Interleukin 8 (IL-8) and vascular endothelial growth factor (VEGF) promote tumor angiogenesis, growth, and metastasis and are coexpressed by human head and neck squamous cell carcinomas (HNSCCs) and a variety of other cancers. The promoters of the IL-8 and VEGF genes contain different recognition sites for transcription factors nuclear factor (NF)-kappaB and activator protein-1 (AP-1), which we showed previously are coactivated in HNSCCs. NF-kappaB and AP-1 may be modulated by the inhibitor kappaB kinase (IKK) and mitogen-activated protein kinase (MAPK) signal pathways, but the contribution of these pathways to expression of IL-8 and VEGF and as potential targets for antiangiogenesis therapy in HNSCC is not known. In this study, we examined the effects of modulation of the MAPK and IKK pathways on expression of IL-8 and VEGF by UM-SCC-9 and UM-SCC-11B cell lines. Interruption of IKK-mediated activation of NF-kappaB by expression of an inhibitor kappaB alpha mutant (IkappaB alphaM) in UM-SCC-9 cells resulted in partial inhibition of expression of IL-8 but not VEGF. Analysis of possible alternative pathways for induction of these genes revealed activation of the MAPK extracellular signal-regulated kinase (ERK1/2) in cell lines UM-SCC-9 and UM-SCC-11B. Basal and tumor necrosis factor-alpha-inducible phosphorylation of ERK1/2 and secretion of IL-8 and VEGF could be specifically inhibited by a MEK inhibitor, U0126. Expression of IL-8 and VEGF in the cell lines was associated with coactivation of both NF-kappaB and AP-1, and U0126 inhibited both NF-kappaB and AP-1 reporter activity in UM-SCC-9 and UM-SCC-11B cells. The ERK pathway appears to contribute to expression of IL-8 and VEGF and transactivation of NF-kappaB as well as AP-1 in HNSCC. Combined inhibition of both MAPK and IKK pathways may be needed for suppression of the signal transduction mechanism(s) regulating VEGF and IL-8 secretion and angiogenesis by human HNSCC.