Heat shock induces transient p53-dependent cell cycle arrest at G1/S.

Heat shock (43 degrees C, 45 min) induced transient nuclear accumulation of p53 in primary human fibroblasts without any clonogenically toxic effects. The accumulation of p53 reached a maximal level 3 approximately 5 h after heat shock, and returned to the basal level within 12 h. Following the increase in p53 level, cell cycle arrest at G1/S was observed in normal fibroblasts, whereas neither nuclear accumulation of p53 nor cell cycle arrest were observed in HeLa cells. By comparing cell cycle patterns of heat-treated mouse cells with different genotypes at the p53 locus (+/+, +/-, -/-), the observed cell cycle arrest at G1/S was demonstrated to be p53-dependent. Cell cycle arrest in normal human fibroblasts continued for nearly 24 h, resulting in a one day delay of cell growth compared with non-treated cells. Following enhancement of the p53 level, the amount of p21/WAF1/ CIP1 increased, and the high level of p21 was sustained for almost one day in a cell cycle-independent manner, suggesting the involvement of p21 in the inhibition of cell cycle progression by heat shock.