Phosphatidylinositide 3-kinase activity is required for stabilin-1-mediated endosomal transport of acLDL

• Published in: Immunobiology (1979) 2005-01, Vol.210 (2), p.161-173
• Main Authors: Kzhyshkowska, Julia, Gratchev, Alexei, Brundiers, Heike, Mamidi, Srinivas, Krusell, Liis, Goerdt, Sergij
• Format: Article
• Language: English
• Subjects: Androstadienes - pharmacology; Animals; Biological Transport - physiology; Blotting, Western; CHO Cells; Cricetinae; EEA1; Endocytosis - drug effects; Endocytosis - physiology; Endosomes - drug effects; Endosomes - metabolism; Flow Cytometry; Humans; Lipoproteins, LDL - metabolism; Macrophage; Macrophages - drug effects; Macrophages - metabolism; Microscopy, Confocal; Phosphatidylinositol 3-Kinases - metabolism; PI3K; Protein Kinase Inhibitors - pharmacology; Receptor; trans-Golgi Network - metabolism; Transfection
• ISSN: 0171-2985; 1878-3279
• DOI: 10.1016/j.imbio.2005.05.022

Stabilin-1 is a type 1 transmembrane receptor specifically expressed by tissue macrophages and sinusoidal endothelial cells. We recently demonstrated that stabilin-1 is involved in the endocytic/recycling pathway and shuttles between the endosomal system and the trans-Golgi network (TGN) in human macrophages. In the present study, we designed a model cell system to study the mechanisms of stabilin-1-mediated endocytosis. Using CHO-K1 cells stably transfected with stabilin-1, we demonstrated that acetylated low-density lipoprotein (acLDL) induces recruitment of stabilin-1 into the endocytic pathway. Stabilin-1 mediates internalisation of acLDL and its delivery to early endosomes, and it is translocated together with its ligand to the late endosomal compartment. Treatment with wortmannin, a specific inhibitor of phosphatidylinositide 3-kinase (PI3K), did not block stabilin-1 mediated internalisation of acLDL as well as its trafficking to early endosomes, whereas it induced enlargement of stabilin-1/acLDL positive endosomes as well as partial dissociation of EEA1 from these structures. The major effect of wortmannin was the abrogation of stabilin-1/acLDL trafficking into the late endocytic pathway. In stabilin-1 positive human type 2 macrophages, wortmannin treatment resulted in formation of both enlarged and small stabilin-1 positive endosomes. This effect, however, was significantly weaker in macrophages as compared to CHO-stabilin-1 cells. Our data indicate that PI3K activity is required for the transfer of stabilin-1 and its ligand acLDL from early to late endosomal compartments.