Systematic Evaluation of Transcellular Activities of Secretory Phospholipases A2

In an effort to elucidate the functions of secreted phospholipase A 2 (sPLA 2 ) enzymes in vivo, we generated transgenic (Tg) mice for group V sPLA 2 (sPLA 2 -V) and group X sPLA 2 (sPLA 2 -X), which act potently on phosphatidylcholine in vitro. We found that sPLA 2 -V Tg mice died in the neonatal period because of respiratory failure. The lungs of sPLA 2 -V Tg mice exhibited atelectasis with thickened alveolar walls and narrow air spaces, accompanied by infiltration of macrophages and only modest changes in eicosanoid levels. This severe pulmonary defect in sPLA 2 -V Tg mice was attributable to marked reduction of the lung surfactant phospholipids, phosphatidylcholine and phosphatidylglycerol. Given that the expression of sPLA 2 -V is greatly elevated in human lungs with severe inflammation, our present results raise the intriguing possibility that this isozyme may contribute to ongoing surfactant hydrolysis often observed in the lungs of patients with respiratory distress syndrome. In contrast, sPLA 2 -X Tg neonates displayed minimal abnormality of the respiratory tract with normal alveolar architecture and surfactant composition. This unexpected result was likely because sPLA 2 -X protein existed as an inactive zymogen in most tissues. The active form of sPLA 2 -X was detected in tissues with inflammatory granulation in sPLA 2 -X Tg mice. These results suggest that sPLA 2 -X mostly remains inactive under physiological conditions and that its proteolytic activation occurs during inflammation or other as yet unidentified circumstances in vivo.

Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 99%

Transgenic Expression of Group V, but Not Group X, Secreted Phospholipase A2 in Mice Leads to Neonatal Lethality because of Lung Dysfunction

Ohtsuki

Taketomi

Arata

et al. 2006

“…7A). Although mast cells express group V sPLA 2 , which reportedly has the potential to act on neighboring cells through the transcellular route after secretion (38,70,71), our study using Pla2g5 Ϫ/Ϫ BMMCs argues against the contribution of this sPLA 2 isoform to coculture augmented fibroblastic PGE 2 production. These observations suggest that AA is released mainly by cPLA 2 ␣ from phospholipids in mast cells, transferred to proximal fibroblasts through the juxtacrine route, and then sequentially metabolized to PGE 2 by fibroblastic mPGES-1.…”

Section: Discussionmentioning

confidence: 49%

“…We also used BMMCs obtained from group V sPLA 2 -null (Pla2g5 Ϫ/Ϫ ) mice, because it has been reported that group V sPLA 2 , which is expressed in BMMCs, is able to promote transcellular eicosanoid synthesis by adjacent cells (38,70,71). As shown in Fig.…”

Section: Mast Cell Cpla 2 ␣ Is Coupled With Fibroblastic Mpges-1-depementioning

confidence: 99%

Analysis of Two Major Intracellular Phospholipases A2 (PLA2) in Mast Cells Reveals Crucial Contribution of Cytosolic PLA2α, Not Ca2+-independent PLA2β, to Lipid Mobilization in Proximal Mast Cells and Distal Fibroblasts

Ueno

Taketomi

Yamamoto

et al. 2011

Background: Mast cells express cPLA 2 ␣ and iPLA 2 ␤. Results: Knock-out of cPLA 2 ␣, not iPLA 2 ␤, hampers arachidonic acid mobilization in mast cells and adjacent fibroblasts. Conclusion: Mast cell cPLA 2 ␣ is coupled with stromal synthesis of anti-allergic PGE 2 , whereas iPLA 2 ␤ is dispensable for mast cell function. Significance: The cPLA 2 ␣-dependent transcellular PGE 2 synthesis opens new insight into the lipid biochemistry and mast cell biology fields.

“…It has been reported that sPLA 2 s can exert cellular effects through different mechanisms (12). Based on the earlier finding that the level of sPLA 2 was elevated in inflammatory exudates (13,14), it was generally thought that sPLA 2 s are released to the extracellular medium in response to specific stimuli and act on different target cells by a transcellular or paracrine mechanism.…”

mentioning

confidence: 99%

Unique Membrane Interaction Mode of Group IIF Phospholipase A2

Wijewickrama

Albanese

Kim

et al. 2006

Self Cite

The mechanisms by which secretory phospholipases A 2 (PLA 2 s) exert cellular effects are not fully understood. Group IIF PLA 2 (gIIFPLA 2 ) is a structurally unique secretory PLA 2 with a long C-terminal extension. Homology modeling suggests that the membrane-binding surface of this acidic PLA 2 contains hydrophobic residues clustered near the C-terminal extension. Vesicle leakage and monolayer penetration measurements showed that gIIFPLA 2 had a unique ability to penetrate and disrupt compactly packed monolayers and bilayers whose lipid composition recapitulates that of the outer plasma membrane of mammalian cells. Fluorescence imaging showed that gIIFPLA 2 could also readily enter and deform plasma membrane-mimicking giant unilamellar vesicles. Mutation analysis indicates that hydrophobic residues (Tyr 115 , Phe 116 , Val 118 , and Tyr 119 ) near the C-terminal extension are responsible for these activities. When gIIFPLA 2 was exogenously added to HEK293 cells, it initially bound to the plasma membrane and then rapidly entered the cells in an endocytosis-independent manner, but the cell entry did not lead to a significant degree of phospholipid hydrolysis. GIIFPLA 2 mRNA was detected endogenously in human CD4؉ helper T cells after in vitro stimulation and exogenously added gIIFPLA 2 inhibited the proliferation of a T cell line, which was not seen with group IIA PLA 2 . Collectively, these data suggest that unique membrane-binding properties of gIIFPLA 2 may confer special functionality on this secretory PLA 2 under certain physiological conditions.