Cohort movement of different ligands and receptors in the intracellular endocytic pathway of alveolar macrophages.
The rate of movement of different receptors and ligands through the intracellular endocytic apparatus was studied in alveolar macrophages. Cells were exposed to iodinated alpha-macroglobulin-protease complexes, mannose terminal glycoproteins, diferric transferrin, and maleylated proteins. By use of the diaminobenzidine density shift procedure, we demonstrated that these ligands were internalized into the same endocytic vesicle. We then compared the rates of transfer to the lysosome or recycling to the cell surface of different ligands/receptors contained in the same endosome. We found that although the rate constant for degradation was ligand specific, the lag time prior to the initiation of degradation was the same for all three ligands. We also found that molecules taken up nonspecifically by fluid-phase pinocytosis had the same lag time prior to degradation as ligands internalized via receptor-mediated endocytosis. These data suggest that different molecules within the same endocytic compartment are transferred to the lysosome (or degradative compartment) at the same rate. We measured the rate of return of receptors to the cell surface by either inactivating surface receptors by protease treatment at 0 degrees C, or by incubating cells with saturating amounts of nonradioactive ligand at 37 degrees C. We then measured the rate of appearance of "new" receptors on the cell surface. Using these approaches, we found that three different receptors were transferred from internal pools to the cell surface at the same rate. The rate of transfer was independent of whether receptors were initially occupied or unoccupied. Our observations indicate that receptor/ligands, once inside alveolar macrophages, are transported by vesicles which transfer their contents as a cohort from one compartment to another. The rate of movement of these receptors is determined by the movement of vesicles and is independent of their content.
Ward
D M
DM
Department of Pathology, University of Utah College of Medicine, Salt Lake City 84132.
Ajioka
R
R
Kaplan
J
J
D015100:3,3'-Diaminobenzidine; D000418:Albumins / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D004705:Endocytosis; D007700:Kinetics; D037181:Lectins, C-Type; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008247:Lysosomes / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism*; D008358:Mannose / Q000378:metabolism; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D010873:Pinocytosis; D011650:Pulmonary Alveoli / Q000166:cytology*; D011817:Rabbits; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic / Q000378:metabolism; D012709:Serum Albumin; D012710:Serum Albumin, Bovine / Q000378:metabolism; D014168:Transferrin / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism; D000511:alpha-Macroglobulins / Q000378:metabolism
D000418:Albumins; D037181:Lectins, C-Type; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D012709:Serum Albumin; D014168:Transferrin; D000511:alpha-Macroglobulins; C028283:diferric transferrin; C049877:maleylalbumin; C023840:mannose-bovine serum albumin conjugate; D012710:Serum Albumin, Bovine; D015100:3,3'-Diaminobenzidine; D014357:Trypsin; D008358:Mannose