Preferential repair of the N-ras gene in K 562 cells after exposure to cisplatin

Cisplatin is one of the most active and widely used anticancer drugs; howev er, its clinical efficiacy is often limited by the development of resistanc e. Since several studies indicated that ras oncogenes may modulate the cell ular response to cisplatin or radiation, we investigated the gene-specific repair of the N-ras gene in the human K 562 cell line after exposure to cis platin using a novel nonradioactive polymerase chain reaction inhibition as say. This assay is based on the fact that DNA lesions can block the Tag pol ymerase and thereby result in a decreased amplification of a damaged segmen t compared to the amplification of the same segment in a non-damaged templa te. The overall genomic repair rate was measured by atomic absorption spect roscopy. Immediately after cisplatin exposure no amplification segment was observed. However, a complete restoration of the N-ras gene (2.4 kb) was se en after 8 h posttreatment incubation. In contrast, only 60% of the overall genome was repaired at this time. Our results clearly indicate that cispla tin-induced DNA lesions are more efficiently removed from transcribed regio ns within the DNA, suggesting that the efficiency of DNA repair in a given gene may be correlated to its transcriptional activity. Since ras oncogenes control several cellular signal transduction pathways, known to be involve d in DNA damage response, preferential repair of the N-ras gene could there fore be an important step to prevent inactivation of cellular defense mecha nisms after exposure to genotoxic agents. [(C) 1999 Lippincott Williams & W ilkins.].