Nicotine, the addictive component of tobacco smoke, is known to promote proliferation, migration, and invasion of multiple cancer cells, including those of the lung and the pancreas. In addition, nicotine can promote the growth and metastasis of such cancers in mouse xenograft models. More recently, nicotine has also been implicated in promotion of cancer stem cell properties such as self-renewal. Our lab has shown that stimulation of lung cancer cells with nicotine results in activation of Src kinase in a β-arrestin-1 dependent manner, resulting in inactivation of the Rb tumor suppressor protein and subsequently the activation of E2F-mediated transcription of proliferative and survival genes. In addition to proliferative and survival genes, the E2F family of transcription factors has been shown to activate genes like matrix metalloproteinases that are involved in invasion and migration, indicating a role for E2F in the growth and metastasis of cancers downstream of nicotine. Our recent studies have shown that E2F1 can also induce genes which promote stemness, such as Stem Cell Factor (SCF/c-kit ligand), promoting nicotine-mediated enhancement of self-renewal of stem-like cells. In addition to these findings, here we demonstrate the ability of nicotine to induce the embryonic stem cell factor Sox2, which is indispensable for self-renewal and maintenance of stem cell properties, as well as the ability of E2F1 transcription factor to regulate Sox2 gene expression in non-small cell lung cancer cells. Western blot analysis revealed an induction of Sox2 protein at 18 and 24 hours post nicotine stimulation, which diminished by 48 hours. Similarly, quantitative real time PCR analysis showed an increase in Sox2 mRNA levels at 18 and24, hours post nicotine stimulation. Analysis of a 1500bp region of the human Sox2 gene promoter revealed multiple predicted E2F binding sites. Chromatin immunoprecipitation assays demonstrated E2F transcription factors to associate with the Sox2 promoter at multiple predicted binding sites. Transient transfection experiments further demonstrated the ability of E2F1 to induce the expression of a Sox2-luciferase reporter. These results suggest that nicotine may enhance lung cancer stem cell properties in part through the induction of Sox2, and this could potentially be mediated via E2F transcriptional activation. Further studies are underway to elucidate the impact of nicotine mediated induction of Sox2 on stemness, the underlying mechanism of activation, and the implications this has for non-small cell lung cancer. These studies can be expected to have a direct impact on our understanding of the molecular mechanism involved in the initiation, growth and metastasis of non-small cell lung cancer, especially in smokers.
Citation Format: Courtney Schaal, Namrata Bora Singhal, Smitha Pillai, Jonathan Nguyen, Srikumar Chellappan. Nicotine-mediated regulation of Sox2 and its implications in the biology of non-small cell lung adenocarcinoma stem-like cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2085. doi:10.1158/1538-7445.AM2015-2085