title: High-affinity ligand probes of CD22 overcome the threshold set by cis ligands to allow for binding, endocytosis, and killing of B cells.
abstract: CD22 (Siglec-2) is a key regulator of B cell signaling whose function is modulated by interaction with extracellular glycan ligands mediated through its N-terminal Ig domain. Its preferred ligand is the sequence Sia alpha2-6Gal that is abundantly expressed on N-linked glycans of B cell glycoproteins, and by binding to CD22 in cis causes CD22 to appear "masked" from binding to synthetic sialoside probes. Yet, despite the presence of cis ligands, CD22 redistributes to sites of cell contact by binding to trans ligands on neighboring cells. In this study, we demonstrate the dynamic equilibrium that exists between CD22 and its cis and trans ligands, using a high-affinity multivalent sialoside probe that competes with cis ligands and binds to CD22 on native human and murine B cells. Consistent with the constitutive endocytosis reported for CD22, the probes are internalized once bound, demonstrating that CD22 is an endocytic receptor that can carry ligand-decorated "cargo" to intracellular compartments. Conjugation of the sialoside probes to the toxin saporin resulted in toxin uptake and toxin-mediated killing of B lymphoma cell lines, suggesting an alternative approach for targeting CD22 for treatment of B cell lymphomas.
authors.affiliation: Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92024, USA.
authors.forename: Brian E
authors.initials: BE
authors.lastname: Collins
authors.forename: Ola
authors.initials: O
authors.lastname: Blixt
authors.forename: Shoufa
authors.initials: S
authors.lastname: Han
authors.forename: Bao
authors.initials: B
authors.lastname: Duong
authors.forename: Hongyi
authors.initials: H
authors.lastname: Li
authors.forename: Jay K
authors.initials: JK
authors.lastname: Nathan
authors.forename: Nicolai
authors.initials: N
authors.lastname: Bovin
authors.forename: James C
authors.initials: JC
authors.lastname: Paulson
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology / Q000378:metabolism*; D016923:Cell Death; D002478:Cells, Cultured; D004705:Endocytosis; D006801:Humans; D008024:Ligands; D051379:Mice; D015394:Molecular Structure; D051918:Sialic Acid Binding Ig-like Lectin 2 / Q000276:immunology* / Q000378:metabolism*; D013400:Sugar Acids / Q000737:chemistry / Q000378:metabolism*
chemical_list: D008024:Ligands; D051918:Sialic Acid Binding Ig-like Lectin 2; D013400:Sugar Acids; C050008:3-deoxyglycero-galacto-nonulosonic acid