Mitogenic effects of gastrin-releasing peptide in head and neck squamous cancer cells are mediated by activation of the epidermal growth factor receptor

Abstract

Head and neck squamous cell carcinomas (HNSCC) are characterized by upregulation of the epidermal growth factor receptor (EGFR), where EGFR serves as a potential therapeutic target. We previously reported that a gastrin-releasing peptide/gastrin-releasing peptide receptor (GRP/GRPR) autocrine growth pathway is activated early in HNSCC carcinogenesis. In the present study, we examined the mechanism of EGFR activation by GRP/GRPR in HNSCC proliferation. In HNSCC cells that express elevated levels of both GRPR and EGFR, we found that GRP induced rapid phosphorylation of EGFR as well as p44/42-MAPK activation. Using several EGFR-specific tyrosine kinase inhibitors and cells derived from EGFR knockout mice, we demonstrated that GRPinduced p44/42-MAPK activation was dependent upon EGFR activation. Further investigation demonstrated that cleavage of transforming growth factor-alpha (TGF-a) by matrix metalloproteinases mediated GRP-induced MAPK activation. In addition, HNSCC proliferation stimulated by GRP was eliminated upon specific inhibition of EGFR or MEK, and GRP failed to stimulate proliferation in EGFR-deficient cells. These results imply that the mitogenic effects of GRP in HNSCC are mediated by extracellular release of TGF-a and require the activation of an EGFR-dependent MEK/MAPK-dependent pathway.

GPCRs and cancer

“…The four receptors for the Gastrin-releasing peptide (GrP) were shown to be able to transactivate EGFR in lung, head and neck squamous tumor cells [45,46] . In addition, ligand-stimulation of GrP receptors contributed to the growth of several malignancies through the activation of diverse phospholipases and protein kinases [47] .…”

Phosphorylation of TNF-α converting enzyme by gastrin-releasing peptide induces amphiregulin release and EGF receptor activation

“…We previously reported that Src family kinases regulate gastrinreleasing peptide (GRP)-induced EGFR proligand cleavage leading to downstream EGFR and MAPK activation in SCCHN, which contributes to cell proliferation and invasion (15,27). In addition, blockade of endogenous GRP by using the 2A11 antibody decreased SCCHN cell proliferation and tumor growth in vivo (28).…”

“…Our prior studies in SCCHN demonstrated that amphiregulin and TGF-␣, but not heparin-binding-EGF or EGF, are released after treatment with GRP (27). To determine the role of TACE in GRP-mediated EGFR ligand release, we performed an amphiregulin ELISA after GRP stimulation in cell medium.…”

Gastrin-releasing peptide (GRP) induces angiogenesis and the specific GRP blocker 77427 inhibits tumor growth in vitro and in vivo

“…In addition, GRP plays a role as an autocrine growth factor for cancer cells of different origins (Kim et al, 2002;Lango et al, 2002), probably mediated through activation of the epidermal growth factor receptor and MAPK (Lui et al, 2003). Inhibitors of GRP have shown promising antitumor effects in animal models (Kiaris et al, 1999;Moody et al, 2003a, b;Nock et al, 2005) and in the clinic (Chaudhry et al, 1999).…”