A real-time fluorogenic phospholipase A(2) assay for biochemical and cellular activity measurements

Development of a bis-pyrene phospholipid probe for fluorometric detection of phospholipase A2 inhibition

In this work, we report the design, synthesis, and application of a bis-pyrene phospholipid probe for detection of phospholipase A2 action through changes in pyrene monomer and excimer fluorescence intensities. Continuous fluorometric assays enabled detection of the activities of multiple PLA2 enzymes as well as the decrease in catalysis by PLA2 from honey bee venom caused by the inhibitor p-bromo phenacylbromide. Thin-layer chromatography and mass spectrometry analysis were also used to validate probe hydrolysis by PLA2. Mass spectrometry data also supported cleavage of the probe by phospholipase C and D enzymes, although changes in fluorescence were not observed in these cases. Nevertheless, the bis-pyrene phospholipid probe developed in this work is effective for detection of PLA2 enzyme activity through an assay that enables screening for inhibitor development.

Peptide lipidation in lysophospholipid micelles and lysophospholipid-enriched membranes

Acyl transfer from lipids to membrane-associated peptides is a well-documented process, leading to the generation of a lipidated peptide and a lysolipid. In this article, we demonstrate that acyl transfer from lysophosphatidylcholines (lysoPCs) to the peptide melittin also occurs, both in micelles of pure lysolipid and in lipid/lysolipid mixtures. In the case of bilayers containing lysolipids, acyl transfer from the lysolipid is marginally favoured over transfer from the lipid. In pure bilayers of saturated lipids, the introduction of even small amounts of lysolipid appears to significantly increase the reactivity towards lipidation.

Imaging mycobacterial growth and division with a fluorogenic probe

Control and manipulation of bacterial populations requires an understanding of the factors that govern growth, division, and antibiotic action. Fluorescent and chemically reactive small molecule probes of cell envelope components can visualize these processes and advance our knowledge of cell envelope biosynthesis (e.g., peptidoglycan production). Still, fundamental gaps remain in our understanding of the spatial and temporal dynamics of cell envelope assembly. Previously described reporters require steps that limit their use to static imaging. Probes that can be used for real-time imaging would advance our understanding of cell envelope construction. To this end, we synthesized a fluorogenic probe that enables continuous live cell imaging in mycobacteria and related genera. This probe reports on the mycolyltransferases that assemble the mycolic acid membrane. This peptidoglycan-anchored bilayer-like assembly functions to protect these cells from antibiotics and host defenses. Our probe, quencher-trehalose-fluorophore (QTF), is an analog of the natural mycolyltransferase substrate. Mycolyltransferases process QTF by diverting their normal transesterification activity to hydrolysis, a process that unleashes fluorescence. QTF enables high contrast continuous imaging and the visualization of mycolyltransferase activity in cells. QTF revealed that mycolyltransferase activity is augmented before cell division and localized to the septa and cell poles, especially at the old pole. This observed localization suggests that mycolyltransferases are components of extracellular cell envelope assemblies, in analogy to the intracellular divisomes and polar elongation complexes. We anticipate QTF can be exploited to detect and monitor mycobacteria in physiologically relevant environments.

IR spectroscopy analysis of pancreatic lipase-related protein 2 interaction with phospholipids: 3. Monitoring DPPC lipolysis in mixed micelles

Usual methods for the continuous assay of lipolytic enzyme activities are mainly based on the titration of free fatty acids, surface pressure monitoring or spectrophotometry using substrates labeled with specific probes. These approaches only give a partial information on the chemistry of the lipolysis reaction and additional end-point analyses are often required to quantify both residual substrate and lipolysis products. We used transmission infrared (IR) spectroscopy to monitor simultaneously the hydrolysis of phospholipids by guinea pig pancreatic lipase-related protein 2 (GPLRP2) and the release of lipolysis products. The substrate (DPPC, 1,2-Dipalmitoyl phosphatidylcholine) was mixed with sodium taurodeoxycholate (NaTDC) to form mixed micelles in D₂O buffer at pD 6 and 8. After hydrogen/deuterium exchange, DPPC hydrolysis by GPLRP2 (100nM) was monitored at 35°C in a liquid cell by recording IR spectra and time-course variations in the CO stretching region. These changes were correlated to variations in the concentrations of DPPC, lysophospholipids (lysoPC) and palmitic acid (Pam) using calibration curves established with these compounds individually mixed with NaTDC. We were thus able to quantify each compound and its time-course variations during the phospholipolysis reaction and to estimate the enzyme activity. To validate the IR analysis, variations in residual DPPC, lysoPC and Pam were also quantified by thin-layer chromatography coupled to densitometry and similar hydrolysis profiles were obtained using both methods. IR spectroscopy can therefore be used to monitor the enzymatic hydrolysis of phospholipids and obtain simultaneously chemical and physicochemical information on substrate and all reaction products (H-bonding, hydration, acyl chain mobility).

Screening of phospholipase A activity and its production by new actinomycete strains cultivated by solid-state fermentation

Novel microbial phospholipases A (PLAs) can be found in actinomycetes which have been poorly explored as producers of this activity. To investigate microbial PLA production, efficient methods are necessary such as high-throughput screening (HTS) assays for direct search of PLAs in microbial cultures and cultivation conditions to promote this activity. About 200 strains isolated with selected media for actinomycetes and mostly belonging to Streptomyces (73%) and Micromonospora (10%) genus were first screened on agar-plates containing the fluorophore rhodamine 6G and egg yolk phosphatidylcholine (PC) to detect strains producing phospholipase activity. Then, a colorimetric HTS assay for general PLA activity detection (cHTS-PLA) using enriched PC (≈60%) as substrate and cresol red as indicator was developed and applied; this cHTS-PLA assay was validated with known PLAs. For the first time, actinomycete strains were cultivated by solid-state fermentation (SSF) using PC as inductor and sugar-cane bagasse as support to produce high PLA activity (from 207 to 2,591 mU/g of support). Phospholipase activity of the enzymatic extracts from SSF was determined using the implemented cHTS-PLA assay and the PC hydrolysis products obtained, were analyzed by TLC showing the presence of lyso-PC. Three actinomycete strains of the Streptomyces genus that stood out for high accumulation of lyso-PC, were selected and analyzed with the specific substrate 1,2-α-eleostearoyl-sn-glycero-3-phosphocholine (EEPC) in order to confirm the presence of PLA activity in their enzymatic extracts. Overall, the results obtained pave the way toward the HTS of PLA activity in crude microbial enzymatic extracts at a larger scale. The cHTS-PLA assay developed here can be also proposed as a routine assay for PLA activity determination during enzyme purification,directed evolution or mutagenesis approaches. In addition, the production of PLA activity by actinomycetes using SSF allow find and produce novel PLAs with potential applications in biotechnology.

Multivalent nanoparticle networks enable point-of-care detection of human phospholipase-A2 in serum

A rapid and highly sensitive point-of-care (PoC) lateral flow assay for phospholipase A2 (PLA2) is demonstrated in serum through the enzyme-triggered release of a new class of biotinylated multiarmed polymers from a liposome substrate. Signal from the enzyme activity is generated by the adhesion of polystreptavidin-coated gold nanoparticle networks to the lateral flow device, which leads to the appearance of a red test line due to the localized surface plasmon resonance effect of the gold. The use of a liposome as the enzyme substrate and multivalent linkers to link the nanoparticles leads to amplification of the signal, as the cleavage of a small amount of lipids is able to release a large amount of polymer linker and adhesion of an even larger amount of gold nanoparticles. By optimizing the molecular weight and multivalency of these biotinylated polymer linkers, the sensitivity of the device can be tuned to enable naked-eye detection of 1 nM human PLA2 in serum within 10 min. This high sensitivity enabled the correct diagnosis of pancreatitis in diseased clinical samples against a set of healthy controls using PLA2 activity in a point-of-care device for the first time.

Minimalist Approaches to Protein Labelling: Getting the Most Fluorescent Bang for Your Steric Buck

Fluorescence methods allow one to monitor protein conformational changes, protein–protein associations, and proteolysis in real time, at the single molecule level and in living cells. The information gained in such experiments is a function of the spectroscopic techniques used and the strategic placement of fluorophore labels within the protein structure. There is often a trade-off between size and utility for fluorophores, whereby large size can be disruptive to the protein’s fold or function, but valuable characteristics, such as visible wavelength absorption and emission or brightness, require sizable chromophores. Three major types of fluorophore readouts are commonly used: (1) Förster resonance energy transfer (FRET); (2) photoinduced electron transfer (PET); and (3) environmental sensitivity. This review focuses on those probes small enough to be incorporated into proteins during ribosomal translation, which allows the probes to be placed on the interiors of proteins as they are folded during synthesis. The most broadly useful method for doing so is site-specific unnatural amino acid (UAA) mutagenesis. We discuss the use of UAA probes in applications relying on FRET, PET, and environmental sensitivity. We also briefly review other methods of protein labelling and compare their relative merits to UAA mutagenesis. Finally, we discuss small probes that have thus far been used only in synthetic peptides, but which have unusual value and may be candidates for incorporation using UAA methods.

Activatable Optical Probes for the Detection of Enzymes

The early detection of many human diseases is crucial if they are to be treated successfully. Therefore, the development of imaging techniques that can facilitate early detection of disease is of high importance. Changes in the levels of enzyme expression are known to occur in many diseases, making their accurate detection at low concentrations an area of considerable active research. Activatable fluorescent probes show immense promise in this area. If properly designed they should exhibit no signal until they interact with their target enzyme, reducing the level of background fluorescence and potentially endowing them with greater sensitivity. The mechanisms of fluorescence changes in activatable probes vary. This review aims to survey the field of activatable probes, focusing on their mechanisms of action as well as illustrating some of the in vitro and in vivo settings in which they have been employed.

Recent progress on phospholipases: different sources, assay methods, industrial potential and pathogenicity

Significant studies on phospholipases optimization, characterization, physiological role and industrial potential have been conducted worldwide. Some of them have been directed for biotechnological advances such as gene discovery and functional enhancement by protein engineering. Others reported phospholipases as virulence factor and major cause of pathophysiological effects. A general overview on phospholipase is needed for the identification of new reliable and efficient phospholipase, which would be potentially used in number of industrial and medical applications. Phospholipases catalyse the hydrolysis of one or more ester and phosphodiester bonds of glycerophospholipids. They vary in site of action on phospholipid which can be used industrially for modification/production of new phospholipids. Catalytically active phospholipase mainly use phosphatidylcholine as major substrate, but they can also show specificity with other phospholipids. Several accurate phospholipase assay methods are known, but a rapid and reliable method for high-throughput screening is still a challenge for efficient supply of superior phospholipases and their practical applications. Major application of phospholipase is in industries like oil refinery, health food manufacturing, dairy, cosmetics etc. All types of phospholipases can be involved as virulence factor. They can also be used as diagnostic markers for microbial infection. The importance of phospholipase in virulence is proven and inhibitors of the enzyme can be used as candidate for preventing the associated disease.

Determination of lipoprotein lipase activity using a novel fluorescent lipase assay

A novel, real-time, homogeneous fluorogenic lipoprotein lipase (LPL) assay was developed using a commercially available substrate, the EnzChek lipase substrate, which is solubilized in Zwittergent. The triglyceride analog substrate does not fluoresce, owing to apposition of fluorescent and fluorescent quenching groups at the sn-1 and sn-2 positions, respectively, fluorescence becoming unquenched upon release of the sn-1 BODIPY FA derivative following hydrolysis. Increase in fluorescence intensity at 37°C was proportional to LPL concentration. The assay was more sensitive than a similar assay using 1,2-O-dilauryl-rac-glycero-3-glutaric acid-(6-methylresorufin ester) and was validated in biological samples, including determination of LPL-specific activity in postheparin mouse plasma. The simplicity and reproducibility of the assay make it ideal for in vitro, high-throughput screening for inhibitors and activators of LPL, thus expediting discovery of drugs of potential clinical value.

Synthesis of oligo(ethylene glycol) substituted phosphatidylcholines: secretory PLA2-targeted precursors of NSAID prodrugs

A series of new phosphatidylcholine analogues with structurally modified sn-2-substituents have been prepared. The synthetic compounds include oligo(ethylene glycol) derivatives with chain-terminal pharmacophores that upon catalytic hydrolysis by phospholipase A(2) yielded a series of oligo(ethylene glycol)-conjugates of the respective drugs. The approach here outlined may open a new way to employ OEG derivatives of phospholipids for therapeutic applications as secretory PLA(2)-targeted precursors of prodrugs.

Conjugated polyelectrolyte supported bead based assays for phospholipase A2 activity

A fluorescence based assay for human serum-derived phospholipase activity has been developed in which cationic conjugated polyelectrolytes are supported on silica microspheres. The polymer-coated beads are overcoated with an anionic phospholipid (1,2-dimyristoyl-sn-glycero-3-[phospho- rac-(1-glycerol)) (DMPG) to provide "lipobeads" that serve as a sensor for PLA2. The lipid serves a dual role as a substrate for PLA2 and an agent to attenuate quenching of the polymer fluorescence by the external electron transfer quencher 9,10-anthraquinone-2,6-disulfonic acid (AQS). In this case quenching of the polymer fluorescence by AQS increases as the PLA2 digests the lipid. The lipid can also be used itself as a quencher and substrate by employing a small amount of energy transfer quencher substituted lipid in the DMPG. In this case the fluorescence of the polymer is quenched when the lipid layer is intact; as the enzyme digests the lipid, the fluorescence of the polymer is restored. The sensing of PLA2 activity has been studied both by monitoring fluorescence changes in a multiwell plate reader and by flow cytometry. The assay exhibits good sensitivity with EC50 values in the nanomolar range.

Synthesis of Phosphatidylcholine Analogues Derived from Glyceric Acid: a New Class of Biologically Active Phospholipid Compounds

Synthesis of a new class of phosphatidylcholine analogues derived from glyceric acid is reported for spectroscopic studies of phospholipases and conformation of phospholipid side-chains in biological membranes, using fluorescence resonance energy transfer (FRET) techniques.

Probing phospholipase a(2) with fluorescent phospholipid substrates

The Foerster resonance energy transfer-based sensor, PENN, measures intracellular phospholipase A(2) (PLA(2)) activity in living cells and small organisms. In an attempt to modify the probe for the detection of particular isoforms, we altered the sn-2 fatty acid in such a way that either one or three of the Z double bonds in arachidonic acid were present in the sensor molecule. Arachidonic-acid-mimicking fatty acids were prepared by copper-mediated coupling reactions. Probes with a single double bond in the 5-position exhibited favorable substrate properties for secretory PLA(2)s. In vitro experiments with the novel unsaturated doubly labeled phosphatidylethanolamine derivatives showed preferred cleavage of the sensor PENN2 (one double bond) by the physiologically important group V sPLA(2), while the O-methyl-derivative PMNN2 was accepted best by the isoform from hog pancreas. For experiments in living cells, we demonstrated that bioactivation via S-acetylthioethyl (SATE) groups is essential for probe performance. Surprisingly, membrane-permeant versions of the new sensors that contained double bonds, PENN2 and PENN3, were only cleaved to a minor extent in HeLa cells while the saturated form, PENN, was well accepted.

A colorimetric assay for measuring phospholipase A2 degradation of phosphatidylcholine at physiological pH

Phospholipase A(2) is an important enzyme in various pathologies. Although fluorescent substrate assays for it have been recently developed, there is a need for an assay with inexpensive commercially available substrates, useful when samples interfered with fluorescent assays, that is nonisotopic, continuous, conducted at physiological pH, and in a 96 well format. A reaction using bromothymol blue was developed that meets all these requirements.

A New Synthesis of Lysophosphatidylcholines and Related Derivatives. Use of p-Toluenesulfonate for Hydroxyl Group Protection

A new stereoselective synthesis of lysophosphatidylcholines is reported. The synthesis is based upon (1) the use of 3-p-toluenesulfonyl-sn-glycerol to provide the stereocenter for construction of the optically active lysophospholipid molecule, (2) tetrahydropyranylation of the secondary alcohol function to achieve orthogonal protection of the sn-2- and sn-3-glycerol positions, and (3) elaboration of the phosphodiester headgroup using a 2-chloro-1,3,2-dioxaphospholane/trimethylamine sequence. In the course of developing the synthesis it has been discovered that methoxyacetate displacement of the sn-3-p-toluenesulfonate yields a reactive methoxyacetyl ester, which in turn can be selectively cleaved with methanol/tert-butylamine, while the ester group at the sn-1-position remains unaffected. The sequence has been shown to be suitable for preparation of spectroscopically labeled lysophosphatidylcholines. One of these compounds was readily converted to a double-labeled mixed-chain phosphatidylcholine applicable for real-time fluorescence resonance energy transfer (FRET) assay of lipolytic enzymes. In addition, the work led to new synthetic strategies based on chemoselective manipulation of the tosyl group in the presence of other base-labile groups such as FMOC derivatives that are often used for the protection of amino and hydroxyl groups in syntheses.

A continuous fluorescence assay for the determination of calcium-dependent secretory phospholipase A2 activity in serum

BACKGROUND

Calcium-dependent secretory phospholipase A(2)-IIA (sPLA(2)-IIA) in the circulation is a marker of inflammation, associated with acute and chronic disease processes. We describe a quick, sensitive and reliable microplate continuous fluorescence assay for determining sPLA(2) activity in serum.

METHODS

Liposomes composed of a fluorescent probe and varying amounts of L-alpha-phosphatidylglycerol (PG) and 1,2-dioleoyl-L-alpha-phosphatidylcholine (DOPC) were used as substrates to determine the optimal protocol for sPLA(2) activity determination without interference from serum albumin and lipoproteins.

RESULTS

Hydrolysis of the labeled substrate by sPLA(2)-IIA, characterized by increase in fluorescence intensity (FI) and confirmed by end-product analysis, occurred in a time-, calcium-, and protein-dependent manner. Liposomes containing 100% PG were most suitable for measurement of sPLA(2) activity without interference from serum components; LDL produced a Ca(2+)-independent increase in FI when liposomes containing DOPC were used. The assay determined that sPLA(2) activity in serum spiked with sPLA(2)-IIA and illustrated that endogenous sPLA(2) activity was markedly higher in sera from patients with sepsis than in healthy subjects. Intra-assay and inter-assay CVs were in the ranges of 1.6-8.8% and 3.0-11.5%, respectively.

CONCLUSIONS

The described method has potential for rapid and sensitive screening of sPLA(2) activity in both clinical and research settings.

M1 muscarinic receptors inhibit L-type Ca2+ current and M-current by divergent signal transduction cascades

Ion channels reside in a sea of phospholipids. During normal fluctuations in membrane potential and periods of modulation, lipids that directly associate with channel proteins influence gating by incompletely understood mechanisms. In one model, M(1)-muscarinic receptors (M(1)Rs) may inhibit both Ca(2+) (L- and N-) and K(+) (M-) currents by losing a putative interaction between channels and phosphatidylinositol-4,5-bisphosphate (PIP(2)). However, we found previously that M(1)R inhibition of N-current in superior cervical ganglion (SCG) neurons requires loss of PIP(2) and generation of a free fatty acid, probably arachidonic acid (AA) by phospholipase A(2) (PLA(2)). It is not known whether PLA(2) activity and AA also participate in L- and M-current modulation in SCG neurons. To test whether PLA(2) plays a similar role in M(1)R inhibition of L- and M-currents, we used several experimental approaches and found unanticipated divergent signaling. First, blocking resynthesis of PIP(2) minimized M-current recovery from inhibition, whereas L-current recovered normally. Second, L-current inhibition required group IVa PLA(2) [cytoplasmic PLA(2) (cPLA(2))], whereas M-current did not. Western blot and imaging studies confirmed acute activation of cPLA(2) by muscarinic stimulation. Third, in type IIa PLA(2) [secreted (sPLA(2))](-/-)/cPLA(2)(-/-) double-knock-out SCG neurons, muscarinic inhibition of L-current decreased. In contrast, M-current inhibition remained unaffected but recovery was impaired. Our results indicate that L-current is inhibited by a pathway previously shown to control M-current over-recovery after washout of muscarinic agonist. Our findings support a model of M(1)R-meditated channel modulation that broadens rather than restricts the roles of phospholipids and fatty acids in regulating ion channel activity.

Caspase-3-dependent Activation of Calcium-independent Phospholipase A2 Enhances Cell Migration in Non-apoptotic Ovarian Cancer Cells

Calcium-independent phospholipase A(2) (iPLA(2)) plays a pivotal role in phospholipid remodeling and many other biological processes, including inflammation and cancer development. iPLA(2) can be activated by caspase-3 via a proteolytic process in apoptotic cells. In this study we identify novel signaling and functional loops of iPLA(2) activation leading to migration of non-apoptotic human ovarian cancer cells. The extracellular matrix protein, laminin-10/11, but not collagen I, induces integrin- and caspase-3-dependent cleavage and activation of overexpressed and endogenous iPLA(2). The truncated iPLA(2) (amino acids 514-806) generates lysophosphatidic acid and arachidonic acid. Arachidonic acid is important for enhancing cell migration toward laminin-10/11. Lysophosphatidic acid activates Akt that in turn acts in a feedback loop to block the cleavage of poly-(ADP-ribose) polymerase and DNA fragmentation factor as well as prevent apoptosis. By using pharmacological inhibitors, blocking antibodies, and genetic approaches (such as point mutations, dominant negative forms of genes, and siRNAs against specific targets), we show that beta(1), but not beta(4), integrin is involved in iPLA(2) activation and cell migration to laminin-10/11. The role of caspase-3 in iPLA(2) activation and cell migration are supported by several lines of evidence. 1) Point mutation of Asp(513) (a cleavage site of caspase-3 in iPLA(2)) to Ala blocks laminin-10/11-induced cleavage and activation of overexpressed iPLA(2), whereas mutation of Asp(733) to Ala has no such effect, 2) treatment of inhibitors or a small interfering RNA against caspase-3 results in decreased cell migration toward laminin-10/11, and 3) selective caspase-3 inhibitor blocks cleavage of endogenous iPLA(2) induced by laminin-10/11. Importantly, small interfering RNA-mediated down-regulation of endogenous iPLA(2) expression in ovarian carcinoma HEY cells results in decreased migration toward laminin, suggesting that our findings are pathophysiologically important.

Destabilization of the acrosome results in release of phospholipase A2 from human spermatozoa and subsequent formation of lysophospholipids

Phospholipase A(2) controls the phospholipid composition in spermatozoal membranes and is released from the acrosome of human spermatozoa. The extracellular phospholipase A(2) activity of human spermatozoa was determined by matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF) mass spectrometry after destabilization of acrosome by the calcium-ionophore calcimycin. MALDI-TOF mass spectrometry allowed the monitoring of changes in both substrate and products of spermatozoal phospholipase A(2) (PLA(2)) without the use of labelled phospholipids. The spermatozoal PLA(2) was characterized as a secretory one (sPLA(2)). Secretory PLA(2) exhibited a high substrate specificity for 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (PDPC), the most abundant spermatozoal phospholipid. A time- and cell number-dependent formation of the lysophospholipid PDPC was observed following incubation of extracellular medium of calcimycin-treated spermatozoa (CTS) with PDPC. Antibodies against sPLA(2), specific inhibitors of sPLA(2) and Ca(2+)-chelators could inhibit its generation. An antibody against lysophospholipase enhanced the lysoproduct concentration in the extracellular medium of CTS containing sPLA(2) because further metabolization of these products was blocked. The results demonstrated that destabilization of the acrosome is able to induce a release of secretory phospholipase A(2) from human spermatozoa with subsequent generation of lysophosphocholine in the surrounding of spermatozoa.

Synthesis and evaluation of fluorogenic substrates for phospholipase D and phospholipase C

Fluorogenic analogues of phosphatidylcholine and lysophosphatidylcholine, DDPB and lysoDDPB, were synthesized by an enzyme-assisted strategy. The analogues were evaluated as substrates for phospholipases C and D and lysophospholipase D. DDPB was cleaved by bacterial and plant phospholipase D (PLD) enzymes and represents the first direct fluorogenic substrate for real-time measurement of PLD activity. Both fluorogenic substrates have potential in screening for PLD and PC-PLC inhibitors and for monitoring spatiotemporal changes in PLD activity in cells. [structure: see text]

Fluorogenic phospholipid substrate to detect lysophospholipase D/autotaxin activity

[reaction: see text] Lysophospholipase D (lysoPLD), also known as autotaxin (ATX), is an important source of the potent mitogen lysophosphatidic acid (LPA). Two fluorogenic substrate analogues for lysoPLD were synthesized in nine steps from (S)-PMB-glycerol. The substrates (FS-2 and FS-3) show significant increases in fluorescence when treated with recombinant ATX and have potential applications in screening for this emerging drug target.

Fluorogenic phospholipids as head group-selective reporters of phospholipase A activity

PLA (phospholipases A) are important mediators of cell signaling, generating bioactive fatty acids and LPLs (lysophospholipids). PLA products having different head groups can initiate vastly different types of signaling. Fluorogenic analogues of the PLs (phospholipids) PA (phosphatidic acid), PC (phosphatidylcholine), PE (phosphatidylethanolamine), and PG (phosphatidylglycerol) were synthesized as PLA substrates for rapidly determining in real time the influence of head group modifications on cell signaling both in vitro and in cells. Enzyme-assisted remodeling of the sn-2 position of the diacylglyceryl moiety with cobra venom PLA 2 and transphosphatidylation with a particular PLD (phospholipase D) were central steps in the preparation of these enzymatic probes. The resulting fluorogenic Dabcyl- and BODIPY-containing PL analogues, DBPA, DBPC, DBPE, and DBPG, were used in mixed micelle assays to determine PLA 2 kinetics. Next, the assays were used to determine the X i (50) value of a common PLA 2 inhibitor. Finally, the head group selectivities of a series of commercially available PLA 2 enzymes were readily established using the DBPLs (Dabcyl-BODIPY PLs) as substrates.

Lysophosphatidic acid is constitutively produced by human peritoneal mesothelial cells and enhances adhesion, migration, and invasion of ovarian cancer cells

Lysophosphatidic acid (LPA) is both a potential marker and a therapeutic target for ovarian cancer. It is critical to identify the sources of elevated LPA levels in ascites and blood of patients with ovarian cancer. We show here that human peritoneal mesothelial cells constitutively produce LPA, which accounts for a significant portion of the chemotactic activity of the conditioned medium from peritoneal mesothelial cells to ovarian cancer cells. Both production of LPA by peritoneal mesothelial cells and the chemotactic activity in the conditioned medium can be blocked by HELSS [an inhibitor of the calcium-independent phospholipase A(2) (iPLA(2))] and AACOCF(3) [an inhibitor of both cytosolic PLA(2) (cPLA(2)) and iPLA(2)]. Moreover, cell-based enzymatic activity assays for PLA(2) indicate that peritoneal mesothelial cells have strong constitutive PLA(2) activity. Receptors for LPA, LPA(2), and LPA(3) are involved in the conditioned medium-induced chemotactic activity. Invasion of ovarian cancer cells into peritoneal mesothelial cells has also been analyzed and shown to require PLA(2), LPA receptors, and the mitogen-activated protein/extracellular signal-regulated kinase kinase/extracellular signal-regulated kinase signaling pathway. Thus, we show here, for the first time, that human peritoneal mesothelial cells constitutively produce bioactive lipid signaling molecules, such as LPA, via iPLA(2) and/or cPLA(2) activities. Conditioned medium from peritoneal mesothelial cells stimulate migration, adhesion, and invasion of ovarian cancer cells, and may play similar roles in vivo.

Visualization and perturbation of phosphoinositide and phospholipid signaling

Cells signal through lipids that are produced by phospholipid (PL) and phosphoinositide (PIPn) metabolism involve three enzymatic processes: (i) ester and phosphodiester hydrolysis by phospholipases, (ii) monophosphate hydrolysis by phosphatases, and (iii) phosphorylation of hydroxy groups by kinases. Unregulated enzyme activity correlates with specific pathologies, which are specific targets for therapeutic intervention. A variety of reagents now permit monitoring of in vitro enzyme activity, spatiotemporal changes of intracellular lipid concentrations, and identification of lipid-protein interactions. This minireview summarizes a chemical biology approach that illustrates how chemically synthesized affinity probes can be used to characterize changes in lipid signaling in cellular and molecular biology.