title: High-mobility group 1 protein inhibits helicase catalyzed displacement of cisplatin-damaged DNA.
abstract: We have determined the effect of HMG-1 bound to cisplatin-damaged DNA on the activities of calf helicase E. DNase I protection analysis demonstrated HMG-1 bound a cisplatin-damaged 24 base oligonucleotide annealed to M13mp18. Exonuclease digestion experiments revealed that greater than 90% of the DNA substrates contained a single site specific cisplatin adduct and, maximally, 65% of the substrates were bound by HMG-1. Helicase E catalyzed displacement of the cisplatin-damaged DNA oligonucleotide was inhibited by HMG-1 in a concentration-dependent manner. Time course experiments revealed a decreased rate of displacement in reactions containing HMG-1. The maximum inhibition observed was 55% and taking into account that only 65% of the substrates had HMG-1 bound, approximately 85% inhibition was observed on platinated DNA substrates containing HMG-1. Inhibition of helicase activity was proportional to the amount of substrate bound by HMG-1 based on the displacement and exonuclease assays at varying HMG-1 concentrations. The ability of helicase E to displace an undamaged DNA oligonucleotide from a cisplatin-damaged DNA template was also inhibited by HMG-1. Interestingly, HMG-1 had no effect on the rate of DNA-dependent ATP hydrolysis catalyzed by helicase E on the same DNA substrate. The inhibition of helicase activity by HMG-1 binding cisplatin-damaged DNA further supports a role for HMG-1 inhibiting DNA repair which may contribute to cellular sensitivity to cisplatin.
authors.affiliation: Department of Biochemistry and Molecular Biology, Wright State University, Dayton, OH 45435, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Patrick
authors.forename: K M
authors.initials: KM
authors.lastname: Henkels
authors.forename: J J
authors.initials: JJ
authors.lastname: Turchi
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism / Q000494:pharmacology*; D002384:Catalysis; D002417:Cattle; D002945:Cisplatin / Q000378:metabolism / Q000633:toxicity*; D004247:DNA / Q000378:metabolism*; D004249:DNA Damage / Q000187:drug effects*; D004265:DNA Helicases / Q000037:antagonists & inhibitors*; D003850:Deoxyribonuclease I; D024243:HMGB1 Protein; D006609:High Mobility Group Proteins / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D013379:Substrate Specificity
chemical_list: D002352:Carrier Proteins; D024243:HMGB1 Protein; D006609:High Mobility Group Proteins; D004247:DNA; D003850:Deoxyribonuclease I; D000251:Adenosine Triphosphatases; D004265:DNA Helicases; D002945:Cisplatin