title: Cooperation of factor VII-activating protease and serum DNase I in the release of nucleosomes from necrotic cells.
abstract: OBJECTIVE
  Removal of dead cells is essential in the maintenance of tissue homeostasis, and efficient removal prevents exposure of intracellular content to the immune system, which could lead to autoimmunity. The plasma protease factor VII-activating protease (FSAP) can release nucleosomes from late apoptotic cells. FSAP circulates as an inactive single-chain protein, which is activated upon contact with either apoptotic cells or necrotic cells. The purpose of this study was to investigate the role of FSAP in the release of nucleosomes from necrotic cells.
  
  
  METHODS
  Necrotic Jurkat cells were incubated with serum, purified 2-chain FSAP, and/or DNase I. Nucleosome release was analyzed by flow cytometry, and agarose gel electrophoresis was performed to detect DNA breakdown.
  
  
  RESULTS
  Incubation with serum released nucleosomes from necrotic cells. Incubation with FSAP-deficient serum or serum in which FSAP was inhibited by a blocking antibody was unable to release nucleosomes from necrotic cells, confirming that FSAP is indeed the essential serum factor in this process. Together with serum DNase I, FSAP induced the release of DNA from the cells, the appearance of nucleosomes in the supernatant, and the fragmentation of chromatin into eventually mononucleosomes.
  
  
  CONCLUSIONS
  FSAP and DNase I are the essential serum factors that cooperate in necrotic cell DNA degradation and nucleosome release. We propose that this mechanism may be important in the removal of potential autoantigens.
authors.affiliation: Sanquin Blood Supply Foundation, Amsterdam, The Netherlands.
authors.forename: Femke
authors.initials: F
authors.lastname: Stephan
authors.forename: Gerben
authors.initials: G
authors.lastname: Marsman
authors.forename: Liza M
authors.initials: LM
authors.lastname: Bakker
authors.forename: Ingrid
authors.initials: I
authors.lastname: Bulder
authors.forename: Fabian
authors.initials: F
authors.lastname: Stavenuiter
authors.forename: Lucien A
authors.initials: LA
authors.lastname: Aarden
authors.forename: Sacha
authors.initials: S
authors.lastname: Zeerleder
mesh_terms: D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism*; D003850:Deoxyribonuclease I / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D009336:Necrosis / Q000378:metabolism*; D009707:Nucleosomes / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000378:metabolism*
chemical_list: D009707:Nucleosomes; D003850:Deoxyribonuclease I; C433550:HABP2 protein, human; D012697:Serine Endopeptidases