of HSF binding. The accumulation of Hsp and Hsc 70 mRNA following thiol oxidation reflected the delay in HSF binding. Acquisition of HSF binding activity occurred immediately if diamide-treated cells were subsequently exposed to a heat shock, indicating that HSF was not inactivated by the diamide treatment. Ostensibly, the cellular system for detecting denatured/abnormal proteins failed to immediately recognize the signal generated by thiol oxidation. These results suggest that at least two processes are involved in the induction of Hsp 70 by nonnative disulfide bond formation: destabilization of protein structure resulting in denaturation and recognition of denatured protein.

Protocol for freezing thermotolerant cells and maintaining thermotolerance following thawing

Two independent laboratories have demonstrated that suspension-grown, Chinese hamster ovary (CHO) cells can be made thermotolerant, frozen and subsequently thawed such that they still express thermotolerance. Thermotolerance was determined as the ability to protect cells against hyperthermic cell killing (colony formation assay) and the ability to reduce protein aggregation within the nuclei of heated cells. Cells were frozen either following development of full or partial thermotolerance. In the former case frozen cells maintained thermotolerance upon thawing and in the latter case cells subsequently developed full thermotolerance following thawing and incubation at 37.0 degrees C. After thawing, frozen cells displayed a temporal course of thermotolerance development and decay that was similar to that for never-frozen cells. Success was obtained using either asynchronous or synchronous cell populations, and the heat sensitivity of the cells was not altered by the freezing procedure. The experimental results demonstrate the plausibility of utilizing a frozen stock of thermotolerant cells to make thermotolerance experiments more convenient.

Effect of 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7) on HSP70 and HSP28 gene expression and thermotolerance development in human colon carcinoma cells

The effect of 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), a potent protein kinase C (PKC) inhibitor, on the development of thermotolerance and expression of heat shock genes (HSP70 and HSP28) was investigated in human colon carcinoma HT-29 cells. After acute heating at 45 degrees for 15 min, cells became resistant to a challenge heat shock. The development of thermotolerance was suppressed by adding H-7 after heat shock. Northern blots show that the levels of HSP70 and HSP28 mRNA increased rapidly and reached maximal values within 6 hr. H-7 suppressed the accumulation of HSP70 and HSP28 mRNA as well as their protein synthesis, and the level of suppression was concentration dependent. However, little effect was observed if the drug was added 1 hr before and during heat shock. These results suggest that PKC is involved in the regulation of heat shock gene expression after acute heat shock.

Effect of thermotolerance on heat-induced excess nuclear-associated proteins

Earlier studies reported that thermotolerance had two effects on the heat-induced increase in nuclear-associated proteins (NAPs); reduction in NAP levels immediately following hyperthermia and facilitation of NAP recovery to control levels. It has also been demonstrated that there are two phases of thermotolerance; one that requires newly synthesized proteins (protein synthesis dependent thermotolerance; PSDT), and another that does not (protein synthesis independent thermotolerance; PSIT). This study was designed to determine if these two phases of thermotolerance affected NAP binding in a similar or different manner. The results demonstrated that protein synthesis during thermotolerance development was not required to reduce NAP levels measured immediately following hyperthermia, but was required to facilitate NAP recovery to control levels following hyperthermia. Reducing NAP levels was the predominant mechanism by which thermotolerance protected cells from this lesion at 43.0 degrees C while facilitated NAP recovery predominated in protecting against exposure to 45.5 degrees C. The facilitated recovery of NAPs required only proteins synthesized following thermotolerance induction and prior to the second heat challenge. Proteins synthesized following the second heat challenge were not requisite. Finally, the processes that facilitate NAP recovery were inhibited at 3 degrees C, suggesting that they are enzymatically mediated.

Induction of tolerance to hypothermia and hyperthermia by a common mechanism in mammalian cells

Pretreatment by hypothermic (25 degrees C) cycling (PHC) of attached exponential-phase V79 Chinese hamster cells by Method 4 (24 hr at 25 degrees C + 1.5 hr at 37 degrees C + 24 hr at 25 degrees C + trypsin + 3 hr at 37 degrees C) or by Method 3 (48 hr at 25 degrees C + trypsin + 3 hr at 37 degrees C) make mammalian V79 cells significantly more resistant to 43 degrees C hyperthermia. There is no significant difference in the 43 degrees C curves whether Method 3 or 4 is used for pre-exposure. If pre-exposure at 15 or 10 degrees C, the resistance to hyperthermia is significantly reduced. PHC by Method 4 significantly increases survival of cells exposed to 5 degrees C and, to a lesser extent, to 10 degrees C. The increase in hyper- and hypothermic survival after PHC cannot be accounted for by changes in cell cycle distribution. Heat-shock protein synthesis is not induced by PHC; hence, protection does not result from newly synthesized proteins. When cells are made tolerant to hyperthermia by a pretreatment in 2% DMSO for 24 hr at 37 degrees C (Method 8), the cells are not more resistant to subsequent exposures to hypothermia, either at 5 or 10 degrees C. The results imply that there may be two mechanisms of inducing resistance to hyperthermia, only one of which also confers resistance to hypothermia.

Cycloheximide protection against actinomycin D cytotoxicity

Pretreatment plus concomitant treatment with 10 micrograms/ml cycloheximide protected Chinese hamster ovary cells and Swiss 3T3 cells against the cytotoxicity of actinomycin D. The cycloheximide treatment reduced the intracellular concentration of actinomycin D by reducing the level of actinomycin D bound to the acid precipitable fraction of the cell. Levels of unbound actinomycin D were unaffected by cycloheximide, indicating that the plasma membrane permeability to AD was not reduced. Actinomycin D inhibited total transcription but did not reduce cytoplasmic levels of rRNA nor of most tested mRNA; however, cytoplasmic levels of c-myc mRNA were reduced below detectability. Cycloheximide treatment further inhibited total transcription and had no effect on cytoplasmic levels of rRNA nor of most tested mRNA. Cytoplasmic levels of c-myc were elevated by cycloheximide and remained so even in the presence of actinomycin D. These data suggested that a reduction in cytoplasmic levels of short lived, essential mRNA, such as c-myc mRNA, was one lethal lesion of actinomycin D. Furthermore, cycloheximide's protection may result, in part, from its ability to stabilize and/or elevate cytoplasmic levels of these mRNA, thus counteracting their depletion by actinomycin D. Protection may also result from the cycloheximide-induced reduction of actinomycin D bound to the acid precipitable fraction of the cells.

Absence of HSP28 synthesis and phosphorylation during the development of chronic thermotolerance in murine L929 cells

We investigated the correlation between chronic thermotolerance development and phosphorylation, synthesis, or expression of the HSP28 family in murine L929 cells. Chronic thermotolerance developed during heating at 41.5 degrees C as indicated by a biphasic survival curve. However, heat-induced phosphorylation of HSP28 was not detected. Furthermore, we failed to detect HSP28 synthesis during chronic heating by using two-dimensional polyacrylamide gel electrophoresis. The lack of HSP28 synthesis was also confirmed in acute thermotolerance. Similar results were observed in NIH 3T3 cells. Although Southern blots clearly demonstrated the presence of the HSP28 gene in genomic DNA, Northern blots failed to demonstrate its expression. Unlike HSP28, the expression of constitutive and inducible HSP70 genes, along with the synthesis of their proteins, were stimulated during chronic heating at 41.5 degrees C in L929 cells. These results suggest that HSP28 synthesis and its phosphorylation are not required to develop both chronic and acute thermotolerance in L929 cells.

Reduction of levels of nuclear-associated protein in heated cells by cycloheximide, D2O, and thermotolerance

Hyperthermia increases levels of nuclear-associated proteins in a manner that correlates with cell killing. If the increase in nuclear-associated proteins represents a lethal lesion then treatments that protect against killing by heat should reduce and/or facilitate the recovery of levels of the proteins in heated cells. This hypothesis was tested using three heat protection treatments: cycloheximide, D2O, and thermotolerance. All three treatments reduced levels of the proteins measured immediately following hyperthermia at 43.0 or 45.5 degrees C, with the greatest reduction occurring at 43.0 degrees C. In addition to reducing the proteins, thermotolerance facilitated the recovery of the proteins to control levels following hyperthermia. Thus thermotolerance may protect cells by both reducing the initial heat damage and facilitating recovery from that damage. Cycloheximide and D2O did not facilitate recovery of nuclear-associated proteins, suggesting that their protection against cytotoxicity related to the proteins resulted solely from their reduction of increases in levels of the proteins. All three treatments have been shown to stabilize cellular proteins against thermal denaturation. The results of this study suggest that the increase in nuclear-associated proteins may result from thermally denatured proteins adhering to the nucleus and that it is the ability of cycloheximide, D2O, and thermotolerance to thermostabilize proteins that reduces the increase in levels of the proteins within heated cells.

Development of acute thermotolerance in L929 cells: lack of HSP28 synthesis and phosphorylation

We investigated the correlation between the development of acute thermotolerance and the phosphorylation, synthesis, and expression of the HSP28 family in murine L929 cells. Following heating at 43 degrees C for 30 min, thermotolerance developed rapidly in exponential-phase cells and reached its maximum 4-9 h after heat shock. Maximal thermal resistance was maintained for 24 h and then gradually decayed. However, heat-induced phosphorylation of HSP28 was not detected. Furthermore, HSP28 synthesis during incubation at 37 degrees C for 12 h following heat shock was not detected by [3H]-leucine labeling followed by two-dimensional polyacrylamide gel electrophoresis. In addition, Northern blots failed to demonstrate expression of the HSP28 gene. Unlike HSP28, the expression of constitutive and inducible HSP70 genes, along with the synthesis of their proteins, was observed during incubation at 37 degrees C after heat shock. These results demonstrate that HSP28 synthesis and its phosphorylation are not required to develop acute thermotolerance in L929 cells.

Electroporation of extraneous proteins into CHO cells: increased efficacy by utilizing centrifugal force and microsecond electrical pulses

A novel electroporation system employing an oscillating electric pulse and centrifugal force was used to introduce extraneous proteins into CHO cells. Following the electrical pulse, the compression and subsequent rebound induced by the centrifugal acceleration and deceleration, respectively, enhanced protein uptake, presumably by a hydrodynamic pumping of extracellular solutions through the permeabilized membrane. Protein uptake was quantitated by measuring the amount of radiolabeled, extraneous, CHO proteins introduced into unlabeled CHO cells. The amount of protein introduced into electroporated CHO cells was enhanced up to four-fold by a combination of electric pulse and centrifugal force compared to that introduced by electric pulse only. The optimum gradient of centrifugal force (GCF, temporal change of centrifugal force) was 590 and -470 g/s during acceleration and deceleration, respectively. The optimum electric field was 5 kV/cm with a 30-microsecond pulse length. At this optimum electroporation condition, approximately 5 pg of proteins (up to 200 kDa molecular weight) were introduced per CHO cell. These same settings also permitted electroporation of other membrane impermeable substances including propidium iodide and ethidium bromide. Introduction of extraneous materials into the cytoplasm during electroporation was confirmed by the ability of anti alpha-tubulin to stain the microtubules and propidium iodide and ethidium bromide to stain the nuclei. Cells electroporated with optimum device settings exhibited no significant decrease in clonogenic survival.

Microelectrode measurements of the transmembrane potential in baby hamster kidney, (Chinese hamster ovary), NG108-15 neuroblastoma and Swiss 3T3 cells at 37.0 or 43.0 degrees C

Hyperthermia affects the physical state and function of the plasma membrane. This could alter the transmembrane potential (Vm) and associated functions in a manner that promotes cell killing. Previous investigations have reported differing results of the effect of heat on Vm, possibly due to artifacts associated with the methods employed to measure Vm indirectly. One such artifact is a membrane depolarization induced by cationic probes, as demonstrated in this paper. In this study, glass microelectrodes were used to avoid these artifacts and to make direct electrical measurements of Vm. Following 25 min-30 min at 43.0 degrees C, The mean Vm of Chinese hamster ovary (CHO) cells, within clusters of six or more cells, decreased from -16 +/- 5 to -38 +/- 6 mV, and remained at these levels during incubation times up to 3 h. All CHO cells resumed a normal Vm within 4.5 h after returning to 37.0 degrees C, regardless of the time of exposure at 43.0 degrees C (0.5 to 3.0 h, with survival levels of 0.7 and 0.001, respectively). The membrane hyperpolarization decreased with cell to cell contact to where isolated cells exhibited no hyperpolarization. CHO cultures with different cell densities (number of cells per cm2), and thus differing degrees of cell to cell contact, were heated and then subjected to the colony formation assay. The degree of cell to cell contact at the time of heating had no effect on survival. Hence, the heat-induced, cell contact dependent hypolarization of CHO cell membranes was unrelated to clonogenic survival.(ABSTRACT TRUNCATED AT 250 WORDS)

Cycloheximide increases the thermostability of proteins in Chinese hamster ovary cells

Protein denaturation resulting from temperatures between 42.0 degrees C and 50 degrees C has been observed and implicated as the lethal lesion for hyperthermic cell killing. A logical corollary is that protection against hyperthermic killing requires stabilization of cellular proteins against thermal denaturation. To test this, Chinese hamster ovary cells were treated with the heat protector cycloheximide and then subjected to differential scanning calorimetry to measure protein denaturation. Cycloheximide stabilized proteins that denatured between 42 degrees C and 52 degrees C in control cells by increasing their transition (denaturation) temperature by an average of 1.3 degrees C. In addition, cycloheximide reduced the cytotoxicity of actinomycin D and adriamycin, suggesting that protein stabilization protects cells against stresses other than hyperthermia.

Mechanism(s) of heat killing: accumulation of nascent polypeptides in the nucleus?

To investigate the possibility that nascent polypeptides released from polysomes by heat shock accumulate in the nucleus, cells were pulse labeled with [35S]methionine for two minutes and heated immediately thereafter at 45.5 degrees C for 10 minutes. When isolated nuclei were subjected to gel electrophoresis and subsequently autoradiographed, heated nuclei exhibited an approximately 10-fold increase in radioactive polypeptides in comparison to nonheated controls. These nascent polypeptides were nonspecific molecules covering a wide range of molecular weights. It is plausible that the accumulation of polypeptides in the nucleus results in hyperthermic cytotoxicity. Therefore, we propose that a potential target for heat killing is within the nucleus, at sites where nascent polypeptides accumulate after heat shock.

Sensitization to hyperthermia by 3,3'-dipentyloxacarbocyanine iodide: a positive correlation with DNA damage and negative correlations with altered cell morphology, oxygen consumption inhibition, and reduced ATP levels

The cyanine dye 3,3'-dipentyloxacarbocyanine iodide (DiOC5(3)) (concentrations of 0.5 microgram/ml to 5.0 micrograms/ml) was shown to be a potent sensitizer of Chinese hamster ovary (CHO) cells to hyperthermic cell killing at 43.0 degrees C or 45.5 degrees C, while exhibiting no cytotoxicity at 37.0 degrees C. Sensitization to hyperthermic cell killing was accompanied by an increase in damage to the DNA, as measured by DNA unwinding. The increased DNA damage correlated qualitatively with the enhanced heat killing induced by DiOC5(3). This correlation was better in cells heated at 43.0 degrees C than in those heated at 45.5 degrees C. DiOC5(3) is known to affect other cellular functions. It inhibits electron transport, uncouples oxidative phosphorylation, and inhibits calcium ATPases. The effects of DiOC5(3) on oxygen consumption and ATP content were therefore measured at 37.0 degrees C and at hyperthermic temperatures. The results demonstrated that inhibition of oxygen consumption and reduction of cellular ATP levels played no role in inducing heat sensitization in DiOC5(3)-treated cells, or in causing cell death in cells treated with heat alone.

Correlation between redistribution of a 26 kDa protein and development of chronic thermotolerance in various mammalian cell lines

Previous studies suggested that a 26 kDa protein might play an important role in protein synthesis-independent thermotolerance development in CHO cells. To determine if this phenomenon was universal, four mammalian cell lines, viz., CHO, HA-1, murine Swiss 3T3, and human HeLa, were studied. Cells were heated at 42 degrees C, and the level of 26 kDa protein in the nucleus was measured, together with clonogenic survival and protein synthesis. The results demonstrated that 1) the 26-kDa protein was present in the four different cell lines, and 2) the level of the 26 kDa protein in their nuclei was decreased by 30-70% after heating at 42 degrees C for 1 hr. However, restoration of this protein occurred along with development of chronic thermotolerance. The protein synthesis inhibitor cycloheximide (10 micrograms/ml) neither inhibited the development of chronic thermotolerance nor affected the restoration of the 26 kDa protein in the nucleus. In fact, this drug protected cells from hyperthermic killing and heat-induced reduction of 26 kDa protein in the nucleus. Heat sensitizers, quercetin (0.1 mM), 3,3'-dipentyloxacarbocyanine iodide (DiOC5[3]: 5 micrograms/ml), and stepdown heating (45 degrees C-10 min----42 degrees C), potentiated hyperthermic killing and inhibited or delayed the restoration of the 26 kDa protein to the nucleus. These results support a correlated, perhaps causal relationship between the restoration of the 26 kDa protein and chronic thermotolerance development in four different mammalian cell lines.

Time-temperature analysis of cell killing of BHK cells heated at temperatures in the range of 43.5 degrees C to 57.0 degrees C

Baby hamster kidney (BHK) cells were heated at temperatures in the range of 43.5 degrees C to 57.0 degrees C to determine the time-temperature relationship of cell killing. The cells were grown on 0.025 mm thick pieces of mylar to minimize warm-up times. After heating, the cells were plated for the colony formation assay. The endpoints of 1%, 10%, or 90% isosurvival, or the D0 values of the survival curves were used to construct plots of the logarithm of the reciprocol of the exposure time versus the reciprocol of the absolute temperature. The data for each endpoint resulted in a straight line plot, indicating that the time-temperature relationship for cell killing remained constant from 43.5 degrees C to 57.0 degrees C; namely, a 1.8-fold increase in exposure time was required for a 1 degree C decrease in temperature in order to obtain isosurvival. Heated BHK cells were also examined using electron microscopy. The threshold level of altered morphology was the dissociation of polyribosomal structure and the formation of electron-dense granules within the mitochondria. The time-temperature relationship for the induction of this altered morphology was identical to that for the 90% isosurvival endpoint. Hence, the appearance of altered morphology appears to be related to cell killing.

Heat protectors and heat-induced preferential redistribution of 26 and 70 kDa proteins in Chinese hamster ovary cells

An overall increase of 40% in nuclear-associated protein has been shown to be one of the sequellae of exposure of eukaryotic cells to elevated temperatures. Several investigators have shown that the increased protein/DNA ratios correlated well with the degree of cytotoxicity. In previous investigations, we have shown that cycloheximide, which protects the cell from the killing effects of heat, produces a dramatic reduction of the bulk nuclear-associated proteins after heating. In this investigation, we studied a previously unobserved efflux of a 26 kDa protein after heat shock and the preferential accumulation of the 70 kDa protein. The 26 kDa protein was shown not to be a member of previously described heat shock protein families. Preferential reduction of a 26 kDa protein and accumulation of a 70 kDa protein was observed in nuclei isolated from Chinese hamster ovary cells after heating at 43 degrees C. After heat treatment, the 26 kDa protein in the nucleus was decreased to a level 0.1-0.3 times the original amount in unheated cells, and the 70 kDa protein in the nucleus increased by a factor of 1.6-1.8. The normal levels of these two proteins were restored when cells were incubated at 37 degrees C following heat shock. Cells treated with heat protectors, cycloheximide and histidinol, demonstrated approximately the same redistribution in nuclear 26 and 70 kDa proteins immediately after heating as those not exposed to these drugs. On the other hand, restoration to control levels was much faster in the protector-treated cells, suggesting that "repair" of heat-induced damage is an important factor in the cells ability to survive this insult. Return to normal protein levels did not require new protein synthesis.

Mechanism of killing Chinese hamster ovary cells heated in G1: effects on DNA synthesis and blocking in G2

To determine where in the cell cycle Chinese hamster ovary cells die following heating in G1, a mild hyperthermia treatment, i.e., 10 or 11.5 min at 45.5 degrees C, resulting in 40-50% cell kill was used. After a 7-14-h delay in G1, the cells heated in G1 eventually entered S phase and replicated all their DNA. Both an autoradiographic analysis with tritiated thymidine and a bromodeoxyuridine-propidium iodide bivariate analysis by flow cytometry revealed that both clonogenic and nonclonogenic cells were delayed in progression through S phase for at least 4 h. Then they completed replication of all their DNA and entered G2. Alkaline sucrose gradient sedimentation analysis revealed that these heated cells could complete replicon elongation into cluster-sized molecules of 120-160 S which persisted for 2-12 h after heating. However, further replicon elongation into multicluster-sized molecules greater than 160 S required an additional 12 h in heated cells compared to the 4 h needed in unheated control cells. Our results when compared with the literature suggest that when G1 cells are heated to a survival level of about 50%, the nonclonogenic cells recover from a long delay in G1, traverse S at a reduced rate, and then die either in G2 or as multinucleated cells after an aberrant division.

Evidence that the feeder effect in mammalian cells is mediated by a diffusible substance

Chinese hamster ovary (CHO), baby hamster kidney (BHK), and NG108-15 neuroblastoma cells were heated and then plated for the colony-formation assay either with or without feeder cells present. Besides these cell lines, four other cell types were used as feeders. All cell lines functioned equally well as feeders for each of the heated cell lines. In some experiments the heated and feeder cells were separated by semipermeable membranes. This separation had no effect on the feeder effect, indicating that cell-to-cell contact was not requisite. The feeder effect appears to be mediated by a low molecular weight, diffusible substance produced by the feeder cells.

Protection from heat-induced protein migration and DNA repair inhibition by cycloheximide

The mechanism by which Cycloheximide (CHM) protects cells from heat induced killing has been investigated. Cycloheximide (10 micrograms/ml) added for 2 hr before and during a 3 hour heating at 43 degrees C prevented a 40% increase of heat-induced protein accumulation in the nucleus and protected cells (0.0001 vs. 0.15 surviving fraction) from heat-induced killing. Heat-induced DNA repair inhibition was also suppressed when cells were treated with CHM in the above manner. This combination of results suggests that protein accumulation in the nucleus and inhibition of DNA repair are related and these events are associated with CHM protection from heat induced cell killing.

A method for freezing synchronous mitotic and G1 cells

A modification of the protocol developed by Kawamoto, J C & Barrett, J N, Brain res (1986), in press for freezing primary neuron cultures in a solution containing low sodium and high lactate and potassium concentrations was used to freeze synchronous mitotic and G1 CHO cells. After thawing, the cells behaved as if they had never been frozen with respect to cell growth, cell division, plating efficiency, and hyperthermic sensitivity.

Ion-sensitive microelectrode measurements of free intracellular chloride and potassium concentrations in hyperthermia-treated neuroblastoma cells

Murine NG108-15 neuroblastoma cells were heated for times of 5-40 min at 45.5 degrees C, and survival ranged from 0.7-0.0015, respectively. Ion-sensitive microelectrodes (ISM) were used to measure the free intracellular concentrations of Cl- and K+ immediately after heating and up to 30 hr later. The free intracellular Cl- and K+ concentrations, [Cl-]i and [K+]i respectively, of the heated cells remained identical to those of the controls for the first 10 hr after heating. At later times, some cells had increased [Cl-]i values and decreased [K+]i values identical to those of the extracellular medium. These cells had a mottled morphology, no longer excluded the vital stain trypan blue, and had no membrane potential. The number of these dye-including, physiologically dead cells increased with time, and was always greater following longer heating times. No changes in mean cellular volume were observed until 25 hr after heating. All trypan-blue-excluding, physiologically live cells had the same [Cl-]i and [K+]i as the control cells, even when the majority of them were destined for clonogenic death.

A direct correlation between hyperthermia-induced membrane blebbing and survival in synchronous G1 CHO cells

Heating synchronous G1 cells at 45.5 degrees C for 3-20 min induced varying degrees of membrane blebbing ranging from nonblebbed cells indistinguishable from control cells to those with blebs larger than the cell itself. Both the proportion of cells exhibiting blebbing and the mean diameter of the blebs increased with heating duration. Scoring individual cells for both blebbing and colony formation demonstrated that cells with blebs larger than 50% of the cell diameter did not survive to form colonies. Electron microscopy showed that all subcellular organelles, save the ribosomes, were absent from the membrane blebs. Freeze fracture replicas revealed no changes in membrane ultrastructure, except on some 15% of the blebs that contained bald patches devoid of membrane particles.

A simple method for making ion-selective microelectrodes suitable for intracellular recording in vertebrate cells

A simple procedure for manufacturing Cl-, K+, and pH liquid membrane ion-sensitive microelectrodes is presented in detail. Electrodes suitable for recording from the specimen of interest are back-filled with a small amount of silane solution and heated for 5 min on a hot plate at a temperature between 400 and 500 degrees C, after which they are injected with the ion-sensitive resin. The procedure is adaptable to many different glass stocks, e.g., single-barreled, double-barreled, or theta glass, and can be used to produce electrodes having a wide range of tip sizes for recording either extracellular or intracellular ion activities. Another advantage of the method is speed; up to 10 electrodes can be prepared simultaneously, permitting over 40 functional electrodes to be made per hour.

The effect of preparative protocol on the cytoskeleton ultrastructure observed in extracted whole-mount BHK cells

Extracted BHK cells (baby hamster kidney) were prepared for electron microscopy by air-drying (with Freon 113), critical-point-drying, and freeze-drying. Variations in the drying procedures had a marked effect on the resultant cytoskeleton ultrastructure. Air drying had to be done in a Freon-saturated atmosphere, residual water had to be removed from the dehydrating solutions and carbon dioxide for critical-point-dried specimens, and freeze-drying had to be done at temperatures lower than -90 degrees C. Failure to exercise these precautions resulted in a cytoskeleton ultrastructure artifact, possibly caused by fusion of the cytoskeleton filaments.