title: Nuclear accumulation and activation of p53 in embryonic stem cells after DNA damage.
abstract: BACKGROUND
  P53 is a key tumor suppressor protein. In response to DNA damage, p53 accumulates to high levels in differentiated cells and activates target genes that initiate cell cycle arrest and apoptosis. Since stem cells provide the proliferative cell pool within organisms, an efficient DNA damage response is crucial.
  
  
  RESULTS
  In proliferating embryonic stem cells, p53 is localized predominantly in the cytoplasm. DNA damage-induced nuclear accumulation of p53 in embryonic stem cells activates transcription of the target genes mdm2, p21, puma and noxa. We observed bi-phasic kinetics for nuclear accumulation of p53 after ionizing radiation. During the first wave of nuclear accumulation, p53 levels were increased and the p53 target genes mdm2, p21 and puma were transcribed. Transcription of noxa correlated with the second wave of nuclear accumulation. Transcriptional activation of p53 target genes resulted in an increased amount of proteins with the exception of p21. While p21 transcripts were efficiently translated in 3T3 cells, we failed to see an increase in p21 protein levels after IR in embryonal stem cells.
  
  
  CONCLUSIONS
  In embryonic stem cells where (anti-proliferative) p53 activity is not necessary, or even unfavorable, p53 is retained in the cytoplasm and prevented from activating its target genes. However, if its activity is beneficial or required, p53 is allowed to accumulate in the nucleus and activates its target genes, even in embryonic stem cells.
authors.affiliation: Institute of Toxicology and Genetics, Forschungszentrum Karlsruhe, PO-Box 3640, 76021 Karlsruhe, Germany. valeriya.solozobova@itg.fzk.de
authors.forename: Valeriya
authors.initials: V
authors.lastname: Solozobova
authors.forename: Alexandra
authors.initials: A
authors.lastname: Rolletschek
authors.forename: Christine
authors.initials: C
authors.lastname: Blattner
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000235:genetics / Q000378:metabolism; D051017:Apoptosis Regulatory Proteins; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D049109:Cell Proliferation; D002470:Cell Survival; D003593:Cytoplasm / Q000378:metabolism; D004249:DNA Damage; D053595:Embryonic Stem Cells / Q000378:metabolism* / Q000528:radiation effects; D005720:Gamma Rays; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D000071317:Nanog Homeobox Protein; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D000090682:Neuro-Oncological Ventral Antigen; D051736:Proto-Oncogene Proteins c-mdm2 / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D000951:Antigens, Neoplasm; D051017:Apoptosis Regulatory Proteins; D018398:Homeodomain Proteins; D000071317:Nanog Homeobox Protein; C475540:Nanog protein, mouse; D009419:Nerve Tissue Proteins; D000090682:Neuro-Oncological Ventral Antigen; C488588:PUMA protein, mouse; D016601:RNA-Binding Proteins; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2