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Transcriptional control of p53 expression participates in the generation of appropriate levels of active p53 in response to mitogenic stimulation. This prompted us to study the role of a putative AP-1 and a NF-kB motif in the human p53 promoter for transcriptional regulation. We show that mutation of the AP-1 or the NF-kB motif abolishes transcription from the human p53 promoter in HeLa, HepG2 and adenovirus type 5 E1-transformed 293 cells. In comparison, mutation of the previously characterized Myc/Max/USF binding site in the human p53 promoter reduces the transcription rate ®vefold. The AP-1 motif in the human p53 promoter binds c-Fos and c-Jun and the NF-kB motif binds p50 NF-kB1 and p65 RelA . The cooperative nature of transcriptional activation by these factors was documented by repression of c-fos or NF-kB1 translation: Pretreatment of the cells with a cfos or p50 NF-kB1 antisense oligonucleotide suppresses transcription from the human p53 promoter completely. In addition, we show that (a) the level of endogenous p53 mRNA and (b) transcription from the strictly p53-dependent human mdm2 promoter are reduced in the presence of c-fos, c-jun, p50 NF-kB1 , p65 RelA or c-myc antisense oligonucleotides, underscoring the importance of these transcription factors for the expression of functional p53.

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