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  • Title: Phosphatidylinositide 3-kinase activity is required for stabilin-1-mediated endosomal transport of acLDL.
    Author: Kzhyshkowska J, Gratchev A, Brundiers H, Mamidi S, Krusell L, Goerdt S.
    Journal: Immunobiology; 2005; 210(2-4):161-73. PubMed ID: 16164023.
    Abstract:
    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.
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