MT1-MMP collagenolytic activity is regulated through association with tetraspanin CD151 in primary endothelial cells

MT1-MMP plays a key role in endothelial function, as underscored by the angiogenic defects found in MT1-MMP deficient mice. We have studied the molecular interactions that underlie the functional regulation of MT1-MMP. At lateral endothelial cell junctions, MT1-MMP colocalizes with tetraspanin CD151 (Tspan 24) and its associated partner alpha3beta1 integrin. Biochemical and FRET analyses show that MT1-MMP, through its hemopexin domain, associates tightly with CD151, thus forming alpha3beta1 integrin/CD151/MT1-MMP ternary complexes. siRNA knockdown of HUVEC CD151 expression enhanced MT1-MMP-mediated activation of MMP2, and the same activation was seen in ex vivo lung endothelial cells isolated from CD151-deficient mice. However, analysis of collagen degradation in these experimental models revealed a diminished MT1-MMP enzymatic activity in confined areas around the cell periphery. CD151 knockdown affected both MT1-MMP subcellular localization and its inclusion into detergent-resistant membrane domains, and prevented biochemical association of the metalloproteinase with the integrin alpha3beta1. These data provide evidence for a novel regulatory role of tetraspanin microdomains on the collagenolytic activity of MT1-MMP and indicate that CD151 is a key regulator of MT1-MMP in endothelial homeostasis.