Author:

Keywords:

Basolateral Endocytic Pathways, Suckling Rat Ileum, Mdck Cells, Transferrin Receptors, Nonpolarized Cells, Membrane-Proteins, Cultured Neurons, Absorptive Cells, Autoantigen Eea1, Plasma-Membrane, Science & Technology, Life Sciences & Biomedicine, Cell Biology, BASOLATERAL ENDOCYTIC PATHWAYS, SUCKLING RAT ILEUM, MDCK CELLS, TRANSFERRIN RECEPTORS, NONPOLARIZED CELLS, MEMBRANE-PROTEINS, CULTURED NEURONS, ABSORPTIVE CELLS, AUTOANTIGEN EEA1, PLASMA-MEMBRANE, Animals, Cell Line, Cell Polarity, Cells, Cultured, Dendrites, Dogs, Endosomes, Epithelial Cells, Fibroblasts, Hippocampus, Membrane Proteins, Microscopy, Fluorescence, Microscopy, Immunoelectron, Neurons, Rats, Vesicular Transport Proteins, 06 Biological Sciences, 11 Medical and Health Sciences, Developmental Biology, 3101 Biochemistry and cell biology

Abstract:

EEA1 is an early endosomal Rab5 effector protein that has been implicated in the docking of incoming endocytic vesicles before fusion with early endosomes. Because of the presence of complex endosomal pathways in polarized and nonpolarized cells, we have examined the distribution of EEA1 in diverse cell types. Ultrastructural analysis demonstrates that EEA1 is present on a subdomain of the early sorting endosome but not on clathrin-coated vesicles, consistent with a role in providing directionality to early endosomal fusion. Furthermore, EEA1 is associated with filamentous material that extends from the cytoplasmic surface of the endosomal domain, which is also consistent with a tethering/docking role for EEA1. In polarized cells (Madin-Darby canine kidney cells and hippocampal neurons), EEA1 is present on a subset of "basolateral-type" endosomal compartments, suggesting that EEA1 regulates specific endocytic pathways. In both epithelial cells and fibroblastic cells, EEA1 and a transfected apical endosomal marker, endotubin, label distinct endosomal populations. Hence, there are at least two distinct sets of early endosomes in polarized and nonpolarized mammalian cells. EEA1 could provide specificity and directionality to fusion events occurring in a subset of these endosomes in polarized and nonpolarized cells.