Poly(ADP-ribose) polymerase (PARP-1) is not involved in DNA double-strand break recovery

BACKGROUND: The cytotoxicity and the rejoining of DNA double-strand breaks induced by γ-rays, H(2)O(2 )and neocarzinostatin, were investigated in normal and PARP-1 knockout mouse 3T3 fibroblasts to determine the role of poly(ADP-ribose) polymerase (PARP-1) in DNA double-strand break repair. RESULTS: PARP-1(-/- )were considerably more sensitive than PARP-1(+/+ )3T3s to induced cell kill by γ-rays and H(2)O(2). However, the two cell lines did not show any significant difference in the susceptibility to neocarzinostatin below 1.5 nM drug. Restoration of PARP-1 expression in PARP-1(-/- )3T3s by retroviral transfection of the full PARP-1 cDNA did not induce any change in neocarzinostatin response. Moreover the incidence and the rejoining kinetics of neocarzinostatin-induced DNA double-strand breaks were identical in PARP-1(+/+ )and PARP-1(-/- )3T3s. Poly(ADP-ribose) synthesis following γ-rays and H(2)O(2 )was observed in PARP-1-proficient cells only. In contrast neocarzinostatin, even at supra-lethal concentration, was unable to initiate PARP-1 activation yet it induced H2AX histone phosphorylation in both PARP1(+/+ )and PARP-1(-/- )3T3s as efficiently as γ-rays and H(2)O(2). CONCLUSIONS: The results show that PARP-1 is not a major determinant of DNA double-strand break recovery with either strand break rejoining or cell survival as an endpoint. Even though both PARP-1 and ATM activation are major determinants of the cell response to γ-rays and H(2)O(2), data suggest that PARP-1-dependent poly(ADP-ribose) synthesis and ATM-dependent H2AX phosphorylation, are not inter-related in the repair pathway of neocarzinostatin-induced DNA double-strand breaks.