Induction of mutations in Ki-ras and INK4a in liver tumors of mice exposed in utero to 3-methylcholanthrene

Abstract

An understanding of the basic mechanisms responsible for the pathogenesis of liver neoplasms is needed in order to develop better therapeutic strategies. The present study utilized a pharmacogenetic mouse model to assess the role of cytochrome P4501A1 (Cyp1a1) in modulating genetic damage to oncogenic and tumor suppressor loci following in utero exposure to the polycyclic aromatic hydrocarbon, 3-methylcholanthrene (MC). Analysis of the Ha-ras, Ki-ras, INK4a and p53 genes was carried out with lysates from paraffin-embedded liver tissue from transplacentally-treated mice. The lysates were subjected to DNA amplification by the PCR technique followed by allele-specific oligonucleotide hybridization screening and SSCP analysis. All of the 26 neoplasms screened (23 hepatocellular carcinomas, two hepatocellular adenomas and one sarcoma) exhibited a GGC-->CGC (GLY13-->ARG13) transversion at the Ki-ras gene locus. None of the tumors had Ki-ras mutations at codon 12 of exon 1. Approximately 12% (3/26) of the liver tumors exhibited point mutations in exon 1 of the INK4a gene, with each of the three tumors exhibiting two point mutations. Analysis of exon 2 of the INK4a gene showed the presence of a CCG-->CTG (PRO73-->LEU73) transition in two of the 26 neoplasms. No mutations were found in exons 1 or 2 of the Ha-ras gene, or in exons 5-8 of the p53 gene. Analysis of tumor RNAs showed overexpression of Ha-ras, cip1 and c-jun in approximately 38% of the liver tumor samples. The results of this study suggest that mutagenic damage to oncogenes and tumor suppressor genes may be critical factors in mediating transplacentally-induced liver tumorigenesis. The fact that Ki-ras mutations were found in all of the tumors suggests that mutation at this gene locus may be an early event in liver tumor pathogenesis, while mutation in tumor suppressor genes may occur later during tumor progression. These combined results are consistent with the pathogenesis of cancer in humans.

Frequent mutation of p16CDKN2A exon 1 during rat tongue carcinogenesis induced by 4‐nitroquinoline‐1‐oxide

“…These results, to the best of our knowledge, have not been reported in previous studies. Contrast to our study, low frequent mutation was detected on codon 9, 16 of p16 CDKN2A exon 1 in (DA × WF) F1 rat tongue carcinoma induced by 4NQO 15, and only 12% of tumor tissues was demonstrated point mutations of p16 CDKN2A exon 1 in the liver tumor induced by 3‐methylcholanthrene (a polycyclic aromatic hydrocarbon similar to 4NQO) 16. Moreover, mutations of p16 CDKN2A were only found in fully developed SCCs but not in cutaneous hyperplasias or keratoacanthomas in UV‐induced skin squamous cell carcinoma (SCC) of mice 17.…”

Genotoxicity of 3-methylcholanthrene in liver of transgenic Big Blue� mice

“…The mutation types were mainly G:C 3 C:G transversions at codon 13 and A:T 3 T:A transversions at codon 61. The same findings were shown in liver of mice exposed in utero to 3MC and all resulting hepatocellular neoplasms showed a G:C 3 C:G transversion at codon 13 of Ki-ras gene [Gressani et al, 1998]. G:C 3 T:A transversions and G:C 3 A:T transitions were also described in exons 5-8 of the p53 gene in mouse 3-methylcholanthrene-induced sarcomas [Shimokado et al, 1998].…”

In utero Exposure of Mice to Dibenzo[a,l]Pyrene Produces Lymphoma in the Offspring: Role of the Aryl Hydrocarbon Receptor

“…A responsive fetus exhibits enhanced risk for tumor formation independently of the maternal phenotype as induction of Cyp1a1 and/or Cyp1b1 in target organs produces greater bioactivation. In the B6D2F1 Â D2 crosses, 3-methylcholanthrene transplacentally induced lung and liver adenomas and carcinomas in the offspring with a high incidence of Ki-ras mutations (21)(22)(23). Ki-ras activating mutations have been linked to tumor susceptibility.…”