Epidermal growth factor (EGF)-induced generation of hydrogen peroxide. Role in EGF receptor-mediated tyrosine phosphorylation

Recent evidence indicates that reactive oxygen species (RES) may function as intracellular messengers in receptor signaling pathways. The possible role of ROS in epidermal growth factor (EGF) signaling was therefore investigated. Stimulation of A431 human epidermoid carcinoma cells with EGF resulted in a transient increase in the intracellular concentration of ROS, measured with the oxidation-sensitive fluorescent probe 2',7'- dichlorofluorescin diacetate and laser-scanning confocal microscopy. The predominant Res produced appeared to be H₂O₂, because the EGF-induced increase in fluorescence was completely abolished by incorporation of catalase into the cells by electroporation. The elimination of H₂O₂ by catalase also inhibited the EGF-induced tyrosine phosphorylation of various cellular proteins including the EGF receptor and phospholipase C-γ1. The dependence of H₂O₂ production on the intrinsic tyrosine kinase activity of the EGF receptor and the autophosphorylation sites located in its COOH- terminal tall was investigated. EGF failed to induce H₂O₂ generation in cells expressing a kinase-inactive EGF receptor. However, normal H₂O₂ generation was observed in cells expressing a mutant receptor from which the 126 COOH-terminal amine acids had been deleted to remove four (out of the total of five) autophosphorylation sites. These results suggest that EGF- induced H₂O₂ formation requires the kinase activity but probably not the autophosphorylation sites of the EGF receptor and that inhibition of protein tyrosine phosphatase activity by H₂O₂ may be required for EGF-induced protein tyrosine phosphorylation to be manifested.