Factor Xa binding to annexin 2 mediates signal transduction via protease-activated receptor 1

Scripps Research Institute, SP-258, 10550 N Torrey Pines Rd, La Jolla, CA 92037, USA.
Circulation Research (Impact Factor: 11.02). 03/2008; 102(4):457-64. DOI: 10.1161/CIRCRESAHA.107.167759
Source: PubMed


The serine protease zymogen factor X is converted to its catalytically active form factor Xa by the binary complex of factor VIIa bound to its cell surface receptor tissue factor (TF) or by the intrinsic Xase complex, which consists of active factors VIII (VIIIa), IX (IXa), factor X, and Ca2+. Factor Xa has procoagulant activity by conversion of prothrombin to thrombin and also induces signal transduction, either alone or in the ternary TF:VIIa:factor Xa coagulation initiation complex. Factor Xa cleaves and activates protease activated receptor (PAR)1 or -2, but factor Xa signaling efficiency varies among cell types. We show here that annexin 2 acts as a receptor for factor Xa on the surface of human umbilical vein endothelial cells and that annexin 2 facilitates factor Xa activation of PAR-1 but does not enhance coagulant function of factor Xa. Overexpression of TF abolishes annexin 2 dependence on factor Xa signaling and diminishes binding to cell surface annexin 2, whereas selectively abolishing TF promotes the annexin 2/factor Xa interaction. We propose that annexin 2 serves to regulate factor Xa signaling specifically in the absence of cell surface TF and may thus play physiological or pathological roles when factor Xa is generated in a TF-depleted environment.

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Available from: Jasimuddin Ahamed
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    • "The basis for the slower cleavage of the PAR2-ALP construct by GD-FXa and E2-FXa is not known and was not further investigated. However, it has been reported that FXa binds to annexin 2 by a Gla-dependent mechanism to elicit intracellular signaling responses through the activation of PAR1 (Bhattacharjee et al., 2008). Whether the higher PAR2 cleavage activity of the full-length FXa is due to its additive annexin 2-dependent cleavage of PAR2 in our over-expressing PAR2-ALP construct is not known. "
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    ABSTRACT: Factor Xa (FXa) elicits intracellular signaling responses through the activation of protease-activated receptor 2 (PAR2) and possibly also through PAR1 in endothelial cells. In this study, we investigated FXa signaling in endothelial cells when the protease was either in free form or assembled into the prothrombinase complex. Furthermore, we prepared several wild-type and mutant PAR1 and PAR2 cleavage-reporter constructs in which their exodomains were fused to cDNA encoding for a soluble alkaline phosphatase (ALP). In the mutants, P2 residues were exchanged between PAR1 and PAR2 cleavage-reporter constructs and the hirudin-like binding site (HLBS) of PAR1 was inserted into the homologous site of PAR2. In non-transfected cells, FXa elicited a protective response which could be blocked by a specific anti-PAR2 but not by an anti-PAR1 antibody. A similar protective activity was observed for FXa in the prothrombinase complex. Further studies revealed that neither the Gla- nor EGF1-domain of FXa is required for its signaling activity, however, the N-terminus Arg-86 and Lys-87 of the EGF2-domain were essential. In the cleavage-reporter transfected cells, FXa cleaved the PAR2 construct effectively, however, replacing its P2-Gly with P2-Pro of PAR1 impaired its cleavage by FXa but improved it by thrombin. A PAR2 construct containing both P2-Pro and HLBS of PAR1 was poorly cleaved by FXa, but effectively by thrombin. A PAR1 construct containing P2 and P3 residues of PAR2 was poorly cleaved by thrombin but effectively by FXa. These results provide new insight into mechanisms through which coagulation proteases specifically interact with their target PAR receptors.
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    • "In certain circumstances factor Xa can activate PAR1 (Blanc-Brude et al., 2005; Bhattacharjee et al., 2008), and PAR2 can be activated by factor Xa (Camerer et al., 2000). Fibroblasts appear to be the only cell type in which the effects of factor Xa are mediated mainly via PAR1 and not PAR2 (Blanc-Brude et al., 2005). "
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    • "In addition to promoting blood coagulation, coagulation proteases induce signal transduction through the activation of G protein–coupled protease-activated receptors (PARs) [62], [63], [64], [65], [66]. Additionally, activated Factor X (Factor Xa) can mediate signal transduction via specific binding to annexin 2 [67]. Endothelial lipase (LIPG) is involved in lipoprotein metabolism and is elevated in inflammation [68], [69]. "
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