title: Impact of cyclin-dependent kinase CDK4 inhibition on eryptosis.
abstract: OBJECTIVE
  The cyclin-dependent kinase 4 (CDK4) participates in the regulation of apoptosis of nucleated cells by altering transcriptional regulation of genes governing cell proliferation and cell death. Similar to apoptosis of nucleated cells, erythrocytes may enter eryptosis, which is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine (PS) exposure at the cell surface. As mature erythrocytes lack nuclei, acute stimulation of eryptosis cannot result from altered gene expression. Eryptosis is triggered by isotonic cell shrinkage following Cl- removal (replacement with the impermeant organic anion gluconate) or by oxidative stress (exposure to 0.3 mM tertbutyl-hydroperoxide [tBOOH]). The present study explored whether CDK4 is expressed in erythrocytes and whether the CDK4 inhibitors II (NSC625987) and III (ryuvidine) influence eryptosis.
  
  
  METHODS
  Western blotting was utilized for determination of the presence of CDK4 protein in human erythrocytes, and FACS analysis to determine Fluo3 fluorescence (reflecting cytosolic Ca2+), annexin-V-binding (reflecting PS-exposure) and forward scatter (reflecting cell volume).
  
  
  RESULTS
  CDK4 protein was present in human erythrocytes. Cl- removal was followed by decrease of forward scatter and increase of both annexin-V-binding and Fluo3 fluorescence, an effect significantly curtailed by CDK4 inhibitors II and III. Furthermore, CDK4 inhibition blunted enhanced PS-exposure elicited by tBOOH treatment.
  
  
  CONCLUSIONS
  The present observations disclose the presence of CDK4 protein in human erythrocytes and the suppression of suicidal erythrocyte death by pharmacological inhibition of CDK4.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Lang
authors.forename: Christine
authors.initials: C
authors.lastname: Zelenak
authors.forename: Matthias
authors.initials: M
authors.lastname: Eberhard
authors.forename: Rosi
authors.initials: R
authors.lastname: Bissinger
authors.forename: Anand
authors.initials: A
authors.lastname: Rotte
authors.forename: Mehrdad
authors.initials: M
authors.lastname: Ghashghaeinia
authors.forename: Adrian
authors.initials: A
authors.lastname: Lupescu
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
authors.forename: Syed M
authors.initials: SM
authors.lastname: Qadri
mesh_terms: D017209:Apoptosis; D002470:Cell Survival / Q000187:drug effects; D051358:Cyclin-Dependent Kinase 4 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004912:Erythrocytes / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D010718:Phosphatidylserines / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D020122:tert-Butylhydroperoxide / Q000494:pharmacology
chemical_list: D010718:Phosphatidylserines; D047428:Protein Kinase Inhibitors; D020122:tert-Butylhydroperoxide; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4