title: Loss of granuphilin and loss of syntaxin-1A cause differential effects on insulin granule docking and fusion.
abstract: The Rab27 effector granuphilin/Slp4 is essential for the stable attachment (docking) of secretory granules to the plasma membrane, and it also inhibits subsequent fusion. Granuphilin is thought to mediate these processes through interactions with Rab27 on the granule membrane and with syntaxin-1a on the plasma membrane and its binding partner Munc18-1. Consistent with this hypothesis, both syntaxin-1a- and Munc18-1-deficient secretory cells, as well as granuphilin null cells, have been observed to have a deficit of docked granules. However, to date there has been no direct comparative analysis of the docking defects in those mutant cells. In this study, we morphometrically compared granule-docking states between granuphilin null and syntaxin-1a null pancreatic β cells derived from mice having the same genetic background. We found that loss of syntaxin-1a does not cause a significant granule-docking defect, in contrast to granuphilin deficiency. Furthermore, we newly generated granuphilin/syntaxin-1a double knock-out mice, characterized their phenotypes, and found that the double mutant mice represent a phenocopy of granuphilin null mice and do not represent phenotypes of syntaxin-1a null mice, including their granule-docking behavior. Because granuphilin binds to syntaxin-2 and syntaxin-3 as well as syntaxin-1a, it likely mediates granule docking through interactions with those multiple syntaxins on the plasma membrane.
authors.affiliation: Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma 371-8512, Japan.
authors.forename: Hao
authors.initials: H
authors.lastname: Wang
authors.forename: Ray
authors.initials: R
authors.lastname: Ishizaki
authors.forename: Eri
authors.initials: E
authors.lastname: Kobayashi
authors.forename: Tomonori
authors.initials: T
authors.lastname: Fujiwara
authors.forename: Kimio
authors.initials: K
authors.lastname: Akagawa
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Izumi
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D007328:Insulin / Q000235:genetics / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D051938:Munc18 Proteins / Q000235:genetics / Q000378:metabolism; D050765:Qa-SNARE Proteins / Q000235:genetics / Q000378:metabolism; D022142:Secretory Vesicles / Q000235:genetics / Q000378:metabolism*; D050827:Syntaxin 1 / Q000235:genetics / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D007328:Insulin; D051938:Munc18 Proteins; D050765:Qa-SNARE Proteins; C497938:Stxbp1 protein, mouse; D050827:Syntaxin 1; C122015:Sytl4 protein, mouse; D033921:Vesicular Transport Proteins