Poly(ADP-ribose)polymerase-1 regulates activation of AP-1 by DNA damage

808 PARP-1 catalytic activity is stimulated by variety of genotoxic agents and ionizing radiation. Accordingly, PARP-1 has been regarded as a component of cellular responses to genotoxic stress, albeit its function was attributed exclusively to DNA damage repair. Recent studies, including data from our laboratory (1-3), have also implicated PARP-1 in the regulation of physiological gene expression and in transcriptional response to various pathophysiological stimuli (reviewed in Soldatenkov and Potaman, Current Drug Targets, 2004). Here we investigated the PARP-1 function in the activation of nuclear transcription factors, such as activator protein-1 (AP-1), which participates in adaptive responses of genome to various oxidant and toxic stimuli. In PARP-1 expressing cells radiation-induced DNA damage resulted in strong stimulation of the PARP-1 catalytic activity which was abrogated by pre-treatment of cells with the EB-47 or DPQ, specific and potent inhibitors of the reaction of poly(ADP-ribosyl)ation. We found that although PARP-1 (+/+) cells were capable of responding to genotoxic insult by activating the AP-1 pathway, PARP-1 deficient cells evidently lose their ability to activate AP-1 in response to DNA damage. Genetic inhibition of PARP-1 resulted in delayed activation of Jun B, Jun D and c-Jun, and dramatically diminished DNA-binding activity of Fos family proteins. Furthermore, using a real-time PCR we show that PARP-1 proficient cells exposed to DNA-damaging treatment exhibit early and marked induction of the AP-1 components, and that stimulation of AP-1 expression by DNA damage was dramatically attenuated in cells with PARP-1 null genetic background. Reduced activation of AP-1 transcription factors as part of faulty induction of stress-inducible cytoprotective genes may provide an explanation for enhanced susceptibility of PARP-1 deficient cells to genotoxic stimuli. This work was supported in part by grant CA74175 from the National Cancer Institute. (1) J. Biol. Chem. 2002, 277: 665; (2) J. Biol. Chem. 2005, 280: 17076; (3) J. Mol. Biol. 2005, 348: 609.