Receptor-independent activation of guanine nucleotide-binding regulatory proteins by terminal complement complexes.
Activation of heterotrimeric guanine nucleotide-binding proteins (G proteins) by terminal complement complexes (TCC) was investigated on human lymphoblastoid B-cell line JY25 and its mutant JY5 deficient in glycosylphosphatidylinositol-anchored proteins. TCC assembly achieved by antibody-dependent activation of C7-deficient serum reconstituted with C7 increased specific guanosine-5'-(gamma-thio)triphosphate (GTP gamma S) binding, 4- and 8-fold, in JY25 and JY5 membranes, respectively, between 2 and 10 min, over the level without C7. TCC also increased GTPase activity 5- and 4-fold in JY25 and JY5, respectively, between 5 and 10 min. Increased GTPase activity was noted first with C5b-7 assembly, which increased further with C5b-8 and C5b-9. The presence of G proteins in anti-TCC immunoprecipitates of cell lysates was investigated by demonstration of G alpha subunit that can be ADP-ribosylated by pertussis toxin (PTX). Immunoprecipitated TCC complexes contained a PTX-sensitive 41-kDa Gi alpha/Go alpha subunit, as shown by SDS-PAGE and Western blotting. These complexes were functionally active as determined by GTP gamma S binding. We have further shown that enhanced TCC elimination from the plasma membrane induced by TCC-generated signals was inhibited by PTX. In conclusion the biological activities induced by TCC in nucleated cells may be mediated in part by activation of PTX-sensitive G proteins.
Niculescu
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University of Maryland, School of Medicine, Department of Pathology, Baltimore 21201.
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Shin
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D001402:B-Lymphocytes / Q000378:metabolism; D002460:Cell Line; D003167:Complement Activation; D015938:Complement Membrane Attack Complex / Q000378:metabolism*; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D037342:Pertussis Toxin; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D015398:Signal Transduction; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D015938:Complement Membrane Attack Complex; D010566:Virulence Factors, Bordetella; D006160:Guanosine Triphosphate; D011065:Poly(ADP-ribose) Polymerases; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins