The Studies on the Carcinogen Effect of Nicotine on Human Breast
Cancer and its Molecular Mechanism
Previous study indicated that tobacco-smoking is a well nderstanding carcinogenic factors that promote the
lung cancer formation(1,2). The mechanisms of nicotine-induced carcinogenesis were demonstrated in our
recent report (Toxicology and Applied Pharmacology, 2004, in press) indicated as specific binding of nicot
ine to the nicotinic acetylcholine receptor (nAchRs) in lung epithelial cells by activation of the cyclin D1 p
romoter through the NFkB signaling proteins to induced cell proliferation(3,4). To further investigate the t
obacco smoking habits and its correlations of breast tumor formation(5-7), therefore, we suggested that spe
cific nAchR subunits will be identified in the breast tumor. In this study, our results demonstrated that (nA
chR) was detected in breast tumor tissue in Taiwanese patients. We first demonstrated that the a5 and a9 n
AchRs were detected in both the MCF-7 and MDA-MB-231 breast cancer cell lines. We further study the e
xpression of the nAchR mRNA levels in breast tumor tissues collected from forty cases of breast cancer pa
tients in Taiwan and found that the α9 and α10 subunits of the nAchR was the most prevalence in both nor
mal and tumor tissue. Quantitative assays of the mRNA levels of the nAchRs was measured by Real-time P
CR analysis technique and revealed that expression of the a9-nAchR was higher in the tumor tissue when c
ompared to the normal tissue which dissected form the tumor margin. Western blotting analysis was then p
erformed and demonstrated that the PI3K/Akt-regulated proteins were the major signaling pathway that inv
olved in cell proliferation stimulated by nicotine treatment. Different clones of cell lines that inhibited the a
9 and a5 receptor expression by SiRNA technique was established in the MDAMB 231 cells. We found th
at cell growth curve was significant inhibited in the a9-siRAN-nAchR cells. Such results implied that the a
9-nAchR may play some important role involved in nicotine-mediated breast tumor carcinogenesis.
