CD39 is induced by hypoxia. (A) Vascular endothelia (HMEC-1) were exposed to hypoxia (2% oxygen) over indicated time periods, and CD39 transcript levels were determined by real-time RT-PCR. β-actin was used to control for starting template (n = 3, *P < .05). CD39 luciferase reporter assays. (B) Orientation of the human CD39 promoter, the location of Sp1 and GATA-3–binding sites in the human and mouse CD39 promoter, the location of the TSS, and the location of truncations used for transient transfections (see “CD39 promoter assays” for additional details). (C) Confluent HMEC-1 monolayers were transiently transfected with plasmids expressing sequence corresponding to full-length CD39 (−1417 to +83 bp) or the following 5′ truncations: CD39-898 (−815 to +83 bp), CD39-300 (−217 to +83 bp), CD39-150 (−67 to +83 bp), and CD39-122 (−39 to +83 bp) upstream from the luc reporter gene. Also shown is full-length mdr-1 promoter as a positive control. Twelve hours later, cells were exposed to hypoxia or normoxia for 48 hours and assessed for luciferase activity. All transfections were normalized to cotransfected Renilla promoter. Data are mean plus or minus SEM from 3 separate experiments.