Biphasic alteration of glucose transport in 3T3-L1 cells during differentiation to the adipocyte-like phenotype.
Glucose transport activity and subcellular distribution of glucose transporters, GLUT1 and GLUT4 were studied in non-confluent (NCF), confluent (CF), and differentiated 3T3-L1 cells (A). During growth of the fibroblasts to confluence, basal transport activity decreased to 20% of that in non-confluent cells. Corresponding with the reduction in transport activity, the abundance of GLUT1 in plasma membranes as normalized per cell decreased by 75% during growth of the cells to confluence. This effect was mainly due to a reduction of total cellular GLUT1. In addition, the portion of GLUT1 located in intracellular vesicles (low-density microsomes) was moderately increased in confluent cells, and was further increased in cells differentiated to the adipocyte-like phenotype (in NCF 11%, in CF 24.5%, and in A 60% of the total GLUT1). GLUT4, in contrast, was approximately 10-times more abundant in low-density microsomes than in the plasma membranes of the differentiated cells. Insulin failed to stimulate glucose transport activity in non-confluent cells but produced an approximately 2-fold stimulation in confluent cells, probably through translocation of the GLUT1 from the intracellular compartment to the plasma membrane. In the differentiated adipocytes, insulin stimulated a 10-fold increase in glucose transport activity, the maximum levels approaching basal transport rates of non-confluent cells; both GLUT1 and GLUT4 were translocated in response to insulin. These data indicate that insulin sensitivity in 3T3-L1 cells develops in a biphasic pattern. In confluent fibroblasts, a moderate effect of insulin conferred exclusively by GLUT1 is detectable, probably reflecting the small intracellular compartment of GLUT1.(ABSTRACT TRUNCATED AT 250 WORDS)
Ziehm
D
D
Institut für Pharmakologie und Toxikologie, RWTH Aachen, Germany.
Schürmann
A
A
Weiland
M
M
Joost
H G
HG
D016475:3T3 Cells; D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002454:Cell Differentiation; D002462:Cell Membrane / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology; D051379:Mice; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D010641:Phenotype; D013347:Subcellular Fractions / Q000378:metabolism
D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495678:Slc2a1 protein, mouse; C495693:Slc2a4 protein, mouse; D005947:Glucose