Search

The article discusses the findings of a study on the binding of coagulation protease factor XA to annexin 2 and the role of annexin 2 in regulating factor XA-mediated signal transduction independent of procoagulant activity. The authors state the enhanced interaction of factor Xa/annexin 2 in machrophages with lower tissue factor (TF) levels. The study explains the importance of autoproteolysis to binding. It reveals that the total level of factor Xa signaling remains unchanged in the presence of TF.

Leukaemia inhibitory factor (LIF) and interleukin (IL)-6 are members of a cytokine group that share a common signal transducer gp130 and induce pleiotropic biological effects in cells of diverse lineage. In monocytes, LIF facilitates differentiation, which may stimulate the biosynthesis of tissue factor (TF) that initiates the coagulation cascade. We tested the hypothesis that LIF would enhance TF expression in human monocyte-derived macrophages (MDMs). Human peripheral blood mononuclear cells separated from whole blood by density centrifugation were allowed to differentiate into MDMs in primary culture, and were then exposed to LIF, IL-6 and oncostatin M (OSM) for 24 h. LIF and IL-6 receptors, and gp130 were demonstrated in MDMs by immunocytochemistry and RT-PCR. TF procoagulant activity (TF-PCA) was measured by recalcification clotting time and TF protein by Western blotting. The results show that both TF procoagulant activity and TF protein increased significantly in response to LIF over the concentration range of 1–100 nm (P < 0.03). Although OSM and IL-6 tended to enhance TF expression by MDMs, the increase did not reach statistical significance. Anti-LIF receptor and anti-gp130 antibodies attenuated the effect of LIF on TF expression as assayed by both bioassay and flow-cytometry. In conclusion, LIF increases TF-PCA and TF protein in MDMs, and specific anti-LIF receptor antibodies attenuate this effect. Thus, LIF may regulate by a gp130-dependent pathway macrophage-mediated procoagulant function in diverse pathological states involving inflammation and thrombosis and seems to serve as an important mediator at the interface between these processes. [ABSTRACT FROM AUTHOR]

Circulating monocytes as well as resident monocyte-derived macrophages (MDMs) in the atherosclerotic plaque express tissue factor. We tested the hypothesis that differentiation of monocytes into macrophages increases their tissue factor expression. This was done by isolating monocytes from human blood and culturing them for 24 h or allowing their differentiation into macrophages for 8 days before assay. Tissue factor procoagulant activity was assessed by recalcification clotting assay while Western blotting quantitated tissue factor protein. Immunocytochemistry was applied to localize antigenic tissue factor in cells. The results showed that freshly-isolated monocytes expressed low baseline procoagulant activity (0.0004±0.0003 ng rhTF/106 cells) which increased 100-fold in 24-h cultured monocytes (0.04±0.01 ng/106 cells, P<0.0001) and was associated with detectable tissue factor protein by Western blotting. Furthermore, MDMs expressed 25-fold higher procoagulant activity (1.0±0.5 ng/106 cells, P<0.04) and increased tissue factor protein content compared with 24-h monocytes as corroborated by immunocytochemistry. LPS stimulation increased baseline binding activity of transcription factor κB three-fold (P<0.03) and 2.6-fold (P<0.09) in monocytes and in macrophages, respectively. The results demonstrate that differentiation of human monocytes into macrophages in culture enhances their tissue factor expression. The observed tissue factor increase that can be further stimulated by LPS may contribute to thrombogenicity of macrophage-rich atheroma. Activation of the TF-κB transduction pathway suggests its potential role in the transcriptional regulation of TF gene in response to acute stimulation in these cells. This cell-culture model may provide the opportunity to evaluate the effect of various interventions on macrophage procoagulant activity. [Copyright &y& Elsevier]