Direct or C5a-induced activation of heterotrimeric Gi2 proteins in human neutrophils is associated with interaction between formyl peptide receptors and the cytoskeleton.

The binding of ligands to N-formyl peptide chemoattractant receptors in human neutrophils results in a rapid association of these receptors with a cytoskeletal fraction and a specific activation and release of Gi2 alpha-subunits from this fraction. In the present study we could show that pretreating neutrophils with GDPbetaS prevented the fMet-Leu-Phe-induced association of its receptor with a cytoskeletal fraction and also blocked the release of Gi2 alpha-subunits from the same cytoskeletal fraction. In contrast, direct activation of Gi2 proteins by addition of GTPgammaS or AlF4- not only caused a release of Gi2 alpha-subunits from the cytoskeleton but also an association of formyl peptide receptors with the cytoskeleton. The receptor for complement fragment 5a, which transduces its signaling through the same Gi2 protein, triggers both a release of Gi2 alpha-subunits from the cytoskeleton fraction and, of even greater interest, an association between formyl peptide receptors and the cytoskeleton. The close relationship between the activation and release of Gi2 alpha-subunits from the cytoskeleton and the association of formyl peptide receptors with the cytoskeleton might, however, not be a matter of protein-protein exchange, since the increased binding of formyl peptide receptors to the cytoskeleton occurs more rapidly than the release of Gi2 alpha-subunits from the cytoskeleton. The present findings suggest a possible mechanism for the initiation of formyl peptide receptor desensitization during neutrophil locomotion.