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:3.1.4.3 (phospholipase C)
18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In a previous report we demonstrated the presence of a vasotocin (AVT)-like peptide in chromaffin cells of the amphibian adrenal gland and showed that synthetic AVT is a potent stimulator of corticosterone and aldosterone secretion by frog adrenocortical cells. In the present study we evaluated the relative potency of various AVT analogs and investigated the mechanism of action of AVT on frog interrenal (adrenal) tissue. Several AVT agonists, including hydrin 2, oxytocin (OXT), arginine vasopressin (AVP), Lys-conopressin G, and mesotocin (MT), were able to mimic the stimulatory effect of AVT on steroid secretion, but AVT was by far the most potent stimulator of steroidogenesis. In the series of analogs studied, the order of potency was: AVT greater than hydrin 2 greater than OXT greater than AVP greater than Lys-conopressin G greater than MT greater than [deamino-Cys1,D-Arg8]AVP greater than [d(CH2)5,Tyr(OMe)2] AVP. The effect of AVT (5 x 10(-10) M) was totally blocked by both the antidiuretic V2 antagonist [d(CH2)5,D-Phe2,Ile4,Ala9-NH2]AVP (10(-6) M) and the oxytocinergic antagonist [d(CH2)5,Tyr(OMe)2,Orn8]AVT (10(-6) M); the V2 antagonist was approximately twice as potent as the OXT antagonist. In contrast, the V1 antagonist 1-(1-mercapto-4-phenylcyclohexaneacetic acid)-AVP (10(-6) M) did not affect the response of the interrenal tissue to AVT. Indomethacin (5 microM), a cyclooxygenase inhibitor, induced a dramatic decrease in the spontaneous secretion of corticosteroids, but did not impair the stimulatory effect of AVT (5 x 10(-9) M) on corticosterone and aldosterone secretion. In addition, AVT did not stimulate the production of prostaglandin E2, suggesting that prostaglandins are not involved in the mechanism of action of AVT. Concurrently, AVT did not modify cAMP production by frog adrenal slices. In contrast, AVT induced both an increase in inositolphosphate production and a reduction of membrane phospholipid content. We conclude that in the frog adrenal gland, the stimulatory effect of AVT on steroid secretion is mediated through activation of receptors related to the mammalian V2 and/or OXT receptors, which are positively coupled to phosphoinositide-specific phospholipase C.
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PMID:Pharmacological characterization of vasotocin stimulation of phosphoinositide turnover in frog adrenal gland. 130 45

The effect of quisqualate, an excitatory amino acid agonist, on the breakdown of exogenously added phosphatidylinositol was investigated in a membrane preparation from the cerebellum of young rats. Quisqualate stimulated phospholipase C activity in a dose-dependent manner in the presence of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S). Half-maximal activation of the quisqualate response required 0.15 microM GTP gamma S and was optimal at a free Ca2+ concentration of 300 nM. Phosphoinositide breakdown was also stimulated by quisqualate using either exogenous phosphatidylinositides 4,5-bisphosphate or endogenous labeled phosphoinositides as the substrate for phospholipase C in cerebellar membranes. In the presence of guanine nucleotides, other excitatory amino acid agonists, such as L-glutamate, trans-D,L-1-aminocyclopentyl-1,3-dicarboxylic acid, and ibotenate, but not N-methyl-D-aspartate, stimulated phosphatidylinositol breakdown. However, quisqualate displayed the highest response among these excitatory amino acid agonists. These data indicate that there is a direct activation of phosphoinositide-specific phospholipase C by excitatory amino acids through a process dependent on the presence of guanine nucleotides.
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PMID:Quisqualate-stimulated phosphatidylinositol breakdown in rat cerebellar membranes. 130 70

Gq mediates hormonal stimulation of phosphoinositide-specific phospholipase C (PI-PLC). We mutated the alpha subunit of Gq (alpha q) to replace arginine 183 with cysteine. Mutations that substitute cysteine for the corresponding arginine residues of alpha s and alpha i2 constitutively activate their respective effector pathways, creating the gsp and gip2 oncogenes. Transient expression of alpha q-R183C in COS-7 and HEK-293 cells constitutively activates PI-PLC, but wild type (WT) alpha q does not. This suggests that the mutated arginines in alpha s, alpha i2, and alpha q share a common function in regulating the active state of these proteins and that the alpha q gene may serve as a target for oncogenic mutations in human tumors. In an attempt to develop an assay for receptor stimulation of recombinant alpha q, we co-expressed receptors with alpha q-WT. We found that the alpha 2-adrenoceptor stimulates PI-PLC activation in HEK-293 cells in a fashion that depends completely on co-expression of alpha q-WT. These findings create an experimental model, similar to that provided for alpha s by S49 cyc- cells, that should make it possible to analyze receptor and effector coupling by mutant alpha q against a null background.
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PMID:Recombinant Gq alpha. Mutational activation and coupling to receptors and phospholipase C. 130 40

Cell lines selected in multiple steps for increasing resistance to hydroxyurea have been shown to have corresponding increases in ribonucleotide reductase activity. We have isolated a number of cDNA clones from a cDNA library constructed from a highly hydroxyurea-resistant hamster cell line, 600H, in which the activity of ribonucleotide reductase is elevated more than 80-fold. These clones correspond to genomic DNA sequences amplified in the 600H cell line compared with the V79 parental line. One of these cDNA clones, termed P5, codes for a 50 kDa protein detected by in vitro translation of poly(A)+ RNA isolated by hybridization/selection. The cDNA sequence contains a single open reading frame of 1317 nucleotides which encodes a polypeptide of 439 amino acids. The amino acid sequence deduced from the cDNA insert contains two copies of the 11-amino-acid sequence Val-Glu-Phe-Tyr-Ala-Pro-Trp-Cys-Gly-His-Cys. Duplicate copies of this sequence also occur in the active site of rat and human protein disulphide isomerase (also known as the beta-subunit of human prolyl 4-hydroxylase, tri-iodothyronine-binding protein) and in Form I phosphoinositide-specific phospholipase C, indicating that P5 falls into this newly defined superfamily of proteins. Genomic sequences similar to the cDNA clone are amplified 10-20-fold in hamster cells selected for resistance to increasing concentrations of hydroxyurea, a phenomenon observed earlier with cDNA clones for the M2 subunit of ribonucleotide reductase and ornithine decarboxylase. RNA blots probed with P5 cDNA show two poly(A)+ RNA species which are elevated in hydroxyurea-resistant cells.
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PMID:The gene for a novel protein, a member of the protein disulphide isomerase/form I phosphoinositide-specific phospholipase C family, is amplified in hydroxyurea-resistant cells. 131 Nov 71

These studies sought to test the hypothesis that the expression of myometrial proteins is modulated as the onset of parturition approaches. Myometrial proteins from timed-pregnant rats were analyzed utilizing sodium dodecylsulfate polyacrylamide gel and 2-dimensional electrophoresis, and Western blot techniques. SDS-PAGE gels demonstrated increased expression of at least 10 protein bands from 17 to 200+ KD. 2-dimensional gels confirmed the presence of at least five groups of gestationally modulated proteins. Western blots for phosphoinositide-specific phospholipase C demonstrated significant modulation of the expression of three isozymes. These studies have confirmed differential expression of myometrial proteins near term in the timed-pregnant rat; some of which play an important role in intracellular signal transduction in response to hormones and pharmacologic agents.
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PMID:Gestational modulation of myometrial proteins in the timed-pregnant Sprague-Dawley rat. 131 37

We found phosphoinositide-specific phospholipase C (PtdIns-PLC) activity in nuclei isolated from rat liver. The enzyme hydrolyzed phosphatidylinositol, phosphatidylinositol 4-monophosphate (PIP) and phosphatidylinositol 4,5-bisphosphate in a Ca(2+)-dependent manner, and produced inositol mono-, bis-, and triphosphate, respectively. Neither phosphatidylcholine, phosphatidylethanolamine, nor phosphatidylserine was utilized as a substrate. After partial hepatectomy, the PtdIns-PLC activity in isolated nuclei increased transiently in the S phase (20-22 h post-hepatectomy), to 2.5-fold higher than in the control, when measured with PIP. This result suggests a close relationship between the nuclear PtdIns-PLC, especially its PIP-hydrolyzing activity, and cell proliferation.
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PMID:Existence of phosphoinositide-specific phospholipase C in rat liver nuclei and its change during liver regeneration. 131 90

A possible role for altered signal transduction mechanisms in impaired alpha 1-adrenergic-stimulated secretory function during aging was investigated in parotid cells prepared from adult (6 mo) and old (24 mo) rats. Compared with adults, epinephrine-stimulated 45Ca2+ efflux and inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] production were reduced 31 and 36% in cells of old rats, respectively. There was a highly significant correlation between 45Ca2+ efflux and Ins(1,4,5)P3 production. In saponin-permeabilized cells, no significant differences in Ins(1,4,5)P3-stimulated 45Ca2+ efflux in adult and old preparations were observed. When G proteins were stimulated by guanosine 5'-O-(3-thiotriphosphate) or NaF, no age differences in Ins(1,4,5)P3 production were detected. Stimulation of phosphoinositide-specific phospholipase C (PLC) by CaCl2 in adult and old cells was also comparable. Moreover, no differences in immunolabeled common alpha (GTP binding site), Gi alpha, PLC-gamma, or PLC-delta could be detected in either cytosol or membranes of adult and old preparations. In the absence of 5'-guanylylimidodiphosphate [Gpp(NH)p], no age-related changes in epinephrine competition for [3H]prazosin binding sites were observed. Approximately 30% of the agonist binding sites existed in a high-affinity form at both ages. Gpp(NH)p caused large rightward shifts of epinephrine displacement curves in adult membranes (converting all binding sites to the low-affinity form), but not old. Moreover, epinephrine was much more effective in stimulating G protein low-Km GTPase in parotid membranes from adult than old rats. These data suggest that age-related impairments in alpha 1-adrenergic responsiveness are mediated, at least in part, by the functional alterations in the coupling of G proteins with alpha 1-adrenergic receptors.
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PMID:Altered coupling of alpha 1-adrenergic receptor-G protein in rat parotid during aging. 131 99

A 60-kDa protein homologous to phosphoinositide-specific phospholipase C-alpha was purified to apparent homogeneity on sodium dodecyl sulfate-polyacrylamide gel electrophoresis from the rough endoplasmic reticulum of rat liver through three sequential chromatographies on DEAE Toyopearl 650, AF-heparin Toyopearl 650M, and TSK gel G3000SW. The purified protein was monomeric, with an M(r) of 60,000. Eight types of protein were further separated from the 60-kDa protein and named ER60A-ER60H according to the order of their elution from a TSK gel DEAE-5PW column. They were essentially identical in terms of immunochemical properties and the NH2-terminal amino acid sequence. The partial amino acid sequence of ER60F showed homology to that of phosphoinositide-specific phospholipase C-alpha. ER60A-ER60H showed no phosphoinositide-specific phospholipase C activity. However, ER60A-ER60H catalyzed cleavage of themselves and the endoplasmic reticulum proteins protein disulfide-isomerase and calreticulin. Proteolytic degradation was inhibited by p-chloromercuribenzoate. These results indicate that ER60A-ER60H comprise a group of endoplasmic reticulum resident proteins and show thiol group-related proteolytic activity.
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PMID:Protein degradation by the phosphoinositide-specific phospholipase C-alpha family from rat liver endoplasmic reticulum. 132 29

The addition of ammonium sulfate to starved yeast cells leads to a 3- to 4-fold rapid increase of the second messengers inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG), the products of phosphoinositide-specific phospholipase C (PI-PLC). This response is reduced by dissecting the RAS-activating Cdc25 protein, and is completely abolished by the cdc25-1 mutation even at permissive temperature. Starved cdc25-1 mutant cells have a strongly reduced IP3 content, but an at least 10-fold increased DAG level compared to the isogenic wild-type strain. NH4 does not stimulate cAMP synthesis, and glucose does not induce IP3 and DAG. Our data suggest that the Cdc25 protein controls a nitrogen-specific signalling pathway involving the effector PI-PLC, in addition to the glucose-induced activation of adenylyl cyclase (AC).
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PMID:CDC25-dependent induction of inositol 1,4,5-trisphosphate and diacylglycerol in Saccharomyces cerevisiae by nitrogen. 132 32

The relative specificities of members of the G alpha q family of GTP-binding proteins were tested for their ability to activate different phosphoinositide-specific phospholipase C (PI-PLC) beta isozymes. Cos-7 cells were transfected with cDNA corresponding to G alpha q, G alpha 11, G alpha 14, and G alpha 16. Most of the recombinant protein was bound to the cell membrane and these membranes were washed to elute endogenous PI-PLC activity. The membrane preparation was reconstituted with purified preparations of the PI-PLC beta isozymes and guanosine 5'-O-thiotriphosphate (GTP gamma S)-stimulated enzyme activity was measured. All four proteins of the G alpha q family were found to stimulate PI-PLC beta 1, with G alpha q and G alpha 11 being most efficient. On the other hand, G alpha 16 was found to most effectively activate PI-PLC beta 2, while G alpha q, G alpha 11, and G alpha 14 showed less stimulation. Specific anti- G alpha 16 antibody blocked the stimulation of both PI-PLC beta 1 and PI-PLC beta 2 in the enriched membrane fraction. We conclude that there is specificity in the interaction of different members of the Gq family with different PI-PLC beta effectors. This specificity may be important in generating tissue- or receptor-specific responses in vivo.
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PMID:Members of the Gq alpha subunit gene family activate phospholipase C beta isozymes. 132 89


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