Carcinogenic heavy metals replace Ca2+ for DNA binding and annealing activities of mono-ubiquitinated annexin A1 homodimer

Mono-ubiquitinated annexin A1 was purified from rat liver nuclei. The homodimer form of mono-ubiquitinated annexin A1 was able to unwind dsDNA in a Mg2+- and ATP-dependent manner, and to anneal ssDNA in a Ca2+-dependent manner. Phospholipids decreased the concentration of Ca2+ required for maximal annealing activity. Heavy metals such as As3+, Cr6+, Pb2+ and Cd2+ substituted for Ca2+ in the ssDNA binding and annealing activities of annexin A1. While these metals inhibited the unwinding of dsDNA by nuclear annexin A1 in the presence of Mg2+ and ATP, they enhanced dsDNA-dependent ATPase activity of annexin A1. Heavy metals may have produced dsDNA, a substrate for the DNA unwinding reaction, via the DNA annealing reaction. DNA synthesomes were isolated from L5178Y tk(+/−) mouse lymphoma cells in exponential growth, and were found to contain helicase activities. The As3+- or Cr6+-induced increases in ssDNA binding activity of DNA synthesomes were reduced by a mono-specific anti-annexin A1 antibody, but not by anti-Ig antibody. Anti-annexin A1 antibody also blocked the inhibitory and stimulatory effects of As3+ or Cr6+ towards DNA unwinding and annealing activities of DNA synthesomes. Based on these observations, it can be concluded that the effects of heavy metals on DNA annealing and unwinding activities are mediated, at least in substantial part, through actions of the mono-ubiquitinated annexin A1 homodimer.