Endoglin controls cell migration and composition of focal adhesions: function of the cytosolic domain

Mutations in the human endoglin gene result in hereditary hemorrhagic telangiectasia type 1, a vascular disorder characterized by multisystemic vascular dysplasia, arteriovenous malformations, and focal dilatation of postcapillary venules. Previous studies have implicated endoglin in the inhibition of cell migration in vivo and in vitro. In the course of studies to address the relationship of the conserved cytosolic domain to endoglin function, we identified zyxin, a LIM domain protein that is concentrated at focal adhesions, as an interactor with endoglin in human umbilical vein vascular endothelial cells. This interaction is localized within the 47-amino acid carboxyl-terminal cytosolic domain of endoglin, and maps within zyxin residues 326-572. The endoglin-zyxin interaction was found to be largely mediated by the third LIM domain of zyxin, and is specific for endoglin because the homologous cytosolic domain of the transforming growth factor-beta type III receptor, betaglycan, fails to interact with zyxin. Expression of endoglin is associated with reduction of zyxin, as well as its interacting proteins p130(cas) and CrkII, from a focal adhesion protein fraction, and this reduction is correlated with inhibition of cell migration. We also show that endoglin-dependent: (i) inhibition of cell migration, (ii) reduction of focal adhesion-associated p130(cas)/CrkII protein levels, (iii) tyrosine phosphorylation of p130(cas), and (iv) focal adhesion-associated endoglin levels are mediated by the cytosolic domain of endoglin. These results suggest a novel mechanism of endoglin function involving its interaction with LIM domain-containing proteins, and associated adapter proteins, affecting sites of focal adhesion.