In vitro study of normoxic epidermal growth factor receptor-induced hypoxia-inducible factor-1-alpha, vascular endothelial growth factor, and BNIP3 expression in head and neck squamous cell carcinoma cell lines: Implications for anti-epidermal growth factor receptor therapy.

We previously showed that activation of epidermal growth factor receptor (EGFR) induces hypoxia inducible factor-1α (HIF-1α) in head and neck squamous cell carcinoma (HNSCC) cells. In this study, we have furthered this by investigating the mechanism of HIF-1α activation by epidermal growth factor (EGF) and its association with the sensitivity to gefitinib. EGFR/HIF-1α signaling was tested by immunoblot, polymerase chain reaction (PCR), cell proliferation, and apoptosis assays. HIF-1α accumulated in cells overexpressing EGF and phosphorylated epidermal growth factor receptor (pEGFR), phosphatidylinositol-3-kinase (pPI3K), and mitogen-activated protein kinase (pMAPK). EGF-induced expression of HIF-1α and its targets, vascular endothelial growth factor (VEGF) and BNIP3, were blocked by gefitinib and PI3K-inhibitors and MAPK-inhibitors. HIF-1α-siRNAs abrogated EGF-induced BNIP3 but not VEGF expression. Gefitinib inhibited cell proliferation and induced apoptosis more strongly in cells with constitutively active EGFR/HIF-1α signaling than in cells lacking activation of these pathways. HIF-1α-siRNA treatment reduced sensitivity to gefitinib. The search for molecular predictors of sensitivity to gefitinib in HNSCC should be extended to the activation status of EGFR-downstream pathways, phosphorylated protein kinase B, pMAPK, and HIF-1α.