Journal
AMERICAN JOURNAL OF RESPIRATORY CELL AND MOLECULAR BIOLOGY
Volume 30, Issue 4, Pages 540-547Publisher
AMER THORACIC SOC
DOI: 10.1165/rcmb.2003-0233OC
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We have previously shown that exposure to zinc ions can activate epidermal growth factor (EGF) receptor (EGFR) signaling in murine fibroblasts and A431 cells through a mechanism involving Src kinase. While studying the effects of zinc ions in normal human bronchial epithelial cell, we uncovered evidence for an additional mechanism of Zn2+-induced EGFR activation. Exposure to Zn2+ induced phosphorylation of EGFR at tyrosine 1068, a major autophosphorylation site, in a dose- and time-dependent fashion. This effect of Zn2+ on EGFR was significantly blocked with an antibody against the ligand-binding domain of the receptor. Neutralizing antibodies against EGFR ligands revealed the involvement of heparin-binding EGF (HB-EGF) in Zn2+-induced EGFR phosphorylation. This observation was further supported by immunoblots showing elevated levels of HBEGF released by Zn2+-exposed cells. Zymography showed the existence of matrix metalloproteinase-3 in Zn2+-challenged cells. Incubation with a specific matrix metalloproteinase-3 inhibitor suppressed Zn2+-induced EGFR phosphorylation as well as HB-EGF release. Therefore, these data support an autocrine or paracrine mechanism whereby Zn2+ induces EGFR phosphorylation through the extracellular release of EGFR ligands, which may be mediated by metalloproteinases.
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