Insulin signaling meets vesicle traffic of GLUT4 at a plasma-membrane-activated fusion step.
A hypothesis that accounts for most of the available literature on insulin-stimulated GLUT4 translocation is that insulin action controls the access of GLUT4 vesicles to a constitutively active plasma-membrane fusion process. However, using an in vitro fusion assay, we show here that fusion is not constitutively active. Instead, the rate of fusion activity is stimulated 8-fold by insulin. Both the magnitude and time course of stimulated in vitro fusion recapitulate the cellular insulin response. Fusion is cell cytoplasm and SNARE dependent but does not require cell cytoskeleton. Furthermore, insulin activation of the plasma-membrane fraction of the fusion reaction is the essential step in regulation. Akt from the cytoplasm fraction is required for fusion. However, the participation of Akt in the stimulation of in vitro fusion is dependent on its in vitro recruitment onto the insulin-activated plasma membrane.
Koumanov
Françoise
F
Department of Biology and Biochemistry, University of Bath, UK.
Jin
Bo
B
Yang
Jing
J
Holman
Geoffrey D
GD
D000255:Adenosine Triphosphate / Q000378:metabolism; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D003402:Creatine Kinase / Q000378:metabolism; D005089:Exocytosis; D036681:Fluorescence Recovery After Photobleaching; D005947:Glucose / Q000378:metabolism; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D008081:Liposomes; D015636:Magnesium Chloride / Q000378:metabolism; D008561:Membrane Fusion; D008954:Models, Biological; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D010725:Phosphocreatine / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D022161:Transport Vesicles / Q000378:metabolism*
D051275:Glucose Transporter Type 4; D007328:Insulin; D008081:Liposomes; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D011518:Proto-Oncogene Proteins; C495694:Slc2a4 protein, rat; D010725:Phosphocreatine; D015636:Magnesium Chloride; D000255:Adenosine Triphosphate; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D003402:Creatine Kinase; D005947:Glucose