title: Processing of Neutrophil α-Defensins Does Not Rely on Serine Proteases In Vivo.
abstract: The α-defensins, human neutrophil peptides (HNPs) are the predominant antimicrobial peptides of neutrophil granules. They are synthesized in promyelocytes and myelocytes as proHNPs, but only processed in promyelocytes and stored as mature HNPs in azurophil granules. Despite decades of search, the mechanisms underlying the posttranslational processing of neutrophil defensins remain unidentified. Thus, neither the enzyme that processes proHNPs nor the localization of processing has been identified. It has been hypothesized that proHNPs are processed by the serine proteases highly expressed in promyelocytes: Neutrophil elastase (NE), cathepsin G (CG), and proteinase 3 (PR3), all of which are able to process recombinant proHNP into HNP in vitro. We investigated whether serine proteases are in fact responsible for processing of proHNP in human bone marrow cells and in human and murine myeloid cell lines. Subcellular fractionation of the human promyelocytic cell line PLB-985 demonstrated proHNP processing to commence in fractions containing endoplasmic reticulum. Processing of 35S-proHNP was insensitive to serine protease inhibitors. Simultaneous knockdown of NE, CG, and PR3 did not decrease proHNP processing in primary human bone marrow cells. Furthermore, introduction of NE, CG, and PR3 into murine promyelocytic cells did not enhance the proHNP processing capability. Finally, two patients suffering from Papillon-Lefèvre syndrome, who lack active neutrophil serine proteases, demonstrated normal levels of fully processed HNP in peripheral neutrophils. Contradicting earlier assumptions, our study found serine proteases dispensable for processing of proHNPs in vivo. This calls for study of other protease classes in the search for the proHNP processing protease(s).
authors.affiliation: The Granulocyte Research Laboratory, Department of Hematology, Rigshospitalet, University of Copenhagen, Denmark.
authors.forename: Andreas
authors.initials: A
authors.lastname: Glenthøj
authors.affiliation: Poliklinik für Parodontologie, Zentrum der Zahn-, Mund- und Kieferheilkunde (Carolinum), Johann Wolfgang Goethe-Universität, Frankfurt, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Nickles
authors.affiliation: The Granulocyte Research Laboratory, Department of Hematology, Rigshospitalet, University of Copenhagen, Denmark.
authors.forename: Jack
authors.initials: J
authors.lastname: Cowland
authors.affiliation: The Granulocyte Research Laboratory, Department of Hematology, Rigshospitalet, University of Copenhagen, Denmark.
authors.forename: Niels
authors.initials: N
authors.lastname: Borregaard
mesh_terms: D056649:Cathepsin G / Q000235:genetics; D045744:Cell Line, Tumor; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D019272:Leukocyte Elastase / Q000235:genetics; D053146:Myeloblastin / Q000235:genetics; D009504:Neutrophils / Q000276:immunology*; D010214:Papillon-Lefevre Disease / Q000235:genetics; D011499:Protein Processing, Post-Translational / Q000235:genetics*; D057057:Serine Proteases / Q000235:genetics* / Q000378:metabolism; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D023084:alpha-Defensins / Q000235:genetics* / Q000276:immunology
chemical_list: D015842:Serine Proteinase Inhibitors; D023084:alpha-Defensins; D057057:Serine Proteases; C534094:CTSG protein, human; D056649:Cathepsin G; D019272:Leukocyte Elastase; D053146:Myeloblastin