MITOGEN-ACTIVATED PROTEIN-KINASE IN NEUTROPHILS AND ENUCLEATE NEUTROPHIL CYTOPLASTS - EVIDENCE FOR REGULATION OF CELL-CELL ADHESION

We employed neutrophils and enucleate neutrophil cytoplasts to study t he activation of the mitogen-activated protein kinases (MAPKs) p44(erk 1) and p42(erk2) in neutrophils by inflammatory agonists that engage G protein-linked receptors. Formyl-methionyl-leucyl-phenylalanine (FMLP ) rapidly and transiently activated MAPK in neutrophils and cytoplasts , consistent with a role in signaling for neutrophil functions. FMLP s timulated p21(ras) activation in neutrophils and Raf-1 translocation f rom cytosol to plasma membrane in cytoplasts, with kinetics consistent with events upstream of MAPK activation. Insulin, a protein tyrosine kinase receptor (PTKR) agonist, stimulated neutrophil MAPK activation, demonstrating an intact system of PTKR signaling in these post-mitoti c cells. FMLP- and insulin-stimulated MAPK activation in cytoplasts we re inhibited by Bt(2)cAMP, consistent with signaling through Raf-1 and suggesting a mechanism for cAMP inhibition of neutrophil function. Ho wever, Bt(2)cAMP had no effect on FMLP-stimulated MAPK activation in n eutrophils. The extent of MAPK activation by various chemoattractants correlated with their capacity to stimulate neutrophil and cytoplast h omotypic aggregation. Consistent with its effects on MAPK, Bt(2)cAMP i nhibited FMLP-stimulated aggregation in cytoplasts but not neutrophils . Insulin had no independent effect but primed neutrophils for aggrega tion in response to FMLP. Our studies support a p21(ras)-, Raf-1-depen dent pathway for MAPK activation in neutrophils and suggest that neutr ophil adhesion may be regulated, in part, by MAPK.