Lj. Foster et al., Insulin accelerates inter-endosomal GLUT4 traffic via phosphatidylinositol3-kinase and protein kinase B, J BIOL CHEM, 276(47), 2001, pp. 44212-44221
Insulin enhances plasmalemmal-directed traffic of glucose transporter-4 (GL
UT4), but it is unknown whether insulin regulates GLUT4 traffic through end
osomal compartments. In L6 myoblasts expressing Myc-tagged GLUT4, insulin m
arkedly stimulated the rate of GLUT4myc recycling. In myoblasts stimulated
with insulin to maximize surface GLUT4myc levels, we followed the rates of
surface-labeled GLUT4myc endocytosis and chased its intracellular distribut
ion in space and time using confocal immunofluorescence microscopy. Surface
-labeled GLUT4myc internalized rapidly (t(1/2) 3 min), reaching the early e
ndosome by 2 min and the transferrin receptor-rich, perinuclear recycling e
ndosome by 20 min. Upon re-addition of insulin, the t(1/2) of GLUT4 disappe
arance from the plasma membrane was unchanged (3 min), but strikingly, GLUT
4myc reached the recycling endosome by 10 and left by 20 min. This effect o
f insulin was blocked by the phosphatidylinositol 3-kinase inhibitor LY2940
02 or by transiently transfected dominant-negative phosphatidylinositol 3-k
inase and protein kinase B mutants. In contrast, insulin did not alter the
rate of arrival of rhodamine-labeled transferrin at the recycling endosome.
These results reveal a heretofore unknown effect of insulin to accelerate
interendosomal travel rates of GLUT4 and identify the recycling endosome as
an obligatory stage in insulin-dependent GLUT4 recycling.