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 cultured rabbit vascular smooth muscle cells (VSMC), platelet-derived growth factor (PDGF), a potent mitogen for VSMC, induced the dose- and time-dependent formation of inositol mono-, bis- and trisphosphates (IP1, IP2 and IP3, respectively). The doses of PDGF necessary for these reactions were similar to those for DNA synthesis. The maximal level of IP1 was comparable to, and those of IP2 and IP3 were about half of those induced by angiotensin II, a potent vasoconstrictor. However, the time courses of the PDGF-induced reactions were slower than those of the angiotensin II-induced ones. Moreover, protein kinase C-activating phorbol esters inhibited the angiotensin II-induced reactions, but did not the PDGF-induced ones. These results indicate that PDGF induces the phospholipase C reactions in VSMC but suggest that the signaling mechanism of PDGF to the phospholipase C is different from that of angiotensin II.
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PMID:Platelet-derived growth factor (PDGF)-induced phospholipase C-mediated hydrolysis of phosphoinositides in vascular smooth muscle cells--different sensitivity of PDGF- and angiotensin II-induced phospholipase C reactions to protein kinase C-activating phorbol esters. 284 20

Expression of a transforming Harvey or Kirsten ras gene caused opposing effects in the ability of platelet-derived growth factor (PDGF) and bradykinin to activate phospholipase C-mediated phosphoinositide hydrolysis. In [3H]inositol-labeled rat-1 fibroblasts, PDGF (5 ng/ml) resulted in a 2-fold increase in the level of [3H]inositol trisphosphate (InsP3) after 2 min and, in the presence of LiCl, a 3- to 8-fold increase in the level of [3H]inositol monophosphate (InsP1) after 30 min. However, in EJ-ras-transfected rat-1 cells, which exhibit near normal levels of PDGF receptors, PDGF resulted in little or no accumulation of either [3H]InsP3 or [3H]InsP1. Similarly, marked stimulations by PDGF were observed in NIH 3T3 cells, as well as in v-src-transformed 3T3 cells, but not in 3T3 cells transformed by Kirsten sarcoma virus or by transfection with v-Ha-ras DNA. This diminished phosphoinositide response in ras-transformed cells was associated with a markedly attenuated mitogenic response to PDGF. On the other hand, both phosphoinositide metabolism and DNA synthesis in ras-transformed fibroblasts were stimulated several-fold by serum. In NIH 3T3 cells carrying a glucocorticoid-inducible v-Ha-ras gene, a close correlation was found between the expression of p21ras and the loss of PDGF-stimulated [3H]InsP1 accumulation. In contrast to this ras-induced desensitization to PDGF, ras-transformed NIH 3T3 cells exhibited an enhanced sensitivity to bradykinin; this effect was associated with an elevated level of high-affinity [3H]bradykinin binding. We propose that a ras gene product (p21) can, directly or indirectly, influence growth factor-stimulated phosphoinositide hydrolysis, as well as DNA synthesis, via alterations in the properties of specific growth factor receptors.
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PMID:Opposing effects of a ras oncogene on growth factor-stimulated phosphoinositide hydrolysis: desensitization to platelet-derived growth factor and enhanced sensitivity to bradykinin. 288 54

The mode of phospholipase C activation initiated with platelet-derived growth factor (PDGF) has been studied in comparison with that initiated with vasopressin and bombesin in a rat fibroblast line, WFB. Stimulation of WFB cells by PDGF, vasopressin, and bombesin elicites rapid hydrolysis of polyphosphoinositides and an increase in cytoplasmic free Ca2+ concentration ([Ca2+]i). On stimulation by PDGF, there was a lag period of about 10 s before an increase in [Ca2+]i. No measurable lag period was observed in the [Ca2+]i response induced by vasopressin or bombesin. Pretreatment of WFB cells with phorbol 12-myristate 13-acetate profoundly inhibited inositol phosphate formation evoked by vasopressin and bombesin, but enhanced to some extent inositol phosphate formation stimulated by PDGF. In membranes prepared from WFB cells, GTP markedly augmented inositol polyphosphate formation induced by vasopressin and bombesin. It was not successful in showing the PDGF-stimulated formation of inositol phosphates in the membrane preparation. The effects of GTP, guanosine 5'-O-(2-thiodiphosphate) (GDP beta S), and guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) on polyphosphoinositide hydrolysis stimulated by growth factors were studied in WFB cells made permeable to nucleotides by treatment with either saponin or Pseudomonas aeruginosa cytotoxin. PDGF, vasopressin, and bombesin elicited inositol phosphate production in the permeabilized WFB cells in the absence of added GTP. GDP beta S, a competitive inhibitor of GTP-binding proteins (G-proteins), markedly reduced the bombesin- and vasopressin-stimulated production of inositol phosphates. However, the PDGF-stimulated production of inositol phosphates was not affected by the addition of GDP beta S. GTP gamma S, an agonist of G-proteins, largely enhanced the vasopressin- and bombesin-stimulated hydrolysis of inositol lipids when added at 10-100 microM. In the presence of GTP gamma S, the PDGF-stimulated hydrolysis of inositol lipids was not enhanced, but was reduced: 100 microM GTP gamma S reduced the stimulated hydrolysis to about a half of the control level. Only GTP gamma S, and no other nucleoside triphosphates, was found to have these effects. Activation of G-proteins in WFB cells by fluoroaluminate resulted in the inhibition of inositol phosphate production elicited with not only PDGF, but also with vasopressin and bombesin. These results indicate that a G-protein couples vasopressin and bombesin receptors to the activation of phospholipase C. Moreover, these results suggest that coupling of the PDGF receptor to phospholipase C is not mediated through a G-protein.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Pathway of phospholipase C activation initiated with platelet-derived growth factor is different from that initiated with vasopressin and bombesin. 304 15

Data indicating that the 21-kDa protein (p21) Harvey-ras gene product shares sequence homology with guanine nucleotide-binding proteins (G proteins) has stimulated research on the influence(s) of p21 on G-protein-regulated systems in vertebrate cells. Our previous work demonstrated that NIH-3T3 mouse cells expressing high levels of the cellular ras oncogene isolated from the EJ human bladder carcinoma (EJ-ras) exhibited reduced hormone-stimulated adenylate cyclase activity. We now report that in these cells another enzyme system thought to be regulated by G proteins is inhibited, namely phospholipases A2 and C. NIH-3T3 cells incubated in plasma-derived serum release significant levels of prostaglandin E2 (PGE2) as determined by radioimmunoassay when exposed to platelet-derived growth factor (PDGF) at 2 units/ml; the levels of PGE2 released from EJ-ras-transfected cells are only 3% those of controls despite a similar basal (unstimulated) release from control and EJ-ras-transfected cells. The lack of PDGF-stimulated PGE2 release from EJ-ras-transfected cells is not due to a defect in the prostaglandin cyclooxygenase enzyme, since incubation of control cells and EJ-ras-transfected cells in 0.33, 3.3, or 33 microM arachidonate resulted in identical levels of PGE2 release. The lack of PDGF-stimulated PGE2 release from EJ-ras-transfected cells also does not result from the loss of functional PDGF receptors. EJ-ras-transformed cells bind 70% as much 125I-labeled PDGF as control cells and are stimulated to incorporate [3H]thymidine and to proliferate after exposure to PDGF. Moreover, this inhibition is not likely the result of a secondary cellular effect related to the transformed phenotype, since NIH-3T3 cells transformed by v-src released PGE2 at wild-type levels after exposure to PDGF. Determination of total water-soluble inositolphospholipids and changes in the specific activities of phosphatidylcholine in control and EJ-ras-transfected cells demonstrated that PDGF-stimulated phospholipase C and A2 activities are inhibited in the EJ-ras-transfected cells.
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PMID:Loss of platelet-derived growth factor-stimulated phospholipase activity in NIH-3T3 cells expressing the EJ-ras oncogene. 309 98

Our previous work demonstrated that NIH-3T3 cells expressing high levels of the mutated cellular ras oncogene (EJ-ras gene) exhibited reduced hormone-sensitive adenylate cyclase and platelet-derived growth factor-stimulated (PDGF) phospholipase A2/C activities. We now report that although the ras-transformed cells display markedly reduced phospholipase C activity, as measured by the levels of inositol 1,4,5-trisphosphate synthesized after PDGF-stimulation, normal levels of phospholipase A2 activity can be uncovered; thus, similar levels of prostaglandin E2 were synthesized in EJ-ras transformed and control cells after stimulation with phorbol myristate acetate (PMA) and/or the calcium ionophore A-23187, agents which stimulate protein kinase C and intracellular Ca2+ levels, respectively. These data suggest that the EJ-ras gene product uncouples the PDGF receptor from the phospholipase C, resulting in reduced PDGF-stimulated Ca2+ mobilization, protein kinase C stimulation and an apparent decrease in Ca2+-dependent phospholipase A2.
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PMID:The lack of PDGE-stimulated PGE2 release from ras-transformed NIH-3T3 cells results from reduced phospholipase C but not phospholipase A2 activity. 311 66

The role of ras proteins in signal transduction was assessed by studying inositol phospholipid metabolism and inositol phospholipid-mediated cellular responsiveness to agonists in cells transformed by ras and other oncogenes. Specific alterations were observed in the inositol phospholipid cycle of ras-transformed fibroblasts, but similar changes were also produced by spontaneous transformation or transformation mediated by either membrane-associated oncogenes, such as src, met, or trk, or cytoplasmic oncogenes, mos and raf; the nuclear oncogenes fos and myc did not produce these changes. The alterations included (i) stimulation of phospholipase A2 activity as indicated by elevated levels of glycerophosphoinositol and nonesterified arachidonic acid and (ii) specific uncoupling between surface receptor-mediated stimulation by platelet-derived growth factor, bombesin, or serum and activation of intracellular phospholipase C. These findings suggest the existence of common biochemical pathways for transformation by cytoplasmic and membrane-associated oncogenes and are not consistent with the hypothesis that 21-kDa ras proteins (p21) are direct or distinct regulatory elements of phospholipase C or phospholipase A2 in inositol phospholipid signal transduction pathways.
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PMID:Malignant transformation by ras and other oncogenes produces common alterations in inositol phospholipid signaling pathways. 328 89

NIH-3T3 cells transformed by the EJ-ras oncogene synthesize only 10-15% as much inositol 1,4,5-trisphosphate (InsP3) as control cells after stimulation with platelet-derived growth factor (PDGF). This is despite the fact that the basal (unstimulated) levels of InsP3 synthesized in control and EJ-ras-transformed cells are not significantly different. Using the fluorescent indicator fura-2 and digital-imaging techniques, we have visualized and quantified changes in intracellular Ca2+ concentrations in control and EJ-ras-transformed NIH-3T3 cells in response to PDGF. Within 3 min after exposure of control cells to PDGF, intracellular Ca2+ levels are increased 3- to 9-fold, paralleling the increase in InsP3. In contrast, the majority (greater than 90%) of the EJ-ras-transformed cells show no increase in Ca2+ levels after PDGF exposure and the few that did respond exhibited only a small transient increase. Pronounced differences in the intracellular localization of Ca2+ increases in control and the responding EJ-ras-transformed cells were also observed. Despite the inhibition of InsP3 synthesis and subsequent Ca2+ mobilization, the EJ-ras-transformed cells respond mitogenically to PDGF. These data do not support the hypothesis that the EJ-ras gene product (p21) stimulates a phosphatidylinositol 4,5-bisphosphate-specific phospholipase C in NIH-3T3 cells; instead they suggest that the EJ-ras p21 may uncouple the PDGF receptor from phospholipase C resulting in inhibition of PDGF-stimulated activity of phospholipase C, InsP3 synthesis, and Ca2+ mobilization.
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PMID:NIH-3T3 cells transformed by the EJ-ras oncogene exhibit reduced platelet-derived growth factor-mediated Ca2+ mobilization. 328 91

The mesangial cell occupies a central position in the renal glomerulus. It has characteristics of a modified smooth muscle cell, but is also capable of a number of other functions. Among these are generation of prostaglandins (PGs) and mediators of inflammation; production and breakdown of basement membrane and other biomatrix material; synthesis of cytokines; and uptake of macromolecules, including immune complexes. In terms of its smooth muscle activity, the mesangial cell contracts or relaxes in response to a number of vasoactive agents. This ability allows the cells to modify glomerular filtration locally. The cellular mechanism of action of many agents influencing mesangial cells involves activation of phospholipase C for phosphatidylinositol 4,5-bisphosphate. This results in generation of inositol trisphosphate and release of intracellular calcium. Mesangial cell relaxation can be mediated by enhanced cAMP or cGMP generation. Many vasoactive substances also stimulate PG production by mesangial cells. This involves activation of both phospholipase C and A2, the latter being responsible for the release of arachidonic acid. Mesangial cells are also capable of endocytosis of macromolecules, including immune complexes. This is initiated by binding to a specific receptor, resulting in formation of PG, platelet-activating factor, and reactive oxygen species. Mesangial cells can generate interleukin 1 and platelet-derived growth factor and respond to these in an autocrine manner. Thus, the mesangial cell not only can control glomerular filtration, but may also be involved in the response to local injury, including cell proliferation and basement membrane remodeling.
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PMID:The glomerular mesangial cell: an expanding role for a specialized pericyte. 330 11

Platelet-activating factor (PAF) and platelet-derived growth factor (PDGF) likely play important roles in glomerular processes. To identify mechanisms of PAF- and PDGF-induced mesangial cell activation, we characterized effects of both agents on cytosolic free [Ca2+] ([Ca2+]f) and phospholipase activation. When cultured rat renal mesangial cells were stimulated by PAF, [Ca2+]f increased (within 10 s) from 110 +/- 6 to 209 +/- 14 nM, due to release of Ca2+ from intracellular storage sites, as well as entry of Ca2+ from external milieu. PAF also rapidly increased free arachidonate, diacylglycerol, and inositol trisphosphate (IP3) levels. PDGF increased [Ca2+]f from 78 +/- 12 to 192 +/- 22 nM, but the time response was different from that seen with PAF. Peak [Ca2+]f increase occurred at approximately 1 min subsequent to stimulation. Like PAF, increased [Ca2+]f was due to release of Ca2+ from intracellular stores and entry from extracellular media. PDGF increased levels of free arachidonate prior to an increase in diacylglycerol levels. PDGF increased inositol bisphosphate and IP3 levels at 2 min but not at 15 s. Thus, PDGF may mediate a phospholipase C-independent activation of phospholipase A2. In permeabilized mesangial cells, IP3 released Ca2+ from nonmitochondrial storage sites. Thus, PAF- and PDGF-induced increases in [Ca2+]f were likely secondary to activation of phospholipase C, resulting in increased levels of IP3. Understanding differences in mechanisms of mesangial cell activation by PAF and PDGF will likely lead to a better understanding of signal transduction pathways and provide insight into the role of these activators in glomerular disease.
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PMID:PAF and PDGF increase cytosolic [Ca2+] and phospholipase activity in mesangial cells. 333 46

The classic pathway for agonist-induced generation of diacylglycerol is via activation of a phospholipase C-mediated hydrolysis of the "phosphoinositides." We now report findings from a variety of cell types, which indicate that tumor-promoting phorbol diesters, serum, and platelet-derived growth factor activate within seconds the hydrolysis of phosphatidylcholine, as detected by the formation of diacylglycerol and phosphocholine. It is known that phorbol diesters do not stimulate hydrolysis of the phosphoinositides. Yet, in cells prelabeled with either [14C]oleate or [32P]orthophosphate, addition of the tumor promoter phorbol dibutyrate (PBt2) resulted in the rapid generation of both diacylglycerol and phosphatidate in a time- and dose-dependent manner. The fatty acid composition of the phosphatidate most resembled the fatty acid profile of phosphatidylcholine from the same cell type. Taken together, these findings suggested a role for protein kinase C in the generation of diacylglycerol (and phosphatidate) from phosphatidylcholine. To define further the pathways involved, the metabolism of cellular phosphatidylcholine was studied. In cells prelabeled with [3H]choline, addition of PBt2, but not 4 alpha-phorbol, stimulated the formation of intracellular phosphocholine within 45 sec. Furthermore, addition of platelet-derived growth factor (PDGF) or serum to "serum-starved" cells prelabeled with [3H]choline resulted in increased levels of intracellular phosphocholine within 15-30 sec. Thus, the data suggest that agonists that stimulate protein kinase C either directly (e.g., PBt2) or indirectly via activation of phosphoinositide hydrolysis (e.g., PDGF and serum) may stimulate degradation of phosphatidylcholine by phospholipase C in intact cells. However, prior down-regulation of protein kinase C by prolonged pretreatment of cells with PBt2 almost totally abolished subsequent stimulation of phosphatidylcholine degradation by PBt2 but only partially attenuated subsequent stimulation by PDGF and serum. These observations suggest that PDGF and serum act, at least partially, through a protein kinase C-independent mechanism. Lastly, the size of the cellular choline and CDP-choline pools were shown to be small and relatively insensitive to agonist addition, as compared to the size and behavior of the phosphocholine pool. Thus, the rapidly increased levels of phosphocholine (and diacylglycerol) arising in response to agonist addition appear to be derived directly from phosphatidylcholine by a phospholipase C-mediated mechanism.
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PMID:Rapid formation of diacylglycerol from phosphatidylcholine: a pathway for generation of a second messenger. 346 27


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