title: Aberrant overexpression of miR-421 downregulates ATM and leads to a pronounced DSB repair defect and clinical hypersensitivity in SKX squamous cell carcinoma.
abstract: BACKGROUND
  Cellular and clinical sensitivity to ionizing radiation (IR) is determined by DNA double-strand breaks (DSB) repair. Here, we investigate the molecular mechanism underlying the extreme response of a head and neck tumor case (SKX) to standard radiotherapy.
  
  
  METHODS
  Immunofluorescence (IF) was used for the assessment of DSB repair, Western blot and real-time PCR for protein and mRNA expression, respectively.
  
  
  RESULTS
  SKX cells exhibited a pronounced radiosensitivity associated with numerous residual γ-H2AX foci after IR. This was not associated with lacking canonical repair proteins. SKX cells did not express any ATM protein. Accordingly, immunoblotting revealed no ATM kinase activity toward substrates such as p-SMC1, p-CHK2 and p-KAP1. Sequencing of all 66 exons of ATM showed no mutation. ATM mRNA level was moderately reduced, which could be reverted by 5'-Aza-C treatment but without restoring protein levels. Importantly, we demonstrated a post-transcriptional regulation in SKX cells via 6-fold enhanced levels of miR-421, which targets the 3'-UTR of ATM mRNA. Transfection of SKX cells with either anti-miR-421 inhibitor or a microRNA-insensitive ATM vector recovered ATM expression and abrogated the hyper-radiosensitivity.
  
  
  CONCLUSIONS
  This is the first report describing microRNA-mediated down-regulation of ATM leading to clinically manifest tumor radiosensitivity.
authors.affiliation: Institute of Radiobiology and Molecular Radiation Oncology, Philipps-University, Marburg, Germany. wmansour@uke.uni-hamburg.de
authors.forename: Wael Y
authors.initials: WY
authors.lastname: Mansour
authors.forename: Natalia V
authors.initials: NV
authors.lastname: Bogdanova
authors.forename: Ulla
authors.initials: U
authors.lastname: Kasten-Pisula
authors.forename: Thorsten
authors.initials: T
authors.lastname: Rieckmann
authors.forename: Sabrina
authors.initials: S
authors.lastname: Köcher
authors.forename: Kerstin
authors.initials: K
authors.lastname: Borgmann
authors.forename: Michael
authors.initials: M
authors.lastname: Baumann
authors.forename: Mechtild
authors.initials: M
authors.lastname: Krause
authors.forename: Cordula
authors.initials: C
authors.lastname: Petersen
authors.forename: Hailiang
authors.initials: H
authors.lastname: Hu
authors.forename: Richard A
authors.initials: RA
authors.lastname: Gatti
authors.forename: Ekkehard
authors.initials: E
authors.lastname: Dikomey
authors.forename: Thilo
authors.initials: T
authors.lastname: Dörk
authors.forename: Jochen
authors.initials: J
authors.lastname: Dahm-Daphi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D064007:Ataxia Telangiectasia Mutated Proteins; D002294:Carcinoma, Squamous Cell / Q000235:genetics / Q000532:radiotherapy*; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors* / Q000172:deficiency / Q000502:physiology; D045744:Cell Line, Tumor; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors* / Q000172:deficiency / Q000502:physiology; D015536:Down-Regulation; D015972:Gene Expression Regulation, Neoplastic; D006258:Head and Neck Neoplasms / Q000235:genetics / Q000532:radiotherapy*; D006801:Humans; D035683:MicroRNAs / Q000037:antagonists & inhibitors / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000172:deficiency / Q000502:physiology; D011836:Radiation Tolerance; D000077195:Squamous Cell Carcinoma of Head and Neck; D025521:Tumor Suppressor Proteins / Q000037:antagonists & inhibitors* / Q000172:deficiency / Q000502:physiology
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C547665:MIRN421 microRNA, human; D035683:MicroRNAs; D025521:Tumor Suppressor Proteins; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases