Formyl peptide leukocyte chemoattractant uptake and release by cultured human umbilical vein endothelial cells

Abstract

Recent observations support an active role for the vascular endothelial cell in the induction and evolution of the inflammatory response. Since prior studies suggested that cultured bovine endothelial cells express high affinity binding sites for the neutrophil chemotactic oligopeptide formyl methionyl-leucyl-phenylalanine (f-Met-Leu-Phe), we sought to further characterize the interaction between formyl peptide chemoattractants and human vascular endothelial cells. Cultured human umbilical vein endothelial cells and peripheral blood neutrophils specifically bound f-Met-Leu-[3H]Phe, whereas specific binding to cultured fibroblasts, smooth muscle, and epithelial cells was negligible. Endothelial cells expressed 3.6 +/- 0.7 X 10(5) binding sites/cell with a Kd of 210 +/- 31 nM. Although the hexapeptide formyl norleucyl-leucyl-phenylalanyl-norleucyl-tyrosyl-lysine (f-Nle-Leu-Phe-Nle-Tyr-Lys) and the tetrapeptide f-Met-Leu-Phe-Lys completed with f-Met-Leu-[3H]Phe for binding to endothelial cells, specific binding of 125I-f-Nl-Leu-Phe-Tyr-Lys or f-Met-Leu-Phe-Lys-fluorescein to endothelial cells was not observed, suggesting that steric constraints on formyl peptide binding differ between endothelial cells and leukocytes. At 37 degrees C, cell-associated f-Met-Leu-[3H]Phe greatly exceeded that bound at 0 degrees C and was incorporated predominantly into a nondisplaceable compartment. Release of f-Met-Leu-[3H]Phe or radioactive breakdown products from this compartment was time- and temperature-dependent with a t1/2 of approximately equal to 20 min at 37 degrees C. Resolution of the radioactive products released from f-Met-Leu-[3H]Phe-loaded endothelial cells by thin layer chromatography indicated that greater than or equal to 57% of the released material co-migrated with intact f-Met-Leu-[3H]Phe. Degradative release was blocked by agents that interfere with lysosomal acidification. The radioactive material released from f-Met-Leu-[3H]Phe-loaded endothelial cells bound specifically to neutrophils. This binding was inhibited 50.2 +/- 6.4% by a greater than or equal to 10(3)-fold excess of nonradioactive f-Met-Leu-Phe whereas binding of authentic f-Met-Leu-[3H]Phe was inhibited 89.4 +/- 3.0%. Supernatant obtained from f-Met-Leu-[3H]Phe-loaded endothelial cells elicited a rise in neutrophil cytosolic free calcium ([Ca2+]i) measured by quin2 fluorescence. The change in neutrophil [Ca2+]i depended on ligand binding to the neutrophil formyl peptide receptor since endothelial supernatants were devoid of activity in the presence of the f-Met-Leu-Phe antagonist, tert-butoxycarbonyl-Phe-Leu-Phe-Leu-Phe.(ABSTRACT TRUNCATED AT 400 WORDS)