title: Pasteurella haemolytica A1-derived leukotoxin and endotoxin induce intracellular calcium elevation in bovine alveolar macrophages by different signaling pathways.
abstract: Leukotoxin and endotoxin derived from Pasteurella haemolytica serotype 1 are the primary virulence factors contributing to the pathogenesis of lung injury in bovine pneumonic pasteurellosis. Activation of bovine alveolar macrophages with endotoxin or leukotoxin results in the induction of cytokine gene expression, with different kinetics (H. S. Yoo, S. K. Maheswaran, G. Lin, E. L. Townsend, and T. R. Ames, Infect. Immun. 63:381-388, 1995; H. S. Yoo, B. S. Rajagopal, S. K. Maheswaran, and T. R. Ames, Microb. Pathog. 18:237-252, 1995). Furthermore, extracellular Ca2+ is required for leukotoxin-induced cytokine gene expression. However, the involvement of Ca2+ in endotoxin effects and the precise signaling mechanisms in the regulation of intracellular Ca2+ by leukotoxin and endotoxin are not known. In fura-2-acetoxymethyl ester-loaded alveolar macrophages, intracellular Ca2+ regulation by leukotoxin and endotoxin was studied by video fluorescence microscopy. Leukotoxin induced a sustained elevation of intracellular Ca2+ in a concentration-dependent fashion by influx of extracellular Ca2+ through voltage-gated channels. In the presence of fetal bovine serum, endotoxin elevated intracellular Ca2+ even in the absence of extracellular Ca2+. Leukotoxin-induced intracellular Ca2+ elevation was inhibited by pertussis toxin, inhibitors of phospholipases A2 and C, and the arachidonic acid analog 5,8,11,14-eicosatetraynoic acid. Intracellular Ca2+ elevation by endotoxin was inhibited by inhibitors of phospholipase C and protein tyrosine kinase, but not by pertussis toxin, or the arachidonic acid analog. To the best of our knowledge, this is the first report of Ca2+ signaling by leukotoxin through a G-protein-coupled mechanism involving activation of phospholipases A2 and C and release of arachidonic acid in bovine alveolar macrophages. Ca2+ signaling by endotoxin, on the other hand, involves activation of phospholipase C and requires tyrosine phosphorylation. The differences in the Ca2+ signaling mechanisms may underlie the reported temporal differences in gene expression during leukotoxin and endotoxin activation.
authors.affiliation: Department of Veterinary PathoBiology, College of Veterinary Medicine, University of Minnesota, St. Paul, Minnesota 55108, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: Hsuan
authors.forename: M S
authors.initials: MS
authors.lastname: Kannan
authors.forename: S
authors.initials: S
authors.lastname: Jeyaseelan
authors.forename: Y S
authors.initials: YS
authors.lastname: Prakash
authors.forename: G C
authors.initials: GC
authors.lastname: Sieck
authors.forename: S K
authors.initials: SK
authors.lastname: Maheswaran
mesh_terms: D015117:5,8,11,14-Eicosatetraynoic Acid / Q000494:pharmacology; D000818:Animals; D001427:Bacterial Toxins / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004963:Estrenes / Q000494:pharmacology; D005098:Exotoxins / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000378:metabolism; D006358:Hot Temperature; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008262:Macrophage Activation / Q000187:drug effects; D016676:Macrophages, Alveolar / Q000187:drug effects*; D016978:Mannheimia haemolytica / Q000472:pathogenicity*; D008954:Models, Biological; D009543:Nifedipine / Q000494:pharmacology; D012766:Pasteurellosis, Pneumonic / Q000209:etiology; D037342:Pertussis Toxin; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011489:Protein Denaturation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011760:Pyrrolidinones / Q000494:pharmacology; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D001427:Bacterial Toxins; D002121:Calcium Channel Blockers; D004963:Estrenes; D005098:Exotoxins; D008070:Lipopolysaccharides; D010726:Phosphodiesterase Inhibitors; D011760:Pyrrolidinones; D010566:Virulence Factors, Bordetella; C018579:leukotoxin; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D015117:5,8,11,14-Eicosatetraynoic Acid; D037342:Pertussis Toxin; D011505:Protein-Tyrosine Kinases; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D009543:Nifedipine; D002118:Calcium