Endothelin (ET) B receptor (ET_BR), which is overexpressed in human cutaneous melanomas, promotes tumorigenesis upon activation by ET-1 or ET-3, thus representing a potential novel therapeutic target. Hypoxia-inducible factor-1α (HIF-1α) is the transcriptional factor that conveys signaling elicited by hypoxia and growth factor receptors. Here, we investigated the interplay between ET axis and hypoxia in primary and metastatic melanoma cell lines. We report that under normoxic conditions, ET_BR activation by ET-1/ET-3 enhances vascular endothelial growth factor (VEGF) up-regulation, cyclooxygenase (COX)-1/COX-2 protein expression and COX-2 promoter activity, prostaglandin E₂ (PGE₂) production, and do so to a greater extent under hypoxia. Moreover, COX-1/COX-2 inhibitors block ET-induced PGE₂ and VEGF secretion, matrix metalloproteinase (MMP) activation, and cell invasion, indicating that both enzymes function as downstream mediators of ET-induced invasive properties. The ET_BR selective antagonist BQ788 or transfection with ET_BR small interfering RNA (siRNA) block the ET-mediated effects. ETs also increase HIF-1α expression under both normoxic and hypoxic conditions and its silencing by siRNA desensitizes COX-2 transcriptional activity, PGE₂ and VEGF production, and MMP activation in response to ET-3, implicating, for the first time, HIF-1α/COX as downstream targets of ET_BR signaling leading to invasiveness. In melanoma xenografts, specific ET_BR antagonist suppresses tumor growth, neovascularization, and invasiveness-related factors. Collectively, these results identify a new mechanism whereby ET-1/ET-3/ET_BR axis can promote and interact with the HIF-1α–dependent machinery to amplify the COX-mediated invasive behavior of melanoma. New therapeutic strategies using specific ET_BR antagonist could provide an improved approach to the treatment of melanoma by inhibiting tumor growth and progression. [Cancer Res 2007;67(4):1725–34]