Alterations in the K-ras and p53 Genes in Rat Lung Tumors
Steven A. Belinsky,1 Deborah S. Swafford,1 Gregory L. Finch,1 Charles E. Mitchell,1 Gregory Kelly,1* Fletcher F. Hahn,1 Marshall W. Anderson,2 and Kristen J. Nikula1
1Inhalation Toxicology Research Institute, Albuquerque, New Mexico
2St. Mary's Hospital, Grand Junction, Colorado
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)
Key words: K-ras, p53, rat lung tumors, NNK, beryllium, plutonium, X-ray, diesel exhaust, carbon black
This paper is based on a presentation at the symposium on Mechanisms and Prevention of Environmentally Caused Cancers held 21-25 October 1995 in Santa Fe, New Mexico. Manuscript received at EHP 16 April 1996; accepted 11 July 1996.
This research was supported by the Office of Health and Environmental Research and the Assistant Secretary for Defense Programs, U.S. Department of Energy, under contract DE-AC04-76EV01013, in facilities fully accredited by the American Association for the Accreditation of Laboratory Animal Care.
Address correspondence to Dr. S.A. Belinsky, Inhalation Toxicology Research Institute, P.O. Box 5890, Albuquerque, NM 87185. Telephone: (505) 845-1165. Fax: (505) 845-1198. E-mail: sbelinsk@lrri.org
*Present address: Southwest Scientific Resources, Albuquerque, NM 87120.
Abbreviations used: NNK, 4-methylnitrosamino-1-(3-pyridyl)-1-butanone; SSCP, single-strand conformation polymorphism; TNM, tetranitromethane.
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