EDN1 and melanoma: Because hydroxylation at the 4-position of Pro402 and Pro564 within the ODDD of HIF-1α is responsible for its degradation under normoxia [10], we further investigated the role of ET-1 on the stability of HIF-1α by transfecting melanoma cells with a reporter plasmid expressing HIF-1α ODDD fused with luciferase (CMV-Luc-ODDD).