RAD18 and poly(ADP-ribose) polymerase independently suppress the access of nonhomologous end joining to double-strand breaks and facilitate homologous recombination-mediated repair.
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.
Saberi
Alihossein
A
CREST Research Project, Radiation Genetics, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
Hochegger
Helfrid
H
Szuts
David
D
Lan
Li
L
Yasui
Akira
A
Sale
Julian E
JE
Taniguchi
Yoshihito
Y
Murakawa
Yasuhiro
Y
Zeng
Weihua
W
Yokomori
Kyoko
K
Helleday
Thomas
T
Teraoka
Hirobumi
H
Arakawa
Hiroshi
H
Buerstedde
Jean-Marie
JM
Takeda
Shunichi
S
D000818:Animals; D034961:Antigens, Nuclear / Q000502:physiology; D002166:Camptothecin / Q000494:pharmacology; D002460:Cell Line; D002645:Chickens; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D006801:Humans; D000072200:Ku Autoantigen; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics / Q000502:physiology*; D011995:Recombination, Genetic; D059004:Topoisomerase I Inhibitors; D044767:Ubiquitin-Protein Ligases
D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; C485954:RAD18 protein, human; D059004:Topoisomerase I Inhibitors; D044767:Ubiquitin-Protein Ligases; D011065:Poly(ADP-ribose) Polymerases; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen; D002166:Camptothecin