Thrombin receptor expression and responsiveness of human monocytic cells to thrombin is linked to interferon‐induced cellular differentiation

Abstract

Human thrombin has been shown to stimulate monocyte chemotaxis, phagocytosis, and interleukin (IL8) production, but the mechanisms responsible for stimulation are not well defined. In some cells, thrombin stimulation of proliferation appears to require both cleavage of the proteolytically activated receptor for thrombin (PAR1) and activation of a nonproteolytically activated thrombin receptor (N-PAR), while in others activation of either receptor alone may be sufficient for stimulation. We, therefore, have initiated studies to address thrombin receptor expression and cell responsiveness to thrombin in interferon gamma (IFNgamma)-differentiated and nondifferentiated U937 monocytic cells. Northern blot analysis shows that PAR1 expression is upregulated upon differentiation. Experiments with biotinylated and 125I-thrombin show that specific thrombin binding is dramatically increased by differentiation although it is not clear if this binding is to PAR1 or to a separate binding component such as N-PAR which is present on fibroblasts and other cells. Addition of thrombin at concentrations of 1-10 microg/ml (30-300 nM, concentrations where specific thrombin binding is observed) stimulates proliferation of IFNgamma-differentiated U937 cells but not of undifferentiated U937 cells. Thrombin also stimulates interleukin-6 (IL6) production in IFNgamma-differentiated U937 cells. Moreover, thrombin induces high levels of IL6, interleukin-1beta (IL1beta), and tumor necrosis factor-alpha (TNF alpha) production by peripheral blood mononuclear cells (PBMC) and monocytes. These results show that differentiated U937 cells and mature PBMC are responsive to thrombin whereas nondifferentiated U937 are not. Further, this responsiveness appears to correlate with expression of PAR1 and to a dramatic increase in specific thrombin binding. That thrombin stimulates cytokine production and proliferation in populations of differentiated monocytes suggests that thrombin may be an important regulator of inflammation and wound healing.

Effect of blood flow on platelets, leukocytes, and extracellular vesicles in thrombosis of simulated neonatal extracorporeal circulation

“…Last, only the low‐flow and high‐flow circuits documented a log‐fold increase in a proinflammatory cytokine. Tumor necrosis factor alpha, a specific marker of monocyte activation, is associated with a significant increase in thrombogenicity . The combined generation of procoagulant and proinflammatory stimuli likely contribute to ECMO‐related morbidity and offer targets for therapeutic intervention.…”

Inhibition of interleukin‐12 expression by α‐thrombin in human peripheral blood mononuclear cells: a potential mechanism for modulating Th1/Th2 responses

“…It is well recognized that thrombin elicits proinflammatory activities by activation of PAR‐1 receptor ( Cirino et al , 2000 ; Vergnolle et al , 2001 ). In previous studies, we showed that PAR‐1 expression and responsiveness of cells to thrombin were linked to IFN γ ‐induced differentiation ( Naldini et al , 1998 ). Other laboratories have also shown that leukocytes express PAR‐1 ( Howells et al , 1993 ) and that PARs are associated with inflammation ( Cirino et al , 1996 ).…”

Protease‐activated receptors and prostaglandins in inflammatory lung disease

“…Additionally, PAR 1 ‐ and PAR 2 ‐APs, but not PAR 3 ‐ or PAR 4 ‐APs, induced IL‐6, but not IL‐13, release from cultured human T cells (Li and He, 2006). PAR 1 activators have also been reported to induce CCL2, IL‐1β and TNF‐α release from macrophages (Naldini et al. , 1998; 2002; Riewald et al.…”