Regulation of Binding of Tumor Suppressor Protein p53 to DNA by Transition Metals
Human p53 protein binds preferentially to supercoiled (sc) DNA in both the presence and absence of the p53 consensus sequence (p53CON) . This binding produces a ladder of retarded bands on an agarose gel detected by ethidium-staining DNA and by immunoblotting with specific primary antibodies . p53 binds to p53CON in linear DNA producing a retarded band. This kind of binding is observed also with isolated core domain of human p53 protein (p53CD, amino acids 94-312). Binding of p53CD to sc DNA is accompanied by only small retardation, without formation of the band ladder . We have shown previously that binding of p53 to scDNA is modulated by the redox state of the protein [4, 5] and that physiological concentrations of Zn2+ (1-20 mM) inhibit binding of p53 to sc and linear DNA with and without p53CON . Effect of Zn2+ on p53 binding to DNA can be reverted by EDTA. Cobalt, nickel and iron ions also inhibit p53 binding to scDNA and to p53CON but at least an order of magnitude higher concentrations (far above physiological levels) of these metals are required to obtain the same effect as with zinc.
We show that in addition to Zn2+ other ions of transition metals (Cd2+, Hg2+, Cu2+) at micromolar concentrations efficiently inhibit binding of p53 to DNA. These ions influence p53 binding to scDNA as well as to p53CON in linear DNA. Inhibition effect is found both with full length p53 and with p53CD at similar concentrations of metal ions. Substantially higher concentrations (milimolar) of Ca2+, Mg2+, Sr3+ and Ba2+ are necessary to observe effects on binding of p53 to DNA. These ions inhibit partially binding of p53CD to scDNA as well as its sequence-specific binding to linear DNA molecules. The strong inhibition efects of transition metals can be explained by their predominant interaction with cysteine and histidine residues followed by changes of the protein conformation of p53 from "wild type" (necessary for the tumor suppressor function of p53) to "mutant" form.
1. E. Palecek, D. Vlk, V. Stankova, V. Brazda, B. Vojtesek, T. R. Hupp, A. Schaper and T. M. Jovin, Oncogene 15, 2201-2209 (1997).
Marie Brazdova, Hana Cernocka, Sarka Postuvkova, Lenka Karlovska, Vaclav Brázda, Vinod Subramaniam1, Thomas M.Jovin1, and Emil Palecek
Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, 612 65 Brno, Czech Republic. 1Max Planck Institute for Biophysical Chemistry, Göttingen, Germany