Genetic and non-genetic factors that cause inter-individual variations in CYP2A13 gene expression

The overall goal of this dissertation is to investigate the mechanisms underlying the large interindividual variations in susceptibility to lung carcinogenesis. We focused on CYP2A13, a respiratory tract-specifically expressed enzyme, which is the most efficient P450 towards bioactivation of a tobacco-related carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). The expression level of CYP2A13 varies substantially among human lung samples. Our central hypothesis is that CYP2A13 expression level is affected by both genetic regulators and non-genetic factors. The specific aims are (1) to identify the mechanisms underlying the decreased allelic expression of a CYP2A13 allele (7520C>G); (2) to identify frequent single-nucleotide polymorphisms (SNPs), associated with altered allelic expression, in the CYP2A13 gene and flanking intergenic regions; (3) to examine the effects of inflammation on CYP2A13 expression and dissect the underlying mechanisms.;In the first aim (chapter 2), we found that the CYP2A13 7520C>G variation, associated with low CYP2A13 allelic expression in human lung samples, is likely a marker, but not a causative SNP, for low CYP2A13 expression. We have further identified three causative SNPs (-1479T>C, -3101T>G and -7756G>A) that are likely responsible for the substantially decreased expression of the 7520G allele.;In the second aim (chapter 3), we developed array-based resequencing analysis for SNP discovery in the CYP2A13 gene and flanking region. Fifty-eight frequent SNPs were identified and confirmed using manual DNA sequencing. We further identified four major haplotype blocks as well as 14 tagSNPs. The G allele at 2805 is associated with decreased allelic expression in five heterozygotes and four SNPs (-7080G>T, -6673G>A, -6353A>G, -4559T>C) were identified as potential causative SNPs. This study provided biological basis for future population studies designed to associate CYP2A13 polymorphisms with incidence of smoking-related diseases.;In the third aim (chapter 4), we found that CYP2A13 was downregulated by Lipopolysaccharide (LPS)-induced inflammation and the underlying mechanisms possibly involved inflammation-related transcription factors NF-kappaB and C/EBP. These studies may explain why we detected the relatively low levels of CYP2A13 in human lung biopsy where inflammation would occur. Knowledge of the mechanisms underlying inflammation-mediated CYP2A13 expression will further encourage development of novel approaches for lung cancer prevention or therapy based on CYP2A13 suppression.