The interaction of u.v.- and methyl methanesulfonate-induced DNA repair synthesis: a role for poly(ADP-ribose)?

Treatment of a human lymphoblastoid line ( GM606 ) with methyl methanesulfonate (MMS) or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) initially stimulates and then drastically inhibits repair synthesis. This inhibition is overcome and repair appears to be stimulated by the poly(ADP-ribose) synthetase inhibitor 3-aminobenzamide (3-AmB). The repair activity of older cultures is much diminished compared to those rapidly dividing, but the 3-AmB effect is seen in both 2- and 7-day cultures. The action of 3-AmB is very rapid and its removal results in a diminution of repair synthesis within 30 min. U.v.-induced repair synthesis was not affected by 3-AmB. However, the level of u.v.-induced repair synthesis was drastically reduced by treatment of cells with MMS. This MMS inhibition of u.v.-induced repair synthesis was completely counteracted by the presence of 3-AmB. Insofar as the effective action of 3-AmB is on poly(ADP-ribose) synthesis, the data suggest that activation of poly(ADP-ribose) synthesis by alkylation of DNA reduces the NAD and therefore the ATP level in the lymphoblastoid cells used. Reduced ATP levels result in a lessened ability to carry out u.v.-induced repair synthesis.