Subcellular localization of leukotriene receptors in human endothelial cells

Leukotriene B4 (LTB4), a potent chemotactic and immune-modulating mediator, signals via two receptors, BLT1 and BLT2. Recently, we reported that BLT1 is the predominating BLT expressed on human umbilical vein endothelial cells (HUVEC), and that BLT1 mediated functions are enhanced by LTB4 and lipopolysaccharide (LPS), but not by TNFα. Here, we demonstrate that BLT1 is found on the outer cell membrane of HUVECs but also in intracellular granules, co-localized with monocyte chemotactic protein-1 and P-selectin, but not with interleukin-8 and von Willebrand factor. Upon stimulation with LTB4 or LPS, more BLT1 protein is found, now evenly distributed over the cytoplasm and in the cell nucleus, but less on the cell surface. An MAP kinase inhibitor prevented this enhancement and translocation, suggesting this signaling pathway to be crucial. Thus, BLT1, a G-protein-coupled 7-transmembrane receptor, is located in various subcellular compartments in endothelial cells, which may have implications for cellular LT dependent responses and target accessibility for BLT1 antagonists.