title: Quiescence and γH2AX in neuroblastoma are regulated by ouabain/Na,K-ATPase.
abstract: BACKGROUND
  Cellular quiescence is a state of reversible proliferation arrest that is induced by anti-mitogenic signals. The endogenous cardiac glycoside ouabain is a specific ligand of the ubiquitous sodium pump, Na,K-ATPase, also known to regulate cell growth through unknown signalling pathways.
  
  
  METHODS
  To investigate the role of ouabain/Na,K-ATPase in uncontrolled neuroblastoma growth we used xenografts, flow cytometry, immunostaining, comet assay, real-time PCR, and electrophysiology after various treatment strategies.
  
  
  RESULTS
  The ouabain/Na,K-ATPase complex induced quiescence in malignant neuroblastoma. Tumour growth was reduced by >50% when neuroblastoma cells were xenografted into immune-deficient mice that were fed with ouabain. Ouabain-induced S-G2 phase arrest, activated the DNA-damage response (DDR) pathway marker γH2AX, increased the cell cycle regulator p21(Waf1/Cip1) and upregulated the quiescence-specific transcription factor hairy and enhancer of split1 (HES1), causing neuroblastoma cells to ultimately enter G0. Cells re-entered the cell cycle and resumed proliferation, without showing DNA damage, when ouabain was removed.
  
  
  CONCLUSIONS
  These findings demonstrate a novel action of ouabain/Na,K-ATPase as a regulator of quiescence in neuroblastoma, suggesting that ouabain can be used in chemotherapies to suppress tumour growth and/or arrest cells to increase the therapeutic index in combination therapies.
authors.affiliation: Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm SE-17177, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Hiyoshi
authors.forename: S
authors.initials: S
authors.lastname: Abdelhady
authors.forename: L
authors.initials: L
authors.lastname: Segerström
authors.forename: B
authors.initials: B
authors.lastname: Sveinbjörnsson
authors.forename: M
authors.initials: M
authors.lastname: Nuriya
authors.forename: T K
authors.initials: TK
authors.lastname: Lundgren
authors.forename: L
authors.initials: L
authors.lastname: Desfrere
authors.forename: A
authors.initials: A
authors.lastname: Miyakawa
authors.forename: M
authors.initials: M
authors.lastname: Yasui
authors.forename: P
authors.initials: P
authors.lastname: Kogner
authors.forename: J I
authors.initials: JI
authors.lastname: Johnsen
authors.forename: M
authors.initials: M
authors.lastname: Andäng
authors.forename: P
authors.initials: P
authors.lastname: Uhlén
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D020552:Comet Assay; D005260:Female; D005434:Flow Cytometry; D006657:Histones / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009447:Neuroblastoma / Q000378:metabolism*; D010042:Ouabain / Q000378:metabolism* / Q000494:pharmacology; D060888:Real-Time Polymerase Chain Reaction; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014183:Transplantation, Heterologous
chemical_list: C468783:H2AX protein, human; D006657:Histones; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase