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At least 487 records · Page 27Linked to original sources
PubMed1999

Regulation of cyclooxygenase-2 expression by phosphatidate phosphohydrolase in human amnionic WISH cells.

Prostaglandins are known to play a key role in the initiation of labor in humans, but the mechanisms governing their synthesis in amnion are largely unknown. In this study, we have examined the regulatory pathways for prostaglandin E(2) (PGE(2)) production during protein kinase C-dependent activation of human WISH cells. In these cells, PGE(2) synthesis appears to be limited not by free arachidonic acid availability but by the expression levels of cyclooxygenase-2 (COX-2). Concomitant with the cells being able to synthesize and secrete PGE(2), we detected significant elevations of both COX-2 protein and mRNA levels. Specific inhibition of COX-2 by NS-398 totally ablated PGE(2) synthesis. All of these responses were found to be strikingly dependent on an active phosphatidate phosphohydrolase 1 (PAP-1). Inhibition of PAP-1 activity by three different strategies (i.e. use of bromoenol lactone, propranolol, and ethanol) resulted in inhibition of COX-2 expression and hence of PGE(2) production. These data unveil a novel signaling mechanism for the regulation of PGE(2) production via regulation of COX-2 expression and implicate phosphatidate phosphohydrolase 1 as a key regulatory component of eicosanoid metabolic pathways in the amnion.

Amnion↗
PubMed1999

A phosphatidic acid-activated protein kinase and conventional protein kinase C isoforms phosphorylate p22(phox), an NADPH oxidase component.

Using a phosphorylation-dependent cell-free system to study NADPH oxidase activation (McPhail, L. C., Qualliotine-Mann, D., and Waite, K. A. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 7931-7935), we previously showed that p47(phox), a cytosolic NADPH oxidase component, is phosphorylated. Now, we show that p22(phox), a subunit of the NADPH oxidase component flavocytochrome b(558), also is phosphorylated. Phosphorylation is selectively activated by phosphatidic acid (PA) versus other lipids and occurs on a threonine residue in p22(phox). We identified two protein kinase families capable of phosphorylating p22(phox): 1) a potentially novel, partially purified PA-activated protein kinase(s) known to phosphorylate p47(phox) and postulated to mediate the phosphorylation-dependent activation of NADPH oxidase by PA and 2) conventional, but not novel or atypical, isoforms of protein kinase C (PKC). In contrast, all classes of PKC isoforms could phosphorylate p47(phox). In a gel retardation assay both the phosphatidic acid-dependent kinase and conventional PKC isoforms phosphorylated all molecules of p22(phox). These findings suggest that phosphorylation of p22(phox) by conventional PKC and/or a novel PA-activated protein kinase regulates the activation/assembly of NADPH oxidase.

Cell-Free System↗
PubMed2002

TAPAS-1, a novel microdomain within the unique N-terminal region of the PDE4A1 cAMP-specific phosphodiesterase that allows rapid, Ca2+-triggered membrane association with selectivity for interaction with phosphatidic acid.

Here we identify an 11-residue helical module in the unique N-terminal region of the cyclic AMP-specific phosphodiesterase PDE4A1 that determines association with phospholipid bilayers and shows a profound selectivity for interaction with phosphatidic acid (PA). This module contains a core bilayer insertion unit that is formed by two tryptophan residues, Trp(19) and Trp(20), whose orientation is optimized for bilayer insertion by the Leu(16):Val(17) pairing. Ca(2+), at submicromolar levels, interacts with Asp(21) in this module and serves to gate bilayer insertion, which is completed within 10 ms. Selectivity for interaction with PA is suggested to be achieved primarily through the formation of a charge network of the form (Asp(21-):Ca(2+):PA(2-):Lys(24+)) with overall neutrality at the bilayer surface. This novel phospholipid-binding domain, which we call TAPAS-1 (tryptophan anchoring phosphatidic acid selective-binding domain 1), is here identified as being responsible for membrane association of the PDE4A1 cAMP-specific phosphodiesterase. TAPAS-1 may not only serve as a paradigm for other PA-binding domains but also aid in detecting related phospholipid-binding domains and in generating simple chimeras for conferring membrane association and intracellular targeting on defined proteins.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2002

Tight binding inhibition of protein phosphatase-1 by phosphatidic acid. Specificity of inhibition by the phospholipid.

Phosphatidic acid (PA) has been identified as a bioactive lipid second messenger, yet despite extensive investigation, no cellular target has emerged as a mediator of its described biological effects. In this study, we identify the gamma isoform of the human protein phosphatase-1 catalytic subunit (PP1c gamma) as a high affinity in vitro target of PA. PA inhibited the enzyme dose-dependently with an IC(50) of 15 nm. Mechanistically, PA inhibited the enzyme noncompetitively with the kinetics of a tight binding inhibitor and a K(i) value of 0.97 +/- 0.24 nm. Together, these data describe one of the most potent in vitro effects of PA. To further elucidate the interaction between PA and PP1c gamma, structure/function analysis of the lipid was carried out using commercially available and synthetically generated analogs of PA. These studies disclosed that the lipid-protein interaction is dependent on the presence of the lipid phosphate as well as the presence of the fatty acid side chains, because lipids lacking either of these substituents resulted in complete loss of inhibition. However, the specific composition of the fatty acid side chains was not important for inhibition. Using 1-O-hexadecyl,2-oleoyl-PA, it was also shown that the carbonyl group of the sn-1 acyl linkage is not required for the lipid-protein interaction. Finally, using a lipid-protein overlay assay, it was demonstrated that PP1c gamma specifically and directly interacts with phosphatidic acid while not significantly binding other phospholipids. These results identify PA as a tight binding and specific inhibitor of PP1, and they raise the hypothesis that PP1c gamma may function as a mediator of PA action in cells. They also argue for the existence of a specific high affinity PA-binding domain on the enzyme.

Escherichia coli↗
PubMed2006

The Saccharomyces cerevisiae Lipin homolog is a Mg2+-dependent phosphatidate phosphatase enzyme.

Mg(2+)-dependent phosphatidate (PA) phosphatase (3-sn-phosphatidate phosphohydrolase, EC 3.1.3.4) catalyzes the dephosphorylation of PA to yield diacylglycerol and P(i). In this work, we identified the Saccharomyces cerevisiae PAH1 (previously known as SMP2) gene that encodes Mg(2+)-dependent PA phosphatase using amino acid sequence information derived from a purified preparation of the enzyme (Lin, Y.-P., and Carman, G. M. (1989) J. Biol. Chem. 264, 8641-8645). Overexpression of PAH1 in S. cerevisiae directed elevated levels of Mg(2+)-dependent PA phosphatase activity, whereas the pah1Delta mutation caused reduced levels of enzyme activity. Heterologous expression of PAH1 in Escherichia coli confirmed that Pah1p is a Mg(2+)-dependent PA phosphatase enzyme and showed that its enzymological properties were very similar to those of the enzyme purified from S. cerevisiae. The PAH1-encoded enzyme activity was associated with both the membrane and cytosolic fractions of the cell, and the membrane-bound form of the enzyme was salt-extractable. Lipid analysis showed that mutants lacking PAH1 accumulated PA and had reduced amounts of diacylglycerol and its derivative triacylglycerol.ThePAH1-encoded Mg(2+)-dependent PA phosphatase shows homology to mammalian lipin, a fat-regulating protein whose molecular function is unknown. Heterologous expression of human LPIN1 in E. coli showed that lipin 1 is also a Mg(2+)-dependent PA phosphatase enzyme.

Cell Membrane↗
PubMed2006

Lipopolysaccharide-induced cyclooxygenase-2 expression in human U937 macrophages is phosphatidic acid phosphohydrolase-1-dependent.

Cyclooxygenase (COX) has two isoforms, COX-1 and -2, which catalyze the key step in the conversion of cellular arachidonic acid into prostaglandins. In recent years, interest in COX-2 has significantly increased since it has been a target for the development of specific non-steroidal anti-inflammatory drugs. We report that COX-2 expression is up-regulated in phorbol ester (phorbol myristate acetate, PMA)-differentiated human U937 macrophage-like cells stimulated with lipopolysaccharide (LPS), whereas COX-1 is not up-regulated. We show that the LPS-induced up-regulation of COX-2 depends on the activity of the Mg(+2)-dependent phosphatidic acid phosphohydrolase 1 (PAP-1). Inhibition of PAP-1 by bromoenol lactone, propranolol, or ethanol resulted in a decrease in LPS-induced COX-2 mRNA transcript production, COX-2 protein expression, and prostaglandin E(2) release from U937 macrophages. To ensure that these results did not arise because of PMA treatment of the U937 cells, similar experiments were conducted with the P388D(1) cell line, which does not require PMA differentiation. LPS increased the levels of endogenous cellular diacylglycerol (DAG) within 2 min of stimulation. This increase was observed to be sensitive to the PAP-1 inhibitors. Furthermore, phosphatidic acid phosphohydrolase activity assays showed that the bromoenol lactone-sensitive PAP-1 activity was translocated from the cytosolic fraction to the membrane fraction within 2 min of LPS exposure. Finally, DAG add-back experiments demonstrate that LPS-induced COX-2 expression is enhanced by the addition of exogenous DAG.

Animals↗
PubMed2006

Three mammalian lipins act as phosphatidate phosphatases with distinct tissue expression patterns.

We previously identified mutations in the Lpin1 gene, encoding lipin-1, as the underlying cause of lipodystrophy in the fatty liver dystrophy (fld) mutant mouse. Lipin-1 is normally expressed at high levels in adipose tissue and skeletal muscle, and deficiency in the fld mouse causes impaired adipose tissue development, insulin resistance, and altered energy expenditure. We also identified two additional lipin protein family members of unknown function, lipin-2 and lipin-3. Han et al. (Han, G. S., Wu, W. I., and Carman, G. M. (2006) J. Biol. Chem. 281, 9210-9218) recently demonstrated that the single lipin homolog in yeast, Smp2, exhibits phosphatidate phosphatase type-1 (PAP1) activity, which has a key role in glycerolipid synthesis. Here we demonstrate that lipin-1 accounts for all of the PAP1 activity in white and brown adipose tissue and skeletal muscle. However, livers of lipin-1-deficient mice exhibited normal PAP1 activity, indicating that other members of the lipin protein family could have PAP1 activity. Consistent with this possibility, recombinant lipin-2 and lipin-3 possess PAP1 activity. Each of the three lipin family members showed Mg2+-dependent activity that was specific for phosphatidate under the conditions employed. The different lipins showed distinct tissue expression patterns. Our results establish the three mammalian lipin proteins as PAP1 enzymes and explain the biochemical basis for lipodystrophy in the lipin-1-deficient fld mouse.

Adipose Tissue, Brown↗
PubMed2006

Phospholipid signalling through phospholipase D and phosphatidic acid.

Phospholipase D (PLD) hydrolyzes the phosphodiester bond of the predominant membrane phospholipid, phosphatidylcholine producing phosphatidic acid and free choline. This activity can participate in signal transduction pathways and impact on vesicle trafficking for secretion and endocytosis, as well as receptor signalling. Phospholipids can regulate PLD activity directly, through specific intermolecular interactions, or indirectly, through their effect on the localization or activity of PLD's protein effectors. This short review highlights these various phospholipid inputs into the regulation of PLD activity and also reviews potential roles for PLD-generated phosphatidic acid, particularly a mechanism by which the phospholipid may participate in the process of vesicular trafficking.

ADP-Ribosylation Factors↗
PubMed1998

Molecular cloning of two alternatively spliced forms of human phosphatidic acid phosphatase cDNAs that are differentially expressed in normal and tumor cells.

Phosphatidic acid (PA) and diacylglycerol (DG) are lipids involved in signal transduction and in structural membrane-lipid biosynthesis in cells. Phosphatidic acid phosphatase (PAP) catalyzes the conversion of PA to DG. This enzyme exists in at least two isoforms, one of which (PAP1) is presumed to be cytosolic and membrane associated and the other (PAP2) to be an integral membrane protein. Homology search of the GenBank database using a murine sequence probe enabled the cloning of several putative human isoenzymes. Two isoforms, presumed to be alternative splice variants from a single gene, designated as PAP2-alpha1 and PAP2-alpha2, have been cloned and expressed. The PAP2-alpha1 and PAP2-alpha2 have a 84% and a 72% overall match, respectively, with the published mouse PAP amino acid sequence. The area of alternative exon usage was confined to the coding region at amino acids 20 to 70. Ectopic expression of PAP2-alpha1 and PAP2-alpha2 cDNAs in ECV304 endothelial cells led to a 6- to 8-fold and a 2-fold increase in PAP activity, respectively, in cell-free extracts using an in vitro assay that measured the conversion of [14C]PA to [14C]DG. The increase in PAP activity in PAP2-alpha-transfected cells correlated with a >50% decrease in the steady-state PA level. Northern analysis showed that PAP2-alpha mRNA expression was suppressed in several tumor tissues, notably those derived from the lower alimentary tract. Subsequent analysis of colon tumor tissue derived from four donors confirmed lower expression of PAP2-alpha than in matching normal colon tissue. Considering these data and previous demonstrations that certain transformed cell lines have lower PAP activity, we suggest that human PAP cDNAs may be candidates for gene therapy for certain tumors.

Alternative Splicing↗
PubMed1999

Sequential actions of phospholipase D and phosphatidic acid phosphohydrolase 2b generate diglyceride in mammalian cells.

Phosphatidylcholine (PC) is a major source of lipid-derived second messenger molecules that function as both intracellular and extracellular signals. PC-specific phospholipase D (PLD) and phosphatidic acid phosphohydrolase (PAP) are two pivotal enzymes in this signaling system, and they act in series to generate the biologically active lipids phosphatidic acid (PA) and diglyceride. The identity of the PAP enzyme involved in PLD-mediated signal transduction is unclear. We provide the first evidence for a functional role of a type 2 PAP, PAP2b, in the metabolism of PLD-generated PA. Our data indicate that PAP2b localizes to regions of the cell in which PC hydrolysis by PLD is taking place. Using a newly developed PAP2b-specific antibody, we have characterized the expression, posttranslational modification, and localization of endogenous PAP2b. Glycosylation and localization of PAP2b appear to be cell type and tissue specific. Biochemical fractionation and immunoprecipitation analyses revealed that PAP2b and PLD2 activities are present in caveolin-1-enriched detergent-resistant membrane microdomains. We found that PLD2 and PAP2b act sequentially to generate diglyceride within this specialized membrane compartment. The unique lipid composition of these membranes may provide a selective environment for the regulation and actions of enzymes involved in signaling through PC hydrolysis.

Amino Acid Sequence↗
PubMed1991

The mitogenic activities of phosphatidate are acyl-chain-length dependent and calcium independent in C3H/10T1/2 cells.

Phosphatidates (PA or phosphatidic acid) were shown to have mitogenic properties, including the stimulation of DNA synthesis and calcium mobilization in C3H/10T1/2 cells. Their continuous presence for a minimum of 7 h induced DNA synthesis with kinetics similar to that observed when 10% fetal bovine serum was used as a mitogen. PAs with long chain saturated fatty acid moieties were more mitogenic, in a dose-dependent fashion, than PAs with short saturated or unsaturated fatty acid moieties. When compared with lysostearoyl-PA (LSPA), distearoyl-PA (DSPA) was as potent with respect to the induction of DNA synthesis. Lysooleoyl-PA (LOPA) was slightly more potent than dioleoyl-PA (DOPA), but much weaker than DSPA and LSPA. Preincubation with dilauroyl-PA (DLPA) reduces the mitogenic effect of DSPA by 85%. The pattern of mitogenic inhibition suggests that a chain-length-independent, yet PA-specific, mechanism is involved. Both DSPA and DLPA are equally taken up by the cells after 30 min. LOPA, but not LSPA, produced a large calcium transient (1.3 microM), which we found to be derived from intracellular sources. DSPA, the most mitogenic PA tested, produced a weaker transient (0.6 microM). Interestingly, LSPA did not produce any detectable calcium transient. These results suggest that the chain-length-specific step in the signaling mechanism of PA occurs after the initial chain-length-independent partitioning and/or binding to the membrane and that the induction of DNA synthesis is not related to the observed calcium transients.

Animals↗
PubMed1994

Phosphatidic acid induces the release of beta-glucuronidase but not lactoferrin from electropermeabilized human neutrophils.

We studied the degranulation reaction of electropermeabilized human neutrophils induced by 1,2-didecanoyl-3-sn-phosphatidic acid (PA10). PA10 dose-dependently induced the release of beta-glucuronidase, an enzyme of azurophil granules, but did not induce the release of lactoferrin, a protein of specific granules. The enzyme release by PA10 absolutely required Ca2+, ATP, and Mg2+ and the concentrations for the half-maximal response were 2.5 microM, 60 microM, and 0.25 mM, respectively. Although Ca2+ alone at concentrations higher than 10 microM induced the release of both beta-glucuronidase and lactoferrin, the extents of the release were far less than that of the beta-glucuronidase release by PA10. Phorbol myristate acetate (PMA) and 1-oleoyl-2-acetyl-sn-glycerol induced the release of lactoferrin alone at concentrations of Ca2+ below 0.5 microM while they induced the release of both beta-glucuronidase and lactoferrin at higher Ca2+ concentrations, indicating that the degranulation induced by PA10 is not mediated by diacylglycerol which might be formed from PA. The degranulation reactions induced by PA10 and PMA were dose-dependently inhibited by staurosporine and calphostin C, protein kinase C inhibitors, although no direct activation of protein kinase C by PA10 was observed. The extent of the beta-glucuronidase release by PA10 was not enhanced by the addition of PMA. Propranolol, which inhibits protein kinase C as well as phosphatidic acid phosphohydrolase, strongly inhibited the degranulation reactions induced by PA10 and PMA. Ethanol, a metabolic modulator of phospholipase D, and cyclic AMP did not affect the degranulation reactions by PMA and PA10.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1982

Rapid breakdown of phosphatidylinositol accompanied by accumulation of phosphatidic acid and diacylglycerol in rat lymphocytes stimulated by concanavalin A.

Concanavalin A stimulated the [32P]phosphate incorporation into phospholipids of rat lymph-node cells in a dose-dependent manner up to 200 microgram of the lectin per ml of the lymphocyte culture. The initial step in the concanavalin A-stimulated phospholipid metabolism was examined by use of rat lymphocytes prelabeled with radioactive arachidonic acid. Concanavalin A induced a small but significant decrease, up to 10%, in the phosphatidylinositol radiolabel at 1 to 5 min after the lectin addition. A small increase, about 10%, in the diacylglycerol radiolabel and a twofold increase in the phosphatidate radiolabel were observed concomitant with the breakdown of phosphatidylinositol. The increase in the phosphatidic acid radioactivity amounted to about one-fifth of the decrease in the phosphatidylinositol radioactivity. No significant change in radiolabel was found in the other major phospholipids or in triacylglycerol. The results suggest that the breakdown of pre-existing phosphatidylinositol is the initial step in the lymphocyte phosphatidylinositol response.

Animals↗
PubMed1992

Regulation of phosphatidic acid phosphohydrolase activity during stimulation of human polymorphonuclear leukocytes.

Phosphatidic acid phosphohydrolase (PPH) activity was determined in human polymorphonuclear leukocytes (PMNs) by measuring the hydrolysis of [32P]phosphatidic acid (PA) added to cell sonicates. Enzyme activity was localized primarily to a soluble fraction. Soluble and particulate activities required magnesium and were inhibited by calcium, N-ethylmaleimide, sphingosine, and propranolol. The activity in unstimulated PMNs was 0.64 +/- 0.11 nmol of PA hydrolyzed.mg protein-1.min-1 in particulate and 4.20 +/- 0.42 in soluble fractions. Stimulation of PMNs with 1 microM f-Met-Leu-Phe (FMLP) for 10 min caused a slight decrease in soluble activity and a small increase in the activity of particulate fractions. Preincubation with 10 microM cytochalasin B for 5 min before FMLP stimulation markedly enhanced both of these changes. The effect of FMLP plus cytochalasin B was rapid (less than 10 s), whereas the calcium ionophore A23187 (1 microM) and phorbol myristate acetate (100 ng/ml) caused slower and smaller changes in enzyme activity. These results indicate that after chemoattractant stimulation; PPH activity decreases in the soluble fraction and increases in the particulate fraction suggesting that PPH may participate in signal transduction in the PMN.

Calcimycin↗
PubMed2024

DGKH-mediated phosphatidic acid oncometabolism as a driver of self-renewal and therapy resistance in HCC.

BACKGROUND AND AIMS: HCC is characterized by metabolic pathway aberrations, which enable cancer cells to meet their energy demands and accelerate malignant progression. Identifying novel metabolic players governing therapy resistance and self-renewal in HCC is crucial, as these properties are likely responsible for tumor recurrence. APPROACH AND RESULTS: Clinical traits and RNA-seq of patients with HCC in The Cancer Genome Atlas were used for weighted gene coexpression network analysis, where 1 module was significantly correlated with advanced pathological stage and stem cell population maintenance. Further analysis of this module by integrating data obtained from HCC patient nonresponders to tyrosine kinase inhibitors identified 361 commonly deregulated genes. Intriguingly, these genes are significantly enriched in the intracellular signal transduction pathway, with diacylglycerol kinase eta (DGKH) ranked as the most enriched gene in poorly differentiated HCC tumors. Clinically, DGKH was elevated in tumor tissues compared to nontumor tissues. Patients with higher DGKH expression exhibited a more undifferentiated state and were less responsive to tyrosine kinase inhibitors. Functional assays using DGKH-manipulated HCC cell lines demonstrated that DGKH augmented aggressive features, including cancer stemness, therapy resistance, and metastasis. Upstream of DGKH , we discovered that the E1A-associated protein p300 (EP300) binds to DGKH's promoter region, thereby increasing its transcriptomic expression. Mechanistically, DGKH promotes mTOR signaling by producing phosphatidic acid. In an immunocompetent mouse model, cotreatment with sorafenib and liver-directed AAV8-mediated Dgkh depletion significantly reduced tumor burden, self-renewal, phosphatidic acid production, and mTOR signaling. CONCLUSIONS: Our research demonstrated that DGKH is a crucial oncometabolic regulator of cancer stemness and therapy resistance, suggesting that inhibiting DGKH may lead to more effective HCC treatment.

Humans↗
PubMed1986

Metabolism of phosphatidyl-dCMP in sarcoma 180 cells. Effect of chlorpromazine, phosphatidic acid and inositol.

The synthesis and degradation of phosphatidyl-dCMP was studied in intact and permeabilized Sarcoma 180 cells as well as in isolated nuclei. It was verified that chlorpromazine greatly enhanced phosphatidyl-dCMP synthesis and completely abolished its hydrolysis in intact cells. The former effect was reversible and was partially lost upon permeabilization or isolation of nuclei. Phosphatidic acid also increased liponucleotide synthesis and the combination of phosphatidic acid with chlorpromazine was not additive. When inositol was added to cells which had accumulated phosphatidyl-[3H]dCMP, the recovery of radioactivity in the organic phase decreased; this effect was dose-dependent and specific for inositol, and was accompanied by an increased release of [3H]dCMP to the cell medium. In isolated microsomes, addition of Ptd-dCMP determined incorporation of [3H]inositol into phosphatidyl-inositol. These results strongly suggest that phosphatidyl-dCMP is utilized for the synthesis of phosphatidyl-inositol.

Animals↗
PubMed1992

Bimodal distribution of phosphatidic acid phosphohydrolase in NG108-15 cells. Modulation by the amphiphilic lipids oleic acid and sphingosine.

The properties and bimodal distribution of phosphatidic acid phosphohydrolase (PAP) were investigated in neuroblastoma X glioma hybrid NG108-15 cells. Two PAP activities distinguished by their differential sensitivity to Mg2+ and Triton X-100 were identified in the cytosolic and microsomal fractions. A digitonin permeabilization method was employed to study the basal distribution of the cytosolic PAP and its redistribution upon cell exposure to amphiphilic lipids. Under conditions which release 100% of the cytosolic marker enzyme lactate dehydrogenase, only 60% of total cellular PAP activity was released into the medium through the digitonin-induced membrane pores, suggesting that about 40% of the total are membrane associated. Elevated plasma-membrane levels of phosphatidic acid, accomplished by incubating cells with Streptomyces chromofuscus phospholipase D, did not affect the distribution of cytosolic PAP. In contrast, oleic acid induced a marked concentration-dependent redistribution of the cytosolic enzyme to the particulate fraction. PAP redistribution was completely abolished in the presence of the sphingoid base sphingosine, previously shown to inhibit PAP activity in vitro (Lavie, Y., Piterman, O. & Liscovitch, M. (1990) FEBS Lett. 277, 7-10). Thus, the distribution of cytosolic PAP is reciprocally regulated by a long-chain (fatty) acid and a long-chain (sphingoid) base which are breakdown products of phospholipids and sphingolipids, respectively. These effects might influence PAP function in glycerolipid metabolism and signal transduction under physiological and pathophysiological conditions.

Cations, Divalent↗
PubMed2004

Regulation of phospholipid biosynthesis by phosphatidylinositol transfer protein Sec14p and its homologues. A critical role for phosphatidic acid.

Transcription of yeast phospholipid biosynthesis structural genes, which contain an inositol-sensitive upstream activating sequence in their promoters, responds to the availability of the soluble precursors inositol and choline and to changes in phospholipid metabolism. The INO1 gene is deregulated (derepressed when inositol is present) under the conditions of increased phosphatidylcholine (PtdCho) turnover, as occurs in the sec14Delta cki1Delta strain (SEC14 encodes the major yeast phosphatidylinositol transfer protein; CKI1 encodes choline kinase of the cytidine diphosphate choline pathway of PtdCho biosynthesis). Five proteins (Sfhp) share sequence homology with phosphatidylinositol transfer protein Sec14p. Two (Sfh2p and Sfh4p), when overexpressed largely complement the otherwise essential Sec14p requirement concerning growth and secretion. In this study, we analysed the ability of Sec14 homologues to correct the defect in regulation of phospholipid biosynthesis resulting from defective or missing Sec14p. We also analysed how PtdCho turnover relates to the transcriptional regulation of phospholipid biosynthesis. The results show that (a) none of the Sec14 homologues was able to substitute for Sec14p in its regulatory aspects of phospholipid biosynthesis, (b) removal of phospholipase D activity corrected the aberrant INO1 gene regulation in yeast strains with otherwise high PtdCho turnover, and (c) increased steady-state phosphatidic acid levels correlated with derepressed levels of the INO1 gene. Overall, the results support the model in which high phosphatidic acid levels lead to derepression of the genes of phospholipid biosynthesis [Henry, S.A. & Patton-Vogt, J.L. (1998) Prog. Nucleic Acid Res. Mol. Biol.61, 133-179].

Gene Expression Regulation, Enzymologic↗