Nicotine-Mediated Regulation of Nicotinic Acetylcholine Receptors in Non-Small Cell Lung Adenocarcinoma by E2F1 and STAT1 Transcription Factors

Abstract

Cigarette smoking is the major risk factor for non-small cell lung cancer (NSCLC), which accounts for 80% of all lung cancers. Nicotine, the addictive component of tobacco smoke, can induce proliferation, migration, invasion, epithelial-mesenchymal transition (EMT), angiogenesis, and survival in NSCLC cell lines, as well as growth and metastasis of NSCLC in mice. This nicotine-mediated tumor progression is facilitated through activation of nicotinic acetylcholine receptors (nAChRs), specifically the α7 subunit; however, how the α7 nAChR gene is regulated in lung adenocarcinoma is not fully clear. Here we demonstrate that the α7 nAChR gene promoter is differentially regulated by E2F and STAT transcription factors through a competitive interplay; E2F1 induces the promoter, while STAT transcription factors repress it by binding to an overlapping site at a region -294 through -463bp upstream of the transcription start site. Treatment of cells with nicotine induced the mRNA and protein levels of α7 nAChR; this could be abrogated by treatment with inhibitors targeting Src, PI3K, MEK, α7 nAChR, CDK4/6 or a disruptor of the Rb-Raf-1 interaction. Further, nicotine–mediated induction of α7 nAChR was reduced when E2F1 was depleted and in contrast elevated when STAT1 was depleted by siRNAs. Interestingly, extracts from e-cigarettes, which have recently emerged as healthier alternatives to traditional cigarette smoking, can also induce α7 nAChR expression in a manner similar to nicotine. These results suggest an autoregulatory feed-forward loop that induces the levels of α7 nAChR upon exposure to nicotine, which enhances the strength of the signal. It can be imagined that such an induction of α7 nAChR contributes to the tumor-promoting functions of nicotine.

Electronic cigarettes—A review of the physiological health effects

“…DNA breaks could be caused by the known carcinogens that exist in EC vapours, like formaldehyde, as discussed previously. EC vapours can also induce gene expression changes in vivo in nasal epithelium or in vitro in bronchial airway epithelium (Moses et al 2017), or in acetylcholine receptors associated with tumour progression (Schaal and Chellappan 2016). It should be noted that many of the above results were not related to the nicotine that is sometimes present in the vapours but to the humectants like propylene glycol, glycerol, and any flavouring compounds that may exist in the solution (though nicotine sometimes enhanced the damaging effects).…”

α7 nicotinic acetylcholine receptors in lung cancer (Review)

“…α7nAChR is expressed in several types of human lung cancer, including squamous cell lung cancer cells, lung adenocarcinoma and SCLC (11,(46)(47)(48)(49). Notably, the levels of α7nAChR expression are higher in squamous carcinoma compared with adenocarcinoma, particularly in smokers (50).…”

“…Cigarette smoke is a mixture of thousands of chemical compounds, a number of which have potent carcinogenic potential including polycyclic aromatic hydrocarbons, nicotine and the nicotine-derived nitrosamines 4-(methylnitrosamino)-1-(3-pyrydyl)-1-butanone (NNK) and N-nitrosonornicotine (11). The most harmful and addictive component is nicotine (11).…”

“…The most harmful and addictive component is nicotine (11). These carcinogens and their metabolites may induce the formation of DNA adducts which result in mutations of a number of key cancer suppressor genes, including retinoblastoma tumor suppressor protein (Rb), KRAS proto-oncogene, GTPase and tumor protein p53 (11) and eventually contributing to tumorigenesis in different ways. Accumulating evidences have suggested that nicotine not only contributes to tumorigenesis but may also increase the spread of cancer in the body (12)(13)(14).…”

In vivo effect of chronic nicotine exposure on outcome of Plasmodium berghei ANKA malaria

“…Although tobacco contains a large variety of substances, nicotine, which acts at nicotinic acetylcholine receptors (nAChRs) in the central and peripheral nervous systems, is considered as the major addictive component [8]. The main route of exposure to nicotine is through inhalation of the tobacco smoke.…”