title: Caspase-independent type III programmed cell death in chronic lymphocytic leukemia: the key role of the F-actin cytoskeleton.
abstract: BACKGROUND
  Programmed cell death has been traditionally related with caspase activation. However, it is now accepted that caspase-independent forms of programmed cell death also regulate cell death. In chronic lymphocytic leukemia, CD47 ligation induces one of these alternative forms of cell death: type III programmed cell death. This poorly understood process is characterized by cytoplasmic hallmarks, such as mitochondrial damage. To gain insights into the molecular pathways regulating type III programmed cell death in chronic lymphocytic leukemia, we performed extensive biochemical and cell biology assessments.
  
  
  METHODS
  After CD47 triggering, purified B-cells from 20 patients with chronic lymphocytic leukemia were studied by flow cytometry, immunofluorescence and three-dimensional imaging, immunoblotting, electron microscopy, and fibrillar/globular actin measurements. Finally, we subjected CD47-treated chronic lymphocytic leukemia cells to a phagocytosis assay.
  
  
  RESULTS
  We first confirmed that induction of type III programmed cell death is an efficient means of triggering cell death in chronic lymphocytic leukemia. Further, we demonstrated that the signaling events induced by CD47 ligation provoked a reduction in cell size. This alteration is related to F-actin disruption, as the two other cytoskeleton networks, microtubules and intermediate filaments, remain undisturbed in type III programmed cell death. Strikingly, we revealed that the pharmacological modulation of F-actin dynamics regulated this type of death. Finally, our data delineated a new programmed cell death pathway in chronic lymphocytic leukemia initiated by CD47 triggering, and followed by serine protease activation, F-actin rearrangement, mitochondrial damage, phosphatidylserine exposure, and cell clearance.
  
  
  CONCLUSIONS
  Our work reveals a key molecular tool in the modulation of cell death in chronic lymphocytic leukemia: F-actin. By assessing the regulation of F-actin and type III programmed cell death, this analysis provides new options for destroying chronic lymphocytic leukemia cells, such as a combination of therapies based on apoptosis regulators (e.g., caspases, Bcl-2, Bax) along with alternative therapies based on type III death effectors (e.g., F-actin).
authors.affiliation: Rue de l'Ecole de Médecine, 75006 Paris, France.
authors.forename: Sandrine
authors.initials: S
authors.lastname: Barbier
authors.forename: Laurent
authors.initials: L
authors.lastname: Chatre
authors.forename: Marlène
authors.initials: M
authors.lastname: Bras
authors.forename: Patricia
authors.initials: P
authors.lastname: Sancho
authors.forename: Gaël
authors.initials: G
authors.lastname: Roué
authors.forename: Clémence
authors.initials: C
authors.lastname: Virely
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Yuste
authors.forename: Sylvie
authors.initials: S
authors.lastname: Baudet
authors.forename: Manuel
authors.initials: M
authors.lastname: Rubio
authors.forename: Josep E
authors.initials: JE
authors.lastname: Esquerda
authors.forename: Marika
authors.initials: M
authors.lastname: Sarfati
authors.forename: Hélène
authors.initials: H
authors.lastname: Merle-Béral
authors.forename: Santos A
authors.initials: SA
authors.lastname: Susin
mesh_terms: D000199:Actins / Q000378:metabolism*; D017209:Apoptosis / Q000276:immunology*; D001402:B-Lymphocytes / Q000473:pathology; D020169:Caspases; D003599:Cytoskeleton / Q000276:immunology / Q000473:pathology*; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000276:immunology / Q000378:metabolism / Q000473:pathology*; D014407:Tumor Cells, Cultured
chemical_list: D000199:Actins; D020169:Caspases