MCF7 meme kanser hücre hattında nikotinden etkilenmiş gen ifade profilleri ve CHRNA5 ifadesinde estrojenin rolü

Breast cancer, highly heterogeneous in nature, has been classified into multiplemolecular subtypes based on hormone receptor status and also possess variable geneticand environmental etiologies. Prognosis and therapy of breast cancer depends on thepresence or absence of these molecular markers. Nicotine, the major psychoactiveaddictive component in tobacco smoke, has been associated with multiple cancersbecause of its ability to increase cell proliferation, migration, and angiogenesis, and todecrease apoptosis. Nicotine binds to cholinergic receptors made up of multiple subunits,one of which, the alpha 5 (CHRNA5) whose polymorphisms have recently beenimplicated in nicotine addiction and lung cancer as functional. Microarray datasetsprovide genomic and functional information on the whole transcriptome when exposed toa certain treatment or under different pathological conditions allowing for molecularclassification. The association between nicotine use and breast cancer has beencontroversial and to our knowledge no high-throughput expression profiling of breastcancer cells exposed to nicotine exists in the literature. In the present study, wedetermined that 1 uM nicotine affects cell proliferation in MCF7 cells measured by MTTassay only under serum starvation (0.1% Serum) condition at days 5 or 7 but not earlier.Similarly, effects on the protein levels of selected molecular markers with roles inproliferation and/or apoptosis, i.e., CyclinE, bcl-xl, and p53 were affected under serumstarved conditions in more pronounced ways. Effects of nicotine at the transcriptome levelwere studied in MCF7 cells when exposed to 1uM Nicotine using Affymetrix HumanHGU133 plus 2 arrays under the 10% serum levels. Our findings indicated that nicotineaffects multiple pathways including MAPK, focal adhesion, and apoptosis although themagnitude of changes was mild. Preliminary analyses performed under serum-starvationindicated that starvation resulted in drastic changes in MCF7 transcriptome, some ofwhich can be reversed, by 1uM nicotine. CHRNA5 expression was highly modulated byserum levels. Multiple microarray datasets on breast cancer cell lines and primary tumorsin GEO were re-analyzed to assess the dependency of CHRNA5 expression on estrogen.Our findings were: 1) CHRNA5 expression increased in the presence of estrogen in adose- and time-dependent fashion; 2) CHRNA5 was found to be a likely secondary targetof estrogen; 3) CHRNA5 expression was higher in ER negative and/or Grade 3 breastcancer patients, implicating CHRNA5 with prognosis; 4) DNA replication and cell cyclegenes seemed to be highly correlated with CHRNA5 expression; 5) the coexpressed genescould predict ER and Grade status of primary tumors with high accuracies. In conclusion,cholinergic signaling as modulated by nicotine through acetylcholine receptors mighthave a role in breast cancer etiology. CHRNA5 represents a novel candidate for breastcancer diagnostic and prognostic studies.