ASCL1 Regulates Expression of the CHRNA5/A3/B4 Lung Cancer Susceptibility Locus

摘要

Tobacco contains a variety of carcinogens as well as the addictive compound nicotine. Nicotine addiction begins with the binding of nicotine to its cognate receptor, the nicotinic acetylcholine receptor (nAChR). Genome-wide association studies have implicated the nAChR gene cluster, CHRNA5/A3/B4, in nicotine addiction and lung cancer susceptibility. To further delineate the role of this gene cluster in lung cancer, we examined the expression levels of these three genes as well as other members of the nAChR gene family in lung cancer cell lines and patient samples using quantitative reverse transcription polymerase chain reaction. Over-expression of the clustered nAChR genes was observed in small cell lung carcinoma (SCLC), an aggressive form of lung cancer highly associated with cigarette smoking. The over-expression of the genomically clustered genes in SCLC suggests their coordinate regulation. In silico analysis of the promoter regions of these genes revealed putative binding sites in all three promoters for achaete-scute complex homolog-1 (ASCL1), a transcription factor implicated in the pathogenesis of SCLC, raising the possibility that this factor may regulate expression of the clustered nAChR genes. Consistent with this idea, knockdown of ASCL1 in SCLC, but not NSCLC, led to a significant decrease in expression of the α3 and β4 genes, without having an effect on any other highly expressed nAChR gene. Our data indicate a specific role for ASCL1 in regulating expression of the CHRNA3/A5/B4 lung cancer susceptibility locus. This regulation may contribute to the predicted role ASCL1 plays in SCLC tumorigenesis.