DNA-REPAIR DEFECT IN POLY(ADP-RIBOSE) POLYMERASE-DEFICIENT CELL-LINES

To investigate the physiological function of poly(ADP-ribose) polymera se (PARP), we used a gene targeting strategy to generate mice lacking a functional PARP gene. These PARP(-/-)mice were exquisitely sensitive to the monofunctional-alkylating agent N-methyl-N-nitro-sourea (MNU) and gamma-irradiation. In this report, we have analysed the cause of t his increased lethality using primary and/or spontaneously immortalize d mouse embryonic fibroblasts (MEFs) derived from PARP(-/-)mice. We fo und that the Back of PARR renders cells significantly more sensitive t o methylmethane-sulfonate (MMS), causing cell growth retardation, G(2) /M accumulation and chromosome instability An important delay in DNA s trand-break resealing was observed following treatment with MMS, This severe DNA repair defect appears to be the primary cause for the obser ved cytoxicity of monofunctional-alkylating agents, leading to cell de ath occurring after G(2)/M arrest. Cell viability following MMS treatm ent could be fully restored after transient expression of the PARP gen e. Altogether, these results unequivocally demonstrate that PARR is re quired for efficient base excision repair in vivo and strengthens the role of PARP as a survival factor following genotoxic stress.