title: Identification of PP1alpha as a caspase-9 regulator in IL-2 deprivation-induced apoptosis.
abstract: One of the mechanisms that regulate cell death is the reversible phosphorylation of proteins. ERK/MAPK phosphorylates caspase-9 at Thr(125), and this phosphorylation is crucial for caspase-9 inhibition. Until now, the phosphatase responsible for Thr(125) dephosphorylation has not been described. Here, we demonstrate that in IL-2-proliferating cells, phosphorylated serine/threonine phosphatase type 1alpha (PP1alpha) associates with phosphorylated caspase-9. IL-2 deprivation induces PP1alpha dephosphorylation, which leads to its activation and, as a consequence, dephosphorylation and activation of caspase-9 and subsequent dissociation of both molecules. In cell-free systems supplemented with ATP caspase-9 activation is induced by addition of cytochrome c and we show that in this process PP1alpha is indispensable for triggering caspase-9 as well as caspase-3 cleavage and activation. Moreover, PP1alpha associates with caspase-9 in vitro and in vivo, suggesting that it is the phosphatase responsible for caspase-9 dephosphorylation and activation. Finally, we describe two novel phosphatase-binding sites different from the previously described PP1alpha consensus motifs, and we demonstrate that these novel sites mediate the interaction of PP1alpha with caspase-9.
authors.affiliation: Laboratoire d'Immunologie Cellulaire et Tissulaire, Hôpital Pitié-Salpêtrière, Unité 543 INSERM, Bâtiment CERVI, 83 Boulevard de l'Hôpital, 75013 Paris, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Dessauge
authors.forename: Xavier
authors.initials: X
authors.lastname: Cayla
authors.forename: Juan Pablo
authors.initials: JP
authors.lastname: Albar
authors.forename: Aarne
authors.initials: A
authors.lastname: Fleischer
authors.forename: Ata
authors.initials: A
authors.lastname: Ghadiri
authors.forename: Marianne
authors.initials: M
authors.lastname: Duhamel
authors.forename: Angelita
authors.initials: A
authors.lastname: Rebollo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D001665:Binding Sites; D053453:Caspase 9; D020169:Caspases / Q000096:biosynthesis / Q000378:metabolism* / Q000502:physiology; D002460:Cell Line; D004789:Enzyme Activation / Q000276:immunology; D006801:Humans; D007376:Interleukin-2 / Q000172:deficiency* / Q000235:genetics / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D010749:Phosphoprotein Phosphatases / Q000502:physiology*; D010766:Phosphorylation; D013601:T-Lymphocytes / Q000166:cytology / Q000201:enzymology / Q000276:immunology
chemical_list: D007376:Interleukin-2; D010749:Phosphoprotein Phosphatases; C506433:CASP9 protein, human; C506434:Casp9 protein, mouse; D053453:Caspase 9; D020169:Caspases