Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The cytoplasmic domain of the human insulin receptor (HIR) from the baculovirus expression system (BIRK) is a soluble, constitutively activated protein-tyrosine kinase. In a cell-free system, BIRK is phosphorylated on serine and threonine residues by protein kinase C (PKC) purified from rat brain. Two-dimensional tryptic phosphopeptide mapping of PKC-phosphorylated BIRK identified one phosphothreonine and three phosphoserine peptides, which were also in tryptic digests of insulin receptors from insulin- or PMA-treated Chinese hamster ovary (CHO) cells transfected with the HIR. After Lys-C proteolysis of PKC-phosphorylated BIRK, radioactive phosphopeptides were purified on a C8 reverse-phase high pressure liquid chromatography column. Amino acid sequence analysis identified a phosphothreonine peptide corresponding to amino acids 1331-1340 of the HIR. This peptide contains only one threonine, amino acid 1336, which is identified as a site for PKC phosphorylation in BIRK. CHO cells transfected with the wild type (CHO/HIR) or a mutant human insulin receptor (CHO/HIRT1336N), in which threonine 1336 was substituted with asparagine, were 32P labeled and then stimulated with insulin or phorbol 12-myristate 13-acetate (PMA). Two-dimensional phosphopeptide analysis of the HIR revealed that phosphorylation of phosphothreonine peptide T, shown to be in PKC-phosphorylated BIRK, was increased by insulin or PMA. However, the corresponding peptide was not in the mutant receptor. Therefore, the present study directly identifies threonine 1336 in the HIR as a phosphorylation site for insulin and PMA. These data also show that BIRK can be used as a model for the study of the regulation of the insulin receptor kinase.
 ...
PMID:Interaction of the human insulin receptor tyrosine kinase from the baculovirus expression system with protein kinase C in a cell-free system. 846 87

The effects of phorbol ester induced activation of protein kinase C on insulin receptor phosphorylation and tyrosine kinase activity have been investigated in transfected fibroblasts expressing high levels of the human insulin receptor. Receptor phosphorylation was stimulated more than two-fold over basal levels upon treating CHO.T cells with PMA. This phosphorylation was additive with, rather than antagonistic to, that induced by insulin. Furthermore, PMA treatment was completely without effect on insulin-stimulated receptor tyrosine kinase activity. Similar results were obtained in NIH3T3 HIR3.5 and Rat 1 HIRc-B cells. It is concluded that the previously reported inhibitory effect of PMA on receptor kinase activity is not of general regulatory significance in all cell types.
 ...
PMID:Phorbol esters induce insulin receptor phosphorylation in transfected fibroblasts without affecting tyrosine kinase activity. 850 28

The insulin resistance of skeletal muscle plays an important role in the pathogenesis of the metabolic endocrine syndrome and diabetes mellitus Type II. Impairment of the signal transmission from the insulin receptor to glycogen synthase and the glucose transport system was shown in insulin resistant subjects. A reduced receptor activation contributes also to insulin resistance. We investigated the mechanisms of modulation of receptor function in isolated cell systems which are transfected with human insulin receptor. Action of TNF alpha and acute hyperglycaemic effects were studied in particular. Acute hyperglycaemia gives rise, in the isolated cell system, to inhibition of the tyrosine kinase activity of the insulin receptor within a few minutes. This inhibitory effect seems to be mediated by translocation and activation of various isoforms of protein kinase C. Activation of protein kinase C probably leads to phosphorylation of the beta-subunit of the insulin receptor at serine residues. The domains of the insulin receptor, which are responsible for the inhibitory effect of hyperglycaemia do not seem to be localized either in the C terminus or in the juxtamembranary region of the insulin receptor. The hyperglycaemic effect can be antagonized in the isolated cell system both by protein kinase C inhibitors and so-called insulin sensitizers such as thiazolidindiones. Similar inhibitory effects, as induced by hyperglycaemia, can also be mediated by administration of the cytokine TNF alpha. As TNF alpha is probably increasingly expressed in obesity, the modulation of receptor kinase activity by TNF alpha could be an important factor for insulin resistance in obesity.
 ...
PMID:Pathogenesis of insulin resistance: modulation of the insulin signal at receptor level. 852 11

Insulin resistance of the skeletal muscle plays a key role in the development of the metabolic endocrine syndrome and its further progression to type II diabetes. Impaired signaling from the insulin receptor to the glucose transport system and to glycogen synthase is thought to be the cause of skeletal muscle insulin resistance. An incomplete activation of the insulin receptor tyrosine kinase, which is found in type II diabetes, appears to contribute to the pathogenesis of the signaling defect. Available data suggest that the impaired tyrosine kinase function of the insulin receptor is not due to an inherited defect but rather is caused by a modulation of insulin receptor function. We used rat-1 fibroblasts and NIH-3T3 cells stably overexpressing human insulin receptor and 293 cells transiently overexpressing human insulin receptor to characterize conditions modulating the signaling function of the insulin receptor kinase. Using these cell models, we could demonstrate that activation of different protein kinase C (PKC) isoforms by high glucose levels or phorbol esters causes a rapid inhibition of the receptor tyrosine kinase activity. This effect is most likely mediated through serine phosphorylation of the receptor beta-subunit. It can be prevented by PKC inhibitors and the new oral antidiabetic agent thiazolidindione. The data suggest that PKC might be an important negative regulator of insulin receptor function. Because we have recently shown that bradykinin activates different isoforms of PKC in these cell types, an inhibitory cross talk between the bradykinin receptor and the insulin receptor through PKC activation seemed possible. However, we were unable to observe an insulin receptor tyrosine kinase inhibition through bradykinin, suggesting that different isoforms of PKC are activated by hyperglycemia and bradykinin. On the other hand, a modulation of bradykinin signals by insulin could be demonstrated in these cells. Bradykinin-induced tyrosine phosphorylation of proteins of approximately 130 and 70 kDa was inhibited by insulin treatment of rat-1 fibroblasts. These data suggest that signals from the insulin receptor modify signaling from the bradykinin receptor to tyrosine phosphorylation of different cellular proteins.
 ...
PMID:Modulation of insulin receptor signaling. Potential mechanisms of a cross talk between bradykinin and the insulin receptor. 852 91

Regulation of the activity of the extracellular signal regulated kinase (ERK) mitogen-activated protein kinases was examined in Rat-1 HIR, a fibroblast cell line overexpressing the human insulin receptor. Insulin or phorbol ester induced partial activations of ERKs, while a combination of insulin and phorbol ester resulted in a synergistic activation. Preincubation with phorbol ester increased the subsequent response to insulin. Phorbol ester did not enhance tyrosine phosphorylation of the insulin receptor. Insulin did not enhance activation of phospholipase D in response to phorbol ester. Lysophosphatidic acid also acted synergistically with insulin to induce ERK activation. Lysophosphatidic acid alone had little effect on ERK, and did not activate phospholipase D. The combination of phorbol ester and insulin maintained tyrosine phosphorylation of focal adhesion kinase, while insulin alone decreased its tyrosine phosphorylation. Phorbol ester induced phosphorylation of She on serine/threonine, while insulin induced tyrosine phosphorylation of She and She-Grb2 binding. These results suggest that full activation of ERKs in fibroblasts can require the cooperation of at least two signaling pathways, one of which may result from a protein kinase C-dependent phosphorylation of effectors regulating ERK activation. In this manner, phorbol esters may enhance mitogenic signals initiated by growth factor receptors.
 ...
PMID:Synergistic effects of insulin and phorbol ester on mitogen-activated protein kinase in Rat-1 HIR cells. 857 69

A new p56lck tyrosine kinase inhibitor WIN 61651 [1,4-dihydro-7-(4-methyl-1-piperizinyl)-1-(4-(4-methyl-1-piperi zinyl))phenyl- 4-oxo-3-quinolinecarboxamide) is described. WIN 61651, which is competitive with ATP, demonstrates selectivity for the lymphoid restricted tyrosine kinase p56lck over serine/threonine kinases, such as protein kinase C and protein kinase A, and over some other tyrosine kinases, including erbB2, epidermal growth factor receptor, and insulin receptor; however, it is equipotent for inhibition of p56lck and the platelet derived growth factor receptor tyrosine kinases. WIN 61651 inhibits p56lck activity in cell-free assays, tyrosine kinase activity in a T lymphocytic cell line, and T cell activation, as measured by IL-2 production by purified CD4 positive peripheral blood T lymphocytes and the mixed lymphocyte reaction. WIN 61651 constitutes a new tool for studies on the role for tyrosine kinases in lymphocyte function.
 ...
PMID:Inhibition of T lymphocyte activation by a novel p56lck tyrosine kinase inhibitor. 858 49

Studies with detergent:lipid mixed micelles reveal that diacylglycerol directly stimulates the intrinsic tyrosine kinase activity of the insulin receptor. Kinetic analyses indicate that diacylglycerol activates the kinase by causing a marked increase in the affinity of the receptor for insulin. In contrast, diacylglycerol has no effect on the insulin receptor's catalytic activity or its affinity for ATP. Stimulation of the insulin receptor is not a result of protein kinase C activation. First, phorbol myristate acetate, a potent activator of protein kinase C, has no effect on insulin receptor activity. Second, the activation by diacylglycerol is not stereospecific, in marked contrast to the specificity for 1,2-diacyl-sn-glycerol in the activation of protein kinase C. Because circulating levels of insulin are below the Kd of the insulin receptor for insulin, the ability of diacylglycerol to modulate the affinity of the receptor for ligand suggests that increases in cellular levels of diacylglycerol directly sensitize the receptor to insulin.
 ...
PMID:Diacylglycerol directly stimulates the insulin receptor tyrosine kinase. 860 47

Elevated glucose concentrations have been reported to inhibit insulin receptor kinase activity. We studied the effects of high glucose on insulin action in Rat1 fibroblasts transfected with wild-type human insulin receptor (HIRcB) and a truncated receptor lacking the COOH-terminal 43 amino acids (delta CT). In both cell lines, 25 mM glucose impaired receptor and insulin receptor substrate-1 phosphorylation by 34%, but IGF-1 receptor phosphorylation was unaffected. Phosphatidylinositol 3-kinase activity and bromodeoxyuridine uptake were decreased by 85 and 35%, respectively. This was reversed by coincubation with a protein kinase C (PKC) inhibitor or microinjection of a PKC inhibitor peptide. Phosphopeptide mapping revealed that high glucose or PMA led to serine/threonine phosphorylation of similar peptides. Inhibition of the microtubule-associated protein (MAP) kinase cascade by the MAP kinase kinase inhibitor PD98059 did not reverse the impaired phosphorylation. We conclude that high glucose inhibits insulin action by inducing serine phosphorylation through a PKC-mediated mechanism at the level of the receptor at sites proximal to the COOH-terminal 43 amino acids. This effect is independent of activation of the MAP kinase cascade. Proportionately, the impairment of insulin receptor substrate-1 tyrosine phosphorylation is greater than that of the insulin receptor resulting in attenuated phosphatidylinositol 3-kinase activation and mitogenic signaling.
 ...
PMID:Glucose-induced phosphorylation of the insulin receptor. Functional effects and characterization of phosphorylation sites. 860 15

We have developed a one-dimensional isoelectric focusing technique to measure changes in the steady-state phosphorylation of the cap-binding initiation factor, eIF-4E. We have used a Chinese hamster ovary cell line transfected with the human insulin receptor (CHO.T cells) to study the regulation of eIF-4E phosphorylation by insulin and other stimuli. Exposure of CHO.T cells to insulin, phorbol ester or serum resulted in a rapid increase (up to twofold) in eIF-4E phosphorylation. As a control, we have also performed experiments with the parental cell line, CHO.K1 cells, in which both serum and phorbol ester, but not nanomolar concentrations of insulin, produce similar changes in eIF-4E phosphorylation. We have used two complementary approaches to study the role of protein kinase C (PKC) in these responses: a highly specific inhibitor of PKC and down-regulation of PKC by prior treatment of the cells with phorbol ester. In CHO.T cells, both approaches indicate that PKC is required for the response to phorbol ester but that insulin and serum each increase eIF-4E phosphorylation by a mechanism(s) independent of this protein kinase. Similarly, PKC is necessary for the effects of phorbol ester, but not of serum, on eIF-4E phosphorylation in CHO.K1 cells. These data indicate that multiple signal transduction mechanisms are involved in the modulation of eIF-4E phosphorylation and the implications of these findings are discussed.
 ...
PMID:Insulin and phorbol ester stimulate initiation factor eIF-4E phosphorylation by distinct pathways in Chinese hamster ovary cells overexpressing the insulin receptor. 861 84

Inhibition of insulin receptor signaling by high glucose levels and by TNF-alpha was recently observed in different cell systems. The aim of the present study was to characterize the mechanism of TNF-alpha-induced insulin receptor inhibition and to compare the consequences of TNF-alpha- and hyperglycemia-induced insulin receptor inhibition for signal transduction downstream from the IR. TNF-alpha (0.5-10 nM) and high glucose (25 mM) showed similar rapid kinetics of inhibition (5-10 min, > 50%) of insulin receptor autophosphorylation in NIH3T3 cells overexpressing the human insulin receptor. TNF-alpha effects were completely prevented by the phosphotyrosine phosphatase (PTPase) inhibitors orthovanadate (40 microM) and phenylarsenoxide (35 microM), but they were unaffected by the protein kinase C (PKC) inhibitor H7 (0.1 mM), the phosphatidylinositol-3 kinase inhibitor wortmannin (5 microM), and the thiazolidindione troglitazone (CS045) (2 microgram/ml). In contrast, glucose effects were prevented by PKC inhibitors and CS045 but unaffected by PTPase inhibitors and wortmannin. To assess effects on downstream signaling, tyrosine phosphorylation of the following substrate proteins of the insulin receptor was determined: insulin receptor substrate-1, the coupling protein Shc, focal adhesion kinase (FAK125), and unidentified proteins of 130 kD, 60 kD. Hyperglycemia (25 mM glucose) and TNF-alpha showed analogous (> 50% inhibition) effects on tyrosine phosphorylation of insulin receptor substrate-1, Shc, p60, and p44, whereas opposite effects were observed for tyrosine phosphorylation of FAK125, which is dephosphorylated after insulin stimulation. Whereas TNF-alpha did not prevent insulin-induced dephosphorylation of FAK125, 25 mM glucose blocked this insulin effect completely. In summary, the data suggest that TNF-alpha and high glucose modulate insulin receptor-signaling through different mechanisms: (a) TNF-alpha modulates insulin receptor signals by PTPase activation, whereas glucose acts through activation of PKC. (b) Differences in modulation of the insulin receptor signaling cascade are found with TNF-alpha and high glucose: Hyperglycemia-induced insulin receptor inhibition blocks both insulin receptor-dependent tyrosine phosphorylation and dephosphorylation of insulin receptor substrate proteins. In contrast, TNF-alpha blocks only substrate phosphorylation, and it does not block insulin-induced substrate dephosphorylation. The different effects on FAK125 regulation allow the speculation that long-term cell effects related to FAK125 activity might develop in a different way in hyperglycemia- and TNF-alpha-dependent insulin resistance.
 ...
PMID:Tumor necrosis factor-alpha- and hyperglycemia-induced insulin resistance. Evidence for different mechanisms and different effects on insulin signaling. 861 80


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