THE ANTITUMOR AGENT CISPLATIN INHIBITS DNA GYRASE AND PREFERENTIALLY INDUCES GYRB GENE-EXPRESSION IN ESCHERICHIA-COLI

Cisplatin is a widely used anticancer agent that exerts its biological activity principally by damaging DNA. Although detailed knowledge exi sts concerning mechanisms that lead to cisplatin adducts in DNA, there are few insights into the processes that result in its antitumor acti on. To explore some of the cellular responses elicited by cisplatin tr eatment, we studied its influence on DNA supercoiling and DNA gyrase g ene expression in E. coil. We found that cisplatin inhibits DNA gyrase in a concentration-dependent manner leading to a transient alteration of DNA supercoiling and to an induction of gyrase gene expression. Th e induction effect was asymmetrical, affecting gyrB stronger than gyrA . Furthermore, we studied the influence of cisplatin on the supercoili ng activity of purified DNA gyrase in vitro and found that cisplatin w as an efficient inhibitor of DNA gyrase in the standard assay. However , cisplatin was an excellent inhibitor when added to DNA gyrase before it could interact with its substrate. In this assay GyrB was also mor e affected by cisplatin than GyrA. This strong ly suggests that cispla tin inhibits DNA gyrase primarily by direct interaction with the enzym e. The data from this work present evidence that further cellular resp onses following cisplatin treatment include DNA gyrase inhibition, alt ered DNA supercoiling and enhanced DNA gyrase gene expression. This su ggests an important role of DNA topology in the induction of defense m echanisms against the action of cisplatin in addition to the processes related to DNA damage and repair.