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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The binding of insulin to rat Sertoli cells was investigated to establish if effects of insulin on Sertoli cells can be mediated via insulin receptors. Sertoli cells were isolated from the testes of 3-week-old rats, and preincubated for 3 days in the absence of hormones. Binding of 125I-porcine insulin to the Sertoli cells was 75-80% specific and this binding was time- and pH-dependent and reversible. Scatchard analysis of the binding data resulted in curvilinear plots with a high affinity binding of Kd = 1.8 X 10(-9) M. Porcine and bovine insulin competed equally well for 125I-porcine insulin binding. Porcine proinsulin was 10-50 times less potent, corresponding to its lower biological activity. Insulin-like growth factor-I (IGF-I) was 30-40 times less potent, indicating low affinity binding of IGF-I to the insulin receptor. Lutropin which was used as a control gave no competition with the 125I-insulin binding. Affinity labelling of Sertoli cell membrane proteins with 125I-insulin using the cross-linking agent disuccinimidylsuberate revealed binding of insulin to (a) protein(s) of Mr greater than 300,000 or Mr = 130,000 after electrophoresis under non-reducing or reducing conditions, respectively. Affinity labelling with 125I-insulin was largely prevented by unlabelled insulin. It is concluded that the protein of Mr 130,000 may represent the alpha-subunit of the insulin receptor. The presence of insulin receptors as well as IGF-I receptors on cultured rat Sertoli cells may suggest that insulin and IGF-I have specific functions in regulating the maturation and activities of Sertoli cells during the initiation and maintenance of spermatogenesis.
Mol Cell Endocrinol 1987 Jan
PMID:Identification of insulin receptors on rat Sertoli cells. 354 88

In the adenocarcinoma cell line HT-29 receptor-bound insulin is substrate for a proteolytic process leading to the release of about half of the cell-associated [125I]monoiodoinsulin in the form of [125I]iodide and [125I]monoiodotyrosine. Classical lysosomal inhibitors (NH+4, methylamine, leupeptin) did not inhibit this proteolysis. Inhibitors of membrane traffic (chloroquine and monensin) and of metabolism (CN-) inhibited the fractional receptor-mediated degradation. The former led to an increased cell-associated 125I activity whereas the latter reduced the uptake. Sulphydryl reagents inhibited the receptor-mediated degradation. The data are not compatible with a quantitatively major role of lysosomes in the receptor-mediated insulin degradation. However, since the process requires energy it is suggested that the receptor-mediated degradation takes place in vesicles other than secondary lysosomes. The responsible enzyme(s) may belong to the thiol group of proteases. Both insulin and the insulin receptor are internalized as a consequence of incubation of HT-29 cells with insulin.
Mol Cell Endocrinol 1985 Jan
PMID:Receptor-mediated degradation and internalization of insulin in the adenocarcinoma cell line HT-29 from human colon. 388 81

Studies were carried out in order to characterize specific insulin binding sites in the rat pituitary gland. Binding of labeled insulin by pituitary microsomes reached equilibrium after 4 h at 4 degrees C and remained stable over 16 h; at 25 degrees C the plateau was reached in 20 min. Equilibrium binding data analysis of competitive displacement of bound 125I-iodo insulin by unlabeled insulin yielded a non-linear Scatchard plot. At 25 degrees C the Kd for the high affinity component was 2.8 +/- 0.1 X 10(-9) M and the receptor concentration was 260 +/- 80 fmol/mg of microsomal protein. A Kd value of 4.6 +/- 0.4 X 10(-8) M and a binding capacity of 800 +/- 200 fmol/mg microsomal protein were obtained for the low affinity sites. Insulin binding to microsomes was enhanced 2.7 times by increasing the ionic strength of the incubation medium with 2 M NaCl, and was abolished when the microsome preparation was preincubated with trypsin prior to binding measurements. Other hormones, such as bovine thyrotropin, ovine follitropin, human somatotropin and ovine prolactin did not interact with the insulin receptor. Proinsulin displaced the labeled hormone in direct proportion to its insulin-like biological activity.
Mol Cell Endocrinol 1985 Nov
PMID:Specific binding sites for insulin in the rat pituitary gland. 390 55

Insulin stimulated phosphorylation of tyrosine residues by the insulin receptor kinase may be part of a signalling mechanism associated with insulin's action. We report that indomethacin inhibited the phosphorylation of the beta-subunit of the solubilized adipocyte insulin receptor. Indomethacin also inhibited several insulin-sensitive processes in intact rat adipocytes. Indomethacin (1 mM) inhibited basal phosphorylation of the beta-subunit of the solubilized insulin receptor by 60% and insulin-stimulated phosphorylation by 30%. In adipocytes, indomethacin inhibited basal 3-0-[methyl-14C]-methyl-D glucose transport by 50% (P less than 0.01), D-[6-14C]-glucose oxidation by 50% (P less than 0.01), D-[6-14C]-glucose conversion to lipid by 30% (P less than 0.01), and D-[1-14C]-glucose conversion to lipid by 60% (P less than 0.01). Similarly, indomethacin inhibited insulin-stimulated 3-0-[methyl-14C]-methyl-D-glucose transport by 75% (P less than 0.01), D-[6-14C]-glucose oxidation by 20% (P less than 0.05), D-[1-14C]-glucose oxidation by 35% (P less than 0.01), D-[6-14C] glucose conversion to lipid by 25% (P less than 0.01), and D-[1-14C] glucose conversion to lipid by 45% (P less than 0.01). In contrast, insulin binding to its receptor, basal D-[1-14C]-glucose oxidation and both basal and insulin-stimulated activation of glycogen synthase were unaffected by indomethacin. Thus, indomethacin partially inhibited autophosphorylation of the solubilized insulin receptor on tyrosine and partially inhibited some but not all of insulin's actions.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Cell Biochem 1985 Nov
PMID:Inhibition of insulin receptor phosphorylation by indomethacin. 393 10

Insulin is able to stimulate a growth response in a variety of different cell types. However, the role of the insulin receptor in mediating this response is not clear. Indeed, it has been reported that the ability of insulin to stimulate a growth response is a result of its interaction with other growth factor receptors rather than the insulin receptor. We have previously reported that the H-35 hepatoma cell line responded to physiological concentrations of insulin as a growth factor and that the relative potency of proinsulin suggested that this response was mediated by the insulin receptor. In this report, two experimental approaches are used to demonstrate the involvement of the insulin receptor in mediating the growth response. Two different preparations of antibody to the insulin receptor are found to be capable of stimulating this response. In addition, the human insulin-like growth factors (IGF-I and II) show very low cross-reactivity with the insulin receptor and are significantly less potent than insulin in stimulating the growth response.
Mol Cell Biochem 1984
PMID:The role of the insulin receptor in mediating the insulin-stimulated growth response in Reuber H-35 cells. 614 51

The effects of theophylline on insulin receptors and insulin action in isolated rat adipocytes were studied. Theophylline reduced insulin binding by a decrease of receptor affinity. As concentration-response curves revealed, the effect was paralleled by a reduction of the cellular ATP content. Basal as well as insulin-stimulated glucose transport (2-deoxyglucose and 3-O-methylglucose uptake) were inhibited by much smaller theophylline concentrations (0.15-0.6 mM) than those necessary to reduce insulin binding and to lower ATP levels (1-4.8 mM), or to stimulate lipolysis (0.3-2.4 mM). Insulin fully antagonized the effect of theophylline on lipolysis but failed to reverse the inhibition of glucose transport completely. The results suggest that (a) theophylline impairs insulin action at a post-receptor level and, at higher concentrations, by a decrease of receptor binding, (b) the reduction of insulin receptor affinity probably reflects ATP depletion of the adipocyte, and (c) the xanthine inhibits glucose transport independently from its effects on lipolysis.
Mol Cell Biochem 1983
PMID:Effects of theophylline on insulin receptors and insulin action in the adipocyte. 636 17

Adipocytes from old rats (greater than 450 g) were separated into 2 populations with mean cell volumes of 201 +/- 14 and 813 +/- 41 pl (mean +/- SEM, 20 observations) by filtering through nylon mesh (64 microns diameter) and compared with adipocytes from young rats (less than 150 g) with a mean adipocyte volume of 154 +/- 20 pl (14 observations). Large adipocytes had more insulin receptors per cell but less per unit of surface area. They internalized greater amounts of insulin than small cells in the presence or absence of bacitracin and chloroquine, although the proportion of bound hormone which was internalized was similar in all 3 groups. Down-regulation of the insulin receptor was evident in large and small adipocytes after incubation in the presence of 10(-7)M insulin. Large cells degraded insulin (extracellularly and intracellularly) at significantly greater rates than small cells whether expressed per cell or per unit of surface area. Small cells from old rats had essentially identical properties to small cells from young rats in all parameters examined. The results suggest that the decreased surface density of insulin receptors observed in large adipocytes from old rats is due to size rather than age and that the decreased insulin sensitivity of large adipocytes is not due to an inability to internalize insulin or down-regulate its receptors but may be due to increased rates of insulin degradation.
Mol Cell Endocrinol 1984 Jul
PMID:Effects of cell volume on insulin binding, internalization and degradation in rat adipocytes. 638 Nov 72

Insulin receptors from rat hepatoma cells were studied by the three following methods. Firstly, the alpha subunit (Mr 130000) was labelled using a 125I-photoreactive insulin analogue and UV irradiation. Secondly, using phosphorylation of partially purified and immunoprecipitated receptors with [gamma-32P]ATP, the beta subunit (Mr 95000) was labelled. Thirdly, both alpha and beta subunits were labelled by surface iodination catalysed by lactoperoxidase followed by cell solubilization and immunoprecipitation of the receptor with anti-receptor antibodies. The results show that the native insulin receptor exists under different forms: free alpha and beta subunits and the following combinations of disulphide-linked oligomers: alpha beta, alpha 2, alpha 2 beta and alpha 2 beta 2. In addition, it appears that there is at least one insulin binding site per alpha subunit, and that the alpha and beta subunits may be in close physical association in the plasma membrane even when they are not linked by disulphide bonds. In intact cells, only the alpha subunit is sensitive to extracellular proteases that cleave preferentially the region of the alpha subunit bearing the sulphydryl groups responsible for the interchain binding.
Mol Cell Endocrinol 1984 Jun
PMID:Subunit arrangement of insulin receptors in hepatoma cells. 674 84

The insulin receptor apparent affinity was markedly decreased in fat cells treated with lectins specific either for D-galactose (Ricinus communis agglutinin I, RCAI), D-mannose (concanavalin A, Con A, Lens culinaris agglutinin, LCA) or N-acetyl-D-glucosamine (wheat germ agglutinin, WGA), as indicated by a rightward shift of the binding competition curves and almost lineared Scatchard plots. Limulus polyphemus agglutinin (LPA), specific for sialic acid, was ineffective. All lectins enhanced 2-deoxy-D-glucose uptake with relative bioactivities (maximal lectin effect/maximal insulin effect) of 68-86%. Insulin and lectin stimulatory effects were antagonized by specific carbohydrates used as competitors and inhibited by cytochalasin B (70 microM). Maximal effects of insulin and lectins were not additive and were completely abolished in neuraminidase-treated fat cells. Lectins did not affect insulin degradation. These data show that sialylated glycosidic moieties containing D-galactose, D-mannose and N-acetyl-D-glucosamine units are involved in both processes of insulin 'high affinity' binding and activation of glucose transport but are not implicated in hormone degradation. They suggest that N-linked carbohydrate chains of the complex type may be essential for functional insulin receptor and post-receptor systems.
Mol Cell Endocrinol
PMID:Carbohydrate determinants involved in both the binding and action of insulin in rat adipocytes. 675 1

Insulin action and insulin binding in isolated rat fat cells incubated with adenosine or adenosine deaminase were studied. Adenosine enhanced the effects of insulin on glucose transport and glucose metabolism. The nucleoside shifted the concentration-response curves of insulin-stimulated D-[3-3H]glucose incorporation into total lipids, and of D-[U-14C]glucose conversion to fatty acids to smaller insulin concentrations. In addition, the maximal response of the fatty acid synthesis was increased. Insulin sensitivity and maximal response to insulin of the glucose transport system, as assessed by the rate of uptake of 2-deoxyglucose and 3-O-methylglucose, were increased by adenosine. The adenosine derivative N6-phenylisopropyladenosine similarly enhanced deoxyglucose transport in the presence of insulin. However, insulin binding was not affected by adenosine. The results suggest that adenosine modulates insulin action at a step distal from the insulin receptor, and before, or at, the glucose transport system.
Mol Pharmacol 1982 Nov
PMID:Modulation of insulin sensitivity by adenosine. Effects on glucose transport, lipid synthesis, and insulin receptors of the adipocyte. 675 15


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