A Double-negative Feedback Loop Between E2F3b And MiR-200b Regulates Docetaxel Chemosensitivity Of Human Lung Adenocarcinoma Cells

Background and ObjectiveLung cancer is one of the most common malignancies and the leading cause of cancer-related deaths worldwide.Approximately 70%-80%of lung cancers are non-small cell lung cancer(NSCLC).Chemoresistance remains one of the major obstacles restricting the clinical application of anti-cancer drugs.MicroRNAs(miRNAs)are non-coding small RNAs which negatively regulate gene expressions mainly through 3'-UTR binding of target mRNAs.Recent studies have highlighted the feedback loops between miRNAs and their target genes in physiological and pathological processes including chemoresistance of cancers.Our previous study identified miR-200b/E2F3 axis as a chemosensitivity restorer of human lung adenocarcinoma(LAD)cells.Moreover,E2F3b was bioinformatically proved to be a potential transcriptional regulator of pre-miR-200b gene promoter.The existance of this double-negative feedback minicircuitry comprising E2F3b and miR-200b was confirmed by chromatin immunoprecipitation(ChIP)assay,site-specific mutation and luciferase reporter assay.And the underlying regulatory mechanisms of this feedback loop on docetaxel resistance of LAD cells were further investigated by applying in vitro chemosensitivity assay,colony formation assay,flow cytometric analysis of cell cycle and apoptosis,as well as mice xenograft model.In conclusion,our results suggest that the double-negative feedback loop between E2F3b and miR-200b regulates docetaxel chemosensitivity of human LAD cells mainly through cell proliferation,cell cycle distribution and apoptosis.