title: Glycogen synthase kinase3 beta phosphorylates serine 33 of p53 and activates p53's transcriptional activity.
abstract: BACKGROUND
  The p53 protein is activated by genotoxic stress, oncogene expression and during senescence, p53 transcriptionally activates genes involved in growth arrest and apoptosis. p53 activation is regulated by post-translational modification, including phosphorylation of the N-terminal transactivation domain. Here, we have examined how Glycogen Synthase Kinase (GSK3), a protein kinase involved in tumorigenesis, differentiation and apoptosis, phosphorylates and regulates p53.
  
  
  RESULTS
  The 2 isoforms of GSK3, GSK3alpha and GSK3beta, phosphorylate the sequence Ser-X-X-X-Ser(P) when the C-terminal serine residue is already phosphorylated. Several p53 kinases were examined for their ability to create GSK3 phosphorylation sites on the p53 protein. Our results demonstrate that phosphorylation of serine 37 of p53 by DNA-PK creates a site for GSK3beta phosphorylation at serine 33 in vitro. GSK3alpha did not phosphorylate p53 under any condition. GSK3beta increased the transcriptional activity of the p53 protein in vivo. Mutation of either serine 33 or serine 37 of p53 to alanine blocked the ability of GSK3beta to regulate p53 transcriptional activity. GSK3beta is therefore able to regulate p53 function in vivo. p53's transcriptional activity is commonly increased by DNA damage. However, GSK3beta kinase activity was inhibited in response to DNA damage, suggesting that GSK3beta regulation of p53 is not involved in the p53-DNA damage response.
  
  
  CONCLUSIONS
  GSK3beta can regulate p53's transcriptional activity by phosphorylating serine 33. However, GSK3beta does not appear to be part of the p53-DNA damage response pathway. Instead, GSK3beta may provide the link between p53 and non-DNA damage mechanisms for p53 activation.
authors.affiliation: Department of Radiation Oncology, D810A, Dana-Farber Cancer Institute, Harvard Medical School, 44 Binney St, Boston, MA 02115, USA. aturenne@kendallstrategies.com
authors.forename: G A
authors.initials: GA
authors.lastname: Turenne
authors.forename: B D
authors.initials: BD
authors.lastname: Price
mesh_terms: D002460:Cell Line; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D010766:Phosphorylation / Q000528:radiation effects; D012694:Serine / Q000378:metabolism*; D015534:Trans-Activators / Q000737:chemistry* / Q000378:metabolism*; D015533:Transcriptional Activation; D016159:Tumor Suppressor Protein p53 / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D015534:Trans-Activators; D016159:Tumor Suppressor Protein p53; D012694:Serine; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3