title: Distinct endocytic mechanisms of CD22 (Siglec-2) and Siglec-F reflect roles in cell signaling and innate immunity.
abstract: Sialic acid-binding immunoglobulin-like lectins (siglecs) are predominately expressed on immune cells. They are best known as regulators of cell signaling mediated by cytoplasmic tyrosine motifs and are increasingly recognized as receptors for pathogens that bear sialic acid-containing glycans. Most siglec proteins undergo endocytosis, an activity tied to their roles in cell signaling and innate immunity. Here, we investigate the endocytic pathways of two siglec proteins, CD22 (Siglec-2), a regulator of B-cell signaling, and mouse eosinophil Siglec-F, a member of the rapidly evolving CD33-related siglec subfamily that are expressed on cells of the innate immune system. CD22 exhibits hallmarks of clathrin-mediated endocytosis and traffics to recycling compartments, consistent with previous reports demonstrating its localization to clathrin domains. Like CD22, Siglec-F mediates endocytosis of anti-Siglec-F and sialoside ligands, a function requiring intact tyrosine-based motifs. In contrast, however, we find that Siglec-F endocytosis is clathrin and dynamin independent, requires ADP ribosylation factor 6, and traffics to lysosomes. The results suggest that these two siglec proteins have evolved distinct endocytic mechanisms consistent with roles in cell signaling and innate immunity.
authors.affiliation: Department of Molecular Biology and Molecular and Experimental Medicine, The Scripps Research Institute, San Diego, CA, USA.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Tateno
authors.forename: Hongyi
authors.initials: H
authors.lastname: Li
authors.forename: Melissa J
authors.initials: MJ
authors.lastname: Schur
authors.forename: Nicolai
authors.initials: N
authors.lastname: Bovin
authors.forename: Paul R
authors.initials: PR
authors.lastname: Crocker
authors.forename: Warren W
authors.initials: WW
authors.lastname: Wakarchuk
authors.forename: James C
authors.initials: JC
authors.lastname: Paulson
mesh_terms: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D000818:Animals; D000906:Antibodies / Q000276:immunology; D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism*; D001419:Bacteria / Q000378:metabolism; D016466:CHO Cells; D002784:Cholesterol / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D003599:Cytoskeleton / Q000378:metabolism; D034284:Dynamin I / Q000378:metabolism; D004705:Endocytosis; D006801:Humans; D007113:Immunity, Innate / Q000276:immunology*; D008024:Ligands; D051379:Mice; D009154:Mutation / Q000235:genetics; D019158:N-Acetylneuraminic Acid / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051918:Sialic Acid Binding Ig-like Lectin 2 / Q000378:metabolism*; D063265:Sialic Acid Binding Immunoglobulin-like Lectins; D015398:Signal Transduction; D014443:Tyrosine / Q000235:genetics
chemical_list: D000089982:ADP-Ribosylation Factor 6; D000199:Actins; D000906:Antibodies; D015214:Antigens, Differentiation, Myelomonocytic; D008024:Ligands; D051918:Sialic Acid Binding Ig-like Lectin 2; D063265:Sialic Acid Binding Immunoglobulin-like Lectins; C443130:Siglecf protein, mouse; D014443:Tyrosine; D002784:Cholesterol; D011505:Protein-Tyrosine Kinases; D034284:Dynamin I; D020727:ADP-Ribosylation Factors; C000715348:ARF6 protein, human; C000715727:Arf6 protein, mouse; D019158:N-Acetylneuraminic Acid