Poly(ADP-ribose) polymerase-1 regulates activation of activator protein-1 in murine fibroblasts

Poly(ADP-ribose) polymerase (PARP)-1 is activated in response to DNA injury in the nucleus of eukaryotic cells and has been implicated in cell dysfunction in inflammation. We investigated the role of PARP-1 on the AP-1 pathway, which is involved in the signal transduction of the inflammatory process. In murine wild-type fibroblasts, oxidative challenge by peroxynitrite and hydrogen peroxide or immunological challenge by IL-1 and 20% FCS induced phosphorylation of the mitogen-activated protein kinase kinase-4, activation of c-Jun N-terminal kinase (JNK), and DNA binding of AP-1. In comparative experiments, peroxynitrite induced DNA binding of heat shock factor-1. Pretreatment of wild-type cells with 5-iodo-6-amino-1,2-benzopyrone, a PARP-1 inhibitor, inhibited JNK activation and DNA binding of AP-1. In parallel experiments in PARP-1-deficient fibroblasts, DNA binding of AP-1 was completely abolished. Activation of JNK was significantly elevated at basal condition, but it exhibited a lesser increase after oxidative or immunological challenge than in wild-type fibroblasts. Nuclear content of phosphorylated mitogenactivated protein kinase kinase-4 was observed in PARP-1-deficient cells after peroxynitrite challenge only. Western blotting analysis for AP-1 subunits indicated that c-Fos was similarly expressed in wild-type and PARP-1-deficient cells. Phosphorylated c-Jun was expressed after oxidative or immunological challenge, but not in basal condition, in wild-type cells; however, it was significantly elevated at basal condition and further enhanced after oxidative or immunological challenge in PARP-1-deficient cells. No DNA binding of heat shock factor-1 was observed in PARP-1-deficient cells. These data demonstrate that PARP-1 plays a pivotal role in the modulation of transcription.