Base excision repair defects invoke hypersensitivity to PARP inhibition.
PARP-1 is important for the recognition of both endogenous and exogenous DNA damage, and binds to DNA strand breaks including intermediates of base excision repair (BER). Once DNA-bound, PARP-1 becomes catalytically activated synthesizing PAR polymers onto itself and other repair factors (PARylation). As a result, BER repair proteins such as XRCC1 and DNA polymerase β (pol β) are more efficiently and rapidly recruited to sites of DNA damage. In the presence of an inhibitor of PARP activity (PARPi), PARP-1 binds to sites of DNA damage, but PARylation is prevented. BER enzyme recruitment is hindered, but binding of PARP-1 to DNA is stabilized, impeding DNA repair and leading to double-strand DNA breaks (DSB). Deficiencies in pol β(-/-) and Xrcc1(-/-) cells resulted in hypersensitivity to the PARP inhibitor 4-AN and reexpression of pol β or XRCC1, in these contexts, reversed the 4-AN hypersensitivity phenotype. BER deficiencies also showed evidence of replication defects that lead to DSB-induced apoptosis upon PARPi treatment. Finally, the clinically relevant PARP inhibitors olaparib and veliparib also exhibited hypersensitivity in both pol β(-/-) and Xrcc1(-/-) BER-deficient cells. These results reveal heightened sensitivity to PARPi as a function of BER deficiency.


CONCLUSIONS
BER deficiency represents a new therapeutic opportunity to enhance PARPi efficacy.
Laboratory of Structural Biology, NIEHS, NIH, Research Triangle Park, North Carolina.
Julie K
JK
Horton
Laboratory of Structural Biology, NIEHS, NIH, Research Triangle Park, North Carolina.
Donna F
DF
Stefanick
Laboratory of Structural Biology, NIEHS, NIH, Research Triangle Park, North Carolina.
Rajendra
R
Prasad
Laboratory of Structural Biology, NIEHS, NIH, Research Triangle Park, North Carolina.
Natalie R
NR
Gassman
Laboratory of Structural Biology, NIEHS, NIH, Research Triangle Park, North Carolina.
Padmini S
PS
Kedar
Laboratory of Structural Biology, NIEHS, NIH, Research Triangle Park, North Carolina wilson5@niehs.nih.gov.
Samuel H
SH
Wilson
D000818:Animals; D002460:Cell Line; D004247:DNA / Q000235:genetics; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects; D004249:DNA Damage / Q000187:drug effects / Q000235:genetics; D004260:DNA Repair / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D051379:Mice; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics*; D000076105:X-ray Repair Cross Complementing Protein 1
D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D000076105:X-ray Repair Cross Complementing Protein 1; C000619352:Xrcc1 protein, mouse; D004247:DNA; D011065:Poly(ADP-ribose) Polymerases