INHIBITION OF POLY(ADP-RIBOSE) POLYMERASE RESCUES HUMAN T-LYMPHOCYTESFROM METHYLMERCURY-INDUCED APOPTOSIS

The objective of this investigation was to determine the role of poly( ADP-ribose) polymerase (PARP) in methylmercuric chloride (MeHgCl)-indu ced T-cell apoptosis. Following exposure of human T-cells to 2.5 mu M MeHgCl, we observed PARP activation within 45 min. Maximal activation was observed at 90 min after MeHgCl treatment; thereafter, PARP activi ty declined. The loss in enzyme activity was coincidental with the cle avage of 116-kDa intact PARP protein to an 85-kDa fragment. To address the relationship between PARP activation and induction of apoptosis, we first examined the redox status of T cells treated with MeHgCl. We found that exposure of T cells to low concentrations of this toxicant resulted in decreased levels of reduced pyridine nucleotides and an in crease in the relative amounts of oxidized flavoproteins. Thus, the po ssibility exists that activation of PARP leads to NAD(+) depletion and thereby alters mitochondrial redox status. To determine if PARP activ ation is indeed part of the proapoptotic (destructive) response or a c omponent of the antiapoptotic (protective) response, we employed two i nhibitors: 3-aminobenzamide and nicotinamide. Pretreatment of T cells with these inhibitors protected cells from MeHgCl-induced apoptosis; t his was seen as a reduction in the uptake of Hoechst 33258 and DNA fra gmentation. Moreover, these inhibitors blocked MeHgCl-induced oxidativ e stress as evidenced by a reduction in reactive oxygen species (ROS) generation. These agents, however, failed to block MeHgCl-dependent de cline in mitochondrial transmembrane potential(Delta Psi(m)). We concl ude that PARP activation leads to proapoptotic events that contribute to MeHgCl-induced cell death, (C) 1998 Academic Press.