Mutational specificity of 2-amino-3-methylimidazo-[4,5-f]quinoline in the hprt locus of CHO-K1 cells.
2-Amino-3-methylimidazo[4,5-f]quinoline (IQ), a food carcinogen formed in cooked meats, can induce gene mutation at the hprt locus of CHO-K1 cells in the presence of hepatic S9 mix. To elucidate the molecular nature of IQ-induced mutation, we characterized the entire coding region of the hypoxanthine phosphoribosyl-transferase gene of 23 independent mutants derived from IQ-treated CHO cells by direct sequencing of polymerase chain reaction-amplified cDNA. Ten of the 23 IQ-induced mutants examined contained single base substitutions; one mutant had three single-base substitutions. Among the base substitutions, G.C-->C.G (six of 13) and A.T-->C.G (three of 13) transversions predominated. Most of the base-substitution mutations occurred preferentially at a middle G and had a dA in their 3' ends. Of the 13 other mutations (56.5%), 12 missing one or more complete exons were splice-site mutations, and one mutant had a partial deletion of an exon. A high frequency of complete exon deletion (11 of 12) in exons 2-5 was observed. Interestingly, 75% of the mutants (nine of 12) with splice-site mutations were induced by IQ only at higher concentrations (300-500 microM). This was probably due to the occurrence of GC base-substitution mutations that affected hprt mRNA splicing, especially at the intron-exon boundaries.
Lee
H
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Environmental Toxicological Center, Chung Shan Medical and Dental College, Taichung, Taiwan, Republic of China.
Shih
M K
MK
D000818:Animals; D001483:Base Sequence; D016466:CHO Cells / Q000187:drug effects* / Q000502:physiology; D006224:Cricetinae; D018076:DNA, Complementary / Q000032:analysis / Q000235:genetics; D005091:Exons; D005784:Gene Amplification; D017353:Gene Deletion; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics*; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009153:Mutagens / Q000633:toxicity*; D009154:Mutation; D016133:Polymerase Chain Reaction; D011804:Quinolines / Q000633:toxicity*
D018076:DNA, Complementary; D009153:Mutagens; D011804:Quinolines; C029216:2-amino-3-methylimidazo(4,5-f)quinoline; D007041:Hypoxanthine Phosphoribosyltransferase