Role of p53 and mismatch repair in PhIP-induced perturbations of the cell cycle.

Heterocyclic amines, found ubiquitously in our diet, are carcinogenic and mutagenic. Among this class of compounds, 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP) is the most abundant. To further understand the carcinogenesis of this compound, we studied the effects of PhIP on the progression of human lymphoblastoid cells through the cell-cycle. Cells differing in p53 or mismatch repair status were used to evaluate the role of those proteins. Following PhIP-treatment, a dose and time-dependent accumulation of p53 was found in cells containing functional p53. The augmentation of the p53 protein, accompanied by increases in p21-WAF1, confirms that the p53 is activated. The increase in p53 was independent of the mismatch repair status of the cells. Perturbations in the cell-cycle were also observed. Twenty-four hours after PhIP treatment, the activation of the G2-M checkpoint was evident. Functional p53 and mismatch repair were not required for the PhIP-induced G2-M arrest. The G2-M arrests were reversible and are interpreted as necessary for the repair of the PhIP-DNA lesions. Under treatment conditions where less than 5% of the cells survived, the G2-M arrests were absent.