title: Targeting FAK radiosensitizes 3-dimensional grown human HNSCC cells through reduced Akt1 and MEK1/2 signaling.
abstract: OBJECTIVE
  Focal adhesion kinase (FAK), a main regulator of integrin signaling and cell migration, is frequently overexpressed and hyperphosphorylated in human head-and-neck squamous cell carcinoma (HNSCC). We have previously shown that pharmacologic FAK inhibition leads to radiosensitization of 3-dimensionally grown HNSCC cell lines. To further evaluate the role of FAK in radioresistance and as a potential cancer target, we examined FAK and FAK downstream signaling in HNSCC cell lines grown in more physiologic extracellular matrix-based 3-dimensional cell cultures.
  
  
  METHODS
  Seven HNSCC cell lines were grown in 3-dimensional extracellular matrix and the clonogenic radiation survival, expression, and phosphorylation of FAK, paxillin, Akt1, extracellular signal-regulated kinase (ERK)1/2, and MEK1/2 were analyzed after siRNA-mediated knockdown of FAK, Akt1, MEK1, FAK+Akt1, or FAK+MEK1 compared with controls or stable overexpression of FAK. The role of MEK1/2 for clonogenic survival and signaling was investigated using the MEK inhibitor U0126 with or without irradiation.
  
  
  RESULTS
  FAK knockdown moderately or significantly enhanced the cellular radiosensitivity of 3-dimensionally grown HNSCC cells. The FAK downstream targets paxillin, Akt1, and ERK1/2 were substantially dephosphorylated under FAK depletion. FAK overexpression, in contrast, increased radiation survival and paxillin, Akt1, and ERK1/2 phosphorylation. The degree of radiosensitization upon Akt1, ERK1/2, or MEK1 depletion or U0126 was superimposable to FAK knockdown. Combination knockdown conditions (ie, Akt1/FAK, MEK1/FAK, or U0126/FAK) failed to provide additional radiosensitization.
  
  
  CONCLUSIONS
  Our data provide further evidence for FAK as important determinant of radiation survival, which acts in the same signaling axis as Akt1 and ERK1/2. These data strongly support our hypothesis that FAK is a relevant molecular target for HNSCC radiotherapy.
authors.affiliation: OncoRay-National Center for Radiation Research in Oncology, Medical Faculty Carl Gustav Carus, Dresden University of Technology, Dresden, Germany.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Hehlgans
authors.forename: Iris
authors.initials: I
authors.lastname: Eke
authors.forename: Nils
authors.initials: N
authors.lastname: Cordes
mesh_terms: D002070:Butadienes / Q000494:pharmacology; D002294:Carcinoma, Squamous Cell / Q000378:metabolism / Q000532:radiotherapy*; D018929:Cell Culture Techniques / Q000379:methods; D045744:Cell Line, Tumor; D002470:Cell Survival; D051417:Focal Adhesion Kinase 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006258:Head and Neck Neoplasms / Q000378:metabolism / Q000532:radiotherapy*; D006801:Humans; D048728:MAP Kinase Kinase Kinase 1 / Q000378:metabolism; D048730:MAP Kinase Kinase Kinase 2 / Q000378:metabolism; D020935:MAP Kinase Signaling System; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D058990:Molecular Targeted Therapy / Q000379:methods*; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D051419:Paxillin / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011836:Radiation Tolerance / Q000502:physiology*; D014410:Tumor Stem Cell Assay / Q000379:methods
chemical_list: D002070:Butadienes; D009363:Neoplasm Proteins; D009570:Nitriles; D051419:Paxillin; C113580:U 0126; D051417:Focal Adhesion Kinase 1; D051057:Proto-Oncogene Proteins c-akt; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048728:MAP Kinase Kinase Kinase 1; D048730:MAP Kinase Kinase Kinase 2