Enzymatic analysis of lipid phosphate phosphatases

Phosphate Assay Kit in One Cell for Electrochemical Detection of Intracellular Phosphate Ions at Single Cells

In this paper, phosphate assay kit in one cell is realized for the electrochemical detection of intracellular phosphate ions at single cells. The components of the phosphate assay kit, including maltose phosphorylase, maltose, mutarotase, and glucose oxidase, are electrochemically injected into a living cell through a nanometer-sized capillary with the ring electrode at the tip. These components react with phosphate ions inside the cell to generate hydrogen peroxide that is electrochemically oxidized at the ring electrode for the qualification of intracellular phosphate ions. An average 1.7 nA charge was collected from eight individual cells, suggesting an intracellular phosphate concentration of 2.1 mM. The establishment in the electrochemical measurement of phosphate ions provides a special strategy to monitor the fluctuation of intracellular phosphate at single cells, which is significant for the future investigation of phosphate signal transduction pathway.

Discovery and characterization of selective human sphingomyelin synthase 2 inhibitors

Sphingomyelin synthase (SMS) is a membrane enzyme that catalyzes the synthesis of sphingomyelin, is required for the maintenance of plasma membrane microdomain fluidity, and has two isoforms: SMS1 and SMS2. Although these isoforms exhibit the same SMS activity, they are different enzymes with distinguishable subcellular localizations. It was reported that SMS2 KO mice displayed lower inflammatory responses and anti-atherosclerotic effects, suggesting that inhibition of SMS2 would be a potential therapeutic approach for controlling inflammatory responses and atherosclerosis. This study aimed to discover a novel small-molecule compound that selectively inhibits SMS2 enzymatic activity. We developed a human SMS2 enzyme assay with a high-throughput mass spectrometry-based screening system. We characterized the enzymatic properties of SMS2 and established a high-throughput screening-compatible assay condition. To identify human SMS2 inhibitors, we conducted compound screening using the enzyme assay. We identified a 2-quinolone derivative as a SMS2 selective inhibitor with an IC₅₀ of 950 nM and >100-fold selectivity for SMS2 over SMS1. The 2-quinolone exhibited efficacy in a cell-based engagement assay. We demonstrated that a more potent derivative directly bound to SMS2-expressing membrane fractions in an affinity selection mass spectrometry assay. Mutational analyses revealed that the interaction of the inhibitor with SMS2 required the presence of the amino acids S227 and H229, which are located in the catalytic domain of SMS2. In conclusion, we discovered novel SMS2-selective inhibitors. 2-Quinolone SMS2 inhibitors are considered applicable for leading optimization studies. Further investigations using these SMS2 inhibitors would provide validation tools for SMS2-relevant pathways in vitro and in vivo.

PLD Protein-Protein Interactions With Signaling Molecules and Modulation by PA

We describe methods for studying phospholipase D (PLD) interactions with signaling proteins and modulation of these interactions by the PLD reaction product, phosphatidic acid (PA). PLD is fundamental to the physiological maintenance of cellular/intracellular membranes, protein trafficking, cytoskeletal dynamics, membrane remodeling, cell proliferation, meiotic division and sporulation. PA is an acidic phospholipid involved in the biosynthesis of many other lipids that affects the enzymatic activities of many different signaling proteins via protein-lipid interactions or as a substrate. The involvement of PLD as an effector of protein-protein interactions and downstream signaling via PA-mediated processes has led to the investigation of PA-binding domains in target protein partners. We present here data and protocols detailing the interaction between PLD2-Rac2 interaction and modulation of this interaction by PA. We describe biochemical techniques to measure interactions between PLD, PA, and the small GTPase Rac2, which are associated in the cell. We found two maxima concentrations of PA that contributed to association or dissociation of Rac2 with PLD2, as well as the PLD2 lipase and guanine nucleotide exchange factor (GEF) activities. Fluctuations in the Rac2-PLD2 protein-protein binding interaction facilitate shuttling of Rac2 and/or PLD2 within the cell dependent on local cellular PA concentration. Fluorescence resonance emission transfer stoichiometry for PLD2 and Rac2 binding yielded a 3:1 ratio of Rac2:PLD2. Detection of PA in mammalian cells with a new biosensor showed colocalization in and around the nucleus. We also described methods for quantitation of PA in biological materials by HPLC electrospray ionization tandem mass spectrometry.

LPP3 localizes LPA6 signalling to non-contact sites in endothelial cells

Lysophosphatidic acid (LPA) is emerging as an angiogenic factor, because knockdown of the enzyme that produces it (autotaxin, also known as ENPP2) and its receptors cause severe developmental vascular defects in both mice and fish. In addition, overexpression of autotaxin in mice causes similar vascular defects, indicating that the extracellular amount of LPA must be tightly regulated. Here, we focused on an LPA-degrading enzyme, lipid phosphate phosphatase 3 (LPP3, also known as PPAP2B), and showed that LPP3 was localized in specific cell–cell contact sites of endothelial cells and suppresses LPA signalling through the LPA₆ receptor (also known as LPAR6). In HEK293 cells, overexpression of LPP3 dramatically suppressed activation of LPA₆. In human umbilical vein endothelial cells (HUVECs), LPA induced actin stress fibre formation through LPA₆, which was substantially upregulated by LPP3 knockdown. LPP3 was localized to cell–cell contact sites and was missing in non-contact sites to which LPA-induced actin stress fibre formation mediated by LPA₆ was restricted. Interestingly, the expression of LPP3 in HUVECs was dramatically increased after forskolin treatment in a process involving Notch signalling. These results indicate that LPP3 regulates and localizes LPA signalling in endothelial cells, thereby stabilizing vessels through Notch signalling for proper vasculature.

Summary: In endothelial cells, the membrane-bound LPA-degrading enzyme LPP3 is specifically expressed at cell–cell contact sites, thereby localizing the signal evoked by extracellularly produced LPA.

Arguing the case for the autotaxin-lysophosphatidic acid-lipid phosphate phosphatase 3-signaling nexus in the development and complications of atherosclerosis

The structurally simple glycero- and sphingo-phospholipids, lysophosphatidic acid (LPA) and sphingosine-1-phosphate, serve as important receptor-active mediators that influence blood and vascular cell function and are positioned to influence the events that contribute to the progression and complications of atherosclerosis. Growing evidence from preclinical animal models has implicated LPA, LPA receptors, and key enzymes involved in LPA metabolism in pathophysiologic events that may underlie atherosclerotic vascular disease. These observations are supported by genetic analysis in humans implicating a lipid phosphate phosphatase as a novel risk factor for coronary artery disease. In this review, we summarize current understanding of LPA production, metabolism, and signaling as may be relevant for atherosclerotic and other vascular disease.

Differential display of abundantly expressed genes of Trichoderma harzianum during colonization of tomato-germinating seeds and roots

The identification of Trichoderma genes whose expression is altered during early stages of interaction with developing roots of germinated seeds is an important step toward understanding the rhizosphere competency of Trichoderma spp. The potential of 13 Trichoderma strains to colonize tomato root and promote plant growth has been evaluated. All used strains successfully propagated in spermosphere and continued their growth in rhizoplane simultaneously root enlargement while the strains T6 and T7 were the most abundant in the apical segment of roots. Root colonization in most strains associated with promoting the roots and shoots growth while they significantly increased up to 43 and 40 % roots and shoots dry weights, respectively. Differential display reverse transcriptase-PCR (DDRT-PCR) has been developed to detect differentially expressed genes in the previously selected strain, Trichoderma harzianum T7, during colonization stages of tomato-germinating seeds and roots. Amplified DDRT-PCR products were analyzed on gel agarose and 62 differential bands excised, purified, cloned, and sequenced. Obtained ESTs were submit-queried to NCBI database by BLASTx search and gene ontology hierarchy. Most of transcripts (29 EST) corresponds to known and hypothetical proteins such as secretion-related small GTPase, 40S ribosomal protein S3a, 3-hydroxybutyryl-CoA dehydrogenase, DNA repair protein rad50, lipid phosphate phosphatase-related protein type 3, nuclear essential protein, phospholipase A2, fatty acid desaturase, nuclear pore complex subunit Nup133, ubiquitin-activating enzyme, and 60S ribosomal protein L40. Also, 13 of these sequences showed no homology (E > 0.05) with public databases and considered as novel genes. Some of these ESTs corresponded to genes encodes enzymes potentially involved in nutritional support of microorganisms which have obvious importance in the establishment of Trichoderma in spermosphere and rhizosphere, via potentially functioning in acquisition of nutrients from energy-rich carbon compounds leaked from the germinating seeds and roots.

Stored platelets alter glycerophospholipid and sphingolipid species, which are differentially transferred to newly released extracellular vesicles

BACKGROUND

Stored platelet concentrates (PLCs) for transfusion develop a platelet storage lesion (PSL), resulting in decreased platelet (PLT) viability and function. The processes leading to PSL have not been described in detail and no data describe molecular changes occurring in all three components of stored PLCs: PLTs, PLC extracellular vesicles (PLC-EVs), and plasma.

STUDY DESIGN AND METHODS

Fifty PLCs from healthy individuals were stored under standard blood banking conditions for 5 days. Changes in cholesterol, glycerophospholipid, and sphingolipid species were analyzed in PLTs, PLC-EVs, and plasma by mass spectrometry and metabolic labeling. Immunoblots were performed to compare PLT and PLC-EV protein expression.

RESULTS

During 5 days, PLTs transferred glycerophospholipids, cholesterol, and sphingolipids to newly formed PLC-EVs, which increased corresponding lipids by 30%. Stored PLTs significantly increased ceramide (Cer; +53%) and decreased sphingosine-1-phosphate (-53%), shifting sphingolipid metabolism toward Cer. In contrast, plasma accumulated minor sphingolipids. Compared to PLTs, fresh PLC-EVs were enriched in lysophosphatidic acid (60-fold) and during storage showed significant increases in cholesterol, sphingomyelin, dihydrosphingomyelin, plasmalogen, and lysophosphatidylcholine species, as well as accumulation of apolipoproteins A-I, E, and J/clusterin.

CONCLUSION

This is the first detailed analysis of lipid species in all PLC components during PLC storage, which might reflect mechanisms active during in vivo PLT senescence. Stored PLTs reduce minor sphingolipids and shift sphingolipid metabolism toward Cer, whereas in the plasma fraction minor sphingolipids increase. The composition of PLC-EVs resembles that of lipid rafts and confirms their role as carriers of bioactive molecules and master regulators in vascular disease.

Lipid phosphate phosphatase inhibitors locally amplify lysophosphatidic acid LPA1 receptor signalling in rat brain cryosections without affecting global LPA degradation

Background

Lysophosphatidic acid (LPA) is a signalling phospholipid with multiple biological functions, mainly mediated through specific G protein-coupled receptors. Aberrant LPA signalling is being increasingly implicated in the pathology of common human diseases, such as arteriosclerosis and cancer. The lifetime of the signalling pool of LPA is controlled by the equilibrium between synthesizing and degradative enzymatic activity. In the current study, we have characterized these enzymatic pathways in rat brain by pharmacologically manipulating the enzymatic machinery required for LPA degradation.

Results

In rat brain cryosections, the lifetime of bioactive LPA was found to be controlled by Mg²⁺-independent, N-ethylmaleimide-insensitive phosphatase activity, attributed to lipid phosphate phosphatases (LPPs). Pharmacological inhibition of this LPP activity amplified LPA₁ receptor signalling, as revealed using functional autoradiography. Although two LPP inhibitors, sodium orthovanadate and propranolol, locally amplified receptor responses, they did not affect global brain LPA phosphatase activity (also attributed to Mg²⁺-independent, N-ethylmaleimide-insensitive phosphatases), as confirmed by P_i determination and by LC/MS/MS. Interestingly, the phosphate analog, aluminium fluoride (AlF_x^-) not only irreversibly inhibited LPP activity thereby potentiating LPA₁ receptor responses, but also totally prevented LPA degradation, however this latter effect was not essential in order to observe AlF_x^--dependent potentiation of receptor signalling.

Conclusions

We conclude that vanadate- and propranolol-sensitive LPP activity locally guards the signalling pool of LPA whereas the majority of brain LPA phosphatase activity is attributed to LPP-like enzymatic activity which, like LPP activity, is sensitive to AlF_x^- but resistant to the LPP inhibitors, vanadate and propranolol.

Role of soluble epoxide hydrolase phosphatase activity in the metabolism of lysophosphatidic acids

The EPXH2 gene encodes for the soluble epoxide hydrolase (sEH), which has two distinct enzyme activities: epoxide hydrolase (Cterm-EH) and phosphatase (Nterm-phos). The Cterm-EH is involved in the metabolism of epoxides from arachidonic acid and other unsaturated fatty acids, endogenous chemical mediators that play important roles in blood pressure regulation, cell growth, inflammation and pain. While recent findings suggested complementary biological roles for Nterm-phos, its mode of action is not well understood. Herein, we demonstrate that lysophosphatidic acids are excellent substrates for Nterm-phos. We also showed that sEH phosphatase activity represents a significant (20-60%) part of LPA cellular hydrolysis, especially in the cytosol. This possible role of sEH on LPA hydrolysis could explain some of the biology previously associated with the Nterm-phos. These findings also underline possible cellular mechanisms by which both activities of sEH (EH and phosphatase) may have complementary or opposite roles.

Regulation of phosphatidic Acid metabolism by sphingolipids in the central nervous system

This paper explores the way ceramide, sphingosine, ceramide 1-phosphate, and sphingosine 1-phosphate modulate the generation of second lipid messengers from phosphatidic acid in two experimental models of the central nervous system: in vertebrate rod outer segments prepared from dark-adapted retinas as well as in rod outer segments prepared from light-adapted retinas and in rat cerebral cortex synaptosomes under physiological aging conditions. Particular attention is paid to lipid phosphate phosphatase, diacylglycerol lipase, and monoacylglycerol lipase. Based on the findings reported in this paper, it can be concluded that proteins related to phototransduction phenomena are involved in the effects derived from sphingosine 1-phosphate/sphingosine or ceramide 1-phosphate/ceramide and that age-related changes occur in the metabolism of phosphatidic acid from cerebral cortex synaptosomes in the presence of either sphingosine 1-phosphate/sphingosine or ceramide 1-phosphate/ceramide. The present paper demonstrates, in two different models of central nervous system, how sphingolipids influence phosphatidic acid metabolism under different physiological conditions such as light and aging.

Functional characterization of the atypical integral membrane lipid phosphatase PDP1/PPAPDC2 identifies a pathway for interconversion of isoprenols and isoprenoid phosphates in mammalian cells

The polyisoprenoid diphosphates farnesyl diphosphate (FPP) and geranylgeranyl diphosphate (GGPP) are intermediates in the synthesis of cholesterol and related sterols by the mevalonate pathway and precursors for the addition of isoprenyl anchors to many membrane proteins. We developed tandem mass spectrometry assays to evaluate polyisoprenoid diphosphate phosphatase activity of an unusual integral membrane lipid enzyme: type 1 polyisoprenoid diphosphate phosphatase encoded by the PPAPDC2 gene (PDP1/PPAPDC2). In vitro, recombinant PDP1/PPAPDC2 preferentially hydrolyzed polyisoprenoid diphosphates, including FPP and GGPP over a variety of glycerol- and sphingo-phospholipid substrates. Overexpression of mammalian PDP1/PPAPDC2 in budding yeast depletes cellular pools of FPP leading to growth defects and sterol auxotrophy. In mammalian cells, PDP1/PPAPDC2 localizes to the endoplasmic reticulum and nuclear envelope and, unlike the structurally related lipid phosphate phosphatases, is predicted to be oriented with key residues of its catalytic domain facing the cytoplasmic face of the membrane. Studies using synthetic isoprenols with chemical properties that facilitate detection by mass spectrometry identify a pathway for interconversion of isoprenols and isoprenoid diphosphates in intact mammalian cells and demonstrate a role for PDP1/PPAPDC2 in this process. Overexpression of PDP1/PPAPDC2 in mammalian cells substantially decreases protein isoprenylation and results in defects in cell growth and cytoskeletal organization that are associated with dysregulation of Rho family GTPases. Taken together, these results focus attention on integral membrane lipid phosphatases as regulators of isoprenoid phosphate metabolism and suggest that PDP1/PPAPDC2 is a functional isoprenoid diphosphate phosphatase.

Lipid second messengers and related enzymes in vertebrate rod outer segments

Rod outer segments (ROSs) are specialized light-sensitive organelles in vertebrate photoreceptor cells. Lipids in ROS are of considerable importance, not only in providing an adequate environment for efficient phototransduction, but also in originating the second messengers involved in signal transduction. ROSs have the ability to adapt the sensitivity and speed of their responses to ever-changing conditions of ambient illumination. A major contributor to this adaptation is the light-driven translocation of key signaling proteins into and out of ROS. The present review shows how generation of the second lipid messengers from phosphatidylcholine, phosphatidic acid, and diacylglycerol is modulated by the different illumination states in the vertebrate retina. Findings suggest that the light-induced translocation of phototransduction proteins influences the enzymatic activities of phospholipase D, lipid phosphate phosphatase, diacylglyceride lipase, and diacylglyceride kinase, all of which are responsible for the generation of the second messenger molecules.

Inducible capillary formation in lymphatic endothelial cells by blocking lipid phosphate phosphatase-3 activity

Lymphangiogenesis plays critical roles under normal and/or pathological conditions; however, the molecular contributors to this event were unknown until recently. In the present study, we first employed gene chip analysis and confirmed that lipid phosphate phosphatase-3 (LPP3) expression was increased until capillary formation in the conditionally immortalized rat lymphatic endothelial cell line. Signaling responses occur when several lipids induce acute biological functions; further, lipid phosphate phosphatases (LPPs) control their functions via dephosphorylation; however, there is no report on the association between LPP3 and lymphangiogenesis. siRNA-targeted LPP3 significantly increased capillary formation of human lymphatic endothelial cells; in contrast, it decreased cell adhesion to the basement membrane matrix. Furthermore, the inducible effect of the LPP inhibitor on capillary formation was observed. For the first time, we report that LPP3 abolishes accelerated abnormal lymphangiogenesis. Blocking LPP3 activities may aid in the development of novel therapy for lymph vessel defects.

Lipid phosphate phosphohydrolase type 1 (LPP1) degrades extracellular lysophosphatidic acid in vivo

LPA (lysophosphatidic acid) is a lipid mediator that stimulates cell proliferation and growth, and is involved in physiological and pathological processes such as wound healing, platelet activation, angiogenesis and the growth of tumours. Therefore defining the mechanisms of LPA production and degradation are of interest in understanding the regulation of these processes. Extracellular LPA synthesis is relatively well understood, whereas the mechanisms of its degradation are not. One route of LPA degradation is dephosphorylation. A candidate enzyme is the integral membrane exophosphatase LPP1 (lipid phosphate phosphohydrolase type 1). In the present paper, we report the development of a mouse wherein the LPP1 gene (Ppap2a) was disrupted. The homozygous mice, which are phenotypically unremarkable, generally lack Ppap2a mRNA, and multiple tissues exhibit a substantial (35-95%) reduction in LPA phosphatase activity. Compared with wild-type littermates, Ppap2a(tr/tr) animals have increased levels of plasma LPA, and LPA injected intravenously is metabolized at a 4-fold lower rate. Our results demonstrate that LPA is rapidly metabolized in the bloodstream and that LPP1 is an important determinant of this turnover. These results indicate that LPP1 is a catabolic enzyme for LPA in vivo.

Clonorchis sinensis: expression, characterization, immunolocalization and serological reactivity of one excretory/secretory antigen-LPAP homologue

From a Clonorchis sinensis adult cDNA plasmid library, a cDNA clone encoding a novel lysophosphatidic acid phosphatase (LPAP) homologue was isolated. The predicted molecular weight of putative protein was 48.8 kDa and the deduced amino acid sequence had 45%, 32%, and 29% identity with LPAP of Schistosoma japonicum, Danio rerio, and Homo sapiens, respectively. Prediction of signal peptide and Western blot analysis indicated that the CsLPAP homologue was an excretory-secretory antigen (ES antigen) of C. sinensis. Immunostaining revealed that the CsLPAP was markedly localized in the intestinal cecum, seminal receptacle and eggs of the adult worm. The recombinant CsLPAP showed slightly higher sensitivity (82.14%) and specificity (85.86%) than the crude worm antigen by enzyme-linked immunosorbent assay (ELISA), a result which suggested that the recombinant antigen might be valuable in the serodiagnosis of human clonorchiasis.

Cdc42 and ARP2/3-independent regulation of filopodia by an integral membrane lipid-phosphatase-related protein

Filopodia are dynamic cell surface protrusions that are required for proper cellular development and function. We report that the integral membrane protein lipid-phosphatase-related protein 1 (LPR1) localizes to and promotes the formation of actin-rich, dynamic filopodia, both along the cell periphery and the dorsal cell surface. Regulation of filopodia by LPR1 was not mediated by cdc42 or Rif, and is independent of the Arp2/3 complex. We found that LPR1 can induce filopodia formation in the absence of the Ena/Vasp family of proteins, suggesting that these molecules are not essential for the development of the protrusions. Mutagenesis experiments identified residues and regions of LPR1 that are important for the induction of filopodia. RNA interference experiments in an ovarian epithelial cancer cell line demonstrated a role for LPR1 in the maintenance of filopodia-like membrane protrusions. These observations, and our finding that LPR1 is a not an active lipid phosphatase, suggest that LPR1 may be a novel integral membrane protein link between the actin core and the surrounding lipid layer of a nascent filopodium.

Measurement of mammalian sphingosine-1-phosphate phosphohydrolase activity in vitro and in vivo

Sphingolipid metabolites have emerged as key players in diverse processes including cell migration, growth, and apoptosis. Ceramide and sphingosine typically inhibit cell growth and induce apoptosis, while sphingosine-1-phosphate (S1P) promotes cell growth, inhibits apoptosis, and induces cell migration. Thus, enzymes that regulate the levels of these sphingolipid metabolites are of critical importance to understanding cell fate. There are two known mammalian isoforms of S1P phosphohydrolases (SPP1 and SPP2) that reversibly degrade S1P to sphingosine. This chapter discusses the importance of SPPs and describes assays that can be used to measure the activity of these two specific S1P phosphohydrolases in cells and cell lysates.