MAPK-mediated uPAR expression is regulated by DEP-1 phosphatase activity. (A) HEK 293 cells and (B) HUVECs were transfected for reporter gene analysis (Elk-1 activity) with plasmids overexpressing either wild-type DEP-1 or its mutated forms. Cells were harvested after 24 hours and analyzed for luciferase activity. Data are mean ± SEM. *P < .05. **P < .01. Only catalytically active DEP-1 was able to reduce Elk-1 activity. (C) Immunocytofluorimetric detections of cell surface (nonpermeabilized cells; gray) and total (permeabilized cells; black) uPAR in HUVECs overexpressing different DEP-1 mutants and either EGFP or EGFP-ERK1 gated for EGFP fluorescence. *P < .05. Data are mean ± SEM. Values calculated as percentage over EGFP control. Only catalytically active mutants of DEP-1 were able to decrease uPAR expression. This effect could be rescued by ERK1 coexpression. DEP-1 indicates wild-type; C → S, inactivated tyrosine phosphatase resulting from cysteine to serine mutation in the catalytic domain; DeltaCyto, deletion of the intracellular domain (including phosphatase domain); and Myr, deletion of the extracellular domain).