The small GTP-binding protein Rac promotes the dissociation of gelsolin from actin filaments in neutrophils.
Gelsolin is an actin filament-capping protein that has been shown to play a key role in cell migration. Here we have studied the involvement of phosphoinositide 3-kinase (PI 3-kinase) and GTP-binding proteins (G-proteins) in the regulation of gelsolin-actin interactions in neutrophils. Inhibition of PI 3-kinase activity in vivo by wortmannin did not affect the dissociation of actin-gelsolin (1:1) complexes induced by neutrophil stimulation with N-formyl-Met-Leu-Phe. Guanosine 5'-[gamma-thio]triphosphate (GTPgammaS) indirectly promoted the dissociation of actin-gelsolin complexes in a cell-free system using neutrophil cytosol, and this effect was blocked by the GDP dissociation inhibitor for Rho (Rho-GDI). The GTPgammaS-loaded ialpha2 and the beta1gamma2 subunits of heterotrimeric G-proteins (Gialpha2 and Gbeta1gamma2) also triggered actin-gelsolin dissociation in a Rho-GDI-sensitive manner. GTP-loaded activated Rac, but not activated Rho, induced the dissociation of cytosolic actin-gelsolin complexes. The guanine nucleotide exchange on Rac was increased by addition of GTPgammaS-loaded Gialpha2 or Gbeta1gamma2 to neutrophil cytosol. These findings suggest that activation of Rac by G-protein-coupled receptors in neutrophils triggers uncapping of actin filaments, independently of PI 3-kinase.
Arcaro
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Institute of Biochemistry, University of Fribourg, CH-1700 Fribourg, Switzerland. arcaro@ludwig.ucl.ac.uk
D000199:Actins / Q000378:metabolism*; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D018260:Gelsolin / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011506:Proteins / Q000378:metabolism; D011817:Rabbits; D011994:Recombinant Proteins / Q000378:metabolism; D000077191:Wortmannin; D020744:rac GTP-Binding Proteins
D000199:Actins; D000730:Androstadienes; D004791:Enzyme Inhibitors; D018260:Gelsolin; D020662:Guanine Nucleotide Exchange Factors; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011506:Proteins; D011994:Recombinant Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D019204:GTP-Binding Proteins; D020744:rac GTP-Binding Proteins; D002118:Calcium; D000077191:Wortmannin