Secretory phospholipases A 2 (sPLA 2 s) represent a rapidly expanding family of structurally related enzymes found in mammals as well as in insect and snake venoms. In this report, a cDNA coding for a novel sPLA 2 has been isolated from human fetal lung, and its gene has been mapped to chromosome 16p13.1-p12. The mature sPLA 2 protein has a molecular mass of 13.6 kDa, is acidic (pI 5.3), and made up of 123 amino acids. Key structural features of the sPLA 2 include: (i) a long prepropeptide ending with an arginine doublet, (ii) 16 cysteines located at positions that are characteristic of both group I and group II sPLA 2 s, (iii) a C-terminal extension typical of group II sPLA 2 s, (iv) and the absence of elapid and pancreatic loops that are characteristic of group I sPLA 2 s. Based on these structural properties, this sPLA 2 appears as a first member of a new group of sPLA 2 s, called group X. A 1.5-kilobase transcript coding for the human group X (hGX) sPLA 2 was found in spleen, thymus, and peripheral blood leukocytes, while a less abundant 0.8-kilobase transcript was detected in the pancreas, lung, and colon. When the hGX sPLA 2 cDNA was expressed in COS cells, sPLA 2 activity preferentially accumulated in the culture medium, indicating that hGX sPLA 2 is an actively secreted enzyme. It is maximally active at physiological pH and with 10 mM Ca 2؉ . hGX sPLA 2 prefers phosphatidylethanolamine and phosphatidylcholine liposomes to those of phosphatidylserine.

Lyso-phospholipids exert a major injurious effect on lung cell membranes during Acute Respiratory Distress Syndrome (ARDS), but the mechanisms leading to their in vivo generation are still unknown. Intratracheal administration of LPS to guinea pigs induced the secretion of type II secretory phospholipase A2 (sPLA2-II) accompanied by a marked increase in fatty acid and lyso-phosphatidylcholine (lyso-PC) levels in the bronchoalveolar lavage fluid (BALF). Administration of LY311727, a specific sPLA2-II inhibitor, reduced by 60% the mass of free fatty acid and lyso-PC content in BALF. Gas chromatography/mass spectrometry analysis revealed that palmitic acid and palmitoyl-2-lyso-PC were the predominant lipid derivatives released in BALF. A similar pattern was observed after the intratracheal administration of recombinant guinea pig (r-GP) sPLA2-II and was accompanied by a 50-60% loss of surfactant phospholipid content, suggesting that surfactant is a major lung target of sPLA2-II. In confirmation, r-GP sPLA2-II was able to hydrolyze surfactant phospholipids in vitro. This hydrolysis was inhibited by surfactant protein A (SP-A) through a direct and selective protein-protein interaction between SP-A and sPLA2-II. Hence, our study reports an in vivo direct causal relationship between sPLA2-II and early surfactant degradation and a new process of regulation for sPLA2-II activity. Anti-sPLA2-II strategy may represent a novel therapeutic approach in lung injury, such as ARDS. (

No abstract

Type II-secreted phospholipase A 2 (type II-sPLA 2 ) is expressed in smooth muscle cells during atherosclerosis or in response to interleukin-1␤. The present study shows that the induction of type II-sPLA 2 gene by interleukin-1␤ requires activation of the NFB pathway and cytosolic PLA 2 /PPAR␥ pathway, which are both necessary to achieve the transcriptional process. Interleukin-1␤ induced type II-sPLA 2 gene dose-and time-dependently and increased the binding of NFB to a specific site of type II-sPLA 2 promoter. This effect was abolished by proteinase inhibitors that block the proteasome machinery and NFB nuclear translocation. Type II-sPLA 2 induction was also obtained by free arachidonic acid and was blocked by either AACOCF 3 , a specific cytosolic-PLA 2 inhibitor, PD98059, a mitogen-activated protein kinase kinase inhibitor which prevents cytosolic PLA 2 activation, or nordihydroguaiaretic acid, a lipoxygenase inhibitor, but not by the cyclooxygenase inhibitor indomethacin, suggesting a role for a lipoxygenase product. Type II-sPLA 2 induction was obtained after treatment of the cells by 15-deoxy-⌬ 12,14 -dehydroprostaglandin J 2 , carbaprostacyclin, and 9-hydroxyoctadecadienoic acid, which are ligands of peroxisome proliferator-activated receptor (PPAR) ␥, whereas PPAR␣ ligands were ineffective. Interleukin-1␤ as well as PPAR␥-ligands stimulated the activity of a reporter gene containing PPAR␥-binding sites in its promoter. Binding of both NFB and PPAR␥ to their promoter is required to stimulate the transcriptional process since inhibitors of each class block interleukin-1␤-induced type II-sPLA 2 gene activation. We therefore suggest that NFB and PPAR␥ cooperate at the enhanceosome-coactivator level to turn on transcription of the proinflammatory type II-sPLA 2 gene.