ACTIVATION OF MITOGEN-ACTIVATED PROTEIN-KINASES BY FORMYL PEPTIDE RECEPTORS IS REGULATED BY THE CYTOPLASMIC TAIL

Wild type formyl peptide receptors (FPRwt) and receptors deleted of th e carboxyl-terminal 45 amino acids (FPRdel) were stably expressed in u ndifferentiated HL-60 promyelocytes. Expression of FPRwt reconstituted N-formylmethionyl-leucyl-phenylalanine (FMLP)-stimulated extracellula r signal-regulated kinase (ERK) and p38 kinase activity. Expression of FPRdel resulted in a 2-5-fold increase in basal ERK and p38 kinase ac tivity, whereas FMLP failed to stimulate either mitogen-activated prot ein kinase (MAPK). Pertussis toxin abolished FMLP stimulation of both MAPKs in FPRwt cells but had no effect on either basal or FMLP-stimula ted MAPK activity in FPRdel cells. FMLP stimulated a concentration-dep endent increase in guanosine 5'-3-O-(thio)triphosphate (GTP gamma S) b inding in membranes from FPRwt but not FPRdel cells. GTP gamma S inhib ited FMLP binding to FPRwt but not FPRdel membranes. Photoaffinity lab eling with azidoanilide-[gamma-P-32]GTP in the presence or absence of FMLP showed increased labeling only in FPRwt membranes. Immunoprecipit ation of alpha(i2) and alpha(q/11) from solubilized, photolabeled memb ranes showed that FPRwt were coupled to alpha(i2) but not to alpha(q/1 1). FPRwt cells demonstrated calcium mobilization following stimulatio n with FMLP, whereas FPRdel cells showed no increase in intracellular calcium. We conclude that the carboxyl-terminal tail of FPRs is necess ary for ligand-mediated activation of G(i) proteins and MAPK cascades. Deletion of the carboxyl-terminal tail results in constitutive activa tion of ERK and p38 kinase through a G(i2)-independent pathway.