Rab4 and Cellubrevin Define Different Early Endosome Populations on the Pathway of Transferrin Receptor Recycling

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 93; no. 18; pp. 9559 - 9564
• Main Authors: Daro, Elizabeth, Van Der Sluijs, Peter, Galli, Thierry, Mellman, Ira
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 03.09.1996; National Acad Sciences; National Academy of Sciences
• Subjects: Animals; Brefeldin A; Cell Compartmentation; Cell Line; Cell Membrane - metabolism; Cell membranes; Cells; Cellular biology; CHO cells; Cricetinae; Cricetulus; Cyclopentanes - pharmacology; Cytoplasm; Endosomes; Endosomes - metabolism; Fluorescein-5-isothiocyanate; Fluorescent Antibody Technique, Direct; GTP-Binding Proteins - metabolism; Humans; Kinetics; Ligands; Membrane Proteins - metabolism; Microscopy; Microscopy, Confocal; Microtubules; Nocodazole - pharmacology; Proteins; rab4 GTP-Binding Proteins; Receptors; Receptors, Transferrin - metabolism; Recycling; Vesicle-Associated Membrane Protein 3
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.93.18.9559

During receptor mediated endocytosis, at least a fraction of recycling cargo typically accumulates in a pericentriolar cluster of tubules and vesicles. However, it is not clear if these endosomal structures are biochemically distinct from the early endosomes from which they are derived. To better characterize this pericentriolar endosome population, we determined the distribution of two endogenous proteins known to be functionally involved in receptor recycling [Rab4, cellubrevin (Cbvn)] relative to the distribution of a recycling ligand [transferrin (Tfn)] as it traversed the endocytic pathway. Shortly after internalization, Tfn entered a population of early endosomes that contained both Rab4 and Cbvn, demonstrated by triple label immunofluorescence confocal microscopy. Tfn then accumulated in the pericentriolar cluster of recycling vesicles (RVs). However, although these pericentriolar endosomes contained Cbvn, they were strikingly depleted of Rab4. The ability of internalized Tfn to reach the Rab4-negative population was not blocked by nocodazole, although the characteristic pericentriolar location of the population was not maintained in the absence of microtubules. Similarly, Rab4-positive and -negative populations remained distinct in cells treated with brefeldin A, with only Rab4-positive elements exhibiting the extended tubular morphology induced by the drug. Thus, at least with respect to Rab4 distribution, the pathway of Tfn receptor recycling consists of at least two biochemically and functionally distinct populations of endosomes, a Rab4-positive population of early endosomes to which incoming Tfn is initially delivered and a Rab4-negative population of recycling vesicles that transiently accumulates Tfn on its route back to the plasma membrane.