Cellular mechanisms for the regulation of VE-cadherin endocytosis

Cadherins maintain adult tissue architecture and direct morphogenic events through homotypic cellular interactions and via signaling pathways that direct cell growth and migration. In the vascular endothelium, the dynamic regulation of cadherin-based cell adhesion is crucial for vascular development. Vascular endothelial (VE)-cadherin is the central adhesion molecule in endothelial adherens junctions and its regulation is crucial for vascular function. p120-catenin (p120) binds to cadherins and regulates cadherin levels by preventing cadherin endocytosis and degradation. In vivo studies have demonstrated that p120 is required for vascular development, and mice lacking p120 in endothelial cells exhibit severe defects in vascular patterning, barrier function, and proliferation. These phenotypes are at least partially dependent on the loss of VE-cadherin observed in vessels lacking p120.;The primary goal of the research described in this dissertation is to understand the mechanism by which p120 regulates VE-cadherin endocytosis. Studies shown here have demonstrated that p120 prevents VE-cadherin from entering a clathrin-mediated endocytic pathway through a mechanism that requires binding of p120 to the cadherin cytoplasmic tail. We demonstrate that p120 prevents VE-cadherin internalization independently of its role in regulating RhoGTPase activity. Rather, we present evidence that p120 stabilizes VE-cadherin at the plasma membrane by competing with the clathrin adaptor AP-2 for interactions with the VE-cadherin juxtamembrane domain.;We have identified a key role for the clathrin adaptor complex AP-2 in regulating VE-cadherin endocytosis. AP-2 interacts with the VE-cadherin cytoplasmic tail, and is required for VE-cadherin endocytosis. Mutation of a tyrosine motif in the VE-cadherin juxtamembrane domain compromises VE-cadherin endocytosis and reduces the efficiency of AP-2 binding to the VE-cadherin tail. These findings support a model in which p120 binding to the VE-cadherin tail inhibits the entry of VE-cadherin into a clathrin-mediated endocytic pathway by preventing interactions with the clathrin adaptor AP-2.;These studies further elucidate the mechanism by which p120 functions as a setpoint for VE-cadherin expression and establish a line of inquiry to investigate the role of VE-cadherin membrane trafficking during vascular development, when it is likely to play an important role in regulating the blood vessel growth and reorganization that occurs during angiogenesis.