Role of alpha7-nicotinic acetylcholine receptor in human non-small cell lung cancer proliferation.

OBJECTIVES: Lung cancer is the most common cause of cancer death in the world. Cigarette smoking represents the major risk factor. Nicotine, an active component of cigarettes, can induce cell proliferation, angiogenesis and apoptosis resistance. All these events are mediated through the nicotinic acetylcholine receptor (nAChR) expressed on lung cancer cells. We speculate that new insights into the pathophysiological roles of nAChR may lead to new therapeutic avenues to reduce non-small cell lung cancer (NSCLC) tumour growth. MATERIALS AND METHODS: Human samples of NSCLC, cell lines and mouse models were utilized in Western blotting, reverse transcriptase polymerase chain reaction and apoptosis studies. RESULTS: Human NSCLC tissues expressed alpha7-nAChR. This expression was higher in smoking patients with squamous carcinomas than those with adenocarcinomas and in male smoking patients than in females. All the data support the hypothesis that major expression of alpha7-nAChR is related to major activation of the Rb-Raf-1/phospho-ERK/phospho-p90RSK pathway. alpha7-nAChR antagonists, via mitochondria associated apoptosis, inhibited proliferation of human NSCLC primary and established cells. Nicotine stimulates tumour growth in a murine model, A549 cells orthotopically grafted. The effects of nicotine were associated with increases in phospho-ERK in tumours. Proliferation effects of nicotine could be blocked by inhibition of alpha7-nAChR by the high affinity ligand alpha-cobratoxin. CONCLUSION: These results showed that alpha7-nAChR plays an important role in NSCLC cell growth and tumour progression as well as in cell death.

Multiple roles of nicotine on cell proliferation and inhibition of apoptosis: implications on lung carcinogenesis.

The genotoxic effects of tobacco carcinogens have long been recognized, the contribution of tobacco components to cancerogenesis by cell surface receptor signaling is relatively unexplored. Nicotine, the principal tobacco alkaloid, acts through nicotinic acetylcholine receptor (nAChR). nAChR are functionally present on human lung airway epithelial cells, on lung carcinoma [SCLC and NSCLC] and on mesothelioma and build a part of an autocrine-proliferative network that facilitates the growth of neoplastic cells. Different nAChR subunit gene expression patterns are expressed between NSCLC from smokers and non-smokers. Although there is no evidence that nicotine itself could induce cancer, different studies established that nicotine promotes in vivo the growth of cancer cells and the proliferation of endothelial cells suggesting that nicotine might contribute to the progression of tumors already initiated. These observations led to the hypothesis that nicotine might be playing a direct role in the promotion and progression of human lung cancers. Here, we briefly overview the role and the effects of nicotine on pulmonary cell growth and physiology and its feasible implications in lung carcinogenesis.

Development of novel therapeutic strategies for lung cancer: targeting the cholinergic system.

One of the earliest descriptions of non-neuronal ACh synthesis was by Morris who reported that ACh was synthesized in the placenta [1]; furthermore, Falugi et al. showed the presence of AChE in human fibrosarcoma cells [2]. Afterward, the expression of ACh, AChE, and cholinergic receptors in non-neuronal cells was reported in several studies [3-16]. Indeed, recent data reported that SCLC expresses a cholinergic autocrine loop that can regulate cell growth. Such work demonstrates that SCLC cells have a cholinergic phenotype and that ACh exerts as an autocrine growth factor in human lung tumours [16]. Moreover, it has been recently reported that nicotine in lung adenocarcinoma A549 cells, potently induces Bad phosphorylation at serine (S)112, S136 and S155 in a mechanism involving activation of MAPKs, ERK1/2, PI3K/AKT and PKA through the linking to alpha7-receptors [9]. Bad phosphorylation results in sequestering Bad from mitochondria and subsequently interacting with 14-3-3 in the cytosol [9]. We have recently reported that human malignant pleural mesothelioma expresses a cholinergic system, involved in cell growth regulation. Hence, mesothelioma cells growth is modulated by the cholinergic system in which agonists (i.e. nicotine) have a proliferative effect and antagonists (i.e. curare or alpha-cobratoxin) have an inhibitory effect. Furthermore apoptosis mechanisms are under the control of the cholinergic system (nicotine antiapoptotic via induction of NF-kappaB complexes and phosphorylation of Bad at S112, curare proapoptotic via G0-G1 arrest p21waf-1-dependent, but p53-independent) [16]. The involvement of the non-neuronal cholinergic system in lung cancer and mesothelioma appears reasonable and opens up new translational research strategies.

Characterization of apoptosis induced by marine natural products in non small cell lung cancer A549 cells.

The effects of different marine derived agents were studied in A549 cell growth. These drugs induced cell cycle arrest at the G2-M phase associated with the up-regulation of GADD45alpha-gamma and down-regulation of c-Myc. In treated cells, GADD45alpha-gamma and c-Myc were up- and down-regulated, respectively. A cascade of events leading to apoptotic mitochondrial 'intrinsic' pathway was observed in treated cells: (1) dephosphorylation of BAD serine136; (2) BAD dissociation from 14-3-3 followed by its association with BCL-XL; (3) cytochrome c release; (4) caspase-3 activation, and (5) cleavage of vimentin. Caspase(s) inhibitor prevented the formation of cleavage products and, in turn, apoptosis was inhibited through a p53-independent mechanism. Moreover, these compounds did not activate NF-kappaB. Our findings may offer new insights into the mechanisms of action of these agents in A549 cells. The better understanding of their effects might be important to fully exploit the potential of these new drugs.