PGE₂ promotes membrane clustering of MT1-MMP. (A) HUVECs treated over a time course with 1 μM PGE₂, or with 100 μM DETA-NONOate (DETA) as a positive control, were immunostained with anti–MT1-MMP antibody. Top panel: the histogram shows the means plus or minus SD from 3 independent experiments of the number per cell of lamellae and membrane clusters containing MT-1-MMP. The data are presented as fold induction above control conditions (C). *P < .05 vs control; **P < .01 vs control. Bottom panel: micrographs showing representative fields of untreated control cells or cells treated with either 1 μM PGE₂ for 5 minutes or 100 μM DETA-NONOate (DETA). (B) HUVECs transfected with MT1-MMP-GFP were either left untreated or incubated with 1 μM PGE₂ for the times indicated. Left panel: the histogram shows the means plus or minus SD from 2 independent experiments of the number per cell of lamellae and membrane clusters containing MT-1-MMP-GFP. The data are shown as fold induction over control conditions. (C). **P < .01 vs control; #P < .001 vs control. Right panel: micrographs showing representative fields of control cells or cells treated with 1 μM PGE₂ for 15 minutes. Arrows indicate MT1-MMP membrane clusters, and arrowheads denote MT1-MMP–containing lamellae.