Role of N-glycosylation in trafficking of apical membrane proteins in epithelia.
Polarized distribution of plasma membrane transporters and receptors in epithelia is essential for vectorial functions of epithelia. This polarity is maintained by sorting of membrane proteins into apical or basolateral transport containers in the trans-Golgi network and/or endosomes followed by their delivery to the appropriate plasma membrane domains. Sorting depends on the recognition of sorting signals in proteins by specific sorting machinery. In the present review, we summarize experimental evidence for and against the hypothesis that N-glycans attached to the membrane proteins can act as apical sorting signals. Furthermore, we discuss the roles of N-glycans in the apical sorting event per se and their contribution to folding and quality control of glycoproteins in the endoplasmic reticulum or retention of glycoproteins in the plasma membrane. Finally, we review existing hypotheses on the mechanism of apical sorting and discuss the potential roles of the lectins, VIP36 and galectin-3, as putative apical sorting receptors.
Vagin
Olga
O
Department of Physiology, David Geffen School of Medicine at University of California, Bldg. 113, Rm. 324, 11301 Wilshire Blvd., Los Angeles, California 90073, USA. olgav@ucla.edu
Kraut
Jeffrey A
JA
Sachs
George
G
D004721:Endoplasmic Reticulum / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism*; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism; D021962:Membrane Microdomains / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D017510:Protein Folding; D021382:Protein Sorting Signals; D055550:Protein Stability
D006023:Glycoproteins; D008565:Membrane Proteins; D021382:Protein Sorting Signals