title: Hrs regulates early endosome fusion by inhibiting formation of an endosomal SNARE complex.
abstract: Movement through the endocytic pathway occurs principally via a series of membrane fusion and fission reactions that allow sorting of molecules to be recycled from those to be degraded. Endosome fusion is dependent on SNARE proteins, although the nature of the proteins involved and their regulation has not been fully elucidated. We found that the endosome-associated hepatocyte responsive serum phosphoprotein (Hrs) inhibited the homotypic fusion of early endosomes. A region of Hrs predicted to form a coiled coil required for binding the Q-SNARE, SNAP-25, mimicked the inhibition of endosome fusion produced by full-length Hrs, and was sufficient for endosome binding. SNAP-25, syntaxin 13, and VAMP2 were bound from rat brain membranes to the Hrs coiled-coil domain. Syntaxin 13 inhibited early endosomal fusion and botulinum toxin/E inhibition of early endosomal fusion was reversed by addition of SNAP-25(150-206), confirming a role for syntaxin 13, and establishing a role for SNAP-25 in endosomal fusion. Hrs inhibited formation of the syntaxin 13-SNAP-25-VAMP2 complex by displacing VAMP2 from the complex. These data suggest that SNAP-25 is a receptor for Hrs on early endosomal membranes and that the binding of Hrs to SNAP-25 on endosomal membranes inhibits formation of a SNARE complex required for homotypic endosome fusion.
authors.affiliation: The University of Texas Health Science Center, Dept. of Neurobiology and Anatomy, 6431 Fannin Street, MSB 7.208, Houston, TX 77030, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Sun
authors.forename: Qing
authors.initials: Q
authors.lastname: Yan
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Vida
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Bean
mesh_terms: D000818:Animals; D004705:Endocytosis / Q000502:physiology*; D056827:Endosomal Sorting Complexes Required for Transport; D011992:Endosomes / Q000378:metabolism*; D005057:Eukaryotic Cells / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D046911:Macromolecular Substances; D008561:Membrane Fusion / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism*; D008954:Models, Biological; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D051381:Rats; D050600:SNARE Proteins; D013347:Subcellular Fractions / Q000378:metabolism; D050825:Synaptosomal-Associated Protein 25; D033921:Vesicular Transport Proteins
chemical_list: D056827:Endosomal Sorting Complexes Required for Transport; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D010750:Phosphoproteins; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; C494208:SNAP25 protein, human; D050600:SNARE Proteins; C494210:Snap25 protein, rat; D050825:Synaptosomal-Associated Protein 25; D033921:Vesicular Transport Proteins; C096164:hepatocyte growth factor-regulated tyrosine kinase substrate