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Purification and characterization of a calcium-independent acidic phospholipase A2 from rat lung.

ABSTRACT: Several phospholipase A2 (PLA2) activities have been identified in rat lung homogenate and shown to be important in metabolism of lung phospholipids. One PLA2 activity is Ca(2+)-independent, active in vitro at pH 4, and inhibited by a substrate analogue, 1-hexadecyl-3-trifluoroethylglycero-sn-2-phosphomethanol (MJ33). Purification of this rat lung PLA2 by approx. 550-fold was carried out by sequential column chromatographies using DE-52, Sephacryl-100, heparin-Sepharose, and phenyl-Sepharose columns. The purified activity had an acidic pH optimum, was Ca(2+)-independent, was inhibited by MJ33 in a dose-dependent manner (50% inhibition at 3 mol%), was unaffected by treatment with p-bromophenacyl bromide or mercaptoethanol, and had a unique N-terminal amino acid sequence. The apparent molecular mass was 15 kDa on gel electrophoresis and activity was recovered in part by renaturation of protein from the gel. The properties of this enzyme suggest a new class of PLA2.

SUBMITTER: Wang R

PROVIDER: S-EPMC1137462 | biostudies-other | 1994 Nov

REPOSITORIES: biostudies-other

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Project description:BackgroundAntimicrobial peptides derived from the natural processing of chromogranin A (CgA) are co-secreted with catecholamines upon stimulation of chromaffin cells. Since PMNs play a central role in innate immunity, we examine responses by PMNs following stimulation by two antimicrobial CgA-derived peptides.Methodology/principal findingsPMNs were treated with different concentrations of CgA-derived peptides in presence of several drugs. Calcium mobilization was observed by using flow cytometry and calcium imaging experiments. Immunocytochemistry and confocal microscopy have shown the intracellular localization of the peptides. The calmodulin-binding and iPLA2 activating properties of the peptides were shown by Surface Plasmon Resonance and iPLA2 activity assays. Finally, a proteomic analysis of the material released after PMNs treatment with CgA-derived peptides was performed by using HPLC and Nano-LC MS-MS. By using flow cytometry we first observed that after 15 s, in presence of extracellular calcium, Chromofungin (CHR) or Catestatin (CAT) induce a concentration-dependent transient increase of intracellular calcium. In contrast, in absence of extra cellular calcium the peptides are unable to induce calcium depletion from the stores after 10 minutes exposure. Treatment with 2-APB (2-aminoethoxydiphenyl borate), a store operated channels (SOCs) blocker, inhibits completely the calcium entry, as shown by calcium imaging. We also showed that they activate iPLA2 as the two CaM-binding factors (W7 and CMZ) and that the two sequences can be aligned with the two CaM-binding domains reported for iPLA2. We finally analyzed by HPLC and Nano-LC MS-MS the material released by PMNs following stimulation by CHR and CAT. We characterized several factors important for inflammation and innate immunity.Conclusions/significanceFor the first time, we demonstrate that CHR and CAT, penetrate into PMNs, inducing extracellular calcium entry by a CaM-regulated iPLA2 pathway. Our study highlights the role of two CgA-derived peptides in the active communication between neuroendocrine and immune systems.

Project description:Calcium-independent phospholipase A(2)? (iPLA(2)?) (PNPLA8) is the predominant phospholipase activity in mammalian mitochondria. However, the chemical mechanisms that regulate its activity are unknown. Here, we utilize iPLA(2)? gain of function and loss of function genetic models to demonstrate the robust activation of iPLA(2)? in murine myocardial mitochondria by Ca(2+) or Mg(2+) ions. Calcium ion stimulated the production of 2-arachidonoyl-lysophosphatidylcholine (2-AA-LPC) from 1-palmitoyl-2-[(14)C]arachidonoyl-sn-glycero-3-phosphocholine during incubations with wild-type heart mitochondrial homogenates. Furthermore, incubation of mitochondrial homogenates from transgenic myocardium expressing iPLA(2)? resulted in 13- and 25-fold increases in the initial rate of radiolabeled 2-AA-LPC and arachidonic acid (AA) production, respectively, in the presence of calcium ion. Mass spectrometric analysis of the products of calcium-activated hydrolysis of endogenous mitochondrial phospholipids in transgenic iPLA(2)? mitochondria revealed the robust production of AA, 2-AA-LPC, and 2-docosahexaenoyl-LPC that was over 10-fold greater than wild-type mitochondria. The mechanism-based inhibitor (R)-(E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one (BEL) (iPLA(2)? selective), but not its enantiomer, (S)-BEL (iPLA(2)? selective) or pyrrolidine (cytosolic PLA(2)? selective), markedly attenuated Ca(2+)-dependent fatty acid release and polyunsaturated LPC production. Moreover, Ca(2+)-induced iPLA(2)? activation was accompanied by the production of downstream eicosanoid metabolites that were nearly completely ablated by (R)-BEL or by genetic ablation of iPLA(2)?. Intriguingly, Ca(2+)-induced iPLA(2)? activation was completely inhibited by long-chain acyl-CoA (IC(50) ?20 ?m) as well as by a nonhydrolyzable acyl-CoA thioether analog. Collectively, these results demonstrate that mitochondrial iPLA(2)? is activated by divalent cations and inhibited by acyl-CoA modulating the generation of biologically active metabolites that regulate mitochondrial bioenergetic and signaling functions.

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Purification and characterization of a calcium-independent acidic phospholipase A2 from rat lung.

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