Base Excision Repair Is Impaired in Mammalian Cells Lacking Poly(ADP-ribose) Polymerase-1

TLDR

Base excision repair in mammalian cells corrects damaged bases via short‑patch and long‑patch pathways, replacing one or several nucleotides, respectively. PARP‑1 participates in both repair pathways, as shown by reduced repair in PARP‑1‑deficient extracts and by its constitutive interaction with DNA polymerase β, which itself is required for both short‑ and long‑patch repair of uracil‑derived lesions. Loss of PARP‑1 reduces short‑patch repair efficiency by about half and severely impairs long‑patch repair, and when combined with DNA polymerase β deficiency the pathways collapse, demonstrating that PARP‑1 is an essential component of base excision repair.

Abstract

In mammalian cells, damaged bases in DNA are corrected by the base excision repair pathway which is divided into two distinct pathways depending on the length of the resynthesized patch, replacement of one nucleotide for short-patch repair, and resynthesis of several nucleotides for long-patch repair. The involvement of poly(ADP-ribose) polymerase-1 (PARP-1) in both pathways has been investigated by using PARP-1-deficient cell extracts to repair single abasic sites derived from uracil or 8-oxoguanine located in a double-stranded circular plasmid. For both lesions, PARP-1-deficient cell extracts were about half as efficient as wild-type cells at the polymerization step of the short-patch repair synthesis, but were highly inefficient at the long-patch repair. We provided evidence that PARP-1 constitutively interacts with DNA polymerase β. Using cell-free extracts from mouse embryonic cells deficient in DNA polymerase β, we demonstrated that DNA polymerase β is involved in the repair of uracil-derived AP sites via both the short and the long-patch repair pathways. When both PARP-1 and DNA polymerase β were absent, the two repair pathways were dramatically affected, indicating that base excision repair was highly inefficient. These results show that PARP-1 is an active player in DNA base excision repair.