EC:2.7.11.13 - FACTA Search

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)

Aging of the vascular wall, arteriosclerosis and focal lipidic plaques, atheromatosis, often occur together but may occur separately as lipidic lesions in young children or vascular aging in some animal species resistant to lipid-rich diet as the rat. Most theories of athero-arteriosclerosis claim an endothelial lesion for its initiation, without proposing a detailed mechanism. The elastin-laminin receptor present also on endothelial cells, mediates NO.-dependent vasorelaxation. It could be shown that chronic exposure to higher concentrations of the agonist, elastin peptides, present in human blood at microgram/ml concentrations, and also during aging, the receptor gets "uncoupled" from its transmission pathway (G-protein, PLC, PKC) but continues releasing free radicals as superoxyde. NO. and O2-. give peroxynitrite, a toxic anion, needing GSH for its neutralisation. GSH production decreases with age. This process decreases available NO. for vasorelaxation and could then contribute to age-dependent blood pressure increase and produce the endothelial lesions leading to the development of athero-arteriosclerosis.
...
PMID:Aging of the vascular wall and atherogenesis: role of the elastin-laminin receptor. 878 48

We previously reported that the activity of gamma-glutamylcysteine synthetase (GCS; EC 6.3.2.2), the rate-limiting enzyme in GSH synthesis, can be acutely inhibited approximately 20-40% by agonists of various signal transduction pathways in rat hepatocytes [Lu, Kuhlenkamp, Garcia-Ruiz and Kaplowitz (1991) J. Clin. Invest. 88, 260-269]. We have now examined the possibility that GCS is phosphorylated directly by activation of protein kinase A (PKA), protein kinase C (PKC) and Ca2+/calmodulin-dependent kinase II (CMK). Phosphorylation of GCS was studied using both purified rat kidney GCS and cultured rat hepatocytes by immunoprecipitating the reaction product with specific rabbit anti-(rat GCS heavy subunit) (anti-GCS-HS) antibodies. All three kinases, PKA, PKC and CMK, phosphorylated rat kidney GCS-HS in a Mg(2+)-concentration-dependent manner, with the highest degree of phosphorylation occurring at 20 mM Mg2+. The maximum incorporation of phosphate in mol/mol of GCS was 1.17 for PKA, 0.70 for PKC and 0.62 for CMK. The degree of phosphorylation was correlated with the degree of loss of GCS activity, and no additional inhibition occurred when GCS was phosphorylated by all three kinases, suggesting that the kinases phosphorylated the same site(s). Phosphoamino analysis showed that all three kinases phosphorylated serine and threonine residues. Two-dimensional phosphopeptide mapping demonstrated that all three kinases phosphorylated the same five peptides, both PKA and PKC phosphorylated two other peptides, and only PKA phosphorylated one additional peptide. Phosphorylation of GCS decreased its Vmax for cysteine and glutamate without changing its K(m). Finally, treatment of cultured rat hepatocytes with dibutyryl cAMP and phenylephrine significantly increased the phosphorylation of GCS, suggesting a potentially important physiological role. In summary, we have demonstrated that GCS is phosphorylated and suggest that phosphorylation/dephosphorylation may regulate GCS activity.
...
PMID:Regulation of gamma-glutamylcysteine synthetase by protein phosphorylation. 894 4

This study examined the effect of streptozotocin-induced diabetes on biliary reduced glutathione (GSH) efflux. Biliary GSH efflux was measured before and after acivicin, an irreversible inhibitor of gamma-glutamyl transpeptidase (GGT). One week after streptozotocin treatment, liver GGT activity doubled in diabetic rats but was inhibited by approximately 90% after acivicin to levels comparable to controls. Despite maximal GGT inhibition, biliary GSH efflux in untreated diabetic rats decreased progressively to approximately 10% of control levels by week 4 and was partially restored by insulin. The mechanism for the decrease in biliary GSH efflux was not increased paracellular permeability. GSH transport kinetics, ATP-stimulated taurocholate, and oxidized glutathione (GSSG) transport in canalicular liver plasma membrane prepared from diabetic and control rats were similar. Inhibition of protein kinase C (PKC) with high-dose H-7 increased biliary GSH efflux in diabetic animals to near control basal levels. In conclusion, streptozotocin-induced diabetic rats exhibit a progressive impairment in biliary GSH transport. One of the responsible mechanisms is heightened PKC tone in diabetic animals.
...
PMID:Progressive defect in biliary GSH secretion in streptozotocin-induced diabetic rats. 912 63

Five in vitro assays have been applied to screen the efficacy of potential chemopreventive agents. These assays measure a) inhibition of morphological transformation in rat tracheal epithelial (RTE) cells, b) inhibition of anchorage independence in human lung tumor (A427) cells, c) inhibition of hyperplastic alveolar nodule formation in mouse mammary organ cultures (MMOC), d) inhibition of anchorage independence in mouse JB6 epidermal cells, and e) the inhibition of calcium tolerance in human foreskin epithelial cells. The efficacy of many of these same agents in whole animal studies of lung, colon, mammary gland, skin, and urinary bladder carcinogenesis has also been measured. The aim herein is to estimate the positive and negative predictive values of these in vitro assays against whole animal chemopreventive efficacy data using the same chemicals. For three of these assays--using RTE, A427 cells and mouse mammary organ culture (MMOC)-enough data are available to allow the estimate to be made. Such extrapolations of in vitro data to the in vivo situation are difficult at best. There are many dissimilarities between the two assay systems. The in vitro assays use respiratory and mammary epithelial cells, while the in vivo assays use respiratory, mammary, colon, bladder and skin cells. The in vitro assays use the carcinogens benzo(a)pyrene (B(a)P) and 7,12-dimethylbenz(a)anthracene (DMBA), while the in vivo assays use B(a)P, DMBA, N-methyl-N-nitrosourea (MNU), N,N'-diethylnitrosamine (DEN), azoxymethane (AOM), and N-butyl-N-(4-hydroxybutyl)nitrosoamine (OH-BBN). There are vast differences in pharmacodynamics and pharmacokinetics in vitro and in vivo, yet it is possible to rapidly screen chemicals in vitro for efficacy at one-tenth the cost and complete tests in weeks instead of months. A positive in vitro assay was defined as a 20% inhibition (compared with control) for the RTE and A427 assays and a 60% inhibition for the MMOC assay at nontoxic concentrations. For in vivo assays, the criterion for a positive result was a statistically significant inhibition of incidence, multiplicity or a significant increase in latency (mean time to first tumor). For an agent to be considered negative in animals, it required negative results in at least two different organ systems and no positive results. Using the battery of three in vitro tests, the positive predictive value for having one, two, or three positive in vitro assays and at least one positive whole animal test was 76%, 80%, and 83% respectively. The negative predictive values for one, two or all three in vitro assays was 25%, 27%, and 50%. From these data it is observed that in vitro assays give valuable positive predictive values and less valuable negative predictive values. The mechanisms of chemoprevention are not well understood. Seven categories of agents were examined for their cancer preventing both in vitro and in vivo: antiinflammatories, antioxidants, arachadonic acid metabolism inhibitors, GSH inducers, GST inducers, ODC inhibitors, and PKC inhibitors. Three or even five in vitro assays cannot be all-inclusive of the many mechanisms of cancer prevention. However, three assays help to predict whole animal efficacy with reasonable positive predictive values. Much work and development remains to be done to rapidly identify new chemopreventive drugs.
...
PMID:Use of in vitro assays to predict the efficacy of chemopreventive agents in whole animals. 915 67

Intrinsic low-level resistance to anti-cancer drugs is a major problem in the treatment of gastrointestinal malignancies. To address the problem presented by intrinsically resistant tumours, we have isolated two monoclonal lines from LoVo human colon adenocarcinoma cells: LoVo/C7, which is intrinsically resistant to doxorubicin (DOX); and LoVo/C5, which shows the same resistance index for DOX as the mixed parental cell population. For comparison, we have included in the study a LoVo-resistant line selected by continuous exposure to DOX and expressing a typical multidrug resistant (MDR) phenotype. In these cell lines we have studied the expression and/or activity of a number of proteins, including P-glycoprotein 170 (P-gp), multidrug resistance-associated protein (MRP), lung resistance-related protein (LRP), glutathione (GSH)-dependent enzymes and protein kinase C (PKC) isoforms, which have been implicated in anti-cancer drug resistance. Intracellular DOX distribution has been assessed by confocal microscopy. The results of the present study indicate that resistance in LoVo/C7 cells cannot be attributed to alterations in P-gp, LRP or GSH/GSH-dependent enzyme levels. Increased expression of MRP, accompanied by alterations in the subcellular distribution of DOX, has been observed in LoVo/C7 cells; changes in PKC isoform pattern have been detected in both intrinsically and pharmacologically resistant cells.
...
PMID:Characterization of a clonal human colon adenocarcinoma line intrinsically resistant to doxorubicin. 921 35

Naphthoquinone compounds have various pharmacological effects such as antiviral, antifungal and anticancer activities. We demonstrated the differentiation of the inducing effect of a naphthoquinone derivative, 2-chloro-3-amino-1,4-nahpthoquinone (NQCA) on the human leukemia cell line U-937. When U-937 cells were treated with NQCA for 4 days, phenotypes indicative of differentiation such as nitroblue tetrazolium (NBT)-reducing activity and phagocytosis were induced. To evaluate the route of differentiation of U-937 cells induced by NQCA, we determined naphthol AS-D chloroacetate esterase and alpha-naphthyl acetate esterase activities. Four days treatment of U-937 cells with NQCA increased alpha-naphthyl acetate esterase activity about 63.5% but naphthol AS-D chloroacetate esterase was not detected. These results indicate that NQCA caused differentiation of U-937 cells into macrophage-like cells. Since protein kinase C (PKC) and protein kinase A (PKA) have important roles in cell-differentiation and proliferation, we employed a PKC inhibitor NA-382 and a PKA inhibitor H-89 to examine the effects of each kinase on the differentiation of U-937 cells. The PKC inhibitor NA-382 decreased the effect of NQCA on U-937 cells, while the PKA inhibitor H-89 did not. Also glutathione (GSH) inhibited the effect of NQCA. It is concluded that the differentiation-inducing effect of NQCA on U-937 cells may be attributed to PKC activation followed by production of free radicals.
...
PMID:Induction of differentiation of U-937 cells by 2-chloro-3-amino-1,4-naphthoquinone. 934 33

Menadione (vitamin K-3,2-methyl-1,4-naphthoquinone), a redox cycling reagent, generates reactive oxygen intermediates and causes oxidative injury. The addition of menadione to Hep G2 cells produced a time- and concentration-dependent loss of cell viability. Preincubation of Hep G2 cells with low, nontoxic concentrations of menadione increased the viability of the cells against toxic doses of menadione or H2O2. Maximum protection was found with menadione concentrations of approximately 3 microM and preincubation times of approximately 45 min. This protective effect could be blocked by the protein synthesis inhibitor cycloheximide and by a variety of antioxidants. The transcription factor nuclear factor-kappaF (NF-kappaB) is known to be activated by many compounds, including reactive oxygen intermediates. Menadione activated NF-kappaB as determined by electrophoretic mobility shift assays. This activation was prevented by the same antioxidants that blocked protection against cytotoxicity produced by preincubation with menadione. Anti-p50 IgG prevented the menadione-stimulated binding of NF-kappaB to the oligonucleotide probe, whereas anti-p65 IgG produced a supershift of the NF-kappaB/oligonucleotide complex. Salicylate prevented the activation of NF-kappaB by menadione, and under these conditions, salicylate potentiated the cytotoxicity of menadione or H2O2. Transfection with a plasmid containing cDNA encoding mouse IkappaBbeta, an inhibitor of NF-kappaB, resulted in increased toxicity by menadione. Furthermore, when protein kinase C was down-regulated by prolonged treatment with active phorbol ester (phorbol-12-myristate-13-acetate), the Hep G2 cells became more sensitive to menadione treatment. However, short term treatment with PMA, which activated NF-kappaB, resulted in protection against menadione cytotoxicity. Menadione cytotoxicity was enhanced when the Hep G2 cells were depleted of GSH. An increased level of GSH was observed after menadione pretreatment; this increase was blocked by salicylate, thereby linking the GSH increase to activation of NF-kappaB by menadione. The results of the current study suggest that menadione pretreatment protects Hep G2 cells from oxidative injury through an NF-kappaB-related mechanism, which may involve, in part, increased production of GSH.
...
PMID:Menadione cytotoxicity to Hep G2 cells and protection by activation of nuclear factor-kappaB. 938 28

Since selenite and other redox-active selenocompounds can modify protein kinase C (PKC) in the test tube, we have determined whether or not this redox regulation occurs inside the cell despite having high concentrations of GSH and the role of this regulation in the inhibition of tumor promotion. By using phorbol ester-promoted JB6 epidermal cell transformation assay, the concentrations of selenite, selenocystine, and selenodiglutathione which are optimal for chemopreventive activity were determined. At such concentrations (0.5 to 2 microM) in the cells treated with these agents, only a slight but transient decrease in PKC activity was observed when measured with a low (5 microM), but not with a high (100 microM) concentration of ATP. However, when the cells were serum starved or pretreated with 2-deoxyglucose, there was a pronounced but transient inactivation of PKC when assayed with both low and high concentrations of ATP. The inactivation was reversed in the cell by an endogenous mechanism or by treatment with thiol agents in the test tube. In spite of a substantial (90%) depletion of GSH in the cells by pretreatment with buthionine sulfoximine, there was no further increase in the redox modification of PKC by selenite as well as no change in the inhibitory effect of selenite on the phorbol ester-stimulated induction of ornithine decarboxylase, which is an intermediate marker related to cell transformation. While GSH is known to influence certain actions of selenium, it may not be required to mediate the effects of selenite tested in this study. The water-soluble cytosolic GSH did not interfere with the redox modification of PKC probably due to the shielding of the cysteine-rich region of the enzyme by a weak hydrophobic association with the membrane. Due to the presence of cofactors in the crude cell extracts, PKC was more sensitive to selenite than in the purified form and was inactivated by low concentrations of selenite (IC50 = 0.05 microM). This modification was reversed by thiol agents as well as by NADPH. A protein disulfide reductase, which can regenerate PKC, was present in the homogenate. Conceivably, selenite and other selenocompounds induce a redox modification of cellular PKC, compartmentally independent from the cytosolic GSH, but intimately connected to a NADPH-dependent reductase system, to mediate, at least in part, some of the cancer-preventive actions.
...
PMID:Selenocompounds induce a redox modulation of protein kinase C in the cell, compartmentally independent from cytosolic glutathione: its role in inhibition of tumor promotion. 939 Jan 72

The role of extracellular calcium in glutamate-induced oxidative stress, and the role of glutamatergic neuronal stimulation and oxidative stress in lead neurotoxicity were explored in mouse hypothalamic GT1-7 cells. Glutamate increased the production of reactive oxygen species (ROS) whether or not extracellular calcium was present. Glutamate-induced ROS production was amplified by lead acetate (PbAc), but only in the absence of extracellular calcium. However, PbAc on its own did not increase the production of ROS. A PKC inhibitor (Ro 31-8220) and superoxide dismutase (SOD) abolished the amplification of glutamate-induced production of ROS by PbAc, but did not inhibit ROS production induced by glutamate alone. Both glutamate and PbAc decreased the levels of intracellular glutathione (GSH), and amplified each other's effect on GSH depletion. Glutamate did not decrease cell viability, whereas the cytotoxicity of PbAc was amplified by glutamate. Extracellular calcium, a PKC inhibitor, or SOD did not modify the effects of glutamate, PbAc or their combination on the levels of GSH or cell viability. These data indicate that in GT1-7 cells extracellular calcium is not essential for glutamate-induced ROS production, which is amplified by PbAc, but only without extracellular calcium. The joint cytotoxicity of glutamate and PbAc is mainly induced by PbAc, preferentially through mechanisms other than ROS production.
...
PMID:Modification of glutamate-induced oxidative stress by lead: the role of extracellular calcium. 943 14

The tripeptide glutathione (GSH) is the predominant low molecular weight thiol reductant in mammalian cells. In this report, we show that at concentrations at which GSH is typically present in the intracellular milieu, GSH and the oxidized GSH derivatives GSH disulfide (GSSG) and glutathione sulfonate each irreversibly inactivate up to 100% of the activity of purified Ca2+- and phosphatidylserine (PS)-dependent protein kinase C (PKC) isozymes in a concentration-dependent manner by a novel nonredox mechanism that requires neither glutathiolation of PKC nor the reduction, formation, or isomerization of disulfide bridges within PKC. Our evidence for a nonredox mechanism of PKC inactivation can be summarized as follows. GSSG antagonized the Ca2+- and PS-dependent activity of purified rat brain PKC with the same efficacy (IC50 = 3 mM) whether or not the reductant dithiothreitol was present. Glutathione sulfonate, which is distinguished from GSSG and GSH by its inability to undergo disulfide/thiol exchange reactions, was as effective as GSSG in antagonizing Ca2+- and PS-dependent PKC catalysis. The irreversibility of the inactivation mechanism was indicated by the stability of the inactivated form of PKC to dilution and extensive dialysis. The inactivation mechanism did not involve the nonspecific phenomena of denaturation and aggregation of PKC because it obeyed pseudo-first order kinetics and because the hinge region of PKC-alpha remained a preferential target of tryptic attack following GSH inactivation. The selectivity of GSH in the inactivation of PKC was also indicated by the lack of effect of the tripeptides Tyr-Gly-Gly and Gly-Ala-Gly on the activity of PKC. Furthermore, GSH antagonism of the Ser/Thr kinase casein kinase 2 was by comparison weak (<25%). Inactivation of PKC-alpha was not accompanied by covalent modification of the isozyme by GSH or other irreversible binding interactions between PKC-alpha and the tripeptide, but it was associated with an increase in the susceptibility of PKC-alpha to trypsinolysis. Treatment of cultured rat fibroblast and human breast cancer cell lines with N-acetylcysteine resulted in a substantial loss of Ca2+- and PS- dependent PKC activity in the cells within 30 min. These results suggest that GSH exerts negative regulation over cellular PKC isozymes that may be lost when oxidative stress depletes the cellular GSH pool.
...
PMID:Irreversible inactivation of protein kinase C by glutathione. 957 16

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