title: Extracellular release of acid hydrolases from cultured retinal pigmented epithelium.
abstract: The intracellular and extracellular distribution of acid hydrolases in cultured retinal pigmented epithelium (RPE) was studied. Incubation of cultured RPE in medium containing 20 mM mannose-6-phosphate resulted in the extracellular release of approximately 15% of the cell-associated activity of several acid hydrolases. This represents an approximate 120% increase over control levels after 24 hr of culture with 20 mM mannose-6-phosphate. The extracellular release is not due to cell lysis, since no release of the cytoplasmic marker lactate dehydrogenase was seen. n-Acetyl-beta-glucosaminidase, alpha-mannosidase, and beta-glucuronidase were released into the extracellular medium, while acid phosphatase and beta-glucosidase were not. The release was specific for mannose-6-phosphate, and was dose-dependent. Inhibition of protein synthesis by treatment of RPE cells with cycloheximide (100 micrograms/ml) inhibited extracellular acid hydrolase release. RPE cells exhibited n-Acetyl-beta-glucosaminidase bound to the cell surface via a mannose-6-phosphate sensitive receptor. These results demonstrate a specific extracellular release of acid hydrolases by RPE and the presence of at least one acid hydrolase on the RPE cell surface. This may represent a mechanism for control of cell surface and extracellular levels of these enzymes in RPE via the mannose-6-phosphate receptor.
mesh_terms: D000118:Acetylglucosaminidase / Q000378:metabolism; D000135:Acid Phosphatase / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D005110:Extracellular Space / Q000201:enzymology*; D005136:Eye Proteins / Q000096:biosynthesis; D006801:Humans; D007425:Intracellular Membranes / Q000201:enzymology; D008361:Mannosidases / Q000378:metabolism; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D043323:alpha-Mannosidase; D001617:beta-Glucosidase / Q000378:metabolism
chemical_list: D005136:Eye Proteins; D000135:Acid Phosphatase; D008361:Mannosidases; D001617:beta-Glucosidase; D043323:alpha-Mannosidase; D000118:Acetylglucosaminidase