EPO stimulation of the CIS promoter-luciferase reporter gene in L-ER cells. Schematic representations of each reporter construct are shown in the lower portion (A-D). Boxes indicate MGF boxes, and their disruptions are shown in B, C, and D. The plasmids (10 μg) were introduced into wild-type L cells (open bars) or transformants expressing the EPO receptor (closed bars) using a calcium phosphate method for 12 hours. After transfection, cells were incubated in the presence or absence of EPO for 24 hours and luciferase activity was measured. Luciferase activity (arbitrary units) from triplicate experiments is shown.