The Small GTP-Binding Protein rab4 is Associated with Early Endosomes

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 88; no. 14; pp. 6313 - 6317
• Main Authors: van der Sluijs, Peter, Hull, Michael, Zahraoui, Ahmed, Tavitian, Armand, Goud, Bruno, Mellman, Ira
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 15.07.1991; National Acad Sciences
• Subjects: 550201 - Biochemistry- Tracer Techniques; Analytical, structural and metabolic biochemistry; Animals; Antibodies; BASIC BIOLOGICAL SCIENCES; BETA DECAY RADIOISOTOPES; Binding and carrier proteins; Biological and medical sciences; CELL CONSTITUENTS; Cell Fractionation; Cell Line; CELL MEMBRANES; Centrifugation; CHO cells; DAYS LIVING RADIOISOTOPES; ELECTRON CAPTURE RADIOISOTOPES; ELECTROPHORESIS; Endocytosis; ENDOPLASMIC RETICULUM; Endoplasmic Reticulum - metabolism; Endoplasmic Reticulum - ultrastructure; Endosomes; Fluorescent Antibody Technique; Fundamental and applied biological sciences. Psychology; GLOBULINS; GLOBULINS-BETA; Golgi apparatus; Golgi Apparatus - metabolism; Golgi Apparatus - ultrastructure; GTP-Binding Proteins - isolation & purification; GTP-Binding Proteins - metabolism; HELA CELLS; HeLa Cells - metabolism; Horseradish Peroxidase; Humans; INTERMEDIATE MASS NUCLEI; INTERNAL CONVERSION RADIOISOTOPES; Intracellular Membranes - metabolism; Intracellular Membranes - ultrastructure; IODINE 125; IODINE ISOTOPES; ISOTOPE APPLICATIONS; ISOTOPES; Lysosomes; MEMBRANE PROTEINS; MEMBRANES; METALLOPROTEINS; Microsomes - metabolism; Microsomes - ultrastructure; NUCLEI; ODD-EVEN NUCLEI; ORGANIC COMPOUNDS; PROTEINS; rab4 GTP-Binding Proteins; rab4 protein; RADIOISOTOPES; RADIORECEPTOR ASSAY; RECEPTORS; Recycling; TRACER TECHNIQUES; TRANSFERRIN; Human; Vesicle; GTP; Membrane protein; Transferrin; CHO cell line; Immunological method; Binding protein; Endocytosis; Cell line; Transfection; Membrane transport; Cell cycle
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.88.14.6313

Small GTP-binding proteins of the rab family have been implicated as playing important roles in controlling membrane traffic on the biosynthetic and endocytic pathways. We demonstrate that a distinct rab protein, rab4p, is associated with the population of early endosomes involved in transferrin-receptor recycling. An antibody to human rab4p was found to detect a doublet of ≈24-kDa proteins on immunoblots from various cell types. Seventy-five percent of these proteins were tightly membrane bound and could be released only by detergent treatment. Upon isolation of early endosomes, late endosomes, and lysosomes, by free-flow electrophoresis and Percoll density-gradient centrifugation, most (70%) of the rab4p was found to cofractionate with early endosomes and endocytic vesicles containing125I-labeled transferrin. The rab proteins previously localized to the endoplasmic reticulum and/or Golgi apparatus were not found in these fractions. We also localized rab4p to transferrin-receptor-containing early endosomes by immunofluorescence after expression of rab4 cDNA. The association of rab4p with early endosomes and other vesicles involved in the intracellular transport of transferrin receptor suggests that rab4p may play a role in regulating the pathway of receptor recycling.