title: Highly glycosylated alpha1-acid glycoprotein is synthesized in myelocytes, stored in secondary granules, and released by activated neutrophils.
abstract: Alpha-1-acid glycoprotein (AGP) is an acute-phase protein produced by hepatocytes and secreted into plasma in response to infection/injury. We recently assessed the transcriptional program of terminal granulocytic differentiation by microarray analysis of bone marrow (BM) populations highly enriched in promyelocytes, myelocytes/metamyelocytes (MYs), and BM neutrophils. These analyses demonstrated a transient, high mRNA expression of genuine secondary/tertiary granule proteins and AGP in MYs. In agreement with this, immunocytochemistry revealed the presence of AGP protein and the secondary granule protein lactoferrin in cells from the MY stage and throughout granulocytic differentiation. Immunoelectron microscopy demonstrated the colocalization of AGP and lactoferrin in secondary granules of neutrophils. This finding was substantiated by the failure to detect AGP and lactoferrin in blood cells from a patient with secondary/tertiary (specific) granule deficiency. In addition, Western blot analysis of subcellular fractions isolated from neutrophils revealed that neutrophil-derived AGP, localized in secondary granules, was abundant and highly glycosylated compared with endocytosed, plasma-derived AGP localized in secretory vesicles. Exocytosis studies further demonstrated a marked release of AGP and lactoferrin by activated neutrophils. Finally, induction of CCAAT/enhancer-binding protein (C/EBP)-epsilon in a myeloid cell line was shown to increase AGP transcript levels, indicating that AGP expression in myeloid cells, like in hepatocytes, is partially regulated by members of the C/EBP family. Overall, these findings define AGP as a genuine secondary granule protein of neutrophils. Hence, neutrophils, which constitute the first line of defense, are likely to serve as the primary local source of AGP at sites of infection or injury.
authors.affiliation: Granulocyte Research Laboratory, Department of Hematology, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100 Copenhagen-Ø, Denmark.
authors.forename: Kim
authors.initials: K
authors.lastname: Theilgaard-Mönch
authors.forename: Lars C
authors.initials: LC
authors.lastname: Jacobsen
authors.forename: Thomas
authors.initials: T
authors.lastname: Rasmussen
authors.forename: Carsten U
authors.initials: CU
authors.lastname: Niemann
authors.forename: Lene
authors.initials: L
authors.lastname: Udby
authors.forename: Rehannah
authors.initials: R
authors.lastname: Borup
authors.forename: Maged
authors.initials: M
authors.lastname: Gharib
authors.forename: Peter D
authors.initials: PD
authors.lastname: Arkwright
authors.forename: Adrian F
authors.initials: AF
authors.lastname: Gombart
authors.forename: Jero
authors.initials: J
authors.lastname: Calafat
authors.forename: Bo T
authors.initials: BT
authors.lastname: Porse
authors.forename: Niels
authors.initials: N
authors.lastname: Borregaard
mesh_terms: D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism; D015550:Cell Degranulation / Q000502:physiology*; D002460:Cell Line; D003594:Cytoplasmic Granules / Q000378:metabolism* / Q000648:ultrastructure; D005786:Gene Expression Regulation / Q000502:physiology; D042381:Granulocyte Precursor Cells / Q000378:metabolism* / Q000648:ultrastructure; D022781:Hepatocytes / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007120:Immunochemistry; D007781:Lactoferrin / Q000096:biosynthesis; D008099:Liver / Q000293:injuries / Q000378:metabolism / Q000473:pathology; D046529:Microscopy, Electron, Transmission; D018375:Neutrophil Activation / Q000502:physiology*; D009504:Neutrophils / Q000378:metabolism* / Q000648:ultrastructure; D009961:Orosomucoid / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000096:biosynthesis
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; D009961:Orosomucoid; D012333:RNA, Messenger; D007781:Lactoferrin