Analysis of the Ha-ras oncogene in C3H/He mouse liver tumours derived spontaneously or induced with diethylnitrosamine or phenobarbitone.
In a study of the mechanisms involved in the induction of tumours by chemicals, the Ha-ras oncogene was analysed in liver tumours induced by the genotoxic carcinogen diethylnitrosamine (DEN), or the non-genotoxic agent phenobarbitone (PB) in C3H/He mice. Mutations were detected using the polymerase chain reaction and oligonucleotide hybridization. Codon 61 mutations were detected in 41% of DEN-induced tumours (19/46), either in the first base (CG----AT, 12/19), a transversion, or the second base (AT----GC, 7/19), a transition. Codon 61 mutations were also found in 29% of spontaneous tumours (all CG----AT, 6/21) but none were detected in PB-induced tumours (0/15) or in normal liver tissue of untreated mice (0/30). No mutations were detected at codon 12. Low and variable expression of the Ha-ras gene was detected in all liver tissues with moderately raised levels (175-200%) in spontaneous, DEN and PB-induced tumours as compared to normal liver tissue. The H-ras gene was methylated to some extent in all liver tissues, with no discernible difference between the treatments. The frequency of the Ha-ras mutation at codon 61 in DEN-induced tumours is greater than in spontaneously arising tumours. This increase is not accompanied by any specific alteration in the expression or methylation of the gene. Since PB-induced tumours do not possess mutations in the Ha-ras gene at codons 12 or 61, the data suggest that the non-genotoxic agent PB induces tumours in the C3H/He mouse liver with a mechanism distinct from that of spontaneous tumours or those that result from treatment with a potent genotoxic carcinogen such as DEN.
Rumsby
P C
PC
BIBRA, Carshalton, Surrey, UK.
Barrass
N C
NC
Phillimore
H E
HE
Evans
J G
JG
D000818:Animals; D001483:Base Sequence; D015139:Blotting, Southern; D003062:Codon / Q000235:genetics; D004247:DNA / Q000235:genetics; D004052:Diethylnitrosamine; D015870:Gene Expression / Q000235:genetics; D011905:Genes, ras / Q000235:genetics*; D015151:Immunoblotting; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced / Q000235:genetics* / Q000473:pathology; D008745:Methylation; D051379:Mice; D008809:Mice, Inbred C3H; D008969:Molecular Sequence Data; D009154:Mutation; D010634:Phenobarbital; D012334:RNA, Neoplasm / Q000235:genetics
D003062:Codon; D012334:RNA, Neoplasm; D004052:Diethylnitrosamine; D004247:DNA; D010634:Phenobarbital