PARENT SESSION
1:30 PM to 3:30 PM
Monday, April 22, 2002
Poster Session 12 DNA Damage and Repair I
Room: Nevada Exhibition Center

(P17-157) Repair of Abasic Clustered Damages and Double Strand Breaks in Human Cells.

Sutherland, Betsy^*,1, Bennett, Paula¹, Laval, Jacques², ¹ Biology Dept, Upton, NY² Groupe Réparation de l’ADN, Villejuif, France

ABSTRACT-
Clustered DNA damages—closely spaced lesions on opposing strands—are believed to be difficult to repair and therefore are postulated to be at the origin of lethal or mutagenic events. Specifically, repair of non-double strand break clusters, containing oxidized purines, oxidized pyrimidines or abasic sites, could generate additional double strand breaks (DSBs) over those induced by radiation. Additionally, such clusters could constitute persistent or repair-refractory damages. To test these possibilities, repair of DSBs and abasic clusters was determined in human monocytes exposed to 50 or 10 cGy doses of X-rays. Radiation-induced DSBs were removed within 10 min after irradiation. Subsequently, the cells generated repair-intermediate double strand breaks, postulated to result from attempted repair of clustered damages, including Abasic–, OxyPurine– and OxyPyrimidine clusters. However, the frequency of repair-intermediate DSB corresponded to —at most—10% of the clustered damages that potentially could be repaired via DSB intermediates. Abasic clusters induced by radiation constituted persistent damages, requiring hours for repair. Additional repair-intermediate abasic clusters were generated—presumably during repair of OxyPurine, OxyPyrimidine and OxyPurine-OxyPyrimidine clusters—and were slowly resolved. Results suggest that in human cells, repair of clustered damages avoids generating DSB intermediates, but instead uses alternate paths that circumvent induction of potentially lethal and mutagenic frank double strand breaks.

KEYWORDS: clustered DNA damages, abasic clusters, double strand breaks, human cells