title: Caspase-independent phosphatidylserine exposure during apoptosis of primary T lymphocytes.
abstract: Exposure of phosphatidylserine (PS) on the outer leaflet of the plasma membrane is a key feature of apoptosis. As the signals underlying these phenomena are unknown, it is generally assumed that PS exposure is a consequence of caspase activation, another hallmark of apoptosis. In this study we investigated the role of caspases in PS externalization during apoptosis of activated PBL triggered by drugs (etoposide, staurosporine), CD95 engagement, or IL-2 withdrawal. Anti-CD95 mAb induces a rapid activation of caspases, followed by PS exposure and mitochondrial transmembrane potential (DeltaPsim) disruption. In contrast, etoposide (ETO), staurosporine (STS), or IL-2 withdrawal triggers concomitant caspase activation, PS exposure, and DeltaPsim disruption. Such kinetics suggest that PS exposure could be independent of caspase activation. As expected, in activated PBL treated by anti-CD95 mAb, the pan-caspase inhibitor Cbz-Val-Ala-Asp(OMe)-fluoromethylketone and the caspase-8 inhibitor Cbz-Leu-Glu-Thr-Asp(OMe)-fluoromethylketone, but not the caspase-9 inhibitor Cbz-Leu-Glu-His-Asp(OMe)-fluoromethylketone, inhibit PS externalization and DeltaPsim disruption. Surprisingly, during apoptosis induced by ETO, STS, or IL-2 withdrawal, none of those caspase inhibitors prevents PS externalization or DeltaPsim disruption, whereas they all inhibit DNA fragmentation as well as the morphological features of nuclear apoptosis. In Jurkat and H9 T cell lines, as opposed to activated PBL, PS exposure is inhibited by Cbz-Val-Ala-Asp(OMe)-fluoromethylketone during apoptosis induced by CD95 engagement, ETO, or STS. Thus, caspase-independent PS exposure occurs in primary T cells during apoptosis induced by stimuli that do not trigger death receptors.
authors.affiliation: Laboratoire d'Immunopharmacologie, Institut National de la Santé et de la Recherche Médicale, Unité 503, Centre d'Etudes et de Recherche en Virologie et Immunologie, Lyon, France.
authors.forename: Carole
authors.initials: C
authors.lastname: Ferraro-Peyret
authors.forename: Laurence
authors.initials: L
authors.lastname: Quemeneur
authors.forename: Monique
authors.initials: M
authors.lastname: Flacher
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Revillard
authors.forename: Laurent
authors.initials: L
authors.lastname: Genestier
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000276:immunology*; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism / Q000502:physiology*; D002467:Cell Nucleus / Q000187:drug effects / Q000276:immunology; D002478:Cells, Cultured; D053938:DNA Fragmentation / Q000187:drug effects / Q000276:immunology; D004789:Enzyme Activation / Q000187:drug effects / Q000276:immunology; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D007376:Interleukin-2 / Q000378:metabolism; D007425:Intracellular Membranes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D019169:Jurkat Cells; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000276:immunology; D008928:Mitochondria / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D010539:Permeability / Q000187:drug effects; D010718:Phosphatidylserines / Q000378:metabolism*; D019311:Staurosporine / Q000494:pharmacology; D016176:T-Lymphocyte Subsets / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology* / Q000276:immunology; D014407:Tumor Cells, Cultured
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D061945:Caspase Inhibitors; D007376:Interleukin-2; D010718:Phosphatidylserines; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D005047:Etoposide; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D019311:Staurosporine