Pharmacological inhibition of EGFR tyrosine kinase affects ILK-mediated cellular radiosensitization in vitro.
OBJECTIVE
Integrin-linked kinase (ILK) mediates signals from beta integrins and links integrins to epidermal growth factor receptor (EGFR). Previous studies have identified an antisurvival effect of ILK in irradiated cells. The aim of this study was to evaluate the role of EGFR tyrosine kinase (tk) activity for ILK-mediated radiosensitization.


METHODS
Human FaDu squamous cell carcinoma (SCC) cells stably transfected with hyperactive ILK (ILK-hk) and ILK(fl/fl) and ILK(-/-) mouse fibroblasts were treated with the pharmacological EGFR-tk inhibitor BIBX1382BS without or in combination with single doses of X-rays. Clonogenic radiation survival, protein expression and phosphorylation (EGFR, v-akt murine thymoma viral oncogene homolog 1 (Akt), p42/44 mitogen-activated protein kinase), DNA-double strand break (DSB) repair measured by gammaH2AX foci, cell morphology and cell cycle distribution were examined.


RESULTS
Expression of ILK-hk or ILK(fl/fl) status resulted in significant radiosensitization relative to vector controls or ILK(-/-). Following BIBX1382BS, clonogenic survival of normal fibroblasts and vector controls remained unaffected while ILK-hk-related radiosensitization was significantly diminished. In contrast to BIBX1382BS, which did not affect DNA-DSB repair, ILK-hk-mediated radiosensitization was associated with reduced DNA-DSB repair. At 10 days after BIBX1382BS treatment, FaDu transfectants, in contrast to fibroblasts, showed reduced cell size, accumulation of G1 phase cells and reduced Akt-serine(S)473 phosphorylation.


CONCLUSIONS
Our findings confirm ILK as a cell type-independent antisurvival factor in irradiated cells, which actions in terms of radiosensitization critically depend on proper EGFR-tk activity.
Eke
Iris
I
OncoRay - Center for Radiation Research in Oncology, Medical Faculty Carl Gustav Carus, Dresden University of Technology, Dresden, Germany.
Sandfort
Veit
V
Storch
Katja
K
Baumann
Michael
M
Röper
Barbara
B
Cordes
Nils
N
D000818:Animals; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000502:physiology / Q000528:radiation effects; D002478:Cells, Cultured; D003114:Colony-Forming Units Assay; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D066246:ErbB Receptors / Q000037:antagonists & inhibitors*; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D018345:Mice, Knockout; D009930:Organic Chemicals / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D011836:Radiation Tolerance / Q000187:drug effects / Q000502:physiology*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D000099200:Scaffold Protein ILK
D066246:ErbB Receptors; D009930:Organic Chemicals; D047428:Protein Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011994:Recombinant Proteins; D000099200:Scaffold Protein ILK; C423062:BIBX 1382BS; C512478:EGFR protein, human