Modulation of Tissue Factor-Factor VIIa Signaling by Lipid Rafts and Caveolae

University of Texas Health Science Center at Tyler, Tyler, Texas, United States
Arteriosclerosis Thrombosis and Vascular Biology (Impact Factor: 6). 07/2007; 27(6):1447-55. DOI: 10.1161/ATVBAHA.107.143438
Source: PubMed


Coagulation factor VIIa (VIIa) binding to its cellular receptor, tissue factor (TF), not only initiates the coagulation cascade but also induces cell signaling by activating G-protein coupled protease-activated receptors. The objective of the present study is to investigate the role of lipid rafts and caveolae in modulating TF-VIIa signaling and coagulant functions.
TF-VIIa coagulant function was measured in factor X activation assay and the signaling function was evaluated in phosphoinositide hydrolysis and IL-8 gene induction. Buoyant density gradient centrifugation and immunofluorescence confocal microscopy were used to determine cellular localization of TF and protease-activated receptor 2. The data show that a substantial fraction of TF and protease-activated receptor 2 resides in lipid rafts/caveolae, and disruption of lipid rafts by cholesterol depletion or modification reduced TF-VIIa-induced cell signaling. Disruption of caveolae with caveolin-1 silencing had no effect on the TF-VIIa coagulant activity but inhibited the TF-VIIa-induced cell signaling.
Overall our data show that lipid raft/caveolae play a selective role in modulating the TF-VIIa signaling function without affecting the TF-VIIa coagulant activity.

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    • "Caveolae has also been suggested to be involved in TF-mediated PAR2 signaling. In breast carcinoma cells, both TF and PAR2 are observed co-localized in cholesterol-rich caveolae, and depletion or sequestration of plasma membrane cholesterol significantly impaired TF-VII1 induced cell signaling (146). It would be interesting to see if different proteases prefer targeting PARs at certain membrane microdomains or there is PARs redistribution upon activation by different proteases. "
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    • "It is well known that the ERK1/2 and NF-κB signaling pathways play a pivotal role in many cellular processes, such as proliferation, apoptosis, and differentiation24, 25, 26, 27. PAR2 activation induced by the TF/factor VIIa complex can trigger cell signal transduction through different pathways, including ERK1/2 and NF-κB15, 28. This study investigated whether EGCG could reverse the activation of ERK-1/2 as well as NF-κB by PAR2 activation. "
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    • "Together these studies suggest that localization of PAR1 and EPCR with specific G protein signalling effectors stabilizes a distinct active receptor conformation that favours endothelial barrier protective signalling. Interestingly, caveolae are also required for the activation of PAR2 by the tissue factor-coagulant protease factor VIIa complex but not by synthetic peptide agonists (Awasthi et al., 2008); however, it was not determined whether the different agonists caused biased signalling. "
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