RELATIONSHIP OF LIGAND-RECEPTOR DYNAMICS TO ACTIN POLYMERIZATION IN RBL-2H3 CELLS TRANSFECTED WITH THE HUMAN FORMYL PEPTIDE RECEPTOR

The human formylpeptide receptor (FPR) expressed in RBL-2H3 transfecta nts (RBLFPR) behaves qualitatively like the FPR expressed by neutrophi ls except that it causes sustained F-actin accumulation and cell shape change responses on formyl peptide stimulation, These sustained respo nses were not accounted for by changes in the transfected receptor's a bility to interact with ligand or by receptor density, Signal transduc tion pathways of transfected and neutrophil FPRs are apparently simila r, In transfected cells, dissociation of ligand is sensitive to guanin e nucleotide, the G protein is pertussis toxin-sensitive, FPR and G pr otein appear to be precoupled, the F-actin response is stimulated with the same dose-response profile as in neutrophils, and the F-actin acc umulation response is directly regulated by the FPR, even long after i nitial stimulation, Potentially significant differences between neutro phil and transfected FPR were found when receptor processing was measu red, In neutrophils, practically 100% of the FPR is converted to forms that dissociate slowly from ligand and are inactive in signal transdu ction within 2 min of ligand stimulation, By contrast, 20% or more of transfected FPR remains rapidly dissociating even 5 min after stimulat ion, Although 80% of neutrophil FPR is internalized by 5 min after sti mulation, transfected FPR appears to plateau at 50-60% internalized, B ecause actin responses in neutrophils are regulated by a small number of active receptors, the inefficiency of receptor inactivation in RBLF PR transfectants may account for the prolonged F-actin accumulation re sponse.