title: Enhancement of the antiproliferative function of p53 by phosphorylation at serine 20: an inference from site-directed mutagenesis studies.
abstract: Recent studies have shown that Ser20 of p53 is phosphorylated in vivo in response to DNA damage caused by ionizing radiation (IR) or ultraviolet radiation (UV), treatments that also result in the induction of p21WAF1/Cip1 (p21) expression. We hypothesized that Ser20 phosphorylation enhances the transactivation function of p53. To test this, we generated two p53 mutants, changing the Ser residue to either Ala, an uncharged form that may mimic unphosphorylated p53, or to Asp, a negatively charged form that may mimic constitutively phosphorylated p53. p53-null cells transfected with the Ser20 phosphorylation-mimicking mutant p53Asp20 demonstrated heightened p21 expression and reduced cell proliferation relative to wild-type p53-transfected cells. Moreover, p53Asp20 exhibited reduced capacity to interact with the Mdm-2 protein in vitro. This abridged interaction had no effect, however, on p53 protein stability. These results suggest that the phosphorylation of p53 at Ser20 is an important mechanism in the activation of the p53/p21 cell-growth inhibitory pathways in response to DNA damage by IR and UV.
authors.affiliation: Department of Pathology, The University of Texas, M.D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Jabbur
authors.forename: P
authors.initials: P
authors.lastname: Huang
authors.forename: W
authors.initials: W
authors.lastname: Zhang
mesh_terms: D019943:Amino Acid Substitution; D002455:Cell Division / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000187:drug effects / Q000378:metabolism; D004249:DNA Damage / Q000502:physiology / Q000528:radiation effects; D004355:Drug Stability; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D020014:K562 Cells; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins; D010766:Phosphorylation; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2; D012694:Serine / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000235:genetics* / Q000378:metabolism* / Q000494:pharmacology
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53; D012694:Serine; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2