Translational inhibition of E-selectin expression stimulates P-selectin-dependent neutrophil recruitment.

Abstract

Although known for its role in hemostasis, there is a growing body of evidence that thrombin can induce leukocyte recruitment and contribute to the inflammatory response. An in vitro parallel-plate flow chamber was used to systematically examine thrombin-induced neutrophil interactions with human endothelium. Stimulation of endothelial cells with thrombin (1 U/ml) resulted in an immediate, P-selectin-dependent increase in neutrophil rolling and adhesion that was comparable in magnitude to optimal levels of histamine (the classical inducer of P-selectin). However, thrombin, but not histamine, induced a delayed (4 h) E-selectin-dependent rolling similar to that of tumor necrosis factor-alpha, suggesting that thrombin has the unique ability to recruit neutrophils by an early P-selectin and a delayed E-selectin pathway. Surprisingly, inhibition of E-selectin expression with the general protein synthesis inhibitor cycloheximide induced P-selectin expression 4 h after thrombin stimulation. Cycloheximide and thrombin (4 h) induced sufficient P-selectin-dependent rolling to recruit as many neutrophils as were recruited with 4 h of stimulation with thrombin alone. Histamine in the presence of cycloheximide or cycloheximide alone did not evoke the P-selectin response at 4 h, suggesting that this was not due to direct cycloheximide induction of P-selectin. Treatment of endothelium with tumor necrosis factor-alpha (an E-selectin inducer) and cycloheximide also eliminated E-selectin expression but, much like thrombin, induced P-selectin expression and neutrophil recruitment. In conclusion, inhibition of E-selectin via protein synthesis inhibition activates the protein synthesis-independent pathway of P-selectin expression to support adequate leukocyte recruitment.