Tobacco-related diseases such as lung cancer cause over 4.2 million deaths annually, with approximately 400,000 deaths per year occurring in the US. Genotoxic effects of tobacco components have been described, but effects on signaling pathways in normal cells have not been described. Here, we show activation of the serine/threonine kinase Akt in nonimmortalized human airway epithelial cells in vitro by two components of cigarette smoke, nicotine and the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Activation of Akt by nicotine or NNK occurred within minutes at concentrations achievable by smokers and depended upon α₃-/α₄-containing or α₇-containing nicotinic acetylcholine receptors, respectively. Activated Akt increased phosphorylation of downstream substrates such as GSK-3, p70^S6K, 4EBP-1, and FKHR. Treatment with nicotine or NNK attenuated apoptosis caused by etoposide, ultraviolet irradiation, or hydrogen peroxide and partially induced a transformed phenotype manifest as loss of contact inhibition and loss of dependence on exogenous growth factors or adherence to ECM. In vivo, active Akt was detected in airway epithelial cells and lung tumors from NNK-treated A/J mice, and in human lung cancers derived from smokers. Redundant Akt activation by nicotine and NNK could contribute to tobacco-related carcinogenesis by regulating two processes critical for tumorigenesis, cell growth and apoptosis.

Retrospective studies have shown that patients with tobacco-related cancers who continue to smoke after their diagnoses have lower response rates and shorter median survival compared with patients who stop smoking. To provide insight into the biologic basis for these clinical observations, we tested whether two tobacco components, nicotine or the tobacco-specific carcinogen, 4-(methylnitrosoamino)-1-(3-pyridyl)-1-butanone (NNK), could activate the Akt pathway and increase lung cancer cell proliferation and survival. Nicotine or NNK, rapidly and potently, activated Akt in non-small cell lung cancer (NSCLC) or small cell lung cancer (SCLC) cells. Nicotinic activation of Akt increased phosphorylation of multiple downstream substrates of Akt in a time-dependent manner, including GSK-3, FKHR, tuberin, mTOR and S6K1. Since nicotine or NNK bind to cell surface nicotinic acetylcholine receptors (nAchR), we used RT–PCR to assess expression of nine alpha and three beta nAchR subunits in five NSCLC cell lines and two types of primary lung epithelial cells. NSCLC cells express multiple nAchR subunits in a cell line-specific manner. Agonists of α3/α4 or α7 subunits activated Akt in a time-dependent manner, suggesting that tobacco components utilize these subunits to activate Akt. Cellular outcomes after nicotine or NNK administration were also assessed. Nicotine or NNK increased proliferation of NSCLC cells in an Akt-dependent manner that was closely linked with changes in cyclin D1 expression. Despite similar induction of proliferation, only nicotine decreased apoptosis caused by serum deprivation and/or chemotherapy. Protection conferred by nicotine was NFκB-dependent. Collectively, these results identify tobacco component-induced, Akt-dependent proliferation and NFκB-dependent survival as cellular processes that could underlie the detrimental effects of smoking in cancer patients.