Involvement of calcium and arachidonate metabolism in acetylated-low-density-lipoprotein-stimulated tumor-necrosis-factor-alpha production by rat peritoneal macrophages.
We show that lipopolysaccharide-free actetylated low-density lipoprotein (LDL), but not native LDL, stimulates tumor-necrosis factor-alpha (TNF-alpha) secretion by rat peritoneal macrophages and the signal-transduction pathways involved. The role of the scavenger receptor (SR) in this response was suggested by the absence of an effect induced by native LDL, signal coupling involving pertussis-toxin-dependent guanine-nucleotide-binding regulatory (G) protein, and the complete inhibition of this response by SR ligands [poly(I) and dextran sulfate]. Acetylated LDL induces rapid Ca2+ release from inositol-phosphate-sensitive Ca2+ stores mediated by pertussis-sensitive G proteins and a sustained Ca2+ rise mediated by Ca2+ influx and by Ca2+ release from ryanodine-sensitive Ca2+ stores. Acetylated LDL-induced Ca2+ influx and TNF-alpha production were abolished by inhibitors of phospholipase C (U73122) and phospholipase A2 (bromophenacyl bromide), but were not affected by an inhibitor of protein kinase C (calphostine C). Therefore, Ca2+ influx induced by acetylated LDL is dependent on Ca2+ store depletion. Arachidonate released by acetylated LDL acts as a second messenger to activate TNF-alpha secretion via Ca2+ influx. While the Ca2+ signal was not modified by an inhibitor of protein tyrosine kinases (PTK; herbimycin A), this inhibitor completely blocked TNF-alpha production, suggesting the involvement of PTK downstream of the Ca2+ signal. These results suggest that a sustained elevation of intracellular Ca2+, mediated through Ca2+ influx via the phospholipase-A2-dependent pathway, is essential for induction of TNF-alpha secretion. The type of SR class involved in these pathways remains to be identified.
Pollaud-Chérion
C
C
Macrophages, Médiateurs de l'Inflammation et Interactions cellulaires, UPS EA 2405, INSERM-IFR 31, Toulouse, France.
Vandaele
J
J
Quartulli
F
F
Séguélas
M H
MH
Decerprit
J
J
Pipy
B
B
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D017737:Macrophages, Peritoneal / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins; D008954:Models, Biological; D010741:Phospholipases A / Q000037:antagonists & inhibitors; D054467:Phospholipases A2; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D051381:Rats; D017207:Rats, Sprague-Dawley; D011971:Receptors, Immunologic / Q000819:agonists / Q000378:metabolism; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B; D015290:Second Messenger Systems; D015398:Signal Transduction / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
D004791:Enzyme Inhibitors; D008077:Lipoproteins, LDL; D008565:Membrane Proteins; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D014409:Tumor Necrosis Factor-alpha; C032629:acetyl-LDL; D016718:Arachidonic Acid; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; D010741:Phospholipases A; D054467:Phospholipases A2; D010738:Type C Phospholipases; D002118:Calcium