Reducing CD151 expression augments MT1-MMP–dependent MMP2 activation. (A) Western blot analysis of the expression of MT1-MMP and CD151 in total lysates of HUVECs transfected with negative oligonucleotide or with siRNA specific for CD9 or CD151. Vimentin is shown as a loading control. (B) Flow cytometric analysis of the membrane expression of MT1-MMP in HUVECs transfected with (left) CD9 or (right) CD151 siRNA (thick lines). (Toppanels) Thin lines show MT1-MMP expression in cells transfected with negative control oligonucleotide. Dotted lines correspond to the negative control X63. (Bottom panels) Flow cytometry charts of tetraspanin expression in siRNA transfected cells. Gray-filled profiles correspond to negative oligonucleotide-transfected cells; dotted lines correspond to oligo a and thin lines to oligo b, for both CD9 (left) and CD151 (right) interfered cells. (C) Fibrinogen zymography showing direct MT1-MMP protease activity in total lysates of HUVECs transfected with negative control or CD151-specific oligonucleotides. Numbers below the gel show the quantification of the fibrinolytic activity of MT1-MMP in the experiment shown. The chart shows the mean fibrinolytic activity of MT1-MMP normalized with respect to cells transfected with negative control oligonucleotide (± SD; n = 3). *P < .02 in Student t test. (D) Gelatin zymography of culture supernatants from HUVECs transfected with 2 different target siRNA sequences for CD9 or CD151. Numbers show the quantification of the gelatinolytic activity of mature MMP2 in the experiment shown. The chart shows the mean gelatinolytic activity of mature MMP2 normalized with respect to cells transfected with negative control oligonucleotide (± SD; n = 8 for CD151 siRNAa, n = 2 for CD151 siRNAb and CD9 siRNAs a and b). *P < .02 in a 1-way analysis of variance with respect to negative control oligonucleotide with Dunnett comparison test.