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H Häring

Publications and source records attributed to H Häring.

49 records · Page 3Linked to original sources
PubMed1995

[Pathophysiology of insulin resistance].

Insulin resistance of skeletal muscle, liver and fat combined with an abnormality of insulin secretion characterizes Type 2 (non-insulin-dependent) diabetes mellitus. There is increasing evidence that the insulin resistance of the skeletal muscle plays a key role early in the development of Type 2 diabetes. As a consequence recent research efforts have focussed on the characterization of insulin signal transduction elements in the muscle which are candidates for a localization of a defect causing insulin resistance, i.e. the insulin receptor, phosphatases related to insulin action, glycogen synthase and the glucose transporters. In this review we attempt to summarize present knowledge about abnormalities of these systems in skeletal muscle of Type 2 diabetic and pre-diabetic individuals. We try to classify abnormalities as secondary events or as candidates for putative primary molecular defects which might initiate the development of insulin resistance as early as in the "pre-diabetic" state. Insulin resistance is combined with abnormalities of insulin secretion. Compensatory hypersecretion of insulin is typically found in early stages of the development of the "Metabolic Endocrine Syndrome" and the pre-diabetic state. The transition from this pre-diabetic state to the clinically overt Type 2 diabetes is accompanied or even caused by declining insulin secretion. The molecular mechanism causing declining insulin secretion is not understood in detail. Beside genetically determined factors regulatory events might be important.

Adipose Tissue↗
PubMed1994

Bradykinin induces translocation of the protein kinase C isoforms alpha, epsilon, and zeta.

Bradykinin exerts a broad spectrum of cellular effects on different tissues. It is believed that these effects are predominantly mediated by the recently cloned B2 receptor. The mechanism of post-receptor signal transduction is not known in detail. Involvement of protein kinase C (PKC) was suggested and activation of the classical PKC isoforms alpha and beta was recently demonstrated. The aim of the present study was to investigate whether the B2 receptor also activates new (delta, epsilon) and atypical (zeta) PKC isoforms. To investigate this, chinese hamster ovary (CHO) cells, stably transfected with human B2 receptor, were used. In these cells the PKC isoforms alpha, delta, epsilon and zeta were detected by immunoblotting with specific antibodies. To monitor hormone-induced PKC translocation plasma membranes were prepared. Stimulation of the cells with bradykinin resulted in a rapid (30-60 s) translocation of the PKC isoforms alpha, epsilon, and zeta. Translocation of PKC delta was not detected. The effect of bradykinin was reduced by simultaneous addition of the receptor antagonist HOE 140, a bradykinin-related decapeptide. The data show that the B2 receptor in this cell model is able to activate, in addition to the classical PKC isoform alpha, the new PKC isoform epsilon and the atypical PKC isoform zeta. To test whether these effects are as well observed in a non-transfected cell, the experiments were repeated in human foreskin fibroblasts which naturally express high levels of B2 receptors. In this cell system similar results on PKC alpha, epsilon, and zeta were observed, suggesting that all three PKC isoforms are involved in signal transduction of the B2 receptor.

Animals↗
PubMed1994

Glucose-induced translocation of protein kinase C isoforms in rat-1 fibroblasts is paralleled by inhibition of the insulin receptor tyrosine kinase.

Rat-1 fibroblasts stably overexpressing high levels of human insulin receptor were used as a model system to study the effects of hyperglycemia on insulin receptor tyrosine kinase (IRK) activity and protein kinase C (PKC) translocation in parallel in the intact cell. Glucose (10-25 mM) induced a significant reduction of IRK activity (tyrosine phosphorylation of IR-beta-subunit and IR-substrate-1) within 10 min. This effect was paralleled by a rapid translocation of several PKC isoforms (cPKC alpha, nPKC delta, nPKC epsilon, nPKC zeta) to the plasma membrane within 1 min. Kinetics of IRK inhibition and PKC translocation are consistent with the idea that the glucose effect on IRK is mediated by PKC activation. This hypothesis is supported by further observations. Addition of the protein kinase C inhibitor H-7 can prevent the effect of glucose on IRK. Inhibition of IRK is also observed after stimulation of the cells with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate, which can substitute for a physiological activator of PKC. Glucose (25 mM) increases the 32P incorporation in serine residues of the beta-subunit of IRK. We conclude that high levels of glucose induce inhibition of IRK in vivo. There is indirect evidence that this effect is mediated by a glucose-induced PKC translocation/activation and serine phosphorylation of the insulin receptor.

3-O-Methylglucose↗
PubMed1994

Troglitazone prevents glucose-induced insulin resistance of insulin receptor in rat-1 fibroblasts.

Troglitazone (CS045), a compound belonging to the thiazolidine diones, is being tested as a new oral antidiabetic agent. Evidence exists from animal studies and clinical trials with non-insulin-dependent diabetes mellitus patients that Troglitazone might reduce insulin resistance. The molecular mechanism of this effect is not understood. In this study, we investigated whether Troglitazone might interfere with the mechanism of glucose-induced insulin resistance. Several studies indicate that hyperglycemia reduces the kinase activity of the insulin receptor in different cell types. This effect is paralleled by translocation of several protein kinase C (PKC) isoforms, and it can be prevented by PKC inhibitors, which suggests that glucose-induced receptor desensitization is mediated by activation of PKC. We studied the effect of hyperglycemia on the insulin receptor kinase activity and its modulation by Troglitazone in rat-1 fibroblasts that stably overexpress the human insulin receptor. Before stimulation with insulin (10(-7) M), cells were acutely exposed to hyperglycemic conditions in the absence or presence of Troglitazone (0.01-2 micrograms/ml). The insulin receptor was solubilized from a plasma membrane fraction or whole cell lysates, and proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotted against antiphosphotyrosine and anti-insulin receptor beta-subunit (CT 104) antibodies. Acute hyperglycemia (25 mM glucose) induced a significant inhibition of the insulin receptor kinase (IRK) activity within 30 min (inhibition to 30 +/- 12.5% of maximal insulin-stimulated beta-subunit phosphorylation, n = 9, P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1991

[Clinical-experimental study of muscle activity of complete denture wearers with various prostheses before and after equilibration].

The present electromyographic investigations, which were carried out by patients with full dentures should show if the activity-situation of the masticatory muscles would change either using a new full denture without equilibration or using new full dentures with equilibration. Other questions were: Is it possible to classify the patients in such, who prefer the masseter muscles or the temporalis muscles during mastication? Exist a correlation between the preferred masticatory side and an increased activity of the same side masticatory muscles?

Adult↗
PubMed1989

Phosphorylation of two cytosolic proteins. An early event of T-cell activation.

T lymphocytes can be activated to proliferate by triggering the T-cell antigen-receptor complex (CD3-Ti) with anti-CD3 (Cluster of Differentiation 3) monoclonal antibody (mAb) or with the mitogenic lectin phytohaemagglutinin A (PHA). We have investigated the relationship between lymphocyte activation and protein phosphorylation in the human leukaemic T-cell line Jurkat. Incubation of 32P-labelled Jurkat cells with anti-CD3 mAb or PHA induced the phosphorylation of two cytosolic proteins that migrate with apparent Mr values of 21,000 (pp21) and 23,000 (pp23) and pI values of 5.1 and 5.0 respectively. Peptide mapping of the two proteins produced the same phosphopeptides pattern, suggesting that pp21 and pp23 are closely related. The phosphorylation of pp21 and pp23 induced by anti-CD3 mAb appeared to be transient, since it was already detected 2 min after the addition of the mAb, reached a maximum at 10 min and recovered its basal level after 1 h. Phosphorylation of pp21 and pp23 could also be elicited by the Ca2+ ionophore A23187 and sodium orthovanadate (Na3VO4), two agents that bypass the T-cell-receptor complex and produced an increase in cytosolic Ca2+ concentration. In addition, we found that vanadate, like the Ca2+ ionophore, induced the secretion of interleukin-2 (IL-2) when used in combination with a submitogenic concentration of the phorbol ester 12-O-tetradecanoylphorbol 13-acetate. These results show that the Ca2+-dependent phosphorylation of pp21 and pp23 represents an early event in the process of signal transduction through the CD3-Ti receptor complex.

Calcimycin↗
PubMed1987

An Mr 180,000 protein is an endogenous substrate for the insulin-receptor-associated tyrosine kinase in human placenta.

The beta-subunit of the insulin receptor contains a tyrosine-specific protein kinase. Insulin binding activates this kinase and causes phosphorylation of the beta-subunit of the insulin receptor. It is believed that phosphorylation of other proteins might transmit the insulin signal from the receptor to the cell. In the present study we used a polyclonal anti-phosphotyrosine antibody to detect other proteins that become tyrosine phosphorylated upon insulin stimulation. Glycoproteins from human placenta membranes were enriched by wheat germ agglutinin chromatography and phosphorylation was studied with [gamma-32P]ATP and insulin in vitro. Phosphorylated proteins were immunoprecipitated by antibodies against the insulin receptor and by serum containing the anti-phosphotyrosine antibody. Beside the insulin-stimulated phosphorylation of the 95 kDa beta-subunit of the insulin receptor, an insulin-stimulated phosphorylation of a 180 kDa protein was found. The phosphorylation of both proteins occurred only on tyrosine residues. Insulin increased 32P incorporation into the 180 kDa band 2.7-fold (S.E.M. +/- 0.3, n = 5). The 180 kDa protein was not precipitated by antibodies against the insulin receptor. H.p.l.c. chromatograms of tryptic fragments of the phosphorylated 180 kDa protein and of the beta-subunit of the insulin receptor revealed different patterns for both proteins. Insulin-stimulated phosphorylation of the 180 kDa protein was also detectable in unfractionated detergent-solubilized membranes. The phosphorylation of the 180 kDa protein was stimulated by insulin with the same dose-response curve as the phosphorylation of the beta-subunit, suggesting that this protein might be another endogenous substrate of the insulin receptor kinase.

Amino Acids↗
PubMed1987

Insulin receptor kinase defects as a possible cause of cellular insulin resistance.

The insulin receptor contains in its beta-subunit a tyrosine (-) specific protein kinase. It is believed that transmission of an insulin signal across the plasma membrane of target cells of insulin action occurs through activation of this kinase, autophosphorylation of the insulin receptor beta-subunit and subsequent phosphorylation of other cellular substrates. We studied the insulin receptor kinase in a number of insulin resistant cell systems in order to elucidate if defects of this kinase are a possible cause of cellular insulin resistance. Three different patterns of kinase abnormalities were found, in different insulin resistant cells: 1. In an insulin resistance melanoma cell line a reduced receptor kinase autophosphorylation was found apparently due to a defect of the tyrosine autophosphorylation sites of this receptor; 2. Catecholamine and phorbol ester induced insulin resistance of isolated rat fat cells as well as human fat cells was associated with a decreased activity of the insulin receptor tyrosine kinase which was apparently due to a modulation of the ATP binding site of the insulin receptor tyrosine kinase; 3. The receptor kinase isolated from the skeletal muscle of diabetic Zucker rats (fa/fa) was found to be insulin insensitive with no major alteration of maximal responsiveness. These results suggested that different forms of kinase defects exist which can contribute to the pathogenesis of cellular insulin resistance. Based on these data studies in skeletal muscle from type II diabetic patients were started. Results from five patients so far suggest that, here as well, an abnormality of the insulin receptor kinase exists which might be involved in the pathogenesis of insulin resistance in type II diabetes.

Adipose Tissue↗
PubMed1986

Tumor-promoting phorbol esters increase the Km of the ATP-binding site of the insulin receptor kinase from rat adipocytes.

Phorbol ester treatment of isolated rat adipocytes inhibits insulin stimulation of the glucose transport system. We studied whether this effect is related to a modification of the insulin receptor kinase. Insulin receptor of tetradecanoyl-beta-phorbol acetate (TPA)-treated adipocytes was solubilized and partially purified, and its kinase activity was studied in vitro. We found that insulin (10(-7) M) increased the tyrosine autophosphorylation of the insulin receptor kinase from TPA-treated cells only 3-fold in contrast to a 12-fold stimulation in control cells. The rate of insulin-stimulated 32P incorporation into the receptor of TPA-treated cells at insulin concentrations between 10(-10) M and 10(-7) M and at nonsaturating [32P]ATP levels (5 microM) was reduced to only 5-8% of the values found with receptor from control cells. 125I-insulin binding to the solubilized receptor of TPA-treated cells was reduced as well, apparently due to a decreased affinity of the binding site. Decreased binding was however, not sufficient to explain the difference of kinase activity. The inhibition of kinase activity of the receptor from TPA-treated cells decreased when the concentration of [gamma-32P]ATP in the phosphorylation assay was increased. A Lineweaver-Burk analysis of receptor phosphorylation revealed that the Km for ATP of the receptor kinase from TPA-treated cells was increased to greater than 100 microM compared to 25 microM for the receptor of control cells. An analogous change of the Km for ATP was found when we studied the phosphorylation of a synthetic polymer of tyrosine and glutamic acid as a substrate of the receptor kinase. We conclude from the data that phorbol treatment of rat adipocytes modulates the kinase activity of the insulin receptor by increasing its Km for ATP and that this is part of a mechanism leading to insulin resistance in these cells.

Adenosine Triphosphate↗
PubMed1986

Decreased tyrosine kinase activity of insulin receptor isolated from rat adipocytes rendered insulin-resistant by catecholamine treatment in vitro.

Catecholamine treatment of isolated rat adipocytes decreases insulin binding and inhibits insulin stimulation of the glucose-transport system. There is increasing evidence that the insulin signal is transmitted after insulin is bound to the receptor via a tyrosine kinase, which is an intrinsic part of the receptor. To find whether the receptor kinase is modified by catecholamines, we solubilized and partially purified the insulin receptor of isoprenaline-treated adipocytes and studied the effect of insulin on its kinase activity. (1) Insulin increased the tyrosine autophosphorylation of the insulin receptor kinase from catecholamine-treated cells only 4-fold, compared with a 12-fold stimulation in control cells. (2) The rate of insulin-stimulated 32P incorporation into the receptor of isoprenaline-treated cells at non-saturating [32P]ATP concentrations (5 muM) was decreased to 5-8% of the values for receptor from control cells. (3) 125I-insulin binding to the partially purified receptor from catecholamine-treated cells was also markedly decreased. The insulin receptor from catecholamine treated cells bound 25-50% of the amount of insulin bound by the receptor from control cells at insulin concentrations of 10 pM-0.1 muM. Part of the impaired insulin-responsiveness of the receptor kinase of catecholamine-treated cells is therefore explained by impaired binding properties; however, an additional inhibition of the kinase activity of the insulin receptor from catecholamine-treated cells is evident. (4) This inhibition of kinase activity decreased when the concentration of [gamma-32P]ATP in the phosphorylation assay was increased. A Lineweaver-Burk analysis revealed that the Km for ATP of the receptor kinase from isoprenaline-treated cells was increased to approx. 100 muM, compared with approx. 25 muM for receptor of control cells. (5) We conclude from the data that catecholamine treatment of rat adipocytes modulates the kinase activity of the insulin receptor by increasing its Km for ATP and that this is part of the mechanism leading to insulin-resistance in these cells.

Adenosine Triphosphate↗
PubMed1980

Insulin binding and insulin action in rat fat cells after adrenalectomy.

Insulin binding and the effect of insulin on the transport of 3-O-methylglucose, lipogenesis from glucose, glucose oxidation and lipolysis was studied in fat cells of adrenalectomised rats and of a control group of sham-operated rats. The serum insulin level of the adrenalectomised rats (0.7 ng/ml) was lower than that of the controls (1.6 ng/ml). In adrenalectomised rats as compared to sham-operated rats the insulin concentrations causing half-maximal effect were reduced by 50% in lipogenesis and antilipolysis and by 30% in glucose transport. The increase in sensitivity to submaximal insulin concentrations was not observed in glucose oxidation. The maximal responsiveness was unchanged in all test systems. The increase in sensitivity in three of the four studied insulin effects may be related to the 37% increase in the binding capacity of fat cells from adrenalectomised compared with sham-operated rats. The unchanged sensitivity with respect to glucose oxidation indicates possible post-receptor modulation. When adrenalectomised rats were substituted with either insulin or cortisol serum insulin levels were elevated above normal; however, the changes in the receptor were prevented in the cortisol supplemented rats and only partially in the insulin supplemented rats. The observation suggests, that the insulin receptor is regulated not only by the serum insulin level but also by cortisol.

Adipose Tissue↗