Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In human erythrocytes Ser/Thr- and Tyr-phosphorylations of cytoplasmic domain of band 3 are catalyzed by casein kinase I and Tyr-protein kinase respectively, both distributed between cytosol and membrane structures. The results reported here show that purified cytosolic Tyr-protein kinase activity, assayed on added substrates such as poly(Glu,Tyr)4:1 and isolated chymotryptic fragments of band 3 cytoplasmic domain (cdb3), is potently inhibited by PIP and even more by PIP2. Similar inhibitory effects are displayed by these polyphosphoinositides also on the endogenous Tyr-phosphorylation of band 3, when they are added to the isolated native membranes, thus suggesting their involvement in regulating in-vivo Tyr-phosphorylation of membrane proteins.
 ...
PMID:Tyrosine-protein kinase inhibition in human erythrocytes by polyphosphoinositides (PIP and PIP2). 138 23

Two forms (I and II) of phosphoinositide-specific phospholipase C (PLC) were purified from the cytosol of bovine iris sphincter by sequential chromatography on DEAE-Sepharose, EAH-Sepharose, heparin-Sepharose, Sephacryl S-200 gel filtration and Mono Q HR columns. The final step resulted in specific activities of PLC-I and PLC-II of 4.3 and 5.9 mumol of phosphatidylinositol (PI) cleaved/min per mg of protein, which represented up to 295-fold purification compared with that of the starting supernatant. The purified enzymes were further investigated for the presence of isoenzymes and characterized for molecular mass, substrate specificity, pH, Ca2+ requirements and kinetic parameters. Using monoclonal antibodies, PLC-I was identified as PLC-delta 1. The apparent molecular mass of PLC-I as determined by SDS/PAGE and gel filtration was 85 kDa. PLC-II contained an apparently invisible protein band that reacted with the antibody against PLC-gamma 1, and a major 109 kDa protein band that was not recognized by any of the PLC monoclonal antibodies. Further purification of PLC-II by size-exclusion h.p.l.c. resulted in elution of the enzyme activity as a single peak which corresponded to 109 kDa position. Again, this PLC activity was not recognized by any of the PLC monoclonal antibodies. However, the 109 kDa protein activity was recognized by a polyclonal antibody raised against a rat PLC-gamma 1 fragment (amino acids 1272-1287), thus suggesting that this protein is a proteolytic product of PLC-gamma 1. PLC-delta 1 and PLC-gamma 1 were identified in the supernatant fraction and PLC-beta 1 in the membrane fraction of the iris sphincter. Although immunologically different, the catalytic properties of PLC-I and PLC-II were quite similar. The Vmax and Km values for phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis were three to five times greater than those for PI hydrolysis. Both forms preferred PIP and PIP2 over PI and both were inactive against phosphatidylcholine. With PIP2 as substrate, the optimal pH values for PLC-I and PLC-II were 6.5 and 7.5 respectively. Unlike PIP2, PI hydrolysis by both forms was dependent on the presence of free Ca2+. The maximal hydrolysis of PI and PIP2 by both forms occurred at 200 and 5 microM Ca2+ respectively. Incubation of the purified enzymes with the catalytic subunit of protein kinase A (PKA) and [gamma-32P]ATP resulted in increased phosphorylation of PLC-I and PLC-II, but it had no inhibitory effect on their enzyme activities.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Purification and characterization of phosphoinositide-specific phospholipase C from bovine iris sphincter smooth muscle. 838 Sep 92

The endogenous cyclic adenosine monophosphate (AMP) antagonist, cyclic PIP, has been identified as a prostaglandylinositol cyclic phosphate. It inhibits protein kinase A 100% and activates protein serine phosphatase about sevenfold. It is biosynthesized by an enzyme of the plasma membrane when the assay mixture contains adenosine triphosphate (ATP), Mg2+, prostaglandin E and a novel inositol polyphosphate, which cannot be substituted by commercially available inositol phosphates. This novel inositol polyphosphate is a very labile compound. On anion exchange chromatography it elutes in the range of ATP, which may indicate the presence of three phosphate groups. It adsorbs on charcoal, which suggests the presence of a hydrophobic component, possibly a guanosine. Pyrophosphates obtained from inositol 1,4- and inositol 2,4-bisphosphate are accepted by cyclic PIP synthetase for the synthesis of cyclic PIP. The biosynthesis is characterized by enzyme kinetic parameters like dependence on time, enzyme and substrate concentration. The pH optimum of the enzyme is in the range 7.5-8. The enzyme functions optimally with prostaglandin E and poorly with prostaglandin A as the substrate. The presence of fluoride in the assay causes a three- to fourfold increase in cyclic PIP synthesis, which may be correlated with activation via G proteins. These data support previous reports on the chemical structure and action of cyclic PIP. With respect to the possible isomers of cyclic PIP, these indicate that it is most likely the C4-hydroxyl group of the inositol which binds the C15-hydroxyl group of prostaglandin E. A model of hormone-stimulated synthesis of cyclic PIP is proposed: phospholipase A2 and phospholipase C, activated by G proteins upon alpha-adrenergic stimulation, liberate either unsaturated fatty acids or inositol phosphates, which are transformed to prostaglandins and to novel inositol polyphosphate with an energy-rich bond. The cyclic PIP synthetase combines these two substrates to cyclic PIP.
 ...
PMID:Biosynthesis of the endogenous cyclic adenosine monophosphate (AMP) antagonist, prostaglandylinositol cyclic phosphate (cyclic PIP), from prostaglandin E and activated inositol polyphosphate in rat liver plasma membranes. 887 Aug 15

Reduced ability or failure to stimulate cyclic adenosinemonophosphate (AMP) synthesis on a second addition of hormone 30 min after a first stimulation was taken as an indirect indication of the synthesis of the cyclic AMP antagonist prostaglandylinositol cyclic phosphate (cyclic PIP). In diabetic rats, because of an increased possibility of restimulating cyclic AMP synthesis, the formation of cyclic PIP should be reduced. Additionally, severalfold increased basal cyclic AMP synthesis can be observed in diabetic hepatocytes in comparison with controls. Upon measuring cyclic PIP levels after hormonal stimulation in all organs of diabetic rats, it was found that stimulation of cyclic PIP synthesis by insulin decreased gradually in a time-dependent manner. Plasma membranes were prepared from diabetic Ksj db/db mice and from spontaneously hypertensive rats (SHR), and in a subsequent assay for cyclic PIP synthetase, an up to 60% decrease of enzyme activity was found. Cyclic PIP synthetase can be completely inhibited by preincubation with protein kinase A. It is most likely that this serine phosphorylation reaction by which the enzyme is inhibited also in vivo is a result of increased cyclic AMP levels. The addition of 10(-5)-10(-4) M sulfonylureas to the enzyme assay of liver plasma membrane causes full inhibition, and the addition of 10(-5)-10(-4) M biguanides, a two- to fourfold activation of the enzyme. Activation of cyclic PIP synthetase by biguanides can also be demonstrated in intact cells. It is a fast reaction and additive with respect to the activation by fluoride or guanylyl-imidodiphosphate (GMP-PNP), and it is most likely the effect with which the biguanides produce the correcting changes in metabolism. Furthermore, antihypertensive drugs like captopril, guanethidine, and dihydralazine also activate cyclic PIP synthetase. In contrast to the activation by the biguanides, this effect is not additive to the activation by fluoride. It appears that essential hypertension and type 2 diabetes are connected with or may be the result of a reduction in synthesis of the intracellular messenger cyclic PIP, whose synthesis is stimulated by hormones like insulin and noradrenaline (alpha-adrenergic action).
 ...
PMID:Insulin resistance, a result of reduced synthesis of prostaglandylinositol cyclic phosphate, a mediator of insulin action? Regulation of cyclic PIP synthetase activity by oral antidiabetic and antihypertensive drugs. 945 69

While a differential sensitivity to cyclic AMP (cAMP)-mediated signaling between Th1 and Th2 cells has been hypothesized, differential activity of downstream signaling through cAMP-dependent protein kinase (cAK) isoforms remains unexplored. We herein report the effects of type 1- and type 2-specific cAK agonists and antagonists on proliferative responses and cytokine generation from ragweed-driven peripheral blood mononuclear cells (PBMCs) and Amb a 1-specific Th1 and Th2 clones. Rp-8-Cl- and Rp-8-CPT-cAMP were utilized as single agent antagonists of cAKI and cAKII, respectively; 8-AHA-cAMP, with and without 8-PIP-cAMP, and 8-CPT-cAMP, with and without 6-Bnz-cAMP, were used as synergistic agonist pairs specific for the cAKI and cAKII, respectively. Activation of either cAKI or cAKII individually was ineffective in down-regulating proliferative responses of PBMCs or T cell clones; concentration-response curves for the Th1 and Th2 clones were identical. Moreover, inhibition of either cAKI or cAKII individually was ineffective in overcoming the down-regulatory effects of phosphodiesterase inhibition. Activation of either cAKI or cAKII individually was ineffective in down-regulating proinflammatory cytokine generation from T cell clones (interleukin-4 from Th2; interferon-gamma from Th1). However, concurrent activation of both cAKI and cAKII produced down-regulatory effects equivalent to those of the phosphodiesterase inhibitor on both proliferation and cytokine generation. These data suggest a critical role for concurrent activation of cAKI and cAKII in the functional efficacy of antigen-driven downstream signaling due to elevations of intracellular cAMP and argue against differential regulation of Th1 and Th2 responses by cAK subtypes.
 ...
PMID:Co-regulation of antigen-specific T lymphocyte responses by type I and type II cyclic AMP-dependent protein kinases (cAK). 977 49

Elevation of cyclic AMP (cAMP) in platelets inhibits agonist-induced, G protein-mediated responses and activation of polyphosphoinositide-specific phospholipase C (PLC) by ill-defined mechanism(s). Signal transduction steps downstream of PLC are inhibited by elevated cAMP, suggesting an inhibitory effect of cAMP, via protein kinase A, on PLC. In [32P]i-prelabeled platelets, forskolin increased intracellular cAMP (104 nmol/1011 cells at 10-5 M forskolin) and [32P]phosphatidylinositol 4-phosphate (Delta[32P]PIP) (30% at 10-7-10-6 M forskolin). The thrombin-induced (0.1 U/ml) increase in production of [32P]PA, 'overshoots' in [32P]PIP and [32P]PIP2 ([32P]phosphatidylinositol 4,5-bisphosphate), and the increase in [32P]PI and secretion of ADP+ATP were abolished by forskolin (10-7 M). Forskolin stimulated total [32P]Pi uptake in resting platelets (48%), increased 32P incorporation into PIP (110%), and inhibited 32P incorporation into PI (50%). The latter inhibition was most likely considerably greater due to the forskolin-induced stimulation of [32P]Pi uptake. The changes in radioactive PA, PIP and PIP2 are regarded as being proportional with their masses in the prelabeled platelets, while the increase in PI (phosphatidylinositol) is regarded as a change in specific radioactivity, and hence in its synthesis. The results suggest that cAMP elevation inhibits the flux in the polyphosphoinositide cycle through both inhibition of PIP 5-kinase and PI synthesis. The inverse relation between forskolin-produced DeltaPIP and [32P]PA production suggests that the PLC reaction is inhibited by elevated cAMP through reduction of substrate (PIP2) resynthesis, and not by inhibition of the PLC enzyme.
 ...
PMID:Elevation of cyclic AMP decreases phosphoinositide turnover and inhibits thrombin-induced secretion in human platelets. 979 33

Inositol lipid synthesis is regulated by several distinct families of enzymes [1]. Members of one of these families, the type II phosphatidylinositol phosphate kinases (PIP kinases), are 4-kinases and are thought to catalyse a minor route of synthesis of the multifunctional phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) from the inositide PI(5)P [2]. Here, we demonstrate the partial purification of a protein kinase that phosphorylates the type IIalpha PIP kinase at a single site unique to that isoform - Ser304. This kinase was identified as protein kinase CK2 (formerly casein kinase 2). Mutation of Ser304 to aspartate to mimic its phosphorylation had no effect on PIP kinase activity, but promoted both redistribution of the green fluorescent protein (GFP)-tagged enzyme in HeLa cells from the cytosol to the plasma membrane, and membrane ruffling. This effect was mimicked by mutation of Ser304 to alanine, although not to threonine, suggesting a mechanism involving the unmasking of a latent membrane localisation sequence in response to phosphorylation.
 ...
PMID:Regulation of type IIalpha phosphatidylinositol phosphate kinase localisation by the protein kinase CK2. 1050 90

Phosphatidylinositol 4-phosphate 5-kinase (PIPK) catalyzes a final step in the synthesis of phosphatidylinositol 4,5-bisphosphate (PIP(2)), a lipid signaling molecule. Strict regulation of PIPK activity is thought to be essential in intact cells. Here we show that type I enzymes of PIPK (PIPKI) are phosphorylated by cyclic AMP-dependent protein kinase (PKA), and phosphorylation of PIPKI suppresses its activity. Serine 214 was found to be a major phosphorylation site of PIPK type Ialpha (PIPKIalpha) that is catalyzed by PKA. In contrast, lysophosphatidic acid-induced protein kinase C activation increased PIPKIalpha activity. Activation of PIPKIalpha was induced by dephosphorylation, which was catalyzed by an okadaic acid-sensitive phosphatase, protein phosphatase 1 (PP1). In vitro dephosphorylation of PIPKIalpha with PP1 increased PIPK activity, indicating that PP1 plays a role in lysophosphatidic acid-induced dephosphorylation of PIPKIalpha. These results strongly suggest that activity of PIPKIalpha in NIH 3T3 cells is regulated by the reversible balance between PKA-dependent phosphorylation and PP1-dependent dephosphorylation.
 ...
PMID:Phosphatidylinositol 4-phosphate 5-kinase type I is regulated through phosphorylation response by extracellular stimuli. 1108 61

Activation of protein kinase C-zeta (PKC-zeta) by insulin requires phosphatidylinositol (PI) 3-kinase-dependent increases in phosphatidylinositol-3,4,5-(PO(4))(3) (PIP(3)) and phosphorylation of activation loop and autophosphorylation sites, but actual mechanisms are uncertain. Presently, we examined: (a) acute effects of insulin on threonine (T)-410 loop phosphorylation and (b) effects of (i) alanine (A) and glutamate (E) mutations at T410 loop and T560 autophosphorylation sites and (ii) N-terminal truncation on insulin-induced activation of PKC-zeta. Insulin acutely increased T410 loop phosphorylation, suggesting enhanced action of 3-phosphoinositide-dependent protein kinase-1 (PDK-1). Despite increasing in vitro autophosphorylation of wild-type PKC-zeta and T410E-PKC-zeta, insulin and PIP(3) did not stimulate autophosphorylation of T560A, T560E, T410A/T560E, T410E/T560A, or T410E/T560E mutant forms of PKC-zeta; thus, T560 appeared to be the sole autophosphorylation site. Activating effects of insulin and/or PIP(3) on enzyme activity were completely abolished in T410A-PKC-zeta, partially compromised in T560A-PKC-zeta, T410E/T560A-PKC-zeta, and T410A/T560E-PKC-zeta, and largely intact in T410E-PKC-zeta, T560E-PKC-zeta, and T410E/T560E-PKC-zeta. Activation of the T410E/T560E mutant suggested a phosphorylation-independent mechanism. As functional correlates, insulin effects on epitope-tagged GLUT4 translocation were compromised by expression of T410A-PKC-zeta, T560A-PKC-zeta, T410E/T560A, and T410A/T560E-PKC-zeta but not T410E-PKC-zeta, T560E-PKC-zeta, or T410E/T560E-PKC-zeta. Insulin, but not PIP(3), activated truncated, pseudosubstrate-lacking forms of PKC-zeta and PKC-lambda by a wortmannin-sensitive mechanism, apparently involving PI 3-kinase/PDK-1-dependent phosphorylations but independent of PIP(3)-dependent conformational activation. Our findings suggest that insulin, via PIP(3), provokes increases in PKC-zeta enzyme activity through (a) PDK-1-dependent T410 loop phosphorylation, (b) T560 autophosphorylation, and (c) phosphorylation-independent/conformational-dependent relief of pseudosubstrate autoinhibition.
 ...
PMID:Insulin and PIP3 activate PKC-zeta by mechanisms that are both dependent and independent of phosphorylation of activation loop (T410) and autophosphorylation (T560) sites. 1114 Oct 77

Phosphatidylinositol 4,5 bisphosphate (PIP(2)) is widely implicated in cytoskeleton regulation, but the mechanisms by which PIP(2) effect cytoskeletal changes are not defined. We used recombinant adenovirus to infect CV1 cells with the mouse type I phosphatidylinositol phosphate 5-kinase alpha (PIP5KI), and identified the players that modulate the cytoskeleton in response to PIP(2) signaling. PIP5KI overexpression increased PIP(2) and reduced phosphatidylinositol 4 phosphate (PI4P) levels. It promoted robust stress-fiber formation in CV1 cells and blocked PDGF-induced membrane ruffling and nucleated actin assembly. Y-27632, a Rho-dependent serine/threonine protein kinase (ROCK) inhibitor, blocked stress-fiber formation and inhibited PIP(2) and PI4P synthesis in cells. However, Y-27632 had no effect on PIP(2) synthesis in lysates, although it inhibited PI4P synthesis. Thus, ROCK may regulate PIP(2) synthesis by controlling PI4P availability. PIP5KI overexpression decreased gelsolin, profilin, and capping protein binding to actin and increased that of ezrin. These changes can potentially account for the increased stress fiber and nonruffling phenotype. Our results establish the physiological role of PIP(2) in cytoskeletal regulation, clarify the relation between Rho, ROCK, and PIP(2) in the activation of stress-fiber formation, and identify the key players that modulate the actin cytoskeleton in response to PIP(2).
 ...
PMID:Phosphatidylinositol 4,5-bisphosphate induces actin stress-fiber formation and inhibits membrane ruffling in CV1 cells. 1123 45


1 2 3 4 5 6 7 8 9 Next >>