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Biomedical subjects

W C Dewey

Publications and source records attributed to W C Dewey.

At least 109 records · Page 6Linked to original sources
PubMed1984

Cycle progression and division of viable and nonviable Chinese hamster ovary cells following acute hyperthermia and their relationship to thermal tolerance decay.

Cell cycle progression delays and subsequent growth kinetics of viable and nonviable Chinese hamster cells following acute (45.5 degrees) hyperthermia were documented in an attempt to correlate these changes with the decay of thermal tolerance. Following heating for various lengths of time, cells exhibited a delay in subsequent division which was related to cell survival by a power function relationship. A cell was considered to be viable if it retained the ability to divide to form a colony of 50 or more cells. The components of the delay in cycle transit for viable cells heated in G1 for a treatment of 20 min at 45.5 degrees were approximately 28 hr in G1 and 20 hr in S and G2-M. This represents a 7-fold decrease in the rate progression through G1 and a 2-fold decrease through S and G2-M relative to control rates. The doubling times of viable cells, in subsequent generations, were significantly decreased to a rate 61% of that of control up to 120 hr after heating. This reduction was in part due to lethal sectoring, i.e., a division which produces only one daughter that is capable of forming a viable subclone, within the viable progeny. Within a viable subclone, up to 30% of the cells that divided from 48 to 91 hr after a heat treatment of 20 min at 45.5 degrees were found to be nonclonogenic. Following resumption of division, nonviable cells slowly lost their capacity for proliferation. Nearly all thermal tolerance development induced by a 20-min pretreatment occurred while the viable cells remained in G1. Subsequent progression into heat-sensitive S and G2-M phases modulated thermal tolerance only slightly. Finally, maximal loss of thermal tolerance was exhibited at the time corresponding to the resumption of viable cell division.

Animals↗
PubMed1984

Fluorescence-activated cell sorting analysis of the induction and expression of acute thermal tolerance within the cell cycle.

We have examined the cell cycle specificity of 45.5 degrees heat-induced toxicity and the induction and expression of thermal tolerance. Ultrapure populations of G1-, S-, and G2-M-phase cells were obtained through sequential centrifugal elutriation and flow cytometric cell sorting of Hoechst 33342-stained cells. We found no interaction of Hoechst 33342 with hyperthermia under staining conditions that gave good cytometric resolution of DNA distributions. Single dose-response survival curves indicated that S phase was the most sensitive to 45.5 degrees hyperthermia (Do = 1.97, 1.26, and 1.95 min for G1, S, and G2-M, respectively). Both S and G2-M phases exhibited a decreased ability from G1 to accumulate sublethal heat lesions as evidenced by decreased heat survival curve shoulders (Dq) = 13.7, 9.51, and 8.39 min for G1, S, and G2-M, respectively). Thermal tolerance, as measured by the decreased inactivation slope of the split-dose treatment, could be induced and expressed in G1, S, and G2-M phases. However, both the magnitude and temporal expression of tolerance were dependent on the position of the cell within the cell cycle at the time of the initial heat treatment. S-phase cells exhibited slightly less thermal tolerance as compared to G1 cells given isosurvival thermal induction doses as measured by the split-dose inactivation rate constants (heated/control = 8.37 and 5.62 for G1 cells at 12 and 24 hr and 7.68 and 5.27 for S-phase cells at 12 and 28 hr). Also, split-dose survival curves for cells heated in G2-M indicated a near total inability to accumulate heat-induced sublethal damage. Simultaneous bivariate (90 degrees light scatter and DNA content) progression analysis of heated replicates indicated that tolerance could probably be expressed in those cells which moved into other cycle compartments following the initial heat treatment. For instance, G1-phase cells preheated for 20 min began progression into normally heat-sensitive S phase between 24 and 28 hr after the heat treatment. This corresponded to approximately the time of maximal thermal tolerance expression. [3H]Thymidine suicide experiments also indicated that the ultimately clonogenic cells began movement into S phase at or near the time of maximal tolerance. In this case then, tolerance expression appeared to supersede the S-phase acute heat sensitivity. Heated S-phase cells began progression into G2-M between 4 and 12 hr, which corresponded temporally to large amounts of tolerance expression4 +

Animals↗
PubMed1983

Effect of hyperthermia on isolated DNA polymerase-beta.

Hyperthermia has been shown to inhibit the activity of DNA polymerase-beta when either the intact Chinese hamster cells or partially purified enzyme samples from CHO cells are heated (42.2 or 45.5 degrees C). However, the loss of activity from heating isolated enzyme samples can be either greater or less than the loss from heating intact cells. For example, treating cells with the membrane-active agent procaine-HCl greatly sensitizes the cells to heat-induced loss of enzyme activity but has no effect on the heat sensitivity of isolated enzyme. Furthermore, the heat sensitivity of the isolated enzyme depends greatly on the purification steps and can be reduced by heating the enzyme in the presence of bovine serum albumin, activated DNA, or Langendorf salts. These observations, considered in relation to others in the literature, suggest that heat inactivation of polymerase-beta occurs from heat-induced changes in the intracellular environment, which in turn modify the direct thermal denaturation of the enzyme within the cell.

Animals↗
PubMed1982

The effect of chronic and acute heat conditioning on the development of thermal tolerance.

Survival studies with Chinese hamster ovary cells showed that thermal tolerance, which developed during chronic heating (treatment times greater than or equal to 1 hr) or after acute heating (treatment times less than 1 hr) involves similar mechanisms. For example, cells that expressed thermal tolerance during a 6-14 hr chronic heat treatment at 41.5 degrees C or 42 degrees C also expressed thermal tolerance to a subsequent acute treatment at 45.5 degrees C. Also, cells heated acutely for 10 min at 45.5 degrees C and incubated at 37 degrees C for 12 hr showed tolerance to both 45.5 degrees C acute and 42 degrees C chronic hyperthermia. Finally, thermal tolerance developed between fractionated acute heat treatment at 45.5 degrees C and fractionated chronic heat treatments at 42.5 degrees C. These data indicate that when cells are tolerant to chronic hyperthermia they are also tolerant to acute hyperthermia and that the reverse is also true.

Adaptation, Physiological↗
PubMed1982

Effects of hyperthermia on dividing Chinese hamster ovary cells and on microtubules in vitro.

The ultrastructure of Chinese hamster ovary cells was examined immediately after heating cells in mitosis, and the findings were compared with (a) the behavior of heated cells monitored with time lapse cinematography following heat shocks and (b) proliferative survival of individual cells followed for 7 days after heating. Treatment of dividing cells at 45.5 degrees (5 to 15 min) disassembled the spindle and disrupted both the contractile ring and the midbody-cytoplasmic bridge complex to varying degrees depending on the length of heating. The spindle did not reform upon return to 37.0 degrees. Microtubular proteins were heated in vitro to determine if their inactivation was responsible for the inability of the spindle to reform. Heat completely disassembled the intact microtubules and inactivated a proportion of the microtubular proteins in vitro; however, a fraction of the microtubular proteins from heat-disassembled microtubules still was capable of reassembly. The time lapse studies indicated that cells in division at the time of heating entered G1 without completing division. Of the resultant tetraploid cells, 88% had greater than or equal to 2 nuclei; 59% of the tetraploid cells divided 35 +/- 7 (S.D.) hr following the heat shock (control generation time, 13 +/- 2 hr), and 95% of the flattened progeny had more than one nucleus. The fate of individual cells that were in mitosis or G1 when treated at 45.5 degrees for 4.5 min was monitored for 7 days. The survival of the total heated population of cells was 19%, but the surviving cells were almost totally accounted for by the G1 cells present as contaminants in the heated population. Less than 2% (2 of 115) of the monitored cells that were heated in mitosis formed colonies. Therefore, the morphological disruption of the spindle, contractile ring, or midbody-cytoplasmic bridge complex by a heat of 45.5 degrees prevented cytokinesis, and the resultant tetraploid cells became proliferatively dead.

Animals↗