Identification of a membrane glycoprotein found primarily in the prelysosomal endosome compartment.

Abstract

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 *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°C block site in the endocytic pathway to lysosomes (~83% of the prelysosomes were positive for plgp57 but <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 intraceUular 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 •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.

Immunocytochemical characterization of the endocytic and phagolysosomal compartments in peritoneal macrophages.

“…We found that this antigen was highly expressed in the TC, including phagolysosomes ; it was undetectable, or present at low levels, in the plasma membrane, early endosomes, carrier vesicles, and lysosomes. This distribution resembles that of a 57-kD membrane glycoprotein recently reported to be predominantly in the PLC/late endosomes ofbovine cells (Park et al, 1991).…”

Characterization of Coated Vesicles that Participate in Endocytic Recycling

“…To identify the transport pathway mediated by the purified vesicles, we examined the cargo content of the purified vesicles. As judged by immunoblotting, the purified vesicles lacked Sec61βp [ER marker, (25)], giantin [Golgi marker, (26)], mannose‐6‐phosphate receptor [M6PR, late endosome marker, (27)], lamp‐1 [lysosome marker, (28)], and sodium/potassium (Na + /K + ) ATPase [plasma membrane marker, (29)] (Figure 9A). In contrast, the purified vesicles contained a significant level of transferrin receptor, suggesting that these vesicles were derived from the early endosome (Figure 9B).…”

Yeast vacuolar proenzymes are sorted in the late Golgi complex and transported to the vacuole via a prevacuolar endosome-like compartment.

“…The steady state amount of both these transient markers within this compartment is negligible. Future efforts will be directed toward the identification of integral membrane proteins associated with the prevacuolar endosomal compartment to serve as functional markers like the recently identified 57-kD protein of the mammalian prelysosomal compartment (Park et al, 1991). Interestingly, the density of this organelle in yeast (",,1.12 g/ml) is nearly identical to the density of the mammalian prelysosomal compartment (Mullock et al, 1989;Park et al, 1991).…”