Localization of transferrin receptors and insulin-like growth factor II receptors in vesicles from 3T3-L1 adipocytes that contain intracellular glucose transporters.
Transferrin receptors in detergent extracts of subcellular membrane fractions prepared from 3T3-L1 adipocytes were measured by a binding assay. There was a small but significant increase (1.2-fold) in the amount of receptor in a crude plasma membrane fraction and a 40% decrease in the number of transferrin receptors in microsomal membranes prepared from insulin-treated cells, when compared with corresponding fractions from control cells. Intracellular vesicles containing insulin-responsive glucose transporters (GT) have been isolated by immunoadsorption from the microsomal fraction (Biber, J. W., and G. E. Lienhard. 1986. J. Biol. Chem. 261:16180-16184). All of the transferrin receptors in this fraction were localized in these vesicles; however, because the GT vesicles contain approximately 30-fold fewer transferrin receptors than GT, on the average only one vesicle in three contains a transferrin receptor. The binding of 125I-pentamannose 6-phosphate BSA to 3T3-L1 adipocytes at 4 degrees C was used to monitor surface insulin-like growth factor II (IGF-II)/mannose 6-phosphate receptors. Exposure of cells to insulin at 37 degrees C for 5 min resulted in a 2.5-4.5-fold increase in surface receptors. There was a corresponding 20% decrease in the amount of IGF-II receptors in the microsomal membranes prepared from insulin-treated cells, as assayed by immunoblotting. Moreover, the IGF-II receptors and GT were located in the same intracellular vesicles, since antibodies to the carboxyterminal peptide of either protein immunoadsorbed vesicles containing 70-95% of both proteins initially present in the microsomal fraction. In conjunction with other studies, these results indicate that in 3T3-L1 adipocytes, three membrane proteins (the GT, the transferrin receptor, and the IGF-II receptor) respond similarly to insulin, by redistributing to the surface from intracellular compartment(s) in which they are colocalized.
Tanner
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Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03756.
Lienhard
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D000273:Adipose Tissue / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D007328:Insulin / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000302:isolation & purification / Q000378:metabolism*; D017451:Receptors, Somatomedin; D011990:Receptors, Transferrin / Q000187:drug effects / Q000378:metabolism*; D013002:Somatomedins / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
D007328:Insulin; D009004:Monosaccharide Transport Proteins; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D011990:Receptors, Transferrin; D013002:Somatomedins; D007335:Insulin-Like Growth Factor II