Evidence for modulation of insulin action and degradation independently of insulin binding

1981 ◽  
Vol 240 (3) ◽  
pp. E325-E332
Author(s):  
J. F. Caro ◽  
J. M. Amatruda
Keyword(s):  
Plasma Membrane ◽  
Insulin Receptor ◽  
Insulin Action ◽  
Insulin Binding ◽  
Isolated Hepatocytes ◽  
Insulin Degradation ◽  
Acetate Incorporation ◽  
Large Excess ◽  
Receptor Antibody

The interrelationships between insulin binding, action, and degradation were investigated in isolated hepatocytes with the aid of an insulin-receptor antibody (IRA) preparation that does not affect insulin binding. These IRA have insulin-like effects as determined by their ability to stimulate [14C]acetate incorporation into lipids. However, this effect is less than that of insulin; and in the presence of insulin and IRA, the effects of insulin are partially inhibited. The IRA have no effect on lipogenesis stimulated by postreceptor insulin "mimickers." The IRA also significantly inhibit insulin degradation. However, they do not affect insulin degradation in the presence of a large excess of unlabeled hormone. Taken together these data demonstrate that insulin action and degradation can be modulated independently of binding and suggest that the IRA partially inhibit insulin action and degradation through a portion of the insulin receptor that is not a determinant of insulin binding. It is possible, however, that there exist in the antiserum heterogeneous antibodies that bind to nonreceptor sites on the plasma membrane and mediate some of the phenomena observed.

Insulin receptors: binding kinetics and structure-function relationship of insulin

1984 ◽  
Vol 64 (4) ◽  
pp. 1321-1378 ◽  
Author(s):  
S. Gammeltoft
Keyword(s):  
Plasma Membrane ◽  
Binding Affinity ◽  
Insulin Action ◽  
Molecular Mechanisms ◽  
Physiological Role ◽  
Insulin Receptors ◽  
Binding Kinetics ◽  
Antigenic Determinants ◽  
Insulin Degradation ◽  
Recent Advances

During the last decade, earlier suggestions that insulin acts at the plasma membrane level via combination with receptors have been amply confirmed in studies of 125I-labeled insulin binding kinetics. Efforts have been devoted to the development of homogeneous, stable, and bioactive tracers, and a preparation of monoiodo[TyrA14]insulin showed 100-125% biological activity. The initially simple model of reversible, bimolecular, and noncooperative interaction between receptor and insulin has been revised to include the existence of at least three affinity states that may be linked to modulation of the biological response induced by the insulin-receptor complex. Thus negative cooperativity seems important in reducing oscillations of insulin action with variations in plasma insulin concentration, and formation of a high-affinity state or positive cooperativity may lead to desensitization of receptors. The kinetic phenomena suggest that receptor-binding affinity and function are actively regulated by insulin itself. At present the receptor model is purely functional and does not imply molecular mechanisms. However, recent advances in the analysis of receptor structure and biochemistry promise that the molecular equivalents of the kinetic phenomena may be elucidated in the near future. Furthermore the reaction between receptor and insulin is irreversible because of degradation of receptor-bound insulin, which may result in termination of the metabolic activation. Morphological and biochemical work suggests that internalization of the receptor-insulin complex from the plasma membrane transfers insulin to intracellular organelles like the lysosomes, the Golgi apparatus, or nucleus, where degradation by insulin protease takes place, whereas the receptor is recycled back to the membrane. Recent advances in the studies of biosynthesis and cellular dynamics of receptors indicate that intracellular processing and redistribution of binding sites may play a role in the mechanism of insulin action. Insulin receptors are widely distributed in all cell types, but evidence has accumulated that receptors show tissue and species variations in their functional properties regarding binding affinity, insulin specificity, cooperativity, and insulin degradation and in structural properties such as antigenic determinants and glycosidic composition. Perhaps these differences reflect cellular adaptations and variations in the physiological role of insulin.(ABSTRACT TRUNCATED AT 400 WORDS)

Dexamethasone modulates insulin receptor expression and subcellular distribution of the glucose transporter GLUT 1 in UMR 106-01, a clonal osteogenic sarcoma cell line

1996 ◽  
Vol 17 (1) ◽  
pp. 7-17 ◽  
Author(s):  
D M Thomas ◽  
S D Rogers ◽  
K W Ng ◽  
J D Best
Keyword(s):  
Plasma Membrane ◽  
Insulin Receptor ◽  
Glucose Transport ◽  
Glucose Transporter ◽  
Insulin Binding ◽  
Receptor Expression ◽  
Glut 1 ◽  
Receptor Mrna ◽  
Insulin Receptor Expression ◽  
Umr 106

ABSTRACT Corticosteroids have profound effects on bone metabolism, though the underlying mechanisms remain unclear. They are also known to alter glucose metabolism, in part by induction of insulin resistance. To determine whether corticosteroids impair glucose metabolism in bone cells, we have examined the actions of dexamethasone (DEX) on glucose transport and insulin receptor expression using osteoblast-like UMR 106-01 cells. DEX was shown to inhibit basal 2-deoxyglucose uptake by up to 30% in a time- and dose-dependent manner. It inhibited insulin-stimulated glucose transport by 13%. By Northern and Western blot analysis, DEX was shown to stimulate insulin receptor mRNA and protein by up to 5·6-fold, but it had no effect on expression of the glucose transporter GLUT 1 mRNA or protein under basal conditions. However, DEX augmented insulin-stimulated GLUT 1 mRNA and protein levels. By Scatchard analysis of labelled insulin binding, DEX increased insulin receptor number per cell by 54%. Subcellular fractionation and Western blot analysis demonstrated that DEX caused a redistribution of immunoreactive GLUT 1 from plasma membrane to intracellular microsomes, resulting in a 21% decrease in GLUT 1 at the plasma membrane. These data suggest that (i) DEX impairs basal glucose transport by post-translational mechanisms in UMR 106-01 cells, (ii) DEX increases insulin receptor mRNA, protein and insulin binding and (iii) the inhibition of glucose transport by DEX dominates its effects on the insulin receptor. It is possible that DEX inhibition of glucose transport in osteoblasts may contribute to steroid-induced osteoporosis.

scholarly journals Effects of monensin on insulin interactions with isolated hepatocytes. Evidence for inhibition of receptor recycling and insulin degradation

1986 ◽  
Vol 234 (2) ◽  
pp. 463-468 ◽  
Author(s):  
J Whittaker ◽  
V A Hammond ◽  
R Taylor ◽  
K G M M Alberti
Keyword(s):  
Time Course ◽  
Rat Hepatocytes ◽  
Insulin Binding ◽  
Isolated Hepatocytes ◽  
Insulin Degradation ◽  
Receptor Recycling ◽  
Surface Binding ◽  
Binding Studies ◽  
Isolated Rat Hepatocytes ◽  
Receptor Concentration

Recent evidence suggests that, during endocytosis, receptors for many polypeptide ligands are spared degradation and are recycled to the plasma membrane for re-utilization. The univalent ionophore monensin was shown to inhibit membrane recycling. We therefore examined its effects on insulin interactions with isolated rat hepatocytes to characterize further receptor endocytosis and recycling in these cells. At 10 degrees C, in the absence of endocytosis, no change in insulin binding was observed. However, at 37 degrees C a concentration-dependent decrease in 125I-insulin binding was seen in the presence of insulin; this reached a maximum of 60% at 1 nM-insulin. Competitive binding studies showed this to be due to a 50-60% decrease in cell-surface insulin-receptor concentration, although the total cellular receptor concentration remained unchanged, suggesting that monensin causes the intracellular sequestration of receptors. Time-course studies of the processing of 2.5 nM-insulin showed that monensin produced a 50-60% decrease in surface binding, accompanied by a similar decrease in internalization and total inhibition of insulin degradation. When hepatocytes with 125I-insulin prebound to their surface receptors at 10 degrees C were warmed to 37 degrees C, monensin had no effect on internalization, but caused marked impairment of intracellular insulin degradation. It is concluded that monensin inhibits receptor recycling and cellular insulin degradation.

Female sex hormones, perinatal, and peripubertal androgenization on hepatocyte insulin dynamics in rats

1993 ◽  
Vol 264 (3) ◽  
pp. E342-E347 ◽  
Author(s):  
G. R. Krakower ◽  
D. A. Meier ◽  
A. H. Kissebah
Keyword(s):  
Cell Surface ◽  
Insulin Receptor ◽  
Sex Hormones ◽  
Insulin Binding ◽  
Ovariectomized Rats ◽  
Insulin Degradation ◽  
Insulin Metabolism ◽  
Female Sex ◽  
Female Sex Hormones ◽  
Receptor Number

The effects of female sex hormones on insulin binding and receptor-mediated insulin degradation were investigated in hepatocytes from ovariectomized rats. The influences of perinatal and peripubertal androgenization on these events were examined. Estradiol treatment increased insulin binding and receptor-mediated insulin degradation by increasing cell surface insulin receptor number. Progesterone also increased both binding and degradation, but the increase in degradation exceeded the increase in binding. Perinatal exposure to testosterone blunted the estradiol-induced increase in insulin binding and decreased degradation, whereas the progesterone-mediated increases were completely suppressed. Peripubertal testosterone decreased binding, with a much greater reduction in insulin degradation. Perinatal androgenization did not influence the peripubertal testosterone effects. Thus peripubertal female sex hormones exert regulatory influences on both hepatic cell surface insulin receptor number and postreceptor events mediating insulin degradation. These events are modulated by perinatal and peripubertal exposure to androgens. Abnormalities in sex hormone levels and/or hepatic androgenization could therefore contribute to altered insulin metabolism and hyperinsulinemia in some hyperandrogenized women with abdominal obesity and increased androgenic activity.

Effect of exercise on insulin receptor binding and kinase activity in skeletal muscle

1989 ◽  
Vol 256 (1) ◽  
pp. E138-E144 ◽  
Author(s):  
J. L. Treadway ◽  
D. E. James ◽  
E. Burcel ◽  
N. B. Ruderman
Keyword(s):  
Skeletal Muscle ◽  
Insulin Receptor ◽  
Insulin Action ◽  
White Muscle ◽  
Kinase Activity ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Insulin Receptors ◽  
Insulin Binding ◽  
Similar Data

Insulin action in skeletal muscle is markedly enhanced for several hours after an acute bout of exercise. The purpose of this study was to examine the possible involvement of the intrinsic tyrosine kinase activity of the insulin receptor in mediating these effects. Red and white muscles were removed from rats either at rest or following a treadmill run (45 min at 18 m/min), and insulin receptors were isolated in partially purified form. Basal and insulin-stimulated receptor kinase activity was higher in red than in white muscle, in agreement with previous studies (J. Biol. Chem. 261: 14939-14944, 1986). There was no effect of exercise on insulin binding, basal and insulin-stimulated receptor autophosphorylation, or basal and insulin-stimulated exogenous kinase activity, in either red or white muscle. Similar data were obtained when phosphatase inhibitors were used during receptor isolation. The structure of insulin receptors isolated from the muscle of exercised and control rats was similar as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of affinity cross-linked insulin receptors. We conclude that enhanced insulin action in muscle during the postexercise state is not related to increased kinase activity of the insulin receptor.

scholarly journals Receptor- and non-receptor-mediated uptake and degradation of insulin by hepatocytes

1982 ◽  
Vol 208 (1) ◽  
pp. 211-219 ◽  
Author(s):  
David B. Donner
Keyword(s):  
Plasma Membrane ◽  
Insulin Receptor ◽  
Degradation Products ◽  
Insulin Degradation ◽  
Hormone Concentration ◽  
Maximal Inhibition ◽  
Extracellular Medium ◽  
Association Reaction ◽  
Native Insulin

Native insulin inhibits the binding and degradation of 125I-labelled insulin in parallel. Half-maximal inhibition of degradation occurs with 10nm-insulin, a hormone concentration sufficient to saturate the insulin receptor. The proportion of bound hormone that is degraded increases as the insulin concentration is increased, suggesting that low-affinity uptake is functionally related to degradation. Since only a small fraction (approx. 10%) of the overall degradation occurs at the plasma membrane, or in the extracellular medium, translocation of bound hormone into the cell is the predominant mechanism mediating the degradation of insulin. In the presence of 0.6nm-insulin, a concentration at which most cell-associated hormone is receptor-bound, chloroquine increases the amount of 125I-labelled insulin retained by hepatocytes. However, chloroquine increases the retention of degradation products of insulin in incubations containing sufficient hormone (6nm) to saturate the receptor and permit occupancy of low-affinity sites. Glucagon does not compete for the interaction of 125I-labelled insulin (1nm) with the insulin receptor. In contrast, 20μm-glucagon inhibits 75% of the uptake of insulin (0.1μm) by low-affinity sites. A fraction of the cell-bound radioactivity is not intact insulin throughout a 90min association reaction at 37°C. During dissociation, fragments of 125I-labelled insulin are released to the medium more rapidly than is intact hormone. The production and transient retention of degradation products of the hormone complicates the characterization of the insulin receptor by equilibrium or kinetic methods of assay. It is proposed that insulin degradation occurs by receptor- and non-receptor-mediated pathways. The latter may be related to the action of glutathione–insulin transhydrogenase, with which both insulin and glucagon interact.

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