Regulation of Vascular Endothelial Growth Factor Signaling by Nicotine in a Manner Dependent on Acetylcholine-and/or β-Adrenergic-Receptors in Human Lung Cancer Cells

Nicotine, a highly addictive component in cigarette smoke, facilitates tumorigenesis and the accelerated development of non-small cell lung cancer (NSCLC), which is known to account for similar to 80% of all lung cancer cases. This study sheds light on how the nicotine treatment of NSCLC cells regulates vascular endothelial growth factor (VEGF) signaling, known to be important in the progression of vascular disease and cancer, by acting through nicotinic acetylcholine receptors and by leading to the activation of beta-adrenergic receptors through increased levels of the stress neurotransmitters, norepinephrine/noradrenaline, and epinephrine/adrenaline. Nicotine-induced activation of VEGF promoted the function of proteins involved in increased cell survival and suppressed the function of a crucial tumor suppressor, blocking cell death. This work expands our scientific knowledge of mechanisms employed by nicotine in regulating VEGF signaling in a manner dependent on the acetylcholine and/or beta-adrenergic receptors, leading to lung cancer cell survival, and also provides significant insights into novel future therapeutic strategies to combat lung cancer. In addition to binding to nicotinic acetylcholine receptors (nAChRs), nicotine is known to regulate the beta-adrenergic receptors (beta-ARs) promoting oncogenic signaling. Using A549 (p53 wild-type) and H1299 (p53-null) lung cancer cells, we show that nicotine treatment led to: increased adrenaline/noradrenaline levels, an effect blocked by treatment with the alpha 7nAChR inhibitor (alpha-BTX) but not by the beta-blocker (propranolol) or the alpha 4 beta 2nAChR antagonist (Dh beta E); decreased GABA levels in A549 and H1299 cell media, an effect blocked by treatment with Dh beta E; increased VEGF levels and PI3K/AKT activities, an effect diminished by cell co-treatment with alpha-BTX, propranolol, and/or Dh beta E; and inhibited p53 activity in A549 cells, that was reversed, upon cell co-treatment with alpha-BTX, propranolol, and/or Dh beta E or by VEGF immunodepletion. VEGF levels increased upon cell treatment with nicotine, adrenaline/noradrenaline, and decreased with GABA treatment. On the other hand, the p53 activity decreased in A549 cells treated with nicotine, adrenaline/noradrenaline and increased upon cell incubation with GABA. Knockdown of p53 led to increased VEGF levels in the media of A549 cells. The addition of anti-VEGF antibodies to A549 and H1299 cells decreased cell viability and increased apoptosis; blocked the activities of PI3K, AKT, and NF kappa B in the absence or presence of nicotine; and resulted in increased p53 activation in A549 cells. We conclude that VEGF can be upregulated via alpha 7nAChR and/or beta-ARs and downregulated via GABA and/or p53 in response to the nicotine treatment of NSCLC cells.