title: Loss of Cell Surface CD47 Clustering Formation and Binding Avidity to SIRPα Facilitate Apoptotic Cell Clearance by Macrophages.
abstract: CD47, a self recognition marker expressed on tissue cells, interacts with immunoreceptor SIRPα expressed on the surface of macrophages to initiate inhibitory signaling that prevents macrophage phagocytosis of healthy host cells. Previous studies suggested that cells may lose surface CD47 during aging or apoptosis to enable phagocytic clearance. In the current study, we demonstrate that the level of cell surface CD47 is not decreased, but the distribution pattern of CD47 is altered, during apoptosis. On nonapoptotic cells, CD47 molecules are clustered in lipid rafts forming punctates on the surface, whereas on apoptotic cells, CD47 molecules are diffused on the cell surface following the disassembly of lipid rafts. We show that clustering of CD47 in lipid rafts provides a high binding avidity for cell surface CD47 to ligate macrophage SIRPα, which also presents as clusters, and elicits SIRPα-mediated inhibitory signaling that prevents phagocytosis. In contrast, dispersed CD47 on the apoptotic cell surface is associated with a significant reduction in the binding avidity to SIRPα and a failure to trigger SIRPα signal transduction. Disruption of plasma membrane lipid rafts with methyl-β-cyclodextrin diffuses CD47 clusters, leading to a decrease in the cell binding avidity to SIRPα and a concomitant increase in cells being engulfed by macrophages. Taken together, our study reveals that CD47 normally is clustered in lipid rafts on nonapoptotic cells but is diffused in the plasma membrane when apoptosis occurs; this transformation of CD47 greatly reduces the strength of CD47-SIRPα engagement, resulting in the phagocytosis of apoptotic cells.
authors.affiliation: School of Life Sciences, Nanjing University, Nanjing 210023, China; Program of Cellular Biology and Immunology, Department of Biology, Georgia State University, Atlanta, GA 30303; and.
authors.forename: Zhiyuan
authors.initials: Z
authors.lastname: Lv
authors.affiliation: School of Life Sciences, Nanjing University, Nanjing 210023, China; Program of Cellular Biology and Immunology, Department of Biology, Georgia State University, Atlanta, GA 30303; and.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Bian
authors.affiliation: School of Life Sciences, Nanjing University, Nanjing 210023, China; Program of Cellular Biology and Immunology, Department of Biology, Georgia State University, Atlanta, GA 30303; and.
authors.forename: Lei
authors.initials: L
authors.lastname: Shi
authors.affiliation: Program of Cellular Biology and Immunology, Department of Biology, Georgia State University, Atlanta, GA 30303; and.
authors.forename: Shuo
authors.initials: S
authors.lastname: Niu
authors.affiliation: Program of Cellular Biology and Immunology, Department of Biology, Georgia State University, Atlanta, GA 30303; and.
authors.forename: Binh
authors.initials: B
authors.lastname: Ha
authors.affiliation: Program of Cellular Biology and Immunology, Department of Biology, Georgia State University, Atlanta, GA 30303; and.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Tremblay
authors.affiliation: Program of Cellular Biology and Immunology, Department of Biology, Georgia State University, Atlanta, GA 30303; and.
authors.forename: Liangwei
authors.initials: L
authors.lastname: Li
authors.affiliation: Program of Cellular Biology and Immunology, Department of Biology, Georgia State University, Atlanta, GA 30303; and.
authors.forename: Xiugen
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Program of Cellular Biology and Immunology, Department of Biology, Georgia State University, Atlanta, GA 30303; and.
authors.forename: John
authors.initials: J
authors.lastname: Paluszynski
authors.affiliation: Program of Cellular Biology and Immunology, Department of Biology, Georgia State University, Atlanta, GA 30303; and Department of Cardiology, Putuo Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai 200062, China.
authors.forename: Ming
authors.initials: M
authors.lastname: Liu
authors.affiliation: School of Life Sciences, Nanjing University, Nanjing 210023, China; Program of Cellular Biology and Immunology, Department of Biology, Georgia State University, Atlanta, GA 30303; and.
authors.forename: Ke
authors.initials: K
authors.lastname: Zen
authors.affiliation: Program of Cellular Biology and Immunology, Department of Biology, Georgia State University, Atlanta, GA 30303; and yliu@gsu.edu.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Liu
mesh_terms: D000818:Animals; D000943:Antigens, Differentiation / Q000235:genetics / Q000276:immunology*; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects*; D001665:Binding Sites; D051928:CD47 Antigen / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D045744:Cell Line, Tumor; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000276:immunology / Q000528:radiation effects*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000276:immunology / Q000528:radiation effects; D005786:Gene Expression Regulation; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000166:cytology / Q000187:drug effects / Q000276:immunology / Q000528:radiation effects; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000276:immunology / Q000528:radiation effects*; D021962:Membrane Microdomains / Q000187:drug effects / Q000528:radiation effects; D051379:Mice; D008810:Mice, Inbred C57BL; D010587:Phagocytosis / Q000187:drug effects / Q000528:radiation effects; D061251:Primary Cell Culture; D011485:Protein Binding; D021381:Protein Transport / Q000187:drug effects / Q000528:radiation effects; D011971:Receptors, Immunologic / Q000235:genetics / Q000276:immunology*; D015398:Signal Transduction; D013154:Spleen / Q000166:cytology / Q000187:drug effects / Q000276:immunology / Q000528:radiation effects; D014466:Ultraviolet Rays; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: D000943:Antigens, Differentiation; D051928:CD47 Antigen; C497894:CD47 protein, human; D011971:Receptors, Immunologic; C501920:SIRPA protein, human; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin