Overexpression of wild-type Akt1 promoted insulin-stimulated p70S6 kinase (p70S6K) activity and affected GSK3 beta regulation, but did not promote insulin-stimulated GLUT4 translocation or glucose transport in L6 myotubes.
We have developed a simple, direct and sensitive method to detect GLUT4 on the cell surface. Using this system, we found that PI3-kinase plays a key role in the signaling pathway of insulin-stimulated GLUT4 translocation. One of the down stream effectors of PI3-kinase is serine-threonine kinase Akt (protein kinase B, RAK-PK), but the involvement of Akt in insulin-stimulated GLUT4 translocation is controversial. To investigate whether Akt1 regulates insulin-stimulated GLUT4 translocation and glucose uptake in L6 myotubes, we established L6 myotubes stably expressing c-myc epitope-tagged GLUT4 (GLUT4myc) and mouse wild type (WT) Akt1. We found that overexpression of WT Akt1 promoted insulin-stimulated p70S6 kinase (p70S6K) activity and increased the basal activity of GSK3 beta, but did not promote insulin-stimulated GLUT4 translocation or glucose uptake. These data supported the result that Akt is not a main signaling molecule to transmit the signal of insulin-stimulated GLUT4 translocation or glucose uptake from insulin-activated PI3-kinase.
Noda
S
S
Department of Radiology, University of Tokushima School of Medicine, Japan.
Kishi
K
K
Yuasa
T
T
Hayashi
H
H
Ohnishi
T
T
Miyata
I
I
Nishitani
H
H
Ebina
Y
Y
D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002460:Cell Line; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D038362:Glycogen Synthase Kinase 3; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D051379:Mice; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009124:Muscle Proteins; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*
D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; C495693:Slc2a4 protein, mouse; C495694:Slc2a4 protein, rat; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3; D005947:Glucose