DNA Strand-Specific Repair of (±)-3α,4β-Dihydroxy-1α,2 α-Epoxy-1,2,3,4-Tetrahydrobenzo[c]Phenanthrene Adducts in the Hamster Dihydrofolate Reductase Gene

We evaluated the formation and removal of (±)-3α,4β-dihydroxy-1α,2α-epoxy- 1,2,3,4-tetrahydrobenzo[c]phenanthrene (BcPHDE)-DNA adducts in two Chinese hamster ovary (CHO) cell lines. One line of repair-proficient cells (MK42) carries a stable 150-fold amplification of the dihydrofolate reductase (DHF...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 1992-12, Vol.89 (24), p.11925-11929
Main Authors: Carothers, Adelaide M., Zhen, Weiping, Mucha, Jitka, Zhang, Yu-Jing, Santella, Regina M., Grunberger, Dezider, Bohr, Vilhelm A.
Format: Article
Language:English
Subjects:
Adducts
Carcinogens
Cell lines
CHO cells
DNA
DNA adducts
DNA damage
Genes
Genetic mutation
Genomes
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Summary:We evaluated the formation and removal of (±)-3α,4β-dihydroxy-1α,2α-epoxy- 1,2,3,4-tetrahydrobenzo[c]phenanthrene (BcPHDE)-DNA adducts in two Chinese hamster ovary (CHO) cell lines. One line of repair-proficient cells (MK42) carries a stable 150-fold amplification of the dihydrofolate reductase (DHFR) locus. The other line of repair deficient cells (UV-5) is diploid for this gene and is defective in excision of bulky DNA lesions. Two methods were used to quantitate adduct levels in treated cells: Escherichia coli UvrABC excision nuclease cleavage and32P-postlabeling. DNA repair was examined in the actively transcribed DHFR gene, in an inactive region located 25 kilobases downstream, and in the overall genome. Between 8 and 24 hr after BcPHDE exposure, preferential repair of the DHFR gene compared to the noncoding region was apparent in MK42 cells. This gene-specific repair was associated with adduct removal from the DHFR transcribed strand. However, UV-5 cells showed no lesion reduction from this strand of the gene. By both quantitation methods, regions accessible to repair in MK42 cells showed a 2-fold reduction in DNA adduct levels by 24 hr. That the decline in adducts reflects genomic repair was demonstrated by the constant damage level remaining in UV-5 cells. Since BcPHDE-induced mutations in DHFR apparently arise from adducted purines on the nontranscribed strand, results from the present study support the idea that a consequence of strand-specific repair is strand-biased mutations.
ISSN:0027-8424