Hyperthermia and the heat-shock proteins of HeLa cells

HSP90 inhibition acts synergistically with heat to induce a pro-immunogenic form of cell death in colon cancer cells

BACKGROUND

Sub-ablative heat induces pleiotropic biological effects in cancer cells, activating programmed cell death or survival processes. These processes decide the fate of the heated cell. This study investigates these and assesses whether heat, in combination with HSP90 inhibition, augments cell death and induces a pro-immune phenotype in these cells.

METHODS

HCT116 and HT29 cells were subjected to thermal doses (TID) of 60 and 120CEM43 using a PCR thermal cycler. HSP90 was inhibited with NVP-AUY922. Viability was assessed using the MTT assay. Cellular ATP and HSP70 release were assessed using ATP and Enzyme-linked Immunosorbent assays, respectively. Flow cytometry and immunoblotting were used to study the regulation of biomarkers associated with the heat shock response, the cell cycle, and immunogenic and programmed cell death.

RESULTS

Exposure of HCT116 and HT29 cells to TIDs of 60 and 120CEM43 decreased their viability. In addition, treatment with 120CEM43 increased intracellular HSP70 and the percentage of HCT116/HT29 cells in the G2/M cell cycle phase, ATP release and Calreticulin/HSP70/HSP90 exposure in the plasma membrane, while downregulating CD47 compared to sham-exposed cells. When combined with NVP-AUY922, treatment of HCT116/HT29 cells with 120CEM43 resulted in a synergistic decrease of cell viability associated with the induction of apoptosis. Also, the combined treatments increased Calreticulin exposure, CD47 downregulation, and HSP70 release compared to the sham-exposed cells.

CONCLUSION

Sub-ablative heating can act synergistically with the clinically relevant HSP90 inhibitor NVP-AUY922 to induce a pro-immunogenic form of cell death in colon cancer cells.

Complete regression of mouse mammary carcinoma with a size greater than 15 mm by frequent repeated hyperthermia using magnetite nanoparticles

Magnetite cationic liposomes (MCLs) have a positive surface charge and are used as a heating mediator for hyperthermia, because they generate heat in an alternating magnetic field (AMF) due to hysteresis loss. In our previous paper, hyperthermia using MCLs was applied to animals having several types of tumors in mice, rats, hamsters, and rabbits, and a strong anticancer effect was observed. For mice, complete tumor regression was observed when the tumor size was smaller than 5 mm. However, a protocol for large tumors is necessary for the clinical application. In the present paper, a protocol for tumors with a size greater than 15 mm in mice was investigated. MCLs were injected into an MM46 tumor (size, 15 mm) in C3H/HeN mice, which were subjected to AMF for 30 min. The temperature at the surface of the tumor reached 45 degrees C and was maintained by controlling the magnetic field intensity. Hyperthermia treatment was repeated twice with 24-h intervals (repeated hyperthermia; RH), and RH was carried out until complete tumor regression was observed. Complete tumor regression was achieved in all mice treated once, twice or six times with RH, and mice acquired antitumor immunity. This protocol, which is termed frequent RH, is a potent approach for cancer therapy.

Anticancer effect of hyperthermia on prostate cancer mediated by magnetite cationic liposomes and immune-response induction in transplanted syngeneic rats

BACKGROUND

The hyperthermic effect of magnetic particles was examined in rat prostate cancer in vivo. Magnetic cationic liposomes (MCLs) have a positive surface charge and generate heat in an alternating magnetic field (AMF) due to hysteresis losses.

METHODS

Rat prostate cancer cells (PLS 10; androgen independent) were injected subcutaneously into the flank of F344 rats. MCLs were injected into rat prostate cancer nodules that had grown to 5-6 mm in diameter, and were then exposed to an AMF. Tumor growth rates were measured. To examine whether hyperthermia caused immune induction for PLS 10, cytotoxicity assays and immunohistochemical staining for CD3, CD4, CD8, and Heat Shock Protein (HSP) 70 were performed.

RESULT

The tumor temperature increased to 45 degrees C whereas the body temperature remained at around 38 degrees C. Tumor regression was observed in the hyperthermic group. CD3, CD4, and CD8 immunocytes were present in the tumor tissues of the rats exposed to hyperthermia, but they were not detected in any of the tumor tissue of untreated rats. HSP70 also appeared in the viable area at its boundary with the necrotic area. The cytotoxic activity of tumor-transplanted rats for PLS 10 cells increased in hyperthermic-treatment rats.

CONCLUSION

These results suggest that hyperthermia using MCLs is an effective therapy for prostate cancer, since this treatment appears to kill the prostate cancer cells not only directly by heating but also by inducing an immune response. This therapy may cure not only the primary lesion but also metastatic lesions.

Anticancer effect and immune induction by hyperthermia of malignant melanoma using magnetite cationic liposomes

The hyperthermic effect of magnetic particles was examined in an in vivo study of mouse B16 melanoma. Magnetite cationic liposomes (MCLs) have a positive surface charge and generate heat under an alternating magnetic field (AMF) by hysteresis loss. MCLs were injected into melanoma nodules, which were then subjected to an AMF. The mice were divided into four groups: group I (control), group II (hyperthermia at 43 degrees C for 30 min, once), group III (hyperthermia at 46 degrees C for 30 min, once) and group IV (hyperthermia at 46 degrees C for 30 min, twice). Complete tumour regression was observed in 90% of the mice in group IV, while no mice in groups I and II and only 40% in group III showed regression. To examine whether hyperthermia caused immune induction in B16 melanoma, in vitro cytotoxicity assays and rechallenge experiments were performed. Cytotoxic activity was observed in the spleen cells of the cured mice in group IV. In the rechallenge experiment, 66% of the cured mice rejected melanoma cells. These results suggest that hyperthermia using MCLs is an effective therapy for melanoma, since this treatment can kill the tumour cells not only by heat but also by inducing an immune response.

Tumor regression by combined immunotherapy and hyperthermia using magnetic nanoparticles in an experimental subcutaneous murine melanoma

Immunotherapy (IT) has become an accepted therapeutic modality. We previously reported that intracellular hyperthermia (IH) using magnetic nanoparticles induces antitumor immunity. We undertook these studies in order to study the combined effects of IT and IH on melanoma. Magnetite cationic liposomes (MCLs) have a positive surface charge and generate heat in an alternating magnetic field (AMF) due to hysteresis loss. MCLs were injected into a B16 melanoma nodule in C57BL/6 mice, which were subjected to AMF for 30 min. The temperature at the tumor reached 43 degrees C and was maintained by controlling the magnetic field intensity. At 24 h after IH, interleukin-2 (IL-2) or granulocyte macrophage-colony stimulating factor (GM-CSF) was injected directly into the melanoma. Mice were divided into six groups: group I (control), group II (IH), group III (IL-2), group IV (GM-CSF), group V (IH + IL-2), and group VI (IH + GM-CSF). Complete regression of tumors was observed in mice of groups V and VI (75% (6/8) and 40% (4/10) of the mice, respectively), while no tumor regression was observed in mice of the other groups. This study supports the combined use of IT and IH using MCLs in patients with advanced malignancies.

Pre-treatment with mild whole-body heating prevents gastric ulcer induced by restraint and water-immersion stress in rats

The purpose of this study was to assess the preventive effect of pre-mild whole-body heating (WBH) on gastric ulcer induced by restraint and water-immersion stress. The ulcer index and ulcer area ratio in rats exposed to restraint and water-immersion stress were significantly decreased (p < 0.05 for both) after pre-treatment with mild WBH, compared with non-pre-treated rats. Mortality of rats among the pre-treated with mild WBH (0%) was lower than in the control group (33%). The concentration of HSP 70f in the stomach (both fundic and pyloric mucosal areas) of rats pre-treated with mild WBH was significantly higher than in animals exposed to restraint and water-immersion stress alone (p < 0.05) before exposed to stress, but was not significantly higher immediately after stress or 1 or 3 days later. The HSP 70f content of peripheral lymphocytes was increased by the pre-treatment with mild WBH. These results suggest that HSP 70f induced by pre-treatment with mild hyperthermia protects against more severe stress due to restraint and water-immersion, thereby preventing gastric ulcer formation. Pre-treatment with mild WBH is the safest cytoprotective method through the accumulation of HSP 70f. The concentration of HSP 70f in peripheral lymphocytes may be a useful clinical laboratory indicator for assessing the level of HSP 70f as having cytoprotective activity.

Cell survival effect of activin against heat shock stress on OVCAR3

Activin has been known as the hormone protein which regulates either cell proliferation or cell differentiation. Recently, it has also been reported that activin may have cell survival function. In this study, we have investigated, 1) the expression of inhibin subunits and activin receptors (ActRs) in ovarian carcinoma cell line (OVCAR3), 2) the binding property between activin and its receptors under the exposure to stress, and 3) the effect of activin on cell proliferation. All of inhibin subunits and ActR Ia, IIa and IIb mRNA were amplified by RT-PCR in OVCAR3. By Western blot analysis, ActR IIa and IIb proteins were detected. The binding property between activin and ActRs was analyzed with the fixed complex, using chemical cross linker. The bigger molecular weight signals, which had been shown to form the heterotrimeric complex among activin, ActR type I and ActR type II were detected after cross linking. These upper signals were apparently increased by rh-Activin and decreased by rh-Follistatin. Therefore, it was suggested that they were resultant from activin and Act-R complex. OVCAR3 was exposed to the stress (42C, 1 hour heat shock), the protein level of ActR IIa increased and ActR IIb decreased from about 3 h to 24 h after the exposure to the heat stress (HS). On the other hand, the complex between activin and ActR IIa and IIb increased from 3 h after the exposure to HS. To investigate the effect of activin and follistatin on OVCAR3 proliferation after the exposure to HS, we counted the cell number at 96 h after the treatment with activin or follistatin in the condition either with or without HS. Proliferation of the cell in the presence of HS was stimulated by rh-Activin and inhibited by rh-Follistatin. These data suggest that activin might have the function to survive and to proliferate OVCAR3, due to, at least in part the increase in its binding capacity to ActRs through either autocrine or paracrine manner.

Flow cytometric measurements of heat shock proteins

A fixation and immunofluorescence staining procedure for measurements of heat shock proteins (hsp) by flow cytometry is reported. Three fixatives were compared: 80% methanol at -20 degrees C for 1 h, 70% ethanol at 0 degree C for 1 h, and 3% paraformaldehyde at 4 degrees C for 1 h followed by 0.2% NP-40. Cells fixed with methanol showed strongest immunofluorescence and lowest nonspecific fluorescence. The level of hsp 70 as a function of time after heating followed the same kinetics as the development of thermotolerance reported by others. The level of hsp 70 increased with increasing heat dose up to a maximum heat dose, and above this heat dose a decrease in the level of hsp 70 was observed. Correlated measurements of the level of hsp 70 and DNA showed that hsp 70 was found in all phases of the cell cycle. The level of hsp 70 increased about two-fold in unheated cells throughout the cell cycle. The increase in G2 + M cells compared with G1 cells was lower in cells heated at 45 degrees C for 20 min followed by incubation at 37 degrees C for 24 h before fixation and staining, than in unheated cells. The results show that flow cytometry provides a rapid and quantitative technique for measuring hsp. Correlated measurements of hsp and other cellular parameters might also be obtained.

The role of apoptosis in the response of cells and tumours to mild hyperthermia

There is now abundant evidence that apoptosis, the cell death mechanism responsible for physiological deletion of cells, can be triggered by mild hyperthermia. However, the overall importance of this mode of death in heated tumours has not yet been established. In this light and electron microscopic study, apoptosis induced by 43 degrees C or 44 degrees C water bath heating for 30 min in a range of murine and human tumours growing in vitro and in four murine tumours growing as solid nodules in vivo, was identified on the basis of its characteristic morphology, and the amount present quantified. Apoptosis was found to play a variable role in the response of tumours to heating, with the lowest levels produced in human melanoma lines (less than 1%) and the highest levels in some Burkitt's lymphoma lines (up to 97%). In these latter tumours the induction of apoptosis is clearly a major component of the hyperthermic response.

Cell death induced in a murine mastocytoma by 42-47 degrees C heating in vitro: evidence that the form of death changes from apoptosis to necrosis above a critical heat load

The pathogenesis of heat-induced cell death is controversial. Categorizing the death occurring after various heat loads as either apoptosis or necrosis might help to elucidate this problem, since it has been shown that these two processes differ in their mode of initiation as well as in their morphological and biochemical features. Log-phase cultures of mastocytoma P-815 x 2.1 were heated at temperatures ranging from 42 to 47 degrees C for 30 min. After 42 degrees C heating a slight increase in apoptosis was observed morphologically. However, after heating at 43, 43.5 and 44 degrees C, there was marked enhancement of apoptosis, and electrophoresis of DNA showed characteristic internucleosomal cleavage. With heating at 45 degrees C both apoptosis and necrosis were enhanced, whereas at 46 and 47 degrees C only necrosis was produced. DNA extracted from the 46 and 47 degrees C cultures showed virtually no degradation, which contrasts with the random DNA breakdown observed in necrosis produced by other types of injury; lysosomal enzymes released during heat-induced necrosis may be inactivated at the higher temperatures. It is suggested that apoptosis following heating may be triggered either by a limited increase in cytosolic calcium levels resulting from mild membrane changes or by DNA damage. Necrosis, on the other hand, is likely to be a consequence of severe membrane disruption.

Organization and disorganization of actin filaments in human epidermal keratinocytes: heat-shock treatment and recovery process

We investigated alterations of actin organization due to heat shock and recovery from the collapse in human epidermal keratinocytes. Exposure of keratinocytes to elevated temperature caused the rapid disintegration of actin filaments. With a heat-shock treatment at 45 degrees C for 10 min, actin filaments disappeared and granular actin was distributed diffusely in the cytoplasm. After return to 37 degrees C, recovery of actin organization was observed. Completely disintegrated granular actin assembled to form actin dots, which tended to group. The grouping actin dots often took a circular, semicircular or arched form. Filamentous actin then extended out from the actin dots. Fine short bundles of actin filaments had a rippled appearance or were polygonal in structure, with actin filaments converged at many points. On the seventh day after heat-shock treatment, actin organization had almost returned to the pre-heat-shock condition, with diffusely distributed actin filaments. In previous studies, we observed such aberrant structures in human malignant keratinocytes and human epidermal keratinocytes treated with 12-O-tetradecanoylphorbol-13-acetate. The observations presented here indicate that those structures are not specific to malignancy or to the process of malignant transformation, but represent less mature and aberrant organizations of actin.

Protein synthesis and protein phosphorylation during heat stress, recovery, and adaptation

Incubating cells at elevated temperatures causes an inhibition of protein synthesis. Mild heat stress at 41-42 degrees C inhibits the fraction of active, polysomal ribosomes from greater than 60% (preheating) to less than 30%. A return to 37 degrees C leads to an increase in protein synthesis, termed "recovery." Continuous incubation at 41-42 degrees C also leads to a gradual restoration of protein synthesis (greater than 70% of ribosomes reactivated by 2-4 h), termed "adaptation". Protein synthesis inhibition and reactivation is prestressed, recovered cells that contain elevated levels of the heat stress proteins occur to the same extent and at the same rate as in "naive" cells. The adaptation response requires transcription of new RNA whereas recovery does not. A large number of phosphorylation changes are induced by severe heat stress and occur with kinetics similar to the inhibition of protein synthesis. These include phosphorylation of eukaryotic protein synthesis initiation factor (eIF)-2 alpha and dephosphorylation of eIF-4B and eIF-4Fp25 (eIF-4E). However, the extent to which the modification occurs is proportional to the severity of the stress, and, under mild (41-42 degrees C) heat stress conditions, these initiation factor phosphorylation changes do not occur. Similarly, under conditions of severe heat stress eIF-2 alpha and eIF-4B frequently recover to their prestress phosphorylation state before the recovery of protein synthesis. eIF-4E dephosphorylation likewise does not occur under mild heat stress conditions. Therefore, these changes in phosphorylation states, which are thought to be sufficient cause, are not necessary for the inhibition of protein synthesis observed.

Differential regulation of closely related members of the hsp16 gene family in Caenorhabditis elegans

The heat-inducible genes encoding 16-kD heat shock polypeptides in Caenorhabditis elegans are found at two separate loci, one containing the 16-1 and 16-48 genes (locus A), and the other, the 16-2 and 16-41 genes (locus B). Despite the highly conserved structures of these genes and their promoters, the B locus produces up to sevenfold more mRNA during heat induction than does the A locus. Since there are two copies of the 16-1 and 16-48 genes at the A locus, the discrepancy in mRNA production is actually as high as 14:1 on a per gene basis. Measurements of the rate of hsp16 mRNA decay during recovery from a heat shock suggest that this difference is not caused by differential mRNA stability; furthermore, nuclear runon experiments yield rates of transcription for the 16-1/48 locus that are approximately threefold higher than those from the 16-2/41 locus. The higher levels of mRNA from the 16-2/41 locus, particularly at longer induction times, seem to be due to a marked difference in the temporal pattern of mRNA production from the two loci. While both loci are transiently activated by a heat shock, the 16-1 and 16-48 genes of the A locus are down-regulated to a lower transcription rate sooner than the genes from the B locus.

Ultrastructural changes induced by hyperthermia in Chinese hamster V79 fibroblasts

The effects of hyperthermic treatment on some intracellular components and on the general morphology of Chinese hamster V79 fibroblasts have been studied. After 1 h of heating at 42 degrees C cells show small interruptions of the plasma membrane, dilation of the mitochondrial cristae and dissociation of the polyribosomes. These modifications become progressively more pronounced after 1 or 3 h treatment at 43 degrees C. Severe alterations in the general morphology of the cells are evident after 1 h heating at 45 degrees C.

Thermotolerance of xenografted human gastric cancer

To compare the thermotolerance in vivo of two human gastric cancers with different doubling times, the xenografted tumors were warmed twice at 43.5 +/- 0.1 degree C in a water bath for 20 minutes at a predetermined interval. In the tumors with doubling times of 5.2 and 10.9 days, a 7-day interval heat treatment resulted in a prolongation in tumor tripling times by 156 per cent and 132 per cent, respectively, compared with a single heat treatment for 40 minutes. On the contrary, two heat treatments given at intervals of 3 to 5 days had a short tumor tripling time, compared to that of the 40-minute single treatment. Thus, the thermotolerance of these human gastric cancers gradually increased to a maximum within a 3- to 4-day interval and disappeared completely after a 7-day interval. These results indicate that the times required to reach maximal thermotolerance in these human gastric cancers were longer than those previously demonstrated for human and rodent cancer cell lines in vitro. The development and decay of thermotolerance in these human gastric cancers need to be considered in the design of multiple-fractionated regimens.

Cell proliferation and oxidative stress

Antioxidants such as mannitol, butylated hydroxytoluene and alpha-tocopherol enhance the growth of polyoma virus transformed and non-transformed BHK-21 cells. In the case of mannitol this is observed even in the absence of added calf serum. In part these effects may operate to protect cellular growth control mechanisms. On the other hand oxidants such as H2O2 and t-butyl hydroperoxide can inhibit growth and overall cellular protein synthesis, through mechanisms that are likely to involve radicals. In the case of H2O2 the inhibitory effects can nevertheless be reduced by 'prestressing' the cells with mild heat or with H2O2 itself. Paradoxically very low concentrations (10(-8) M) of H2O2 or t-butyl hydroperoxide can actually stimulate cell growth, even in the absence of serum. These stimulatory effects however do not appear to involve radicals as they are enhanced by inclusion of mannitol or DMSO in the medium.

Hyperthermia in cancer therapy

Tumor hyperthermia is a rediscovered technique of oncotherapy which has confirmed value in many studies on cell cultures, rodent and mammalian tumors as well as first investigations on patients with tumors. The biological basis for using heat in the treatment of cancer is well established. Various direct and indirect mechanisms are significant for the effect of hyperthermia on tumor tissue. Whereas there are already extensive studies on the direct effects of hyperthermia on DNA, RNA, and protein synthesis, energy metabolism, and the membrane properties of tumor cells, the indirect effects have only been investigated more closely in recent years. These are likewise important for the damage to the tumor tissue and are mediated above all via alterations in the microcirculation and the environment. The recently gained increasing significance of this new technique in combination with other treatment modalities is well documented. Technical problems of heat application must be overcome, especially in deeper tumors and problems of thermometry must be solved in order to be able to apply tumor hyperthermia not only to selected advanced or recurrent tumors, but in order to use it as the fourth pillar of tumor therapy besides surgery, radiotherapy and chemotherapy. This article considers the biological basis and important aspects of hyperthermia therapy in combination with radiotherapy and chemotherapy.

Regulation of protein synthesis in intact rat liver by calcium mobilizing agents

1. Exposure of intact perfused rat liver to EGTA, vasopressin or phenylephrine resulted in a rapid decrease in polysome formation. Pretreatment with phentolamine, an alpha-adrenergic antagonist, blocked the effect of phenylephrine. 2. Hormonal inhibitions of leucine incorporation into protein in isolated hepatocytes and of polysome formation in perfused liver were reversed in the presence of supraphysiologic extracellular Ca2+ concentrations. 3. The beta-adrenergic agonist isoproterenol exerted minimal effects on polysome content. 4. It is proposed that intracellular Ca2+ stores sensitive to hormonal modulation are necessary for maintenance of protein synthesis in hepatocytes.

Oxidative stress and heat shock protein induction in human cells

Agents which induce heat shock protein synthesis in cultured monolayers of Hela cells such as hyperthermia, ethanol and sodium arsenite can also cause increases in the levels of lipid peroxidation as determined by the formation of TBA-products. The heat induced increases may be diminished by addition to the medium of mannitol or EGTA. These compounds are known to depress heat shock protein synthesis. Following hyperthermia there is also a decrease in protein synthesis. In vitro studies indicate possible damage to ribosomes, and since the heat induced loss of protein synthetic capacity can be increased by superoxide dismutase inhibitors, and prevented by mannitol, such effects may be linked to the increases observed in lipid peroxidation. It is suggested that a connection exists between lipid peroxidation and heat shock protein gene activation.

Characterization of the heat shock response in M-14 human melanoma cells continuously exposed to supranormal temperatures

The heat shock response elicited in a human melanoma cell line (M-14) by continuous exposures to supranormal temperatures has been characterized. The electrophoretic patterns of polypeptides labeled in vivo at different time-intervals during a continuous heating at 42 degrees C show that the hyperthermic stress induces the synthesis of three HSPs, with molecular weights, respectively, of 86 kDa, 70-72 kDa and 26 kDa. The relative rate of synthesis of the 70-72 kDa HSP--the preeminent HSP--increases during the first hours of treatment, reaching the maximum value after about 9 hr. Later on, the rate of synthesis of this protein progressively decreases, finally attaining a steady state level only slightly exceeding the constitutive one. On the contrary, the smaller molecular weight HSP is synthesized at an apparently constant rate in the course of 21 hr of heating treatment. A continuous exposure at 40 degrees C induces the synthesis of the same three HSPs observed in cells heated at 42 degrees C, but the rate of synthesis of all these HSPs is not so greatly enhanced over the control values as in the 42 degrees C-heated cells. Moreover, the repression of the 70-72 kDa HSP synthesis is faster, taking place within 4-6 hr of treatment. Coomassie blue stained gels show that a polypeptide, coincident with the 70-72 kDa HSP, accumulates in the course of a continuous heating either at 42 degrees C and at 40 degrees C. The final intracellular level attained by this protein species results higher in 42 degrees C-treated cells than in 40 degrees C-treated ones. Hybridization experiments between total RNAs obtained from cells heated at 42 degrees C and a radioactive DNA probe (containing sequences complementary to the mRNA coding for the human 70 kDa HSP) demonstrate that the kinetics of accumulation and decay of the 70 kDa HSP-mRNAs correlate with the kinetics of induction and repression of the corresponding protein.

Heat shock induces variably the major heat shock proteins of CV1 clones

CV1 cells have been subcloned several times. Five of these clones were studied for the induction of the major heat shock proteins. These CV1 clones exhibit morphological differences as well as differences in SDS-PAGE protein profiles. These clones responded to heat shock variably as judged from the induction of the major heat shock proteins, 70, 72 and 92 kDa. Variable expression of the heat shock proteins suggests that the selective pressure for isolation of cell clones may affect gene expression differently.

Relationship between cell survival and heat-stress protein synthesis in a Drosophila cell line

Heat-stress protein (hsp) kinetics and clonogenic survival were studied at 33, 37 and 42 degrees C in a continuous Drosophila cell line, WR69-DM-1. Induction and repression of hsp were temperature-dependent and independently modulated. The subsequent cell-survival curves were complex; however, survival generally decreased in a time- and temperature-dependent manner during continuous heating at 33, 37 or 42 degrees C. Constant 33 degrees C heating induced five hsp at 90, 72, 70, 24 and 19 kilodaltons (kDa). A 30 min 33 degrees C heat dose led to thermotolerance after 1, 3 or 6 h incubations at 28 degrees C. The hsp synthesized after this dose were quickly repressed, suggesting the cells were able to respond to this stress. Increasing the challenge temperature to 37 degrees C induced three additional hsp at 34, 22 and 14 kDa, but hsp synthesis did not lead to thermotolerance over the 6 h interval. The number and intensity of hsp synthesized was higher and repression was much slower than at 33 degrees C. Heating at 42 degrees C inhibited all protein synthesis, and thermotolerance was not observed. Direct survival data are critical to understanding the role and function of hsp in Drosophila thermotolerance since the relevance of information on number and kinetics of hsp synthesis and their subsequent localization is dubious without it.

Enhanced reactivation of UV-irradiated adenovirus 2 in HeLa cells treated with non-mutagenic chemical agents

Treatment of HeLa cells with ethanol and sodium arsenite, compounds which are known to elicit the heat-shock response, before infection with UV-irradiated adenovirus 2 has been found to result in the enhanced reactivation of the damaged virus in a manner similar to that obtained by pre-irradiation or heating of the cells. Enhanced reactivation may be the result of the inhibition of DNA synthesis caused by these agents since hydroxyurea also produced a significant enhancement.

Heat shock causes diverse changes in the phosphorylation of the ribosomal proteins of mammalian cells

When HeLa cells or BHK cells were subjected to heat shock at 42 degrees C (for 2 h) or 45 degrees C (for 10 min) there was extensive dephosphorylation of ribosomal protein S6. Concomitantly ribosomal protein L14, which is not significantly phosphorylated in normal cells, became phosphorylated, as did a non-structural protein of Mr = 27000, associated with the ribosomes. The latter effects were not prevented by cycloheximide or actinomycin D. When cells shocked at 45 degrees C for 10 min were returned to 37 degrees C for 2 h there was rephosphorylation of ribosomal protein S6 and dephosphorylation of the 27 kDa protein, but not of ribosomal protein L14.

Hyperthermia, Na+K+ATPase and lactic acid production in some human tumour cells

When HeLa cells are exposed to brief heat shock at 45 degrees C there is a reduction in the cellular level of Na+K+ATPase. Return of the cells to the normal growth temperature of 37 degrees C leads to a partial restoration of enzyme activity. The pattern of this recovery of activity suggests that it may be associated with the induction of heat shock proteins. Indeed other means of heat shock protein induction such as continuous heat treatment at 42 degrees C, or treatment of cells at 37 degrees C with sodium arsenite, leads to elevated levels of Na+K+ATPase activity and alterations in the kinetic properties of the enzyme. Continuous hyperthermia at 42 degrees C led to increased lactate production which could be blocked with ouabain suggesting that effects on Na+K+ATPase activity could partly influence glycolysis. A number of other human and hamster cells also showed increased lactate production at 42 degrees C and also an inhibition of lactate production by ouabain. Whilst incubation of HeLa cells with cyanide had little effect on glycolysis at 37 degrees C elevation of the temperature to 42 degrees C (or 45 degrees C), in the presence of cyanide, impaired glycolysis. The possible role in this phenomenon, of an unusual oxygen-sensitive isoenzyme of lactate dehydrogenase, expressed in human cancers, is discussed.

Dephosphorylation of S6 and expression of the heat shock response in Drosophila melanogaster

A basic ribosomal phosphoprotein of 30,000 molecular weight was rapidly dephosphorylated in cultured Drosophila melanogaster cells heat shocked at 37 degrees C. The protein was associated with the 40S ribosomal subunit and had an electrophoretic mobility similar to that of purified rat liver protein S6 on basic two-dimensional polyacrylamide gels as well as a similar partial proteolysis peptide map. In logarithmically growing cultures, this D. melanogaster S6 protein appeared to have a single phosphorylated species consisting of 30 to 40% of the total cellular S6. Thus, the nearly complete dephosphorylation of this protein observed in heat shock involves a large fraction of the cellular S6. The significance of this dephosphorylation in the expression of the heat shock response was investigated by examining the phosphorylation status of S6 in recovery from heat shock and in response to chemical inducers of the heat shock response. During recovery from a 30-min heat shock, the recovery of normal protein synthesis was almost complete in 2 to 4 hr, whereas there was no significant rephosphorylation of S6 for 8 h. Two chemical inducers of the heat shock response, canavanine and sodium arsenite, induced the synthesis of heat shock proteins in D. melanogaster cells. Sodium arsenite also caused an inhibition of normal protein synthesis similar to that observed in heat shock. Neither agent, however, caused significant dephosphorylation of S6. These results suggest that the dephosphorylation of S6, although invariably observed in heat-shocked cells, may in some cases be dissociated from both the induction of heat shock protein synthesis and the turnoff of normal protein synthesis which occur in a heat shock response.

Hyperthermia enhances the reactivation of irradiated adenovirus in HeLa cells

The reactivation of U.V.-irradiated adenovirus 2 in HeLa cells is enhanced 8-9 fold if the cells are given a brief hyperthermic shock before infection. Maximum reactivation is achieved by heating for 10 min at 45.5 degrees C and with a delay of 36 h between heating and infection. The induction process requires protein synthesis only during the 3 h period immediately following heating; cycloheximide does not prevent the expression of enhanced reactivation if added to the cells after this time. Heat-enhanced reactivation exhibits properties similar in some respects to radiation-enhanced reactivation and indicates an increased capacity of the heated cells to tolerate DNA damage.

Dephosphorylation of S6 and expression of the heat shock response in Drosophila melanogaster

A basic ribosomal phosphoprotein of 30,000 molecular weight was rapidly dephosphorylated in cultured Drosophila melanogaster cells heat shocked at 37 degrees C. The protein was associated with the 40S ribosomal subunit and had an electrophoretic mobility similar to that of purified rat liver protein S6 on basic two-dimensional polyacrylamide gels as well as a similar partial proteolysis peptide map. In logarithmically growing cultures, this D. melanogaster S6 protein appeared to have a single phosphorylated species consisting of 30 to 40% of the total cellular S6. Thus, the nearly complete dephosphorylation of this protein observed in heat shock involves a large fraction of the cellular S6. The significance of this dephosphorylation in the expression of the heat shock response was investigated by examining the phosphorylation status of S6 in recovery from heat shock and in response to chemical inducers of the heat shock response. During recovery from a 30-min heat shock, the recovery of normal protein synthesis was almost complete in 2 to 4 hr, whereas there was no significant rephosphorylation of S6 for 8 h. Two chemical inducers of the heat shock response, canavanine and sodium arsenite, induced the synthesis of heat shock proteins in D. melanogaster cells. Sodium arsenite also caused an inhibition of normal protein synthesis similar to that observed in heat shock. Neither agent, however, caused significant dephosphorylation of S6. These results suggest that the dephosphorylation of S6, although invariably observed in heat-shocked cells, may in some cases be dissociated from both the induction of heat shock protein synthesis and the turnoff of normal protein synthesis which occur in a heat shock response.