Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The relative roles of the adenylate cyclase-protein kinase A system (AC-PKA), the phospholipase C-protein kinase C system (PLC-PKC), and increases in cytosolic calcium in mediating the final actions of parathyroid hormone (PTH) remain ill defined. Although an important role for the PLC-PKC system in the regulation of phosphate transport in response to PTH has been suggested, previous studies from our laboratory and others, in OK cells, have emphasized the major role of AC-PKA. The present studies were designed to dissociate the second messengers for PTH by using an inhibitor of PLC (U-73,122). Studies were performed in confluent cultures of OK cells with and without preincubation with U-73,122 (1 microM). This inhibitor did not alter adenosine 3',5'-cyclic monophosphate (cAMP) production or the activation of PKA in response to PTH. Preincubation with U-73,122, however, totally abolished PTH-stimulated increases in diglyceride mass, consistent with inhibition of PLC. Activation of particulate PKC was then examined in response to PTH in the absence and presence of U-73,122. Although PTH resulted in an increase in particulate PKC activity in control cultures, this effect was abolished in the presence of U-73,122 and actually decreased significantly. Therefore, having documented marked attenuation of PLC-PKC, we next examined the effects of PTH on phosphate transport. Basal phosphate uptake was not altered by 1 microM U-73,122. Dose-response curves of the inhibition of phosphate transport in response to PTH were identical in the presence or absence of U-73,122. Thus inhibition of PLC and PKC activities did not alter the effects of PTH on phosphate transport.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Effect of U-73,122, an inhibitor of phospholipase C, on actions of parathyroid hormone in opossum kidney cells. 751 44

Even though the same Cl channel (CFTR) is common to certain fluid transport functions that are oppositely directed, i.e., secretion and absorption, only fluid secretion has clearly been shown to be acutely regulated. It is now clear that fluid secretion activated by beta-adrenergic stimulation is controlled by cAMP-mediated opening and closing of CFTR-Cl channels. Since the conductance of the human sweat duct is almost wholly due to CFTR-Cl conductance (CFTR-GCl), we sought to determine whether salt absorption via CFTR-Cl channels could also be subject to acute regulation in this purely absorptive epithelium. After alpha-toxin permeabilization, we found that addition of cAMP resulted in a large increase in Cl diffusion potentials across the apical membrane and a more than twofold increase in the average membrane conductance. Since the cAMP effects were dependent on Cl alone, not on Na, and since apical Cl conductance appears to be almost exclusively comprised of CFTR-GCl, we surmise that this form of electrolyte absorption like secretion is also subject to acute control through CFTR-GCl. Acute regulation of absorption involves both activation by phosphorylation (PKA) and inactivation by dephosphorylation (unknown endogenous phosphatase) of CFTR. Phosphorylation of CFTR was shown by the facts that CFTR-GCl could be activated by cAMP and inhibited by the kinase antagonist staurosporine, or by removal of either substrate ATP or Mg2+ cofactor. Inactivation of CFTR-GCl by endogenous phosphatase(s) was indicated by a spontaneous but reversible loss of CFTR-GCl upon removal of cAMP. Such loss of CFTR-GCl activity could be prevented either by application of phosphatase inhibitors or by using phosphatase-resistant ATP-gamma-S as substrate to phosphorylate CFTR. We surmise that absorptive function is subject to rapid regulation which can be switched "on" and "off" acutely by a control system that is common to both absorptive and secretory processes and that this control is crucial to switching between conductive and nonconductive transport mechanisms during salt absorption.
 ...
PMID:Rapid regulation of electrolyte absorption in sweat duct. 751 79

Na+/Ca2+ exchange contributes to the control of cytosolic free Ca2+ levels ([Ca2+]i) in resting and activated cultured human mesangial cells. We have previously shown that activation of phospholipase C by vasoconstrictors enhances Ca2+ influx upon extracellular Na+ withdrawal. This effect is not mediated by concurrent activation of protein kinase (PK) C, since it occurs even after PKC inhibition, and phorbol esters actually blunt both basal and stimulated Na+/Ca2+ exchange. We now studied the effects of PKA and PKG activation by adenylate/guanylate cyclase stimuli or by permeant analogues of cyclic nucleotides in monolayer cultures loaded with the fluorescent Ca(2+)-sensitive probe, fura-2. The exchanger was inhibited by the stable prostaglandin I2 analogue, iloprost, which is transduced by cAMP (peak [Ca2+]i inhibition by 1 microM iloprost 35 +/- 3%). Similarly, non-receptor activation of adenylate cyclase by 10 microM forskolin inhibited basal and agonist-stimulated Na+/Ca2+ exchange by 52 +/- 4 and 66 +/- 4%, respectively. Dibutyryl-cAMP (0.1 mM) also inhibited stimulated Na(+)-dependent Ca2+ influx by 72 +/- 2%. The particulate guanylate cyclase agonist, atriopeptin III, and the soluble guanylate cyclase activator, glyceryltrinitrate, also inhibited both basal and angiotensin II-stimulated Na+Ca2+ exchange (to a maximum of 53 +/- 5 and 62 +/- 3%, respectively). Dibutyryl-cGMP (1 mM) mimicked the effects of cGMP stimuli, reducing stimulated Na+/Ca2+ exchange by 79 +/- 2%. Therefore, similar to PKC, cyclic nucleotide activation of PKA and PKG regulates Na+/Ca2+ exchange, providing a functional link between transmembrane signalling systems for vasoactive agents in cultured human mesangial cells.
 ...
PMID:Cyclic nucleotides inhibit Na+/Ca2+ exchange in cultured human mesangial cells. 752 69

Agonists that elevate calcium in T84 cells stimulate chloride secretion by activating KBIC, an inwardly rectifying K channel in the basolateral membrane. We have studied the regulation of this channel by calcium, nucleotides and phosphorylation using patch clamp and short-circuit current (ISC) techniques. Open probability (Po) was independent of voltage but declined spontaneously with time after excision. Rundown was slower if patches were excised into a bath solution containing ATP (10 microM-5 mM), ATP (0.1 mM)+protein kinase A (PKA; 180 nM), or isobutylmethylxanthine (IBMX; 1 mM). Analysis of event durations suggested that the channel has at least two open and two closed states, and that rundown under control conditions is mainly due to prolongation of the long closed time. Channel activity was restimulated after rundown by exposure to ATP, the poorly hydrolyzable ATP analogue AMP-PNP, or ADP. Activity was further enhanced when PKA was added in the presence of MgATP, but only if free calcium concentration was elevated (400 nM). Nucleotide stimulation and inward rectification were both observed in nominally Mg-free solutions. cAMP modulation of basolateral potassium conductance in situ was confirmed by measuring currents generated by a transepithelial K gradient after permeabilization of the apical membrane using alpha-toxin. Finally, protein kinase C (PKC) inhibited single KBIC channels when it was added directly to excised patches. These results suggest that nonhydrolytic binding of nucleotides and phosphorylation by PKA and PKC modulate the responsiveness of the inwardly rectifying K channel to Ca-mediated secretagogues.
 ...
PMID:Regulation of an inwardly rectifying K channel in the T84 epithelial cell line by calcium, nucleotides and kinases. 753 42

Recombinant human tumor necrosis factor (TNF)-alpha increased the expression of epidermal growth factor receptor (EGFR) mRNA and protein in all of six human pancreatic carcinoma cell lines tested. In addition, TNF-alpha increased the expression of an EGFR ligand, transforming growth factor (TGF)-alpha, at the mRNA and protein level in all cell lines. Increased expression of EGFR protein was associated with elevated steady-state EGFR mRNA levels. Nuclear run-on analysis showed that increase in EGFR mRNA was due to an increased rate of transcription. Induction of EGFR mRNA expression by TNF-alpha was abrogated by cycloheximide but occurred independently of TNF-alpha-induced production of TGF-alpha protein. Protein kinase A or Gi-type guanine nucleotide-binding proteins were not involved in this process as assessed by using appropriate stimulators and inhibitors of these signal transduction pathways. By contrast, staurosporine, an inhibitor of protein kinase C, partially inhibited, and 4-bromophenacyl bromide, a phospholipase inhibitor, completely inhibited TNF-alpha-dependent EGFR mRNA expression. The phospholipase C-specific inhibitor tricyclodecan-9-yl xanthogenate did not alter TNF-alpha-dependent EGFR mRNA expression, suggesting that phospholipase A2 is involved in the modulation of EGFR expression by TNF-alpha. The simultaneous induction of a ligand/receptor system by TNF-alpha suggests that this cytokine modulates autocrine growth-regulatory pathways in pancreatic cancer cells.
 ...
PMID:Tumor necrosis factor alpha induces the expression of transforming growth factor alpha and the epidermal growth factor receptor in human pancreatic cancer cells. 843 98

The anabolic effect of parathyroid hormone (PTH) on bone is partly due to a stimulation of osteoblast proliferation. The PTH signal is transduced by the pathways of adenylyl cyclase (AC)/protein kinase (PK) A and phospholipase C/PKC/Ca++. There is still uncertainty about the relative contribution of the two pathways to the proliferative effects of the hormone. In our study, PTH(1-34), AC/PKA agonists, and phorbol 12-myristate-13-acetate (PMA, a PKC activator) stimulated cell proliferation in cultured mouse calvariae. In isolated osteoblasts, only PMA stimulated proliferation, whereas AC/PKA agonists and PTH(1-34) inhibited it. As already known, PTH in the presence of supramaximal concentrations of transforming growth factor-beta (TGF-beta) stimulated osteoblast growth; under these same conditions, AC/PKA agonists reproduced the stimulatory effect of PTH(1-34), whereas PMA became inhibitory. PTH(1-31), which stimulates AC without affecting PKC, acted similarly to the fully active PTH(1-34) in both calvaria and isolated osteoblasts. On the contrary, midregion fragments that activate only PKC stimulated calvaria cell proliferation faintly in comparison with PTH(1-34); no effect was seen in osteoblasts, either with or without TGF-beta. Our study shows that the effects of PTH on proliferation can be mimicked by agonists of the AC/cAMP pathway. Although PMA is indeed able to stimulate cell growth in tissue explants, its effects on isolated osteoblasts markedly diverge from those of PTH. We conclude that activation of the AC/PKA pathway is the main component of the proliferative effects of PTH.
 ...
PMID:Effects of parathyroid hormone and agonists of the adenylyl cyclase and protein kinase C pathways on bone cell proliferation. 871 38

Glutamatergic neurotransmission is associated with release of arachidonic acid (AA) from membrane phospholipids of both neurons and astrocytes. Since free AA has been shown to enhance glutamate-mediated synaptic transmission, it can be postulated that glutamate release and AA formation constitute a positive feed-back mechanism for sustained excitatory neurotransmission. In the present study, we examined whether the glutamate-evoked release of AA could be modulated by peptides. Using mouse cortical neurons in primary cultures, we show that the release of AA evoked by glutamate is potentiated by vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide (PACAP). This effect is mediated through the activation of PACAP I receptors. However, several arguments show that this potentiating mechanism does not involve the cAMP/PKA pathway. 1) Increasing intracellular cAMP by either cholera toxin, forskolin, or 8-Br-cAMP treatments does not affect the glutamate-evoked release of AA; 2) potentiation of the glutamate response by PACAP is not prevented by the PKA inhibitor 8-Br-Rp-cAMPS. Also, an involvement of the phospholipase C protein kinase C pathways is unlikely since inhibitors of both phospholipase C (i.e. U-73122) and protein kinase C (i.e. Ro 31-8220) do not affect the potentiation of the glutamate response by PACAP. These observations indicate an effect mediated by PACAP I receptors, which does not involve the second messenger pathways classically associated with activation of this type of receptors. Furthermore, results indicate that this potentiating mechanism mediated by PACAP I receptor acts at a level downstream of the glutamate receptor-mediated calcium influx.
 ...
PMID:Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) potentiate the glutamate-evoked release of arachidonic acid from mouse cortical neurons. Evidence for a cAMP-independent mechanism. 879 93

This study examines how interleukin-6 (IL-6) expression by human luteinizing granulosa cells is regulated. IL-6 was assayed in culture supernatants, mRNA in cells by in situ hybridization and by a competitive reverse-transcriptase polymerase chain reaction (RT-PCR). TNF alpha (100 pg-1 ng/ml) induced IL-6 mRNA and protein. Phorbol 12-myristate 13-acetate (PMA) (50 nM) mimicked this effect. DibutyrylcAMP (1 mM) and 10 microM forskolin. C2-, C6- and C8-ceramide (15 microM), all had no effect. The inhibitor of protein tyrosine kinase (PTK), genistein (100 micrograms/ml) reduced tumor necrosis factor (TNF) effects. The inhibitors of protein kinase C (PKC) (staurosporine, 10 nM), of phospholipase C (U73122, 2 microM), of phospholipase A2 (PLA2), (indomethacin 30 microM, mepacrin 50 microM, nordihydroguaiaretic acid 10 microM, ONO-RS-082 3,5 microM), none prevented it. Hence, IL-6 is induced by TNF alpha via activation of PTK. Protein kinase A, phosphoinositide and conventional PKC, sphingomyelin and PLA2 pathways are not implicated.
 ...
PMID:Tumor necrosis factor-alpha induces interleukin-6 mRNA and protein in human granulosa luteinizing cells via protein tyrosine kinase without involving ceramide. 908 55

Parathyroid hormone (PTH) activates multiple intracellular effectors, including adenylyl cyclase (AC) and phospholipase C (PLC), via a single receptor [PTH/parathyroid hormone-related protein receptor (PTHR)] expressed in bone and kidney. Homologous desensitization of PTHR signaling occurs, but the relative importance of reduced receptor expression vs. impaired receptor-effector coupling in this process remains unclear. It also is not known if AC and PLC responses to PTH are desensitized independently or interdependently. In LLC-PK1 cells that expressed transfected wild-type PTHRs, PTH caused dose- and time-dependent desensitization of both the AC and PLC-responses to PTH without altering PTHR expression. Desensitization of AC was blocked in mutant cells resistant to adenosine 3',5'-cyclic monophosphate but not when cells expressed mutant PTHRs with defective PLC coupling. Desensitization of PLC was unaffected by PKA blockade, partially mimicked by phorbol ester, and not reproduced by agents that selectively activated AC. The finding that homologous PTHR desensitization in LLC-PK1 cells is signal specific suggests that prior exposure of other cells to PTH also may induce discordant regulation of subsequent PTHR signaling, altering the character as well as the intensity of the hormonal response.
 ...
PMID:Mechanisms of homologous and heterologous desensitization of PTH/PTHrP receptor signaling in LLC-PK1 cells. 927 93

The effects of carbachol (CCh) on inositol 1,4,5-trisphosphate (IP3) production and intracellular calcium ([Ca2+]i) mobilization, and their regulation by cAMP-elevating agents were investigated in SV-40 transformed cat iris sphincter smooth muscle (SV-CISM-2) cells. CCh produced time- and dose-dependent increases in IP3 production; the t1/2 and EC50 values were 68 s and 0.5 microM, respectively. The muscarinic agonist provoked a transient increase in [Ca2+]i which reached maximum within 77 s, and increased [Ca2+]i mobilization in a concentration-dependent manner with an EC50 of 1.4 microM. Thapsigargin, a Ca(2+)-pump inhibitor, caused a rapid rise in [Ca2+]i and subsequent addition of CCh was without effect. Both CCh-induced IP3 production and CCh-induced [Ca2+]i mobilization were more potently antagonized by 4-DAMP, an M3 muscarinic receptor antagonist, than by pirenzepine, an M1 receptor antagonist, suggesting that both responses are mediated through the M3 receptor subtype. Treatment of the cells with U73122, a phospholipase C (PLC) inhibitor, resulted in a concentration-dependent decrease in both CCh-stimulated IP3 production and [Ca2+]i mobilization. These data indicate close correlation between enhanced IP3 production and [Ca2+]i mobilization in these smooth muscle cells and suggest that the CCh-stimulated increase in [Ca2+]i could be mediated through increased IP3 production. Isoproterenol (ISO) inhibited CCh-induced IP3 production (IC50 = 80 nM) and [Ca2+]i mobilization (IC50 = 0.17 microM) in a concentration-dependent manner. Microsomal fractions isolated from SV-CISM-2 cells contained phospholipase C (PLC) which was stimulated by CCh (10 microM) and GTP gamma S (0.1 microM). Pretreatment of the cells with ISO or forskolin, 5 microM each, produced membrane fractions in which CCh-stimulated PLC activity was significantly attenuated. Furthermore, when microsomal fractions isolated from SV-CISM-2 cells were phosphorylated with Protein kinase A (PKA), the CCh- and GTP gamma S-stimulated IP3 production were significantly inhibited. It can be concluded from these studies that in SV-CISM-2 cells, activation of M3 muscarinic receptors results in stimulation of PLC-mediated PIP2 hydrolysis, generating IP3 which mobilizes [Ca2+]i. Furthermore, elevation of cAMP may inhibit IP3 production and [Ca2+]i mobilization through mechanisms involving PKA-dependent phosphorylation of PLC, G-proteins, IP3 receptor and/or IP3 metabolizing enzymes.
 ...
PMID:Inhibition of muscarinic-stimulated polyphosphoinositide hydrolysis and Ca2+ mobilization in cat iris sphincter smooth muscle cells by cAMP-elevating agents. 937 22


1 2 3 4 5 6 7 8 9 10 Next >>