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)

Prompted by the reversal of skin hyperproliferation to normal by 13-hydroxyoctadecadienoic acid (13-HODE), a 15-lipoxygenase metabolite of linoleic acid, we investigated a possible mechanism for this antiproliferative action. To address this we first demonstrated that 13-HODE is incorporated into epidermal phosphatidyl 4,5-bisphosphate (PtdIns4,5-P2) and released as 13-HODE-containing diacylglycerol by epidermal phospholipase C. Secondly, we tested the possibility whether this putative 13-HODE-containing DAG (13HODE-DAG) could exert a modulatory effect on epidermal protein kinase C (PKC) activity which previously has been associated with skin hyperproliferation. Unlabeled 13HODE-DAG was generated from 13-HODE-containing phosphatidylcholine after phospholipase C hydrolytic cleavage. The effects of the 13HODE-DAG were determined on: i) total epidermal PKC activity; ii) diolein-activated PKC activity; and iii) the two identified epidermal PKC-isozymes (PKC-beta and PKC-alpha). Our data revealed over a twofold activation of total basal PKC activity by diolein. In contrast, replacement of diolein (1,2-dioleoylglycerol) with 13HODE-DAG (1-palmitoyl,2-13HODE-glycerol) in the incubation mixture exerted no effect on total basal PKC activity. In an another experiment, 13HODE-DAG inhibited diolein-activated PKC activity in a dose-dependent manner. To determine whether the effects of 13HODE-DAG are selective, we tested its effects on DEAE-Sephacel-purified and Western blot-confirmed PKC isozymes. Our data revealed that 13HODE-DAG selectively inhibited the activity of PKC-beta isozyme, while exerting negligible effect on the PKC-alpha isozyme. This selective inhibitory effect of 13HODE-DAG on a major epidermal PKC isozyme activity suggests that 13HODE-containing DAG seemingly can modulate epidermal PKC activity, which purportedly is associated with epidermal hyperproliferation.
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PMID:Expression of protein kinase C isozymes in guinea pig epidermis: selective inhibition of PKC-beta activity by 13-hydroxyoctadecadienoic acid-containing diacylglycerol. 807 13

Ceramides and phospholipids constitute two important structural lipids of normal skin that are notably rich in polyunsaturated fatty acids. Although linoleic acid (LA) is high in the ceramides, the localization of its 15-lipoxygenase product, 13-hydroxyoctadecadienoic acid (13-HODE) in the epidermis is unknown. In this study, we investigated the relative incorporation of [14C]LA and [14C]13-HODE into ceramides and phospholipids in isolated epidermal slices. Our data revealed minor incorporation of [14C]LA and [14C]13-HODE into ceramides. In contrast, both [14C]LA and [14C]13-HODE are markedly incorporated into phospholipids, particularly, phosphatidylcholine (PC) and phosphatidylinositol (PtdIns). The incorporation of 13-HODE into the PtdIns pool in particular prompted us to investigate into its fate in the signal transduction process and its possible incorporation into diacylglycerol. Our data revealed that 13-HODE is incorporated into epidermal phosphatidylinositol 4,5-bisphosphate (PtdIns4,5-P2) resulting in epidermal phospholipase C-catalyzed release into a novel 13-HODE-containing diacylglycerol (1-acyl-2-13-HODE-glycerol). The possibility now exists that this novel 13-HODE-containing diacylglycerol could function to modulate the activity of epidermal protein kinase C and hyperproliferation/differentiation.
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PMID:Incorporation of 13-hydroxyoctadecadienoic acid (13-HODE) into epidermal ceramides and phospholipids: phospholipase C-catalyzed release of novel 13-HODE-containing diacylglycerol. 816 29

Treatment of human natural killer (NK) cells with phospholipase A(2) (PLA(2)) inhibitors, mepacrine and 4-bromophenacyl bromide (BPB), diminished their ability to lyse K562 target cells by as much as 100%. The ability of NK cells to bind to K562 cells was significantly affected by BPB above 2 microM, but not by mepacrine at any concentration tested. This indicates that BPB is having effects on NK cells unrelated to its inhibition of PLA(2) activity at concentrations above 2 microM. The activation of phospholipase C in response to K562 cell binding (as measured by inositol phosphate turnover) was unaffected by inhibition of the PLA(2) activity. The products of PLA(2) catabolism are a fatty acid (often arachidonic acid) and a lysophospholipid. Inhibition of NK cytotoxicity by mepacrine or BPB is reversed significantly when lysophosphatidylcholine, but no other lysolipid, is added back to the NK cells before assaying for cytotoxicity. Arachidonic acid, but not linoleic acid, also significantly reverses inhibition of NK cytotoxicity. Finally, the 15-lipoxygenase product, 15S-hydroperoxyeicosatetraenoic acid (15S-HPETE), is also able to reverse mepacrine-induced inhibition of NK cytotoxicity. The 5-lipoxygenase product 5S-HPETE was not effective. These data indicate that PLA(2) activation is a necessary signal in human NK cytotoxicity and that it is not involved in protein tyrosine kinase and subsequent phospholipase C activation; these latter two enzymes are also required in the cytotoxic response. Thus PLA(2) activation is either a more distal signal, dependent on activation of some earlier signal, or an independent cosignal stimulated by tumor-target binding which generates lysophosphatidylcholine, arachidonic acid, and/or a lipoxygenase product(s).
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PMID:Lysophosphatidylcholine and arachidonic acid are required in the cytotoxic response of human natural killer cells to tumor target cells. 1074 96

The 3D structure of pancreatic lipase (PL) consists of two functional domains. The N-terminal domain belongs to the alpha/beta hydrolase fold and contains the active site, which involves a catalytic triad analogous to that present in serine proteases. The beta-sandwich C-terminal domain of PL plays an important part in the binding process between the lipase and colipase, the specific PL cofactor. Recent structure-function studies have suggested that the PL C-terminal domain may have an extra role apart from that of binding colipase. This domain contains an exposed hydrophobic loop (beta5') which was found to be located on the same side as the hydrophobic loops surrounding the active site, and it may be involved in the lipid binding process. Indirect evidence for this new function of the PL C-terminal domain has been provided by studies with monoclonal antibodies directed against the beta5' loop. The catalytic activity of the PL-antibody complexes on water insoluble substrates decreased drastically, whereas their esterase activity on a soluble substrate remained unchanged. During the last few years, a number of protein structures (15-lipoxygenase, alpha-toxin from Clostridium perfringens) have been determined that contain domains with close structural homologies with the beta-sandwich C-terminal domain of PL. Generally speaking, these domains show structural homologies with the C2 domains occurring in a wide range of proteins involved in signal transduction (e.g. phosphoinositide-specific phospholipase C, protein kinase C, cytosolic phospholipase A2), membrane traffic (e.g. synaptotagmin I, rabphilin) and membrane disruption (e.g. perforin). Here it is proposed to review the structure and function of the C2 domains, based on the recent 3D structures and improved sequence alignments.
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PMID:The C-terminal domain of pancreatic lipase: functional and structural analogies with c2 domains. 1236 22

ACh stimulates arachidonic acid (AA) release from membrane phospholipids of vascular endothelial cells (ECs). In rabbit aorta, AA is metabolized through the 15-lipoxygenase pathway to form vasodilatory eicosanoids 15-hydroxy-11,12-epoxyeicosatrienoic acid (HEETA) and 11,12,15-trihydroxyeicosatrienoic acid (THETA). AA is released from phosphatidylcholine (PC) and phosphatidylethanolamine (PE) by phospholipase A2 (PLA2), or from phosphatidylinositol (PI) by phospholipase C (PLC) pathway. The diacylglycerol (DAG) lipase can convert DAG into 2-arachidonoylglycerol from which free AA can be released by monoacylglycerol (MAG) lipase or fatty acid amidohydrolase (FAAH). We used specific inhibitors to determine the involvement of the PLC pathway in ACh-induced AA release. In rabbit aortic rings precontracted by phenylephrine, ACh induced relaxation in the presence of indomethacin and N(omega)-nitro-L-arginine (L-NNA). These relaxations were blocked by the PLC inhibitor U-73122, DAG lipase inhibitor RHC-80267, and MAG lipase/FAAH inhibitor URB-532. Cultured rabbit aortic ECs were labeled with [14C]AA and stimulated with methacholine (10(-5) M). Free [14C]AA was released by methacholine. Methacholine decreased the [14C]AA content of PI, DAG, and MAG fractions but not PC or PE fractions. Methacholine-induced release of [14C]AA was blocked by U-73122, RHC-80267, and URB-532 but not by U-73343, an inactive analog of U-73122. The data suggested that ACh activates PLC, DAG lipase, and MAG lipase pathway to release AA from membrane lipids. This pathway is important in regulating vasodilatory eicosanoid synthesis and vascular relaxation in rabbit aorta.
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PMID:Role of phospholipase C and diacylglyceride lipase pathway in arachidonic acid release and acetylcholine-induced vascular relaxation in rabbit aorta. 1602 67