Role of phospholipase D in Pasteurella haemolytica leukotoxin-induced increase in phospholipase A(2) activity in bovine neutrophils.
The effects of Pasteurella haemolytica leukotoxin (LKT) on the activity of phospholipase D (PLD) and the regulatory interaction between PLD and phospholipase A(2) (PLA(2)) were investigated in assays using isolated bovine neutrophils labeled with tritiated phospholipid substrates of the two enzymes. Exposure of [(3)H]lysophosphatidylcholine-labeled neutrophils to LKT caused concentration- and time-dependent production of phosphatidic acid (PA), the product of PLD. LKT-induced generation of PA was dependent on extracellular calcium. Both production of PA and metabolism of [(3)H]-arachidonate ([(3)H]AA)-labeled phospholipids by PLA(2) were inhibited when ethanol was used to promote the alternative PLD-mediated transphosphatidylation reaction, resulting in the production of phosphatidylethanol rather than PA. The role of PA in regulation of PLA(2) activity was then confirmed by means of an add-back experiment, whereby addition of PA in the presence of ethanol restored PLA(2)-mediated release of radioactivity from neutrophil membranes. Considering the involvement of chemotactic phospholipase products in the pathogenesis of pneumonic pasteurellosis, development and use of anti-inflammatory agents that inhibit LKT-induced activation of PLD and PLA(2) may improve therapeutic management of the disease.
Department of Anatomy, Pathology, and Pharmacology, College of Veterinary Medicine, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
Z
Z
Wang
C R
CR
Clarke
K D
KD
Clinkenbeard
D000818:Animals; D001427:Bacterial Toxins / Q000633:toxicity*; D002118:Calcium / Q000502:physiology; D002417:Cattle; D004789:Enzyme Activation; D005098:Exotoxins / Q000633:toxicity*; D007975:Leukotriene B4 / Q000096:biosynthesis; D016978:Mannheimia haemolytica / Q000472:pathogenicity*; D009504:Neutrophils / Q000201:enzymology*; D010739:Phospholipase D / Q000502:physiology*; D010741:Phospholipases A / Q000096:biosynthesis*
D001427:Bacterial Toxins; D005098:Exotoxins; C018579:leukotoxin; D007975:Leukotriene B4; D010741:Phospholipases A; D010739:Phospholipase D; D002118:Calcium