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(PP268) Requirement of Tyr992 and Tyr1173 in phosphorylation of the epidermal growth factor receptor by ionizing radiation and modulation by SHP2.
Sturla, Lisa-Marie*,1, Amorino, George1, Alexander, Michael1, Mikkelsen, Ross1, Valerie, Kristoffer1, Schmidt-Ullrich, Rupert1, 1 Radiation Oncology, Richmond, VA, USA
ABSTRACT- The epidermal growth factor receptor (EGFR) is activated by ionizing radiation (IR) in many human carcinomas, mediating a cytoprotective response and subsequent radio-resistance. The underlying molecular mechanisms remain to be understood, and we propose here a specific role for the Tyr992 residue of EGFR and examine its regulation by the phosphatase, SHP2. The fold increase in phosphorylation of Tyr992 in response to IR is twice that seen with ligand (EGF) binding. Mutation of Tyr992 blocked completely IR-induced EGFR phosphorylation and reduced activation of the downstream signaling molecule, PLC. IR has previously been demonstrated to inhibit activity of protein tyrosine phosphatases (PTP). Following PTP inhibition by sodium vanadate both EGFR expressing CHO and A431 exhibited up to an 8-fold increase in the basal level of Tyr992 phosphorylation, significantly higher than that seen with Tyr1173, Tyr1068 and total EGFR Tyr. CHO cells expressing a SHP2 mutant also demonstrated up to an 8-fold increase in the basal level of Tyr992 phosphorylation. In this study we show the unique association of SHP2 with EGFR in response to IR, with up to a 2.5-fold increase in the direct association of endogenous SHP2 with EGFRwt in response to 2Gy of IR in both CHO and A431 cells. Mutation of Tyr992 abolished this response. In conclusion we have identified several differentially activated Tyr residues, one of which is not only more sensitive to activation by IR, translating into differential activation of downstream signaling, but uniquely modulated by the phosphatase SHP2.
Key words: ionizing radiation, phosphatase, epidermal growth factor receptor
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