Ionizing radiations in Caenorhabditis elegans induce poly(ADP-ribosyl)ation, a conserved DNA-damage response essential for survival

Poly(ADP-ribosyl)ation is one of the first responses to DNA damage in mammals. Although it is involved in base excision repair, its exact role has not been ascertained yet. Poly(ADP-ribose) polymerase-1 (PARP-1) and PARP-2 mediate most of the poly(ADP-ribosyl)ation response in mammals and are well conserved in evolution. Their respective homologues PME-1 and PME-2 are found in the nematode Caenorhabditis elegans, a well-known genetically tractable model currently used in DNA damage response research. Here we report the functional analysis of PME-1 and PME-2 in presence of DNA damage. Worms irradiated with high doses of ionizing radiations displayed a sharp drop in their NAD(+) content immediately after treatment, and a biphasic increase in poly(ADP-ribose). The physiological importance of the poly(ADP-ribosyl)ation response was highlighted when worms were preincubated with mammalian PARP inhibitors (3AB, DHQ, PJ34) and irradiated. The embryonic survival rate of the progeny was significantly decreased in a dose-dependent manner. The inhibitor 3AB had a weak effect on embryonic survival, followed closely by DHQ. However, PJ34, a member of the phenantridinone family, was very effective even when used at low concentration (100nM). In vitro PARP assay using recombinant PME-1 and PME-2 showed a similar pattern of inhibition where 3AB and DHQ were weak inhibitors, and PJ34 a stronger one. Inhibitors affect mostly the poly(ADP-ribose) polymers elongation at high concentrations. These results suggest that poly(ADP-ribosyl)ation in response to DNA damage is an ancient and very important biochemical process protecting DNA from deleterious modification.