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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2007;27:1447.)
© 2007 American Heart Association, Inc.

Thrombosis

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

Vineet Awasthi; Samir K. Mandal; Veena Papanna; L. Vijaya Mohan Rao; Usha R. Pendurthi

From Biomedical Research Division, The University of Texas Health Center at Tyler, Tex.

Correspondence to L. Vijaya Mohan Rao, Biomedical Research Division, The University of Texas Health Center at Tyler, 11937 US Highway 271, Tyler, TX 75708. E-mail vijay.rao{at}uthct.edu

Objective— 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.

Methods and Results— 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.

Conclusion— 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.

The present study was undertaken to investigate the role of lipid rafts and caveolae in modulating the coagulant and signaling functions of tissue factor. Caveolar localization of tissue factor does not influence its ability to support coagulation but is essential to activate PAR2-mediated cell signaling.

Key Words: caveolae • factor VIIa • lipid rafts • signaling • tissue factor • protease-activated receptors

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