Phosphatidylinositide 3-kinase activity is required for stabilin-1-mediated endosomal transport of acLDL.
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.
Kzhyshkowska
Julia
J
Department of Dermatology, University Medical Centre Mannheim, Ruprecht-Karls University of Heidelberg, Theodor-Kutzer Ufer 1-3, 68167 Mannheim, Germany. julia.kzhyshkowska@haut.ma.uni-heidelberg.de
Gratchev
Alexei
A
Brundiers
Heike
H
Mamidi
Srinivas
S
Krusell
Liis
L
Goerdt
Sergij
S
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D015153:Blotting, Western; D016466:CHO Cells; D006224:Cricetinae; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D018613:Microscopy, Confocal; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D014162:Transfection; D000077191:Wortmannin; D021601:trans-Golgi Network / Q000378:metabolism
D000730:Androstadienes; D008077:Lipoproteins, LDL; D047428:Protein Kinase Inhibitors; C032629:acetyl-LDL; D019869:Phosphatidylinositol 3-Kinases; D000077191:Wortmannin