| Budget Amount *help |
¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 1992: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1991: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
An animal model for the study of genetic alterations during colon carcinogenesis was established. Repeated i.p. injections of 1,2-dimethylhydrazine (DMH) induced colon tumors in F1 hybrid mice between different inbred strains. Their susceptibility to DMH in colon tumor induction largely depended on the parental strains. Extracolonic tumors at the anus, liver, lung, and vascular systems were also induced by DMH treatment.
Mutational activation of the three ras oncogenes (K-, H-, N-) in exons 1 to 3 was examined in 155 colon tumors and 15 extracolonic tumors. Polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis revealed relatively low frequency (10%) of the ras gene mutations in mouse colon tumors. Codon 12 of the K-ras gene was most frequently mutated. In addition to common mutations, several rare mutations at codons 18 and 60 of the K-ras gene and codon 63 of the N-ras gene were also detected. Direct sequencing of the abnormal bands showed that 80% of the base substitutions were G : C to A : T transitions.
PCR-SSCP analysis of exons 5 to 8 of the p53 gene revealed abnormal bands on SSCP gels in 20 out of 155 colon tumors, indicative of point mutations in the conserved regions of the p53 gene. In order to assess the possibility of allelic loss at the p53 gene, PCR-SSCP analysis was carried out with sequence tagged microsatellite (STMS) markers closely linked to the p53 locus. No allelic loss or alteration was observed in 155 colon tumors, except for only one case showing extra CA repeat. Similarly, SSCP analysis with PCR primers spanning intron 6 of the p53 gene, which is polymorphic among some of the inbred strains, did not detect any allelic loss in mouse colon tumors.
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