Stimulus-induced dissociation of alpha subunits of heterotrimeric GTP-binding proteins from the cytoskeleton of human neutrophils.
Previous studies on the mechanism responsible for terminating the generation of second messengers induced by chemotactic factor-receptor complexes have, on one hand, suggested a direct role of a GTP-binding protein(s) (G protein), and, on the other hand, proposed that there is a lateral segregation of the ligand-receptor complexes into G protein-depleted domains of the plasma membrane. In the present investigation, which addresses these apparently contradictory findings, we found that a substantial part of the alpha subunits of the Gn protein (Gn alpha) in unstimulated neutrophils were associated with a cytoskeletal fraction and that release of these subunits occurred upon stimulation with the chemotactic factor fMet-Leu-Phe. An identical Gn alpha release could also be induced by direct activation of G proteins with guanosine 5'-[gamma-thio]triphosphate or AIF4-. In contrast, the alpha subunits of the stimulatory G protein (Gs alpha) also found associated with the cytoskeletal fraction of unstimulated cells were not released by fMet-Leu-Phe stimulation. However, they were effectively released by direct G-protein activation with guanosine 5'-[gamma-thio]triphosphate. In addition, inhibition of the fMet-Leu-Phe-stimulated modulation of the actin network by pertussis toxin did not affect the fMet-Leu-Phe-induced release of Gn alpha from the cytoskeletal fraction. These observations indicate that fMet-Leu-Phe-induced activation of neutrophils involves a specific dissociation of Gn alpha from the cytoskeleton and that this release is not a consequence of the well-known effect of fMet-Leu-Phe on the cytoskeleton of neutrophils. The present data contribute ideas concerning the transducing properties of G proteins in cellular signaling and seem to reconcile the apparently contradictory concepts of how the cytoskeleton participates in the termination of the chemotactic-factor-induced generation of second messengers in human neutrophils.
Särndahl
E
E
Department of Medical Microbiology, University of Linköping, Sweden.
Bokoch
G M
GM
Stendahl
O
O
Andersson
T
T
D002463:Cell Membrane Permeability; D003599:Cytoskeleton / Q000378:metabolism*; D005459:Fluorides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006801:Humans; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D037342:Pertussis Toxin; D011487:Protein Conformation; D015398:Signal Transduction / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D010566:Virulence Factors, Bordetella; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D009240:N-Formylmethionine Leucyl-Phenylalanine; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D005459:Fluorides