Calcium-dependent modulation of poly(ADP-ribose) polymerase-1 alters cellular metabolism and DNA repair

After genotoxic stress poly(ADP-ribose) polymerase-1 (PARP-1) can be hyperactivated, causing (ADP-ribosyl)ation of nuclear proteins (including itself), resulting in NAD(+) and ATP depletion and cell death. Mechanisms of PARP-1-mediated cell death and downstream proteolysis remain enigmatic. beta-lapachone (beta-lap) is the first chemotherapeutic agent to elicit a Ca(2+)-mediated cell death by PARP-1 hyperactivation at clinically relevant doses in cancer cells expressing elevated NAD(P)H:quinone oxidoreductase 1 (NQO1) levels. Beta-lap induces the generation of NQO1-dependent reactive oxygen species (ROS), DNA breaks, and triggers Ca(2+)-dependent gamma-H2AX formation and PARP-1 hyperactivation. Subsequent NAD(+) and ATP losses suppress DNA repair and cause cell death. Reduction of PARP-1 activity or Ca(2+) chelation protects cells. Interestingly, Ca(2+) chelation abrogates hydrogen peroxide (H(2)O(2)), but not N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced PARP-1 hyperactivation and cell death. Thus, Ca(2+) appears to be an important co-factor in PARP-1 hyperactivation after ROS-induced DNA damage, which alters cellular metabolism and DNA repair.