title: MicroRNA profiling in K-562 cells under imatinib treatment:  influence of miR-212 and miR-328 on ABCG2 expression.
abstract: BACKGROUND
  Despite the enormous success of imatinib in chronic myeloid leukemia (CML), therapy resistance has emerged in a significant proportion of patients, partly because of the overexpression of ABC efflux transporters.
  
  
  METHODS
  Using an array comprising 667 miRNAs, we investigated whether the expression of microRNAs (miRNAs) is altered in CML K-562 cells becoming resistant to increasing concentrations of imatinib. ABCB1 and ABCG2 mRNA (quantitative real-time PCR) and protein expression (western blot) were quantified under short-term and 4 months' imatinib treatment. Interaction of miR-212 and miR-328 with ABCG2 was investigated by transfection experiments and reporter gene assays using respective miRNA precursors or miRNA inhibitors.
  
  
  RESULTS
  Although ABCB1 protein was not expressed, ABCG2 protein was 7.2-fold elevated after long-term treatment with 0.3 µmol/l imatinib and decreased gradually at higher concentrations. miRNAs miR-212 and miR-328 were identified to correlate inversely with ABCG2 expression under these conditions. Short-term treatment also induced ABCG2 protein concentration dependently and caused a downregulation of miR-212, but not of miR-328 at all tested concentrations (P=0.050). Reporter gene assays confirmed miR-212 to target the 3'-UTR region of ABCG2. In contrast, transfection of anti-miR-212 revealed an upregulation of ABCG2 protein expression, whereas the effect of anti-miR-328 was weak.
  
  
  CONCLUSIONS
  Our study suggests an association of imatinib treatment, miRNA downregulation and ABCG2 overexpression, possibly contributing to the mechanisms involved in imatinib distribution and response in CML therapy.
authors.affiliation: Institute of Experimental and Clinical Pharmacology, University of Kiel, Kiel, Germany.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Turrini
authors.forename: Sierk
authors.initials: S
authors.lastname: Haenisch
authors.forename: Sandra
authors.initials: S
authors.lastname: Laechelt
authors.forename: Tobias
authors.initials: T
authors.lastname: Diewock
authors.forename: Oliver
authors.initials: O
authors.lastname: Bruhn
authors.forename: Ingolf
authors.initials: I
authors.lastname: Cascorbi
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D001549:Benzamides; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D015973:Gene Expression Regulation, Leukemic / Q000187:drug effects*; D006801:Humans; D000068877:Imatinib Mesylate; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000188:drug therapy* / Q000235:genetics; D035683:MicroRNAs / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D010879:Piperazines / Q000008:administration & dosage*; D011743:Pyrimidines / Q000008:administration & dosage*
chemical_list: C513055:ABCB1 protein, human; C116614:ABCG2 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D001549:Benzamides; C551411:MIRN212 microRNA, human; C548170:MIRN328 microRNA, human; D035683:MicroRNAs; D009363:Neoplasm Proteins; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate