Regulation of poly(ADP-ribose) polymerase-1-dependent gene expression through promoter-directed recruitment of a nuclear NAD ⁺ synthase

NMNAT-1 and PARP-1, two key enzymes in the NAD ⁺ metabolic pathway, localize to the nucleus where integration of their enzymatic activities has the potential to control a variety of nuclear processes. Using a variety of biochemical, molecular, cell-based, and genomic assays, we show that NMNAT-1 and PARP-1 physically and functionally interact at target gene promoters in MCF-7 cells. Specifically, we show that PARP-1 recruits NMNAT-1 to promoters where it produces NAD ⁺ to support PARP-1 catalytic activity, but also enhances the enzymatic activity of PARP-1 independently of NAD ⁺ production. Furthermore, using two-photon excitation microscopy, we show that NMNAT-1 catalyzes the production of NAD ⁺ in a nuclear pool that may be distinct from other cellular compartments. In expression microarray experiments, depletion of NMNAT-1 or PARP-1 alters the expression of about 200 protein- coding genes each, with about 10% overlap between the two gene sets. NMNAT-1 enzymatic activity is required for PARP- 1-dependent poly(ADP-ribosyl)ation at the promoters of commonly regulated target genes, as well as the expression of those target genes. Collectively, our studies link the enzymatic activities of NMNAT-1 and PARP-1 to the regulation of a set of common target genes through functional interactions at target gene promoters.