RAD18 and poly[ADP ribose]polymerase independently suppress the access of nonhomologous end joining to double strand breaks and facilitate homologous recombination mediated repair

Authors:
Saberi A, Hochegger H, Szuts D, Lan L, Yasui A, Sale JE, Taniguchi Y, Murakawa Y, Zheng W, Yokomori K, Helleday T, Teraoka H, Arakawa H, Buerstedde JM, Takeda S
In:
Source: Mol Cell Biol
Publication Date: (2007)
Issue: 27(7): 2562-71
Research Area:
Cancer Research/Cell Biology
Cells used in publication:
DT40
Species: chicken
Tissue Origin: blood
Platform:
Nucleofectorâ„¢ I/II/2b
Abstract
The Saccharomyces cerevisiae RAD18 gene is essential for postreplication repair but is not required for homologous recombination (HR), which is the major double-strand break (DSB) repair pathway in yeast. Accordingly, yeast rad18 mutants are tolerant of camptothecin (CPT), a topoisomerase I inhibitor, which induces DSBs by blocking replication. Surprisingly, mammalian cells and chicken DT40 cells deficient in Rad18 display reduced HR-dependent repair and are hypersensitive to CPT. Deletion of nonhomologous end joining (NHEJ), a major DSB repair pathway in vertebrates, in rad18-deficient DT40 cells completely restored HR-mediated DSB repair, suggesting that vertebrate Rad18 regulates the balance between NHEJ and HR. We previously reported that loss of NHEJ normalized the CPT sensitivity of cells deficient in poly(ADP-ribose) polymerase 1 (PARP1). Concomitant deletion of Rad18 and PARP1 synergistically increased CPT sensitivity, and additional inactivation of NHEJ normalized this hypersensitivity, indicating their parallel actions. In conclusion, higher-eukaryotic cells separately employ PARP1 and Rad18 to suppress the toxic effects of NHEJ during the HR reaction at stalled replication forks.