Poly(ADP-ribose)polymerase-1 May Contribute To The Repair Of Direct UV-Induced Lesions Through Its Interactions With Xeroderma Pigmentosum Complementation Group A

Exposure to solar radiation can lead to direct ultraviolet (UV)-induced lesions such as (6-4)pyrimidine-pyrimidone photoproducts (6-4PPs) and cyclobutane pyrimidine dimers (CPDs) which are repaired by nucleotide excision repair (NER). Poly(ADP-ribose)polymerase-1 (PARP-1), a protein required for repair of DNA strand breaks, is additionally suggested to be involved in NER. We find that chemical inhibition or silencing of PARP-1 leads to the retention of CPDs and 6-4PPs in human keratinocytes. The mechanism of PARP-1’s role in NER has yet to be identified. We hypothesize that PARP-1 plays a role in NER through its enzymatic activation and subsequent generation of poly(ADP-ribose) [pADPr]. We predict that pADPr moieties promote interaction between PARP-1 and other DNA repair proteins such as Xeroderma pigmentosum complementation group A (XPA). XPA is an essential protein in NER and contains a pADPr binding motif. Following exposure to solar simulated light, we observed PARP-1 activation. In addition, cellular fractionation revealed increased nuclear localization of XPA and co-immunoprecipitations showed increased interaction between XPA and pADPr as well as XPA and PARP-1. To test the potential role of pADPr in promoting the interaction between PARP-1 and XPA, we treated cells with a pharmacologic PARP inhibitor. Inhibition of PARP activity decreased the interactions between XPA and PARP-1, nuclear localization of XPA and XPA association with chromatin. Based on these findings, PARP activity may play a role in the repair of UV-induced lesions by reducing the levels of nuclear XPA and affecting protein binding to chromatin which could contribute to the observed lesion retention.