Binding receptors for alpha-L-fucosidase in human B-lymphoid cell lines.
An established mechanism for directing newly made acid hydrolases to lysosomes involves acquisition of mannose 6-phosphate residues by the carbohydrate portion of acid hydrolases followed by binding to specific membrane-bound transport receptors and delivery to lysosomes. Two distinct phosphomannosyl receptors (CI-MPR and CD-MPR) have been identified. Alternative mechanisms for trafficking acid hydrolases exist. This report examines means for the possible receptor-mediated intracellular transport of alpha-L- fucosidase in lymphoid cells. The binding of alpha-L-fucosidase to intact cells and to total cell membrane preparations, in conjunction with immunoassays of solubilized membrane preparations, revealed the presence of CI-MPR and CD-MPR on human lymphoid and fibroblast cell lines. The mean level of CD-MPR in nine lymphoid cell lines was 7.2-fold greater than CI-MPR. The mean level of CI-MPR in two fibroblast lines was 3.8-fold greater than CD-MPR. The mean content of CI-MPR was 19.5-fold greater in the fibroblasts than in the lymphoid cells. The CD-MPR content of fibroblasts and lymphoid cells was nearly equivalent. Among these cell lines were a fibroblast and a lymphoid line from the same individual. These results indicate that human B-lymphoid cells are deficient in CI-MPR and suggest that modulation of expression of CI-MPR and CD-MPR in lymphoid cells differs from that in fibroblasts, including cell lines with identical genomes. No specific receptor capable of binding alpha-L-fucosidase independent of mannose 6-phosphate was demonstrable, despite published results that support the existence of a mannose 6-phosphate independent trafficking mechanism in lymphoid cells for this enzyme.
Dicioccio
R A
RA
Department of Gynaecologic Oncology, Roswell Park Cancer Institute, Buffalo, NY 14263.
Miller
A L
AL
D001402:B-Lymphocytes / Q000378:metabolism*; D002352:Carrier Proteins; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D007118:Immunoassay; D009081:Mucolipidoses / Q000201:enzymology*; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface / Q000032:analysis*; D018160:Receptors, Cytoplasmic and Nuclear; D012016:Reference Values; D005644:alpha-L-Fucosidase / Q000302:isolation & purification / Q000378:metabolism*
D002352:Carrier Proteins; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; C034304:cation-dependent mannose-6-phosphate receptor; D005644:alpha-L-Fucosidase