G-protein-coupled-receptors (GPCRs) have been reported to transactivate epidermal growth factor receptor (EGFR) in a variety of cell lines. We previously reported a gastrin-releasing peptide/gastrin-releasing peptide receptor (GRP/GRPR) aurocrine regulatory pathway in squamous cell carcinoma of head and neck (SCCHN), where GRP stimulates EGFR and MAPK activation leading to SCCHN proliferation and invasion. Further investigation demonstrated that Src family kinases contribute to GRP- induced EGFR phosphorylation by facilitating cleavage of EGFR pro-ligands. The present study was designed to investigate the mechanism of GRP-induced EGFR activation and elucidate the specific metalloproteinases involved in GRP-induced EGFR ligand cleavage. Using two different SCCHN cell lines, we found that GRP-induced EGFR and MAPK activation was abrogated upon knockdown of TNF-α converting enzyme (TACE) expression by siRNA. In addition, GRP failed to induce EGFR ligand release in TACE siRNA transfected cells. Further investigation demonstrated that GRP stimulated TACE activity, which was mediated by Src family kinases, specifically c-Src. Using pharmacological inhibitors and siRNA, PI3 kinase was shown to serve as an intermediate molecule between c-Src and TACE, thereby mediating GRP-induced EGFR and MAPK activation. These results suggest that transactivation of EGFR by GRP in SCCHN involves a complex consisting of TACE, c-Src and PI3 kinase, which mediates cleavage of EGFR proligands resulting in cell proliferation and invasion.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]