Central role for the Werner syndrome protein/poly(ADP-ribose) polymerase 1 complex in the poly(ADP-ribosyl)ation pathway after DNA damage

A defect in the Werner syndrome protein (WRN) leads to the premature aging disease Werner syndrome (WS). Hallmark features of cells derived from WS patients include genomic instability and hypersensitivity to certain DNA-damaging agents. WRN contains a highly conserved region, the RecQ conserved domain, that plays a central role in protein interactions. We searched for proteins that bound to this region, and the most prominent direct interaction was with poly(ADP-ribose) polymerase 1 (PARP-1), a nuclear enzyme that protects the genome by responding to DNA damage and facilitating DNA repair. In pursuit of a functional interaction between WRN and PARP-1, we found that WS cells are deficient in the poly(ADP-ribosyl)ation pathway after they are treated with the DNA-damaging agents H2O2 and methyl methanesulfonate. After cellular stress, PARP-1 itself becomes activated, but the poly(ADP-ribosyl)ation of other cellular proteins is severely impaired in WS cells. Overexpression of the PARP-1 binding domain of WRN strongly inhibits the poly(ADP-ribosyl)ation activity in H2O2-treated control cell lines. These results indicate that the WRN/PARP-1 complex plays a key role in the cellular response to oxidative stress and alkylating agents, suggesting a role for these proteins in the base excision DNA repair pathway.