[1535] Effect of DNA Hypomethylation on Lung Carcinogenesis
S Gokhale, E Steine, J Dausman, R Jaenisch. Roger Williams Medical Center/Boston University Medical Center and Whitehead Institute, Providence/Boston, RI/MA; Whitehead Institute and Massachusetts Institute of Technology (MIT), Cambridge, MA; Whitehead Institute, Cambridge, MA
Background: Lung cancer is the leading cause of cancer-related deaths in both sexes. Aberrant DNA methylation is one of the most common molecular lesions in pathogenesis of lung carcinoma. Enzymes responsible for this methylation are DNA methyltransferases (Dnmts). It has been previously shown that global DNA hypomethylation induced by hypomorphic Dnmt1 alleles suppresses intestinal tumorigenesis in Apc Min/+ mice but promotes T cell lymphoma and sarcoma in mice. Its effect in lung carcinogenesis is not clearly elucidated. The main objective of this project is to study the effect of DNA hypomethylation on lung tumorigenesis in mice.
Design: Different mutant alleles of Dnmt1 were used for this study (chip/c; chip/chip; dnmt1 2lox/2lox) with c being the null allele and chip providing 10% of the methylation. The study was done in a background of LSL-K-ras G12D conditional mouse model for mutant K-ras developed in Jacks' Lab. LSL-K-ras G12D mice were crossed to Dnmt1 chip/chip and Dnmt1 chip/c; and LSL-K-rasG12D,Dnmt1 chip/chip double mutants were crossed to conditional Dnmt1 2lox/2lox mice to obtain various combinations of double mutants. Mice were then infected with AdenoCre intranasally to initiate tumorigenesis via mutational activation of K-ras which is regulated by a removable STOP element flanked by LoxP recognition sites for recombinase Cre. Mice were sacrificed (n=125) at different time points and their lungs dissected. H and E sections were examined and number of lesions, which included atypical adenomatous hyperplasia, adenoma and adenocarcinoma, was counted for each of the LSL-K-ras G12D mice (positive controls) and compared to the experimental hypomethylated mice.
Results: Ratio of average number of lesions in LSL-K-ras G12D versus hypomethylated mice at different time-points is as follows: 2 weeks =1.85; 4 weeks = 1.9; 12 wks = 2.5; 16 weeks = 2.45; 28 weeks = 4.
Conclusions: The data shows that the number of lesions formed in LSL-K-ras G12D mice is about 2 to 4 times more than in the hypomethylated mice and that genomic hypomethylation induced by the mutant alleles of Dnmt1 markedly lowers the number of lung tumors. This may have therapeutic implications in terms of use of demethylating agents in the treatment of lung cancers.
Category: Pathobiology
Tuesday, March 10, 2009 8:45 AM
Platform Session: Section G 1, Tuesday Morning
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