PARP1 (Poly(ADP-Ribose) Polymerase 1 DNA Nick Sensor & NAD+-Consuming Repair Gene)
PARP1 (poly(ADP-ribose) polymerase 1; HGNC:270, NCBI Gene ID 142) is a human locus mapped to chromosome band 1q42.12 that encodes nuclear zinc-finger ADP-ribosyltransferase PARP1 / ARTD1 (1,014 aa; 113 kDa; EC 2.4.2.30). PARP1 acts in single-strand DNA break base-excision repair (XRCC1 recruitment) & chronic DNA-damage NAD+ depletion, together with BRCA1 (Synthetic-Lethal Homologous Recombination Gene), BRCA2 (Synthetic-Lethal Homologous Recombination Gene), and ATM (DNA Double-Strand Break Kinase Gene). Encodes the abundant nuclear enzyme PARP1 that senses DNA strand breaks and consumes NAD+ to synthesize poly(ADP-ribose) repair scaffolds.
Direct target of synthetic-lethal PARP inhibitors (olaparib, niraparib, talazoparib, saruparib) in BRCA1/BRCA2/ATM-mutant cancers
Gene Structure & Expression
Genomic Organization & Cytogenetic Locus: 23-exon gene on chromosome 1q42.12 encoding an abundant nuclear protein (~1–2 million copies per cell) organized into three N-terminal zinc-finger DNA-nick-sensing domains (Zn1, Zn2, Zn3), a central BRCT automodification domain, a WGR domain, and a C-terminal catalytic domain carrying the conserved His-Tyr-Glu (HYE) NAD+-binding triad.
Cellular & Tissue Expression Profile: Ubiquitously expressed at high levels in the nucleus of all proliferating and post-mitotic human cells, accounting for >85–90% of cellular poly(ADP-ribosyl)ation capacity upon DNA damage.
Molecular Function & Pathways
Biochemical & Physiological Mechanism: Within milliseconds of binding a DNA single-strand nick or double-strand break via Zn1/Zn2, an allosteric domain collapse reliefs helical-subdomain autoinhibition and increases catalytic activity >500-fold: PARP1 cleaves nuclear NAD+ (releasing nicotinamide for NAMPT salvage) and polymerizes negatively charged branched chains of poly(ADP-ribose) (PAR) onto itself and histones—recruiting XRCC1, DNA polymerase beta, and DNA ligase III (LIG3) for base-excision repair before electrostatic repulsion releases automodified PARP1 from the repaired DNA.
Clinical & Therapeutic Significance
Human Genetic Variants & Disease Phenotypes: While PARP1 maintains genome stability under physiological stress, chronic hyperactivation of PARP1 by persistent age-related DNA damage, UV radiation, or ischemia-reperfusion exhausts the nuclear/cytosolic NAD+ pool, directly starving NAD+-dependent SIRT1 and SIRT6 deacetylases and triggering parthanatos cell death.
Therapeutic & Clinical Pharmacology: First clinically approved example of synthetic lethality in oncology: small-molecule PARP inhibitors (olaparib, rucaparib, niraparib, talazoparib, and next-generation PARP1-selective saruparib / AZD5305) both block catalytic PARylation and physically "trap" PARP1 on single-strand DNA breaks, which collapse replication forks into double-strand breaks that selectively kill homologous-recombination-deficient BRCA1-, BRCA2-, PALB2-, or ATM-mutant breast, ovarian, pancreatic, and prostate cancers.