Molecular analysis of DNA adducts and hprt mutations produced by 6-nitrosochrysene in Chinese hamster ovary cells.
We have characterized the mutational spectrum of 6-nitrosochrysene in the hprt gene of Chinese hamster ovary (CHO-K1) cells and also examined the adducts formed by this compound in CHO-K1 cells by quantitative 32P-postlabeling analysis. Seventy percent of the identified mutations were simple basepair substitutions, and they occurred more often at A:T (14/17) than at G:C. Furthermore, 13 of the basepair substitutions at A:T had the mutated dA, the probable adducted residue, on the non-transcribed DNA strand. The preference for mutation at A:T contrasted sharply with the distribution of adducts formed by 6-nitrosochrysene: 80% of the identified adducts were with dG, while only 20% were probably formed through binding with dA. Analyses conducted with excision-repair-defective CHO-UV5 cells revealed both a preference for basepair substitution at A:T and an adduct profile that were similar to those found for repair-proficient CHO-K1 cells. However, basepair substitutions from CHO-UV5 cell mutants had the mutated dAs distributed randomly between the non-transcribed and transcribed DNA strands. The mutational spectra found for solvent control CHO-K1 and CHO-UV5 cells differed from those of the 6-nitrosochrysene-treated cultures. These findings suggest that 6-nitrosochrysene-induced mutations are targeted to DNA damage, but that 6-nitrosochrysene-derived dA adducts are much more effective at producing mutations than 6-nitrosochrysene-derived dG adducts. The extreme strand bias for mutated dAs in the CHO-K1 mutational spectrum appears to result from preferential removal of 6-nitrosochrysene-induced DNA lesions from the transcribed DNA strand.
Manjanatha
M G
MG
National Center for Toxocological Research, Division of Genetic Toxicology, Jefferson, AR.
Newton
R K
RK
Mittelstaedt
R A
RA
Villani
G R
GR
Declos
K B
KB
Heflich
R H
RH
D000818:Animals; D001482:Base Composition; D016466:CHO Cells / Q000187:drug effects; D002911:Chrysenes / Q000378:metabolism; D006224:Cricetinae; D004247:DNA / Q000378:metabolism; D004252:DNA Mutational Analysis; D018076:DNA, Complementary / Q000737:chemistry / Q000187:drug effects / Q000235:genetics*; D009154:Mutation / Q000235:genetics*; D013762:Tetrahydrofolate Dehydrogenase / Q000187:drug effects / Q000235:genetics*
D002911:Chrysenes; D018076:DNA, Complementary; C035986:6-nitrochrysene; D004247:DNA; D013762:Tetrahydrofolate Dehydrogenase