title: Silibinin-Induced Apoptosis and Downregulation of MicroRNA-21 and MicroRNA-155 in MCF-7 Human Breast Cancer Cells.
abstract: OBJECTIVE
  MicroRNAs (miRNAs) have received much attention owing to their aberrant expression in various stages of cancer. In many biological processes, miRNAs negatively regulate gene expression, and may be useful in therapeutic strategies. The present study evaluated the effects of silibinin (silybin), a natural flavonoid, on miRNA expression and attempted to elucidate therapeutic targets in MCF-7 breast cancer cells.
  
  
  METHODS
  The rates of cell proliferation and apoptosis were determined in silibinin-treated and untreated MCF-7 cells. Furthermore, the expression levels of miR-21 and miR-155 were measured in MCF-7 cells after incubation with silibinin (100 µg/mL), and the putative targets of the miRNAs within the apoptotic pathways were predicted using bioinformatic approaches. The expression levels of some of these targets were evaluated by quantitative reverse transcription polymerase chain reaction (qRT-PCR).
  
  
  RESULTS
  Silibinin induced apoptosis in MCF-7 cells in a dose- and time-dependent manner. qRT-PCR analysis revealed a decrease in miR-21 and miR-155 expression levels in silibinin-treated cells relative to the levels in the untreated cells. Potential miR-21 and miR-155 targets within the apoptotic pathways, such as CASP-9, BID, APAF-1, CASP-3, CASP-8, and PDCD4, were predicted by in silico analysis. qRT-PCR analysis showed upregulation of some of these potential targets including caspase-9 (CASP-9) and BID after silibinin treatment for 48 hours.
  
  
  CONCLUSIONS
  Our results suggest a correlation between the expression of miR-21 and miR-155, and MCF-7 cell proliferation. The antiproliferative activity of silibinin may partly be attributable to the downregulation of miR-21 and miR-155, and the upregulation of their apoptotic targets. Furthermore, the upregulation of CASP-9 and BID indicates that silibinin induces apoptosis through both the extrinsic and intrinsic pathways.
authors.affiliation: Department of Cell & Molecular Biology, School of Biology, College of Science, University of Tehran, Tehran, Iran.
authors.forename: Masoud Maleki
authors.initials: MM
authors.lastname: Zadeh
authors.affiliation: Department of Cell & Molecular Biology, School of Biology, College of Science, University of Tehran, Tehran, Iran.
authors.forename: Nasrin
authors.initials: N
authors.lastname: Motamed
authors.affiliation: Department of Genetics, College of Science, Rasht Branch, Islamic Azad University, Rasht, Iran.
authors.forename: Najmeh
authors.initials: N
authors.lastname: Ranji
authors.affiliation: National Cell Bank of Iran, Pasteur Institute of Iran, Tehran, Iran.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Majidi
authors.affiliation: Cancer Epigenetics Group, Harry Perkins Institute of Medical Research & School of Anatomy, Physiology and Human Biology, The University of Western Australia, Perth, Australia.
authors.forename: Fahimeh
authors.initials: F
authors.lastname: Falahi
keywords: Apoptosis; MCF-7 cells; MicroRNAs; Silybin