title: How many mutant p53 molecules are needed to inactivate a tetramer?
abstract: The tumor suppressor p53 is transcription factor composed of four identical subunits. The majority of the mutations in p53 are missense mutations that impair DNA binding. On the other hand, the p53-related p63 and p73 genes are rarely mutated, but many cell types express natural variants lacking the N-terminal transactivation domain (NDelta). Compelling evidence indicates that both the DNA binding-defective and NDelta mutants can impair the function of wild-type p53 in a dominant-negative manner. Interestingly, it is uncertain how many mutant subunit(s) a p53 tetramer can tolerate. In this study, we first made theoretical predictions based on the number of mutant p53 monomers needed to inactivate a tetramer and then tested how well the experimental data fit the predicted values. Surprisingly, these experiments reveal that DNA binding-defective p53 mutants (R249S and R273H) are very ineffective in impairing the transcriptional activity of p53: at least three mutants are required to inactivate a tetramer. In marked contrast, p53NDelta is a very potent inhibitor of p53: one NDelta subunit per tetramer is sufficient to abolish the transcriptional activity. DNA binding is not necessary for the NDelta proteins to inactivate p53. Similarly, NDelta variants of p63 and p73 are also powerful inhibitors of members of the p53 family. These results have important implications for our thinking about the mechanism of tumorigenesis involving missense p53 mutants or the N-terminally truncated isoforms.
authors.affiliation: Department of Biochemistry, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong.
authors.forename: Wan Mui
authors.initials: WM
authors.lastname: Chan
authors.forename: Wai Yi
authors.initials: WY
authors.lastname: Siu
authors.forename: Anita
authors.initials: A
authors.lastname: Lau
authors.forename: Randy Y C
authors.initials: RY
authors.lastname: Poon
mesh_terms: D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D016147:Genes, Tumor Suppressor; D006801:Humans; D008962:Models, Theoretical; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2; D015533:Transcriptional Activation; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D025521:Tumor Suppressor Proteins
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D021122:Protein Subunits; D011518:Proto-Oncogene Proteins; C000606460:TP73 protein, human; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2