CHEMOTACTIC PEPTIDE N-FORMYL-MET-LEU-PHE ACTIVATION OF P38 MITOGEN-ACTIVATED PROTEIN-KINASE (MAPK) AND MAPK-ACTIVATED PROTEIN KINASE-2 IN HUMAN NEUTROPHILS

Activation of polymorphonuclear leukocytes (PMN) by chemotactic peptid es initiates a series of functional responses that serve to eliminate pathogens. The intermediate steps that link engagement of the chemoatt ractant receptor to the microbicidal responses involve protein kinases that have yet to be identified. In this study we detected in human PM N the presence of p38 mitogen activated protein kinase (MAPK), which b ecame rapidly tyrosine phosphorylated and activated in response to the chemotactic peptide N-formyl-methionyl-leucylphenylalanine (fMLP). Pr etreatment of PMN with wortmannin, a phosphatidylinositol 3-kinase inh ibitor, or bis-indolylmaleimide, a protein kinase C antagonist, result ed in partial inhibition of p38 phosphorylation upon fMLP stimulation. Similarly, phosphorylation of p38 was only partially inhibited when t he fMLP-induced cytosolic calcium transient was prevented. Stimulation of PMN by the chemoattractant also resulted in the rapid phosphorylat ion and activation of MAPK-activated protein kinase-2 (MAPKAPK-2), whi ch was completely inhibited by the specific p38 inhibitor, SB203580. T he physical interaction of p38 with MAPKAPK-2 was studied by coimmunop recipitation. These two kinases were found to be associated in unstimu lated PMN but dissociated upon activation of the cells by fMLP. Togeth er these findings demonstrate the activation of p38 by chemotactic pep tides in human PMN by a process involving phosphatidylinositol 3-kinas e, protein kinase C, and calcium. p38, in turn, is an upstream activat or of MAPKAPK-2.