Neutral endopeptidase activity in the interaction ofN‐formyl‐l‐methionyl‐l‐leucyl‐l‐phenylalanine with human polymorphonuclear leukocytes

Abstract

Human polymorphonuclear leukocytes (PMN) hydrolyze the synthetic chemoattractant N-formyl-Lmethionly-L-leucyl-L-phenylalanine (fMet-Leu-Phe) at nanomolar concentrations in an autocatalytic-like manner that deviates from classical Michaelis-Menten kinetics [Yuli, I. & Snyderman, R. (1986) J . B i d . Chem. ,761,4902-49081. By using inhibitors of distinct classes of endoproteases, this particular Wet-Leu-Phe degradation was attributed exclusively to an exoplasmic metalloendoprotease that matches the ubiquitous neutral endopeptidase (NEP). Membrane-bound NEP hydrolyzes non-chemotactic substrates according to a classic Michaelis-Menten mechanism. By competitive inhibition with non-chemotactic substrates, fMet-Leu-Phe was found to interact with membrane NEP through a single active site, in a non-cooperative mode with an apparent K,, in the order of 1 mM. The discrepancy between the ordinary hydrolysis of the micromolar and millimolar concentrations of Met-Leu-Phe, reported by others, and the particular degradation of the nanomolar met-Leu-Phe, could not be accounted for by any coherent correlation between NEP activity/inhibition and modulation of met-Leu-Phe binding to its receptor, and/or induction of Met-Leu-Phe-receptor-mediated inflammatory responses. Based on these and previously reported results, a novel model is proposed in which the Met-Leu-Phe-induced inflammatory stimulation of PMN involves both NEP and the fMet-Leu-Phe receptor. By this model, NEP and the Met-Leu-Phe receptor are distinct membrane entities which can form dynamic binary and tertiary complexes; thus accounting for the unusual kinetic features of Wet-Leu-Phe degradation, as well as the two receptor states. The complex of NEP and the Met-Leu-Phe receptor might be conceived as a chemotactic-perception mechanism that combines the high affinity of the receptor and the rapid turnover of NEP.The interaction of the model chemoattractant N-formyl-L-methionyl-L-leucyl-L-phenylalanine (Met-Leu-Phe) [l] with human polymorphonuclear leukocytes (PMN) involves rapid and extensive degradation of the chemoattractant [2]. This effect consists of seuqential proteolytic cleavages of, first, Nformylniethionine. then leucine residues [ 3 ] . Each of these steps suffices to revoke the chemotactic competence of the oligopeptide [4]. and may thus serve as a mechanism for signal termination.The degradation of the Met-Leu-Phe by PMN has been attributed to a plasma-membrane metalloendoprotease [2, 5, 61, which is immunologically related to the well-characterized renal neutral endopeptidase (NEP) [7, 81 and the common acute lymphocytic leukemia antigen [9-121. In contrast to

Expression of neutral endopeptidase activity during clinical and experimental acute lung injury

“…Previous studies have observed the expression of NEP on the surface of PMN [38,39]. In addition, the NEP activity was higher in the LPS-treated mice, in which the recruitment of PMN into the air-space was increased.…”