The enzymatic and DNA binding activity of PARP-1 are not required for NF-κB coactivator function

Poly(ADP-ribose) polymerase 1 (PARP-1)-deficient mice are protected against septic shock, diabetes type 1, stroke, and inflammation. We report that primary cells from PARP-1(-1-) animals are impaired in kappaB-dependent transcriptional activation induced by different stimuli involved in inflammatory and genotoxic stress signaling. PARP-1 was also required for p65-mediated transcriptional activation. PARP-1 enzymatic inhibitors did not inhibit the transcriptional activation of a kappaB-dependent reporter gene in wild type cells. Remarkably, neither the enzymatic activity nor the DNA binding activity of PARP-1 was required for kappaB-dependent transcriptional activation in PARP-1(-/-) cells complemented with different PARP-1 mutants. However, PARP-1 interacted in vitro directly with both subunits of NF-kappaB (p50 and p65), and mapping of the interaction domains revealed that both subunits bind to different PARP-1 domains. Furthermore, a PARP-1 mutant lacking the enzymatic and DNA binding activity interacted comparably to the wild type PARP-1 with p65 or p50. Finally, we showed that PARP-1 is activating the natural inducible nitric-oxide synthase and P-selectin promoter in a kappaB-dependent manner upon stimulation of the cells with inflammatory stimuli or cotransfection of p65. Our results provide evidence that neither the DNA binding nor the enzymatic activity of PARP-1 but its direct protein-protein interaction with both subunits of NF-kappaB is required for its coactivator function, thus expanding the role of PARP-1 as an essential and novel classical transcriptional coactivator for kappaB-dependent gene expression in vivo.