title: MicroRNA regulation of ionizing radiation-induced premature senescence.
abstract: OBJECTIVE
  MicroRNAs (miRNAs) have emerged as critical regulators of many cellular pathways. Ionizing radiation (IR) exposure causes DNA damage and induces premature senescence. However, the role of miRNAs in IR-induced senescence has not been well defined. Thus, the purpose of this study was to identify and characterize senescence-associated miRNAs (SA-miRNAs) and to investigate the role of SA-miRNAs in IR-induced senescence.
  
  
  METHODS
  In human lung (WI-38) fibroblasts, premature senescence was induced either by IR or busulfan (BU) treatment, and replicative senescence was accomplished by serial passaging. MiRNA microarray were used to identify SA-miRNAs, and real-time reverse transcription (RT)-PCR validated the expression profiles of SA-miRNAs in various senescent cells. The role of SA-miRNAs in IR-induced senescence was characterized by knockdown of miRNA expression, using anti-miRNA oligonucleotides or by miRNA overexpression through the transfection of pre-miRNA mimics.
  
  
  RESULTS
  We identified eight SA-miRNAs, four of which were up-regulated (miR-152, -410, -431, and -493) and four which were down-regulated (miR-155, -20a, -25, and -15a), that are differentially expressed in both prematurely senescent (induced by IR or BU) and replicatively senescent WI-38 cells. Validation of the expression of these SA-miRNAs indicated that down-regulation of miR-155, -20a, -25, and -15a is a characteristic miRNA expression signature of cellular senescence. Functional analyses revealed that knockdown of miR-155 or miR-20a, but not miR-25 or miR-15a, markedly enhanced IR-induced senescence, whereas ectopic overexpression of miR-155 or miR-20a significantly inhibited senescence induction. Furthermore, our studies indicate that miR-155 modulates IR-induced senescence by acting downstream of the p53 and p38 mitogen-activated protein kinase (MAPK) pathways and in part via regulating tumor protein 53-induced nuclear protein 1 (TP53INP1) expression.
  
  
  CONCLUSIONS
  Our results suggest that SA-miRNAs are involved in the regulation of IR-induced senescence, so targeting these miRNAs may be a novel approach for modulating cellular response to radiation exposure.
authors.affiliation: Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, South Carolina 29425, USA. wangy@musc.edu
authors.forename: Yong
authors.initials: Y
authors.lastname: Wang
authors.forename: Melissa N
authors.initials: MN
authors.lastname: Scheiber
authors.forename: Carola
authors.initials: C
authors.lastname: Neumann
authors.forename: George A
authors.initials: GA
authors.lastname: Calin
authors.forename: Daohong
authors.initials: D
authors.lastname: Zhou
mesh_terms: D002066:Busulfan; D002460:Cell Line; D016922:Cellular Senescence / Q000235:genetics* / Q000528:radiation effects; D004249:DNA Damage; D015536:Down-Regulation; D005347:Fibroblasts / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D020868:Gene Silencing; D006801:Humans; D035683:MicroRNAs / Q000032:analysis / Q000502:physiology*; D046228:Microarray Analysis; D009369:Neoplasms / Q000532:radiotherapy; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods; D015854:Up-Regulation
chemical_list: D035683:MicroRNAs; D002066:Busulfan