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Staurosporine blocks down-regulation of monocyte-associated tissue factor
J P Brozna1, M Forman, S D Carson
1Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha.
Abstract:
Inflammatory agents including bacterial endotoxin (LPS) and low concentrations of phorbol myristate acetate (PMA) stimulate human peripheral blood monocytes to transiently express tissue factor procoagulant activity. Concentrations of PMA that cause the cytosol-to-membrane translocation of protein kinase C (PKC) (10(-9)-10(-7) M) induce a rapid decrease in monocyte tissue factor activity. Staurosporine, an inhibitor of protein kinase C, enhances the stimulatory effect of low concentrations of PMA on monocyte expression of tissue factor activity and blocks suppression of tissue factor activity at high PMA concentrations. Furthermore, staurosporine prolongs LPS-induced tissue factor expression in monocytes. These results suggest that protein kinases modulate tissue factor activity in human monocytes by regulating both induction and down-regulation.
Insights
Bacterial endotoxin and phorbol myristate acetate stimulate monocytes to express tissue factor. Protein kinase C activation down-regulates this activity, while its inhibition enhances it, suggesting kinases regulate tissue factor expression.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Monocytes play a key role in inflammation and coagulation.
- Tissue factor expression on monocytes is a critical initiator of the coagulation cascade.
- Inflammatory stimuli can modulate monocyte tissue factor procoagulant activity.
Purpose of the Study:
- To investigate the role of protein kinase C (PKC) in regulating tissue factor (TF) expression in human monocytes.
- To elucidate the mechanisms by which inflammatory agents and PKC signaling influence TF activity.
Main Methods:
- Human peripheral blood monocytes were stimulated with bacterial endotoxin (LPS) and phorbol myristate acetate (PMA).
- The effect of varying PMA concentrations on TF activity was assessed, correlating with PKC translocation.
- Staurosporine, a PKC inhibitor, was used to probe the role of PKC in TF regulation.
Main Results:
- LPS and low-concentration PMA transiently increased monocyte TF activity.
- High-concentration PMA, inducing PKC translocation, rapidly decreased TF activity.
- Staurosporine enhanced PMA-induced TF expression and blocked PMA-mediated suppression, also prolonging LPS-induced TF expression.
Conclusions:
- Protein kinases, particularly PKC, play a crucial role in modulating both the induction and down-regulation of tissue factor activity in human monocytes.
- These findings highlight a signaling pathway involving PKC that controls the procoagulant potential of monocytes during inflammation.