title: Ionizing radiation stimulates existing signal transduction pathways involving the activation of epidermal growth factor receptor and ERBB-3, and changes of intracellular calcium in A431 human squamous carcinoma cells.
abstract: Previous studies demonstrated that ionizing radiation activates the epidermal growth factor receptor (EGFR), as measured by Tyr autophosphorylation, and induces transient increases in cytosolic free [Ca2+], [Ca2+]f. The mechanistic linkage between these events has been investigated in A431 squamous carcinoma cells with the EGFR Tyr kinase inhibitor, AG1478. EGFR autophosphorylation induced by radiation at doses of 0.5-5 Gy or EGF concentrations of 1-10 ng/ml is inhibited by >75% at 100 nM AG1478. Activation of EGFR enhances IP3 production as a result of phospholipase C (PLC) activation. At the doses used, radiation stimulates Tyr phosphorylation of both, PLCgamma and erbB-3, and also mediates the association between erbB-3 and PLCgamma not previously described. The increased erbB-3 Tyr phosphorylation is to a significant extent due to transactivation by EGFR as >70% of radiation- and EGF-induced erbB-3 Tyr phosphorylation is inhibited by AG 1478. The radiation-induced changes in [Ca2+]f are dependent upon EGFR, erbB-3 and PLCgamma activation since radiation stimulated IP3 formation and Ca2+ oscillations are inhibited by AG1478, the PLCgamma inhibitor U73122 or neutralizing antibody against an extracellular epitope of erbB-3. These results demonstrate that radiation induces qualitatively and quantitatively similar responses to EGF in stimulation of the plasma membrane-associated receptor Tyr kinases and immediate downstream effectors, such as PLCgamma and Ca2+.
authors.affiliation: Department of Radiation Oncology, Medical College of Virginia/Virginia Commonwealth University, Richmond 23298-0058, USA.
authors.forename: D G
authors.initials: DG
authors.lastname: Todd
authors.forename: R B
authors.initials: RB
authors.lastname: Mikkelsen
authors.forename: W K
authors.initials: WK
authors.lastname: Rorrer
authors.forename: K
authors.initials: K
authors.lastname: Valerie
authors.forename: R K
authors.initials: RK
authors.lastname: Schmidt-Ullrich
mesh_terms: D002118:Calcium / Q000378:metabolism*; D002294:Carcinoma, Squamous Cell / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism*; D004963:Estrenes / Q000494:pharmacology; D006801:Humans; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010766:Phosphorylation; D011760:Pyrrolidinones / Q000494:pharmacology; D011799:Quinazolines; D020893:Receptor, ErbB-3 / Q000378:metabolism*; D015398:Signal Transduction / Q000528:radiation effects*; D014407:Tumor Cells, Cultured; D020032:Tyrphostins / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D004963:Estrenes; D010726:Phosphodiesterase Inhibitors; D011760:Pyrrolidinones; D011799:Quinazolines; D020032:Tyrphostins; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; C101044:RTKI cpd; D066246:ErbB Receptors; D020893:Receptor, ErbB-3; D002118:Calcium