Abstract
We previously reported that expression of angiogenesis factors interleukin‐8 (IL‐8) and vascular endothelial growth factor (VEGF) is promoted by coactivation of transcription factors nuclear factor‐kappaB (NF‐κB) and activator protein‐1 (AP‐1) by interleukin‐1α in human head and neck squamous cell carcinomas (HNSCC). However, expression of IL‐1 receptor antagonist incompletely blocked reporter gene activity and cytokine expression, suggesting that other upstream signals may contribute to activation. Overexpression and autocrine activation of epidermal growth factor receptor (EGFR) is detected in 90% of HNSCC, and EGFR inhibitors have been reported to inhibit IL‐8 and VEGF expression, but the intermediary signal pathways and transcription factors by which EGFR modulates proangiogenic factors is unknown. EGFR can activate the phosphotidylinositol‐3 kinase (PI3K) and mitogen‐activated/extracellular signal‐regulated kinase (MEK) pathways, which can potentially modulate activation of NF‐κB and AP‐1, respectively. In our study, we examined the effect of EGF and antagonists of EGFR, PI3K and MEK on NF‐κB and AP‐1 activation and IL‐8 and VEGF expression in HNSCC cell lines UM‐SCC‐9 and 11B in which EGFR is overexpressed and activated. Recombinant EGF induced EGFR phosphorylation, activation of NF‐κB and AP‐1 reporter genes and IL‐8 and VEGF expression, indicating that EGFR can mediate coactivation of both transcription factors and cytokine genes in HNSCC. EGFR antagonist PD153035 and anti‐EGFR antibody C225 completely inhibited EGF‐induced reporter activity and cytokine expression, but only partially inhibited constitutive activity. MEK inhibitor U0126 preferentially blocked AP‐1 activity and expression of both IL‐8 and VEGF, while PI3K inhibitor LY‐294002 or a dominant negative inhibitor‐κB preferentially blocked NF‐κB activation and expression of IL‐8 but not VEGF. EGFR, PI3K and MEK antagonists inhibited growth of HNSCC. We conclude that antagonists of EGFR, PI3K and MEK signal pathways have inhibitory activity against EGFR‐induced NF‐κB and AP‐1 activation, IL‐8 and VEGF expression and growth by HNSCC. Published 2002 Wiley‐Liss, Inc.