title: Splicing mutations in the CHO DHFR gene preferentially induced by (+/-)-3 alpha,4 beta-dihydroxy-1 alpha,2 alpha-epoxy-1,2,3,4- tetrahydrobenzo[c]phenanthrene.
abstract: Cultured Chinese hamster ovary (CHO) cells were treated with the polycyclic aromatic hydrocarbon racemic 3 alpha,4 beta-dihydroxy-1 alpha,2 alpha-epoxy-1,2,3,4- tetrahydrobenzo[c]phenanthrene. Mutants deficient in dihydrofolate reductase activity were isolated. A carcinogen treatment at 0.1 microM yielded at 46% survival of the treated population and an induced frequency of mutation of 1.7 x 10(-4), 10(3)-fold greater than the spontaneous rate. By polymerase chain reaction amplification and direct DNA sequencing, we determined the base changes in 38 mutants. Base substitutions accounted for 78% (30/38) of the mutations. We obtained, in addition, four frameshift and four complex mutations. The preferred type of mutation was transversion (A.T----T.A and G.C----T.A) occurring in 69% of the analyzed mutants. A purine was on the 3' side of the putative adduct site in every mutant. Mutations were favored at sequences AGG, CAG, and AAG (the underlined base is the target). Surprisingly, 42% of the mutations created mRNA splicing defects (16/38), especially at splice acceptor sites for each of the five introns. Thus, this chemical carcinogen may recognize some aspect of DNA structure in regions corresponding to pre-mRNA splice sites.
authors.affiliation: Institute of Cancer Research, Columbia University, New York, NY 10027.
authors.forename: A M
authors.initials: AM
authors.lastname: Carothers
authors.forename: G
authors.initials: G
authors.lastname: Urlaub
authors.forename: J
authors.initials: J
authors.lastname: Mucha
authors.forename: R G
authors.initials: RG
authors.lastname: Harvey
authors.forename: L A
authors.initials: LA
authors.lastname: Chasin
authors.forename: D
authors.initials: D
authors.lastname: Grunberger
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004790:Enzyme Induction; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects*; D005796:Genes / Q000187:drug effects*; D008969:Molecular Sequence Data; D009153:Mutagens / Q000494:pharmacology; D009154:Mutation; D015345:Oligonucleotide Probes; D010053:Ovary; D010616:Phenanthrenes / Q000494:pharmacology*; D012326:RNA Splicing; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*
chemical_list: D009153:Mutagens; D015345:Oligonucleotide Probes; D010616:Phenanthrenes; C090203:1,2-epoxy-3,4-dihydroxy-1,2,3,4-tetrahydrobenzo(c)phenanthrene; D013762:Tetrahydrofolate Dehydrogenase