The acute-phase protein alpha 1-acid glycoprotein (AGP) induces rises in cytosolic Ca2+ in neutrophil granulocytes via sialic acid binding immunoglobulin-like lectins (siglecs).
We studied whether the acute-phase protein alpha1-acid glycoprotein (AGP) induces rises in [Ca2+]i in neutrophils and sought to identify the corresponding AGP receptor (or receptors). We found that AGP elicited a minimal rise in [Ca2+]i in Fura-2-loaded neutrophils, and this response was markedly enhanced by pretreatment with anti-L-selectin antibodies. (The EC50 value of the AGP-induced Ca2+ response was 9 microg/ml.) Activation of phospholipase-C, Src tyrosine kinases, and PI3 kinases proved to be essential for the AGP-mediated increase in [Ca2+]i, whereas the p38 MAPK and SYK signaling pathways were not involved. Furthermore, antibodies against sialic acid binding, immunoglobulin-like lectin 5 (Siglec-5) and oligosaccharide 3'-sialyl-lactose both antagonized the AGP-induced response and caused an immediate increase in [Ca2+]i in anti-L-selectin-treated neutrophils, which indicates a signaling capacity of Siglec-5. We used modified forms of AGP (treated with mild periodate or neuraminidase) to establish the importance of sialic acid residues. The modified forms of AGP caused a much smaller rise in [Ca2+]i than did unaltered AGP. Affinity chromatography confirmed that unchanged AGP, but not neuraminidase-treated AGP, bound to Siglec-5. Our report provides the first evidence for a signaling capacity by AGP through a defined receptor. Pre-engagement of L-selectin significantly enhanced this signaling capacity.
Division of Pharmacology, Department of Medicine and Care, Linköping University, S-581 85 Linköping, Sweden. petgu@imv.liu.se
Peter
P
Gunnarsson
Louise
L
Levander
Peter
P
Påhlsson
Magnus
M
Grenegård
D015703:Antigens, CD / Q000378:metabolism; D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism*; D018922:HL-60 Cells; D006801:Humans; D037102:Lectins / Q000378:metabolism / Q000502:physiology*; D008024:Ligands; D019158:N-Acetylneuraminic Acid / Q000378:metabolism*; D009504:Neutrophils / Q000378:metabolism*; D009961:Orosomucoid / Q000378:metabolism / Q000502:physiology*; D063265:Sialic Acid Binding Immunoglobulin-like Lectins
D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D002413:Cations, Divalent; D037102:Lectins; D008024:Ligands; D009961:Orosomucoid; C114531:SIGLEC5 protein, human; D063265:Sialic Acid Binding Immunoglobulin-like Lectins; D019158:N-Acetylneuraminic Acid; D002118:Calcium