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MECHANISMS OF ZN-INDUCED SIGNAL INITIATION THROUGH THE EPIDERMAL GROWTH FACTOR RECEPTOR (EGFR)
Citation:
Samet, J M., L. Graves, AND W. Wu. MECHANISMS OF ZN-INDUCED SIGNAL INITIATION THROUGH THE EPIDERMAL GROWTH FACTOR RECEPTOR (EGFR). Presented at American Thoracic Society Meeting, Atlanta, GA, May 17-22, 2002.
Description:
MECHANISMS OF Zn-INDUCED SIGNAL INITIATION THROUGH THE EPIDERMAL GROWTH FACTOR RECEPTOR (EGFR)
James M. Samet*, Lee M. Graves? and Weidong Wu?. *Human Studies Division, NHEERL, ORD, Research Triangle Park, NC 27711, and ?Center for Environmental Medicine, University of North Carolina, Chapel Hill, NC 27599.
Zn is a ubiquitous component of ambient air particulate matter and an occupational toxicant. We have shown that Zn ions induce EGFR activation and signaling. To elucidate the mechanism involved in Zn-induced activation of this receptor kinase, we studied EGFR dimerization, phosphorylation and kinase activity in A431 cells treated with ZnSO4 and compared the effects to those induced by its ligand EGF. A431 extracts were incubated with 500 uM ZnSO4 or 200 ng/ml EGF for 30 min, followed by treatment with a cross-linking agent (BS3) and Western blotting. As expected, EGF induced pronounced dimerization of EGFR molecules. However, Zn treatment failed to induce detectable EGFR dimerization. Analyses of intact A431 cells treated in a similar manner confirmed that Zn does not induce dimerization of EGFR. Western blotting using phospho-specific antibodies showed that Zn induced phosphorylation of EGFR at tyrosines 845, 1068 and 1173, a pattern identical to that produced by EGF treatment. The EGFR kinase inhibitor PD153035 effectively ablated all phosphorylation induced by EGF but none caused by Zn treatment of A431 cells. Similarly, PD153035 abolished EGF-induced phosphorylation of the EGFR substrate cbl, while it had no effect on levels of phospho-cbl that resulted from Zn treatment. Together, these results confirm that Zn ions effectively activate EGFR and show that the mechanism includes EGFR phosphorylation but does not involve EGFR dimerization or EGFR kinase activation, suggesting that Zn induces a transactivation of EGFR in A431 cells. These findings may provide a mechanistic basis for the adverse effects of Zn inhalation. This abstract of a proposed presentation does not necessarily reflect EPA policy.