Kim S J, Wagner S, Liu F, O'Reilly M A, Robbins P D, Green M R
Laboratory of Chemoprevention, National Cancer Institute, Bethesda, Maryland 20892.
Nature. 1992 Jul 23;358(6384):331-4. doi: 10.1038/358331a0.
The retinoblastoma susceptibility gene product (pRb) plays an important role in constraining cellular proliferation and in regulating the cell cycle. The pRb inhibits transcription of genes involved in growth control (reviewed in ref. 3) and can regulate transforming growth factor beta 1 (TGF-beta 1) gene expression. TGF-beta isoforms also down-regulate cellular proliferation. To determine whether pRb also regulates expression of other TGF-beta isoforms, we examined the effect of pRb on the expression of the human TGF-beta 2 gene. The human TGF-beta 2 promoter contains multiple elements including an ATF site, which is essential for basal promoter activity. Here we report that pRb activates transcription of the human TGF-beta 2 gene. The promoter element responsible for pRb-mediated transcriptional regulation is a binding site for ATF proteins, an extensive transcription factor family. We provide evidence that implicates ATF-2 in pRb-responsiveness. First, the ATF promoter element in the TGF-beta 2 gene is a high-affinity ATF-2-binding site. Second, a GAL4-ATF2 fusion protein can support pRb-mediated transcriptional activation of a promoter containing GAL4-binding sites. Third, ATF-2 in nuclear extracts can interact with pRb. Our results reveal a new mechanism by which pRb constrains cellular proliferation: by activating expression of the inhibitory growth factor, TGF-beta 2.
视网膜母细胞瘤易感基因产物（pRb）在限制细胞增殖和调节细胞周期中发挥重要作用。pRb抑制参与生长控制的基因转录（参考文献3中有综述），并可调节转化生长因子β1（TGF-β1）基因表达。TGF-β亚型也下调细胞增殖。为了确定pRb是否也调节其他TGF-β亚型的表达，我们研究了pRb对人TGF-β2基因表达的影响。人TGF-β2启动子包含多个元件，包括一个ATF位点，这对基础启动子活性至关重要。在此我们报告pRb激活人TGF-β2基因的转录。负责pRb介导的转录调控的启动子元件是ATF蛋白（一个广泛的转录因子家族）的结合位点。我们提供的证据表明ATF-2参与了pRb反应。首先，TGF-β2基因中的ATF启动子元件是一个高亲和力的ATF-2结合位点。其次，GAL4-ATF2融合蛋白可以支持pRb介导的含有GAL4结合位点的启动子的转录激活。第三，核提取物中的ATF-2可以与pRb相互作用。我们的结果揭示了pRb限制细胞增殖的一种新机制：通过激活抑制性生长因子TGF-β2的表达。
