Résumé
Neutral endopeptidase (EC 3.4.24.11, NEP) is an ectoenzyme, identified as the common acute lymphoblastic leukemia antigen (CALLA, CD10). This enzyme is involved in the inactivation of regulatory peptides such as enkephalins and atrial natriuretic peptide and its expression on the cell surface is therefore essential. NEP levels have been measured under different conditions on leukemic cell lines. NEP activity per cell was found to increase during the cell growth of Reh6 and CEM cells, a cell-cell contact mechanism being suggested by experiments using Transwell cell chambers. The same process was not observed with ICIG-7 fibroblasts. The numbers of enzymatic sites was also found to be selectively modulated by treatment with 0.1 μM
N-[3-(
R,
S)-[(hydroxyamino)carbonyl]-2-benzyl-1-oxopropyl]glycine (HACBOGly), a potent (
K
i
= 1.4 nM) and specific inhibitor of NEP. A maximal 13% decrease in sites was observed after 8 hr incubation, this effect disappearing after 12 hr. This weak but specific negative modulation was not observed with a compound, chemically related to HACBOGly, which has a 10,000-fold lower inhibitory potency. The modulation was inhibited by low temperature or monensin treatment and could be brought about by an internalization of the enzyme, compensated for by an increased biosynthesis or by the sequestration of NEP in a non-membranous compartment.