Aminopeptidase N/CD13 is directly linked to signal transduction pathways in monocytes

In the present study, we characterized in monocytes the rise in [Ca(2+)](i) evoked by monoclonal antibodies (mAbs) to aminopeptidase N (APN)/CD13, showing a two-phase calcium increase with a small-belled [Ca(2+)](i) rise due to the release of calcium from intracellular stores and a more sustained plateau due to the influx of calcium from the extracellular environment. Tyrosine kinase inhibitors were able to inhibit the rise in [Ca(2+)](i) induced by ligation APN/CD13, as were inhibitors of the phosphatidylinositol 3-kinase. For the first time we can show that mAbs to APN/CD13 provoke phosphorylation of the mitogen-activated protein kinases ERK1/2, JNK, and p38. Furthermore, we show that mRNA of the chemotactic cytokine IL-8 is upregulated under the influence of APN/CD13 ligation. Although the in vivo ligand as well as possible cooperating membrane molecules remains to be identified, our results suggest that the membrane ectoenzyme APN/CD13 is a novel signal transduction molecule in monocytes.