Suppression of mTOR Expression by siRNA Leads to Cell Cycle Arrest and Apoptosis Induction in MDA-MB-231 Breast Cancer Cells.

Abstract

Mammary carcinogenesis, being ranked second in cancer-related mortality and the inadequacy of existing chemotherapy advocates the development of a novel treatment approach targeting its molecular signalling. Hyperactivation of mammalian target of rapamycin (mTOR) has a critical role in developing invasive mammary cancer and it can be a potential target. This experiment was to explore the efficacy of mTOR-specific siRNA on therapeutic targeting of the mTOR gene, assess its proficiency in suppressing in vitro breast cancer and determine underlying molecular mechanisms. Specific siRNA targeting mTOR was transfected into MDA-MB-231 cells and mTOR downregulation was validated through qRT-PCR and western blot analysis. Cell proliferation was analysed by MTT assay and confocal microscopy. Apoptosis was studied through flow cytometry and S6K, GSK-3β and caspase 3 expression were estimated. Further, the effect of mTOR blockade on cell cycle progression was determined. Following transfection of mTOR-siRNA into the MDA-MB-231 cells, cell viability and apoptosis were examined which indicates that clinically relevant concentration of mTOR-siRNA inhibited cell growth and proliferation and promote apoptosis, resulting from the suppression of mTOR. This leads to the downregulation of mTOR downstream S6K and upregulation of GSK-3β. An increased level of caspase 3 symbolises that the apoptotic activity is mediated through caspasedependent pathway. Further, mTOR downregulation causes cell cycle arrest in G0/G1 phase as observed in the flow cytometry study. With these results, we can conclude that mTOR-siRNA exerts direct 'anti-breast cancer' activity propagated by the S6K-GSK-3β- caspase 3 mediated apoptosis and by inducing cell cycle arrest.