Abstract
Rab GTPases and ubiquitination are critical regulators of transmembrane cargo sorting in endocytic and lysosomal targeting pathways. The endosomal protein Rabex-5 intersects these two layers of regulation by being both a guanine nucleotide exchange factor (GEF) for Rab5 and a substrate for ubiquitin (Ub) binding and conjugation. The ability of trafficking machinery components to bind ubiquitinated proteins is known to have a function in cargo sorting. Here, we demonstrate that Ub binding is essential for the recruitment of Rabex-5 from the cytosol to endosomes, independently of its GEF activity and of Rab5. We also show that monoubiquitinated Rabex-5 is enriched in the cytosol. These observations are consistent with a model whereby a cycle of Ub binding and monoubiquitination regulates the association of Rabex-5 with endosomes.
Publication types
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Research Support, N.I.H., Intramural
MeSH terms
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Animals
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Cattle
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Endosomes / metabolism*
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Guanine Nucleotide Exchange Factors / chemistry
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Guanine Nucleotide Exchange Factors / genetics
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Guanine Nucleotide Exchange Factors / metabolism*
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HeLa Cells
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Humans
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Models, Molecular
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Protein Binding
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Protein Conformation
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Proto-Oncogene Proteins c-myc / genetics
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Proto-Oncogene Proteins c-myc / metabolism
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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Ubiquitin / chemistry
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Ubiquitin / genetics
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Ubiquitin / metabolism*
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Vesicular Transport Proteins / genetics
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Vesicular Transport Proteins / metabolism
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rab5 GTP-Binding Proteins / genetics
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rab5 GTP-Binding Proteins / metabolism
Substances
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Guanine Nucleotide Exchange Factors
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Proto-Oncogene Proteins c-myc
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Recombinant Fusion Proteins
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Ubiquitin
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Vesicular Transport Proteins
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rab5 GTP-Binding Proteins