Transient Stabilization of p53 in Non-Small Cell Lung Carcinoma Cultures Arrested for Growth by Retinoic Acid

Abstract

Proliferation of five non-small cell lung carcinoma (NSCLC) cultures was inhibited after 16 h exposure to retinoic acid. We investigated whether expression of the p53 protein correlated with the growth pattern of NSCLC lines observed in the presence of retinoic acid. Levels of wild-type p53 protein underwent fivefold increases in lines H460a and H226b after 16 to 48 h treatment with 5 μM retinoic acid but then decreased to undetectable amounts in these cell lines after 72 h retinoic acid treatment. Levels of p53 transcripts remained unchanged during the time of increases in protein expression in retinoic acid-treated H460a cells, suggesting that a post-translational mechanism was involved in the increased expression of the protein. Pulse—chase analysis demonstrated that wild-type p53 was significantly more stabile in H460a cells treated with retinoic acid, exhibiting a half-life greater than 6 h, in contrast to 3 h for the protein in untreated control cells. The retinoic acid-mediated effect was specific for wild-type p53, since expression of mutant p53 in the H596b and H322j cell lines remained relatively unchanged even after 72 h exposure to retinoic acid. We conclude that retinoic acid induces stabilization of wild-type p53 in NSCLC cells by a post-translational mechanism. Furthermore, increases in expression of p53 were not responsible for the retinoic acid-induced transient inhibition of growth of NSCLC cells, since the growth of H358 p53-null cells also was inhibited by retinoic acid.