title: MicroRNA-21 modulates chemosensitivity of breast cancer cells to doxorubicin by targeting PTEN.
abstract: OBJECTIVE
  Ovexpression of microRNA-21 (miR-21) is found in various human cancers. Our aim is to investigate the association of miR-21 expression with the sensitivity of breast cancer cells to doxorubicin (ADR).
  
  
  METHODS
  The half maximal inhibitory concentration (IC(50)) value of ADR in resistant MCF-7/ADR or parental MCF-7 cells was determined by MTT assay. TaqMan RT-PCR or Western blot assay was performed to detect the expression of mature miR-21 and tumor suppressor gene (PTEN) protein. MCF-7 or MCF-7/ADR cell line was transfected with miR-21mimic or inhibitor. The IC(50) value of ADR was determined. Flow cytometry and TUNEL assays were performed to analyze apoptosis. The activity of caspase-3 was analyzed.
  
  
  RESULTS
  The IC(50) of ADR in MCF-7 and MCF-7/ADR cells was 0.21 ± 0.05 and 16.5 ± 0.08 μmol/L, respectively. We showed that upregulation of miR-21 in MCF-7/ADR cells was concurrent with downregulation of PTEN protein. MiR-21 mimic or inhibitor could obviously affect the sensitivity of breast cancer cells to ADR. Moreover, miR-21 inhibitor could enhance caspase-3-dependent apoptosis in MCF-7/ADR cells. Overexpression of PTEN could mimic the same effects of miR-21 inhibitor in MCF-7/ADR cells and PTEN-siRNA could increase the resistance of MCF-7 cells to ADR. MiR-21 inhibitor could increase PTEN protein expression and the luciferase activity of a PTEN 3' untranslated region-based reporter construct in MCF-7/ADR cells. PTEN-siRNA could partially reverse the increased chemosensitivity of MCF-7/ADR cells induced by miR-21 inhibitor.
  
  
  CONCLUSIONS
  Dysregulation of miR-21 plays critical roles in the ADR resistance of breast cancer, at least in part via targeting PTEN.
authors.affiliation: Department of Oncology, The Second Affiliated Hospital of Nanjing Medical University, Jiangsu, PR China. wangzhaox@yahoo.com.cn
authors.forename: Zhao-Xia
authors.initials: ZX
authors.lastname: Wang
authors.forename: Bin-Bin
authors.initials: BB
authors.lastname: Lu
authors.forename: He
authors.initials: H
authors.lastname: Wang
authors.forename: Zhi-Xiang
authors.initials: ZX
authors.lastname: Cheng
authors.forename: Yong-Mei
authors.initials: YM
authors.lastname: Yin
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor / Q000187:drug effects*; D004317:Doxorubicin / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D020128:Inhibitory Concentration 50; D035683:MicroRNAs / Q000378:metabolism*; D051059:PTEN Phosphohydrolase / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism
chemical_list: D000903:Antibiotics, Antineoplastic; C524940:MIRN21 microRNA, human; D035683:MicroRNAs; D034741:RNA, Small Interfering; D004317:Doxorubicin; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human; D053148:Caspase 3