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APEX2-mediated RAB proximity labeling identifies a role for RAB21 in clathrin-independent cargo sorting

ABSTRACT: RAB GTPases are central modulators of membrane trafficking. They are under the dynamic regulation of activating guanine exchange factors (GEFs) and inactivating GTPase activating proteins (GAPs). Once activated, RABs recruit a large spectrum of effectors to control trafficking functions of eukaryotic cells. Multiple proteomic studies, using pull-down or yeast two-hybrid approaches, have identified a number of RAB interactors. However, due to the in vitro nature of these and to inherent limitations of each technique, a comprehensive definition of RAB interactors is still lacking. By comparing quantitative affinity purifications of GFP:RAB21 with APEX2-mediated proximity labeling of RAB4a, RAB5a, RAB7a and RAB21, we find that APEX2 proximity labeling allows for the comprehensive identification of RAB regulators and interactors. Importantly, through biochemical and genetic approaches, we establish a novel link between RAB21 and the WASH and retromer complexes, with functional consequences on cargo sorting. Hence, APEX2-mediated proximity labeling of RAB neighboring proteins represents a new and efficient tool to define RAB functions.

SUBMITTER: Tomas Del Olmo

PROVIDER: S-SCDT-91748_2_1551690886_jats | biostudies-other |

REPOSITORIES: biostudies-other

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APEX2-mediated RAB proximity labeling identifies a role for RAB21 in clathrin-independent cargo sorting.

Project description:RAB GTPases are central modulators of membrane trafficking. They are under the dynamic regulation of activating guanine exchange factors (GEFs) and inactivating GTPase-activating proteins (GAPs). Once activated, RABs recruit a large spectrum of effectors to control trafficking functions of eukaryotic cells. Multiple proteomic studies, using pull-down or yeast two-hybrid approaches, have identified a number of RAB interactors. However, due to the in vitro nature of these approaches and inherent limitations of each technique, a comprehensive definition of RAB interactors is still lacking. By comparing quantitative affinity purifications of GFP:RAB21 with APEX2-mediated proximity labeling of RAB4a, RAB5a, RAB7a, and RAB21, we find that APEX2 proximity labeling allows for the comprehensive identification of RAB regulators and interactors. Importantly, through biochemical and genetic approaches, we establish a novel link between RAB21 and the WASH and retromer complexes, with functional consequences on cargo sorting. Hence, APEX2-mediated proximity labeling of RAB neighboring proteins represents a new and efficient tool to define RAB functions.

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4 RABs proxymity labelling - APEX2-mediated RAB proximity labeling identifies a role for RAB21 in clathrin-independent cargo sorting

Project description:APEX2-mediated proximity labeling was performed with 4 endosomal RABs allowed an efficient and comprehensive identification of their protein neighbors. APEX2-mediated proximity labeling was performed in triplicate. Protein enrichments obtained from all RABs were compared to APEX2-nude proximity labeling results. Finally, bioinformatic and biochemical approaches were used to confirm functional validity of RAB protein neighbor’s identification.

2019-01-07 | PXD010950 | Pride

Sorting of Clathrin-Independent Cargo Proteins Depends on Rab35 Delivered by Clathrin-Mediated Endocytosis.

Project description:Clathrin-mediated endocytosis (CME) and clathrin-independent endocytosis (CIE) co-exist in most cells but little is known about their communication and coordination. Here we show that when CME was inhibited, endocytosis by CIE continued but endosomal trafficking of CIE cargo proteins was altered. CIE cargo proteins that normally traffic directly into Arf6-associated tubules after internalization and avoid degradation (CD44, CD98 and CD147) now trafficked to lysosomes and were degraded. The endosomal tubules were also absent and Arf6-GTP levels were elevated. The altered trafficking, loss of the tubular endosomal network and elevated Arf6-GTP levels caused by inhibition of CME were rescued by expression of Rab35, a Rab associated with clathrin-coated vesicles, or its effector ACAPs, Arf6 GTPase activating proteins (GAP) that inactivate Arf6. Furthermore, siRNA knockdown of Rab35 recreated the phenotype of CME ablation on CIE cargo trafficking without altering endocytosis of transferrin. These observations suggest that Rab35 serves as a CME detector and that loss of CME, or Rab35 input, leads to elevated Arf6-GTP and shifts the sorting of CIE cargo proteins to lysosomes and degradation.

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Syp1 regulates the clathrin-mediated and clathrin-independent endocytosis of multiple cargo proteins through a novel sorting motif.

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Microtubule-dependent endosomal sorting of clathrin-independent cargo by Hook1.

Project description:Many plasma membrane (PM) proteins enter cells nonselectively through clathrin-independent endocytosis (CIE). Here, we present evidence that cytoplasmic sequences in three CIE cargo proteins-CD44, CD98, and CD147-were responsible for the rapid sorting of these proteins into endosomal tubules away from endosomes associated with early endosomal antigen 1 (EEA1). We found that Hook1, a microtubule- and cargo-tethering protein, recognized the cytoplasmic tail of CD147 to help sort it and CD98 into Rab22a-dependent tubules associated with recycling. Depletion of Hook1 from cells altered trafficking of CD44, CD98, and CD147 toward EEA1 compartments and impaired the recycling of CD98 back to the PM. In contrast, another CIE cargo protein, major histocompatibility complex class I, which normally traffics to EEA1 compartments, was not affected by depletion of Hook1. Loss of Hook1 also led to an inhibition of cell spreading, implicating a role for Hook1 sorting of specific CIE cargo proteins away from bulk membrane and back to the PM.

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SEC-10 and RAB-10 coordinate basolateral recycling of clathrin-independent cargo through endosomal tubules in Caenorhabditis elegans.

Project description:Despite the increasing number of regulatory proteins identified in clathrin-independent endocytic (CIE) pathways, our understanding of the exact functions of these proteins and the sequential manner in which they function remains limited. In this study, using the Caenorhabditis elegans intestine as a model, we observed a unique structure of interconnected endosomal tubules, which is required for the basolateral recycling of several CIE cargoes including hTAC, GLUT1, and DAF-4. SEC-10 is a subunit of the octameric protein complex exocyst. Depleting SEC-10 and several other exocyst components disrupted the endosomal tubules into various ring-like structures. An epistasis analysis further suggested that SEC-10 operates at the intermediate step between early endosomes and recycling endosomes. The endosomal tubules were also sensitive to inactivation of the Rab GTPase RAB-10 and disruption of microtubules. Taken together, our data suggest that SEC-10 coordinates with RAB-10 and microtubules to form the endosomal tubular network for efficient recycling of particular CIE cargoes.

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Enzyme-mediated proximity labeling identifies small RNAs in the endoplasmic reticulum lumen

Project description:In eukaryotic cells, the subcellular targeting of RNA controls many fundamental aspects of cellular physiology. RNA molecules are broadly distributed throughout the nucleoplasm and cytoplasm, but are conventionally believed to be excluded from the secretory pathway compartments, including the endoplasmic reticulum (ER). Recent discovery of RNA N-glycan modification (glycoRNAs) has challenged this view, but direct evidence of RNA localization in the ER lumen has been lacking. In this study, we applied enzyme-mediated proximity labeling to profile the ER lumen-localized RNAs in human embryonic kidney 293T cells and rat cortical neurons. Our dataset revealed the presence of small non-coding RNAs in the ER lumen, including U RNAs, sco/sca RNAs and Y RNAs, which partially overlap with glycoRNAs. These findings shed light on novel RNA targeting mechanism and raise interesting questions regarding the biological functions of ER lumenal RNAs.

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Binding to any ESCRT can mediate ubiquitin-independent cargo sorting.

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