Arti C. Patel, Ph.D.

Dissertation research performed under the guidence of Dr. J. Carl Barrett and Dr. Theodora R. Devereux

ABSTRACT
    The combined contributions of genetic and environmental factors to the development of human lung cancer make it difficult to identify the genes involved in tumorigenesis.  Mouse lung adenocarcinomas closely resemble human lung adenocarcinomas and provide an excellent model for delineating the genes and mechanisms involved in human lung cancer.  These studies focused on candidate susceptibility genes on mouse chromosomes 4, 9, and 18 and the involvement DNA methylation in mouse lung carcinogenesis.  The p16Ink4a tumor suppressor, which maps to mouse chromosome 4, was hypermethylated in AB6F1, B6AF1, B6CF1, and B6C3F1 primary mouse lung tumors but not normal lung tissue.  No allele-specific or site-specific methylation was detected in these tumors.  Methylation status correlated with p16 expression in 85% of the B6C3F1 laser capture microdissected tumor areas with relatively high and low p16 expression by immunohistochemistry.  Expression of p16Ink4a was observed in mouse lung tumor cell lines lacking p16Ink4a expression following treatment with the demethylating agent, 5-aza-deoxycytidine.  Collectively, these studies demonstrate a role for p16Ink4a inactivation by DNA methylation in mouse lung carcinogenesis.  Evidence from one mouse lung tumor cell line also implicates DNA methylation as mechanism for p15Ink4b and p19Arf gene inactivation.  The Ras-GRF guanine nucleotide exchange factor, which maps to a region of susceptibility on mouse chromosome 9, was exami a modifier of the K-ras  proto-oncogene.  The Ras-GRF transcript was detected in mouse lung, but no differences in expression or polymorphisms were observed between susceptible and resistant strains.  A functional assay did not detect differences in GDP-GTP exchange activity on H-ras in the presence of Ras-GRF isolated from the different mouse strains.  This evidence does not support a role for Ras-GRF as a modifier gene of Ras.  Additionally, examination of Smad2 (mouse homolog of human JV18-1 gene) coding regions for polymorphisms did not identify any sequence differences between the A/J and BALB/c mice, suggesting that Smad2 is not a lung tumor susceptibility gene on mouse chromosome 18.  Together these studies add to our understanding of mouse lung carcinogenesis and will aid in identifying genes and mechanisms involved in human lung carcinogenesis.