Tissue Factor Binding of Activated Factor VII Triggers Smooth Muscle Cell Proliferation via Extracellular Signal–Regulated Kinase Activation

Abstract

Background-Tissue factor (TF) is the main initiator of coagulation in vivo. Recently, however, a role for TF as a cell receptor involved in signal transduction has been suggested. The aim of the present study was to assess whether activated factor VII (FVIIa) binding to TF could induce smooth muscle cell (SMC) proliferation and to clarify the possible intracellular mechanism(s) responsible for this proliferation. Methods and Results-Cell proliferation was induced by FVIIa in a dose-dependent manner, as assessed by [3 H]thymidine incorporation and direct cell counting, whereas no response was observed with active site-inhibited FVIIa (FVIIai), which is identical to FVIIa but is devoid of enzymatic activity. Similarly, no proliferation was observed when binding of FVIIa to TF was prevented by the monoclonal anti-TF antibody AP-1. Activation of the p44/42 mitogen-activated protein (MAP) kinase (extracellular signal-regulated kinases 1 and 2 [ERK 1/2]) pathway on binding of FVIIa to TF was demonstrated by transient ERK phosphorylation in Western blots and by suppression of proliferation with the specific MEK (MAP kinase/ERK kinase) inhibitor UO126. ERK phosphorylation was not observed with FVIIai or when cells were pretreated with AP-1. Conclusions-These data indicate a specific effect by which binding of FVIIa to TF on the surface of SMCs induces proliferation via a coagulation-independent mechanism and possibly indicate a new link between coagulation, inflammation, and atherosclerosis. Key Words: coagulants Ⅲ signal transduction Ⅲ cell division T issue factor (TF) is a cell surface-anchored glycoprotein that binds both the zymogen factor VII (FVII) and the active serine protease factor VIIa (FVIIa). 1 TF/FVIIa complex activates coagulation by cleaving its natural substrates, factors IX and X, ultimately leading to thrombin generation, fibrin deposition, and platelet activation. 1,2 On these grounds, TF has been considered to function as a major initiator of blood coagulation in vivo. Recently, however, some evidence has suggested that TF may mediate important coagulationindependent biological phenomena, including embryonic and oncogenic angiogenesis, 3,4 and inflammation. 5 In addition, recent data indicate that TF/FVIIa interaction may activate different intracellular signals, culminating in a variety of cell responses, thus suggesting a role for TF as a "true" cell membrane receptor. For example, TF/FVIIa interaction has been shown to be a strong chemotactic stimulus for smooth muscle cells (SMCs), mediating their migration in vitro. 6 FVIIa has been also shown to induce phosphorylation of the extracellular signalregulated kinases 1 and 2 (ERK 1/2) 7 and to upregulate poly(A) polymerase, 8 urokinase-type plasminogen activator receptor, 9 and a host of genes identified with the use of cDNA microarrays. 10 However, despite evidence suggesting close links between TF, activation of coagulation, and intracellular signaling, no direct effects of TF/FVIIa on SMC proliferation have yet been demonstrated. Thus, in the pr...

Factor VII Deficiency Impairs Cutaneous Wound Healing in Mice

“…Indeed, FVIIa-initiated fibrin clot forma- tion is critical to control active bleeding immediately after wounding occurs and FXa, thrombin and fibrin have been shown to affect wound healing through a number of mechanisms, for example, as chemotactic and mitogenic factors for leukocytes (41)(42)(43). However, several considerations encouraged an exploration of other mechanisms to identify roles of FVIIa, independent of thrombin generation, in regulation of wound healing: (a) restoring thrombin generation in hemophilia B did not normalize wound healing to the level of WT mice (44); (b) the response of FVIIa treatment in keratinocytes is abrogated by TF-neutralizing antibody, but is not affected by hirudin (26); (c) FVIIa signaling, independent of coagulation, affects smooth muscle cell migration and proliferation (45), as well as transcriptional responses in keratinocytes (26); and (d) FVIIa-mediated inflammatory signaling, independent of thrombin and FXa, has been shown to occur in the response of mice to lethal endotoxemia (32). In addition, the initial observations in this study, for example, the extended delay of wound healing up to day 11 post wound, the reduced keratinocyte migration, and the diminished inflammation in FVII tTA/tTA mice, suggest that the role of FVII in wound healing extends beyond the coagulation cascade.…”

Tissue factor gene promoter haplotype associates with carotid intima-media thickness in subjects in cardiovascular risk prevention

“…Moreover, although evaluation in silico in another study did not indicate effects of the 4 investigated polymorphisms on transcription factor binding [11], gel shift experiments by Terry et al indeed demonstrated such effects of the Del-1208Ins polymorphism, providing a possible explanation for the genotypic differences in TF expression and activity [17]. An influence on local TF activity in the vessel wall may in turn modulate processes involved in atherosclerosis such as inflammation and VSMC migration and proliferation [2,9,10,[25][26][27][28][29][30], which could result in measurable differences in C-IMT as observed in this study. We cannot rule out, however, that the observed effect of A/G TF promoter haplotype on C-IMT may be explained by linkage disequilibrium with other genetic variants influencing the atherosclerotic process.…”

“…Indeed, experimental studies in vitro and in vivo have shown involvement of TF in inflammation and VSMC migration/proliferation mediated via intracellular signalling by the TF cytoplasmic tail and/or TF:FVIIa-promoted extracellular proteolytic cascades and activation of protease-activated receptors (PARs) [2,9,10,[25][26][27][28][29][30]. The association between tertiles of TF and C-IMT, tested by multivariable linear regression analysis, was analysed in the subgroup of subjects (n = 120) who underwent plasma TF level determinations.…”

Stress repair mechanism activity explains inflammation and apoptosis

“…Factor VII activation by tissue factor initiates the enzymatic interaction and determines its magnitude and location [208,209,212]. Factors IX and X amplify Factor VII thrombin production to moderate levels that energize tissue repair [27,121,215].…”