DETECTION OF CODON-12 POINT MUTATIONS OF THE K-RAS GENE FROM MOUSE LUNG ADENOCARCINOMA BY ENRICHED PCR

Purpose: Recent studies have shown that chemical carcinogens induce a high frequency of point mutations in the K-ras oncogene from mouse lun g tumours at codons 12, 13 and 61. These experiments were performed to identify K-ras mutations in tissues from control and radiation-expose d mice. Materials and methods: By modifying the technique of the 'enri ched' polymerase chain reaction (PCR), it was possible to detect point mutations at codon 12 of the K-ras oncogene from 25-year-old paraffin -embedded normal lungs and lung adenocarcinomas from mice exposed to r adiation. Together, a total of 120 lung tissues were screened for poin t mutations at codon 12 of the K-ras oncogene in this study. Results: A significant increase in K-ras codon 12 point mutations was observed in the normal lungs from mice exposed to 24 once-weekly neutron irradi ations (100%), compared with normal lungs from mice with sham-irradiat ion (50%) (p<0.05). Lung adenocarcinomas from mice receiving 24 once-w eekly neutron irradiations also had a significantly higher frequency o f K-ras codon 12 point mutations (100%) than the lung adenocarcinomas of mice receiving 24 or 60 once-weekly gamma-ray irradiations (50%), b ut the higher frequency was not significantly different from that in s pontaneous lung adenocarcinomas from mice (75%; p>0 05). The validity of the technique was confirmed by sequencing two of the mutants. In do ing so, a K-ras 13(Asp) point mutation was observed. Conclusions: The data suggest that high-linear energy transfer (LET) neutron radiation was more effective than low-LET gamma-rays in inducing K-ras point mut ations at codon 12 in the lungs of BGCF(1) mice.