Adsorptive endocytosis of lysosomal enzymes by human fibroblasts: presence of two different functional systems that deliver an acid hydrolase to lysosomes.
Endocytosis of human spleen beta-glucuronidase by human fibroblasts can be completely impaired by the competitive inhibitor mannose 6-phosphate or by pretreatment with acid phosphatase or endoglycosidases H or F. However, endocytosis of bovine spleen and liver beta-glucuronidase is partially impaired by the same treatments, suggesting that the bovine enzyme contains two endocytosis recognition markers located in separate enzyme domains. The mannose 6-phosphate recognition marker seems to be responsible for approximately 23% of the bovine enzyme endocytosis. The existence of two lysosomal endocytosis systems in human fibroblasts is supported by the following facts: (a) the rate of endocytosis of mannose 6-phosphate-containing human beta-glucuronidase was not affected by the presence of high levels of the bovine enzyme (which has only the other marker). (b) Anti-215K mannose 6-phosphate receptor antibodies selectively impair the endocytosis of the beta-glucuronidase containing mannose 6-phosphate. (c) Weak bases exert a differential effect on human and bovine endocytosis. beta-Glucuronidase internalized by either system is targeted to secondary lysosomes of human beta-glucuronidase-deficient fibroblasts, where it is able to degrade accumulated glycosaminoglycans. These results suggest that human fibroblasts have two different and independent endocytic systems for targeting of acid hydrolases to lysosomes.
González-Noriega
A
A
Unidad de Genética de la Nutrición, Universidad Nacional Autónoma de México.
Coutiño
R
R
Saavedra
V M
VM
Barrera
R
R
D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D002738:Chloroquine / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects; D005347:Fibroblasts / Q000502:physiology; D005966:Glucuronidase / Q000378:metabolism*; D006026:Glycoside Hydrolases / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008247:Lysosomes / Q000201:enzymology*; D008360:Mannosephosphates / Q000494:pharmacology
D008360:Mannosephosphates; D000643:Ammonium Chloride; C027693:mannose-6-phosphate; D002738:Chloroquine; D006026:Glycoside Hydrolases; D005966:Glucuronidase