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

Mounting evidence suggests that the physiological function of the various subtypes of adrenergic receptors is controlled by phosphorylation/dephosphorylation reactions. It seems intuitively unlikely that this phenomenon will be limited simply to the adrenergic receptors, since these receptors share transmembrane signaling pathways with a host of other plasma membrane receptors. Different types of kinases appear to be involved. On the one hand, phosphorylation reactions may operate in a classical feedback regulatory sense. Thus, the cAMP-dependent protein kinase, once activated by a beta-agonist, can feedback-regulate the function of the receptors by phosphorylating and desensitizing them. Similarly, protein kinase C appears to be able to feedback-regulate the function of alpha 1-adrenergic receptors by phosphorylation. There may also be "cross talk" between the systems. Thus, protein kinase C, when stimulated by phorbols, is able to phosphorylate and desensitize the beta-adrenergic receptors. Moreover, very recently we have found that the cAMP-dependent protein kinase can phosphorylate the alpha 1-adrenergic receptors in vitro. These are examples of one transmembrane signaling system regulating the function of another. Perhaps most interestingly, it appears that there may be a previously unappreciated class of receptor kinases in the cytosol of cells. The first of these, which we have recently found and named beta-ARK, serves to phosphorylate only the agonist-occupied form of the beta-adrenergic receptor. As noted, it is somewhat analogous to the rhodopsin kinase. Such highly specific receptor kinases, which can phosphorylate only the agonist-occupied form of a receptor, represent a potentially elegant mechanism for controlling the function of receptors in a fashion which is linked to their physiological stimulation. How widespread such kinases are, and the actual roles which they play in regulating receptor function, remain to be determined. Finally, it should be stressed that although this review has focused on the regulatory role of receptor phosphorylation, it is by no means our intent to suggest that receptors are the only locus for physiological control of sensitivity to hormone and drug reaction. There is already evidence that guanine nucleotide regulatory proteins can be regulated, and it seems likely that each of the components of the system, including the adenylate cyclase, are likely to be involved in various forms of complex regulation. To date, however, the receptors represent that component of the system whose regulation we understand in the greatest detail.
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PMID:Regulation of adrenergic receptor function by phosphorylation. 302 10

Studies were performed on purified brush-border membranes from the kidney of the rabbit to examine the relation between protein kinase C and the Na+/H+ exchanger in these membranes. The brush-border membranes were transiently opened by exposure to hypotonic media and the membrane proteins phosphorylated by exposure to ATP and phorbol esters or partially purified protein kinase C. The membranes were resealed and the intravesicular space acidified by incubation in a sodium-free isotonic solution (pH 5.5). The rate of uptake of 1 mM 22Na+ (pH 7.5), with and without amiloride (1 mM), was assayed and the proton gradient-stimulated, amiloride-inhibitable component of 22Na+ taken as a measure of the activity of the Na+/H+ exchanger. 12-0-tetradecanoyl phorbol-13-acetate (TPA) increased the amiloride-sensitive component of 22Na+ uptake. TPA did not affect the amiloride-insensitive component of 22Na+ uptake or the equilibrium concentration of sodium. TPA also did not affect the rate of dissipation of the proton gradient in the absence of sodium or the rate of sodium-dependent or -independent uptake of D-glucose. Other "active" phorbol esters stimulated the rate of Na+/H+ exchange, but phorbol esters of the 4 alpha configuration did not. Incubation of the opened membranes in partially purified protein kinase C increased the rate of proton gradient-stimulated, amiloride-inhibitable sodium uptake. The stimulatory effect of TPA and protein kinase C was not additive. In the absence of ATP, neither TPA nor protein kinase C affected Na+/H+ exchange transport. To determine the membrane-bound protein substrates, parallel experiments were conducted with gamma-[32P] ATP in the phosphorylating solutions.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Protein kinase C activates the renal apical membrane Na+/H+ exchanger. 302 47

In contrast to our previous report (Biochem. Biophys. Res. Comm. 134:587, 1986), we now find that protein kinase C (PKC) is mobilized in human polymorphonuclear neutrophils (PMN) stimulated with platelet-activating factor (PAF) or leukotriene (LT)B4. Thus nanomolar concentrations of each compound caused PMN to lose cytosolic, PKC-specific protein phosphorylating activity, as well as receptors for phorbol myristate acetate (PMA). Smaller gains in membrane-associated PMA receptors accompanied these changes. Diacylglycerol and PMA had very similar effects on PKC. However, unlike these direct PKC activators, PAF and LTB4 induced only moderate decreases in cytosolic PKC; acted only on PMN pretreated with cytochalasin B; did not mobilize PKC in disrupted PMN or activate PKC in a cell-free system; and with respect to PAF, induced responses that partially reversed within 30 min. Furthermore, PAF, LTB4, and several of their structural analogues mobilized PKC at concentrations correlating closely with their respective affinities for cellular LTB4 or PAF receptors. Thus PAF and LTB4 acted by indirect and apparently receptor-mediated mechanisms. Four observations indicated that the cytochalasin B-dependent degranulating actions of PAF and LTB4 involved PKC. First, PKC mobilization and degranulation occurred at the same stimulus concentrations. Second, 5-hydroxyicosatetraenoate dramatically enhanced both PKC mobilization and degranulation when elicited by PAF; it had relatively little influence on LTB4-induced responses. Third, PAF-induced mobilization (t1/2 less than 7 sec) preceded degranulation (t1/2 approximately 20 sec). Finally, a PKC blocker, polymyxin B, was similarly effective in inhibiting degranulation responses to PAF, LTB4, and PMA. Because stimulated PMN may produce and use PAF, LTB4, and 5-hydroxyicosatetraenoate as secondary intracellular mediators, our results implicate PKC as a central and potentially critical regulator of function.
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PMID:Arachidonate metabolites, platelet-activating factor, and the mobilization of protein kinase C in human polymorphonuclear neutrophils. 302 24

Second-messenger systems play a major role in mediating neurotransmitter actions. In recent years our understanding of the organization and function of two prominent second-messenger systems has progressed rapidly--the adenylate cyclase and phosphoinositide systems. Guanosine triphosphate-binding proteins, which are especially abundant in brain, couple transmitter receptors to the key second-messenger generating enzymes in both of these systems. Whereas activation of adenylate cyclase produces a single intracellular messenger, cyclic AMP, stimulation of the phosphoinositide system generates at least two, inositol trisphosphate and diacylglycerol. Inositol trisphosphate mobilizes calcium from intracellular stores, and diacylglycerol, like cyclic adenosine monophosphate, activates a phosphorylating enzyme, protein kinase C. These second-messenger systems are particularly enriched in the brain where they modulate many aspects of synaptic transmission.
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PMID:Beyond receptors: multiple second-messenger systems in brain. 303 86

The Ca2+ and calmodulin sensitivity of endogenous protein kinase activity in synaptosomal membrane fragments from rat brain was studied in medium containing Ca2+ plus EGTA using a modified computer programme to calculate free Ca2+ concentrations that took into account the effect of all competing cations and chelators. The Ca2+-dependent phosphorylation of 10 major polypeptide acceptors with Mr values ranging from 50 to 360 kilodaltons required calmodulin in reactions that were all equally sensitive to Ca2+; half-maximal phosphorylation required a free Ca2+ concentration of 45 nM and maximal phosphorylation approximately 110 nM. The significance of these values in relation to published data on the intracellular concentration of free Ca2+ in the nervous system is discussed. One acceptor of 45 kilodaltons was phosphorylated in a Ca2+-dependent reaction that did not require calmodulin. This polypeptide appeared to correspond to the B-50 protein, an established substrate of the lipid-dependent protein kinase C. Further study of this phosphorylating system showed that the reaction was only independent of calmodulin at saturating concentrations of Ca2+; at subsaturating concentrations (in the range 50-130 nM), a small but significant stimulation of the enzyme by calmodulin was demonstrated. The possible significance of this finding is discussed.
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PMID:Ca2+ sensitivity of Ca2+-dependent protein kinase activities toward intrinsic proteins in synaptosomal membrane fragments from rat cerebral tissue. 307 18

We have used primary cultures of swine granulosa cells to investigate the regulatory role of the protein kinase C pathway in the ovary. In this system, we observed the following. Swine granulosa cells bound [3H]phorbol 12,13-dibutyrate [( 3H]PDB) specifically with high affinity [apparent Ki for 12-O-tetradecanoylphorbol 13-acetate (TPA) = 3.1 (2.1-4.7) nM] and low capacity [0.68 (0.34-0.99) pmol/10(7) cells]. The cytosol of granulosa cells contained functionally active protein kinase C capable of phosphorylating distinct proteins in response to stimulation with active phorbol ester. TPA and PDB induced dose-dependent inhibition (greater than 85%) of follicle-stimulating-hormone (FSH)-stimulated progesterone production. Half-maximally inhibitory concentrations were 0.10 and 0.75 nM for TPA and PDB respectively, whereas phorbol analogues that do not activate protein kinase C were not inhibitory. TPA did not impede cyclic AMP generation in response to FSH, cholera toxin or forskolin acutely (within 48 h), but did inhibit the stimulatory effects of 8-bromo cyclic AMP, insulin and oestradiol on progesterone biosynthesis. In the presence of maximally effective concentrations of 25-hydroxy-, 20 alpha-hydroxy- or 22R-hydroxy-cholesterol as exogenous sterol substrates for cholesterol side-chain cleavage, treatment with TPA suppressed pregnenolone, progesterone and 20 alpha-hydroxypregn-4-en-3-one biosynthesis by more than 80%. The inhibitory effects of phorbol esters were not attributable to non-specific cytotoxicity, since prostaglandin F2 alpha production increased in the same cultures and aromatization of exogenously supplied testosterone to oestradiol was not suppressed. In intact granulosa cells, the effects of phorbol esters were mimicked by a synthetic non-diterpene diacylglycerol, 1-octanoyl-2-acetylglycerol, and the tumour promoter, mezerein, which specifically activates protein kinase C. We conclude that swine granulosa cells contain specific high-affinity receptors for phorbol esters that are functionally coupled to protein phosphorylation. Moreover, treatment with phorbol esters or non-phorbol activators of protein kinase C results in selective inhibition of cholesterol side-chain cleavage activity without impairing cyclic AMP generation or oestrogen biosynthesis.
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PMID:An inhibitory role for the protein kinase C pathway in ovarian steroidogenesis. Studies with cultured swine granulosa cells. 310 2

The vertebrate central nervous system contains very high concentrations of protein kinase C, a calcium- and phospholipid-stimulated phosphorylating enzyme. Phorbol esters, compounds with inflammatory and tumor-promoting properties, bind to and activate this enzyme. To clarify the role of protein kinase C in neuronal function, we have localized phorbol ester receptors in the rat hippocampus by autoradiography and examined the electrophysiological effects of phorbol esters on hippocampal pyramidal neurons in vitro. Phorbol esters blocked a calcium-dependent potassium conductance. In addition, phorbol esters blocked the late hyperpolarization elicited by synaptic stimulation even though other synaptic potentials were not affected. The potencies of several phorbol esters in exerting these actions paralleled their affinities for protein kinase C, suggesting that protein kinase C regulates membrane ionic conductance.
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PMID:Protein kinase C regulates ionic conductance in hippocampal pyramidal neurons: electrophysiological effects of phorbol esters. 315 91

We have previously observed major differences in the phosphorylation of membrane proteins in sparse, proliferating versus confluent, quiescent pig aortic endothelial cells (EC) (Kazlauskas and DiCorleto, 1987). In the present study we examined whether EC growth state can influence the activity of a specific phosphorylating enzyme, protein kinase C (PKC) in cytosolic and membrane fractions of pig aortic EC. Levels of PKC were measured using two methods: 1) Ca2+ and phospholipid-dependent phosphorylation of exogenous histones using gamma-labeled [32P]ATP, and 2) [3H]phorbol-12,13-dibutyrate (PDBu) binding activity. The total amount of PKC activity in the quiescent versus proliferating cells was similar but the percentage of PKC activity in the membrane fraction correlated with the proliferative index of the cells: confluent, quiescent cultures exhibited a majority of PKC activity in the cytosolic fraction (67%), whereas sparse, proliferating cultures contained principally membrane-bound PKC (70%). We also examined the role of PKC in the mitogenic response of pig aortic EC to fetal calf serum. Following serum stimulation of sparse, serum-deprived pig aortic EC, PKC activity redistributed from the cytosolic to the membrane fraction in a rapid process that correlated with subsequent DNA synthesis. A potent activator of PKC, 12-O-tetradecanoylphorbol-13-acetate (TPA), induced a minimal mitogenic response in pig aortic EC when added alone but acted synergistically with low concentrations of fetal calf serum to greatly stimulate DNA synthesis. Furthermore, pig aortic EC treated with TPA for 24 h to down-regulate PKC exhibited only 25% of the serum-stimulated mitogenic activity of control cultures. These results suggest a role for PKC activation and translocation in the proliferation of pig aortic EC.
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PMID:Growth-dependent subcellular redistribution of protein kinase C in cultured porcine aortic endothelial cells. 317 Jun 40

To examine the hypothesis that protein kinase C (PKC) plays a role in the release of dopamine (DA) in the nigrostriatal pathway, a new thiophosphorylation procedure was developed to monitor PKC activity. In this method, tissues were incubated with adenosine 5'-[gamma-thio35S]triphosphate, and the transfer of the gamma-thiophosphoryl group to histones or endogenous substrate proteins was measured. The thiophosphorylation showed a marked dependency on both calcium and lipids, and the endogenous substrate proteins being thiophosphorylated were similar to those reported as being specific substrates of PKC using [32P]ATP. Furthermore, the thiophosphorylation activity measured in the presence of calcium and lipids did not reflect cAMP-dependent or calmodulin-dependent protein kinase activities. Besides providing an accurate measure of PKC activity, thiophosphorylation has the advantage that it measures a phosphorylating activity that is independent of phosphatase activity because the thiophosphorylated substrates are resistant to the action of phosphatases.
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PMID:Protein kinase C and dopamine release--I. Measurement by thiophosphorylation. 319 Jul 44

Protein kinase P (PK-P), which has previously been detected from both human and murine leukemic cells, is characterized by distinctive patterns of phospholipid stimulation and substrate preferences, and is chromatographically separable from protein kinase C (PK-C). We have developed a three-step purification of PK-P from the interleukin 3 (IL-3)-dependent DA-1 murine leukemic cell line, entailing DEAE-Sephacel chromatography followed by TSK-3000 size exclusion and Mono-Q anion exchange HPLC steps. This yielded a 27-kd protein (from sodium dodecyl sulfate polyacrylamide gel electrophoresis) capable of preferentially phosphorylating the characteristic 75.5- and 77-kd endogenous substrates of PK-P previously noted. These observations were the basis for the development of a quantitative assay for PK-P, utilizing its separation from PK-C upon DEAE-Sephacel minicolumns followed by measurement of phosphatidylglycerol-stimulated histone H2B phosphorylation. This assay, and an analogous assay for PK-C, was then used to study the response of IL-3-starved DA-1 cells to IL-3 restimulation. PK-C exhibited cytosol to particulate redistribution following either IL-3 or phorbol 12-myristate 13-acetate (PMA) treatment, as has been previously described by others using similar systems. PK-P exhibited a rapid decrease in total activity following either IL-3 or PMA treatment, suggesting a response to PK-C activation. This was followed by a recovery phase during which PK-P activity slowly increased, with preferential redistribution into the particulate fraction of IL-3- but not PMA-treated cells. This difference in redistribution was thus likely to be under the control of signal transduction events other than PK-C activation. DA-1 PK-P thus exhibits a complex pattern of modulation by IL-3 and PMA, and may therefore constitute a new component of the cellular signal transduction cascade.
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PMID:Purification and assay of a phosphatidylglycerol-stimulated protein kinase from murine leukemic cells and its perturbation in response to IL-3 and PMA treatment. 326 27


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