Pancreatic phospholipase A2: isolation of the human gene and cDNAs from porcine pancreas and human lung

Modulation of immunity by the secreted phospholipase A2 family

Among the phospholipase A2 (PLA2 ) superfamily, which typically catalyzes the sn-2 hydrolysis of phospholipids to yield fatty acids and lysophospholipids, the secreted PLA2 (sPLA2 ) family contains 11 isoforms in mammals. Individual sPLA2 s have unique enzymatic specificity toward fatty acids and polar heads of phospholipid substrates and display distinct tissue/cellular distributions, suggesting their distinct physiological functions. Recent studies using knockout and/or transgenic mice for a full set of sPLA2 s have revealed their roles in modulation of immunity and related disorders. Application of mass spectrometric lipidomics to these mice has enabled to identify target substrates and products of individual sPLA2 s in given tissue microenvironments. sPLA2 s hydrolyze not only phospholipids in the plasma membrane of activated, damaged or dying mammalian cells, but also extracellular phospholipids such as those in extracellular vesicles, microbe membranes, lipoproteins, surfactants, and dietary phospholipids, thereby exacerbating or ameliorating various diseases. The actions of sPLA2 s are dependent on, or independent of, the generation of fatty acid- or lysophospholipid-derived lipid mediators according to the pathophysiological contexts. In this review, we make an overview of our current understanding of the roles of individual sPLA2 s in various immune responses and associated diseases.

The Roles of sPLA2s in Skin Homeostasis and Disease

Among the phospholipase A₂ (PLA₂) family, the secreted PLA₂ (sPLA₂) family in mammals contains 11 members that exhibit unique tissue or cellular distributions and enzymatic properties. Current studies using knockout and/or transgenic mice for a nearly full set of sPLA₂s, in combination with comprehensive lipidomics, have revealed the diverse pathophysiological roles of sPLA₂s in various biological events. Individual sPLA₂s exert specific functions within tissue microenvironments, likely through the hydrolysis of extracellular phospholipids. Lipids are an essential biological component for skin homeostasis, and disturbance of lipid metabolism by deletion or overexpression of lipid-metabolizing enzymes or lipid-sensing receptors often leads to skin abnormalities that are easily visible on the outside. Over the past decades, our studies using knockout and transgenic mice for various sPLA₂s have uncovered several new aspects of these enzymes as modulators of skin homeostasis and disease. This article summarizes the roles of several sPLA₂s in skin pathophysiology, providing additional insight into the research fields of sPLA₂s, lipids, and skin biology.

The phospholipase A2 superfamily as a central hub of bioactive lipids and beyond

In essence, "phospholipase A₂" (PLA₂) means a group of enzymes that release fatty acids and lysophospholipids by hydrolyzing the sn-2 position of glycerophospholipids. To date, more than 50 enzymes possessing PLA₂ or related lipid-metabolizing activities have been identified in mammals, and these are subdivided into several families in terms of their structures, catalytic mechanisms, tissue/cellular localizations, and evolutionary relationships. From a general viewpoint, the PLA₂ superfamily has mainly been implicated in signal transduction, driving the production of a wide variety of bioactive lipid mediators. However, a growing body of evidence indicates that PLA₂s also contribute to phospholipid remodeling or recycling for membrane homeostasis, fatty acid β-oxidation for energy production, and barrier lipid formation on the body surface. Accordingly, PLA₂ enzymes are considered one of the key regulators of a broad range of lipid metabolism, and perturbation of specific PLA₂-driven lipid pathways often disrupts tissue and cellular homeostasis and may be associated with a variety of diseases. This review covers current understanding of the physiological functions of the PLA₂ superfamily, focusing particularly on the two major intracellular PLA₂ families (Ca²⁺-dependent cytosolic PLA₂s and Ca²⁺-independent patatin-like PLA₂s) as well as other PLA₂ families, based on studies using gene-manipulated mice and human diseases in combination with comprehensive lipidomics.

Phospholipase A2, a nonnegligible enzyme superfamily in gastrointestinal diseases

Gastrointestinal tract is important for digestion, absorption, detoxification and immunity. Gastrointestinal diseases are mainly caused by the imbalance of protective and attacking factors in gastrointestinal mucosa, which can seriously harm human health. Phospholipase A₂ (PLA₂) is a large family closely involved in lipid metabolism and is found in almost all human cells. A growing number of studies have revealed that its metabolites are deeply implicated in various inflammatory pathways and also regulates the maintenance of numerous biological events such as dietary digestion, membrane remodeling, barrier action, and host immunity. In addition to their phospholipase activity, some members of the superfamily also have other catalytic activities. Based on the in-depth effects of phospholipase A2 on bioactive lipid metabolism and inflammatory cytokines, PLA₂ and its metabolites are likely to be involved in the pathogenesis, development or prevention of gastrointestinal diseases. Therefore, this review will focus on the physiological and pathogenic roles of several important PLA₂ enzymes in the gastrointestinal tract, and reveals the potential of PLA₂ as a therapeutic target for gastrointestinal diseases.

Updating Phospholipase A2 Biology

The phospholipase A2 (PLA2) superfamily contains more than 50 enzymes in mammals that are subdivided into several distinct families on a structural and biochemical basis. In principle, PLA2 has the capacity to hydrolyze the sn-2 position of glycerophospholipids to release fatty acids and lysophospholipids, yet several enzymes in this superfamily catalyze other reactions rather than or in addition to the PLA2 reaction. PLA2 enzymes play crucial roles in not only the production of lipid mediators, but also membrane remodeling, bioenergetics, and body surface barrier, thereby participating in a number of biological events. Accordingly, disturbance of PLA2-regulated lipid metabolism is often associated with various diseases. This review updates the current state of understanding of the classification, enzymatic properties, and biological functions of various enzymes belonging to the PLA2 superfamily, focusing particularly on the novel roles of PLA2s in vivo.

Intestinal phospholipase A2 from Sparidae species: Functional properties and cytotoxic potential evaluation

Marine species have gained significant attention as potential source for a broad spectrum of bioactive proteins. Fish phospholipases A₂ (PLA₂) have attracted renewed interest due to their excellent properties in lipid digestion. Herein, we report for the first time the catalytic properties of two intestinal secreted PLA₂ (sPLA₂) identified from Diplodus sargus (IDsPLA₂) and Sparus aurata (ISaPLA₂). The highest sequence identity was obtained with recently isolated Sparidae digestive PLA₂ (45%) and Human pancreatic PLA₂ (42%). IDsPLA₂ and ISaPLA₂ were overexpressed in E. coli as inclusion bodies, refolded and purified. Both enzymes have improved thermostability compared to mammalian pancreatic sPLA₂ since they are active and stable at 55 °C, with specific activities of 320 and 190 U mg^-1 measured on phosphatidylcholine, respectively. Interestingly, IDsPLA₂, but not ISaPLA₂, revealed weak toxicity towards macrophages and suggests its involvement in cell membrane degradation. ISaPLA₂ was found to be more active than IDsPLA₂ when using the monolayer technique at 20 mN m^-1. Structural models of both enzymes revealed their differences. In silico docking of phospholipids with both models allowed proposing key amino-acids in substrate binding and selectivity. Overall, these results provide insight into the enzymatic and structural properties of two novel sPLA₂ with potential for future applications.

Pancreatic and mucosal enzymes in choline phospholipid digestion

The digestion of choline phospholipids is important for choline homeostasis, lipid signaling, postprandial lipid and energy metabolism, and interaction with intestinal bacteria. The digestion is mediated by the combined action of pancreatic and mucosal enzymes. In the proximal small intestine, hydrolysis of phosphatidylcholine (PC) to 1-lyso-PC and free fatty acid (FFA) by the pancreatic phospholipase A₂ IB coincides with the digestion of the dietary triacylglycerols by lipases, but part of the PC digestion is extended and must be mediated by other enzymes as the jejunoileal brush-border phospholipase B/lipase and mucosal secreted phospholipase A₂ X. Absorbed 1-lyso-PC is partitioned in the mucosal cells between degradation and reacylation into chyle PC. Reutilization of choline for hepatic bile PC synthesis, and the reacylation of 1-lyso-PC into chylomicron PC by the lyso-PC-acyl-CoA-acyltransferase 3 are important features of choline recycling and postprandial lipid metabolism. The role of mucosal enzymes is emphasized by sphingomyelin (SM) being sequentially hydrolyzed by brush-border alkaline sphingomyelinase (alk-SMase) and neutral ceramidase to sphingosine and FFA, which are well absorbed. Ceramide and sphingosine-1-phosphate are generated and are both metabolic intermediates and important lipid messengers. Alk-SMase has anti-inflammatory effects that counteract gut inflammation and tumorigenesis. These may be mediated by multiple mechanisms including generation of sphingolipid metabolites and suppression of autotaxin induction and lyso-phosphatidic acid formation. Here we summarize current knowledge on the roles of pancreatic and mucosal enzymes in PC and SM digestion, and its implications in intestinal and liver diseases, bacterial choline metabolism in the gut, and cholesterol absorption.

Roles of secreted phospholipase A2 group IIA in inflammation and host defense

Among all members of the secreted phospholipase A₂ (sPLA₂) family, group IIA sPLA₂ (sPLA₂-IIA) is possibly the most studied enzyme. Since its discovery, many names have been associated with sPLA₂-IIA, such as "non-pancreatic", "synovial", "platelet-type", "inflammatory", and "bactericidal" sPLA_2. Whereas the different designations indicate comprehensive functions or sources proposed for this enzyme, the identification of the precise roles of sPLA₂-IIA has remained a challenge. This can be attributed to: the expression of the enzyme by various cells of different lineages, its limited activity towards the membranes of immune cells despite its expression following common inflammatory stimuli, its ability to interact with certain proteins independently of its catalytic activity, and its absence from multiple commonly used mouse models. Nevertheless, elevated levels of the enzyme during inflammatory processes and associated consistent release of arachidonic acid from the membrane of extracellular vesicles suggest that sPLA₂-IIA may contribute to inflammation by using endogenous substrates in the extracellular milieu. Moreover, the remarkable potency of sPLA₂-IIA towards bacterial membranes and its induced expression during the course of infections point to a role for this enzyme in the defense of the host against invading pathogens. In this review, we present current knowledge related to mammalian sPLA₂-IIA and its roles in sterile inflammation and host defense.

Group IID, IIE, IIF and III secreted phospholipase A2s

Among the 11 members of the secreted phospholipase A₂ (sPLA₂) family, group IID, IIE, IIF and III sPLA₂s (sPLA₂-IID, -IIE, -IIF and -III, respectively) are “new” isoforms in the history of sPLA₂ research. Relative to the better characterized sPLA₂s (sPLA₂-IB, -IIA, -V and -X), the enzymatic properties, distributions, and functions of these “new” sPLA₂s have remained obscure until recently. Our current studies using knockout and transgenic mice for a nearly full set of sPLA₂s, in combination with comprehensive lipidomics, have revealed unique and distinct roles of these “new” sPLA₂s in specific biological events. Thus, sPLA₂-IID is involved in immune suppression, sPLA₂-IIE in metabolic regulation and hair follicle homeostasis, sPLA₂-IIF in epidermal hyperplasia, and sPLA₂-III in male reproduction, anaphylaxis, colonic diseases, and possibly atherosclerosis. In this article, we overview current understanding of the properties and functions of these sPLA₂s and their underlying lipid pathways in vivo.

Lipoquality control by phospholipase A2 enzymes

The phospholipase A₂ (PLA₂) family comprises a group of lipolytic enzymes that typically hydrolyze the sn-2 position of glycerophospholipids to give rise to fatty acids and lysophospholipids. The mammalian genome encodes more than 50 PLA₂s or related enzymes, which are classified into several subfamilies on the basis of their structures and functions. From a general viewpoint, the PLA₂ family has mainly been implicated in signal transduction, producing bioactive lipid mediators derived from fatty acids and lysophospholipids. Recent evidence indicates that PLA₂s also contribute to phospholipid remodeling for membrane homeostasis or energy production for fatty acid β-oxidation. Accordingly, PLA₂ enzymes can be regarded as one of the key regulators of the quality of lipids, which I herein refer to as lipoquality. Disturbance of PLA₂-regulated lipoquality hampers tissue and cellular homeostasis and can be linked to various diseases. Here I overview the current state of understanding of the classification, enzymatic properties, and physiological functions of the PLA₂ family.

The Roles of the Secreted Phospholipase A2 Gene Family in Immunology

Within the phospholipase A₂ (PLA₂) family that hydrolyzes phospholipids to yield fatty acids and lysophospholipids, secreted PLA₂ (sPLA₂) enzymes comprise the largest group containing 11 isoforms in mammals. Individual sPLA₂s exhibit unique tissue or cellular distributions and enzymatic properties, suggesting their distinct biological roles. Although PLA₂ enzymes, particularly cytosolic PLA₂ (cPLA₂α), have long been implicated in inflammation by driving arachidonic acid metabolism, the precise biological roles of sPLA₂s have remained a mystery over the last few decades. Recent studies employing mice gene-manipulated for individual sPLA₂s, in combination with mass spectrometric lipidomics to identify their target substrates and products in vivo, have revealed their roles in diverse biological events, including immunity and associated disorders, through lipid mediator-dependent or -independent processes in given microenvironments. In this review, we summarize our current knowledge of the roles of sPLA₂s in various immune responses and associated diseases.

A new era of secreted phospholipase A₂

Among more than 30 members of the phospholipase A2 (PLA2) superfamily, secreted PLA2 (sPLA2) enzymes represent the largest family, being Ca(2+)-dependent low-molecular-weight enzymes with a His-Asp catalytic dyad. Individual sPLA2s exhibit unique tissue and cellular distributions and enzymatic properties, suggesting their distinct biological roles. Recent studies using transgenic and knockout mice for nearly a full set of sPLA2 subtypes, in combination with sophisticated lipidomics as well as biochemical and cell biological studies, have revealed distinct contributions of individual sPLA2s to various pathophysiological events, including production of pro- and anti-inflammatory lipid mediators, regulation of membrane remodeling, degradation of foreign phospholipids in microbes or food, or modification of extracellular noncellular lipid components. In this review, we highlight the current understanding of the in vivo functions of sPLA2s and the underlying lipid pathways as revealed by a series of studies over the last decade.

The finding of a group IIE phospholipase A2 gene in a specified segment of Protobothrops flavoviridis genome and its possible evolutionary relationship to group IIA phospholipase A2 genes

The genes encoding group IIE phospholipase A₂, abbreviated as IIE PLA₂, and its 5' and 3' flanking regions of Crotalinae snakes such as Protobothrops flavoviridis, P. tokarensis, P. elegans, and Ovophis okinavensis, were found and sequenced. The genes consisted of four exons and three introns and coded for 22 or 24 amino acid residues of the signal peptides and 134 amino acid residues of the mature proteins. These IIE PLA₂s show high similarity to those from mammals and Colubridae snakes. The high expression level of IIE PLA₂s in Crotalinae venom glands suggests that they should work as venomous proteins. The blast analysis indicated that the gene encoding OTUD3, which is ovarian tumor domain-containing protein 3, is located in the 3' downstream of IIE PLA₂ gene. Moreover, a group IIA PLA₂ gene was found in the 5' upstream of IIE PLA₂ gene linked to the OTUD3 gene (OTUD3) in the P. flavoviridis genome. It became evident that the specified arrangement of IIA PLA₂ gene, IIE PLA₂ gene, and OTUD3 in this order is common in the genomes of humans to snakes. The present finding that the genes encoding various secretory PLA₂s form a cluster in the genomes of humans to birds is closely related to the previous finding that six venom PLA₂ isozyme genes are densely clustered in the so-called NIS-1 fragment of the P. flavoviridis genome. It is also suggested that venom IIA PLA₂ genes may be evolutionarily derived from the IIE PLA₂ gene.

UVB-induced gene expression in the skin of Xiphophorus maculatus Jp 163 B

Xiphophorus fish and interspecies hybrids represent long-standing models to study the genetics underlying spontaneous and induced tumorigenesis. The recent release of the Xiphophorus maculatus genome sequence will allow global genetic regulation studies of genes involved in the inherited susceptibility to UVB-induced melanoma within select backcross hybrids. As a first step toward this goal, we report results of an RNA-Seq approach to identify genes and pathways showing modulated transcription within the skin of X. maculatus Jp 163 B upon UVB exposure. X. maculatus Jp 163 B were exposed to various doses of UVB followed by RNA-Seq analysis at each dose to investigate overall gene expression in each sample. A total of 357 genes with a minimum expression change of 4-fold (p-adj<0.05) were identified as responsive to UVB. The molecular genetic response of Xiphophorus skin to UVB exposure permitted assessment of; (1) the basal expression level of each transcript for each skin sample, (2) the changes in expression levels for each gene in the transcriptome upon exposure to increasing doses of UVB, and (3) clusters of genes that exhibit similar patterns of change in expression upon UVB exposure. These data provide a foundation for understanding the molecular genetic response of fish skin to UVB exposure.

Structural characteristics and evolution of the Protobothrops elegans pancreatic phospholipase A2 gene in contrast with those of Protobothrops genus venom phospholipase A2 genes

The nucleotide sequence of the gene encoding Protobothrops elegans (Crotalinae) pancreatic phospholipase A(2) (PLA(2)), abbreviated PePancPLA(2), was determined by means of inverted PCR techniques. Since its deduced amino acid sequence contains a pancreatic loop and shows high similarity to that of Laticauda semifasciata (Elapinae) group IB pancreatic PLA(2), PePancPLA(2) is classified into group IB PLA(2). The nucleotide sequences of the PePancPLA(2) gene, the L. semifasciata group IB pancreatic PLA(2) gene, and the L. semifasciata group IA venom PLA(2) gene are similar to one another but greatly dissimilar to those of Protobothrops genus (Crotalinae) group II venom PLA(2) genes, suggesting that the Elapinae group IB PLA(2) gene and the group IA PLA(2) gene appeared after Elapinae was established, and that the Crotalinae group II venom PLA(2) genes came into existence before Elapinae and Crotalinae diverged. A phylogenetic analysis of their amino acid sequences confirms this.

Phospholipase A2 purification and characterization: a case study

We compared here the purification procedures, the pH, the calcium, the bile salts, and the temperature dependencies as well as the catalytic activities on phosphatidylcholine (PC) and phosphatidylethanolamine (PE) of two purified secreted PLA2 from chicken pancreatic (ChPLA2-IB) and chicken intestinal (ChPLA2-IIA) origins. Interestingly, ChPLA2-IB hydrolyzes efficiently both purified PC and PE, whereas ChPLA2-IIA hydrolyzes only PE and not PC, even after a long incubation period. These analytical results clearly indicate that the catalytic activity of ChPLA2-IIA, measured with the pH-stat and using egg yolk as substrate, is mainly due to the hydrolysis of the PE fraction present in egg yolk.

Surfactant protein B inhibits secretory phospholipase A2 hydrolysis of surfactant phospholipids

Hydrolysis of surfactant phospholipids (PL) by secretory phospholipases A(2) (sPLA(2)) contributes to surfactant damage in inflammatory airway diseases such as acute lung injury/acute respiratory distress syndrome. We and others have reported that each sPLA(2) exhibits specificity in hydrolyzing different PLs in pulmonary surfactant and that the presence of hydrophilic surfactant protein A (SP-A) alters sPLA(2)-mediated hydrolysis. This report tests the hypothesis that hydrophobic SP-B also inhibits sPLA(2)-mediated surfactant hydrolysis. Three surfactant preparations were used containing varied amounts of SP-B and radiolabeled tracers of phosphatidylcholine (PC) or phosphatidylglycerol (PG): 1) washed ovine surfactant (OS) (pre- and postorganic extraction) compared with Survanta (protein poor), 2) Survanta supplemented with purified bovine SP-B (1-5%, wt/wt), and 3) a mixture of dipalmitoylphosphatidylcholine (DPPC), 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC), and 1-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG) (DPPC:POPC:POPG, 40:40:20) prepared as vesicles and monomolecular films in the presence or absence of SP-B. Hydrolysis of PG and PC by Group IB sPLA(2) (PLA2G1A) was significantly lower in the extracted OS, which contains SP-B, compared with Survanta (P = 0.005), which is SP-B poor. Hydrolysis of PG and PC in nonextracted OS, which contains all SPs, was lower than both Survanta and extracted OS. When Survanta was supplemented with 1% SP-B, PG and PC hydrolysis by PLA2G1B was significantly lower (P < 0.001) than in Survanta alone. When supplemented into pure lipid vesicles and monomolecular films composed of PG and PC mixtures, SP-B also inhibited hydrolysis by both PLA2G1B and Group IIA sPLA2 (PLA2G2A). In films, PLA2G1B hydrolyzed surfactant PL monolayers at surface pressures ≤30 mN/m (P < 0.01), and SP-B lowered the surface pressure range at which hydrolysis can occur. These results suggest the hydrophobic SP, SP-B, protects alveolar surfactant PL from hydrolysis mediated by multiple sPLA(2) in both vesicles (alveolar subphase) and monomolecular films (air-liquid interface).

Drastic changes in the tissue-specific expression of secreted phospholipases A2 in chicken pulmonary disease

Infectious bronchitis is one of the most important diseases in poultry and it causes major economic losses. Infectious bronchitis is an acute, highly contagious, viral disease of chickens, characterized by rales, coughing, and sneezing.

Because secreted phospholipases A2 (sPLA2) are involved in inflammatory processes, the gene expressions of sPLA2s were investigated in both healthy chickens and chickens with infectious bronchitis and lung inflammation. The draft chicken genome was first scanned using human sPLA2 sequences to identify chicken sPLA2s (ChPLA2), chicken total mRNA were isolated and RT-PCR experiments were performed to amplify and then sequence orthologous cDNAs. Full-length cDNA sequences of ChPLA2-IB, -IIA, -IIE, -V and -X were cloned. The high degree of sequence identity of 50–70% between the avian and mammalian (human and mouse) sPLA2 orthologs suggests a conservation of important enzymatic functions for these phospholipases.

Quantitation by qPCR of the transcript levels of ChPLA2-IB, -IIA, -IIE, -V and -X in several tissues from healthy chicken indicated that the expression patterns and mRNA levels diverged among the phospholipases tested. In chicken with infectious bronchitis, an over expression of ChPLA2-V was observed in lungs and spleen in comparison with healthy chicken. These findings suggest that ChPLA2-V could be a potential biomarker for lung inflammation. Conversely, a down regulation of ChPLA2-IB, -IIA and -X was observed in lungs and spleen in case of infectious bronchitis. A significant increase in the expression level of ChPLA2-X and ChPLA2-IB was also noticed in pancreas. No or minor changes have been detected in the expression of ChPLA2-IIE in lungs and small intestine, but it shows a significant increase in several infected tissues.

Enzymatic toxins from snake venom: structural characterization and mechanism of catalysis

Snake venoms are cocktails of enzymes and non-enzymatic proteins used for both the immobilization and digestion of prey. The most common snake venom enzymes include acetylcholinesterases, l-amino acid oxidases, serine proteinases, metalloproteinases and phospholipases A(2) . Higher catalytic efficiency, thermal stability and resistance to proteolysis make these enzymes attractive models for biochemists, enzymologists and structural biologists. Here, we review the structures of these enzymes and describe their structure-based mechanisms of catalysis and inhibition. Some of the enzymes exist as protein complexes in the venom. Thus we also discuss the functional role of non-enzymatic subunits and the pharmacological effects of such protein complexes. The structures of inhibitor-enzyme complexes provide ideal platforms for the design of potent inhibitors which are useful in the development of prototypes and lead compounds with potential therapeutic applications.

Integrated lipidomics in the secreted phospholipase A(2) biology

Mammalian genomes encode genes for more than 30 phospholipase A(2)s (PLA(2)s) or related enzymes, which are subdivided into several subgroups based on their structures, catalytic mechanisms, localizations and evolutionary relationships. More than one third of the PLA(2) enzymes belong to the secreted PLA(2) (sPLA(2)) family, which consists of low-molecular-weight, Ca(2+)-requiring extracellular enzymes, with a His-Asp catalytic dyad. Individual sPLA(2) isoforms exhibit unique tissue and cellular localizations and enzymatic properties, suggesting their distinct pathophysiological roles. Recent studies using transgenic and knockout mice for several sPLA(2) isoforms, in combination with lipidomics approaches, have revealed their distinct contributions to various biological events. Herein, we will describe several examples of sPLA(2)-mediated phospholipid metabolism in vivo, as revealed by integrated analysis of sPLA(2) transgenic/knockout mice and lipid mass spectrometry. Knowledge obtained from this approach greatly contributes to expanding our understanding of the sPLA(2) biology and pathophysiology.

Purification and biochemical characterization of a secreted group IIA chicken intestinal phospholipase A₂

Background

Secretory phospholipase A2 group IIA (IIA PLA2) is a protein shown to be highly expressed in the intestine of mammals. However, no study was reported in birds.

Results

Chicken intestinal group IIA phospholipase A₂ (ChPLA₂-IIA) was obtained after an acidic treatment (pH.3.0), precipitation by ammonium sulphate, followed by sequential column chromatographies on Sephadex G-50 and mono-S ion exchanger. The enzyme was found to be a monomeric protein with a molecular mass of around 14 kDa. The purified enzyme showed a substrate preference for phosphatidylethanolamine and phosphatidylglycerol, and didn't hydrolyse phosphatidylcholine. Under optimal assay conditions, in the presence of 10 mM NaTDC and 10 mM CaCl_2, a specific activity of 160 U.mg^-1 for purified ChPLA₂-IIA was measured using egg yolk as substrate. The fifteen NH2-terminal amino acid residues of ChPLA₂-IIA were sequenced and showed a close homology with known intestinal secreted phospholipases A₂. The gene encoding the mature ChPLA₂-IIA was cloned and sequenced. To further investigate structure-activity relationship, a 3D model of ChPLA₂-IIA was built using the human intestinal phospholipase A₂ structure as template.

Conclusion

ChPLA2-IIA was purified to homogeneity using only two chromatographic colomns. Sequence analysis of the cloned cDNA indicates that the enzyme is highly basic with a pI of 9.0 and has a high degree of homology with mammalian intestinal PLA₂-IIA.

Recent progress in phospholipase A₂ research: from cells to animals to humans

Mammalian genomes encode genes for more than 30 phospholipase A₂s (PLA₂s) or related enzymes, which are subdivided into several classes including low-molecular-weight secreted PLA₂s (sPLA₂s), Ca²+-dependent cytosolic PLA₂s (cPLA₂s), Ca²+-independent PLA₂s (iPLA₂s), platelet-activating factor acetylhydrolases (PAF-AHs), lysosomal PLA₂s, and a recently identified adipose-specific PLA. Of these, the intracellular cPLA₂ and iPLA₂ families and the extracellular sPLA₂ family are recognized as the "big three". From a general viewpoint, cPLA₂α (the prototypic cPLA₂ plays a major role in the initiation of arachidonic acid metabolism, the iPLA₂ family contributes to membrane homeostasis and energy metabolism, and the sPLA₂ family affects various biological events by modulating the extracellular phospholipid milieus. The cPLA₂ family evolved along with eicosanoid receptors when vertebrates first appeared, whereas the diverse branching of the iPLA₂ and sPLA₂ families during earlier eukaryote development suggests that they play fundamental roles in life-related processes. During the past decade, data concerning the unexplored roles of various PLA₂ enzymes in pathophysiology have emerged on the basis of studies using knockout and transgenic mice, the use of specific inhibitors, and information obtained from analysis of human diseases caused by mutations in PLA₂ genes. This review focuses on current understanding of the emerging biological functions of PLA₂s and related enzymes.

Pancreatic acinar cell-specific overexpression of group 1B phospholipase A2 exacerbates diet-induced obesity and insulin resistance in mice

Genome-wide association studies have identified significant association between polymorphisms of the Group 1B phospholipase A(2) (PLA2G1B) gene and central obesity in humans. Previous studies have shown that Pla2g1b inactivation decreases post-prandial lysophospholipid absorption, and as a consequence increases hepatic fatty acid oxidation and protects against diet-induced obesity and glucose intolerance in mice. The present study showed that transgenic mice with pancreatic acinar cell-specific overexpression of the human PLA2G1B gene gained significantly more weight and displayed elevated insulin resistance characteristics, such as impaired glucose tolerance, compared with wild-type (WT) mice, when challenged with a high-fat/carbohydrate diet. Pre- and post-prandial plasma β-hydroxybutyrate levels were also lower, indicative of decreased hepatic fatty acid oxidation, in the hypercaloric diet-fed PLA2G1B transgenic mice. These, along with earlier observations of Pla2g1b-null mice, document that Pla2g1b expression level is an important determinant of susceptibility to diet-induced obesity and diabetes, suggesting that the relationship between PLA2G1B polymorphisms and obesity may be due to differences in PLA2G1B expression levels between these individuals. The ability of pancreas-specific overexpression of PLA2G1B to promote obesity and glucose intolerance suggests that target phospholipase activity in the digestive tract with non-absorbable inhibitors should be considered as a therapeutic option for metabolic disease therapy.

Emerging roles of secreted phospholipase A2 enzymes: Lessons from transgenic and knockout mice

Among the emerging phospholipase A(2) (PLA(2)) superfamily, the secreted PLA(2) (sPLA(2)) family consists of low-molecular-mass, Ca(2+)-requiring extracellular enzymes with a His-Asp catalytic dyad. To date, more than 10 sPLA(2) enzymes have been identified in mammals. Individual sPLA(2)s exhibit unique tissue and cellular localizations and enzymatic properties, suggesting their distinct pathophysiological roles. Despite numerous enzymatic and cell biological studies on this enzyme family in the past two decades, their precise in vivo functions still remain largely obscure. Recent studies using transgenic and knockout mice for several sPLA(2) enzymes, in combination with lipidomics approaches, have opened new insights into their distinct contributions to various biological events such as food digestion, host defense, inflammation, asthma and atherosclerosis. In this article, we overview the latest understanding of the pathophysiological functions of individual sPLA(2) isoforms fueled by studies employing transgenic and knockout mice for several sPLA(2)s.

Phospholipase A2 in meconium-induced lung injury

Although the triggering mechanisms of tissue inflammation and injury in meconium-contaminated lungs are still unclear, there is increasing evidence to suggest a central role for phospholipase A(2)'s (PLA(2)). In fact, elevated PLA(2) activities together with high enzyme concentrations, especially the amount of pancreatic (group I) secretory PLA(2) (PLA(2)-I), have been detected in human meconium and in meconium-contaminated lungs. Recent data from our laboratory further indicate that human pancreatic PLA(2), introduced in high amounts within aspirated particulate meconium, is a potent inducer of lung tissue inflammatory injury. Our finding of elevated human PLA(2)-I concentrations in plasma during the first hours after intratracheal meconium administration in newborn piglets further suggests that intrapulmonary aspiration of meconium could also have systemic inflammatory and injurious effects. This, however, remains to be studied in further detail.

Role of secretory phospholipase a(2) in CNS inflammation: implications in traumatic spinal cord injury

Secretory phospholipases A(2) (sPLA(2)s) are a subfamily of lipolytic enzymes which hydrolyze the acyl bond at the sn-2 position of glycerophospholipids to produce free fatty acids and lysophospholipids. These products are precursors of bioactive eicosanoids and platelet-activating factor (PAF). The hydrolysis of membrane phospholipids by PLA(2) is a rate-limiting step for generation of eicosanoids and PAF. To date, more than 10 isozymes of sPLA(2) have been found in the mammalian central nervous system (CNS). Under physiological conditions, sPLA(2)s are involved in diverse cellular responses, including host defense, phospholipid digestion and metabolism. However, under pathological situations, increased sPLA(2) activity and excessive production of free fatty acids and their metabolites may lead to inflammation, loss of membrane integrity, oxidative stress, and subsequent tissue injury. Emerging evidence suggests that sPLA(2) plays a role in the secondary injury process after traumatic or ischemic injuries in the brain and spinal cord. Importantly, sPLA(2) may act as a convergence molecule that mediates multiple key mechanisms involved in the secondary injury since it can be induced by multiple toxic factors such as inflammatory cytokines, free radicals, and excitatory amino acids, and its activation and metabolites can exacerbate the secondary injury. Blocking sPLA(2) action may represent a novel and efficient strategy to block multiple injury pathways associated with the CNS secondary injury. This review outlines the current knowledge of sPLA(2) in the CNS with emphasis placed on the possible roles of sPLA(2) in mediating CNS injuries, particularly the traumatic and ischemic injuries in the brain and spinal cord.

Biology of secretory phospholipase A2

Introduction

The secretory phospholipase A₂ (sPLA₂) family provides a seemingly endless array of potential biological functions that is only beginning to be appreciated. In humans, this family comprises 9 different members that vary in their tissue distribution, hydrolytic activity, and phospholipid substrate specificity. Through their lipase activity, these enzymes trigger various cell-signaling events to regulate cellular functions, directly kill bacteria, or modulate inflammatory responses. In addition, some sPLA₂’s are high affinity ligands for cellular receptors.

Objective

This review merely scratches the surface of some of the actions of sPLA₂s in innate immunity, inflammation, and atherosclerosis. The goal is to provide an overview of recent findings involving sPLA₂s and to point to potential pathophysiologic mechanisms that may become targets for therapy.

Interferon gamma-induced gene expression of the novel secretory phospholipase A2 type IID in human monocyte-derived macrophages is inhibited by lipopolysaccharide

Phospholipase A(2) (PLA(2)) is a superfamily of enzymes that may play a major role in airways inflammation. We investigated the effect of interferon-gamma (IFN-gamma) on the gene expression of 19 different PLA(2) types in human monocyte-derived macrophages and nasal epithelial cells (RPMI 2650). The cells were stimulated with IFN-gamma for different lengths of time (up to 48 h), and the mRNA levels of the different PLA(2) types were determined by reverse transcriptase-PCR (RT-PCR) and normalized to those of the house-keeping gene, GAPDH. It appeared that IFN-gamma clearly increased the expression of secretory PLA(2) IID (but not IIA) in macrophages, while both PLA(2) IID and IIA were upregulated in RPMI 2650 cells. Moreover, after 18 h, the mRNA levels of cytosolic PLA(2) IVA were 2-3 times higher in IFN-gamma-stimulated macrophages than controls, while there was no such effect of IFN-gamma in RPMI 2650 cells. Lipopolysaccharide (LPS) augmented the increased gene expression of PLA(2) IVA but decreased both the basal and the IFN-gamma-induced PLA(2) IID mRNA expression in macrophages (but not in RPMI 2650 cells). The NF-kappaB inhibitor Pyrrolidine dithiocarbamate (PDTC) and the phoshatidylinositol 3-kinase (PI3K) inhibitor wortmannin were employed to get an insight into the mechanism behind these observations. Incubation of macrophages with PDTC had no effect on the LPS impairment of PLA(2) IID gene expression, but inhibited the LPS mediated activation of PLA(2) IVA. No significant effect was noted of PDTC on IFN-gamma stimulation, while PI3K had no effect at all on any of the stimuli used. Furthermore, LPS (but not IFN-gamma) increased the mRNA levels of the nuclear factor (NF)-kappaB inhibitors alpha and xi in macrophages, but not in RPMI 2650 cells. These findings indicate that (a) the gene expression of secretory types PLA(2) IID and IIA in response to IFN-gamma is much dependent on cell type, and (b) the regulation of PLA(2) type IID in human macrophages is clearly different from that of PLA(2) type IVA. (c) PLA(2) IVA is probably under control of both NF-kappaB and IFN-gamma-responsive elements (GRE) or IFN-gamma-activating sites (GAS). The possibility that PLA(2) IID is involved in cytokine-mediated inflammation in the nasal mucosa is inferred, as is the potential role of PLA(2) IID in the host defense against LPS-containing bacteria.

Human pancreatic digestive enzymes

A primary function of the pancreas is to produce digestive enzymes that are delivered to the small intestine for the hydrolysis of complex nutrients. Much of our understanding of digestive enzymes comes from studies in animals. New technologies and the availability of the sequence of the human genome allow for a critical review of older reports and assumptions based on animal studies. This report updates our understanding of human pancreatic digestive enzymes with a focus on new insights into the biology of human proteases, lipases and amylases.

Human secretory phospholipase A2, group IB in normal eyes and in eye diseases

PURPOSE

Secretory phospholipases A(2) (sPLA(2)) are enzymes involved in lipid turnover. We recently identified sPLA(2) group IB (GIB) in the rat retina as well as in cerebral neurons and found upregulation to occur in response to light damage and seizures, respectively. The purpose of the present study was to identify human GIB (hGIB) in the normal human eye and investigate the pattern of expression in patients with eye diseases involving hGIB-rich cells.

METHODS

Human GIB mRNA was identified in the human retina by means of in situ hybridization and polymerase chain reaction. Antibodies against hGIB were obtained and immunohistochemical staining was performed on paraffin-embedded sections of normal and pathological eyes. Donor eyes from patients with descemetization of the cornea, Fuchs' corneal endothelial dystrophy, age-related macular degeneration, malignant choroidal melanoma, retinitis pigmentosa and glaucoma were evaluated.

RESULTS

Expression of hGIB was found in various cells of the eye. The most abundant expression was found in retinal pigment epithelium (RPE) cells, the inner photoreceptor segments, ganglion cells and the corneal endothelium. We explored diseases involving hGIB-rich cells and found downregulation of hGIB in proliferating RPE cells as well as in diseased corneal endothelial cells.

CONCLUSIONS

Human GIB is highly expressed in cells with neurodermal origin. The pattern of expression of hGIB in diseases involving hGIB-rich cells demonstrated a downregulation of hGIB in migrating RPE cells and in diseased corneal endothelium.

Calcineurin/Nfat signaling is required for perinatal lung maturation and function

Pulmonary surfactant proteins and lipids are required for lung function after birth. Lung immaturity and resultant surfactant deficiency cause respiratory distress syndrome, a common disorder contributing to morbidity and mortality in preterm infants. Surfactant synthesis increases prior to birth in association with formation of the alveoli that mediate efficient gas exchange. To identify mechanisms controlling perinatal lung maturation, the Calcineurin b1 (Cnb1) gene was deleted in the respiratory epithelium of the fetal mouse. Deletion of Cnb1 caused respiratory failure after birth and inhibited the structural maturation of the peripheral lung. Synthesis of surfactant and a lamellar body-associated protein, ABC transporter A3 (ABCA3), was decreased prior to birth. Nuclear factor of activated T cells (Nfat) calcineurin-dependent 3 (Nfatc3), a transcription factor modulated by calcineurin, was identified as a direct activator of Sftpa, Sftpb, Sftpc, Abca3, Foxa1, and Foxa2 genes. The calcineurin/Nfat pathway controls the morphologic maturation of lungs prior to birth and regulates expression of genes involved in surfactant homeostasis that are critical for adaptation to air breathing.

Secretory phospholipases A2 stimulate mucus secretion, induce airway inflammation, and produce secretory hyperresponsiveness to neutrophil elastase in ferret trachea

Secretory phospholipases A(2) (sPLA(2)) are increased in the bronchoalveolar lavage fluid of patients with asthma and acute respiratory distress syndrome. Intratracheal sPLA(2) instillation induces acute lung injury in the rat and guinea pig. We hypothesized that sPLA(2) would stimulate mucus secretion in vitro and that intratracheal sPLA(2) exposure would induce mucus hypersecretion and airway inflammation in the ferret trachea in vivo. In vitro, porcine pancreatic sPLA(2) at a concentration of 0.5 or 5 U/ml significantly increased mucous glycoconjugate (MG) secretion from the excised ferret trachea. P-bromophenacylbromide (a sPLA(2) inhibitor), quercetin (a lipoxygenase inhibitor), or MK-886 (a 5-lipoxygenase inhibitor), each at 10(-4) M, significantly reduced sPLA(2)-induced MG secretion. sPLA(2)-stimulated MG secretion was decreased in Ca(2+)-free medium. In vivo, ferrets were intubated for 30 min once per day for 3 days using an ETT coated with 20 units of porcine pancreatic sPLA(2) mixed in water-soluble jelly. Constitutive MG secretion increased 1 day after sPLA(2) exposure and returned to control 5 days later. Human neutrophil elastase (HNE) at 10(-8) M increased MG secretion in the sPLA(2)-exposed trachea compared with that in the control trachea, but methacholine at 10(-7) M did not. sPLA(2)-induced secretory hyperresponsiveness continued for at least 5 days after sPLA(2) exposure ended. sPLA(2) increased tracheal inflammation, MG secretion, and secretory hyperresponsiveness to HNE probably through enzymatic action rather than by activation of its receptor.

Purification and biochemical characterization of phospholipase A2 from dromedary pancreas

Dromedary pancreatic PLA2 (DrPLA2) was purified from delipidated pancreases. Pure protein was obtained after heat and acidic treatment (70 degrees C; pH 3.0), precipitation by ammonium sulphate and ethanol respectively, followed by sequential column chromatographies on Sephadex G-50, MonoS Sepharose, MonoQ Sepharose and C-8 reverse phase high pressure liquid chromatography. Purified DrPLA2, which is not glycosylated protein, was found to be monomeric protein with a molecular mass of 13748.55 Da. A specific activity of 600 U/mg for purified DrPLA2 was measured at optimal conditions (pH 8.0 and 37 degrees C) in the presence of 3 mM NaTDC and 7 mM CaCl(2) using PC as substrate. The sequence of the first fourteen amino-acid residues at the N-terminal extremity of DrPLA2 was determined by automatic Edman degradation. One single sequence was obtained and shows a close similarity with all other known pancreatic secreted phospholipases A2.

Analysis of expression of secreted phospholipases A2 in mouse tissues at protein and mRNA levels

Secreted phospholipases A(2) (sPLA(2)) form a group of low-molecular weight enzymes that catalyze the hydrolysis of phospholipids. Some sPLA(2)s are likely to play a role in inflammation, cancer, and as antibacterial enzymes in innate immunity. We developed specific and sensitive time-resolved fluroimmunoassays (TR-FIA) for mouse group (G) IB, GIIA, GIID, GIIE, GIIF, GV and GX sPLA(2)s and measured their concentrations in mouse serum and tissues obtained from both Balb/c and C57BL/6J mice. We also analyzed the mRNA expression of the sPLA(2)s by quantitative real-time reverse transcriptase PCR (qPCR). In most tissues, the concentrations of sPLA(2) proteins corresponded to the expression of sPLA(2)s at the mRNA level. With a few exceptions, the sPLA(2) proteins were found in the gastrointestinal tract. The qPCR results showed that GIB sPLA(2) is synthesized widely in the gastrointestinal tract, including esophagus and colon, in addition to stomach and pancreas. Our results also suggest that the loss of GIIA sPLA(2) in the intestine of GIIA sPLA(2)-deficient C57BL/6J mice is not compensated by other sPLA(2)s under normal conditions. Outside the gastrointestinal tract, sPLA(2)s were expressed occasionally in a number of tissues. The TR-FIAs developed in the current study may serve as useful tools to measure the levels of sPLA(2) proteins in mouse serum and tissues in various experimental settings.

Pancreatic phospholipase A2 contributes to lung injury in experimental meconium aspiration

To investigate the role of pancreatic (group I) secretory PLA2 (sPLA2-I) in the pathogenesis of meconium aspiration syndrome, human particulate meconium or its supernatant either before or after extraction of PLA2-I was insufflated into rat lungs. In addition, the pulmonary effects of intra-tracheal human and bovine PLA2-I were studied. Lungs with saline instillation served as controls. Intrapulmonary particulate meconium (both before and after PLA2-I extraction), unlike meconium supernatant, resulted in markedly elevated lung tissue PLA2 catalytic activity and human PLA2-I concentrations when compared with controls. On the other hand, tissue concentrations of the group II PLA2 remained unchanged in all meconium lungs. Pulmonary PLA2-I concentrations further correlated positively with lung injury scores. Instillation of meconium-derived human PLA2-I, at a concentration of one-third of that in particulate meconium, did not raise PLA2 activity or concentrations of PLA2-I or PLA2-II in the lung tissue from the control level, but still resulted in significantly elevated lung wet/dry ratio and injury score. In contrast, insufflation of bovine pancreatic PLA2 increased the lung tissue enzyme activity and wet/dry ratio from the control level, but had no effect on the type II PLA2 concentration or lung injury score. Our data thus indicate that human pancreatic PLA2, introduced in high amounts within aspirated meconium especially in particulate form, is a potent inducer of lung tissue inflammatory injury.

Time-resolved fluoroimmunoassays of the complete set of secreted phospholipases A2 in human serum

Time-resolved fluoroimmunoassays (TR-FIA) were developed for all human secreted phospholipases A(2) (PLA(2)), viz. group (G) IB, GIIA, GIID, GIIE, GIIF, GIII, GV, GX and GXIIA PLA(2) and the GXIIB PLA(2)-like protein. Antibodies were raised in rabbits against recombinant human PLA(2) proteins and used in sandwich-type TR-FIAs as both catching and detecting antibodies, the latter after labeling with Europium. The antibodies were non-cross-reactive. The analytical sensitivities were 1 microg/L for the TR-FIA for GIB PLA(2), 1 microg/L (GIIA), 35 microg/L (GIID), 3 microg/L (GIIE), 4 microg/L (GIIF), 14 microg/L (GIII), 11 microg/L (GV), 2 microg/L (GX), 92 microg/L (GXIIA) and 242 microg/L (GXIIB). All secreted PLA(2)s were assayed by these TR-FIAs in serum samples from 34 patients (23 men and 11 women, mean age 53.2 years) treated in an intensive care unit for septic infections, and in control samples from 28 volunteer blood donors (14 men and 14 women, mean age 57.0 years). Five serum samples (3 in the sepsis group and 2 in the blood donor group) gave high TR-FIA signals that were reduced to background (blank) levels by the addition of non-immune rabbit IgG to the sera. This reactivity was assumed to be due to the presence of heterophilic antibodies in these subjects. In all other subjects, including septic patients and healthy blood donors, the TR-FIA signals for GIID, GIIE, GIIF, GIII, GV, GX and GXIIA PLA(2) and the GXIIB PLA(2)-like protein were at background (blank) levels. Four patients in the sepsis group had pancreatic involvement and elevated concentration of GIB PLA(2) in serum (median 19.0 microg/L, range 13.1-33.7 microg/L, n = 4) as compared to the healthy blood donors (median 1.8 microg/L, range 0.8-3.4 microg/L, n = 28, P < 0.0001). The concentration of GIIA PLA(2) in the sera of septic patients (median 315.7 microg/L, range 15.9-979.6 microg/L, n = 34) was highly elevated as compared to that of the blood donors (median 1.8 microg/L, range 0.8-5.8 microg/L, n = 28, P < 0.0001). Our current results confirmed elevated concentrations of GIB and GIIA PLA(2) in the sera of patients suffering from acute pancreatitis or septic infections, respectively, as compared to healthy subjects. However, in the same serum samples, the concentrations of the other secreted PLA(2)s, viz. GIID, GIIE, GIIF, GIII, GV, GX and GXIIA PLA(2) and the GXIIB PLA(2)-like protein were below the respective analytical sensitivities of the TR-FIAs. It is concluded that generalized bacterial infections do not lead to elevated serum levels of GIIE, GIIF, GIII, GV and GX PLA(2)s above the detection limits of the current TR-FIAs.

Genetic association between the phospholipase A2 gene and unipolar affective disorder: a multicentre case-control study

The co-segregation in one pedigree of bipolar affective disorder with Darier's disease whose gene is on chromosome 12q23-q24.1, and findings from linkage and association studies with the neighbouring gene of phospholipase A2 (PLA2) indicate that PLA2 may be considered as a candidate gene for affective disorders. All relevant genetic association studies, however, were conducted on bipolar patients. In the present study, the possible association between the PLA2 gene and unipolar affective disorder was examined on 321 unipolar patients and 604 controls (all personally interviewed), recruited from six countries (Belgium, Bulgaria, Croatia, Germany, Greece, and Italy) participating in the European Collaborative Project on Affective Disorders. After controlling for population group and gender, one of the eight alleles of the investigated marker (allele 7) was found to be more frequent among unipolar patients with more than three major depressive episodes than among controls (P<0.01); genotypic association was also observed, under the dominant model of genetic transmission (P<0.02). In addition, presence of allele 7 was correlated with a higher frequency of depressive episodes (P<0.02). These findings suggest that structural variations at the PLA2 gene or the chromosomal region around it may confer susceptibility for unipolar affective disorder.

Molecular evolution of myotoxic phospholipases A2 from snake venom

After two decades of study, we draw the conclusion that venom-gland phospholipase A2 (PLA2) isozymes, including PLA2 myotoxins of Crotalinae snakes, have evolved in an accelerated manner to acquire their diverse physiological activities. In this review, we describe how accelerated evolution of venom PLA2 isozymes was discovered. This type of evolution is fundamental for other venom isozyme systems. Accelerated evolution of venom PLA2 isozyme genes is due to rapid change in exons, but not in introns and the flanking regions, being completely opposite to the case of the ordinary isozyme genes. The molecular mechanism by which proper base substitutions had occurred in the particular sites of venom isozyme genes is a puzzle to be solved in future studies. It should be noted that accelerated evolution occurred until the isozymes had acquired their particular function and, since then, they have evolved with less frequent mutation, possibly for functional conservation. We also found that interisland mutations occurred in venom PLA2 isozymes. The relationships between mutation and its driving force are speculative and the real mechanism remains a mystery.

Group IB phospholipase A2 from Pseudonaja textilis

Pseudonaja textilis, an Australian Elapid, is known to produce a highly toxic venom. Both protein profiling and N-terminal sequence analysis showed the presence of four new phospholipases A(2) in this venom. Besides being non-lethal, the phospholipase A(2) proteins were found to be moderately active enzymes and they showed procoagulant property. cDNA cloning and characterization indicated the presence of two isoforms of PLA(2) proteins in a single snake, each containing the "pancreatic loop," characteristic of group IB phospholipase A(2). The genomic cloning also confirmed the presence of two genes each containing four exons that are interrupted by three introns. Phylogenetic analysis showed that the venom group IB PLA(2) gene is primitive and could have evolved from the same ancestor as the mammalian and venom group IA PLA(2) genes. In the present study, we report that the Pt-PLA2 gene could be responsible for the production of PL1, 2, and 3 possibly via RNA editing process.

Phospholipase A(2)

Considerable progress has been made in characterizing the individual participant enzymes and their relative contributions in the generation of eicosanoids, lipid mediators derived from arachidonic acid, such as prostaglandins and leukotrienes. However, the role of individual phospholipase (PL) A(2) enzymes in providing arachidonic acid to the downstream enzymes for eicosanoid generation in biologic processes has not been fully elucidated. In this review, we will provide an overview of the classification of the families of PLA(2) enzymes, their putative mechanisms of action, and their role(s) in eicosanoid generation and inflammation.