A revised model for the secretion of tPA and cytokines from cultured endothelial cells.
Endothelial cells are reported to contain several distinct populations of regulated secretory organelles, including Weibel-Palade bodies (WPBs), the tissue plasminogen activator (tPA) organelle, and the type-2 chemokine-containing organelle. We show that the tPA and type-2 organelles in human endothelial cells represent a single compartment primarily responsible for unstimulated secretion of tPA or, in cells exposed to interleukin-1β (IL-1β), the cytokines IL-8, IL-6, monocyte chemoattractant protein-1 (MCP-1), and growth-regulated oncogene-α (GRO-α). This compartment was distinct from WPBs in that it lacked detectable von Willebrand factor, P-selectin, Rab27a, or CD63 immunoreactivity, displayed no time-dependent decrease in intragranule pH, underwent detectable unstimulated exocytosis, and was very poorly responsive to Ca(2+)-elevating secretagogues. WPBs could also contain tPA, and in IL-1β-treated cells, IL-8, IL-6, MCP-1, and GRO-α, and were the primary source for histamine or ionomycin-stimulated secretion of these molecules. However, analysis of the storage efficiency of cytokines and tPA revealed that all were very poorly stored compared with von Willebrand factor. The nonmammalian, nonsecretory protein EGFP, when expressed in the secretory pathway, also entered WPBs and had a storage efficiency similar to tPA and the cytokines tested. Based on these data, we proposed a revised model for storage and secretion of cytokines and tPA.
Medical Research Council, National Institute for Medical Research, London, UK.
Laura
L
Knipe
Athinoula
A
Meli
Lindsay
L
Hewlett
Ruben
R
Bierings
John
J
Dempster
Paul
P
Skehel
Matthew J
MJ
Hannah
Tom
T
Carter
D002451:Cell Compartmentation; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism*; D042783:Endothelial Cells / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology*; D006801:Humans; D008954:Models, Biological; D010959:Tissue Plasminogen Activator / Q000378:metabolism*; D020302:Weibel-Palade Bodies / Q000378:metabolism
D016207:Cytokines; D010959:Tissue Plasminogen Activator