Runx1 down-regulates the activities of the Flk-1 promoter in BAEC. (A) The activity of luciferase reporter gene under the control of the -640 bp/+299 bp promoter fragment of mouse Flk-1 was measured in the presence of the indicated amounts (nanograms) of Runx1 expression vector (left panel). Note that luciferase activity was down-regulated in the presence of Runx1 in a dose-dependent manner, whereas luciferase activity driven by elongation factor (EF-1) promoter was not affected (right panel). (B) The repressive effect of Runx1 on the Flk-1 promoter was augmented in the presence of PEBP2β (left panel), whereas EF-1 promoter activity was not affected (right panel). (C) Putative Runx1-binding sites in the murine Flk-1 promoter and functional analysis of the promoter. (○) Putative Runx1-binding sites. (•) Binding sites mutated by PCR. (D) Activity of luciferase reporter under control of mutant Flk-1 promoters in BAECs. Results shown are representative of 3 independent experiments. RLU indicates relative light unit.