PUTATIVE O-GLYCOSYLATION SITES AND A MEMBRANE ANCHOR ARE NECESSARY FOR APICAL DELIVERY OF THE HUMAN NEUROTROPHIN RECEPTOR IN CACO-2 CELLS

We have expressed the human neurotrophin receptor p75 (p75(NTR)) in th e intestinal epithelial cell line Caco-2 as a model to study intracell ular transport and subcellular sorting signals in intestinal cells. p7 5(NTR) was localized at the apical membrane of Caco-2 cells and reache d this membrane mainly via an indirect pathway. Apical localization, i ntracellular routing, and basolateral to apical transcytosis were not affected by truncation of the cytoplasmic domain or replacement of the transmembrane domain by a glycosyl phosphatidylinositol anchor. Remov al of membrane anchoring resulted in basolateral secretion of the ecto domain of p75(NTR) in Caco-2 cells but in apical secretion in Madin-Da rby canine kidney (MDCK) cells. Substitution of potential O-glycosylat ion sites present in the stalk of p75NTR led to intracellular cleavage and secretion of the ectodomain into the basolateral medium both in C aco-2 and MDCK cells. These results suggest that the stalk of p75NTR c arries an apical sorting information that is recognized efficiently by Caco-2 cells only when attached to the membrane. This apical sorting information is linked to the presence of predicted O-glycosylation sit es in that region. These putative O-glycosylation sites also play a ro le in the regulation of p75NTR transport to the cell surface and in th e prevention of rapid degradation by cleavage of the stalk domain.