title: Annexin A5 inhibits engulfment through internalization of PS-expressing cell membrane patches.
abstract: Apoptosis and subsequent clearance of apoptotic cells are important for the prevention of diseases. Therefore, it is essential to understand the mechanisms underlying the biology of phagocytic clearance of apoptotic cells. The best characterized "eat me" signal on the surface of apoptotic cells is phosphatidylserine (PS). Recently, we demonstrated that annexin A5 mediates the internalization of PS-expressing membrane patches and down regulates surface expression of tissue factor. Here, we investigated the role of PS in the phagocytosis of apoptotic cells using annexin A5. Using a novel flow cytometric-based phagocytosis assay, we observed that engulfment was inhibited with 20% if annexin A5 was added to PS-expressing cells that had completed apoptosis. The inhibition increased to more than 50% if annexin A5 was added during the apoptotic process. This inhibition is specific for annexin A5, since the mutant M23 and annexin A1 did not further increase the inhibition of phagocytosis when added during the apoptotic process. Interestingly, cells with internalized annexin A5 still express PS at their surface. We conclude that other ligands within the PS-expressing membrane patch act together with PS as an "eat me" signal.
authors.affiliation: Department of Biochemistry, Cardiovascular Research Institute Maastricht, PO Box 616, 6200 MD Maastricht, The Netherlands.
authors.forename: Heidi
authors.initials: H
authors.lastname: Kenis
authors.forename: Hugo
authors.initials: H
authors.lastname: van Genderen
authors.forename: Niko M
authors.initials: NM
authors.lastname: Deckers
authors.forename: Petra A G
authors.initials: PA
authors.lastname: Lux
authors.forename: Leo
authors.initials: L
authors.lastname: Hofstra
authors.forename: Jagat
authors.initials: J
authors.lastname: Narula
authors.forename: Chris P M
authors.initials: CP
authors.lastname: Reutelingsperger
mesh_terms: D000818:Animals; D017304:Annexin A5 / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D021961:Cell Membrane Structures / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D003001:Cloning, Molecular; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry / Q000379:methods; D006801:Humans; D006863:Hydrogen-Ion Concentration; D019169:Jurkat Cells; D008264:Macrophages / Q000187:drug effects / Q000502:physiology; D051379:Mice; D010587:Phagocytosis / Q000187:drug effects* / Q000502:physiology; D010718:Phosphatidylserines / Q000037:antagonists & inhibitors / Q000502:physiology*
chemical_list: D017304:Annexin A5; D010718:Phosphatidylserines