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I ' I I I I I I I I I I I I I I I I POINT MUTATION AT CODON 11 AND 12 OF H-RAS AND K-RAS ONCOGENES IN HUMAN FETAL EPITHELIAL CELLS TREATED WITIa BENZO(a)PYRENE trans-7,8-DIOL-anti-9,10-EPOIIIDE Zhan De-iin, Chen Jia-kun, Jin Bo, Yi Fei and Wu Zhong-liang, Institute for Chemical Carcinogenesis, Guangzhou Medical College, Guangzhou, China Six samples of human fetal tracheal epithelium (HFTE) cultured in vi r were exposed for 2-6 weeks to trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (B(a)PDE), an oxida- tive metabolite of benzo[alpyrene (B(a)P). The point mutations at codons 11 (GCC) and 12 (GGC) of H-ras, codon 11 (GCT) and 12 (GGT) of K-ras oncogenes in these HFTEs were detected by polymerase chain reaction combined with restriction fragment length polymorphism (RFLP) analysis and direct DNA sequencing. The primary results showed that all of these six HFTEs treated with B(a)PDE exhibited point mutations at codons 11 and 12 of the H-ras gene. Among them, one was GGC~>GTC at codon 12, one was CCGG-CTGG at codons 11 and 12, one was CCGG-CTTG at codons 11 and 12, one was CCGG-CTGT at codons 11 and 12, and one was CCGG-+CTGG and CCAG at codons 11 and 12. Only one HFTE had point mutations at codon 12 of K-ras gene (GGT-GAT). These six HFTEs did not exhibit any transformed characteristics in cellular morphology. The proportions of B(a)PDE induced base pair substitution in human fetal trachael epithelium, which occurred in DNA sequence 5'-CCGG-3' of the H-ras gene, were higher than those in the DNA sequence 5'CTGG-3' of the K-ras gene, with the predominant mutation being the G-+A transition. This suggests that point mutation and activation of H-ras or K-ras oncogenes may occur before the cells display transformed phenotypes. The mutational sensitivities to B(a)PDE appear to be related to the sequence of DNA. N O OD ~ V 00 W 4a i W I