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Published 7 July 2003. doi:10.1083/jcb.200302083
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© The Rockefeller University Press, 0021-9525/2003/7/125 $5.00
The Journal of Cell Biology, Volume 162, Number 1, 125-137

Article

 Hrs regulates early endosome fusion by inhibiting formation of an endosomal SNARE complex

Wei Sun1, Qing Yan1, Thomas A. Vida2 and Andrew J. Bean1,3

1 Department of Neurobiology and Anatomy, The University of Texas Health Science Center at Houston Medical School, Houston, TX 77030
2 Microbiology and Molecular Genetics, The University of Texas Health Science Center at Houston Medical School, Houston, TX 77030
3 Program in Cell and Regulatory Biology, The University of Texas Health Science Center at Houston Medical School, Houston, TX 77030

Address correspondence to Andrew J. Bean, The University of Texas Health Science Center, Dept. of Neurobiology and Anatomy, 6431 Fannin Street, MSB 7.208, Houston, TX 77030. Tel.: (713) 500-5614. Fax: (713) 500-0621. E-mail: a.bean{at}uth.tmc.edu

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.

Key Words: SNAP-25; syntaxin; EGF; receptor; endocytosis

* Abbreviations used in this paper: BoNT/E, botulinum neurotoxin E; DMEM, Dulbecco's minimum essential medium; EGFR, EGF receptor; FRET, fluorescence resonance energy transfer; Hrs, hepatocyte responsive serumphosphoprotein; TMR, tetramethylrhodamine; UIM, ubiquitin interacting motif.


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