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G C Li

Publications and source records attributed to G C Li.

At least 109 records · Page 6Linked to original sources
PubMed1985

Amino acid analogs while inducing heat shock proteins sensitize CHO cells to thermal damage.

Amino acid analogs have been shown to induce heat shock proteins (HSPs). We have examined the effect of these analogs on the thermal sensitivity of Chinese hamster fibroblasts (HA-1) and their stable heat-resistant variants. We found that exposure of HA-1 cells and their heat-resistant variants to canavanine or L-azetidine-2-carboxylic acid cause enhanced synthesis of the three major mammalian HSPs (molecular weight 70,000, 87,000, and 110,000 kd). Although the synthesis of HSPs was increased, the analogs did not induce thermotolerance, a transient ability to protect cells from thermal damage. On the contrary, the analog treatment increased the thermal sensitivity of HA-1 cells, but not of the heat-resistant strains, when these cells were exposed subsequently to elevated temperatures. Our tentative explanation for these findings is that the incorporation of amino acid analogs into HSPs or other cellular proteins sensitizes HA-1 cells to heat. The heat-resistant strains contain higher levels of constitutive HSPs. The additional functional HSPs in the heat-resistant variants may protect these cells from thermal stress. The presence of some newly synthesized analog-substituted, perhaps nonfunctional, HSPs need not affect this thermal protection.

Animals↗
PubMed1985

Elevated levels of 70,000 dalton heat shock protein in transiently thermotolerant Chinese hamster fibroblasts and in their stable heat resistant variants.

The function of one or more shock proteins (HSPs) may be to confer protection of cells against thermal damage. The quantitative relationship between heat sensitivity and concentration of several HSPs was examined in thermotolerant Chinese hamster HA-1 cells and in their heat-resistant variants. Low molecular weight HSPs (22-27 kd) showed no correlation with cell survival. The best correlation was found between concentration of 70 kd HSP and the logarithm of cell survival. There was no difference between the HSP 70 induced by heat shock and that present in a constitutive form. The 70 kd HSP may actually confer heat resistance on cells, but in any case HSP 70 appeared to be the best predictor of heat response.

Actins↗
PubMed1985

Heat-resistant variants of Chinese hamster fibroblasts altered in expression of heat shock protein.

Heat-resistant variants of the Chinese hamster HA-1 line have been isolated after repeated heat treatments. The heat-resistant phenotype has been stable for over 70 passages. One of the members of the 70-kDa heat shock protein family was found to be synthesized at greater levels in the heat-resistant variants under normal growth conditions. Mild heat treatment of the variant lines induced a transient thermotolerance that was accompanied by additional increase in the synthesis of the 70-kDa heat shock proteins. Cell-free translation of total cellular RNA revealed greater amounts of 70-kDa heat shock protein mRNA in both control and heated variant cells. The greater levels of 70-kDa heat shock protein synthesized in the variant cells presumably are a reflection of altered levels of its messenger mRNA. In addition, we found that translational control plays a role in the elevated expression of heat shock proteins in heat-shocked HA-1 cells and their heat-resistant variants. The association of the heat-resistant phenotype with increased levels of a 70-kDa heat shock protein suggests strongly that this gene product plays a role in protecting cells from damage inflicted by elevated temperatures.

Animals↗
PubMed1985

Induction of heat shock protein synthesis in murine tumors during the development of thermotolerance.

The function of one or more heat shock proteins (HSPs) may be to confer protection of cells against thermal damage. We examined the induction kinetics of thermotolerance and the synthesis of HSPs in murine tumor models. Squamous cell carcinomas (SCC VII/SF) or radiation-induced fibrosarcomas (RIF) were implanted in the flanks of C3H mice. These flank tumors were first exposed to an elevated temperature (41 degrees-45 degrees C) for a fixed duration, for example, 43 degrees C for 15 min. Some of the tumors were excised immediately, and tumor cell suspensions were made. The other mice with tumors were returned to the cages and left undisturbed for various times up to 72 h before being sacrificed. Again, tumors were then removed and tumor cell suspensions were prepared. These tumor cells were either challenged with a second heat treatment at 45 degrees C in vitro or labeled with [35S]methionine at 37 degrees C in vitro. The tumor cell survival after the combined heat treatments was measured using the in vitro cloning assay. The cellular proteins were analyzed by one- or two-dimensional gel electrophoresis. We found that mild heat shock induced thermotolerance in murine tumors, a result consistent with those of others. The kinetics of induction and decay of thermotolerance depended on the temperature and duration of the priming treatment. Mild heat shock also enhanced the rate of synthesis and accumulation of some HSPs during the development of thermotolerance. For example, after an initial treatment at 43 degrees C for 15 min, the rates of synthesis of HSPs with molecular weights 68,000, 70,000, and 88,000 were greatly enhanced in SCC VII/SF tumors when compared to unheated controls. Qualitatively similar results were seen with radiation-induced fibrosarcoma tumors. The rate of synthesis of Mr 68,000 to 70,000 HSPs reached maximum value (300% of control value) 2 to 4 h after heat shock and decreased to the control value 6 to 24 h later. On the other hand, the rate of synthesis of actin, a major structural cellular protein, remained relatively constant throughout the 72 h of experiments. We then determined the relationship between the synthesis and accumulation of these HSPs and the expression of thermotolerance in murine tumors after a priming heat treatment. The data indicate that the levels of Mr 68,000 to 70,000 HSPs correlate well with thermotolerance.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed1985

Thermotolerance and profile of protein synthesis in murine bone marrow cells after heat shock.

In this study, we first investigated the survival of colony-forming units, granulocyte and macrophage (CFU-GM), after a single heat treatment. We then examined the induction, development, and decay of thermotolerance in CFU-GM. Finally, we analyzed the profiles of protein synthesis in the total murine bone marrow population during the development of thermotolerance. Several salient features emerged from our study: (a) granulocyte-macrophage progenitors were very sensitive to heat as compared to other mammalian cell lines; (b) CFU-GM can develop thermotolerance after both prolonged heating at 41-42 degrees C or an acute heat treatment at 43 degrees C in vitro; (c) thermotolerance in CFU-GM can be induced in vivo; the kinetics of development of thermotolerance in vivo is similar to that in vitro; (d) in contrast to other cell lines where thermotolerance lasts for several days, tolerance acquired by CFU-GM disappeared within 24 h, regardless of the temperature or duration of the initial heat treatment. The difference between the kinetics of systemic thermotolerance and thermotolerance in CFU-GM in the same animal model shows that bone marrow stem cells, or at least CFU-GM, are not the critical targets for systemic thermal death. When protein synthesis profiles of the heat-shocked bone marrow cells were compared to those from nonheated controls by one- and two-dimensional gel electrophoresis, the rates of synthesis of the Mr 70,000 and 87,000 proteins were shown to be enhanced during the development of thermotolerance. The enhanced rate of synthesis of these polypeptides lasted only 2-4 h and then returned to the control value.

Adaptation, Physiological↗
PubMed1985

Mechanistic implications of the induction of thermotolerance in Chinese hamster cells by organic solvents.

Several organic solvents were shown to induce thermotolerance. These included: aliphatic alcohols (ethanol to octanol); local anesthetics; dimethyl sulfoxide; and dimethyl formamide. The minimum concentrations of the various alcohols required to induce tolerance were similar to the threshold doses for cytotoxicity. When only intramembrane concentrations were considered (by multiplying by the appropriate membrane:buffer partition coefficient), then the alcohols' threshold dose to induce tolerance was only mildly a function of carbon number. The efficiency increased almost linearly with a membrane dose from propanol to pentanol, but was slightly reduced for octanol. All alcohols induced tolerance rapidly (within a few hours after 30-min exposure), but the thermotolerance ratio decreased with increasing carbon number. Of the three anesthetics examined, lidocaine was a highly efficient inducer, procaine less so, and tetracaine did not induce tolerance even at a concentration mildly cytotoxic. Dimethyl sulfoxide and dimethyl formamide induced tolerance without cytotoxicity, but the kinetics of doing so was different from that seen with the other solvents. Only cells exposed to these water-soluble agents for 18 h or longer showed evidence of induced heat resistance. Our results indicate that membranes likely are the site for the initiation of solvent-induced cell killing and thermotolerance. The minimum dose of induction may be related to the degree of disorder induced by the individual alcohol, but the amount of tolerance induced is inversely related to this. The data on the effects of local anesthetics show that neither their common functional mode of inhibiting nerve transmission nor their similar level of cytotoxicity insures similar efficiency as tolerance inducers. Results with dimethyl sulfoxide and dimethyl formamide suggest that tolerance can be induced by more than one mechanism, or alternately, that a multiple-step mechanism can be activated at different points along this pathway. We also measured heat shock protein synthesis after several treatments; efficient inducers of thermotolerance also induced these proteins.

Alcohols↗
PubMed1985

Effects of proliferation on the decay of thermotolerance in Chinese hamster cells.

Development and decay of thermotolerance were observed in Chinese hamster HA-1 cells. The thermotolerance kinetics of exponentially growing and fed plateau-phase cells were compared. Following a 10-min heat exposure at 45 degrees C, cells in both growth states had similar rates of development of tolerance to a subsequent 45-min exposure at 45 degrees C. This thermotolerant state started to decay between 12 and 24 hr after the initial heat exposure. The decay appeared to initiate slightly sooner in the exponentially growing cells when compared to the fed plateau-phase cells. During the decay phase, the rate of thermotolerance decay was similar in the two growth conditions. In other experiments, cells were induced to divide at a slower rate by chronic growth (3 months) in a low concentration of fetal calf serum. Under these low serum conditions cells became more sensitive to heat and the rate of decay of thermotolerance remained the same for exponentially growing cells. Plateau-phase cells were also more sensitive, but thermotolerance decayed more rapidly in these cells. Although dramatic cell cycle perturbations were seen in the exponentially growing cells, these changes appeared not to be related to thermotolerance kinetics.

Acclimatization↗
PubMed1985

Effect of heat shock on the intracellular distribution of proteins.

Exposure of cells to heat induces thermotolerance, a transient resistance to subsequent heat challenges. It has been shown that thermotolerance is correlated in time with the enhanced synthesis of heat shock proteins. In this study, the association of induced heat shock proteins with various cellular fractions was investigated and the heat-induced changes in skeletal protein composition in thermotolerant and control cells was compared. All three major heat shock proteins induced in Chinese hamster fibroblasts after a 46 degrees C, 4-min heat treatment (70, 87, and 110 kDa) were purified with the cytoplasmic fraction, whereas only the 70-kDa protein was also found in other cell fractions, including that containing the cellular skeleton. Immediately after a second heat treatment at 45 degrees C for 45 min, the 110-kDa protein from thermotolerant cells also purified extensively with the cellular skeletal fraction. In this regard, the 110-kDa protein behaved similarly to many other cellular proteins, since we observed an overall temperature-dependent increase in the total labeled protein content of the high-salt-resistant cellular skeletal fraction after heat shock. Pulse-chase studies demonstrated that this increased protein content gradually returned to normal levels after a 3-hr incubation at 37 degrees C. The alteration or recovery kinetics of the total labeled protein content of the cellular skeletal fraction after heat shock did not correlate with the dramatic increase in survival observed in thermotolerant cells. The relationship between heat shock proteins and thermotolerance, therefore, does not correlate directly with changes in the heat-induced cellular alterations leading to differences in protein fractionation.

Acclimatization↗
PubMed1984

Effect of hyperthermia on murine cell surface histocompatibility antigens.

The effect of heat on the density of cell surface histocompatibility antigens was examined. Antigen density and distribution were determined by radioimmunoassay and flow cytometry after the binding of radioiodinated or fluoresceinated monoclonal antibody (anti-H-2Kk and anti-H-2Kb) to murine lymphoma cells in suspension cultures. Antibody binding was unaffected by temperatures between 37 degrees and 41 degrees following a 30-min heat exposure. At 42 degrees, some inhibition of binding was measurable. However, at 43 degrees, antibody binding was reduced by 30 to 50%, and a further 15 to 20% reduction was observed at 45 degrees. Flow cytometry showed that all cells were equally affected. There was no indication of the selection of a specific cell population. The temperature-dependent decrease in antibody binding was due to a decrease in receptor number and not to changes in the affinity. Measurement of the diffusion coefficient of the lipid probe N,N-dioctadecyl indocarbocyanine iodide showed that heat did not affect significantly the fluidity of the membrane lipids. Hyperthermic temperatures, therefore, have a direct effect on these membrane proteins.

Animals↗
PubMed1984

Thermal biology and physiology in clinical hyperthermia: current status and future needs.

The current status and needs of thermal biology and physiology as related to clinical hyperthermia are summarized. Emphasis is placed on heat-induced modification of blood flow and microenvironment in tissues, on the biological effects of heat and X-rays, and on the relationship between drug resistance, heat resistance, and thermotolerance in thermochemotherapy. Results from recent studies investigating the relationships between thermotolerance and heat shock proteins in tissue culture cell lines, in rodent tumors, and in normal tissues are presented. These data strongly suggest that the levels of Mr 70,000 heat shock protein can be used as an assay to predict the thermal sensitivity of tissues during fractionated hyperthermia.

Animals↗
PubMed1983

Induction of thermotolerance and enhanced heat shock protein synthesis in Chinese hamster fibroblasts by sodium arsenite and by ethanol.

Synthesis of a family of proteins called "heat shock" proteins is enhanced in cells in response to a wide variety of environmental stresses. This suggests that these proteins may have functions essential to cell survival under stressful conditions. A causative relationship between heat shock protein synthesis and development of thermotolerance would imply that agents known to induce heat shock protein synthesis, such as sodium arsenite, also induce thermotolerance. Conversely, agents known to induce thermotolerance, such as ethanol, would also enhance heat shock protein synthesis. To test this hypothesis, I have examined the effect of sodium arsenite or ethanol treatment on protein synthesis and cell survival in Chinese hamster ovary HA-1 cells. After either sodium arsenite or ethanol treatment, the synthesis of heat shock proteins was greatly enhanced over that of untreated cells. In parallel, cell survival was increased as much as 10(4)-fold when cells exposed to either agent were challenged by a subsequent heat treatment. The synthesis of heat shock proteins correlated well with the development of thermotolerance. A qualitative analysis of individual proteins suggests that the synthesis of 70,000 and 87,000 molecular weight proteins most closely mirrored the development of thermotolerance. The results, therefore, strongly reinforce the hypothesis that a causal relationship exists between the enhanced synthesis of heat shock protein and cell survival under specific stresses.

Actins↗
PubMed1983

Heat-induced protection of mice against thermal death.

The possibility that the exposure of organisms to whole-body hyperthermia may provide protection against subsequent thermal exposures is intriguing and may play an important role in the clinical scheduling of fractionated hyperthermia. We used C3H mice to investigate whether whole-body heating can be used as a conditioning treatment to induce protection of mice against thermal death from a subsequent heat treatment. Our data clearly show that a conditioning whole-body heat dose (41 degrees for 40 min), by itself nonlethal, can give substantial protection to animals against a later heat treatment. The heat-induced protection is transient in nature: it reaches a maximum by 6 to 24 hr following the 41 degrees conditioning dose and decays by approximately 60% by 72 hr. The data presented do not shed any light on the cause of death following whole-body hyperthermia. Our results show clearly that the response of a complex organism to heat can be altered by previous heat exposure.

Animals↗