ISOLATION AND CELLULAR-LOCALIZATION OF THE DECORIN ENDOCYTOSIS RECEPTOR

The small dermatan sulfate proteoglycans decorin and biglycan are effi ciently internalized by a variety of cells of mesenchymal origin. This process is modulated, at least under tissue culture conditions, by ce ll surface-associated heparan sulfate proteoglycans. Receptor proteins of 51 and 26 kDa, respectively, bind to leucine-rich repeat structure s of the core proteins of the small proteoglycans but also to highly s ulfated domains of heparan sulfate. The 51 kDa protein was purified fr om rat brain tissue by subcellular fractionation, heparin affinity chr omatography and subsequent SDS-PAGE, and was used for raising a polycl onal antiserum. Affinity-purified antibodies also recognize the 26 kDa protein and a few other low molecular weight proteins, suggesting tha t these proteins represent proteolytic degradation products of the 51 kDa receptor. By confocal laser microscopy, it could be demonstrated t hat the affinity-purified antibody reacted at 0 degrees C with a prote in that became internalized and was transported to a perinuclear compa rtment during 15 min of incubation at 37 degrees C. These findings pro vide direct evidence that the receptor protein(s) are internalized tog ether with the ligand and reach an endosomal compartment where further sorting can occur.