Kinetic evidence for unique regulation of GLUT4 trafficking by insulin and AMP-activated protein kinase activators in L6 myotubes.
In L6 myotubes, redistribution of a hemagglutinin (HA) epitope-tagged GLUT4 (HA-GLUT4) to the cell surface occurs rapidly in response to insulin stimulation and AMP-activated protein kinase (AMPK) activation. We have examined whether these separate signaling pathways have a convergent mechanism that leads to GLUT4 mobilization and to changes in GLUT4 recycling. HA antibody uptake on GLUT4 in the basal steady state reached a final equilibrium level that was only 81% of the insulin-stimulated level. AMPK activators (5-aminoimidazole-4-carboxyamide ribonucleoside (AICAR) and A-769662) led to a similar level of antibody uptake to that found in insulin-stimulated cells. However, the combined responses to insulin stimulation and AMPK activation led to an antibody uptake level of approximately 20% above the insulin level. Increases in antibody uptake due to insulin, but not AICAR or A-769662, treatment were reduced by both wortmannin and Akt inhibitor. The GLUT4 internalization rate constant in the basal steady state was very rapid (0.43 min(-1)) and was decreased during the steady-state responses to insulin (0.18 min(-1)), AICAR (0.16 min(-1)), and A-769662 (0.24 min(-1)). This study has revealed a nonconvergent mobilization of GLUT4 in response to activation of Akt and AMPK signaling. Furthermore, GLUT4 trafficking in L6 muscle cells is very reliant on regulated endocytosis for control of cell surface GLUT4 levels.
Fazakerley
Daniel J
DJ
Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA27AY, United Kingdom.
Holman
Geoffrey D
GD
Marley
Anna
A
James
David E
DE
Stöckli
Jacqueline
J
Coster
Adelle C F
AC
D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000818:Animals; D001713:Biphenyl Compounds; D002460:Cell Line; D004705:Endocytosis / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D051275:Glucose Transporter Type 4 / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D011753:Pyrones / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D013876:Thiophenes / Q000494:pharmacology
D001713:Biphenyl Compounds; D051275:Glucose Transporter Type 4; D007328:Insulin; D011753:Pyrones; D013876:Thiophenes; D055372:AMP-Activated Protein Kinases; C512408:4-hydroxy-3-(4-(2-hydroxyphenyl)phenyl)-6-oxo-7H-thieno(2,3-b)pyridine-5-carbonitrile