title: miRNA-196b inhibits cell proliferation and induces apoptosis in HepG2 cells by targeting IGF2BP1.
abstract: BACKGROUND
  Tumor hypoxia is one of the features of tumor microenvironment that contributes to chemoresistance. miRNAs have recently been shown to play important roles in tumorigenesis and drug resistance. Moreover, hypoxia also regulates the expression of a series of miRNAs. However, the interaction between chemoresistance, hypoxia and miRNAs has not been explored yet. The aim of this study is to understand the mechanisms activated/inhibited by miRNAs under hypoxia that induce resistance to chemotherapy-induced apoptosis.
  
  
  METHODS
  TaqMan low-density array was used to identify changes in miRNA expression when cells were exposed to etoposide under hypoxia or normoxia. The effects of miR-196b overexpression on apoptosis and cell proliferation were studied in HepG2 cells. miR-196b target mRNAs were identified by proteomic analysis, luciferase activity assay, RT-qPCR and western blot analysis.
  
  
  RESULTS
  Results showed that hypoxia down-regulated miR-196b expression that was induced by etoposide. miR-196b overexpression increased the etoposide-induced apoptosis and reversed the protection of cell death observed under hypoxia. By a proteomic approach combined with bioinformatics analyses, we identified IGF2BP1 as a potential target of miR-196b. Indeed, miR-196b overexpression decreased IGF2BP1 RNA expression and protein level. The IGF2BP1 down-regulation by either miR-196b or IGF2BP1 siRNA led to an increase in apoptosis and a decrease in cell viability and proliferation in normal culture conditions. However, IGF2BP1 silencing did not modify the chemoresistance induced by hypoxia, probably because it is not the only target of miR-196b involved in the regulation of apoptosis.
  
  
  CONCLUSIONS
  In conclusion, for the first time, we identified IGF2BP1 as a direct and functional target of miR-196b and showed that miR-196b overexpression reverses the chemoresistance induced by hypoxia. These results emphasize that the chemoresistance induced by hypoxia is a complex mechanism.
authors.affiliation: Laboratory of Biochemistry and Cellular Biology (URBC), NARILIS, University of Namur, 61 rue de Bruxelles, 5000, Namur, Belgium. magali.rebucci@unamur.be.
authors.forename: Magali
authors.initials: M
authors.lastname: Rebucci
authors.affiliation: Laboratory of Biochemistry and Cellular Biology (URBC), NARILIS, University of Namur, 61 rue de Bruxelles, 5000, Namur, Belgium. audrey_sermeus@hotmail.com.
authors.forename: Audrey
authors.initials: A
authors.lastname: Sermeus
authors.affiliation: Laboratory of Biochemistry and Cellular Biology (URBC), NARILIS, University of Namur, 61 rue de Bruxelles, 5000, Namur, Belgium. elodie.leonard@student.unamur.be.
authors.forename: Elodie
authors.initials: E
authors.lastname: Leonard
authors.affiliation: Laboratory of Biochemistry and Cellular Biology (URBC), NARILIS, University of Namur, 61 rue de Bruxelles, 5000, Namur, Belgium. edouard.delaive@unamur.be.
authors.forename: Edouard
authors.initials: E
authors.lastname: Delaive
authors.affiliation: Laboratory of Biochemistry and Cellular Biology (URBC), NARILIS, University of Namur, 61 rue de Bruxelles, 5000, Namur, Belgium. marc.dieu@unamur.be.
authors.forename: Marc
authors.initials: M
authors.lastname: Dieu
authors.affiliation: Laboratory of Biochemistry and Cellular Biology (URBC), NARILIS, University of Namur, 61 rue de Bruxelles, 5000, Namur, Belgium. maude.fransolet@unamur.be.
authors.forename: Maude
authors.initials: M
authors.lastname: Fransolet
authors.affiliation: Laboratory of Biochemistry and Cellular Biology (URBC), NARILIS, University of Namur, 61 rue de Bruxelles, 5000, Namur, Belgium. thierry.arnould@unamur.be.
authors.forename: Thierry
authors.initials: T
authors.lastname: Arnould
authors.affiliation: Laboratory of Biochemistry and Cellular Biology (URBC), NARILIS, University of Namur, 61 rue de Bruxelles, 5000, Namur, Belgium. carine.michiels@unamur.be.
authors.forename: Carine
authors.initials: C
authors.lastname: Michiels
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000235:genetics*; D015687:Cell Hypoxia / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects / Q000235:genetics*; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005047:Etoposide / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000235:genetics; D056945:Hep G2 Cells; D006801:Humans; D035683:MicroRNAs / Q000235:genetics*; D040901:Proteomics / Q000379:methods; D016601:RNA-Binding Proteins / Q000235:genetics*
chemical_list: C406144:IGF2BP1 protein, human; D035683:MicroRNAs; D016601:RNA-Binding Proteins; D005047:Etoposide