Efficiency of von Willebrand factor-mediated targeting of interleukin-8 into Weibel-Palade bodies

Background: After de novo synthesis in endothelial cells, the chemokine interleukin-8 (IL-8) is targeted to endothelial cell-specific storage vesicles, the Weibel-Palade bodies (WPBs), where it colocalizes with von Willebrand factor (VWF). Objective: In this study we investigated a putative regulator function for VWF in the recruitment of IL-8 to WPBs. Methods: We performed a quantitative analysis of the entry of IL-8 into the storage system of the endothelium using pulse-chase analysis and subcellular fractionation studies. Results: Using pulse-chase analysis of IL-1 beta-stimulated human umbilical vein endothelial cells, we found that a small part of de novo synthesized IL-8 was retained in endothelial cells after 4 h. In density gradients of endothelial cell homogenates nearly equimolar amounts of VWF and IL-8 were present in subcellular fractions that contained WPBs. Furthermore, we found that IL-8 binds to immobilized VWF under the slightly acidic conditions thought to prevail in the lumen of the late secretory pathway. Conclusions: These observations indicate that the sorting efficiency of IL-8 into the regulated secretory pathway of the endothelium is tightly controlled by the entry of VWF into WPBs.