Structure, Conformations, and Repair of DNA Adducts from Dibenzo[a,l]pyrene:  ³²P-Postlabeling and Fluorescence Studies

Abstract

The nature of stable DNA adducts derived from the very potent carcinogen dibenzo[a,l]pyrene (DB[a,l]P) in the presence of rat liver microsomes in vitro and in mouse skin in vivo has been studied using 32P-postlabeling and laser-based fluorescence techniques. Analysis of DB[a,l]P-DNA adducts via 32P-postlabeling has been obtained by comparison of the adduct patterns to those obtained from reactions of synthetic (+/-)-anti-, (+)-anti-, (-)-anti-, and (+/-)-syn-DB[a,l]P-11,12-diol 13,14-epoxide (DB[a,l]PDE) with single nucleotides and calf thymus DNA. anti-DB[a,l]PDE-dA adducts derived from the (-)-enantiomer are the major adducts formed in calf thymus DNA and in mouse skin DNA. The ratio of deoxyadenosine to deoxyguanosine modification is approximately 2:1 in mouse skin exposed to DB[a,l]P; activation by rat liver microsomes leads to a similar profile of adducts but with two additional spots. The conformations of DB[a,l]P adducts in native DNA, as well as the possibility of conformation-dependent repair, have been explored by low-temperature fluorescence spectroscopy. These studies have been performed using polynucleotides and calf thymus DNA reacted in vitro with DB[a,l]PDE and native DNA from mouse epidermis exposed to DB[a, l]P. The results show that adducts are heterogeneous, possess different structures, and adopt different conformations. External, external but base-stacked and intercalated adduct conformations are observed in calf thymus DNA and in mouse skin DNA samples. Differences in adduct repair rates are also revealed; namely, the analysis of mouse skin DNA samples obtained at 24 and 48 h after exposure to DB[a,l]P clearly shows that external adducts are repaired more efficiently than intercalated adducts. These results, taken together with those for B[a]P-DNA adducts [Suh et al. (1995) Carcinogenesis 16, 2561-2569], indicate that the repair of DNA damage resulting from PAH diol epoxides is conformation-dependent.

Evidence that a burst of DNA depurination in SENCAR mouse skin induces error-prone repair and forms mutations in the H-ras gene

“…Clustered adduct formation has been noted by electron microscopic (Paules et al, 1988) and¯uores-cence spectroscopic (Jankowiak et al, 1998a) studies. The data from the¯uorescence study suggest that once formed, a bulky DNA adduct may induce cooperative in¯uences on neighboring bases to form additional adducts (Jankowiak et al, 1998a). Furthermore, the extent of adduct formation may depend on the cell cycle.…”

Dibenzo[A,L]pyrene‐induced genotoxic and carcinogenic responses are dramatically suppressed in aryl hydrocarbon receptor‐deficient mice

“…The shaved area of dorsal skin was treated with 60 μg DB[ a,l ]P for 3 times with an interval of 4 days. Twenty hours after the last application, DB[ a,l ]P‐DNA adduct was detected by 32 P‐postlabeling method as described elsewhere 14, 15, 16. In brief, DNA was extracted by the standard procedure.…”

Formation and Repair of Tobacco Carcinogen‐Derived Bulky DNA Adducts

“…Similar to the B[ a ]P-derived adducts, the bulky adducts formed by (±)- anti -DBPDE possess different structures and adopt different conformations [141]. They are differentially repaired by NER in human cells with some being poorly removed, as shown by a recent study [39].…”