title: Identification of a membrane glycoprotein found primarily in the prelysosomal endosome compartment.
abstract: Cells contain an intracellular compartment that serves as both the "prelysosomal" delivery site for newly synthesized lysosomal enzymes by the mannose 6-phosphate (Man6P) receptor and as a station along the endocytic pathway to lysosomes. We have obtained mAbs to a approximately 57-kD membrane glycoprotein, (called here plgp57), found predominantly in this prelysosomal endosome compartment. This conclusion is supported by the following results: (a) plgp57 was primarily found in a population of late endosomes that were located just distal to the 20 degrees C block site in the endocytic pathway to lysosomes (approximately 83% of the prelysosomes were positive for plgp57 but less than 5% of the early endosomes had detectable amounts of this marker); (b) plgp57 and the cation-independent (CI) Man6P receptor were located in many of the same intracellular vesicles; (c) plgp57 was found in the membranes of an acidic compartment; (d) immunoelectron microscopy showed that plgp57 was located in characteristic multilamellar- and multivesicular-type vacuoles believed to be prelysosomal endosomes; and (e) cell fractionation studies demonstrated that plgp57 was predominantly found in low density organelles which comigrated with late endosomes and CI Man6P receptors, and only approximately 10-15% of the antigen was found in high density fractions containing the majority of secondary lysosomes. These results indicate that plgp57 is a novel marker for a unique prelysosomal endosome compartment that is the site of confluence of the endocytic and biosynthetic pathways to lysosomes.
authors.affiliation: Section of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, New York 14853.
authors.forename: J E
authors.initials: JE
authors.lastname: Park
authors.forename: J M
authors.initials: JM
authors.lastname: Lopez
authors.forename: E B
authors.initials: EB
authors.lastname: Cluett
authors.forename: W J
authors.initials: WJ
authors.lastname: Brown
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D002417:Cattle; D002458:Cell Fractionation; D002460:Cell Line; D004705:Endocytosis; D007124:Immunoenzyme Techniques; D008247:Lysosomes / Q000737:chemistry*; D008360:Mannosephosphates / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000032:analysis*; D051379:Mice; D016253:Microscopy, Immunoelectron; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface / Q000032:analysis
chemical_list: D000911:Antibodies, Monoclonal; D008360:Mannosephosphates; D008562:Membrane Glycoproteins; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface