REEXPRESSION OF FUNCTIONAL P-SELECTIN MOLECULES ON THE ENDOTHELIAL-CELL SURFACE BY REPEATED STIMULATION WITH THROMBIN

P-selectin (GMP-140, PADGEM, CD62P) is a cell adhesion receptor which is believed to play an important role in inflammatory diseases by supp orting leucocyte rolling. P-selectin is located on the granule membran e of Weibel-Palade bodies in resting endothelial cells and is expresse d on the cell surface during cellular activation with various stimulat ors such as thrombin. Thereafter, P-selectin is internalized and sorte d to the Golgi region and Weibel-Palade bodies again. However, whether P-selectin is re-expressed upon subsequent cellular stimulation has, to date, been unclear. To address this question, we measured the cellu lar content and surface expression of P-selectin, using indirect immun ofluorescence and confocal laser cytometry. Surface expression of P-se lectin reached a maximum <2 min after thrombin stimulation and decline d to basal levels after 180 min. Rechallenge with thrombin induced rap id surface re-expression of P-selectin, which was independent of de no vo protein synthesis, since cycloheximide did not inhibit re-expressio n. Moreover, re-expressed P-selectin supported the adherence of HL60 p romyelocytic cells. These results clearly demonstrated that functional P-selectin molecule was recycled after repeated stimulation with thro mbin, raising the possibility that P-selectin is involved in chronic i nflammation.