Cholinergic Receptor Nicotinic Alpha 5 (CHRNA5) is an important susceptibility locus for nicotine addiction and lung cancer. Depletion of CHRNA5 has been associated with reduced cell viability, increased apoptosis and alterations in cellular motility in different cancers yet not in breast cancer. Herein we first showed the expression of CHRNA5 was variable and positively correlated with the fraction of total genomic alterations in breast cancer cell lines and tumors indicating its potential role in DNA damage response (DDR). Next, we demonstrated that silencing of CHRNA5 expression in MCF7 breast cancer cell line by RNAi affected expression of genes involved in cytoskeleton, TP53 signaling, DNA synthesis and repair, cell cycle, and apoptosis. The transcription profile of CHRNA5 depleted MCF7 cells showed a significant positive correlation with that of A549 lung cancer cell line while exhibiting a negative association with the CHRNA5 co-expression profile obtained from Cancer Cell Line Encylopedia (CCLE). Moreover, it exhibited high similarities with published MCF7 expression profiles obtained from exposure to TP53 inducer nutlin-3a and topoisomerase inhibitors. We then demonstrated that CHRNA5 siRNA treatment reduced cell viability and DNA synthesis indicating G1 arrest while it significantly increased apoptotic sub-G1 cell population. Accordingly, we observed lower levels of phosphorylated RB (Ser807/811) and an increased BAX/BCL2 ratio in RNAi treated MCF7 cells. We also showed that CHRNA5 RNAi transcriptome correlated negatively with DDR relevant gene expression profile in breast cancer gene expression datasets while the coexposure to topoisomerase inhibitors in the presence of CHRNA5 RNAi enhanced chemosensitivity potentially due to reduced DDR. CHRNA5 RNAi consistently lowered total CHEK1 mRNA and protein levels as well as phosphorylated CHEK1 (Ser345) in MCF7 cells. We also detected a significant positive correlation between the expression levels of CHRNA5 and CHEK1 in CCLE, TCGA and METABRIC breast cancer datasets. Our study suggests CHRNA5 RNAi is associated with cell cycle inhibition, apoptosis as well as reduced DDR and increased drug sensitivity in breast cancer yet future studies are warranted since dose- and cell line-specific differences exist in response to CHRNA5 depletion. Gene expression microarray data can be accessed from GEO database under the accession number GSE89333.
Background: Metformin is one of the most prescribed drug for the treatment of type II diabetes. Its anti-proliferative effect is also taken advantage for the treatment of cancer. Despite many of the studies mention the positive effects of metformin in inhibiting the proliferation of cancer cells, there are also studies which questions this idea as well.Methods: In this study, we investigated the most widely studied breast cancer cell lines, ER(+) MCF7 cells, TNBC MDA-MB-231 and MDA-MB468 cells in terms of metastatic behavior under long-term metformin treatment. MCF7, MDA-MB231 and MDA-MB468 cells were gained resistant to metformin starting from 0.2mM to 3.2mM. Results: Compared to MCF7 and MDA-MB231 cell lines, we only observed dramatic changes in MDA-MB468 cells whose morphology has been changed towards mesenchymal like phenotype. Moreoever, migration capacity of these cells were also significanlty increased which were validated at both mRNA and protein levels as well as wound healing assay. In addition EMT like phenotype and increasing migration capacity of metformin resistant MDA-MB468 cells, they exhibited less sensitivity to PI3K inhibitor. Conclusions: All together, our data pointed out that, metformin’s effects should be questioned depending on the subtype of the breast cancer that’s to be treated.
Purpose: Metformin is one of the most prescribed drug for the treatment of type II diabetes. Its anti-proliferative effect is also taken advantage for the treatment of cancer. Despite many of the studies mention the positive effects of metformin in inhibiting the proliferation of cancer cells, there are also studies which questions this idea as well.Methods: In this study, we investigated the most widely studied breast cancer cell lines, ER(+) MCF7 cells, TNBC MDA-MB-231 and MDA-MB468 cells in terms of metastatic behavior under long-term metformin treatment. MCF7, MDA-MB231 and MDA-MB468 cells were gained resistant to metformin starting from 0.2mM to 3.2mM. Results: Compared to MCF7 and MDA-MB231 cell lines, we only observed dramatic changes in MDA-MB468 cells whose morphology has been changed towards mesenchymal like phenotype. Moreoever, migration capacity of these cells were also significanlty increased which were validated at both mRNA and protein levels as well as wound healing assay. In addition EMT like phenotype and increasing migration capacity of metformin resistant MDA-MB468 cells, they exhibited less sensitivity to PI3K inhibitor. Conclusions: All together, our data pointed out that, metformin’s effects should be questioned depending on the subtype of the breast cancer that’s to be treated.
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