Thrombin induces ICAM‐1 expression via store‐operated Ca2+ influx signaling in endothelial cells

Abstract

Thrombin-induced endothelial cell surface ICAM-1 expression plays a critical role in the pathogenesis of lung vascular injury. NF-κB activation is required for stable thrombin-induced ICAM-1 expression. We explore the role of Ca2+ signaling in the mechanism of NF-κB-dependent ICAM-1 expression human pulmonary artery endothelial cells (HPAEC). We show that IP3-receptor antagonist, 2-APB inhibits thrombin-induced increase in intracellular Ca2+ ([Ca2+]i), NF-κB activation and ICAM-1 expression in HPAEC. 2-APB failed to inhibit TNF-α-induced ICAM-1 mRNA. Thrombin-induced increase in [Ca2+]i is dependent on both ER stored-Ca2+ release and Ca2+-store depletion-mediated Ca2+ influx occurring via TRP channels in endothelial cells. To address the importance of Ca2+ influx signal, we measured thrombin-induced NF-κB activation and ICAM-1 transcript expression in the absence of Ca2+ influx in HPAEC. Thrombin-induced p65 nuclear translocation and ICAM-1 mRNA expression were reduced by preventing Ca2+ influx. Since TRPC4 is the essential component of SOC in mouse endothelial cells, we measured NF-κB activation and ICAM-1 expression in TRPC4 null (TRPC4−/ −) mice. Isolated perfused mouse lung studies showed impaired thrombin-induced NF-κB activation in TRPC4−/ − compared to wild type (WT). Thrombin-induced ICAM-1 mRNA expression was reduced in lung endothelial cells (LEC) from TRPC4−/ − compared to WT LEC. Thus, thrombin-induced store-operated Ca2+ influx signaling is critical in the mechanism of NF- B-dependent ICAM-1 expression in endothelial cells.