title: Inhibition of "self" engulfment through deactivation of myosin-II at the phagocytic synapse between human cells.
abstract: Phagocytosis of foreign cells or particles by macrophages is a rapid process that is inefficient when faced with "self" cells that display CD47-although signaling mechanisms in self-recognition have remained largely unknown. With human macrophages, we show the phagocytic synapse at cell contacts involves a basal level of actin-driven phagocytosis that, in the absence of species-specific CD47 signaling, is made more efficient by phospho-activated myosin. We use "foreign" sheep red blood cells (RBCs) together with CD47-blocked, antibody-opsonized human RBCs in order to visualize synaptic accumulation of phosphotyrosine, paxillin, F-actin, and the major motor isoform, nonmuscle myosin-IIA. When CD47 is functional, the macrophage counter-receptor and phosphatase-activator SIRPalpha localizes to the synapse, suppressing accumulation of phosphotyrosine and myosin without affecting F-actin. On both RBCs and microbeads, human CD47 potently inhibits phagocytosis as does direct inhibition of myosin. CD47-SIRPalpha interaction initiates a dephosphorylation cascade directed in part at phosphotyrosine in myosin. A point mutation turns off this motor's contribution to phagocytosis, suggesting that self-recognition inhibits contractile engulfment.
authors.affiliation: Biophysical Engineering Laboratory, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Richard K
authors.initials: RK
authors.lastname: Tsai
authors.forename: Dennis E
authors.initials: DE
authors.lastname: Discher
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D000943:Antigens, Differentiation / Q000378:metabolism; D051928:CD47 Antigen / Q000378:metabolism; D016466:CHO Cells; D019556:COS Cells; D002450:Cell Communication / Q000502:physiology*; D002522:Chlorocebus aethiops; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D007365:Intercellular Junctions / Q000378:metabolism* / Q000648:ultrastructure; D008264:Macrophages / Q000378:metabolism* / Q000648:ultrastructure; D024507:Nonmuscle Myosin Type IIA / Q000235:genetics / Q000378:metabolism*; D051419:Paxillin / Q000378:metabolism; D010587:Phagocytosis / Q000502:physiology*; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D017354:Point Mutation / Q000235:genetics; D011971:Receptors, Immunologic / Q000378:metabolism; D012756:Sheep; D013569:Synapses / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D000199:Actins; D000943:Antigens, Differentiation; D051928:CD47 Antigen; C496061:PXN protein, human; D051419:Paxillin; D011971:Receptors, Immunologic; C501920:SIRPA protein, human; D019000:Phosphotyrosine; D024507:Nonmuscle Myosin Type IIA