Requirement for galectin-3 in apical protein sorting.
The central aspect of epithelial cells is their polarized structure, characterized by two distinct domains of the plasma membrane, the apical and the basolateral membrane. Apical protein sorting requires various signals and different intracellular routes to the cell surface. The first apical targeting motif identified is the membrane anchoring of a polypeptide by glycosyl-phosphatidyl-inositol (GPI). A second group of apical signals involves N- and O-glycans, which are exposed to the luminal side of the sorting organelle. Sucrase-isomaltase (SI) and lactase-phlorizin hydrolase (LPH), which use separate transport platforms for trafficking, are two model proteins for the study of apical protein sorting. In contrast to LPH, SI associates with sphingolipid/cholesterol-enriched membrane microdomains or "lipid rafts". After exit form the trans-Golgi network (TGN), the two proteins travel in distinct vesicle populations, SAVs (SI-associated vesicles) and LAVs (LPH-associated vesicles) . Here, we report the identification of the lectin galectin-3 delivering non-raft-dependent glycoproteins in the lumen of LAVs in a carbohydrate-dependent manner. Depletion of galectin-3 from MDCK cells results in missorting of non-raft-dependent apical membrane proteins to the basolateral cell pole. This suggests a direct role of galectin-3 in apical sorting as a sorting receptor.
Department of Cell Biology and Cell Pathology, University of Marburg, D-35033 Marburg, Germany.
Delphine
D
Delacour
Catharina I
CI
Cramm-Behrens
Hervé
H
Drobecq
Andre
A
Le Bivic
Hassan Y
HY
Naim
Ralf
R
Jacob
D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D002522:Chlorocebus aethiops; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D037502:Galectin 3 / Q000378:metabolism*; D010694:Lactase-Phlorizin Hydrolase / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D018613:Microscopy, Confocal; D021382:Protein Sorting Signals; D021381:Protein Transport; D013394:Sucrase-Isomaltase Complex / Q000378:metabolism; D014162:Transfection; D022161:Transport Vesicles / Q000378:metabolism*
D037502:Galectin 3; D008562:Membrane Glycoproteins; D021382:Protein Sorting Signals; D013394:Sucrase-Isomaltase Complex; D010694:Lactase-Phlorizin Hydrolase