Abstract 1803: Transcriptional regulation of nicotinic acetylcholine receptors (nAChRs) by E2F family transcription factors in non-small cell lung cancer.

Abstract

Abstract Nicotine, the addictive component of cigarette smoke, has been shown to promote cell proliferation, migration, invasion, and angiogenesis in multiple cancer types. Earlier studies from our lab had shown that nicotine can promote the growth and metastasis of non-small cell lung carcinoma (NSCLC) in mouse models. While a broad range of nAChRs have been found to be expressed on NSCLC cell lines, nicotine-mediated proliferation, invasion, and migration are facilitated predominantly through the α7 subunit. Consistent with this, α7 nAChR levels are elevated in NSCLC in mice that were administered nicotine. Stimulation of α7 nAChR with nicotine has been reported to activate Src, resulting in inactivation of the retinoblastoma (Rb) tumor suppressor protein and enhancing E2F-mediated transcription. The Rb-E2F transcriptional regulation pathway is known to induce genes involved in cell cycle progression, angiogenesis, and metastasis implicating it in tumor survival and progression. Given this background, attempts were made to elucidate whether nAChR genes are regulated by the Rb-E2F pathway. Analysis of a 2000bp promoter region of the human α7 gene revealed the presence of multiple E2F binding sites. Transient transfection experiments showed α7 to be responsive to multiple E2Fs. E2F1 was found to associate with the α7 promoter via chromatin immunoprecipitation assays. Depletion of E2F genes via small interfering RNA demonstrated a differential regulation of α7 by E2F family members 1-5. These results raise the possibility that exposure to nicotine stimulates the α7 signaling cascade resulting in elevated E2F1-mediated activation of various proliferative promoters, including that of α7 itself in a positive feedback mechanism. In addition to the α7 nAChR, recent genome wide association studies (GWAS) have identified a susceptibility locus for human lung cancer at 15q25.1 which encodes for nAChR subunits α3 and α5. Promoter analysis has revealed that both α3 and α5 have multiple potential E2F binding sites, as well. Preliminary knock down of E2F family members via small interfering RNA has suggested these subunits may also be differentially regulated by the E2F family of transcription factors. Further studies are under way to elucidate the role of E2F in the regulation of nAChR α3 and α5, and how this impacts nicotine signaling as well as growth and progression of NSCLC. Citation Format: Courtney M. Schaal, Smitha Pillai, Jackie L. Johnson, Srikumar Chellappan. Transcriptional regulation of nicotinic acetylcholine receptors (nAChRs) by E2F family transcription factors in non-small cell lung cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1803. doi:10.1158/1538-7445.AM2013-1803