title: Hsp27 as a negative regulator of cytochrome C release.
abstract: We previously showed that Hsp27 protects against apoptosis through its interaction with cytosolic cytochrome c. We have revisited this protective activity in murine cell lines expressing different levels of Hsp27. We report that Hsp27 also interferes, in a manner dependent on level of expression, with the release of cytochrome c from mitochondria. Moreover, a decreased level of endogenous Hsp27, which sensitized HeLa cells to apoptosis, reduced the delay required for cytochrome c release and procaspase 3 activation. The molecular mechanism regulating this function of Hsp27 is unknown. In our cell systems, Hsp27 is mainly cytosolic and only a small fraction of this protein colocalized with mitochondria. Moreover, we show that only a very small fraction of cytochrome c interacts with Hsp27, hence excluding a role of this interaction in the retention of cytochrome c in mitochondria. We also report that Bid intracellular relocalization was altered by changes in Hsp27 level of expression, suggesting that Hsp27 interferes with apoptotic signals upstream of mitochondria. We therefore investigated if the ability of Hsp27 to act as an expression-dependent modulator of F-actin microfilaments integrity was linked to the retention of cytochrome c in mitochondria. We show here that the F-actin depolymerizing agent cytochalasin D rapidly induced the release of cytochrome c from mitochondria and caspase activation. This phenomenon was delayed in cells pretreated with the F-actin stabilizer phalloidin and in cells expressing a high level of Hsp27. This suggests the existence of an apoptotic signaling pathway linking cytoskeleton damages to mitochondria. This pathway, which induces Bid intracellular redistribution, is negatively regulated by the ability of Hsp27 to protect F-actin network integrity. However, this upstream pathway is probably not the only one to be regulated by Hsp27 since, in staurosporine-treated cells, phalloidin only partially inhibited cytochrome c release and caspase activation. Moreover, in etoposide-treated cells, Hsp27 still delayed the release of cytochrome c from mitochondria and Bid intracellular redistribution in conditions where F-actin was not altered.
authors.affiliation: Centre de Génétique Moléculaire et Cellulaire, CNRS-UMR-5534, Université Claude Bernard Lyon I, F-69622 Villeurbanne, France.
authors.forename: Catherine
authors.initials: C
authors.lastname: Paul
authors.forename: Florence
authors.initials: F
authors.lastname: Manero
authors.forename: Sandrine
authors.initials: S
authors.lastname: Gonin
authors.forename: Carole
authors.initials: C
authors.lastname: Kretz-Remy
authors.forename: Sophie
authors.initials: S
authors.lastname: Virot
authors.forename: André-Patrick
authors.initials: AP
authors.lastname: Arrigo
mesh_terms: D016475:3T3 Cells; D000199:Actins / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D003574:Cytochrome c Group / Q000378:metabolism*; D004789:Enzyme Activation; D005047:Etoposide / Q000494:pharmacology; D015870:Gene Expression; D005978:Glutathione / Q000378:metabolism; D055551:HSP27 Heat-Shock Proteins; D006367:HeLa Cells; D006360:Heat-Shock Proteins; D006801:Humans; D007700:Kinetics; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D008954:Models, Biological; D018832:Molecular Chaperones; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D019311:Staurosporine / Q000494:pharmacology
chemical_list: D000199:Actins; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; C494815:Bid protein, mouse; D002352:Carrier Proteins; D003574:Cytochrome c Group; D055551:HSP27 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; C486113:Hsbp1 protein, mouse; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D005047:Etoposide; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases; D005978:Glutathione; D019311:Staurosporine