Effects of the anticancer drug cis-diamminedichloroplatinum(II) on the activities of calf thymus DNA polymerase epsilon.

DNA polymerase (pol) epsilon is essential for DNA replication and is thought to be a component of DNA repair systems in eukaryotic cells. The activities of pol epsilon have been examined using a series of synthetic oligonucleotides designed with cis-diamminedichloroplatinum(II) (cis-DDP)-modified specific guanine residues. Pol epsilon was incapable of synthesis over cis-DDP-modified single guanine or adjacent guanine residues present in the template strand. Both single and double guanines modified by cis-DDP present at the 3'-OH end of a primer strand completely inhibited the synthetic activity of pol epsilon and, in addition, sequestered pol epsilon at the platinated 3'-OH termini. The sequestering of pol epsilon on cis-DDP modified DNA may interfere with the function of this enzyme in DNA repair in vivo. The intrinsic 3' to 5' proofreading exonuclease activity of pol epsilon was also examined. Pol epsilon was capable of degrading a single-strand template with internal cis-DDP-modified guanines up to, but not through, the platinated nucleotides. A single platinated guanosine was sufficient to block the 3' to 5' exonuclease activity of pol epsilon. These results suggest that cis-DDP-DNA adducts inhibit DNA synthesis mediated by DNA polymerase epsilon and that platinated sites can arrest the nuclease of pol epsilon, a function exhibited during DNA repair.