Mechanisms of Zn(2+)-induced signal initiation through the epidermal growth factor receptor

Zn(2+) is a ubiquitous ambient air contaminant that is found as a constituent of airborne particulate matter (PM). Previous studies have associated Zn(2+) levels in PM with health effects in exposed populations and have shown proinflammatory properties of Zn(2+) exposure in vivo and in vitro. In the present study, we studied the mechanisms of epidermal growth factor receptor (EGFR) dimerization, phosphorylation, and kinase activity in A431 cells treated with Zn(2+). EGF, but not Zn(2+), induced dimerization of EGFR in A431 cells and membrane extracts. Like EGF, Zn(2+) induced phosphorylation of EGFR at tyrosines 845, 1068, and 1173. However, unlike EGF, Zn(2+) failed to induce detectable dimerization of EGFR. The EGFR kinase inhibitor PD153035 ablated all phosphorylation induced by EGF but none caused by Zn(2+). PD153035 abolished EGF-induced phosphorylation of the EGFR substrate Cbl, but had no effect on levels of phospho-Cbl caused by Zn(2+). Inhibition of EGFR kinase activity did, however, blunt Zn(2+)-induced phosphorylation of ERK. Exposure to Zn(2+), but not EGF, induced phosphorylation of the activating site of c-Src (tyrosine 416), and Zn(2+)-induced phosphorylation of EGFR at tyrosines 845 and 1068 was blocked by the c-Src kinase activity inhibitor PP2. In summary, Zn(2+) ions induce EGFR phosphorylation in a manner dependent on c-Src but not on EGFR dimerization or EGFR kinase activation, suggesting that Zn(2+) induces EGFR transactivation by c-Src.