Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.11.1 (protein kinase)
81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have previously shown that a 222-kDa polypeptide co-immunoprecipitates together with the type-I myoinositol 1,4,5-trisphosphate receptor (IP3R) in WB rat liver epithelial cell extracts, when the immunoprecipitation is carried out with a type-I isoform specific antibody (Joseph, S. K. (1994) J. Biol. Chem. 269, 5673-5679). Utilizing isoform-specific antibodies raised to unique sequences within the COOH-terminal region of IP3 receptors, we now report that the co-immunoprecipitating 222-kDa polypeptide is the type-III IP3R isoform and that type-III IP3R antibodies (Abs) can co-immunoprecipitate the type-I IP3R isoform. Co-immunoprecipitation of IP3R isoforms was not due to cross-reactivity of the antibodies for the following reasons: (a) on immunoblots the type-III antibodies did not cross-react with type-I IP3R and vice versa; (b) inclusion of the COOH-terminal type-III peptide had no effect on the ability of type-I IP3R Ab to co-immunoprecipitate the type-III IP3R but blocked the ability of type-III IP3R Ab to coimmunoprecipitate the type-I isoform; and (c) crude hepatocyte lysates contain undetectable amounts of type-III IP3R, and immunoprecipitation with type-III IP3R Ab does not co-immunoprecipitate any other isoforms. However, type-I and type-II IP3R isoforms were co-immunoprecipitated by their respective antibodies in hepatocyte lysates. Sucrose density gradient analysis of WB cell lysates indicated that the co-immunoprecipitating fraction is exclusively located at the density expected for tetrameric receptors, suggesting that co-immunoprecipitation was not a reflection of the nonspecific aggregation of IP3R isoforms. Phosphorylation of either type-I or type-III immunoprecipitates by protein kinase A indicated that only the type-I IP3R could be phosphorylated in vitro. Fractionation of WB cell membranes and immunofluorescence studies showed that the type-I and type-III isoforms have very similar sub-cellular localizations. We conclude that the WB cell contains both type-I and type-III IP3R isoforms and that a proportion of these receptors exist as heterotetramers.
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PMID:Heteroligomers of type-I and type-III inositol trisphosphate receptors in WB rat liver epithelial cells. 755 86

Limited digestion of rat cerebellum microsomal vesicles with trypsin resulted in the proteolysis of the 240 kDa inositol 1,4,5-trisphosphate receptor (IP3R) and the formation of a 94 kDa species that remained membrane-bound and retained immunoreactivity to an antibody raised against the C-terminal sequence of this protein. The appearance of the 94 kDa species was associated with a loss of [3H]IP3 binding sites in the membrane and the appearance of [3H]IP3 binding sites in the soluble fraction. The 94 kDa fragment retained reactivity to biotinylated concanavalin A. In vitro phosphorylation of the IP3R in membranes with cyclic AMP-dependent protein kinase and [gamma-32P]ATP produced an unlabelled 94 kDa fragment after tryptic digestion. According to current models of the cerebellar IP3R this would place the proteolytic site between the phosphorylation site at serine-1755 and the first transmembrane segment of the IP3R. A second antibody raised to amino acids 401-414 in the N-terminal region of the receptor recognizes a 68 kDa fragment released into the soluble fraction after trypsin treatment. The time course of release of the 68 kDa fragment was correlated with the appearance of soluble binding sites, and the fragment was bound by IP3-Affigel resin. A large proportion of the 68 kDa fragment remained associated with the membrane fraction and could be specifically immunoprecipitated from detergent extracts of digested membranes by anti-C-terminus antibody. Our results provide experimental evidence to further localize the ligand binding domain and suggest that regions of the N-terminus and C-terminus may be non-covalently associated.
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PMID:Trypsin digestion of the inositol trisphosphate receptor: implications for the conformation and domain organization of the protein. 774 18

We have studied the biosynthesis and turnover of the inositol 1,4,5-trisphosphate receptor (IP3R) in WB cells, a rat liver epithelial cell line. In detergent extracts of 35S-labeled WB cells, an affinity-purified antibody directed at the C terminus of the IP3R immunoprecipitated two labeled polypeptides, a major band at 233 kDa and a minor band at 222 kDa. The major band was shown to correspond to the IP3R by immunoblotting. The minor band was not a proteolytic clip of the IP3R because, unlike the IP3R, the 222-kDa band was not a glycoprotein or a substrate for protein kinase A and was not recognized by three different IP3R antibodies on immunoblots. The identity and function of this co-immunoprecipitating protein is unknown. The IP3R in WB cells was 5 kDa smaller than the rat cerebellar IP3R. Significant changes in the molecular weight of the IP3R were not observed in pulse-chase experiments, indicating that extensive proteolytic or carbohydrate processing events do not occur during biosynthesis of the receptor. From the analysis of such experiments in confluent WB cells, it was determined that the half-life of the IP3R protein was 11 h. Chromatography of the 35S-labeled extracts on Sephacryl S-400 columns revealed rapid oligomerization of newly synthesized protein with > 95% of newly synthesized protein forming tetramers during a short (10 min) pulse labeling period. However, significant amounts of mature IP3R were found as incompletely oligomerized forms. Mature IP3R was bound by concanavalin A-Sepharose beads, and binding was greatly reduced by endoglycosidase H treatment of the receptor. Endoglycosidase H sensitivity, absence of binding to wheat germ agglutinin-Sepharose, and insensitivity of biosynthesis or oligomerization to brefeldin A suggest that processing of the WB IP3R does not involve transit through the Golgi apparatus.
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PMID:Biosynthesis of the inositol trisphosphate receptor in WB rat liver epithelial cells. 811 4

We established a novel method to isolate a single type of inositol 1,4,5-trisphosphate receptor (IP3R) among the heterogeneous population of receptors to study the regulatory mechanism of Ca2+ release. We raised in the rabbit a polyclonal antibody against synthetic peptide corresponding to amino acids 2736-2747 (pep 6) of type I IP3R (IP3-R-I) that is most abundant in cerebellum. We purified IP3R-I from a 1% 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid solubilized mouse cerebellar microsomal fraction by immunoaffinity chromatography on an anti-pep 6 antibody-Sepharose 4B column with specific elution by the pep 6 peptide (GHPPHMNVNPQQ) of the IP3R-I C terminus. Immunoaffinity-purified IP3R reconstituted into lipid vesicles formed a homotetramer structure. Monoclonal antibody 18A10, which partially blocks the Ca2+ release from cerebellar microsome, almost completely inhibited IP3-induced 45Ca2+ influx into proteoliposomes, whereas monoclonal antibody that recognizes other regions did not inhibit Ca2+ influx. Both the rate and extent of 45Ca2+ influx into proteoliposomes increased 20% after incubation with the catalytic subunit of cyclic AMP-dependent protein kinase, accompanied by stoichiometric phosphorylation of IP3R protein.
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PMID:Cyclic AMP-dependent phosphorylation of an immunoaffinity-purified homotetrameric inositol 1,4,5-trisphosphate receptor (type I) increases Ca2+ flux in reconstituted lipid vesicles. 812 33

The inositol trisphosphate receptor (IP3R) in brain has been shown to be a substrate for several different protein kinases in vitro. We have studied the phosphorylation of the IP3R in intact cells by using isolated hepatocytes and an antibody to immunoprecipitate the receptor protein from detergent extracts. Stimulation of 32P-labeled hepatocytes with glucagon or N6,2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (db-cAMP) markedly increased phosphorylation of the IP3R. However, no increase was observed in response to angiotensin II, vasopressin, 12-O-tetradecanoyl-phorbol-13-acetate, or epidermal growth factor. The kinetics of phosphorylation in response to glucagon was both rapid and transient. In agreement with previous studies, physiological concentrations of Ca2+ stimulated D-myo-inositol 1,4,5-trisphosphate (IP3) binding to permeabilized hepatocytes (Pietri, F., Hilly, M., and Mauger, J.-P. (1990) J. Biol. Chem. 265, 17478-17485). Pretreatment of cells with db-cAMP had no effect on binding in the absence of added Ca2+ but enhanced binding measured in the presence of basal low concentrations (0.16-0.25 microM) of Ca2+ and decreased the concentration of Ca2+ required for half-maximal stimulation. The effect of db-cAMP was associated with an increase in affinity of the IP3 binding site without a change in maximum number of binding sites. Preincubation of intact hepatocytes with okadaic acid alone produced an increase in basal phosphorylation of the IP3R, and maximal phosphorylation of the receptor was observed in the presence of both okadaic acid and db-cAMP. However, okadaic acid blocked the effect of db-cAMP and inhibited the effect of Ca2+ on IP3 binding. Detergent-solubilized binding sites were already fully activated and insensitive to modulation by Ca2+ or cAMP-dependent protein kinase. It is proposed that the receptor in native membranes is inhibited and that Ca2+ and cAMP-dependent protein kinase may act to relieve this inhibition.
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PMID:Phosphorylation of the inositol trisphosphate receptor in isolated rat hepatocytes. 822 22

A potentially important cross-talk characteristic of transforming growth factor-beta (TGF-beta) is to inhibit platelet-derived growth factor-induced intracellular calcium rise (Baffy, G., Sharma, K., Shi, W., Ziyadeh, F. N., and Williamson, J. R. (1995) Biochem. Biophys. Res. Commun. 210, 378-383) in murine mesangial cells. The present study examined the possible basis for this effect by evaluating the regulation of the type I inositol 1,4,5-trisphosphate receptor (IP3R) by TGF-beta. TGF-beta1 down-regulates IP3R protein expression by >90% with maximal and half-maximal effects after 8 and 2 h, respectively. TGF-beta1 also decreased IP3R mRNA expression by 59% after 1 h. Phosphorylation of the IP3R was also demonstrated as early as 15 min after TGF-beta1 exposure. Back phosphorylation assays of IP3R from TGF-beta1-treated mesangial cells with protein kinase A (PKA), indicated that TGF-beta1-induced phosphorylation of the IP3R occurs at similar sites as for PKA. In vitro kinase assays using the known IP3R peptide substrates for PKA, RPSGRRESLTSFGNP and ARRDSVLAAS, demonstrated that TGF-beta1 induces phosphorylation of both peptides (158 and 123% of control values, respectively). TGF-beta1-induced phosphorylation was prevented by the addition of the PKA inhibitor peptide in the in vitro kinase assay. It is proposed that TGF-beta-mediated effects on the IP3R may be an important characteristic of its ability to modulate the response of cells to factors that employ IP3R-mediated calcium release.
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PMID:Transforming growth factor-beta1 inhibits type I inositol 1,4,5-trisphosphate receptor expression and enhances its phosphorylation in mesangial cells. 916 22

A single gene appears to code for the inositol 1,4,5-trisphosphate receptor (itpr) in Drosophila melanogaster, as compared to three known genes in mammals. Expression of the itpr gene in Drosophila occurs in a wide range of tissues and developmental stages, suggesting its requirement during diverse cellular and physiological processes. A head cDNA for the Drosophila IP3R has previously been cloned and sequenced. Here we present and analyse the sequence of cDNAs encoding the complete IP3R, obtained from embryonic stages. The embryonic cDNA is 10525bp long and is a splice variant of the head cDNA. It differs from the latter in three main respects. It has longer 5' and 3' untranslated regions, two potential casein kinase II sites are missing in the embryo form and it contains an alternate exon which results in the replacement of three residues (VHF) in the head form by five residues (GVGHSV) in the embryo form. The significance of these changes is discussed. An exon-intron map of the gene derived from sequencing of intron-containing genomic fragments is also presented. The gene has a total of 11 introns, of which more than half are clustered in a region of the modulatory domain of the IP3R.
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PMID:Sequencing and exon mapping of the inositol 1,4,5-trisphosphate receptor cDNA from Drosophila embryos suggests the presence of differentially regulated forms of RNA and protein. 1037 44

The regulation of inositol 1,4,5-trisphosphate receptor (IP3R) messenger RNA (mRNA) and protein expression was investigated in glucose-desensitized rat isolated pancreatic islets. Islets were cultured for 4 days with glucose (11 mM; G-treated) to induce desensitization; IP3R-I mRNA levels were similar to basal (5.5 mM glucose) values, whereas IP3R-II mRNA levels were increased and IP3R-III levels were reduced compared with basal levels. Somatostatin increased the expression of IP3R-II mRNA and reduced the expression of IP3R-III mRNA compared with basal values, but did not significantly affect G-treated islet IP3R expression. When forskolin (FSK), 8-bromo-cAMP, and glucagon-like peptide 1-(7-36) amide were added to G-treated islets after 4 days of culture, IP3R-II mRNA levels were reduced, whereas IP3R-III mRNA levels increased, to levels observed in control islets, within 3 h. The levels of IP3R-I mRNA were unaffected by either somatostatin or FSK. The protein kinase A inhibitor. H-89, and actinomycin D prevented the effects of FSK. A Ca2+ ionophore mimicked the effects of FSK on IP3R mRNA expression, whereas blockade of voltage-dependent Ca2+ channels or chelation of intracellular Ca2+ inhibited the actions of FSK. cAMP also increased IP3R-III mRNA in insulinoma cells. In G-treated islets, FSK slowed IP3R-III mRNA degradation. FSK, but not glucose, stimulated protein kinase A activation in G-treated islets. Thus, cAMP mediates changes in IP3R-II and -III mRNA transcription and stability in glucose-desensitized islets. The regulated expression of IP3R-II and -III mRNA is mediated in part by intracellular Ca2+ availability.
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PMID:Regulation of inositol trisphosphate receptor isoform expression in glucose-desensitized rat pancreatic islets: role of cyclic adenosine 3',5'-monophosphate and calcium. 1074 43

Calcium (Ca2+) ions are second messengers in signaling pathways in all types of cells. They regulate muscle contraction, electrical signals which determine the cardiac rhythm and cell growth pathways in the heart. In the past decade cDNA cloning has provided clues as to the molecular structure of the intracellular Ca2+ release channels (ryanodine receptors, RyR, and inositol 1,4,5-trisphosphate receptors, IP3R) on the sarcoplasmic and endoplasmic reticulum (SR/ER) and an understanding of how these molecules regulate Ca2+ homeostasis in the heart is beginning to emerge. The intracellular Ca2+ release channels form a distinct class of ion channels distinguished by their structure, size, and function. Both RyRs and IP3Rs have gigantic cytoplasmic domains that serve as scaffolds for modulatory proteins that regulate the channel pore located in the carboxy terminal 10% of the channel sequence. The channels are tetramers comprised of four RyR or IP3R subunits. RyR2 is required for excitation-contraction (EC) coupling in the heart. Using co-sedimentation and co-immunoprecipitation we have defined a macromolecular complex comprised of RyR2, FKBP12.6, PKA, the protein phosphatases PP1 and PP2A, and an anchoring protein mAKAP. We have shown that protein kinase A (PKA) phosphorylation of RyR2 dissociates FKBP12.6 and regulates the channel open probability (P(o)). In failing human hearts RyR2 is PKA hyperphosphorylated resulting in defective channel function due to increased sensitivity to Ca2+-induced activation.
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PMID:Ryanodine receptors/calcium release channels in heart failure and sudden cardiac death. 1127 16

The inositol 1,4,5-trisphosphate receptor (IP3R) is a ubiquitously expressed intracellular calcium (Ca(2+)) release channel on the endoplasmic reticulum. IP3Rs play key roles in controlling Ca(2+) signals that activate numerous cellular functions including T cell activation, neurotransmitter release, oocyte fertilization and apoptosis. There are three forms of IP3R, all of which are ligand-gated channels activated by the second messenger inositol 1,4,5-trisphosphate. Channel function is modulated via cross-talk with other signaling pathways including those mediated by kinases and phosphatases. In particular IP3Rs are known to be regulated by cAMP-dependent protein kinase (PKA) phosphorylation. In the present study we show that PKA and the protein phosphatases PP1 and PP2A are components of the IP3R1 macromolecular signaling complex. PKA phosphorylation of IP3R1 increases channel activity in planar lipid bilayers. These studies indicate that regulation of IP3R1 function via PKA phosphorylation involves components of a macromolecular signaling complex.
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PMID:Protein kinase A and two phosphatases are components of the inositol 1,4,5-trisphosphate receptor macromolecular signaling complex. 1216 31


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