Phosphatidylinositol 3-phosphate [PtdIns3P] is generated at the plasma membrane by an inositol polyphosphate 5-phosphatase: endogenous PtdIns3P can promote GLUT4 translocation to the plasma membrane.
Exogenous delivery of carrier-linked phosphatidylinositol 3-phosphate [PtdIns(3)P] to adipocytes promotes the trafficking, but not the insertion, of the glucose transporter GLUT4 into the plasma membrane. However, it is yet to be demonstrated if endogenous PtdIns(3)P regulates GLUT4 trafficking and, in addition, the metabolic pathways mediating plasma membrane PtdIns(3)P synthesis are uncharacterized. In unstimulated 3T3-L1 adipocytes, conditions under which PtdIns(3,4,5)P3 was not synthesized, ectopic expression of wild-type, but not catalytically inactive 72-kDa inositol polyphosphate 5-phosphatase (72-5ptase), generated PtdIns(3)P at the plasma membrane. Immunoprecipitated 72-5ptase from adipocytes hydrolyzed PtdIns(3,5)P2, forming PtdIns(3)P. Overexpression of the 72-5ptase was used to functionally dissect the role of endogenous PtdIns(3)P in GLUT4 translocation and/or plasma membrane insertion. In unstimulated adipocytes wild type, but not catalytically inactive, 72-5ptase, promoted GLUT4 translocation and insertion into the plasma membrane but not glucose uptake. Overexpression of FLAG-2xFYVE/Hrs, which binds and sequesters PtdIns(3)P, blocked 72-5ptase-induced GLUT4 translocation. Actin monomer binding, using latrunculin A treatment, also blocked 72-5ptase-stimulated GLUT4 translocation. 72-5ptase expression promoted GLUT4 trafficking via a Rab11-dependent pathway but not by Rab5-mediated endocytosis. Therefore, endogenous PtdIns(3)P at the plasma membrane promotes GLUT4 translocation.
Kong
Anne M
AM
Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia.
Horan
Kristy A
KA
Sriratana
Absorn
A
Bailey
Charles G
CG
Collyer
Luke J
LJ
Nandurkar
Harshal H
HH
Shisheva
Assia
A
Layton
Meredith J
MJ
Rasko
John E J
JE
Rowe
Tony
T
Mitchell
Christina A
CA
D041721:3T3-L1 Cells; D000199:Actins / Q000378:metabolism; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D000818:Animals; D002454:Cell Differentiation; D002462:Cell Membrane / Q000201:enzymology*; D002478:Cells, Cultured; D015870:Gene Expression; D051275:Glucose Transporter Type 4 / Q000378:metabolism*; D006868:Hydrolysis / Q000187:drug effects; D000072181:Inositol Polyphosphate 5-Phosphatases; D007328:Insulin / Q000494:pharmacology; D051379:Mice; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000096:biosynthesis* / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D020691:rab GTP-Binding Proteins / Q000378:metabolism; D000099193:rab11 GTP-Binding Proteins
D000199:Actins; D051275:Glucose Transporter Type 4; D000072181:Inositol Polyphosphate 5-Phosphatases; D007328:Insulin; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010744:Phosphoric Monoester Hydrolases; D020691:rab GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins; C106336:phosphatidylinositol 3,5-diphosphate; C055525:phosphatidylinositol 3-phosphate; C000606432:Inpp5a protein, mouse