Reisman D, Rotter V
Department of Biological Sciences, University of South Carolina, Columbia 29208.
Nucleic Acids Res. 1993 Jan 25;21(2):345-50. doi: 10.1093/nar/21.2.345.
Expression of the wild-type p53 tumor suppressor gene has been found to play an important role in the regulation of cellular proliferation and differentiation. In addition, in many transformed cells and primary tumors, the gene has undergone allelic deletions and mutant forms of the p53 gene are expressed at elevated levels. In defining transcriptional regulatory regions of the p53 gene, we have previously shown that both the human and murine p53 promoters contain a conserved consensus recognition sequence for the basic-helix-loop-helix (bHLH) containing family of DNA-binding proteins. In the murine p53 promoter this element is required for full promoter activity and contains the sequence CACGTG, a sequence identical to the recognition site for the bHLH containing transcription factors c-Myc, USF and TFE3. Here we examine the ability of one of these factors, USF, to bind to the p53 promoter. By assaying the binding activity of in vitro translated USF as well as factors present in nuclear extracts, we conclude that the transcription factor USF binds in a site-specific manner to a CACGTG motif within the murine p53 promoter and represents the major DNA-binding activity observed in nuclear extracts. Elevated levels of USF, generated upon transfection of a vector expressing USF, lead to enhanced activity of the p53 promoter. These findings indicate that USF may play a central role in regulating p53 expression.
野生型p53肿瘤抑制基因的表达已被发现，在细胞增殖和分化的调控中发挥着重要作用。此外，在许多转化细胞和原发性肿瘤中，该基因发生了等位基因缺失，且p53基因的突变形式在高水平表达。在确定p53基因的转录调控区域时，我们先前已表明，人类和小鼠的p53启动子均含有一个保守的共有识别序列，该序列针对含碱性螺旋-环-螺旋（bHLH）的DNA结合蛋白家族。在小鼠p53启动子中，该元件对于启动子的完全活性是必需的，并且包含序列CACGTG，该序列与含bHLH的转录因子c-Myc、USF和TFE3的识别位点相同。在此，我们研究了这些因子之一USF与p53启动子结合的能力。通过检测体外翻译的USF以及核提取物中存在的因子的结合活性，我们得出结论，转录因子USF以位点特异性方式与小鼠p53启动子内的CACGTG基序结合，并代表在核提取物中观察到的主要DNA结合活性。转染表达USF的载体后产生的USF水平升高，导致p53启动子活性增强。这些发现表明，USF可能在调节p53表达中起核心作用。
