Haas AK, Fuchs E, Kopajtich R, Barr FA.. A GTPase-activating protein controls Rab5 function in endocytic trafficking. Nat Cell Biol 7: 887-893
Max-Planck Institute of Biochemistry, Department of Cell Biology, Am Klopferspitz 18, D-82152 Martinsried, Germany. Nature Cell Biology
(Impact Factor: 19.68).
10/2005; 7(9):887-93. DOI: 10.1038/ncb1290
Rab-family GTPases are conserved regulators of membrane trafficking that cycle between inactive GDP-bound and activated GTP-bound states. A key determinant of Rab function is the lifetime of the GTP-bound state. As Rabs have a low intrinsic rate of GTP hydrolysis, this process is under the control of GTP-hydrolysis-activating proteins (GAPs). Due to the large number of Rabs and GAPs that are encoded by the human genome, it has proven difficult to assign specific functional relationships to these proteins. Here, we identify a Rab5-specific GAP (RabGAP-5), and show that RN-Tre (previously described as a Rab5 GAP) acts on Rab41. RabGAP-5 overexpression triggers a loss of the Rab5 effector EEA1 from endosomes and blocks endocytic trafficking. By contrast, depletion of RabGAP-5 results in increased endosome size, more endosome-associated EEA1, and disrupts the trafficking of EGF and LAMP1. RabGAP-5 therefore limits the amount of activated Rab5, and thereby regulates trafficking through endosomes.
Available from: Brian Storrie
- "Similarly, a genome wide RNAi screen with human HeLa cells revealed a single Rab, Rab18, as being significantly important within the early secretory pathway (Simpson et al., 2012). Rab-centric screens based on reductions in GTPase activity achieved through the expression of mutant GAPs, Rab-specific guanine nucleotide activating proteins (Haas et al., 2005, 2007), or overexpression of wild-type or engineered Rab mutations (Dejgaard et al., 2008) have implicated 3 of ~70 mammalian Rab proteins required for Golgi ribbon organization: Rab1, Rab18, and Rab43 (mis-identified as Rab41 in Haas et al., 2005). "
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ABSTRACT: Rab proteins, small GTPases, are key regulators of mammalian Golgi apparatus organization. Based on the effect of Rab activation state, Rab proteins fall into two functional classes. In Class1, inactivation induces Golgi ribbon fragmentation and/or redistribution of Golgi enzymes to the Endoplasmic Reticulum, while overexpression of wild type or activation has little, if any, effect on Golgi ribbon organization. In Class 2, the reverse is true. We give emphasis to Rab6, the most abundant Golgi-associated Rab protein. Rab6 depletion in HeLa cells causes an increase in Golgi cisternal number, longer, more continuous cisternae, and a pronounced accumulation of vesicles; the effect of Rab6 on Golgi ribbon organization is probably through regulation of vesicle transport. In effector studies, motor proteins and their regulators are found to be key Rab6 effectors. A related Rab, Rab41, affects Golgi ribbon organization in a contrasting manner. The balance between minus- and plus-end directed motor recruitment may well be the major Rab-dependent factor in Golgi ribbon organization.
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Available from: Margarita Cabrera
- "Recent studies showed that the Msb3 GTPase-activating protein (GAP) subsequently inactivates Vps21, thus maintaining organelle identity along the endolysosomal pathway (Lachmann et al., 2012; Nickerson et al., 2012). Msb3 function is thus similar to mammalian RabGAP-5, which regulates endocytic transport via its action on Rab5 (Haas et al., 2005). However, the temporal and spatial coordination of Vps21 inactivation reaction remains unclear. "
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ABSTRACT: Membrane microcompartments of the early endosomes serve as a sorting and signaling platform, where receptors are either recycled back to the plasma membrane or forwarded to the lysosome for destruction. In metazoan cells, three complexes, termed BLOC-1 to -3, mediate protein sorting from the early endosome to lysosomes and lysosome-related organelles. We now demonstrate that BLOC-1 is an endosomal Rab-GAP (GTPase-activating protein) adapter complex in yeast. The yeast BLOC-1 consisted of six subunits, which localized interdependently to the endosomes in a Rab5/Vps21-dependent manner. In the absence of BLOC-1 subunits, the balance between recycling and degradation of selected cargoes was impaired. Additionally, our data show that BLOC-1 is both a Vps21 effector and an adapter for its GAP Msb3. BLOC-1 and Msb3 interacted in vivo, and both mutants resulted in a redistribution of active Vps21 to the vacuole surface. We thus conclude that BLOC-1 controls the lifetime of active Rab5/Vps21 and thus endosomal maturation along the endocytic pathway.
Available from: Paul Maddox
- "As expected, GFP-Rip11 can be pulled down efficiently with Rab11 CA and to a lesser extent with Rab11 WT (Fig. 2 I, left). As a negative control, we expressed RN-tre together with GST-Rab11 because RN-tre should not bind Rab11 (Haas et al., 2005). Indeed, RN-tre was not pulled down by any form of Rab11 (Fig. 2 I, middle left). "
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ABSTRACT: Membrane trafficking has well-defined roles during cell migration. However, its regulation is poorly characterized. In this paper, we describe the first screen for putative Rab-GTPase-activating proteins (GAPs) during collective cell migration of Drosophila melanogaster border cells (BCs), identify the uncharacterized Drosophila protein Evi5 as an essential membrane trafficking regulator, and describe the molecular mechanism by which Evi5 regulates BC migration. Evi5 requires its Rab-GAP activity to fulfill its functions during migration and acts as a GAP protein for Rab11. Both loss and gain of Evi5 function blocked BC migration by disrupting the Rab11-dependent polarization of active guidance receptors. Altogether, our findings deepen our understanding of the molecular machinery regulating endocytosis and subsequently cell signaling during migration.
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