title: Induction of MET by ionizing radiation and its role in radioresistance and invasive growth of cancer.
abstract: BACKGROUND
  Ionizing radiation (IR) is effectively used in cancer therapy. However, in subsets of patients, a few radioresistant cancer cells survive and cause disease relapse with metastatic progression. The MET oncogene encodes the hepatocyte growth factor (HGF) receptor and is known to drive "invasive growth", a regenerative and prosurvival program unduly activated in metastasis.
  
  
  METHODS
  Human tumor cell lines (MDA-MB-231, MDA-MB-435S, U251) were subjected to therapeutic doses of IR. MET mRNA, and protein expression and signal transduction were compared in treated and untreated cells, and the involvement of the DNA-damage sensor ataxia telangiectasia mutated (ATM) and the transcription factor nuclear factor kappa B (NF-κB) in activating MET transcription were analyzed by immunoblotting, chromatin immunoprecipitation, and use of NF-κB silencing RNA (siRNA). Cell invasiveness was measured in wound healing and transwell assays, and cell survival was measured in viability and clonogenic assays. MET was inhibited by siRNA or small-molecule kinase inhibitors (PHA665752 or JNJ-38877605). Combinations of MET-targeted therapy and radiotherapy were assessed in MDA-MB-231 and U251 xenografts (n = 5-6 mice per group). All P values were from two-sided tests.
  
  
  RESULTS
  After irradiation, MET expression in cell lines was increased up to fivefold via activation of ATM and NF-κB. MET overexpression increased ligand-independent MET phosphorylation and signal transduction, and rendered cells more sensitive to HGF. Irradiated cells became more invasive via a MET-dependent mechanism that was further enhanced in the presence of HGF. MET silencing by siRNA or inhibition of its kinase activity by treatment with PHA665752 or JNJ-38877605 counteracted radiation-induced invasiveness, promoted apoptosis, and prevented cells from resuming proliferation after irradiation in vitro. Treatment with MET inhibitors enhanced the efficacy of IR to stop the growth of or to induce the regression of xenografts (eg, at day 13, U251 xenografts, mean volume increase relative to mean tumor volume at day 0: vehicle = 438%, 5 Gy IR = 151%, 5 Gy IR + JNJ-38877605 = 76%; difference, IR vs JNJ-38877604 + IR = 75%, 95% CI = 59% to 91%, P = .01).
  
  
  CONCLUSIONS
  IR induces overexpression and activity of the MET oncogene through the ATM-NF-κB signaling pathway; MET, in turn, promotes cell invasion and protects cells from apoptosis, thus supporting radioresistance. Drugs targeting MET increase tumor cell radiosensitivity and prevent radiation-induced invasiveness.
authors.affiliation: IRCC-Institute for Cancer Research at Candiolo, University of Turin Medical School, Candiolo, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: De Bacco
authors.forename: Paolo
authors.initials: P
authors.lastname: Luraghi
authors.forename: Enzo
authors.initials: E
authors.lastname: Medico
authors.forename: Gigliola
authors.initials: G
authors.lastname: Reato
authors.forename: Flavia
authors.initials: F
authors.lastname: Girolami
authors.forename: Timothy
authors.initials: T
authors.lastname: Perera
authors.forename: Pietro
authors.initials: P
authors.lastname: Gabriele
authors.forename: Paolo M
authors.initials: PM
authors.lastname: Comoglio
authors.forename: Carla
authors.initials: C
authors.lastname: Boccaccio
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D064007:Ataxia Telangiectasia Mutated Proteins; D015152:Blotting, Northern; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000528:radiation effects; D002470:Cell Survival / Q000528:radiation effects; D047369:Chromatin Immunoprecipitation; D004249:DNA Damage / Q000528:radiation effects*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D004797:Enzyme-Linked Immunosorbent Assay; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020868:Gene Silencing; D006801:Humans; D020287:In Situ Nick-End Labeling; D007211:Indoles / Q000494:pharmacology; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D009361:Neoplasm Invasiveness / Q000517:prevention & control; D009369:Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000532:radiotherapy; D010766:Phosphorylation / Q000528:radiation effects; D016133:Polymerase Chain Reaction; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D019859:Proto-Oncogene Proteins c-met / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering; D011836:Radiation Tolerance; D011839:Radiation, Ionizing; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D017978:Receptors, Growth Factor / Q000037:antagonists & inhibitors* / Q000187:drug effects / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D015398:Signal Transduction / Q000528:radiation effects*; D013450:Sulfones / Q000494:pharmacology; D014158:Transcription, Genetic / Q000528:radiation effects; D014183:Transplantation, Heterologous; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D015854:Up-Regulation / Q000528:radiation effects
chemical_list: C480541:5-((2,6-dichlorobenzyl)sulfonyl)-3-((3,5-dimethyl-4-((2-(pyrrolidin-1-ylmethyl)pyrrolidin-1-yl)carbonyl)-1H-pyrrol-2-yl)methylene)-1,3-dihydro-2H-indol-2-one; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D007211:Indoles; D016328:NF-kappa B; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011838:Radiation-Sensitizing Agents; D017978:Receptors, Growth Factor; D013450:Sulfones; D025521:Tumor Suppressor Proteins; C491743:MET protein, human; D019859:Proto-Oncogene Proteins c-met; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases