A proteoglycan undergoes different modifications en route to the apical and basolateral surfaces of Madin-Darby canine kidney cells.
We have grown polarized epithelial Madin-Darby canine kidney II (MDCK II) cells on filters in the presence of [(35)S]sulfate, [(3)H]glucosamine, or [(35)S]cysteine/[(35)S]methionine to study proteoglycan (PG) synthesis, sorting, and secretion to the apical and basolateral media. Whereas most of the [(35)S]sulfate label was recovered in basolateral PGs, the [(3)H]glucosamine label was predominantly incorporated into the glycosaminoglycan chains of apical PGs, indicating that basolateral PGs are more intensely sulfated than their apical counterparts. Expression of the PG serglycin with a green fluorescent protein tag (SG-GFP) in MDCK II cells produced a protein core secreted 85% apically, which was largely modified by chondroitin sulfate chains. Surprisingly, the 15% of secreted SG-GFP molecules recovered basolaterally were more heavily sulfated and displayed a different sulfation pattern than the apical counterpart. More detailed studies of the differential modification of apically and basolaterally secreted SG-GFP indicate that the protein cores have been designated to apical and basolateral transport platforms before pathway-specific, post-translational modifications have been completed.
Department of Molecular Biosciences, University of Oslo, Norway.
Heidi
H
Tveit
Gunnar
G
Dick
Venke
V
Skibeli
Kristian
K
Prydz
D000818:Animals; D002460:Cell Line; D004285:Dogs; D005944:Glucosamine / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D011509:Proteoglycans / Q000378:metabolism*; D013431:Sulfates / Q000378:metabolism; D033921:Vesicular Transport Proteins
D011509:Proteoglycans; D013431:Sulfates; D033921:Vesicular Transport Proteins; C075430:serglycin; D005944:Glucosamine