Secretion of heparin-binding protein from human neutrophils is determined by its localization in azurophilic granules and secretory vesicles

• Published in: Blood Vol. 99; no. 5; pp. 1785 - 1793
• Main Authors: Tapper, Hans, Karlsson, Anna, Mörgelin, Matthias, Flodgaard, Hans, Herwald, Heiko
• Format: Journal Article
• Language: English
• Published: Washington, DC Elsevier Inc 01-03-2002; The Americain Society of Hematology
• Subjects: Adult; agonists; Antimicrobial Cationic Peptides; Biological and medical sciences; Blood Proteins; Blood Proteins - agonists; Blood Proteins - metabolism; Blood Proteins : agonists : metabolism : secretion; Carrier Proteins; Carrier Proteins - agonists; Carrier Proteins - metabolism; Carrier Proteins : agonists : metabolism : secretion; Cell Compartmentation; Cell Fractionation; chemistry; Clinical Medicine; Cytoplasmic Granules; Cytoplasmic Granules - chemistry; drug effects; Electron; Fluorescence; Fundamental and applied biological sciences. Psychology; Fundamental immunology; Hematologi; Hematology; HL-60 Cells; Human; Humans; Immunobiology; Immunologi inom det medicinska området; Immunology in the medical area; Klinisk medicin; Medical and Health Sciences; Medicin och hälsovetenskap; metabolism; Microscopy; Microscopy Electron; Microscopy Fluorescence; Myeloid cells: ontogeny, maturation, markers, receptors; Neutrophil Activation; Neutrophil Activation - drug effects; Neutrophils; Neutrophils - metabolism; Neutrophils - ultrastructure; Neutrophils : metabolism : secretion : ultrastructure; Polynuclears; secretion; Secretory Vesicles; Secretory Vesicles - chemistry; Support Non-U.S. Gov't; ultrastructure; Human; Serine endopeptidases; Enzyme; Granulocyte; Natural immunity; Azurocidin; Peptidases; Hydrolases; Immunoelectron microscopy; Secretion granule; Neutrophil; Localization; Phagocytosis
• ISSN: 0006-4971; 1528-0020; 1528-0020
• DOI: 10.1182/blood.V99.5.1785

Human neutrophils have an important role in host defense against microbial infection. At different stages of an infectious process, neutrophils progressively up-regulate receptors and release various effector molecules. These are stored in several distinct types of granules with varying propensity to be secreted. Heparin-binding protein (HBP), also known as CAP37 or azurocidin, is a multifunctional, inactive serine-protease homologue. The present work shows that HBP is released from neutrophils on stimulation with secretagogues that do not trigger the secretion of azurophilic granule content. Therefore, the subcellular localization of HBP was investigated in more detail. Immunofluorescence microscopy revealed that HBP was localized close to the plasma membrane. Further analysis by fractionation of postnuclear supernatants from cavitated neutrophils showed that HBP is stored in azurophilic granules and secretory vesicles but that it is also detected to a minor extent in the plasma membrane. These findings were confirmed by immunoelectron microscopy showing that HBP colocalized with marker proteins of azurophilic granules and secretory vesicles. The presence of HBP in secretory vesicles possibly depends on the stage of cell differentiation, since the promyelocytic cell line HL-60 contains less HBP than mature neutrophils, stored exclusively in the less easily mobilized azurophilic granules. Our findings suggest that HBP can be synthesized or targeted to easily mobilized compartments at a late stage of neutrophil maturation. The ability of neutrophils to secrete HBP from secretory vesicles may be important for proinflammatory functions of this protein, such as the alteration of vascular permeability.