Temporal changes in the mutant frequency and mutation spectra of the 61st codon of the H-ras oncogene following exposure of B6C3F1 mice to N-nitrosodiethylamine (DEN)

Abstract

Hepatocellular tumors were induced in 15 day old male B6C3F1 mice following a single exposure to N-nitrosodiethylamine (DEN; 5 mg/kg, i.p.). Tumors were collected at 38 and 65 weeks to compare the frequencies and types of mutations in the 61st codon of the H-ras oncogene. The 61st codon was amplified using the polymerase chain reaction (PCR). Allele-specific oligonucleotide (ASO) probes were used to determine the frequency and types of mutations present in these tumors. Forty-nine nodular hepatic lesions were obtained from seven animals at the 38 week timepoint. Five of these samples (10%) had mutations at the 61st codon with one CAA-AAA, one CAA-CGA and three CAA-CTA. Thirty-six nodular hepatic lesions were obtained from six animals at the 65 week timepoint. Ten of these samples (28%) had mutations at the 61st codon with one CAA-AAA, five CAA-CGA and four CAA-CTA. These data indicate that DEN-induced mutations at the 61st codon of the mouse H-ras oncogene (i) are an infrequent event, (ii) have different frequencies at the 38 and 65 week timepoints and (iii) are different from the types of mutations seen in spontaneous lesions.

Metabolic Activation Capacity of Neonatal Mice in Relation to the Neonatal Mouse Tumorigenicity Bioassay

“…The H-ras oncogene point mutation in codon 61, a CAA to AAA transversion (G to T in the nontranscribed strand), is the principal ras-oncogene mutation occurring in both spontaneous and carcinogen-induced B6C3F 1 mouse liver tumors [61][62][63][64][65][66][67][68]. Using enzymatic amplification and confirmation by direct sequencing [69], we have also shown that the liver tumors induced in the neonatal B6C3F 1 mouse by the human aromatic amine carcinogen, 4-aminobiphenyl (4-ABP), had a high proportion (16/16) of the same specific codon 61 mutation (CAA to AAA) in the H-ras oncogene (Table 3).…”

Neonatal Mouse Tumorigenicity Bioassay

“…A CAA to AAA transversion (G to T in the nontranscribed strand), in particular, is the principal H-rus point mutation in codon 61 occurring in both the spontaneous and the carcinogen-induced B6C3Fl mouse liver tumors (59,62,(65)(66)(67)(68)(69)(70)(71)(72)(73)(74)(75)(76)(77).…”

Chemoprevention of bicyclol against hepatic preneoplastic lesions

“…50 Such alkylation is correlated to mutations of critical genes for carcinogenesis, e.g., mutations of binding domains of ras gene encoded p21 protein to GTP activating protein that enhances ras-p21 functions. 51,52 Therefore, Bicyclol protects liver cells from DNA damages and attributes to the inhibition of those "activated" oncogenes functions in DEN-induced preneoplastic lesions. Second, DEN-induced DNA damage is initiated by electrophilic species like alkyldiazohydroxides and diazonium ion via the activity of a-hydroxylation by microsomal cytochrome P450 to form deethylational metabolites.…”