The expression and pharmacological characterization of nicotinic acetylcholine receptor subunits in HBE16 airway epithelial cells.
This study characterizes the expression and the biological effects of the nicotinic acetylcholine receptor (nAChR) on human airway epithelial cells. Cultured HBE16 airway epithelial cells were incubated with either nicotine or cigarette smoke extract (CSE). The nAChR gene and protein expression in cells were detected by reverse transcriptase-polymerase chain reaction (RT-PCR), real-time PCR, and western blot. The protein expression of the nAChR subunits, α1, α5, and α7, were evaluated by immunohistochemistry. Cells were subsequently transfected with α1-, α5-, and α7-specific siRNAs, and the effects of nicotine on the production of the pro-inflammatory factors, TNF-α, IL-8, and IL-6 in transfected cells were analyzed using an enzyme-linked immunosorbent assay and real-time PCR. We detected α1, α5, α7, and β2 subunits in untreated HBE16 cells, and their expression was elevated after nicotinic incubation. Importantly, the most significant increase in expression was observed in the α5 and α7 subunits. However, CSE did not cause a significant enhancement in the expression of these genes and proteins. Cells pretreated with nicotine prior to lipopolysaccharide (LPS) stimulation exhibited a lower production of TNF-α, IL-8, and IL-6 compared to LPS-treated (only) cells. Cells that were transfected with α7 siRNA and subsequently incubated with nicotine and LPS, exhibited a higher expression of TNF-α, IL-8, and IL-6 compared with non-transfected cells or α1 and α5 siRNA-transfected cells. In α1- and α5-siRNA-transfected cells, the expression of TNF-α, IL-8, and IL-6 showed no significant difference compared with non-transfected cells. Therefore, we concluded that α1, α5, α7, and β2 nAChR subunits are highly expressed in human bronchial epithelial cells (HBE16) after nicotinic incubation and that the α7 subunit is involved in the nicotine-induced inhibitory effect on the production of inflammatory factors. Moreover, α1, α5, and β2 subunits did not play an important role in this process.
Li Q
，Zhou X
，Kolosov VP
，Perelman JM
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α5 Nicotinic acetylcholine receptor mediates nicotine-induced HIF-1α and VEGF expression in non-small cell lung cancer.
By binding to nicotinic acetylcholine receptors (nAChRs), nicotine induces the proliferation and apoptosis of non-small cell lung cancer (NSCLC). Previous studies have indicated that α5-nAChR is highly associated with lung cancer risk and nicotine dependence. However, the mechanisms through which α5-nAChRs may influence lung carcinogenesis are far from clear. In the present study, we investigated the roles of α5-nAChR in the nicotine-induced expression of hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF). Immunohistochemistry was used to detect the expression of α5-nAChR and HIF-1α in 60 specimens of lung cancer and para-carcinoma tissue. The correlations between the expression levels of α5-nAChR and HIF-1α and other clinicopathological data were analyzed. In a cell line that highly expressed α5-nAChR, the loss of α5-nAChR function by siRNA was used to study whether α5-nAChR is involved in the nicotine-induced expression of HIF-1α and VEGF through the activation of the ERK1/2 and PI3K/Akt signaling pathways. Cell growth was detected using the cell counting kit-8 (CCK-8). α5-nAChR (78.3%) and HIF-1α (88.3%) were both overexpressed in NSCLC, and their expression levels were found to be correlated with each other (P<0.05). In the A549 cell line, α5-nAChR and HIF-1α were found to be expressed under normal conditions, and their expression levels were significantly increased in response to nicotine treatment. The silencing of α5-nAChR significantly inhibited the nicotine-induced cell proliferation compared with the control group and attenuated the nicotine-induced upregulation of HIF-1α and VEGF, and these effects required the cooperation of the ERK1/2 and PI3K/Akt signaling pathways. These results show that the α5-nAChR/HIF-1α/VEGF axis is involved in nicotine-induced tumor cell proliferation, which suggests that α5-nAChR may serve as a potential anticancer target in nicotine-associated lung cancer.
Ma X
，Jia Y
，Zu S
，Li R
，Jia Y
，Zhao Y
，Xiao D
，Dang N
，Wang Y
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