Alterations in the K-ras and p53 Genes in Rat Lung Tumors

Abstract

Activation of the K-ras protooncogene and inactivation of the p53 tumor suppressor gene are events common to many types of human cancers. Molecular epidemiology studies have associated mutational profiles in these genes with specific exposures. The purpose of this paper is to review investigations that have examined the role of the K-ras and p53 genes in lung tumors induced in the F344 rat by mutagenic and nonmutagenic exposures. Mutation profiles within the K-ras and p53 genes, if present in rat lung tumors, would help to define some of the molecular mechanisms underlying cancer induction by various environmental agents. Pulmonary adenocarcinomas or squamous cell carcinomas were induced by tetranitromethane (TNM), 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK), beryllium metal, plutonium-239, X-ray, diesel exhaust, or carbon black. These agents were chosen because the tumors they produced could arise via different types of DNA damage. Mutation of the K-ras gene was determined by approaches that included DNA transfection, direct sequencing, mismatch hybridization, and restriction fragment length polymorphism analysis. The frequency for mutation of the K-ras gene was exposure dependent. Only two agents, TNM and plutonium, led to mutation frequencies of > 10%. In both cases, the transition mutations formed could have been derived from deamination of cytosine. The identification of non-ras transforming genes in rat lung tumors induced by mutagenic and nonmutagenic exposures such as NNK and beryllium would help define some of the mechanisms underlying cancer induction by different types of DNA damage. Alteration in the p53 gene was assessed by immunohistochemical analysis for p53 protein and single-strand conformation polymorphism (SSCP) analysis of exons 4 to 9. None of the 93 adenocarinomas examined was immunoreactive toward the anti-p53 antibody CM1. In contrast, 14 of 71 squamous cell carcinomas exhibited nuclear p53 immunoreactivity with no correlation to type of exposure. However, SSCP analysis only detected mutations in 2 of 14 squamous cell tumors that were immunoreactive, suggesting that protein stabilization did not stem from mutations within the p53 gene. Thus, the p53 gene does not appear to be involved in the genesis of most rat lung tumors-Environ Health Perspect 105(Suppl 4): 901-906 (1997)

Comparative Levels of O6-Methylguanine, Pyridyloxobutyl-, and Pyridylhydroxybutyl-DNA Adducts in Lung and Liver of Rats Treated Chronically with the Tobacco-Specific Carcinogen 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone

“…Multiple mutations due to the presence of O 2 -POB-T have been reported (Sharma et al, 2008). Mutations have not been reported in K-ras and p53 genes isolated from rat lung tumors induced by NNK, so the relative impact of these miscoding events is unclear (Belinsky et al, 1997).…”

Carbon black should not be classified as a human carcinogen based on rodent bioassay data

“…Studies showed the p53 protein was not present in any normal human mucosas tested but was detected at an increasing rate, in squamous tumors of various stages of development (Boorman et al, 1996). Unlike the human, the rat had no detectable p53 mutations following CB exposure (Belinsky et al, 1997;Swafford et al, 1995).…”

“…K-ras point mutations have been found however to be early markers of lung adenocarcinomas and squamous cell carcinomas following exposure to various agents other than CB (Belinsky et al, 1997).…”

“…Most of the rat lung tumors did not appear to involve the p53 gene. Immunoreactivity was thought to occur due to stabilization by other gene products or by the disruption of protein degradation (Belinsky et al, 1997).…”

DU Fragment Carcinogenicity: Extrapolation of Findings in Rodents to Man

“…Detection of K-ras mutations: A mutant codon 12 K-ras PCR enrichment restriction fragment length polymorphism (RFLP) analysis was used to detect K-ras mutations in the soft tissue tumors (Belinsky et al, 1996(Belinsky et al, , 1997Nickell-Brady et al, 1994). The assay relies on the construction of the K-ras 5' first exon primer where the G residue at the first position of codon 11 is replaced with a C. Amplification of a wild-type K-ras allele using this primer 13 creates gene fragments harboring a BstNl restriction enzyme cleavage site (CCTGG)…”