Abstract
The hemolytically inactive complement component complex C5b67, designated iC5b67, can signal human polymorphonuclear leukocytes (PMN) both as a pertussis toxin-inhibitable agonist for chemotaxis and as an antagonist for C5a- and FMLP-stimulated chemotaxis and superoxide production. The signaling pathways utilized by iC5b67 have been further investigated. In contrast to mastoparan, iC5b67 failed to directly activate G proteins to stimulate inositol phosphate formation in COS cells that had been transfected with G alpha 16. In COS cells co-transfected with both G alpha 16 and the C5a receptor, iC5b67 could neither activate phospholipase C nor inhibit C5a receptor-mediated activation of phospholipase C. iC5b67 stimulated GTPase activity in a membrane-enriched fraction from PMN. These data support the hypothesis that iC5b67 signals through a unique receptor, likely G protein linked, but distinct from the C5a receptor. iC5b67 was able to mobilize intracellular stores to elicit increases in intracellular Ca2+. Based on the effects of herbimycin A, wortmannin, and chelerythrine on iC5b67-induced PMN chemotaxis, iC5b67 signaling involved activation of tyrosine and phosphatidylinositol 3-kinases, but not protein kinase C. Relevant to the capacity of iC5b67 to antagonize PMN superoxide production, iC5b67 induced rapid and sustained increases in intracellular cAMP, which others have shown can inhibit superoxide formation. Although iC5b67 antagonizes C5a and FMLP receptor-mediated superoxide generation, iC5b67 had no effect on PMA-induced superoxide formation. The distinct agonist and antagonist signaling pathways activated by iC5b67 in the PMN diverge soon after initial iC5b67 receptor-mediated transduction steps.
Publication types
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Alkaloids
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Androstadienes / pharmacology
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Animals
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Antigens, CD / genetics
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Antigens, CD / metabolism
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Benzophenanthridines
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Benzoquinones
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Calcium / physiology
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Cell Line, Transformed
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Chemotaxis, Leukocyte / physiology*
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Chlorocebus aethiops
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Complement C5*
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Complement System Proteins / physiology*
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Cyclic AMP / physiology
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Enzyme Inhibitors / pharmacology
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GTP Phosphohydrolases / metabolism
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GTP-Binding Proteins / metabolism
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Humans
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Inositol Phosphates / metabolism
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Intercellular Signaling Peptides and Proteins
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Lactams, Macrocyclic
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Naphthalenes / pharmacology
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Neutrophils / physiology*
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Peptides
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Pertussis Toxin
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Phenanthridines / pharmacology
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Phosphatidylinositol 3-Kinases
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Phosphotransferases (Alcohol Group Acceptor) / antagonists & inhibitors
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Phosphotransferases (Alcohol Group Acceptor) / physiology
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Protein-Tyrosine Kinases / antagonists & inhibitors
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Protein-Tyrosine Kinases / physiology
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Quinones / pharmacology
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Receptor, Anaphylatoxin C5a
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Receptors, Complement / genetics
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Receptors, Complement / metabolism
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Recombinant Fusion Proteins / metabolism
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Respiratory Burst / drug effects
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Respiratory Burst / physiology
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Rifabutin / analogs & derivatives
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Signal Transduction / physiology*
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Superoxides / metabolism
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Tetradecanoylphorbol Acetate / pharmacology
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Virulence Factors, Bordetella / pharmacology
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Wasp Venoms / pharmacology
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Wortmannin
Substances
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Alkaloids
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Androstadienes
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Antigens, CD
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Benzophenanthridines
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Benzoquinones
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Complement C5
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Enzyme Inhibitors
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Inositol Phosphates
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Intercellular Signaling Peptides and Proteins
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Lactams, Macrocyclic
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Naphthalenes
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Peptides
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Phenanthridines
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Quinones
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Receptor, Anaphylatoxin C5a
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Receptors, Complement
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Recombinant Fusion Proteins
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Virulence Factors, Bordetella
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Wasp Venoms
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calphostin complex
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Superoxides
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Rifabutin
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herbimycin
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mastoparan
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complement C5b-7 complex
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Complement System Proteins
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Cyclic AMP
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chelerythrine
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Pertussis Toxin
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Phosphotransferases (Alcohol Group Acceptor)
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Protein-Tyrosine Kinases
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GTP Phosphohydrolases
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GTP-Binding Proteins
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Tetradecanoylphorbol Acetate
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Calcium
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Wortmannin