title: Identification of a functional p53 responsive element within the promoter of XAF1 gene in gastrointestinal cancer cells.
abstract: It has been reported that XAF1 expression in gastric cancer is negatively correlated with p53. Our purpose was to clarify the regulatory mechanism of p53 on XAF1 expression. The effects of overexpressed wild-type and mutant p53 on XAF1 expression were evaluated. Binding capacity of core XAF1 promoter sequence to the recombinant p53 protein was examined. Site-directed mutation of putative p53 binding sequence and p53 knockdown by siRNA were performed. The protein expression and promoter activities of XAF1 in cells with null p53 were higher than that with wild-type and mutant p53. Ectopic overexpression of wild-type p53 suppressed XAF1 expression. A half-site (-95 to -86 nt) and a quarter-site (-4 to +1 nt) of p53 responsive element were found within XAF1 promoter. Both sequences bound to recombinant p53 effectively and specifically. Site-mutation of p53 responsive sequences abrogated the binding capacity. However, only the mutation of half-site increased XAF1 promoter activities. Suppression of p53 not only decreased the binding capacity of p53 responsive halfsite but also increased XAF1 transcription. In conclusion, we demonstrated that p53 could suppress the transcription of XAF1 through interaction with a high affinity responsive element (-95 to -86 nt) within XAF1 promoter, indicating a novel exclusive mechanism between these two tumor suppressors.
authors.affiliation: Department of Digestive Medicine, Nanfang Hospital, The Southern Medical University, Guangzhou 510515, P.R. China.
authors.forename: Wenjing
authors.initials: W
authors.lastname: Zhang
authors.forename: Zheng
authors.initials: Z
authors.lastname: Guo
authors.forename: Bo
authors.initials: B
authors.lastname: Jiang
authors.forename: Lingyun
authors.initials: L
authors.lastname: Niu
authors.forename: Guosheng
authors.initials: G
authors.lastname: Xia
authors.forename: Xinying
authors.initials: X
authors.lastname: Wang
authors.forename: Tianming
authors.initials: T
authors.lastname: Cheng
authors.forename: Yusheng
authors.initials: Y
authors.lastname: Zhang
authors.forename: Jide
authors.initials: J
authors.lastname: Wang
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; D001665:Binding Sites; D003110:Colonic Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic; D045325:HCT116 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D011994:Recombinant Proteins / Q000378:metabolism; D020218:Response Elements; D013274:Stomach Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D014158:Transcription, Genetic; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000235:genetics* / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009363:Neoplasm Proteins; D011994:Recombinant Proteins; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; C417551:XAF1 protein, human