Structure and function of HIFdn in vitro. (A) Domain structure of HIF-2α and HIFdn. (B-D) Luciferase reporter gene assays. HEK293 cells were transfected with VEGF promoter-luc (B) or Flk1 promoter-luc (C) reporter constructs. HUE cells were transfected with KDR promoter-luc reporter gene (D). Expression of HIFdn reduced the basal activity of these promoters and inhibited the stimulatory effects of HIF-1α or HIF-2α, respectively. (E) Overexpression of HIF-2α or HIFdn in HUE cells and immunofluorescence staining against the FLAG epitope revealed nuclear localization of HIF-2α, whereas HIFdn was detected in the cytoplasm. Bar indicates 25 μm. #P < .05; *P < .03; **P < .005, unpaired 2-tailed t test.