Thermotolerant cells possess an enhanced capacity to repair heat-induced alterations to centrosome structure and function.

To study the mechanisms of thermotolerance, the adaptive response by which cells become transiently resistant to killing by heat shock, we have focused on the centrosome, an organelle whose disorganization is closely correlated with thermal killing in Chinese hamster ovary (CHO) cells. Centrosome structure was studied by use of antisera directed against pericentrin, a 220 Kd protein of the pericentriolar material (PCM). Centrosome function was measured in intact cells by performing microtubule regrowth following exposure to the drug nocodazole. Immediately following heating at 45 degrees C for 4-18 min, centrosomal staining by antipericentrin decreased. Thereafter, staining gradually recovered, although abnormal configurations of staining appeared in heated cultures 10-20 h later. In contrast, abnormal patterns of staining rarely developed in thermotolerant cultures. Centriole number was not perturbed by heat, indicating that the heat effect was specific for the PCM. Heat also caused an immediate reduction in the number of microtubules nucleated by the PCM. As for staining by antipericentrin, microtubule nucleation recovered during 3-20 h at 37 degrees C after heating. The immediate, heat-induced decrease in antipericentrin staining or microtubule nucleation was similar in thermotolerant and nontolerant cells. In contrast, the inhibition for both endpoints recovered to control levels much more quickly in thermotolerant cells than in nontolerant cells. Furthermore, new protein synthesis was not required for the recovery of microtubule nucleation. These data show that thermotolerant cells have an enhanced capacity to repair thermal damage to centrosome structure and function, and suggest that a faster rate of recovery prevents disorganization of the PCM that is observed in nontolerant cells several hours after heating.