Rab7 Regulates Late Endocytic Trafficking Downstream of Multivesicular Body Biogenesis and Cargo Sequestration

• Published in: The Journal of biological chemistry Vol. 284; no. 18; pp. 12110 - 12124
• Main Authors: Vanlandingham, Phillip A., Ceresa, Brian P.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.05.2009; American Society for Biochemistry and Molecular Biology
• Subjects: Endocytosis - physiology; Endosomes - genetics; Endosomes - metabolism; Epidermal Growth Factor - genetics; Epidermal Growth Factor - metabolism; ErbB Receptors - genetics; ErbB Receptors - metabolism; HeLa Cells; Humans; Lysosomes - genetics; Lysosomes - metabolism; Molecular Basis of Cell and Developmental Biology; Protein Transport - physiology; rab GTP-Binding Proteins - genetics; rab GTP-Binding Proteins - metabolism; rab7 GTP-Binding Proteins; RNA Interference
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M809277200

The small molecular weight G-protein RAB7 is localized to both early and late endosomes and has been shown to be critical for trafficking through the endocytic pathway. The role of RAB7 in the endocytic pathway has been controversial, with some groups reporting that it regulates trafficking from early to late endosomes and others ascribing its role to trafficking between late endosomes and lysosomes. In this study, we use RNA interference to identify the exact step RAB7 regulates in the movement of the epidermal growth factor receptor (EGFR) from the cell surface to the lysosome. In the absence of RAB7, trafficking of the EGF·EGFR complex through the early endosome to the late endosome/multivesicular body (LE/MVB) does not change, but exiting from the LE/MVB is blocked. Ultrastructural analysis reveals that RAB7 is not required for formation of intraluminal vesicles of the LE/MVB, since RAB7-deficient cells have an increased number of enlarged LE/MVBs densely packed with intraluminal vesicles. Biochemical data indicate that the EGFR complex is sequestered in these intraluminal vesicles. Together, these data provide evidence that RAB7 is required for the transfer of cargo from the LE/MVB to the lysosome and for endocytic organelle maintenance.