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)

D,L-Palmitoyl carnitine (PC), an inhibitor of protein kinase C, decreased [125I]epidermal growth factor (EGF) cell-associated radioactivity in rat pancreatic acini. H-7, another inhibitor of protein kinase C, failed to inhibit [125I]EGF binding. Palmitate, carnitine, acetylcarnitine, and 2-tetradecylglycidic acid methyl ester (a specific inhibitor of endogenous PC formation) did not alter [125I]EGF binding. PC conjugated to bovine serum albumin (PC-BSA) decreased [125I]EGF cell-associated radioactivity to the same extent as PC. Neither compound affected the distribution of cell-associated radioactivity into acid-resistant and acid-dissociable compartments. In contrast, cholecystokinin octapeptide (CCK8) and 12-O-tetradecanoyl-phorbol-13-acetate (TPA) markedly inhibited the distribution of [125I]EGF into the acid-resistant compartment. Proglumide, a competitive antagonist of CCK8, reversed the inhibitory action of CCK8 but not that of PC-BSA. PC-BSA did not inhibit [125I]insulin binding, and did not enhance amylase release, a Ca2+-mediated effect. Further, its inhibitory effect on [125I]EGF cell-associated radioactivity was not additive with the inhibitory effect of the calcium ionophore A23187. Both PC-BSA and H-7 inhibited Ca2+- and phospholipid-dependent kinase activity in soluble and particulate fractions when added to disrupted acini, but in the particulate compartment only when added to intact acini. These findings suggest that PC-BSA may regulate EGF binding via a novel mechanism that is independent of protein kinase C activation or Ca2+ mobilization.
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PMID:Inhibition of epidermal growth factor binding in rat pancreatic acini by palmitoyl carnitine: evidence for Ca2+ and protein kinase C independent regulation. 310 49

Cholecystokinin-octapeptide (CCK8) inhibits 125I-labeled epidermal growth factor (EGF) cell-associated radioactivity in pancreatic acini, ostensibly as a result of its ability to mobilize cellular Ca2+. The phorbol ester tetradecanoyl phorbol acetate (TPA), a compound that activates protein kinase C, mimics the inhibitory action of CCK8. In the present study we examined the relationship between occupancy of the cholecystokinin (CCK) receptor, the subsequent inhibition of EGF binding, and the potential role of C-kinase activation in mediating this inhibition. Proglumide and dibutyryl cyclic GMP (dbGMP), two distinct competitive antagonists of CCK8, reversed the inhibitory actions of CCK8. Analysis of steady-state saturation kinetics of 125I-EGF binding indicated that CCK8 decreased the apparent affinity of the EGF receptor, mainly as a result of a marked decrease in the amount of internalized ligand. TPA also inhibited 125I-EGF internalization. Removal of CCK8 and TPA from incubation medium did not abolish their inhibitory actions. Carbachol, but not bombesin, exerted a similar residual inhibitory effect. It is suggested that in addition to acting via Ca2+, certain pancreatic secretagogues may also act through C-kinase to regulate EGF binding.
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PMID:Residual inhibition of epidermal growth factor binding by pancreatic secretagogues and phorbol ester in rat pancreas. 387 45

The association of 125I-labelled epidermal growth factor (125I-EGF) with mouse pancreatic acinar cells was inhibited by secretagogues which increase intracellular free Ca2+ concentrations. These agents included cholecystokinin-octapeptide (CCK8) and the Ca2+ ionophore A23187. Inhibition by CCK8 was blocked by lowering the incubation temperature from 37 degrees C to 15 degrees C. Moreover, in contrast with studies of intact acini, the binding of 125I-EGF to isolated acinar membrane particles was not affected either by CCK8, or by varying the level of Ca2+ in the incubation medium. These results indicated, therefore, that the inhibition of 125I-EGF association with acinar cells required intact cells that are metabolically active. Since intact cells at 37 degrees C are known to internalize bound EGF rapidly, acid washing was used to distinguish membrane-associated hormone from internalized hormone. Under steady-state conditions 86% of the 125I-EGF associated with the acini was found to be internalized by this technique. When agents that increased intracellular Ca2+ were tested they all markedly reduced the amount of internalized hormone, whereas surface binding was only minimally affected. The phorbol ester 12-O-tetradecanoyl-phorbol 13-acetate (TPA), which is known to activate protein kinase C, a Ca2+-regulated enzyme, also inhibited the association of EGF with acini. This inhibition was similar to that induced by elevated intracellular Ca2+. To test whether these two inhibitory phenomena were related, the effects of TPA in combination with the Ca2+ ionophore A23187 were examined. At low concentrations the effects were synergistic, whereas at high concentrations the maximal level of inhibition was not changed. We suggest therefore that elevated intracellular Ca2+ and phorbol esters may inhibit EGF internalization by a mechanism involving activation of protein kinase C.
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PMID:Intracellular Ca2+ and phorbol esters synergistically inhibit internalization of epidermal growth factor in pancreatic acini. 609 11

We investigated digestive enzyme release following a short-term pancreatic duct obstruction in rats. An in vivo experiment demonstrated that a 6-hour pancreatic duct obstruction reduced digestive enzyme release evoked both by endogenously released cholecystokinin (CCK) due to pancreaticobiliary diversion and by exogenous administration of CCK8. In vitro experiments also showed that pancreatic duct obstruction reduced the maximal CCK8-evoked amylase secretion. Amylase secretion evoked by the calcium ionophore A23187 and by phorbol myristate acetate was also markedly decreased. These data suggest that pancreatic duct obstruction probably interferes with the secretory process downstream of hormone receptor binding, intracellular Ca2+ release and protein kinase C activation.
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PMID:Pancreatic exocrine secretion in short-term pancreatic duct obstruction induced acute pancreatitis in rats: an in vivo and in vitro study. 752 Mar 99

In order to establish a regulatory role for phosphoproteins in the process of receptor-stimulated Ca2+ mobilization, isolated pancreatic acinar cells, loaded with fura-2, were stimulated with cholecystokinin-octapeptide (CCK8) in the presence of either staurosporine, a general inhibitor of protein kinase activity, or 12-O-tetradecanoylphorbol 13-acetate (TPA), an activator of protein kinase C. Staurosporine alone did not affect the average free cytosolic Ca2+ concentration ([Ca2+]i,av) in a suspension of acinar cells. However, in the presence of 1.0 microM staurosporine the stimulatory effect of submaximal concentrations of CCK8 was significantly enhanced. The potentiating effect of the inhibitor was paralleled by the increased production of inositol 1,4,5-trisphosphate. In addition, staurosporine evoked a transient increase in [Ca2+]i,av in cells prestimulated with a submaximal concentration of CCK8. The data obtained with staurosporine indicate that CCK8-stimulated phosphorylations exert a negative feedback role in the process of receptor-mediated Ca2+ mobilization. The involvement of protein kinase C was investigated by studying the effects of TPA on CCK8-induced Ca2+ mobilization. The phorbol ester induced a rightward shift of the dose/response curve for the CCK8-evoked increase in [Ca2+]i,av, which, in contrast to the unlimited shift obtained with the receptor antagonist D-lorglumide, reached a maximum of approximately one order of a magnitude at 10 nM TPA. The inhibitory effect of TPA was completely overcome by CCK8 at concentrations at or beyond 10 nM. This observation has led to the hypothesis that protein kinase C, directly or indirectly, converts the CCK receptor from a high-affinity state to a low-affinity state. Substantial evidence in favour of this hypothesis was provided by the observation that the increase in [Ca2+]i,av evoked by the CCK8 analogue JMV-180, which acts as an agonist at the high-affinity receptor, was completely blocked by TPA pretreatment. TPA also evoked a rightward shift of the dose/response curve for the carbachol-induced increase in [Ca2+]i,av, indicating that the protein-kinase-C-mediated transition of the affinity state of receptors is a more general phenomenon. In the presence of submaximal CCK8 concentrations, TPA dose-dependently decreased the poststimulatory elevated [Ca2+]i,av to the prestimulatory level, indicating that protein kinase C also inhibits the process of sustained Ca2+ mobilization. The effects of TPA were counteracted by staurosporine, suggesting that the effects of the inhibitor itself were indeed due to inhibition of the receptor-mediated activation of protein kinase C.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Receptor-evoked Ca2+ mobilization in pancreatic acinar cells: evidence for a regulatory role of protein kinase C by a mechanism involving the transition of high-affinity receptors to a low-affinity state. 769 87

Digital-imaging microscopy of Fura-2-loaded pancreatic acinar cells revealed that the C-terminal octapeptide of cholecystokinin (CCK8) dose-dependently recruited 94% of freshly isolated acinar cells in terms of receptor-evoked Ca2+ mobilization. Maximal and half-maximal cell-recruitment were reached with 0.1 nM and 16.8 pM CCK8, respectively. The upstroke of the dose-recruitment curve consisted of cells displaying oscillatory changes in free cytosolic Ca2+ concentration ([Ca2+]i). After having reached its maximum, the percentage oscillating cells dose-dependently decreased upon further increasing of the CCK8 concentration. Pretreatment of the acinar cells with 0.1 microM TPA caused a rightward shift of the dose-recruitment curve but did not change the maximal effect of CCK8 on the recruitment of oscillating cells. Half-maximal recruitment was obtained with 287 pM CCK8. This observation demonstrates that high levels of protein kinase C activation do not inhibit Ca2+ oscillations at a level downstream to receptor activation. Moreover, this observation demonstrates that protein kinase C-mediated inhibition of Ca2+ oscillations evoked by submaximal CCK8 concentrations occurs at the receptor level, converting it from a high-affinity state into a low-affinity state. This conclusion is supported by the observation that TPA completely inhibited the recruitment of acinar cells in response to the high-affinity receptor agonist JMV-180. The inhibitory action of TPA on CCK8-evoked cell-recruitment was paralleled by an inhibitory effect of the phorbol ester on the CCK8-evoked peak increase in average inositol trisphosphate concentration in a population of acinar cells. This observation indicates that low concentrations of CCK8 interact with the high-affinity CCK receptor to increase [Ca2+]i through the intermediation of inositol trisphosphate.
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PMID:Protein kinase C activation inhibits receptor-evoked inositol trisphosphate formation and induction of cytosolic calcium oscillations by decreasing the affinity-state of the cholecystokinin receptor in pancreatic acinar cells. 874 46

Receptor phosphorylation in response to agonist stimulation is a key regulatory principle in signal transduction. Previous work has suggested the concerted action of protein kinase C (PKC) and a staurosporine-insensitive receptor kinase in homologous phosphorylation of the cholecystokinin (CCK) receptor in freshly isolated rat pancreatic acinar cells [Gates, Ulrich, Miller (1993) Am J Physiol 264:G840-G847]. The present study shows that down-regulation of PKC by prolonged (2 h) treatment with 0.1 muM 12-O-tetradecanoylphorbol-13-acetate (TPA) markedly reduced basal CCK receptor phosphorylation as well as that induced by TPA (0.1 muM) and cholecystokinin-(26-33)-peptide amide (CCK8, 0.1 muM). The phosphorylation level reached was the same with both stimulants and equalled basal phosphorylation in untreated control cells. The absence of any CCK8-stimulated phosphorylation reflecting the activity of a putative staurosporine-insensitive receptor kinase raises the intriguing possibility that a basal level of PKC-mediated receptor phosphorylation is required for the action of such a receptor kinase. Immunoblot analysis revealed that the decrease in receptor phosphorylation coincided with a marked reduction of PKC-alpha and, to a lesser extent, PKC-epsilon. In addition, TPA-induced inhibition of the increase in cytosolic free Ca2+ concentration ([Ca2+]i) evoked by the high-affinity CCK receptor agonist JMV-180 was completely reversed. The time-course of recovery closely matched that of the reduction of PKC-alpha. Finally, digital imaging microscopy of individual PKC down-regulated cells revealed a marked increase in the duration of JMV-180-evoked oscillatory changes in [Ca2+]i. Taken together, the present findings are in agreement with the idea that PKC-alpha-mediated receptor phosphorylation leads to a shortening of the duration of the [Ca2+]i oscillations and eventually to inhibition of high-affinity Ca2+ signalling through the native CCK receptor in pancreatic acinar cells.
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PMID:Reduced cholecystokinin receptor phosphorylation and restored signalling in protein kinase C down-regulated rat pancreatic acinar cells. 942

Freshly isolated human monocytes do not express p125(FAK) but upon adherence to substrata activate the highly related calcium-dependent tyrosine kinase (CADTK), also known as Pyk2, CAKbeta, RAFTK, and FAK2. The monocyte CADTK was 5 kDa smaller than protein from epithelial cells; isolation and sequencing of the monocyte CADTK cDNA revealed a predicted 42-amino acid deletion between the two proline-rich domains of the enzyme. The nucleic acid sequence suggests that the deletion is caused by alternative RNA splicing. This species was also found in T and B lymphocytes and appears to be the predominant form of cytoskeletal associated tyrosine kinase in non-neoplastic, circulating, hematopoietic cells. CADTK was not activated when monocytes maintained in suspension were treated with agents that produce an intracellular calcium (thapsigargin) or protein kinase C (phorbol 12-myristate 13-acetate) signal including a chemokine, RANTES, that binds to the HIV co-receptor, CCK5. In contrast, monocyte adherence to tissue culture plastic-stimulated CADTK tyrosine phosphorylation, a process that was enhanced by thapsigargin, phorbol 12-myristate 13-acetate, and RANTES but that was completely blocked by preincubation with cytochalasin D. When compared with plastic, adherence to fibronectin- or collagen-coated surfaces produced only minimal CADTK activation but permitted significant stimulation by added thapsigargin. These data suggest that in a cell type that lacks p125(FAK), CADTK plays an early role in post-adherence signaling. Its activation involves two stages, cytoskeletal engagement, which is permissive, and co-stimulatory signals (calcium or protein kinase C) generated by extensive cell surface engagement, agonists, or inflammatory chemokines.
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PMID:A calcium-dependent tyrosine kinase splice variant in human monocytes. Activation by a two-stage process involving adherence and a subsequent intracellular signal. 954 57

Receptor-mediated activation of phosphatidylcholine phosphatidohydrolase or phospholipase D (PLD) was studied in Chinese hamster ovary (CHO) cells expressing the cholecystokinin-A (CCK-A) receptor. Cells were labelled with [3H]myristic acid for 24 h and PLD-catalysed [3H]phosphatidylethanol formation was measured in the presence of 1% (v/v) ethanol. Cholecystokinin-(26-33)-peptide amide (CCK8) increased PLD activity both time- and dose-dependently. Maximal activation of protein kinase C (PKC) with 1 microM PMA or sustained elevation of the cytosolic free Ca2+ concentration ([Ca2+]i) with 1 microM thapsigargin increased PLD activity to 50% and 70% of the maximal value obtained with CCK8 respectively. The stimulatory effects of CCK8, PMA and thapsigargin were abolished in cells in which PKC was downregulated or inhibited by chelerythrine. PMA/Ca2+-stimulated PLD activity was absent in a homogenate of PKC-downregulated cells but could be restored upon addition of purified rat brain PKC. CCK8-induced PLD activation was inhibited by 90% in the absence of external Ca2+, demonstrating that receptor-mediated activation of PKC in itself does not significantly add to PLD activation but requires a sustained increase in [Ca2+]i. Taken together, the results presented demonstrate that, in CHO-CCK-A cells, receptor-mediated PLD activation is completely dependent on PKC, but that the extent to which PLD becomes activated depends largely, if not entirely, on the magnitude and duration of the agonist-induced increase in [Ca2+]i.
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PMID:Concerted action of cytosolic Ca2+ and protein kinase C in receptor-mediated phospholipase D activation in Chinese hamster ovary cells expressing the cholecystokinin-A receptor. 988 23

In addition to its fundamental role in stimulating gastric acid secretion, the peptide hormone gastrin induces growth-promoting effects on diversity of target cells. Various mechanisms, including endocrine, paracrine, and autocrine, have been proposed for gastrin's growth-promoting actions. The mitogenic effects of gastrin are mediated by specific cell surface receptors activated after gastrin binding. The functionally defined receptors for gastrin include cholecystokinin A (CCKA) receptor, which is discriminating for sulfated CCK8; cholecystokinin B (CCKB)/gastrin receptor, which binds gastrin17 sulfated, and nonsulfated CCK8 with nearly equal affinities; cholecystokinin C (CCKC), which is a low-affinity gastrin binding protein; and novel, high-affinity receptors selective for amidated gastrin, processing intermediates of gastrin, or both. The signaling pathways mediating gastrin's stimulation of the CCKB/gastrin receptor have been progressively outlined, and the pathways mediating other receptors have been slowly emerging. Engagement of the gastrin receptor initiates various biochemical and molecular events, including recruitment and activation of tyrosine kinases, activation of the phospholipase C signaling pathway leading to phosphoinositide breakdown, intracellular calcium mobilization and protein kinase C stimulation, activation of the mitogen-activated protein kinase pathway, and induction of early response genes. Current emphasis is on understanding the functional significance of processing intermediate forms of gastrin, and the receptor subtypes and pathways that promote the trophic/mitogenic effects of the different molecular forms of gastrin.
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PMID:Signaling pathways mediating gastrin's growth-promoting effects. 1047 91


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