Activating mutations of the c-Ha-ras protooncogene in chemically induced hepatomas of the male B6C3 F1 mouse.

Abstract

Activated c-Ha-ras protooncogenes have recently been identified in the DNA of some spontaneous hepatic tumors found in 2-year-old B6C3 F1 mice. Activation of c-Ha-ras has now been demonstrated in DNA from well-differentiated hepatomas initiated by a single dose of carcinogen given to male B6C3 F1 mice at 12 days of age. DNA from each of 25 hepatomas, induced by N-hydroxy-2-acetylaminofluorene, vinyl carbamate, or l'-hydroxy-2',3'-dehydroestragole, contained transforming activity in the NIH 3T3 transfection assay. Southern analysis of NIH 3T3 cells transformed by DNA from 24 of these hepatomas revealed amplified and/or rearranged restriction fragments homologous to a Ha-ras probe. The other tumor contained an activated Ki-ras gene. Immunoprecipitation and NaDodSO4/PAGE analysis of p21 ras proteins in NIH 3T3 transformants derived from a majority of the hepatomas suggested that the activating mutations were localized in the 61st codon of the c-Ha-ras gene. Creation of a new Xba I restriction site by an AT --TA transversion at the second position of codon 61 was detected in DNA from primary tumors and NIH 3T3 cells transformed by DNA from 6 of 7 vinyl carbamate-and 5 of 10 1'-hydroxy-2',3'-dehydroestragole-induced hepatomas. Selective oligonucleotide hybridization demonstrated a CG -+ AT transversion at the first position of the 61st codon in NIH 3T3 transformants derived from 7 of 7 N-hydroxy-2-acetylaminofluorene-induced hepatomas. By the same criterion, an AT --GC transition at the second position of codon 61 was the activating mutation in 1 of 7 vinyl carbamate-and 5 of 10 1'-hydroxy-2',3'-dehydroestragole-induced tumors. Thus, c-Ha-ras activation is apparently an early event in B6C3 F1 mouse hepatocarcinogenesis that results directly from reaction of ultimate chemical carcinogens with this gene in vivo. protooncogenes, particularly members of the ras family, have been detected in a variety ofhuman malignancies (2) and in a high percentage of several kinds of rodent tumors (4-6). Point mutations in the 12th, 13th, or 61st codons of ras protooncogenes appear to be responsible for activation in vivo (2, 7).Recent studies demonstrated that DNA from some hepatic tumors that developed spontaneously in 2-year-old B6C3 F1 mice contained transforming activity in the NIH 3T3 transfection assay (8, 9). Activated alleles of the c-Ha-ras gene were associated with this transforming activity in 11 of 13 tumors, while non-ras genes were activated in the other two cases (9). Administration of single doses of a wide variety of chemical carcinogens to 12-day-old male B6C3 F1 mice results in the formation of multiple hepatomas by 7-9 months in the absence of any further treatments (10-12). We have now characterized the activated c-Ha-ras genes in hepatomas induced in these mice by three structurally diverse chemical carcinogens. The selection of these three chemicals was based on the reactions of their electrophilic metabolites at different sites on DNA (10-12). The distinct patterns of c-Ha-ras mutations observed for eac...

Mechanisms of Multistep Carcinogenesis and Carcinogen Risk Assessment

“…clusion is supported by the findings of mutational activation of ras proto-oncogenes in rat mammary carcinomas, mouse skin papilomas, and mouse hepatomas (3)(4)(5)(6)(7). (9,10).…”

Loss of the cell cycle inhibitors p21Cip1 and p27Kip1 enhances tumorigenesis in knockout mouse models

“…For these experiments, wild type and p21 Cip1 -null mice were treated with the DNA mutagen, urethane. Urethane has been shown to induce lung and liver tumors in mice by causing mutations in either the ras genes (tumor-sensitive mice) or other as yet unidentified genes (tumor-resistant mice, as used in the study described here) (Dragani et al, 1991;Mirvish, 1968;Nuzum et al, 1990;Wiseman et al, 1986). The second study examines tumor formation in MMTV/v-Ha-ras mice lacking p27 Kip1 rather than p21 Cip1 .…”

Frequent p53 and H-ras Mutations in Benzene- and Ethylene Oxide-Induced Mammary Gland Carcinomas from B6C3F1 Mice

“…Previous studies have demonstrated that EtO exposure was capable of inducing A to T mutations . A number of other chemicals are also known to induce these mutations specifically in H-ras codon 61 (Vousden et al, 1986;Wiseman et al, 1986;Sills et al, 1999). As with A to G mutations, one potential mechanism for inducing A to T mutations would be through the formation of adenine adducts, particularly those that lead to depurination with insertion of an adenine opposite the apurinic site (Sagher and Strauss, 1983).…”