p53CP, a putative p53 competing protein that specifically binds to the consensus p53 DNA binding sites: a third member of the p53 family?
p53 tumor suppressor protein negatively regulates cell growth, mainly through the transactivation of its downstream target genes. As a sequence-specific DNA binding transcription factor, p53 specifically binds to a 20-bp consensus motif 5'-PuPuPuC(A/T) (T/A)GPyPyPyPuPuPuC(A/T)(T/A)GPyPyPy-3'. We have now identified, partially purified, and characterized an additional approximately 40-kDa nuclear protein, p53CP (p53 competing protein), that specifically binds to the consensus p53 binding sites found in several p53 downstream target genes, including Waf-1, Gadd45, Mdm2, Bax, and RGC. The minimal sequence requirement for binding is a 14-bp motif, 5'-CTTGCTTGAACAGG-3' [5'-C(A/T)(T/A)GPyPyPyPuPuPuC(A/T)(T/A)G-3'], which includes the central nucleotides of the typical p53 binding site with one mismatch. p53CP and p53 (complexed with antibody) showed a similar binding specificity to Waf-1 site but differences in Gadd45 and T3SF binding. Like p53, p53CP also binds both double- and single-stranded DNA oligonucleotides. Important to note, cell cycle blockers and DNA damaging reagents, which induce p53 binding activity, were found to inhibit p53CP binding in p53-positive, but not in p53-negative, cells. This finding suggested a p53-dependent coordinate regulation of p53 and p53CP in response to external stimuli. p53CP therefore could be a third member of the p53 family, in addition to p53 and p73, a newly identified p53 homolog. p53CP, if sequestering p53 from its DNA binding sites through competitive binding, may provide a novel mechanism of p53 inactivation. Alternatively, p53CP may have p53-like functions by binding and transactivating p53 downstream target genes. Cloning of the p53CP gene ultimately will resolve this issue.
Bian
J
J
Department of Molecular Biology, Parke-Davis Pharmaceutical Research, Division of Warner-Lambert Company, 2800 Plymouth Road, Ann Arbor, MI 48105, USA.
Sun
Y
Y
D000818:Animals; D001665:Binding Sites; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D016158:Genes, p53; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics* / Q000378:metabolism*
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D016159:Tumor Suppressor Protein p53