EGF-receptor phosphorylation acid signaling are targeted by H2O2 redox stress

Inflammation of the respiratory tract is associated with the production cif reactive oxygen species, such as hydrogen peroxide (H2O2) and superoxide ( O-2(-)), which contribute extensively to lung injury in diseases of the res piratory tract. The mechanisms and target molecules of these oxidants are m ainly unknown but may involve modifications of growth-factor receptors. We have shown that H2O2 induces epidermal growth factor (EGF)-receptor tyrosin e phosphorylation in intact cells as well as in membranes of A549 lung epit helial cells. On the whole, total phosphorylation of the EGF receptor induc ed by H2O2 was lower than that induced by the Ligand EGF. Phosphorylation w as confined to tyrosine residues and was inhibited by addition of genistein , indicating that it was due to the activation of protein tyrosine kinase ( PTK). Phosphoamino acid analysis revealed that although the ligand, EGF, en hanced the phosphorylation of serine. threonine, and tyrosine residues, H2O 2 preferentially enhanced tyrosine phosphorylation of the EGF receptor. Ser ine and threonine phosphorylation did not occur, and the turnover rate of t he EGF receptor was slower after H2O2 exposure. Selective H2O2-mediatrd pho sphorylation of tyrosine residues on the EGF receptor was sufficient to act ivate phosphorylation of an SH2-group-bearing substrate. phospholipase C-ga mma (PLC-gamma). but did not increase mitogen-activated protein (MAP) kinas e activity. Moreover, H2O2 exposure decreased protein kinase C (PKC)-alpha activity by causing trans-location of PKC-alpha from the membrane to the cy toplasm. These studies provide novel insights into the capacity of a reacti ve oxidant, such as H2O2, to modulate EGF-receptor function and its downstr eam signaling. The H2O2-induced increase in tyrosine phosphorylation of the EGF receptor, and the receptor's slower rate of turnover and altered downs tream phosphorylation signals may represent a mechanism by which EGF-recept or signaling can be modulated during inflammatory processes, thereby affect ing cell proliferation and thus having implications in wound repair or tumo r formation.