title: Radiation resistance due to high expression of miR-21 and G2/M checkpoint arrest in breast cancer cells.
abstract: BACKGROUND
  There is evidence that the extent of the G2/M arrest following irradiation is correlated with tumour cell survival and hence therapeutic success. We studied the regulation of cellular response to radiation treatment by miR-21-mediated modulation of cell cycle progression in breast cancer cells and analysed miR-21 expression in breast cancer tissue samples with long-term follow up.
  
  
  METHODS
  The miR-21 expression levels were quantified (qRT-PCR) in a panel of 86 cases of invasive breast carcinomas in relation to metastasis free survival. The cellular radiosensitivity of human breast cancer cells after irradiation was determined comparing two cell lines (T47D and MDA-MB-361) by cell proliferation and colony forming assays. The influence of miR-21 overexpression or downregulation on cell cycle progression and G2/M checkpoint arrest after irradiation was assessed by flow cytometric analysis.
  
  
  RESULTS
  The expression of miR-21 was transiently increased 8 hours after irradiation in the radioresistant T47D cells and significantly changed with lower extent in radiosensitive MDA-MB-361 cells. Anti-miR-21 treated breast cancer cells failed to exhibit the DNA damage-G2 checkpoint increase after irradiation. Apoptotic activity was significantly enhanced from 7% to 27% in T47D cells and from 18% to 30% in MDA-MB-361 cells 24 hours after 5 Gy irradiation. Additionally, we characterized expression of miR-21 in invasive breast carcinomas. In comparison to non-cancerous adjacent breast tissue, tumours samples had increased miR-21 expression that inversely correlated with the distant metastases-free survival of patients (p = 0.029).
  
  
  CONCLUSIONS
  Our data indicate that miR-21 expression in breast cancer cells contributes to radiation resistance by compromising cell cycle progression. These data point to the potential of combining radiotherapy with an anti-miR-21 as a potent G2/M check point inhibitor in overcoming radiation resistance of tumours.
authors.affiliation: Institute of Radiation Biology, Helmholtz Zentrum Muenchen, German Research Center for Environmental Health, Muenchen, Germany. natasa.anastasov@helmholtz-muenchen.de
authors.forename: Nataša
authors.initials: N
authors.lastname: Anastasov
authors.forename: Ines
authors.initials: I
authors.lastname: Höfig
authors.forename: Iria Gonzalez
authors.initials: IG
authors.lastname: Vasconcellos
authors.forename: Kristina
authors.initials: K
authors.lastname: Rappl
authors.forename: Herbert
authors.initials: H
authors.lastname: Braselmann
authors.forename: Natalie
authors.initials: N
authors.lastname: Ludyga
authors.forename: Gert
authors.initials: G
authors.lastname: Auer
authors.forename: Michaela
authors.initials: M
authors.lastname: Aubele
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Atkinson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017209:Apoptosis; D015153:Blotting, Western; D001940:Breast / Q000378:metabolism / Q000473:pathology*; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology / Q000532:radiotherapy; D018270:Carcinoma, Ductal, Breast / Q000235:genetics* / Q000473:pathology / Q000532:radiotherapy; D059447:Cell Cycle Checkpoints / Q000235:genetics*; D049109:Cell Proliferation; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005434:Flow Cytometry; D059565:G2 Phase Cell Cycle Checkpoints / Q000235:genetics*; D006801:Humans; D035683:MicroRNAs / Q000235:genetics*; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D011379:Prognosis; D012333:RNA, Messenger / Q000235:genetics; D011836:Radiation Tolerance / Q000235:genetics*; D011839:Radiation, Ionizing; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015996:Survival Rate; D014407:Tumor Cells, Cultured
chemical_list: C524940:MIRN21 microRNA, human; D035683:MicroRNAs; D012333:RNA, Messenger