Effect of P-selectin on phosphatidylserine exposure and surface-dependent thrombin generation on monocytes.
OBJECTIVE
Stimulation of monocytes with P-selectin induces the synthesis of an array of mediators of inflammation, as well as the expression of tissue factor (TF), the main initiator of coagulation. Because the membrane-bound reactions of coagulation are profoundly influenced by the presence of phosphatidylserine on the membranes of cells, factors that increase its expression may have an impact on coagulation.


RESULTS
Using flow cytometry, we studied the effect of P-selectin on phosphatidylserine expression in blood monocytes and in the monocytic cells, THP-1. Soluble P-selectin at biologically relevant concentrations (0.31 to 2.5 microg/mL) induced a time-dependent increase in phosphatidylserine expression, an effect that could be inhibited with an anti-PSGL-1 blocking antibody, and by genistein, a tyrosine kinase inhibitor. Binding of activated platelets to THP-1 cells also resulted in a significant increase in phosphatidylserine expression that was dependent on PSGL-1. Consistent with the role of phosphatidylserine on surface-dependent reactions of coagulation, treatment of monocytic cells with soluble P-selectin led to increased thrombin generation. We excluded P-selectin induced apoptosis of monocyte as a mechanism for the increased phosphatidylserine exposure.


CONCLUSIONS
In summary, we show that P-selectin, either soluble or in its membrane-bound form, induces phosphatidylserine exposure in monocytes through a mechanism dependent on PSGL-1.
del Conde
Ian
I
Section of Cardiology, Baylor College of Medicine, Houston, Texas, USA.
Nabi
Faisal
F
Tonda
Raúl
R
Thiagarajan
Perumal
P
López
José A
JA
Kleiman
Neal S
NS
D017209:Apoptosis / Q000187:drug effects / Q000276:immunology; D001792:Blood Platelets / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D006801:Humans; D066298:In Vitro Techniques; D008562:Membrane Glycoproteins / Q000378:metabolism; D009000:Monocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019007:P-Selectin / Q000378:metabolism* / Q000494:pharmacology; D010718:Phosphatidylserines / Q000378:metabolism* / Q000494:pharmacology; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects / Q000502:physiology; D012995:Solubility; D013917:Thrombin / Q000096:biosynthesis* / Q000378:metabolism; D013927:Thrombosis / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
D008562:Membrane Glycoproteins; D019007:P-Selectin; C084882:P-selectin ligand protein; D010718:Phosphatidylserines; D014443:Tyrosine; D013917:Thrombin