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G C Li

Publications and source records attributed to G C Li.

At least 73 records · Page 4Linked to original sources
PubMed1993

[Effects of six naphthalenesulfonamide derivatives on LPS-induced release of tumor necrosis factor from mouse peritoneal macrophages].

The effects of six naphthalenesulfonamide derivatives were studied on the LPS-induced release of tumor necrosis factor (TNF) from mouse peritoneal macrophages primed with A23187. The calmodulin (CaM) antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) and its derivatives N-(6-aminobutyl)-5-chloro-1-naphthalenesulfonamide and N-(6-aminoethyl)-5-chloro-1-naphthalenesulfonamide (10-400 ng/ml) were found to inhibit LPS-induced TNF release in a dose-dependent manner, and the protein kinase C (PKC) activator, N-(n-heptyl)-5-chloro-1-naphthalenesulfonamide (SC-10) and its two derivatives, N-(n-quinyl)-5-chloro-1-naphthalenesulfonamide and N-(n-butyl)-5-chloro-1-naphthalenesulfonamide (1-16 micrograms/ml) were shown to increase LPS-induced TNF release at suboptimal doses in a dose-dependent manner. These results suggest that the LPS-induced release of TNF is CaM-dependent and PKC may play an important role in this process.

Animals↗
PubMed1992

Expression of human hsp70 in rat fibroblasts enhances cell survival and facilitates recovery from translational and transcriptional inhibition following heat shock.

We report here our studies on the inhibitional effect of 45 degrees C heat shock on transcriptional and translational activity and their subsequent recovery at 37 degrees C in Rat-1 cells, thermotolerant Rat-1 cells (TT Rat-1), and Rat-1 cells transfected with human hsp70 gene (HR24, M21). Specifically, we ask whether overexpression of hsp70 protects cells from heat-induced inhibition in RNA and protein synthesis, and/or facilitates cells' ability to recover from translational or transcriptional inhibition after heat shock treatment. Our data demonstrate that the constitutive expression of human hsp70, by itself, confers thermal resistance as expressed in enhanced survival and translational tolerance, but not transcriptional tolerance. In addition, the expression of human hsp70 in Rat-1 cells facilitates cells' ability to recover from heat-induced inhibition in protein and RNA synthesis. After healing at 45 degrees C for 25 min, the time required for RNA and protein synthesis to recover is considerably shorter in HR24, M21, and TT Rat-1 cells than that in control Rat-1 cells. These results provide strong evidence for a direct link between the expression of a functional form of mammalian hsp70, and cells' translational tolerance, as well as their ability to recover from translational and transcriptional inhibition after heat shock.

Animals↗
PubMed1992

Heat shock protein hsp70 protects cells from thermal stress even after deletion of its ATP-binding domain.

Retroviral-mediated gene transfer experiments show that rodent cells become heat resistant when stably and constitutively expressing a cloned human gene encoding an intact human 70-kDa heat shock protein (hsp70). Cells expressing higher levels of the hsp70 protein generally tolerate thermal stress better, whereas cells expressing either of two mutated hsp70-encoding genes, one with a 4-base pair out-of-frame deletion and one with an in-frame deletion of codons 438-618, are heat sensitive. These results provide strong evidence that expression of hsp70 leads directly to thermal tolerance. Surprisingly, cells expressing a mutant hsp70 of a human gene missing codons 120-428 are, nevertheless, heat resistant. Because the deleted region of this mutant contains the ATP-binding domain of human hsp70, this domain appears dispensable in the hsp70-mediated protection of cells from thermal stress.

Adenosine Triphosphate↗
PubMed1992

Major heat shock protein hsp70 protects tumor cells from tumor necrosis factor cytotoxicity.

Heat treatment and various other stresses render tumor cells resistant to cytotoxicity mediated by tumor necrosis factors (TNFs). Here, we elucidate the molecular basis of this phenomenon by demonstrating that the major heat shock protein, hsp70, protects tumor cells from TNF cytotoxicity even in the absence of stress. The human hsp70 gene was stably introduced into highly TNF-sensitive WEHI-S tumor cells both in the sense and antisense orientation. All clones constitutively expressing the exogenous human hsp70 gene were protected from TNF-mediated killing approximately 1000-fold. Remarkably, the growth of one clone was actually stimulated by low concentrations of TNF. Moreover, a clone expressing antisense hsp70 RNA was rendered extremely sensitive to TNFs. Hsp70-mediated protection from TNF cytotoxicity was confirmed in transient expression experiments employing retroviral vectors. Changes in cellular sensitivity to TNF were not associated with alterations in the binding of TNF to its receptors. Neither the transfection procedure itself nor overexpression of the low molecular weight heat shock protein, hsp27, had any effect on cellular susceptibility to TNFs. Our data suggest that hsp70 may increase the oncogenic potential of some tumor cells by providing them with an escape mechanism from immunological defense.

Animals↗
PubMed1992

Identification of human hsp-70 expression in stably transfected rodent cells by isoelectrofocus immunoblots.

The major heat-shock protein, hsp-70, is synthesized by cells from a wide variety of organisms in response to heat shock or other stresses. It is assumed that hsp-70 may have an important thermal protective function. To test this hypothesis directly, we have transfected rat fibroblast cells with appropriate expression plasmids containing a cloned human hsp-70 gene. Stable transfectants expressing the human hsp-70 gene product were identified by Western blot analysis. During the course of selecting successful transfectants, we found that when standard methods of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunostaining were employed with the monoclonal antibody raised against the human hsp-70 antigen, we were unable to differentiate the human hsp-70 from the heat-inducible rat hsp-70. This was because the monoclonal antibody cross-reacts with the human and rat proteins, which have the same mobility in SDS-PAGE, and it is difficult to determine which protein is expressed. To improve the resolution of the Western blot technique, we performed additional immunoblot analysis of cellular proteins separated by slab gel isoelectrofocusing. Our study shows that the isoelectrofocusing technique, when combined with antibodies against hsp-70, gave a better resolution for the separation of exogenous human hsp-70 and the endogenous rat hsp-70 than the commonly used SDS-PAGE Western blot analysis. It provides a rapid and specific method to identify positive colonies that express the human hsp-70 gene in transfected rodent cells.

Animals↗
PubMed1991

Thermal response of rat fibroblasts stably transfected with the human 70-kDa heat shock protein-encoding gene.

The major heat shock protein hsp70 is synthesized by cells of a wide variety of organisms in response to heat shock or other environmental stresses and is assumed to play an important role in protecting cells from thermal stress. We have tested this hypothesis directly by transfecting a constitutively expressed recombinant human hsp70-encoding gene into rat fibroblasts and examining the relationship between the levels of human hsp70 expressed and thermal resistance of the stably transfected rat cells. Successful transfection and expression of the gene for human hsp70 were characterized by RNA hybridization analysis, two-dimensional gel electrophoresis, and immunoblot analysis. When individual cloned cell lines were exposed to 45 degrees C and their thermal survivals were determined by colony-formation assay, we found that the expression of human hsp70 conferred heat resistance to the rat cells. These results reinforce the hypothesis that hsp70 has a protective function against thermal stress.

Animals↗
PubMed1990

Thermal response of oncogene-transfected rat cells.

Rat embryo cells or Rat-1 fibroblasts were transfected with either an activated c-myc or a c-Ha-ras from the T24/EJ bladder carcinoma, or they were cotransfected with both. A gene conferring neomycin or hygromycin resistance was also cotransfected so that independent cell lines could be selected by growth in medium containing the antibiotic. Certain isolates from cells transfected with only one type of oncogene were further transformed by exposure to 600 cGy of 250-kVp X-rays. Successful transfection and transformation were characterized by altered morphology, increased plating efficiency, shorter doubling time, longer life span, foci formation, anchorage-independent growth, and Southern and Northern hybridization analysis. The thermal response of these cells at different stages of oncogenic transformation was examined by exposing exponentially growing cells to 45 degrees C for 0 to 45 min and measuring cellular survivals using colony formation assay. We found that cells transfected with myc oncogene, singly or in combination with ras, were more sensitive to thermal stress. Aside from that, the cells' thermal sensitivity was not affected by the degree or the nature of transformation.

Animals↗
PubMed1990

Heat-induced cytotoxicity in H2O2-resistant Chinese hamster fibroblasts.

Hydrogen-peroxide-resistant Chinese hamster fibroblasts, derived from the HA-1 cell line, were isolated following continuous culturing in the presence of progressively increasing concentrations of hydrogen peroxide. The hydrogen-peroxide-resistant phenotype has been stable for over 360 days following removal from H2O2 stress. These H2O2-resistant cell lines demonstrate increased resistance to hyperthermic cell killing mediated by continuous heating at 43 degrees C but not 45 degrees C. The relationship between mammalian cellular adaptation to oxidative stress mediated by H2O2 and resistance to 43 degrees C hyperthermia is discussed.

Animals↗
PubMed1990

Myocardial protection with preconditioning.

Myocardial preconditioning with brief coronary artery occlusions before a sustained ischemic period is reported to reduce infarct size. To determine the number of occlusive episodes required to produce the preconditioning effect, we performed single or multiple occlusions of the left circumflex coronary artery (LCx) followed by a sustained occlusion (60 minutes) of the LCx. Anesthetized dogs underwent one (P1), six (P6), or 12 (P12) 5-minute occlusions of the LCx. Each occlusion period was followed by a 10-minute reperfusion period. A 60-minute occlusion of the LCx followed the preconditioning sequences. A control group received a 60-minute occlusion of the LCx without preconditioning. All groups were subjected to 6 hours of reperfusion after which the heart was removed for calculating infarct size (IS), area at risk (AR), and left ventricular mass (LV). The IS/AR ratio for the control group was 29.8 +/- 4.4% (n = 17), which was substantially greater (p less than 0.001) than that of the preconditioned groups: P1, 3.9 +/- 1.3% (n = 14); P6, 0.4 +/- 0.3% (n = 5); and P12, 2.9 +/- 2.8% (n = 5). There were no significant differences in the IS/AR ratio among the three preconditioned groups. The AR/LV ratio was comparable among all groups and did not differ statistically: control, 40.4 +/- 1.3%; P1, 36.2 +/- 1.7%; P6, 36.1 +/- 1.7%; and P12, 37.3 +/- 2.1%. Collateral blood flow to the inner two thirds of the risk region determined with radiolabeled microspheres during ischemia did not differ significantly between the control group (0.03 +/- 0.01 ml/min/g, n = 8) and single occlusion group (0.06 +/- 0.02 ml/min/g, n = 8), indicating that the marked disparity in infarct size could not be attributed to differences in collateral blood flow. The data indicate that preconditioning with one brief ischemic interval is as effective as preconditioning with multiple ischemic periods.

Animals↗
PubMed1990

Alterations in specific and general protein synthesis after heat shock in heat-sensitive mutants of CHO cells and their wild-type counterparts.

The rates of general and specific protein synthesis were studied in two heat-sensitive strains of CHO cells (Harvey and Bedford, Radiat. Res. 113, 526-542, 1988), both of which show a reduced ability to develop thermotolerance following an initial 45 degrees C heat shock. After various labeling periods with [35S]methionine, wild-type and mutant labeled proteins were separated by one- and two-dimensional polyacrylamide gel electrophoresis. Autoradiograms showed differences in levels of synthesis of several proteins after a 45 degrees C heat shock. In particular, these were in the hsp-70 group referred to as hsp-70a, b, and c, having molecular weights of 76, 73, and 72 kDa and isoelectric focusing pH values of 5.7, 5.5, and 5.7, respectively. Of particular note were changes in the hsp-70c region of the autoradiograms. We found that there was perhaps a low level of synthesis of hsp-70c in unheated wild-type cells but none was detectable in the mutant lines. After an isosurvival (approximately 10%) pulse of 45 degrees C heat there was a gradual increase in the synthesis of hsp-70c for wild-type but a smaller increase for the heat-sensitive strain 36 (HS-36) cells. In contrast, for HS-23 cells there was a very large initial increase by 5 to 7 h after the heat pulse and then a rapid decrease to undetectable levels by 11 to 13 h. The inhibition and recovery of general protein synthesis for both mutant and wild-type cells was also measured following various heat treatments at 45 degrees C. We observed that inhibition and resumption to a "normal" rate of protein synthesis for HS-23 cells paralleled the same response observed for the wild-type 10B2 cells. In sharp contrast, the time for recovery from the inhibition of protein synthesis for HS-36 cells was severely reduced for all heating times tested. Our results show that the period of delay before resumption of protein synthesis after heating does not always correlate with heat sensitivity or the degree of thermotolerance development. Several explanations for these observations are possible. One is that while synthesis of certain heat-shock proteins may indeed be responsible for the development of thermotolerance, the timing of the synthesis of these proteins in relation to the period of inhibition of general protein synthesis is crucial to such development.(ABSTRACT TRUNCATED AT 400 WORDS)

Acclimatization↗
PubMed1989

Relationship between changes in ploidy and stable cellular resistance to hydrogen peroxide.

Stable hydrogen peroxide (H2O2)-resistant variants of the Chinese hamster ovary HA-1 line have been isolated by culturing cells in progressively increasing concentrations of H2O2 (greater than 200 days, in 50-800 microM H2O2). Increases in catalase activity in these variant cell lines were shown to correlate with increased H2O2 resistance. Stable (greater than 240 days) H2O2-resistant cell lines, seven quasidiploid (21-22 chromosomes/cell) and six quasitetraploid (40-44 chromosomes/cell) were clonally isolated from the 800 microM adapted H2O2-resistant variants which were heterogeneous with respect to ploidy. The H2O2 dose-modifying factors (DMFs) were 3, 5, 8, 13, 15, 26, and 27 for the seven quasidiploid cell lines, and 21, 32, 38, 40, 42, and 49 for the six quasitetraploid cell lines. The mean DMF was 14 +/- 10 for the former and 37 +/- 10 for the latter. Our data show that on the average the quasitetraploid cell lines were significantly more resistant to H2O2-mediated cell killing than the quasidiploid cell lines derived from the same mixed population of 800 microM H2O2-adapted cells. When catalase activities (k units/cell) of the HA-1 cells and three of the clonally derived cell lines (two quasidiploid and one quasitetraploid) were determined and plotted vs. H2O2-DMF, a positive linear correlation was obtained (correlation coefficient = 0.99). This result was further confirmed when immunoreactive catalase protein/cell was detected by Western blots. Our data show that chronic exposure of cells to H2O2 stress (800 microM) was accompanied by increases in quasitetraploid cells within the population. Quasitetraploid cell lines derived from this population demonstrated increased stable H2O2-resistance which may be related to stable increases in the expression of catalase.

Animals↗
PubMed1989

Will heat-stable proteins nonspecifically protect cells from thermal stress?

In cell-free systems, stress-resistant proteins nonspecifically stabilize stress-susceptible proteins. This mechanism has been suggested to contribute to thermotolerance in cells (Minton et al.: Proc. Natl. Acad. Sci. USA, 79: 7107-7117, 1982). To test this hypothesis, red-blood-cell-mediated microinjection was used to transfer macromolecules into monolayers of CHO cells. We introduced the heat-stable proteins fetuin and ovomucoid into RBCs during hypotonic hemolysis and then fused the RBCs to CHO cells with polyethylene glycol as fusogen. Fetuin and ovomucoid were successfully transferred into 36-55% of the CHO cells as demonstrated by fluorescence of FITC-conjugated proteins. The plating efficiency of these CHO cells after fusion ranged from 35% to 60%. Three hours after fusion, CHO cells microinjected with fetuin or ovomucoid were exposed to 43 degrees C for 0-180 min or 45 degrees C for 0-40 min, and thermal survival was determined. There was no difference in cell survival between control untreated cells, control cells fused with nonloaded RBCs, and cells fused with RBCs loaded with fetuin or ovomucoid. While our results do not support the hypothesis that heat-stable proteins nonspecifically protect cells from thermal stress, several possible explanations are provided for this observation.

Animals↗
PubMed1989

Characterization of a heat-resistant strain of Tilapia ovary cells.

Tilapia ovary cells (TO-2) cease to proliferate when moved from normal growth temperature of 31 degrees C to 37 degrees C, and arrest in G1 and G2 phases of the cell cycle. The ability of the arrested cells to re-enter the cell cycle when restored to 31 degrees C decreases inversely with time spent at 37 degrees C. A heat-resistant strain, TO-37c, cloned from the surviving fraction of TO-2 after heat treatment, has been found to re-enter the cell cycle with greater facility and to have a higher rate of survival. TO-37c cells have a smaller cell volume than TO-2 and show a distinct morphology at 37 degrees C. Most of the heat-shock proteins (hsps) induced on temperature change were similar, but in TO-37c the decline in the synthesis of a 27 X 10(3) Mr hsp was faster and a 37 degrees C-specific 60 X 10(3) Mr hsp was missing. Ultraviolet (u.v.) sensitivity was slightly affected if heat treatment was given after irradiation. However, when cells were preheated and then u.v. irradiated, the u.v. sensitivity increased sharply for TO-2 cells but not for TO-37c.

Animals↗
PubMed1988

Thermal adaptation and heat shock response of Tilapia ovary cells.

The growth of tissue culture TO-2 cells derived from the warm water fish Tilapia, the induction of thermotolerance, and protein synthesis profiles of these cells in response to temperature changes were examined. TO-2 cells can grow between 15 to 34 degrees, with an optimal growth temperature of 31 degrees. There is no apparent killing of the cells when the temperature is lowered to 4 degrees for up to 3 days. Survival of TO-2 cells at 43 degrees was studied after various preheat treatments: 1) acute heating at 40 degrees for 15 min followed by 31 degrees incubation, 2) chronic exposure at 37 degrees for several hr, or 3) long-term thermal adaptation at 34 degrees. The cells acquire thermotolerance from pre-exposure to 37 degrees for as short as 6 hr. Preheating at 40 degrees followed by incubation at 31 degrees also induces thermotolerance against a subsequent 43 degrees heat challenge. In addition, 34 degrees thermal adapted cells are resistant to 43 degrees heating. One- and two-dimensional gel electrophoresis of proteins after heat treatments show that three major heat shock proteins with molecular weights around 87, 70, and 27 kD are preferentially synthesized. The synthesis of two additional proteins with an isoelectric point of 6.9 and molecular weights of 60 and 44 kD are significantly enhanced in 34 degrees thermal-adapted and 37 degrees chronic heated cells, but not in cells subjected to an acute heat shock at either 40 degrees or 43 degrees. On the other hand, the 27 kD heat shock proteins are mainly present in the 43 degrees, 40 degrees, and 37 degrees heat-shocked cells, but not in the 34 degrees thermal-adapted cells.

Adaptation, Physiological↗
PubMed1988

Procainamide-induced lupus anticoagulants and thrombosis.

The specific factors predisposing to thrombosis in patients with LAs have not been resolved. With extensive cross-reactivity, and several proposed sites of action, LAs and their effects may be heterogeneous. While the risk of thrombosis with phenothiazine-induced LAs is probably low, the incidence of thrombosis in association with procainamide-induced LAs is uncertain. Procainamide is a commonly used antiarrhythmic drug associated with the induction of autoantibodies, and occasionally with a lupus-like syndrome. Serologic and coagulation profile monitoring may be required to detect patients in whom LAs develop since these individuals may be at increased risk for thrombosis. Monitoring may be especially important in patients who are receiving procainamide and who have atherosclerosis and cardiac disease, since they may be at increased risk for thrombosis of coronary and other arteries. Future prospective studies are needed to investigate whether the development of lupus anticoagulants during procainamide therapy increases the risk of thrombosis.

Aged↗
PubMed1988

Treatment of advanced malignancies with ifosfamide under protection with mesna.

Fifty-seven patients with advanced malignant tumours were treated with ifosfamide (Holoxan) and mesna (Uromitexan) in our department from November 1979 to December 1984. This series comprised eight cases of soft tissue sarcoma, nine cases of ovarian carcinoma, five cases of non-seminomatous testicular tumour, 11 cases of bronchogenic carcinoma, three cases of renal carcinoma, seven cases of non-Hodgkin's lymphoma, two cases of skeletal fibrosarcoma, two cases of breast carcinoma, one case each of Ewing's tumour, prostatic carcinoma, seminoma, plasma cell tumour, multiple myeloma, malignant teratoma, nasopharyngeal carcinoma, Wilms's tumour, neuroblastoma and mycosis fungoides. Out of these 57 cases, 53 were evaluable. There were five complete remissions and 20 partial remissions, corresponding to a total response rate of 47%. The overall median survival time (MST) of the 53 evaluable patients was 7.5 months. The responders had a longer survival time (MST 10 months) than the non-responders (MST 4.75 months) (p greater than 0.05). Analysis of the results according to sex, age, dosage of ifosfamide and degree of histological differentiation of the tumour cells failed to show any influence of these factors on the therapeutic results. The response rate to ifosfamide found in this study might be related to the histological origin of the tumours and to whether the primary tumours had been resected. The non-seminomatous testicular tumours, non-Hodgkin's lymphomas and ovarian carcinomas showed a high response rate. The response rate was higher in the group in which the primary tumour had been resected (61%) than in the non-resected group (12%) (except the non-Hodgkin's lymphoma). The side-effects of this regimen were moderate. Dyspepsia, nausea, vomiting, myelodepression, dizziness, and alopecia were common. Cystitis could be prevented nearly completely by concomitant administration of mesna, when given correctly, for preventing side-effects of ifosfamide on the urinary system (haemorrhagic cystitis, etc.).

Adult↗