Rabex-5 is a Rab22 effector and mediates a Rab22-Rab5 signaling cascade in endocytosis.
Rabex-5 targets to early endosomes and functions as a guanine nucleotide exchange factor for Rab5. Membrane targeting is critical for Rabex-5 to activate Rab5 on early endosomes in the cell. Here, we report the identification of Rab22 as a binding site on early endosomes for direct recruitment of Rabex-5 and ... activation of Rab5, establishing a Rab22-Rab5 signaling relay to promote early endosome fusion. Rab22 in guanosine 5'-O-(3-thio)triphosphate-loaded form, but not guanosine diphosphate-loaded form, binds to the early endosomal targeting domain (residues 81-230) of Rabex-5 in pull-down assays. Rabex-5 targets to Rab22-containing early endosomes, and Rab22 knockdown by short hairpin RNA abrogates the membrane targeting of Rabex-5 in the cell. In addition, coexpression of Rab22 and Rab5 shows synergistic enlargement of early endosomes, and this synergy is dependent on Rabex-5, providing further support for the collaboration of the two Rab GTPases in regulation of endosome dynamics. This novel Rab22-Rabex-5-Rab5 cascade is functionally important for the endocytosis and degradation of epidermal growth factor.
Mesh Terms:
Animals, Cell Line, Cricetinae, Cricetulus, Endocytosis, Endosomes, Guanine Nucleotide Exchange Factors, Mice, Mice, Knockout, Protein Binding, RNA, Small Interfering, Recombinant Fusion Proteins, Signal Transduction, rab GTP-Binding Proteins, rab5 GTP-Binding Proteins
Animals, Cell Line, Cricetinae, Cricetulus, Endocytosis, Endosomes, Guanine Nucleotide Exchange Factors, Mice, Mice, Knockout, Protein Binding, RNA, Small Interfering, Recombinant Fusion Proteins, Signal Transduction, rab GTP-Binding Proteins, rab5 GTP-Binding Proteins
Mol. Biol. Cell
Date: Nov. 01, 2009
PubMed ID: 19759177
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