Nicotine induces hypoxia-inducible factor-1α expression in human lung cancer cells via nicotinic acetylcholine receptor-mediated signaling pathways

Purpose: Nicotine, the major component in cigarette smoke, can promote tumor growth and angiogenesis in various cancers, including lung cancer. Hypoxia-inducible factor-1 alpha (HIF-1 alpha) is overexpressed in human lung cancers, particularly in non-small cell lung cancers (NSCLC), and is closely associated with an advanced tumor grade, increased angiogenesis, and resistance to chemotherapy and radiotherapy. The purpose of this study was to investigate the effects of nicotine on the expression of HIF-1 alpha and its downstream target gene, vascular endothelial growth factor (VEGF), in human lung cancer cells. Experimental Design: Human NSCLC cell lines A549 and H157 were treated with nicotine and examined for expression of HIF-1 alpha a and VEGF using Western blot or ELISA. Loss of HIF-1 alpha function using specific small interfering RNA was used to determine whether HIF-1 alpha is directly involved in nicotine-induced tumor angiogenic activities, including VEGF expression, cancer cell migration, and invasion. Results: Nicotine increased HIF-1 alpha and VEGF expression in NSCLC cells. Pharmacologically blocking nicotinic acetylcholine receptor -mediated signaling cascades, including the Ca2+/ calmodulin, c-Src, protein kinase C, phosphatidylinositol 3-kinase, mitogen- activated protein kinase/extracellular signal-regulated kinase 1/2, and the mammalian target of rapamycin pathways, significantly attenuated nicotine-induced up-regulation of HIF-1 alpha a protein. Functionally, nicotine potently stimulated in vitro tumor angiogenesis by promoting tumor cell migration and invasion. These proangiogenic and invasive effects were partially abrogated by treatment with small interfering RNA specific for HIF-1 alpha Conclusion: These findings identify novel mechanisms by which nicotine promotes tumor angiogenesis and metastasis and provide further evidences that HIF-1 alpha a is a potential anticancer target in nicotine-associated lung cancer.