title: Non-apoptotic phosphatidylserine externalization induced by engagement of glycosylphosphatidylinositol-anchored proteins.
abstract: The exposure of phosphatidylserine (PS) on the cell surface is a general marker of apoptotic cells. Non-apoptotic PS externalization is induced by several activation stimuli, including engagement of immunoreceptors. Immune cells can also be activated by aggregation of glycosylphosphatidylinositol-anchored proteins (GPI-APs). However, it is unknown whether cell triggering through these proteins, lacking transmembrane and cytoplasmic domains, also leads to PS externalization. Here we show that engagement of GPI-APs in rodent mast cells induces a rapid and reversible externalization of PS by a non-apoptotic mechanism. PS externalization triggered by GPI-AP-specific monoclonal antibodies was dependent on the activity of H(+)-ATP synthase and several other enzymes involved in mast cell signaling but was independent of cell degranulation, free cytoplasmic calcium up-regulation, and a decrease in lipid packing as determined by merocyanine 540 binding. Surprisingly, disruption of actin cytoskeleton by latrunculin B or plasma membrane integrity by methyl-beta-cyclodextrin had opposite effects on PS externalization triggered through GPI-AP or the high affinity IgE receptor. We further show that PS externalization mediated by GPI-APs was also observed in some other cells, and its extent varied with antibodies used. Interestingly, effects of different antibodies on PS externalization were additive, indicating that independent stimuli converge onto a signaling pathways leading to PS externalization. Our findings identify the cell surface PS exposure induced through GPI-AP as a distinct mechanism of cell signaling. Such a mechanism could contribute to "inside-out" signaling in response to pathogens and other external activators and/or to initiation of other functions associated with PS externalization.
authors.affiliation: Department of Signal Transduction, Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, CZ 142 20 Prague 4, Czech Republic.
authors.forename: Daniel
authors.initials: D
authors.lastname: Smrz
authors.forename: L'ubica
authors.initials: L
authors.lastname: Dráberová
authors.forename: Petr
authors.initials: P
authors.lastname: Dráber
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D015550:Cell Degranulation / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D005456:Fluorescent Dyes / Q000494:pharmacology; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D006801:Humans; D008297:Male; D008407:Mast Cells / Q000378:metabolism*; D051379:Mice; D025261:Mitochondrial Proton-Translocating ATPases / Q000378:metabolism; D041681:NIH 3T3 Cells; D010718:Phosphatidylserines / Q000378:metabolism*; D011744:Pyrimidinones / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017455:Receptors, IgE / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D053778:Thiazolidines / Q000494:pharmacology; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: D019086:Bridged Bicyclo Compounds, Heterocyclic; D005456:Fluorescent Dyes; D017261:Glycosylphosphatidylinositols; D010718:Phosphatidylserines; D011744:Pyrimidinones; D017455:Receptors, IgE; D053778:Thiazolidines; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; C003954:merocyanine dye; D025261:Mitochondrial Proton-Translocating ATPases; C037068:latrunculin B