Abstract
Thrombin potently induces endothelial inflammation. One of the responses is upregulation of adhesion molecules such as ICAM-1, resulting in enhanced leukocyte attachment to the endothelium. In this report, we examine the contribution of EphA2 in thrombin-induced expression of ICAM-1 in human umbilical vein endothelial cells (HUVECs). We showed that thrombin transiently induced tyrosine- phosphorylation of EphA2 in a Src-kinase dependent manner. This transactivation was mediated through PAR-1, because a PAR-1 specific agonistic peptide also transactivated EphA2. Expression knockdown of endogenous EphA2 by siRNAs blocked ICAM-1 upregulation and leukocyte/endothelium attachment induced by thrombin. Overexpression of exogenous mouse EphA2 rescued both ICAM-1 expression and leukocyte attachment induced by thrombin in endogenous EphA2-knockdown HUVECs. Mechanistically, we showed EphA2 knockdown suppressed thrombin-induced serine 536 phosphorylation of NFkappaB, an event critical of ICAM-1 transcriptional upregulation. Collectively, our results strongly suggest EphA2 is a necessary component for thrombin-induced ICAM-1 upregulation.