A functional role for nicotine in Bcl2 phosphorylation and suppression of apoptosis

Nicotine is not only a major component in tobacco but is also a survival agonist that inhibits apoptosis induced by diverse stimuli including chemotherapeutic drugs. However, the intracellular mechanism(s) involved in nicotine suppression of apoptosis is unclear. Bcl2 is a potent antiapoptotic protein and tumor promotor that is expressed in both small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) cells. It is possible that nicotine may regulate Bcl2 to stimulate cell survival. Here we report that nicotine can induce Bcl2 phosphorylation exclusively at the serine 70 site in association with prolonged survival of SCLC H82 cells expressing wild-type but not the phosphorylation-deficient S70A mutant Bcl2 after treatment with chemotherapeutic agents (i.e. cisplatin or VP-16). Nicotine induces activation of PKC alpha and the MAPKs ERK1 and ERK2, which are physiological Bcl2 kinases. Furthermore, ET-18-OCH3, a specific phospholipase C (PLC) inhibitor, blocks nicotine-stimulated Bcl2 phosphorylation and promotes apoptosis, suggesting that PLC may be involved in nicotine activation of Bcl2 kinases. Using a genetic approach, the gain-of-function S70E mutant, which mimics Ser(70) site phosphorylation in the flexible loop domain, potently enhances chemoresistance in SCLC cells. Thus, nicotine-induced cell survival results, at least in part, from a mechanism that involves Bcl2 phosphorylation. Therefore, novel therapeutic strategies for lung cancer in which Bcl2 is expressed may be used to abrogate the anti-apoptotic activity of Bcl2 by inhibiting multiple upstream nicotine-activated pathways.