Structure and function of a vimentin-associated matrix adhesion in endothelial cells

The alpha4 laminin subunit is a component of endothelial cell basement memb ranes. An antibody (2A3) against the alpha4 laminin G domain stains focal c ontact-like structures in transformed and primary microvascular endothelial cells (TrHBMECs and HMVECs, respectively), provided the latter cells are a ctivated with growth factors. The 2A3 antibody staining colocalizes with th at generated by alphav and beta3 integrin antibodies and, consistent with t his localization, TrHBMECs and HMVECs adhere to the alpha4 laminin subunit G domain in an alphav beta3-integrin-dependent manner. The alphav beta3 int egrin/2A3 antibody positively stained focal contacts are recognized by vinc ulin antibodies as well as by antibodies against plectin. Unusually, viment in intermediate filaments, in addition to microfilament bundles, interact w ith many of the alphav beta3 integrin-positive focal contacts. We have inve stigated the function of alpha4-laminin and alphav beta3-integrin, which ar e at the core of these focal contacts, in cultured endothelial cells. Antib odies against these proteins inhibit branching morphogenesis of TrHBMECs an d HMVECs in vitro, as well as their ability to repopulate in vitro wounds. Thus, we have characterized an endothelial cell matrix adhesion, which show s complex cytoskeletal interactions and whose assembly is regulated by grow th factors. Our data indicate that this adhesion structure may play a role in angiogenesis.