title: DNA strand-specific repair of (+-)-3 alpha,4 beta-dihydroxy-1 alpha,2 alpha-epoxy-1,2,3,4-tetrahydrobenzo[c]phenanthrene adducts in the hamster dihydrofolate reductase gene.
abstract: We evaluated the formation and removal of (+-)-3 alpha,4 beta-dihydroxy-1 alpha,2 alpha-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 and 32P-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.
authors: Institute of Cancer Research, Columbia University, New York, NY 10032.
authors: A M
authors: AM
authors: Carothers
authors: W
authors: W
authors: Zhen
authors: J
authors: J
authors: Mucha
authors: Y J
authors: YJ
authors: Zhang
authors: R M
authors: RM
authors: Santella
authors: D
authors: D
authors: Grunberger
authors: V A
authors: VA
authors: Bohr
mesh_terms: D000818:Animals; D016466:CHO Cells; D002273:Carcinogens / Q000737:chemistry; D006224:Cricetinae; D004247:DNA / Q000737:chemistry; D004249:DNA Damage; D004260:DNA Repair; D005796:Genes; D010616:Phenanthrenes / Q000737:chemistry*; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*
chemical_list: D002273:Carcinogens; D010616:Phenanthrenes; C090203:1,2-epoxy-3,4-dihydroxy-1,2,3,4-tetrahydrobenzo(c)phenanthrene; D004247:DNA; D013762:Tetrahydrofolate Dehydrogenase