title: Syntaxin4 interacting protein (Synip) binds phosphatidylinositol (3,4,5) triphosphate.
abstract: The insulin responsive Glut4 transport vesicles contain the v-SNARE protein Vamp2 that associate with the plasma membrane t-SNARE protein Syntaxin 4 to drive insulin-stimulated Glut4 translocation in skeletal muscle and adipocytes. The syntaxin 4 interacting protein (Synip) binds to syntaxin 4 in the basal state and dissociates in the insulin-stimulated state allowing for the subsequent binding of Vamp2 containing Glut4 vesicles and fusion with the plasma membrane. In this study, we have found that Synip binds phosphatidylinositol 3,4,5-triphosphate (PIP3), but not phosphatidylinositol 3 phosphate (PIP) or phosphatidylinositol 3,4-biphosphate (PIP2) through the Synip WW domain as deletion of this domain (Synip ΔWW) failed to bind PIP3. Over-expressed Synip ΔWW in 3T3L1 adipocytes reduced the basal levels of Glut4 at the plasma membrane with no effect on the binding to syntaxin 4 in vitro. Subcellular fractionation demonstrated that the amount of Synip ΔWW at the PM was decreased in response to insulin in 3T3L1 adipocytes whereas the amount of Synip WT increased. These data suggest that in the presence of insulin, the dissociated Synip remains anchored to the plasma membrane by binding to PIP3.
authors.affiliation: Department of Medicine and Molecular science, Gunma University School of Medicine, Maebashi, Gunma, Japan. tsaito@med.gunma-u.ac.jp
authors.forename: Tsugumichi
authors.initials: T
authors.lastname: Saito
authors.forename: Shuichi
authors.initials: S
authors.lastname: Okada
authors.forename: Atsushi
authors.initials: A
authors.lastname: Nohara
authors.forename: Yuko
authors.initials: Y
authors.lastname: Tagaya
authors.forename: Aya
authors.initials: A
authors.lastname: Osaki
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Oh-I
authors.forename: Hiroki
authors.initials: H
authors.lastname: Takahashi
authors.forename: Takafumi
authors.initials: T
authors.lastname: Tsuchiya
authors.forename: Koshi
authors.initials: K
authors.lastname: Hashimoto
authors.forename: Tetsurou
authors.initials: T
authors.lastname: Satoh
authors.forename: Masanobu
authors.initials: M
authors.lastname: Yamada
authors.forename: Jeffrey E
authors.initials: JE
authors.lastname: Pessin
authors.forename: Masatomo
authors.initials: M
authors.lastname: Mori
mesh_terms: D041721:3T3-L1 Cells; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D051379:Mice; D050505:Mutant Proteins / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000187:drug effects; D050765:Qa-SNARE Proteins / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; D050505:Mutant Proteins; D018129:Phosphatidylinositol Phosphates; D050765:Qa-SNARE Proteins; C495693:Slc2a4 protein, mouse; D033921:Vesicular Transport Proteins; C060974:phosphatidylinositol 3,4,5-triphosphate; C060980:phosphatidylinositol 3,4-diphosphate; C055525:phosphatidylinositol 3-phosphate