Analysis of HMG protein binding to DNA modified with the anticancer drug cisplatin.

Cisplatin (CDDP) is an effective and widely used cancer chemotherapy drug. High mobility group (HMG) proteins 1 and 2 have been shown to bind with high affinity to CDDP-DNA. In this study we analyzed the interaction of HMG proteins with CDDP-DNA. We demonstrate that after binding, HMG proteins can be removed from CDDP-DNA leaving the Pt adducts intact and capable of rebinding HMG proteins. Furthermore, the very HMG proteins that have been removed remain functionally viable and capable of rebinding CDDP-DNA. We also investigated the role that Cys residues play in protein binding. Replacement of Cys 45 or Cys 106 with a Ser residue reduced HMG2 protein binding to CDDP-DNA. These results indicate that Cys residues play a critical role in the high affinity binding of this protein to CDDP-DNA. From these findings, we speculate that the intracellular oxidative environment could affect the redox state of protein thiols in HMG1 and HMG2 and in addition, regulate the ability of these proteins to recognize cis-Pt-DNA adduct formation in tumor cells.