Activation of neutrophil elastase-related serine proteases in myelomonocytic cells

Abstract ID 97018 Poster Board 085 Elastase, proteinase 3, cathepsin G and NSP4 (Neutrophil Serine Protease 4) are pro-inflammatory serine proteases found within the granules of promyelocytes during neutrophil differentiation in the bone marrow. The vast majority of NSPs are activated by cathepsin C and, to a much lesser degree, by NSPs-AAP-1 (NSP-Alternative Activating Protease-1) from their inactive precursor forms via proteolytic cleavage of their prodipeptides. In this work, we investigated the respective roles of cathepsin C and NSPs-AAP in the activation of NSPs in pro-monocytic cell lines (U937, THP-1) and in primary monocyte-derived macrophages. In U937 cells, we observed a neutrophil-like activation of NSPs involving cathepsin C and NSPs-AAP-1. In THP-1 cells, elastase and proteinase 3 were generated by cathepsin C and a unknown protease called NSPs-AAP-2, while cathepsin G was activated by cathepsin C. Furthermore, we showed that active forms of proteinase 3 and cathepsin G were not stable and proteolytically degraded in THP-1 cells, which explains the relatively low abundance of these NSPs in this cell line, compared to other myelomonocytic cells. In conclusion, our study shows that NSP activation in myelomonocytic cells is cell type-dependent and more importantly, that the human genome contains at least three proteases involved in NSP activation.