A novel p53 transcriptional repressor element (p53TRE) and the asymmetrical contribution of two p53 binding sites modulate the response of the placental transforming growth factor-beta promoter to p53.
Previous studies in our laboratory and others identified placental transforming growth factor-beta (PTGF-beta) as an important downstream mediator of DNA damage signaling and a transcriptional target of p53. Here we show that accumulation of PTGF-beta mRNA in response to p53 overexpression is delayed relative to p21(WAF1), whereas the promoters of these genes respond to p53 with similar kinetics. Mutational analyses of two p53 binding sites within the PTGF-beta promoter revealed that site p53-1 (+29 bp) is responsible for as much as 80% of the transcriptional response to p53. This is consistent with electrophoretic mobility shift assays showing that site p53-1 binds p53 with a much higher affinity than site p53-2 (-850 bp). We also describe for the first time a novel 21-bp element (-222 to -242 bp) that acts to down-regulate the PTGF-beta promoter response to p53. Termed the p53 transcriptional repressor element (p53TRE), this sequence was shown to suppress p53 transactivation in a position- and promoter-independent fashion and to associate with a 28-kDa protein expressed in several tumor cell lines. A p53 suppressor element and asymmetric p53 binding sites may participate determining the activation thresholds of p53-responsive promoters in a cell- and context-specific manner.
Wong
Jeffrey
J
Division of Experimental Therapeutics, Ontario Cancer Institute, Princess Margaret Hospital, University Health Network and the Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 2M9, Canada.
Li
Pei-Xiang
PX
Klamut
Henry J
HJ
D001483:Base Sequence; D001665:Binding Sites; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D004252:DNA Mutational Analysis; D015536:Down-Regulation; D005260:Female; D006133:Growth Substances / Q000235:genetics*; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D011257:Pregnancy Proteins / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics*; D013329:Structure-Activity Relationship; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics* / Q000378:metabolism
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D006133:Growth Substances; D011257:Pregnancy Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53