Abstract
Kindlin-2, a widely distributed cytoskeletal protein, has been implicated in integrin activation, and its absence is embryonically lethal in mice. In the present study, we tested whether hemostasis might be perturbed in kindlin-2(+/-) mice. Bleeding time and carotid artery occlusion time were significantly prolonged in kindlin-2(+/-) mice. Whereas plasma concentrations/activities of key coagulation/fibrinolytic proteins and platelet counts and aggregation were similar in wild-type and kindlin-2(+/-) mice, kindlin-2(+/-) endothelial cells (ECs) showed enhanced inhibition of platelet aggregation induced by adenosine 5'-diphosphate (ADP) or low concentrations of other agonists. Cell-surface expression of 2 enzymes involved in ADP/adenosine 5'-monophosphate (AMP) degradation, adenosine triphosphate (ATP) diphosphohydrolase (CD39) and ecto-5'-nucleotidase (CD73) were increased twofold to threefold on kindlin-2(+/-) ECs, leading to enhanced ATP/ADP catabolism and production of adenosine, an inhibitor of platelet aggregation. Trafficking of CD39 and CD73 at the EC surface was altered in kindlin-2(+/-) mice. Mechanistically, this was attributed to direct interaction of kindlin-2 with clathrin heavy chain, thereby controlling endocytosis and recycling of CD39 and CD73. The interaction of kindlin-2 with clathrin was independent of its integrin binding site but still dependent on a site within its F3 subdomain. Thus, kindlin-2 regulates trafficking of EC surface enzymes that control platelet responses and hemostasis.