ACTIVATION OF MITOGEN-ACTIVATED PROTEIN KINASE EXTRACELLULAR SIGNAL-RELATED KINASE IN HEAD AND NECK SQUAMOUS CELL CARCINOMAS AFTER IRRADIATION AS PART OF A RESCUE MECHANISM

Background. Irradiation plays a pivotal role in head and neck squamous cell carcinoma (HNSCC) treatment. However, especially recurrent tumors frequently show increased radioresistance. We analyzed irradiation-stimulated mitogen-activated protein kinase (MAPK) signaling pathways to define cellular rescue mechanisms. Methods. Irradiated HNSCC cells were screened for MAPK activation and results were confirmed and refined by functional analyses. Extracellular signal-regulated kinase (ERK) inhibitor U0126 application enabled us to specify postradiogenic cellular responses. Vascular endothelial growth factor (VEGF) levels were analyzed additionally. Results. We observed a pronounced and time- dependent ERK stimulation. Pathway inhibition resulted in decreased radioresistance. Likewise, we found a decrease of VEGF release after inhibitor treatment. ERK activation was confirmed in xenotransplants showing elevated postradiogenic phospho-ERK (pERK) and VEGF levels. Conclusions. Our data give evidence for induction of ERK and successive VEGF release in HNSCC during radiotherapy, which might be partially explained by autoregulated cytoprotection maintained by pERK and potentially VEGF. In conclusion, targeting the ERK-VEGF axis might enhance the efficiency of radiotherapy. (C) 2010 Wiley Periodicals, Inc. Head Neck 33: 1448-1457, 2011