Nicotine-Mediated Regulation Of Sox2 And Sternness In Non-Small Cell Lung Cancer

Lung cancer is the leading cause of cancer deaths in both men and women, and is highly correlated with cigarette smoking. Nicotine, the addictive component of tobacco smoke, cannot initiate tumors, but can promote proliferation, migration, and invasion of cells in vitro and promote growth and metastasis of tumors in vivo. More recently, nicotine has been implicated in the promoting self-renewal of stem-like side-population cells from lung cancers. This subpopulation of cancer stem-like cells has been implicated in tumor initiation, generation of entire heterogeneous tumor population, metastasis, dormancy, and drug resistance. We have shown that nicotine promotes the expression of genes that promote stemness, such as Stem Cell Factor (SCF/c-kit ligand), in a specific receptor dependent fashion. Here we demonstrate that nicotine can induce the expression of embryonic stem cell factor Sox2, which is indispensable for self-renewal and maintenance of stem cell properties in non-small cell lung adenocarcinoma cells. High level of Sox2 expression also correlates with poor patient survival outcome in lung cancer, and metastatic lung adenocarcinoma shows higher levels of Sox2 expression than primary tumor or normal tissue, implicating Sox2 in this disease. Nicotine was found to induce Sox2 in A549 cells after 18 and 24 hours of stimulation, an effect which was diminished by 48 hours. This was seen at the mRNA and protein level as assessed by transient transfection and luciferase assay, real-time PCR, western blot, and immunofluorescence respectively. Experiments were conducted to elucidate the mechanism by which nicotine induces Sox2; it was found that siRNA mediated depletion of α7 nicotinic acetylcholine receptor (nAChR), the Hippo pathway effector Yap1, or the transcriptional repressor ID1 could abrogate nicotine-mediated induction of Sox2. Further, treatment with inhibitors of Src kinase or PI3K additionally abrogated the effect, suggesting these proteins play a role in nicotine-mediate induction of Sox2. Interestingly, nicotine could induce Sox2 expression in human mesenchymal stem cells (hMSCs) after 24 hours of stimulation as seen by immunofluorescence and real-time PCR, and this effect was abrogated by treatment with inhibitors to Src kinase, PI3K, Yap1, or α7 nAChR. Additionally, studies are under way to elucidate whether e-cigarettes or flavored tobacco, newer and less studied alternatives to traditional cigarettes, have similar effects on stemness. These studies can be expected to have a direct impact on our understanding of the molecular mechanisms involved in the initiation, growth, and metastasis of non-small cell lung cancer, especially in smokers and tobacco users. Citation Format: Courtney Schaal, Srikumar Chellappan. Nicotine-mediated regulation of Sox2 and stemness in non-small cell lung cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2487.