Ca2+ Influx Induced by Protease-activated Receptor-1 Activates a Feed-forward Mechanism of TRPC1 Expression via Nuclear Factor-κB Activation in Endothelial Cells

Thrombin activation of protease-activated receptor-1 induces Ca 2+ influx through store-operated cation channel TRPC1 in endothelial cells. We examined the role of Ca 2+ influx induced by the depletion of Ca 2+ stores in signaling TRPC1 expression in endothelial cells. Both thrombin and a protease-activated receptor-1-specific agonist peptide induced TRPC1 expression in human umbilical vein endothelial cells, which was coupled to an augmented store-operated Ca 2+ influx and increase in endothelial permeability. To delineate the mechanisms of thrombin-induced TRPC1 expression, we transfected in endothelial cells TRPC1-promoter-luciferase (TRPC1-Pro-Luc) construct containing multiple nuclear factor-κB (NF-κB) binding sites. Co-expression of dominant negative IκBα mutant prevented the thrombin-induced increase in TRPC1 expression, indicating the key role of NF-κB activation in mediating the response. Using TRPC1 promoter-deletion mutant constructs, we showed that NF-κB binding sites located between –1623 and –871 in the TRPC1 5′-regulatory region were required for thrombin-induced TRPC1 expression. Electrophoretic mobility shift assay utilizing TRPC1 promoter-specific oligonucleotides identified that the DNA binding activities of NF-κB to NF-κB consensus sites were located in this domain. Supershift assays using NF-κB protein-specific antibodies demonstrated the binding of p65 homodimer to the TRPC1 promoter. Inhibition of store Ca 2+ depletion, buffering of intracellular Ca 2+ , or down-regulation of protein kinase Cα downstream of Ca 2+ influx all blocked thrombin-induced NF-κB activation and the resultant TRPC1 expression in endothelial cells. Thus, Ca 2+ influx via TRPC1 is a critical feed-forward pathway responsible for TRPC1 expression. The NF-κB-regulated TRPC1 expression may be an essential mechanism of vascular inflammation and, hence, a novel therapeutic target.