Benzpyrene groups bind preferentially to the DNA of active chromatin in human lung cells

The cells of the bronchial epithelium of man are targets for benzo(a)pyrene carcinogenesis. When cultures of these cells, and of non-target fibroblasts, are exposed to [3H]-benzo(a)pyrene, we find that the epithelial cells metabolise and bind to DNA far greater amounts of benzpyrene than do fibroblasts. By analysis of nuclei of benzpyrene-treated cells for sensitivity to limited digestion with pancreatic DNase I, we have shown that benzpyrene groups bind initially to the DNA of expressed (DNase I sensitive) regions of chromatin in both cell types. Covalent binding of benzpyrene groups to non-expressed (DNase I resistant) regions follows rapidly in the target epithelial cells. These maintain high levels of carcinogen adducts in their DNA. In fibroblasts, benzpyrene group binding to non-expressed DNA occurs more slowly and active removal of adducts from the DNA is evident.