Basolateral internalization of GPI-anchored proteins occurs via a clathrin-independent flotillin-dependent pathway in polarized hepatic cells.
In polarized hepatocytes, the predominant route for apical resident proteins to reach the apical bile canalicular membrane is transcytosis. Apical proteins are first sorted to the basolateral membrane from which they are internalized and transported to the opposite surface. We have noted previously that transmembrane proteins and GPI-anchored proteins reach the apical bile canaliculi at very different rates. Here, we investigated whether these differences may be explained by the use of distinct endocytic mechanisms. We show that endocytosis of both classes of proteins at the basolateral membrane of polarized hepatic cells is dynamin dependent. However, internalization of transmembrane proteins is clathrin mediated, whereas endocytosis of GPI-anchored proteins does not require clathrin. Further analysis of basolateral endocytosis of GPI-anchored proteins showed that caveolin, as well as the small GTPase cdc42 were dispensable. Alternatively, internalized GPI-anchored proteins colocalized with flotillin-2-positive vesicles, and down-expression of flotillin-2 inhibited endocytosis of GPI-anchored proteins. These results show that basolateral endocytosis of GPI-anchored proteins in hepatic cells occurs via a clathrin-independent flotillin-dependent pathway. The use of distinct endocytic pathways may explain, at least in part, the different rates of transcytosis between transmembrane and GPI-anchored proteins.
Aït-Slimane
Tounsia
T
Institut National de la Santé et de la Recherche Médicale, Unité Mixte de Recherche S 938, Centre de Recherche Saint-Antoine, 75571 Paris Cedex 12, France. tounsia.ait-slimane@inserm.fr
Galmes
Romain
R
Trugnan
Germain
G
Maurice
Michèle
M
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D018826:CD13 Antigens / Q000235:genetics / Q000378:metabolism; D018957:CD59 Antigens / Q000235:genetics / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D051242:Caveolin 1 / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D016764:Cell Polarity; D002966:Clathrin / Q000235:genetics / Q000378:metabolism*; D018819:Dipeptidyl Peptidase 4 / Q000235:genetics / Q000378:metabolism; D034281:Dynamins / Q000235:genetics / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D017261:Glycosylphosphatidylinositols / Q000235:genetics / Q000378:metabolism*; D022781:Hepatocytes / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D021962:Membrane Microdomains / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D018957:CD59 Antigens; D002135:Calcium-Binding Proteins; D051242:Caveolin 1; D002966:Clathrin; C486206:EPS15 protein, human; D017261:Glycosylphosphatidylinositols; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; C106354:flotillins; D018826:CD13 Antigens; C042807:DPP4 protein, human; D018819:Dipeptidyl Peptidase 4; D020764:cdc42 GTP-Binding Protein; D034281:Dynamins