THROMBIN-INDUCED EXPRESSION OF ENDOTHELIAL P-SELECTIN AND INTERCELLULAR-ADHESION MOLECULE-1 - A MECHANISM FOR STABILIZING NEUTROPHIL ADHESION

Thrombin-induced expression of endothelial adhesivity toward neutrophils (PMN) was studied using human umbilical vein endothelial cells (HUVEC). HUVEC were challenged with human alpha-thrombin for varying durations up to 120 min, after which the cells were fixed with 1% paraformaldehyde and Cr-51-labeled human PMN were added to determine PMN adhesion. Endothelial adhesivity increased within 15 min after alpha-thrombin exposure, and the response persisted up to 120 min. Expression of endothelial adhesion proteins, P-selectin (GMP-140, PADGEM, CD62), and intercellular adhesion molecule-1 (ICAM-1; CD54) on the endothelial surface was quantitated by increase in the specific binding of anti-P-selectin mAb G1 and anti-ICAM1 mAb RR1/1 labeled with I-125. P-selectin expression was maximal at 5-15 min alpha-thrombin exposure and decayed to basal levels within 90 min. In contrast, ICAM-1 activity increased at 30 min and remained elevated for 120 min after alpha-thrombin challenge. The initial endothelial adhesivity was dependent on P-selectin expression since PMN adhesion occurring within the first 30 min after alpha-thrombin challenge was inhibited by mAb G1. The later prolonged PMN adhesion was ICAM-1 dependent since this response was inhibited by mAb RR1/1 and to the same degree by the anti-CD18 mAb IB4. Anti-ELAM-1 mAb BB11 had no effect on adhesion of PMN to the alpha-thrombin-challenged cells. The initial P-selectin expression and PMN adhesion responses were reproduced by the 14-amino peptide (SFLLRNPNDKYEPF) (thrombin-receptor activity peptide; TRP-14) which comprised the NH2 terminus created by thrombin's proteolytic action on its receptors. However, TRP-14-induced PMN adhesion was transient, and TRP-14 did not cause ICAM-1 expression. The ICAM-1-dependent PMN adhesion mediated by alpha-thrombin was protein synthesis independent since ICAM-1 expression and PMN adhesion were not inhibited by cycloheximide pretreatment of HUVEC. Moreover, Northern blot analysis indicated absence of ICAM-1 mRNA signal up to 180 min after alpha-thrombin challenge. In conclusion, thrombin-induced endothelial adhesivity involves early- and late-phase responses. The initial reversible PMN adhesion is mediated by rapid P-selectin expression via TRP-14 generation. Thrombin-induced PMN adhesion is stabilized by a protein synthesis-independent upregulation of the constitutive ICAM-1 activity which enables the interaction of ICAM-1 with the CD18 beta2 integrin on PMN.