Smoking is responsible for approximately one in five premature deaths each year in the USA making it, without question, the single most preventable cause of premature death. In addition, lung cancer, which is predominantly caused by smoking, is the leading cause of cancer deaths in the USA. Recently, a series of 9 papers all reported that single nucleotide polymorphisms (SNPs) within the nicotinic receptor gene cluster CHRNA5-CHRNA3-CHRNB4 are associated with various smoking-related behaviors including nicotine dependence, level of smoking, age of initiation and subjective effects of smoking. Moreover, four studies also reported that variants in this same gene cluster are associated with risk for lung cancer. Whether the association between lung cancer and this gene cluster is indirect though the association with smoking or represents an independent finding remains to be determined. Regardless, due to the multiple replications of the association findings, studies to identify the polymorphism or polymorphisms in this region that influences risk for the single most preventable cause of premature death and the most common cause of cancer death are highly warranted. Therefore, in response to RFA-DA-09-003, which based upon the executive summary """"""""focuses solely on functional characterization of gene variants which are strongly suggested to be associated with common, complex human diseases identified through candidate gene, GWAS, and other approaches"""""""", we propose a series of experiments to evaluate the function of an exceptionally strong candidate SNP in this region, rs16969968. This SNP is a non-synonymous SNP in the nicotinic receptor 15 subunit that leads to an asparagine for aspartic acid substitution at amino acid position 398. We previously have shown that this SNP affect the function of 142215 nicotinic receptors in vitro. In the studies outlined in this application, we will utilize a knockin mouse model in which the """"""""at risk"""""""" asparagine codon has replaced the protective aspartic acid codon in Chrna5 to address the functional relevance of this polymorphism with regards to brain function and lung cancer susceptibility. We also will utilize in vitro experiments to determine whether the CHRNA5 D398N polymorphism affects the function of a subtype of nicotinic receptor (132415) that are expressed in the peripheral nervous system as well as in non-neuronal cells, including bronchial epithelial cells and lung cancer cell lines.
This project will test whether a specific mutation that is associated with risk for nicotine dependence and lung cancer in humans affects brain function and lung cancer susceptibility in a mouse model. Results will lead to a better appreciation of the genetics of these diseases and hopefully provide insight that may lead to more effective treatments for these conditions.
