Brudnick Neuropsychiatric Research Institute, Department of Psychiatry, University of Massachusetts Medical School, Worcester, MA 01604, USA.
Mol Cancer Res. 2010 Feb;8(2):194-203. doi: 10.1158/1541-7786.MCR-09-0185. Epub 2010 Feb 2.
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-PCR. Overexpression 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 overexpression 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 the expression of the clustered nAChR genes. Consistent with this idea, knockdown of ASCL1 in SCLC, but not in non-SCLC, led to a significant decrease in expression of the alpha 3 and beta 4 genes without having an effect on any other highly expressed nAChR gene. Our data indicate a specific role for ASCL1 in regulating the expression of the CHRNA5/A3/B4 lung cancer susceptibility locus. This regulation may contribute to the predicted role that ASCL1 plays in SCLC tumorigenesis.
烟草含有多种致癌物质以及成瘾化合物尼古丁。尼古丁成瘾始于尼古丁与其同源受体烟碱型乙酰胆碱受体（nAChR）的结合。全基因组关联研究表明，nAChR 基因簇 CHRNA5/A3/B4 与尼古丁成瘾和肺癌易感性有关。为了进一步阐明该基因簇在肺癌中的作用，我们使用定量逆转录-PCR 检查了肺癌细胞系和患者样本中这三个基因以及 nAChR 基因家族其他成员的表达水平。在小细胞肺癌（SCLC）中观察到聚类 nAChR 基因的过表达，SCLC 是一种与吸烟高度相关的侵袭性肺癌。基因组聚类基因在 SCLC 中的过表达表明它们的协调调节。对这些基因启动子区域的计算机分析显示，所有三个启动子中都存在 achaete-scute 复合物同源物 1（ASCL1）的潜在结合位点，ASCL1 是一种转录因子，与 SCLC 的发病机制有关，这增加了这种因子可能调节聚类 nAChR 基因表达的可能性。与这一观点一致，ASCL1 在 SCLC 中的敲低，但不在非 SCLC 中，导致 alpha 3 和 beta 4 基因的表达显著下降，而对任何其他高表达的 nAChR 基因没有影响。我们的数据表明 ASCL1 在调节 CHRNA5/A3/B4 肺癌易感性基因座的表达中具有特定作用。这种调节可能有助于预测 ASCL1 在 SCLC 肿瘤发生中的作用。
