The effect of nicotine on the expressions of the α7 nicotinic receptor gene and Bax and Bcl-2 proteins in the mammary gland epithelial-7 breast cancer cell line and its relationship to drug resistance.

Abstract

The binding of nicotine with nicotinic acetylcholine receptors (nAChRs) stimulates cell division and increases drug resistance in cancer. Experiments with specific inhibitors such as RNAi, hexamethonium, and α-bungarotoxin showed that α7 nicotinic receptor plays a key role in the pro-proliferation activity of nicotine. However, the mechanism of nicotine in the progress of breast cancer, the commonest malignancy in women, remains unknown. This study focuses on the effect of nicotine on the expressions of the α7 nicotinic receptor gene and Bax and Bcl-2 proteins in mammary gland epithelial-7 (MCF-7) breast cancer cells and its relationship to drug resistance. To evaluate the effect on drug resistance, human mammary gland epithelial adenocarcinomas from the MCF-7 line were exposed to 100 μl of nicotine at a concentration of 9.2 mg/ml for varying periods of time. Then, the cells were treated with 1, 2, 3 or 5 μl/ml of doxorubicin, either with or without the continued presence of nicotine. Cell viability was determined using the MTT assay. The biochemical parameters of apoptosis, including the expressions of Bax, Bcl-2 and α7 nicotinic receptor proteins were determined via western blotting, and the α7 nicotinic receptor gene expression level was assessed via real-time qPCR using the 2(-ΔΔCt) method. Differences in the target gene expression levels were evaluated with ANOVA with p ≤ 0.05 considered significant. We found a novel and effective signaling pathway of nicotine in the MCF-7 breast cancer cell line. The levels of α7 nicotinic receptor and Bcl-2 protein increased but the Bax protein levels decreased, while the α7 nicotinic receptor gene expression level was not significantly different compared with the control.