Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:2.7.1.137 (phosphatidylinositol 3-kinase)
11,064 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In a previous study, we showed that a chimeric insulin-like-growth-factor-1 (IGF-1) receptor, with the beta subunit C-terminal part of the insulin receptor was more efficient in stimulating glycogen synthesis and p44mapk activity compared to the wild-type IFG-1 receptor [Tartare, S., Mothe, I., Kowalski-Chauvel, A., Breittmayer, J.-P., Ballotti, R. & Van Obberghen, E. (1994) J. Biol. Chem. 269, 11449-11455]. These data indicate that the receptor C-terminal domain plays an important role in the transmission of biological effects. To understand the molecular basis of the differences in receptor specificity, we studied the characteristics of insulin, IGF-1 and chimeric receptor tyrosine kinase activities in a cell-free system. We found that, compared to wild-type insulin and IGF-1 receptors, the chimeric receptor showed a decrease in (a) autophosphorylation, (b) tyrosine kinase activity towards insulin receptor substrate-1 and the insulin receptor-(1142-1158)-peptide, and (c) the ability to activate phosphatidylinositol 3-kinase. However, for all the effects measured in a cell-free system, the chimeric receptor displayed an increased response to IGF-1 compared to the native IGF-1 receptor. Concerning the cation dependence of the tyrosine kinase activity, we showed that, at 10 mM Mg2+, the ligand-stimulated phosphorylation of poly(Glu80Tyr20) by both insulin receptor and chimeric receptor was increased by Mn2+. Conversely at 50 mM Mg2+, the chimeric receptor behaved like the IGF-1 receptor, since the presence of Mn2+ decreased the stimulatory effect of IGF-1 on their kinase activity. Furthermore, the Km of the chimeric receptor for ATP was increased compared to the wild-type receptors. These data demonstrate that the replacement of the C-terminal tail of the IGF-1 receptor by that of the insulin receptor has changed the receptor characteristics studied in a cell-free system. Our findings indicate that the C-terminal domain of the insulin receptor beta subunit plays a key role in regulation of the tyrosine kinase activity. The fine-tuning of the tyrosine kinase by the C-terminal tail could participate in the receptor specificity.
...
PMID:Tyrosine kinase activity of a chimeric insulin-like-growth-factor-1 receptor containing the insulin receptor C-terminal domain. Comparison with the tyrosine kinase activities of the insulin and insulin-like-growth-factor-1 receptors using a cell-free system. 773 84

Insulin stimulates signaling reactions that include insulin receptor autophosphorylation and tyrosine kinase activation, insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation, and phosphatidylinositol 3-kinase (PI 3-kinase) activation. Muscle contraction has metabolic effects similar to insulin, and contraction can increase insulin sensitivity, but little is known about the molecular signals that mediate the effects of contraction. To investigate the effects of muscle contraction on insulin signaling, rats were studied after contraction of hindlimb muscles by electrical stimulation, maximal insulin injection in the absence of contraction, or contraction followed by insulin injection. Insulin increased tyrosine phosphorylation of the insulin receptor and IRS-1, whereas contraction alone had no effect. Contraction before insulin injection decreased the insulin effect on receptor and IRS-1 phosphorylation by 20-25%. Increased tyrosine phosphorylation of other proteins by insulin and/or contraction was not observed. Contraction alone had little effect on PI 3-kinase activity, but contraction markedly blunted the insulin-stimulated activation of IRS-1 and insulin receptor-immunoprecipitable PI 3-kinase. In conclusion, skeletal muscle contractile activity does not result in tyrosine phosphorylation of molecules involved in the initial steps of insulin signaling. Although contractile activity increases insulin sensitivity and responsiveness in skeletal muscle, contraction causes a paradoxical decrease in insulin-stimulated tyrosine phosphorylation and PI 3-kinase activity.
...
PMID:Effects of contractile activity on tyrosine phosphoproteins and PI 3-kinase activity in rat skeletal muscle. 776 55

Considerable evidence has shown that most physiologic responses to insulin require activation of the intrinsic tyrosine kinase of the insulin receptor. Biochemical studies have also supported the hypothesis that receptor kinase activity can be modulated by cellular protein tyrosine phosphatases (PTPases), which have not yet been identified. To test the hypothesis that the transmembrane PTPase LAR can modulate insulin receptor signaling in vivo, antisense RNA expression was used to specifically suppress LAR protein levels by 63% in the rat hepatoma cell line, McA-RH7777. Hormone-dependent autophosphorylation of the insulin receptor was increased by approximately 150% in the antisense-expressing cells at all insulin concentrations tested. This increase in autophosphorylation was paralleled by a 35% increase in insulin receptor tyrosine kinase activity. Reduced LAR levels did not alter non-hormone-dependent tyrosine phosphorylation nor basal insulin receptor tyrosine phosphorylation and kinase activity. Most significantly, reduced LAR levels resulted in a 350% increase in insulin-dependent phosphatidylinositol 3-kinase activity. These studies provide unique in vivo evidence that LAR is involved in the modulation of insulin receptor signaling in intact cells.
...
PMID:Insulin receptor signaling is augmented by antisense inhibition of the protein tyrosine phosphatase LAR. 785 2

Insulin receptor substrate 1 (IRS-1) mediates the activation of a variety of signaling pathways by the insulin and insulin-like growth factor 1 receptors by serving as a docking protein for signaling molecules with SH2 domains. We and others have shown that in response to insulin stimulation IRS-1 binds GRB2/Sos and have proposed that this interaction is important in mediating Ras activation by the insulin receptor. Recently, it has been shown that the interleukin (IL)-4 receptor also phosphorylates IRS-1 and an IRS-1-related molecule, 4PS. Unlike insulin, however, IL-4 fails to activate Ras, extracellular signal-regulated kinases (ERKs), or mitogen-activated protein kinases. We have reconstituted the IL-4 receptor into an insulin-responsive L6 myoblast cell line and have shown that IRS-1 is tyrosine phosphorylated to similar degrees in response to insulin and IL-4 stimulation in this cell line. In agreement with previous findings, IL-4 failed to activate the ERKs in this cell line or to stimulate DNA synthesis, whereas the same responses were activated by insulin. Surprisingly, IL-4's failure to activate ERKs was not due to a failure to stimulate the association of tyrosine-phosphorylated IRS-1 with GRB2/Sos; the amounts of GRB2/Sos associated with IRS-1 were similar in insulin- and IL-4-stimulated cells. Moreover, the amounts of phosphatidylinositol 3-kinase activity associated with IRS-1 were similar in insulin- and IL-4-stimulated cells. In contrast to insulin, however, IL-4 failed to induce tyrosine phosphorylation of Shc or association of Shc with GRB2. Thus, ERK activation correlates with Shc tyrosine phosphorylation and formation of an Shc/GRB2 complex. Thus, ERK activation correlates with Shc tyrosine phosphorylation and formation of an Shc/GRB2 complex. Previous studies have indicated that activation of ERks in this cell line is dependent upon Ras since a dominant-negative Ras (Asn-17) blocks ERK activation by insulin. Our findings, taken in the context of previous work, suggest that binding of GRB2/Sos to Shc may be the predominant mechanism whereby insulin as well as cytokine receptors activate Ras.
...
PMID:Association between GRB2/Sos and insulin receptor substrate 1 is not sufficient for activation of extracellular signal-regulated kinases by interleukin-4: implications for Ras activation by insulin. 786 67

Insulin rapidly stimulates tyrosine kinase activity of its receptor, resulting in phosphorylation of the cytosolic substrate, insulin receptor substrate-1 (IRS-1), which, in turn, associates with phosphatidylinositol 3-kinase (PI 3-kinase), thus activating the enzyme. In the present study we have examined these three early postreceptor components of the insulin action pathway in rat hepatoma (Fao) cells and have determined the effects of two hormones that can induce insulin resistance, dexamethasone and insulin. Dexamethasone (1 microM) induced a time- and dose-dependent increase in insulin receptor levels in Fao cells, reaching 135 +/- 3% of basal levels after 24 h (P < 0.05). There was a simultaneous increase in IRS-1 protein to 255 +/- 66% of the control value (P < 0.05) and a parallel increase in IRS-1 phosphorylation. Insulin stimulation of IRS-1-associated PI 3-kinase was also increased by 70% in cells treated with dexamethasone despite only a minimal increase in PI 3-kinase protein, as determined by immunoblotting. Prolonged insulin treatment induced a time- and dose-dependent decrease in insulin receptor and IRS-1 protein levels, reaching nadirs of 40 +/- 4% (P < 0.01) and 15 +/- 6% (P < 0.005) of control levels, respectively, after 24 h with 100 nM insulin. There was also a decrease in the phosphorylation of insulin receptors and IRS-1, a marked decrease in the association between IRS-1 and PI 3-kinase, and an 82% decrease in insulin-stimulated PI 3-kinase activity without a significant change in PI 3-kinase protein levels. When cells were exposed to both insulin and dexamethasone, the effect of insulin to reduce insulin receptor and IRS-1 levels and insulin-stimulated IRS-1 phosphorylation dominated. These data suggest that regulation of the insulin receptor, IRS-1, and PI 3-kinase contributes significantly to the insulin resistance induced by chronic hyperinsulinemia, but that glucocorticoid-induced insulin resistance is located beyond these early steps in insulin action.
...
PMID:Insulin and dexamethasone regulate insulin receptors, insulin receptor substrate-1, and phosphatidylinositol 3-kinase in Fao hepatoma cells. 789 67

We have developed and characterized a line of Madin-Darby canine kidney (MDCK) cells overexpressing the human insulin receptor. The expressed receptor was found to be processed normally, and its intrinsic tyrosine kinase was determined to be functional from both in vitro and in vivo phosphorylation studies. The expressed receptor was able to mediate an insulin-stimulated increase in both anti-phosphotyrosine-precipitable and anti-insulin receptor substrate 1-precipitable phosphatidylinositol 3-kinase activity. Moreover, insulin-induced glycogen synthase activity was greater and more sensitive to insulin in the transfected cells than in the parental cells. Interestingly, insulin promoted tubule-like growth in cells overexpressing the insulin receptor but not in the parental cells. Another advantage of this cell system lies in its ability to polarize into distinct basolateral and apical membrane compartments. With the use of biotinylation and Western analysis, the expressed insulin receptor was found to be preferentially expressed in the basolateral membrane (fivefold greater) in comparison with the apical membrane. Therefore, MDCK cells overexpressing the insulin receptor represent a novel system to study not only the pathway of insulin signaling, but also this pathway in the context of cell polarity.
...
PMID:Insulin receptor signaling in Madin-Darby canine kidney cells overexpressing the human insulin receptor. 792 3

We have investigated the functional role of the SH2 domain of the 85-kDa subunit (p85) of the phosphatidylinositol 3-kinase in the insulin signal transduction pathway. Microinjection of a bacterial fusion protein containing the N-terminal SH2 domain of p85 inhibited insulin- and other growth factor-induced DNA synthesis by 90% and c-fos protein expression by 80% in insulin-responsive rat fibroblasts. The specificity of the fusion protein was examined by in vitro precipitation experiments, which showed that the SH2 domain of p85 can independently associate with both insulin receptor substrate 1 and the insulin receptor itself in the absence of detectable binding to other phosphoproteins. The microinjection results were confirmed through the use of an affinity-purified antibody directed against p85, which gave the same phenotype. Additional studies were carried out in another cell line expressing mutant insulin receptors which lack the cytoplasmic tyrosine residues with which p85 interacts. Microinjection of the SH2 domain fusion protein also inhibited insulin signaling in these cells, suggesting that association of p85 with insulin receptor substrate 1 is a key element in insulin-mediated cell cycle progression. In addition, coinjection of purified p21ras protein with the p85 fusion protein or the antibody restored DNA synthesis, suggesting that ras function is either downstream or independent of p85 SH2 domain interaction.
...
PMID:Microinjection of the SH2 domain of the 85-kilodalton subunit of phosphatidylinositol 3-kinase inhibits insulin-induced DNA synthesis and c-fos expression. 793 61

We have previously shown that insulin causes inactivation of glycogen synthase kinase-3 (GSK-3) in Chinese hamster ovary cells over-expressing the human insulin receptor (CHO.T cells). We now show that serum and phorbol ester also cause rapid inactivation of GSK-3, both in CHO.T cells and in the nontransfected parental cell line, CHO.K1 cells. Rapamycin was without effect on the inactivation of GSK-3 by insulin, serum or phorbol ester, indicating that the p70 S6 kinase pathway is not involved. In contrast, wortmannin, a potent inhibitor of phosphatidylinositol 3-kinase, blocked the effects of both insulin and serum on GSK-3 activity, and also substantially reduced the activation of both p90 S6 kinase (by insulin) and mitogen-activated protein (MAP) kinase (by insulin and serum). These findings imply (i) that GSK-3 activity is regulated by a cascade involving MAP kinase and p90 S6 kinase and (ii) that wortmannin affects an early step in the MAP kinase pathway. One can infer from this that GSK-3 may be an important regulatory enzyme for the control of several biosynthetic pathways, key enzymes in which are regulated by GSK-3-mediated phosphorylation. Wortmannin had a smaller effect on the activation of MAP kinase by phorbol ester, indicating that phorbol esters may stimulate MAP kinase by a different or additional mechanism to that employed by insulin or serum. Wortmannin had very little effect on the inactivation of GSK-3 by phorbol ester: possible reasons for this are discussed.
...
PMID:Wortmannin inhibits the effects of insulin and serum on the activities of glycogen synthase kinase-3 and mitogen-activated protein kinase. 794 34

Insulin receptor substrate 1 (IRS-1) is the primary cytosolic substrate of the insulin and insulin-like growth factor-I (IGF-I) receptors. Following tyrosine phosphorylation IRS-1 binds to and activates specific proteins containing SH2 domains. Using biochemical and immunocytochemical techniques, we have mapped the distribution of IRS-1 in the CNS of the adult rat and compared it with that of insulin and IGF-I receptors and phosphatidylinositol 3-kinase (PI-3 kinase), a signaling molecule functionally related to IRS-1. Immunoprecipitation and Western blotting experiments demonstrate the presence of substantial amounts of IRS-1, insulin receptor, and PI-3 kinase in the brain. IRS-1 immunoreactivity is widely distributed in neurons from several areas of the brain and spinal cord. The cerebral cortex, the hippocampus, many hypothalamic and thalamic nuclei, the basal ganglia, the cerebellar cortex, the brainstem nuclei, and the lamina X of the spinal cord are particularly rich of immunopositive nerve cells. In these areas most of the neurons immunoreactive for IRS-1 are also stained by either anti-insulin receptor or anti-IGF-I receptor antibodies as well as PI-3 kinase antiserum. IRS-1 immunostaining was very weak or totally absent in neurons of the olfactory bulb, the supraoptic and paraventricular nuclei, the mesencephalic trigeminal nucleus, and the granule cell layer of the cerebellum, despite the fact that these areas were immunolabeled with antibodies against insulin or IGF-I receptors and/or PI-3 kinase. These results show that neurons in the adult rat CNS are endowed with some of the components of the early signaling pathway for growth factors of the insulin/IGF-I family, although IRS-1 has a distribution distinct from that of the two receptors.
...
PMID:Insulin receptor substrate-1 (IRS-1) distribution in the rat central nervous system. 796 46

Insulin receptor substrate-1 (IRS-1) is the major substrate of insulin receptor and IGF-1 receptor tyrosine kinases; it has an apparent relative molecular mass of 160-190,000 (M(r), 160-190K) on SDS polyacrylamide gel. Tyrosine-phosphorylated IRS-1 binds the 85K subunit of phosphatidylinositol 3-kinase which may be involved in the translocation of glucose transporters and the abundant src homology protein (ASH)/Grb2 which may be involved in activation of p21ras and MAP kinase cascade. IRS-1 also has binding sites for Syp and Nck and other src homology 2 (SH2) signalling molecules. To clarify the physiological roles of IRS-1 in vivo, we made mice with a targeted disruption of the IRS-1 gene locus. Mice homozygous for targeted disruption of the IRS-1 gene were born alive but were retarded in embryonal and postnatal growth. They also had resistance to the glucose-lowering effects of insulin, IGF-1 and IGF-2. These data suggest the existence of both IRS-1-dependent and IRS-1-independent pathways for signal transduction of insulin and IGFs.
...
PMID:Insulin resistance and growth retardation in mice lacking insulin receptor substrate-1. 796 41


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---