Differential uncoupling of chemoattractant receptors from G proteins in retinoic acid-differentiated HL-60 granulocytes.
The ability of HL-60 cells differentiated with DMSO or retinoic acid (RA) to serve as models for polymorphonuclear leukocytes was examined. NaF and FMLP stimulated superoxide release from both groups of cells, but the response was attenuated in RA-differentiated cells. Isolated plasma membranes from DMSO-M and RA-differentiated (RA-M) cells were used to examine receptor and guanine nucleotide binding regulatory protein (G protein) expression. Ligand binding showed that formyl peptide and leukotriene B4 receptors were present in equal density on DMSO-M and RA-M. Formyl peptide receptors on RA-M failed to demonstrate high affinity binding sites. Both G alpha i2 and G alpha i3 were present in equal density on RA-M and DMSO-M by immunoblotting. FMLP, but not leukotriene B4, failed to stimulate guanosine 5'-(gamma-thio)triphosphate binding or GTP hydrolysis and guanine nucleotides failed to inhibit FMLP binding to RA-M. Addition of solubilized membranes containing normal formyl peptide receptors to solubilized RA-M reconstituted FMLP stimulated G protein activation, whereas addition of normal G proteins had no effect. We conclude that formyl peptide, but not leukotriene B4, receptors are uncoupled from G proteins in RA-differentiated HL-60 granulocytes. Although RA-differentiated cells are an inadequate model of neutrophil transmembrane signaling, they may provide a unique model by which to study the molecular requirements for formyl peptide receptor-G protein interactions.