ALTERATIONS IN THE K-RAS AND P53 GENES IN RAT LUNG-TUMORS

Activation of the K-ras protooncogene and inactivation of the p53 tumo r suppressor gene are events common to many types of human cancers. Mo lecular epidemiology studies have associated mutational profiles in th ese genes with specific exposures. The purpose of this paper is to rev iew investigations that have examined the role of the K-ras and p53 ge nes in lung tumors induced in the F344 rat by mutagenic and nonmutagen ic exposures. Mutation profiles within the K-ras and p53 genes, if pre sent in rat lung tumors, would help to define some of the molecular me chanisms 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 carbo n black. These agents were chosen because the tumors they produced cou ld arise via different types of DNA damage. Mutation of the K-ras gene was determined by approaches that included DNA transfection. direct s equencing, mismatch hybridization, and restriction fragment length pol ymorphism analysis. The frequency for mutation of the K-ras gene was e xposure dependent. Only two agents, TNM and plutonium, led to mutation frequencies of >10%. In both cases, the transition mutations formed c ould have been derived from deamination of cytosine. The identificatio n of non-ras transforming genes in rat lung tumors induced by mutageni c and nonmutagenic exposures such as NNK and beryllium would help defi ne some of the mechanisms underlying cancer induction by different typ es of DNA damage. Alteration in the p53 gene was assessed by immunohis tochemical analysis for p53 protein and single-strand conformation pol ymorphism (SSCP) analysis of exons 4 to 9. None of the 93 adenocarinom as examined was immunoreactive toward the anti-p53 antibody CM1. In co ntrast, 14 of 71 squamous cell carcinomas exhibited nuclear p53 immuno reactivity with no correlation to type of exposure. However, SSCP anal ysis only detected mutations in 2 of 14 squamous cell tumors that were immunoreactive, suggesting that protein stabilization did not stem fr om mutations within the p53 gene. Thus, the p53 gene does not appear t o be involved in the genesis of most rat lung tumors.