MORPHOLOGICAL ANALYSIS OF LIGAND UPTAKE AND PROCESSING - THE ROLE OF MULTIVESICULAR ENDOSOMES AND CURL IN RECEPTOR-LIGAND PROCESSING

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  • 1 January 1985
    • journal article
    • research article
    • Vol. 36  (2) , 230-238
Abstract
The receptor-mediated endocytosis and intracellular processing of transferrin and mannose receptor ligands were investigated in bone marrow-derived macrophages, fibroblasts and reticulocytes. Mannosylated bovine serum albumin (BSA) conjugated to colloidal Au (Au-man-BSA) or colloidal Au-transferrin (AuTf) were used to trace ligand processing in these cells. These ligands appeared to be processed by mechanisms similar to those observed previously with other mannose receptor and galactose receptor ligand probes. After uptake via coated pits and coated vesicles, Au-man-BSA appeared in small uncoated vesicles and tubular structures and was transferred to large, sometimes multivesicular endosomes (MVEs), which sometimes had arm-like protrusions reminiscent of CURL (compartment of uncoupling of receptor and ligand). Initially these structures became increasingly multivesicular, but during longer incubations the inclusion vesicles appeared to disintegrate to leave a denser, amorphous lumen. Inclusion vesicle disintegeration may result from the introduction of lysosomal enzymes into these structures. These results suggest a model for differential receptor-ligand and ligand-ligand sorting. As suggested membrane constituents may be recycled to the plasma membrane from the arms of CURL. Receptor-bound ligands, such as transferrin, would also recycle. The luminal contents, including dissociated ligands, other soluble proteins and inclusion vesicles (containing some membrane proteins), would target to lysosomes. This would result in the lysosomal degradation of any membrane proteins that were incorporated in the inclusion vesicle membranes.

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