Meprin alpha and beta, members of the astacin family of zinc metalloproteinases, are unique plasma membrane and secreted proteases known to cleave a wide range of biological substrates involved in inflammation, cancer and fibrosis. In this study, we identified proMMP-9 as a novel substrate and show that aminoterminal meprin-mediated clipping improves the activation kinetics of proMMP-9 by MMP-3, an efficient activator of proMMP-9. Interestingly, the NH2-terminus LVLFPGDL, generated by incubation with meprin alpha, is identical to the form produced in conditioned media from human neutrophils and monocytes. Hence, this meprin-mediated processing and enhancement of MMP-9 activation kinetics may have biological relevance in the context of in vivo inflammatory processes. Structured summary of protein interactions: Meprin beta cleaves MMP-9 by enzymatic study (View interaction) Meprin beta cleaves MMP-9 by zymography (View interaction) Meprin alpha cleaves MMP-9 by zymography (View interaction) Meprin alpha cleaves MMP-9 by enzymatic study (View interaction) (C) 2012 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved. ; Fund for Scientific Research-Flanders (FWO-Vlaanderen); Geconcerteerde OnderzoeksActies (grant number GOA 2012-017); Deutsche Forschungsgemeinschaft (DFG)(grant numbers BE 4086/1-2; SFB877); Cluster of Excellence "Inflammation at Interfaces" ; biochemistry & molecular biology; biophysics; cell biology