Targeting FAK radiosensitizes 3-dimensional grown human HNSCC cells through reduced Akt1 and MEK1/2 signaling

Int J Radiat Oncol Biol Phys. 2012 Aug 1;83(5):e669-76. doi: 10.1016/j.ijrobp.2012.01.065. Epub 2012 Apr 6.


Purpose: 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 and materials: 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Butadienes / pharmacology
  • Carcinoma, Squamous Cell / metabolism
  • Carcinoma, Squamous Cell / radiotherapy*
  • Cell Culture Techniques / methods
  • Cell Line, Tumor
  • Cell Survival
  • Focal Adhesion Kinase 1 / antagonists & inhibitors*
  • Focal Adhesion Kinase 1 / metabolism
  • Head and Neck Neoplasms / metabolism
  • Head and Neck Neoplasms / radiotherapy*
  • Humans
  • MAP Kinase Kinase Kinase 1 / metabolism
  • MAP Kinase Kinase Kinase 2 / metabolism
  • MAP Kinase Signaling System
  • Mitogen-Activated Protein Kinase 1 / metabolism
  • Mitogen-Activated Protein Kinase 3 / metabolism
  • Molecular Targeted Therapy / methods*
  • Neoplasm Proteins / antagonists & inhibitors*
  • Neoplasm Proteins / metabolism
  • Nitriles / pharmacology
  • Paxillin / metabolism
  • Phosphorylation
  • Proto-Oncogene Proteins c-akt / metabolism
  • Radiation Tolerance / physiology*
  • Tumor Stem Cell Assay / methods


  • Butadienes
  • Neoplasm Proteins
  • Nitriles
  • Paxillin
  • U 0126
  • Focal Adhesion Kinase 1
  • Proto-Oncogene Proteins c-akt
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3
  • MAP Kinase Kinase Kinase 1
  • MAP Kinase Kinase Kinase 2