Rab4 and Rab7 define distinct nonoverlapping endosomal compartments.
Several Rab GTPases have been localized to distinct compartments of the endocytic pathway. Rab4 is associated with early endosomes and recycling vesicles and regulates membrane recycling from early endosomes. Rab7 is localized to late endosomes and is involved in the regulation of membrane transport between late endosomes and lysosomes. Although Rab4 and Rab7 appear to regulate distinct transport events in endocytosis, it is not clear whether they perform their activities in related or entirely distinct intracellular compartments. To address this question, we generated stable cell lines expressing Rab4 tagged with a novel X31 influenza hemagglutinin (NH) epitope tag. These antibodies are characterized in this paper and were used to immunoisolate endocytic vesicles with cytoplasmically exposed NHRab4. Immunoisolated membranes contain internalized 125I-transferrin, but are devoid of Rab7. Confocal immunofluorescence microscopy showed that the early endosomal GTPases Rab4 and Rab5 both do not codistribute with Rab7 within the same cell. These observations suggest that each of the three Rab GTPases operationally defines a distinct station of the endocytic pathway.
Department of Cell Biology, Utrecht University School of Medicine, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands. pvander@knoware.nl
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D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002451:Cell Compartmentation; D006224:Cricetinae; D004285:Dogs; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007457:Iodine Radioisotopes; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D014162:Transfection; D014168:Transferrin / Q000378:metabolism; D020691:rab GTP-Binding Proteins; D020695:rab4 GTP-Binding Proteins; D000090802:rab7 GTP-Binding Proteins
D007457:Iodine Radioisotopes; D014168:Transferrin; D000090802:rab7 GTP-Binding Proteins; C000716463:rab7 GTP-binding proteins, human; D019204:GTP-Binding Proteins; D020691:rab GTP-Binding Proteins; D020695:rab4 GTP-Binding Proteins