Relationship of dibenzo[a,l]pyrene-DNA binding to the induction of p53, p21^WAF1 and Cell cycle arrest in human cells in culture

The tumor suppressor protein p53 plays an important role in recognition of DNA damage and induction of subsequent cell cycle arrest. One of its target genes encodes the p21^WAF1 protein which is involved in the mediation of growth arrest after DNA damage has occured. The exceptionally potent carcino-genic polycyclic aromatic hydrocarbon (PAH) dibenzo[a,l]pyrene (DB[a,l]P) and its ultimate metabolites, the fjord region (+)-syn- and (-)-anti-11, 12-diol 13, 14-epoxides (DB[a,l]PDE), were used in order to investigate DNA damage via adduct formation, subsequent induction of p53 and p21^WAF1, and cell growth behavior in human mammary carcinoma MCF-7 cells. Exposure of MCF-7 cells to 0.005 μM DB[a,l]P caused a total DNA binding of 25 pmol adducts/mg DNA (48 hrs after treatment) and a significant increase in the level of p53 (12-72 hrs after treatment). 48 hrs after exposure an increased amount of the p21^WAF1 protein was detected and its level remained elevated for the time measured (168 hrs). Treatment of the cells with (+)-syn- and (-)-anti-DB[a,l]PDE also increased p53 levels. However, the concentration needed and the binding level observed were in the range of 0.02-0.03 μM [9-14 pmol (+)-syn-DB[a,l]PDE-DNA adducts/mg] and 0.01 μM [21 pmol (-)-anti-DB[a,l]PDE-DNA adducts/mg], respectively. Cell cycle studies after exposure to the parent PAH indicate an arrest of the DNA-damaged cells with accumulation in G2.