Aminopeptidase N/CD13 is associated with raft membrane microdomains in monocytes

Ectopeptidases play important roles in cell activation, proliferation, and communication. Human monocytic cells express considerable amounts of aminop eptidase N/CD13, a transmembrane protein previously proposed to play a role in the regulation of neuropeptides and chemotactic mediators as well as in adhesion and cell-cell interactions. Here, we report for the first time th at aminopeptidase N/CD13 in monocytes is partially localized in detergent-i nsoluble membrane microdomains enriched in cholesterol, glycolipids, and gl ycosylphosphoinositol-anchored proteins, referred to as "rafts." Raft fract ions of monocytes were characterized by the presence of GM1 ganglioside as raft marker molecule and by the high level of tyrosine-phosphorylated prote ins. Furthermore, similar to polarized cells, rafts in monocytic cells lack Na+, K+-ATPase. Cholesterol depletion of monocytes by methyl-beta-cyclodex trin greatly reduces raft localization of aminopeptidase N/CD13 without aff ecting ala-p-nitroanilide cleaving activity of cells. (C) 2000 Academic Pre ss.