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)

Treatment of segments of ileum from 8-week streptozotocin-induced diabetic rats with phorbol 12,13-dibutyrate (PDBu) in vitro resulted in restoration of the diabetes-induced changes in the expression of enteric VIP- and galanin-like immunoreactive nerve fibres. The increase in fluorescence intensity and density of VIP- and galanin-like immunoreactivity observed in 8-week streptozotocin-treated rats was reduced to a near normal level after 40 min incubation of diabetic tissues in Krebs solution containing PDBu (100 nM). The tissue content of VIP was also affected (control = 2.1 +/- 0.31 pmol/cm; diabetic = 4.6 +/- 0.48 pmol/cm; diabetic + PDBu = 2.9 +/- 0.91 pmol/cm) after incubation with PDBu. The significance of these findings in relation to the possible role of protein kinase C in the regulation of expression and/or storage of these enteric neuropeptides in normal and diabetic states is discussed.
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PMID:Restoration of diabetes-induced changes in enteric nerves by phorbol 12,13-dibutyrate. 137 84

Protein kinase C appears to play an important, yet complex role in the supramaximal inhibition of pancreatic acinar cell secretion observed in response to cholecystokinin (CCK). The addition of protein kinase C activation to the concentration-response curve of a partial agonist acting at the CCK receptor (a phenethyl ester analogue of CCK), transforms a curve without supramaximal inhibition to a full agonist curve typical of CCK. This effect can be elicited by low concentrations of phorbol ester (50pM to 1nM 12-0-tetradecanoyl-phorbol-13-acetate) or by hormonal agonists (0.1 microM carbamylcholine, 10pM bombesin, 1pM CCK-8) which activate protein kinase C, but not by agonists acting via alternate second messengers (VIP). Of interest, this effect is dependent on preincubation of the acinar cells with the protein kinase C activator at 37 degrees C, with the effect rapidly reversed by transient exposure of the cells to lower temperature. This is consistent with mediation by a phosphorylation event. However, the requirement for an extended (greater than 15 min) preincubation period when using minimal kinase activation suggests that this phenomenon is more complicated than a simple bimolecular phosphorylation event and likely includes a series of events such as translocation of substrates and/or enzymes involved.
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PMID:Complex role of protein kinase C in mediating the supramaximal inhibition of pancreatic secretion observed with cholecystokinin. 152 Mar 40

We have reviewed the literature, which supports an important role for dopamine withdrawal in the regulation of PRL secretion. Concentrations of dopamine in the hypophyseal portal circulation are sufficient to occupy the majority of dopamine receptors (1) and tonically suppress PRL secretion (20-26). Brief escapes from dopaminergic regulation associated with the secretion of PRL have been observed (37-41). Therefore, dopamine regulates secretion of PRL both by occupancy of, as well as dissociation from, specific D2 dopamine receptors. The rapid off rate from its receptor (2) is consistent with signals transmitted through brief decreases in dopamine concentration. The removal of dopamine for 10 min results in increases in intracellular cAMP and presumably activation of protein kinase A (39, 138) as well as activation of phospholipase C (137, 138) and protein kinase C (136). The removal of dopamine results directly in the release of PRL (37-41). Furthermore, the brief removal of dopamine results in the long-term potentiation of the PRL-releasing action of TRH (38-40). The potentiating action of dopamine withdrawal appears to be mediated by the activation of protein kinase A since pretreatment with VIP, a hormone that signals via protein kinase A, also potentiates the action of TRH (39). TRH stimulates PRL release via Ca2+/protein kinase C (177-184). The potentiating action of dopamine removal is selective for the Ca2+/protein kinase C pathway since dopamine removal does not potentiate the PRL-secreting action of VIP (38, 87, 92). The action of TRH is potentiated up to 30 min after the return of dopamine and the suppression of PRL to basal levels (38). In Fig. 10, dopamine dissociation from its receptor or VIP association to its receptor are shown separated by a broken line to indicate that by the time the potentiation of the action of TRH is tested, either dopamine is again occupying its receptor or VIP is no longer present. Therefore, the effect of protein kinase A activation is remembered by the lactotroph. We hypothesize that the responsiveness of the cell to TRH is potentiated by the phosphorylation of proteins by protein kinase A. Two potential substrates for protein kinase A are voltage-dependent Ca2+ channels and protein phosphatase inhibitors that would prolong the action of protein kinase C. When TRH occupies its receptor, intracellular Ca2+ levels are increased first from intracellular stores and subsequently by extracellular Ca2+ influx (187-189). Intracellular Ca2+ is mobilized by increased levels of IP3(128). Extracellular Ca2+ enters the lactotroph via voltage-dependent Ca2+ channels (189, 190).(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Dissociation of dopamine from its receptor as a signal in the pleiotropic hypothalamic regulation of prolactin secretion. 161 63

We have reported previously that anterior pituitary cells released interleukin-6 (IL-6) and that this release was stimulated by lipopolysaccharide (LPS), phorbol myristate acetate (PMA), or agents that increased intracellular cAMP concentrations. We now report that IL-1 stimulates IL-6 release from anterior pituitary cells in vitro. IL-1 alpha and IL-1 beta (0.04-25 ng/ml) significantly increased IL-6 release 3- to 4-fold in a concentration-related manner during 6-h incubations; however, there was no change in extracellular or intracellular cAMP concentrations. IL-1 alpha and IL-1 beta (10 ng/ml), vasoactive intestinal peptide (VIP, 500 nM), prostaglandin E2 (PGE2, 1 microM), and LPS (1 ng/ml) stimulated IL-6 release to a similar degree. In the presence of VIP and PGE2, IL-1 alpha and IL-1 beta increased IL-6 release without any apparent further change in extracellular or intracellular cAMP. Conversely, LPS did not increase cAMP concentrations, and IL-1 did not significantly increase IL-6 release in the presence of LPS. The preexposure of anterior pituitary cells to 1 microM PMA caused the apparent down-regulation of protein kinase C activity because 100 nM PMA was no longer effective to stimulate IL-6 release; however, the ability of IL-1 alpha, IL-1 beta, PGE2, or LPS to stimulate IL-6 release was not altered. In addition, IL-1 alpha and IL-1 beta stimulated IL-6 release in the presence of maximally stimulative concentrations of PMA. The synthetic glucocorticoid dexamethasone (10 nM) significantly inhibited IL-6 release induced by IL-1 alpha, IL-1 beta, or LPS. The separation of anterior pituitary cells on unit gravity BSA gradients generated fractions of IL-6-producing cells that were inducible by LPS and IL-1 beta and separate from the PRL-, ACTH-, GH-, or LH-producing cell fractions. These data suggest that IL-1 stimulates IL-6 release from a subpopulation of anterior pituitary cells via a glucocorticoid-sensitive and non-cAMP-mediated pathway that is different from those pathways used by VIP, PGE2, and PMA.
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PMID:Interleukin-1 stimulates interleukin-6 release from rat anterior pituitary cells in vitro. 203 55

12-O-tetradecanoylphorbol 13-acetate (TPA) and cholecystokinin octapeptide stimulate amylase secretion in dispersed pancreatic acini, presumably acting via the activation of protein kinase C. In this study, we examined TPA pretreatment on the subsequent response of rat pancreatic acini to secretagogues. Acini exposed to TPA (3 X 10(-7) M) at 37 degrees C reduced the subsequent amylase secretion as stimulated by cholecystokinin octapeptide and carbachol, but not by A23187 or VIP. The optimal effect was obtained after 5 min of preincubation with TPA. Longer incubation did not result in greater attenuation. The degree of attenuation was dependent on the concentration of TPA used in the pretreatment. Maximal effect was seen at TPA concentrations of 10(-7) M and higher. Preincubation with TPA resulted in alterations of the dose response of pancreatic acini to cholecystokinin octapeptide. A decrease in amylase secretion was obtained at optimal and suboptimal but not at supraoptimal concentrations of cholecystokinin octapeptide. The peak response to cholecystokinin octapeptide, furthermore, was shifted almost 1 log unit to the right, suggesting a decrease in cholecystokinin binding of the acini following TPA treatment. Binding studies demonstrated a reduction in the specific binding of 125I-labelled cholecystokinin octapeptide to acini following TPA treatment. Analysis of binding data revealed a decrease in affinity and binding capacity of the high-affinity component. No significant change in the binding capacity was detected with the low-affinity component, but a great increase in its affinity was observed. This suggests that the attenuation effect by TPA on the cholecystokinin octapeptide response in rat pancreatic acini in vitro is at the receptor level.
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PMID:Phorbol ester attenuates cholecystokinin-stimulated amylase release in pancreatic acini of rats. 244 87

Vasoactive intestinal peptide synergistically stimulated initiation of DNA synthesis in Swiss 3T3 cells. The peptide stimulated [3H]thymidine incorporation in the presence of insulin and either forskolin or an inhibitor of cAMP phosphodiesterase in a concentration-dependent manner. Half-maximal effect was obtained at 1 nM. At mitogenic concentrations, VIP stimulated a marked accumulation (eightfold) of cAMP. In contrast to other growth-promoting neuropeptides, VIP did not induce an increase in cytosolic free Ca2+ or an activation of protein kinase C. We conclude that neuropeptides can modulate long-term cell proliferation through multiple signaling pathways.
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PMID:Vasoactive intestinal peptide synergistically stimulates DNA synthesis in mouse 3T3 cells: role of cAMP, Ca2+, and protein kinase C. 283 26

In this study we have characterized and compared the regulation of the HT29 cell vasoactive intestinal peptide receptor/adenylate cyclase system (VIP-R/AC) by the VIP-R agonist peptide histidineisoleucineamide (PHI) and by activators of protein kinase C (PKC) including phorbol 12-myristate, 13-acetate (PMA) and mezerein. Preincubation with either PHI or PKC activator decreased maximum VIP-stimulated AC activity and decreased the number of cell surface VIP-R. A [125I]VIP binding assay using solubilized VIP-R of the plasma membrane and light vesicle fractions from sucrose density step gradients was developed as a more direct measure of VIP-R internalization. Preincubation with PHI or PMA decreased plasma membrane fraction [125I]VIP binding and increased binding in the light vesicle fraction, thus providing the most direct evidence to date for translocation of VIP-R per se from the plasma membrane to another, presumably intracellular, compartment. Two experimental approaches differentiated between agonist and PKC activator regulation of VIP-R/AC. The protein kinase inhibitors H-7 and staurosporine blocked mezerein-, but not PHI-, induced losses of cell surface VIP-R. Also, down-regulation of PKC did not block PHI-induced loss of cell surface VIP-R. Thus, although both agonist and PKC activators can lead to desensitization and internalization of VIP-R, PKC is apparently not involved in the mechanisms of agonist-induced desensitization.
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PMID:Vasoactive intestinal peptide receptor/adenylate cyclase system: differences between agonist- and protein kinase C-mediated desensitization and further evidence for receptor internalization. 284 20

Treatment of HT29 cells with the tumor promoting phorbol ester PMA resulted in an attenuation of VIP-stimulated cAMP production in intact cells and VIP-stimulated adenylate cyclase activity in cell membranes. PMA did not decrease the ability of cholera toxin and forskolin to elevate cAMP levels in intact cells. Fluoride-stimulated adenylate cyclase activity in HT29 cells homogenates was not affected by PMA. The maximal VIP binding capacity of homogenates prepared from HT29 cells treated with PMA was decreased by 50%. It is concluded that protein kinase C regulates VIP receptor function possibly through phosphorylation of the VIP receptor.
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PMID:Phorbol ester induces loss of VIP stimulation of adenylate cyclase and VIP-binding sites in HT29 cells. 302 47

Figure 4 summarizes the steps by which Ca2+ and cyclic AMP-mediated secretagogues activate enzyme secretion in the pancreatic acinar cell. CCK and acetylcholine bind to specific plasma membrane receptors and through an as yet incompletely understood mechanism give rise to an elevation in free cytoplasmic Ca2+. A question central to this scheme is whether receptor binding leads to intracellular Ca2+ mobilization through generation of a diffusable mediator. Clues to answering this question may come from a) determining whether Ca2+ is released from the plasma membrane in addition to one or more intracellular organelles, and b) examining the role (if any) of membrane phosphatidylinositol metabolism in Ca2+ mobilization. A second class of secretagogues, represented by VIP and secretin, bind to their specific receptors and cause the accumulation of cyclic AMP. Cyclic AMP potentiates Ca2+ in activating secretion, and in some species, cyclic AMP may activate secretion independently of Ca2+. Ca2+ may act by regulating the activity of calmodulin dependent protein kinase(s) and phosphatase(s) and a phospholipid dependent kinase (protein kinase C) which has also been shown to be activated by diacylglycerol; cyclic AMP activates a distinct kinase termed protein kinase A. These kinases and phosphatases then alter the phosphorylation of specific proteins which are presumed to play structural or regulatory roles in exocytosis. Potentiation may thus result from interaction of Ca2+ and cyclic AMP at the level of a protein kinase, phosphatase or protein substrate.
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PMID:Stimulus-secretion coupling in pancreatic acinar cells. 609 80

In vitro exposure of rat cerebrocortical slices to microM concentrations of serotonin (5HT) results in an increased response of adenylate cyclase to isoproterenol (ISO). No change in the affinity of the beta-adrenoceptor toward the agonist was found after 5HT exposure when measuring ISO displacement of [3H]CGP 12177 binding. A similar increase of adenylate cyclase response was also found when using VIP as a stimulatory agent. The dose-response curve of adenylate cyclase to the GTP analogue, GppNHp, was modified by 5HT, which promotes a significantly higher maximal response without altering the potency of GppNHp. Forskolin-stimulated adenylate cyclase activity was not affected by 5HT. Serotonergic 5HT2 receptors are involved in the sensitization of adenylate cyclase to GppNHp, since the selective 5HT2 antagonist ketanserin inhibits the effect of 5HT, whereas the 5HT2 agonist DOI mimics 5HT. The involvement of 5HT2 receptor-coupled activation of protein kinase C is also demonstrated: direct protein kinase C activators such as phorbol esters and s,n-dioctanoylglycerol behave in the same manner as 5HT, while the protein kinase C inhibitor CGP 41251 prevents 5HT from increasing adenylate cyclase responsiveness to GppNHp. Moreover, in vitro exposure of cortical slices to 5HT results in reduced inhibition of adenylate cyclase by somatostatin. Since no change was observed at the receptor level and in the direct stimulation of the catalytic subunit of the enzyme, we propose that 5HT might accomplish the sensitization of adenylate cyclase through protein kinase C by inactivating the inhibitory coupling protein Gi and facilitating the interaction of the exogenous GppNHp with the stimulatory coupling protein Gs.
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PMID:Heterologous sensitization of adenylate cyclase activity by serotonin in the rat cerebral cortex. 790 77


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