D. Chakravarti et al., Evidence that a burst of DNA depurination in SENCAR mouse skin induces error-prone repair and forms mutations in the H-ras gene, ONCOGENE, 20(55), 2001, pp. 7945-7953
Treatment of SENCAR mouse skin with dibenzo[a,l]pyrene results in abundant
formation of abasic sites that undergo error-prone excision repair, forming
oncogenic H-ras mutations in the early preneoplastic period. To examine wh
ether the abundance of abasic sites causes repair infidelity, we treated SE
NCAR mouse skin with estradiol-3,4-quinone (E-2-3,4-Q) and determined adduc
t levels I h after treatment, as well as mutation spectra in the H-ras gene
between 6 h and 3 days after treatment. E-2-3,4-Q formed predominantly (gr
eater than or equal to 99%) the rapidly-depurinating 4-hydroxy estradiol (4
-OHE2)-1-N3Ade adduct and the slower-depurinating 4-OHE2-1-N7Gua adduct. Be
tween 6 h and 3 days, E-2-3,4-Q induced abundant A to G mutations in H-ras
DNA, frequently in the context of a 3'-G residue. Using a T.G-DNA glycosyla
se (TDG)-PCR assay, we determined that the early A to G mutations (6 and 12
h) were in the form of G.T heteroduplexes, suggesting misrepair at A-speci
fic depurination sites. Since G-specific mutations were infrequent in the s
pectra, it appears that the slow rate of depurination of the N7Gua adducts
during active repair may not generate a threshold level of G-specific abasi
c sites to affect repair fidelity. These results also suggest that E-2-3,4-
Q, a suspected endogenous carcinogen, is a genotoxic compound and could cau
se mutations.