Effects of hyperthermia (45 degrees) on macromolecular synthesis in Chinese hamster ovary cells.

Abstract

The inhibition and resumption of biosynthetic activity in asynchronous Chinese hamster ovary cells following 45° hyperthermia were documented in an attempt to correlate changes in macromolecular synthesis either with the recovery of sublethal heat damage or with the development of thermotolerance. Growth curves after a heat shock of either 10 or 17.5 min at 45° indicated that cell division was inhibited for 10 or 17 hr, respectively; following recovery, the doubling time was increased from 13 to 37 or 46 hr, respectively. In the cells heated 10 min at 45°, the doubling time shortened to 16.5 hr by 45 hr posthyperthermia; whereas in the cells heated 17.5 min, the doubling time remained at 46 hr. Nucleic acid synthesis (pulsed [3H]thymidine or [3H]uridine incorporation) was immediately reduced by 90% and resumed after 4 to 6 hr, independently of the hyperthermia exposure time. The rate of DNA synthesis recovered to 20 to 40% of control by 10 hr posthyperthermia, whereas the labeling index remained near control levels until about 12 hr posthyperthermia when it decreased to approximately 20% (25 to 30 hr). In the cells heated 10 min at 45°, the labeling index returned to 45% as the doubling time shortened from 37 to 16.5 hr; whereas after 17.5 min at 45°, the labeling index remained depressed at approximately 22% corresponding to the doubling time of 46 hr. After the onset of recovery, the rate of RNA synthesis increased so that it exceeded 150% of control by 50 hr posthyperthermia. Hyperthermia inhibited protein synthesis (pulsed incorporation of 14C-labeled amino acids), but recovery occurred over the period 4 to 8 hr after 10 min at 45° or 4 to 26 hr after 17.5 min at 45° to approximately 90% of control in both cases. Precursor incorporation was linear over the period of the pulse label, and cellular permeability to the precursors was not significantly altered by hyperthermia. The recovery of protein synthesis over the period of 4 to 8 hr after 10 min at 45° correlated in time with the onset of thermotolerance which also began at 4 hr and was completed by 8 hr after heating. In general, however, hyperthermia-induced perturbation of biosynthetic activity did not exhibit a strong dependence on hyperthermia exposure and did not correlate with recovery from sublethal damage.