Rapid loss of stress fibers in Chinese hamster ovary cells after hyperthermia.

This study was initiated to characterize the effect of hyperthermia (45 degrees) on the distribution of actin stress fibers in Chinese hamster ovary cells using rhodamine-conjugated phalloidin, a probe specific for F-actin. Fluorescent microscopy revealed a rapid loss of stress fibers after immersion in a 45 degrees water bath. After 5-min immersion at 45 degrees, approximately 90% of the cells analyzed did not contain observable stress fibers. Stress fibers were visible after incubation of cells at 37 degrees after heating. The recovery of the appearance of the stress fibers occurred as protein synthesis resumed, and addition of protein synthesis inhibitors following heat treatment blocked the reappearance of these structures. These results support the hypothesis that cytoskeletal components may be a target of hyperthermia, explaining the pleotropic biological effects of heat and, in particular, heat radiosensitization.