title: Externalization of endogenous annexin A5 participates in apoptosis of rat cardiomyocytes.
abstract: OBJECTIVE
  Annexins are Ca(2+)-dependent phospholipid binding proteins. Externalized annexin A5 has been recently suggested to have a proapoptotic effect. Our aim was to determine whether annexin A5, which is intracellular in cardiomyocytes, could be translocated and/or externalized and play a role during the apoptotic process.
  
  
  METHODS
  Apoptosis was induced in rat cardiomyocytes by continuous incubation with staurosporine or 30 min treatment with H(2)O(2) and was measured by phosphatidylserine (PS) externalization, TUNEL staining and DNA ladder. Immunofluorescence labeling of annexin A5 was performed on permeabilized or nonpermeabilized cardiomyocytes.
  
  
  RESULTS
  Staurosporine or H(2)O(2) treatment of neonatal cardiomyocytes resulted in significant increases of apoptosis at 24 h, but H(2)O(2) treatment led to a faster and higher PS externalization than that observed with ST. In both neonatal and adult cardiomyocytes, annexin A5 was intracellular in control conditions but was found at the external face of sarcolemma during apoptosis. Furthermore, neonatal cardiomyocytes with externalized annexin A5 have apoptotic characteristics and their number increased with time. Interestingly, immediately after H(2)O(2) induction, the number of annexin A5-positive cells was higher than that of PS-positive cells (p</=0.05) and colabeling showed that half annexin A5-positive cells were PS-negative. We further demonstrated by immunoblots that free annexin A5 was absent from the media and could not be released from cardiomyocytes by washes at 1.8 mM Ca(2+). Removing annexin A5 by Ca(2+)-free washes 15 or 30 min after H(2)O(2) treatment or blocking externalized annexin A5 by antibodies lead to a significant decrease of apoptotic cardiomyocytes, cytochrome c release and caspase 3 activity.
  
  
  CONCLUSIONS
  This study indicated for the first time that annexin A5 was externalized at a very early stage of apoptosis and could have a proapoptotic effect in cardiomyocytes.
authors.affiliation: INSERM U572, IFR Circulation, Hopital Lariboisière, 41 Boulevard de la Chapelle, 75475 Paris Cedex 10, France.
authors.forename: Virginie
authors.initials: V
authors.lastname: Monceau
authors.forename: Yulia
authors.initials: Y
authors.lastname: Belikova
authors.forename: Gueorgui
authors.initials: G
authors.lastname: Kratassiouk
authors.forename: Dominique
authors.initials: D
authors.lastname: Charue
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Camors
authors.forename: Catherine
authors.initials: C
authors.lastname: Communal
authors.forename: Pascal
authors.initials: P
authors.lastname: Trouvé
authors.forename: Françoise
authors.initials: F
authors.lastname: Russo-Marie
authors.forename: Danièle
authors.initials: D
authors.lastname: Charlemagne
mesh_terms: D000818:Animals; D017304:Annexin A5 / Q000032:analysis / Q000276:immunology / Q000378:metabolism*; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017209:Apoptosis; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D045304:Cytochromes c / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000494:pharmacology; D020287:In Situ Nick-End Labeling; D018613:Microscopy, Confocal; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D051381:Rats; D017208:Rats, Wistar; D012508:Sarcolemma / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology
chemical_list: D017304:Annexin A5; D000911:Antibodies, Monoclonal; D004791:Enzyme Inhibitors; D045304:Cytochromes c; D006861:Hydrogen Peroxide; D011493:Protein Kinase C; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; D019311:Staurosporine