Silencing CD151 expression in HUVECs alters MT1-MMP subcellular localization and its association to α3β1 integrin. (A) HUVECs transfected with negative control oligonucleotide or with CD9- or CD151-specific siRNA were plated at confluence onto collagen I–coated coverslips and stained with anti–MT1-MMP mAb. (B) HUVECs transfected with the negative control oligonucleotide or CD151-specific siRNA were lysed in 0.5% Triton X-100 and fractioned on a linear sucrose gradient (40%-30%-5%). Fractions were recovered sequentially from the top of the gradient and probed by Western blot with antibodies to transferrin receptor, MT1-MMP, CD151, caveolin, and CD59. (C) HUVEC monolayers, transfected with negative control oligonucleotide or with CD151-specific siRNA, were lysed in buffer containing 1% Triton X-100. Samples were immunoprecipitated with anti–MT1-MMP (LEM-2/63) and anti-α3 integrin (VJ1/6) mAbs. Immunoprecipitates were analyzed by Western blot against α3 integrin and MT1-MMP. A sample of total lysate was probed for CD151.