Role of Ki-ras in the Pathogenesis of Lung Cancer

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DESCRIPTION (provided by applicant): Studies in humans and animal models have shown that mutation of Ki-ras is a critical, early event in lung tumorigenesis. We and others have shown that the type of mutation present in Ki-ras may influence tumor progression and appears to correlate with patient survival. We thus hypothesize that different mutations induced in Ki-ras by environmental carcinogens exhibit different oncogenic potential, and that the type of mutation initially induced in this gene will determine how rapidly tumors progress to adenocarcinomas. It is difficult to definitively determine the role of mutated ras genes in tumor initiation and progression because treatment with chemical carcinogens may cause alterations at other genetic loci. We thus propose to develop 3 strains of transgenic mice that contain either the wild type, VAL12, or CYS12 mutant alleles of the human Ki-ras gene linked to a tet-inducible promoter that specifies lung specific expression of the transgene. The biochemical characteristics and activity of the 3 alleles will be compared and correlated with the oncogenicity of each allele. Carcinogenicity bioassays will be employed to determine the effects of different ras mutations on tumor development and progression. The effect of each of the 3 alleles on subsequent damage to tumor suppressor loci implicated in both human and murine lung tumor pathogenesis, in particular the pl6Ink4a, Rb, and cyclin D1 genes, will be assessed by PCR-SSCP, methylation specific PCR, and determination of the levels of expression of the gene products by reverse transcription PCR. The development of these "humanized" Ki-ras transgenic mice will represent a critical advance in this field and provide an important new research tool that will allow us to determine the role of Ki-ras mutations in the pathogenesis of lung cancer. We anticipate that the proposed studies will elucidate the effect of different mutant ras alleles on lung tumor pathogenesis and will have important long term implications for future research on the etiology, genetics, prevention, and development of novel therapies for lung cancer.