Insulin processing and signal transduction in rat adipocytes.
A glycine-HCl buffer (glycine, 50 mM/NaCl, 0.15 M/HCl, pH 3.5) was used to strip insulin bound to adipocyte cell surfaces. Adipocytes retained their integrity in the glycine buffer and their binding capacity for [125I]iodoinsulin could be completely recovered on transfer of the cells to physiological media. At 37 degrees C, [125I]iodoinsulin binds rapidly to plasma membrane receptors; maximal binding occurs within 10 min. At this temperature, the initial binding is followed by rapid internalization, degradation of the hormone and subsequent loss of label. Insulin treatment, at 37 degrees C, induced internalization of 37% of the plasma membrane insulin receptors. Phenylarsine oxide (PAO), a confirmed inhibitor of protein internalization, allowed insulin binding but completely inhibited degradation of the hormone. Monensin, a carboxylic ionophore which impairs uncoupling hormone-receptor complexes, effectively restricted insulin degradation over short time periods (less than 30 min). Addition of monensin to insulin-stimulated cells did not impair D-glucose uptake. It has previously been reported that PAO inhibits hexose transport through the direct interaction with the glucose transporters and low concentrations of PAO (1 microM) transiently inhibit insulin-stimulated glucose uptake. This recovery phenomenon was again observed when PAO was added to insulin-stimulated, monensin-treated adipocytes. The data suggests that lysosomal degradation of insulin is not requisite for signal transduction.
Douen
A G
AG
Department of Biochemistry and Molecular Biology, School of Biological Sciences, University of Manchester, U.K.
Jones
M N
MN
D000273:Adipose Tissue / Q000378:metabolism*; D000818:Animals; D001152:Arsenicals / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D008297:Male; D008985:Monensin / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011972:Receptor, Insulin / Q000378:metabolism; D015398:Signal Transduction
D001152:Arsenicals; D007328:Insulin; C029341:oxophenylarsine; D008985:Monensin; D011972:Receptor, Insulin; D005947:Glucose