Dell H, Hadzopoulou-Cladaras M
Department of Medicine, Section of Molecular Genetics, Cardiovascular Institute, Boston University School of Medicine, Center for Advanced Biomedical Research, Boston, Massachusetts 02118-2394, USA.
J Biol Chem. 1999 Mar 26;274(13):9013-21. doi: 10.1074/jbc.274.13.9013.
Hepatocyte nuclear factor-4 (HNF-4) is a liver-enriched transcription factor that is crucial in the regulation of a large number of genes involved in glucose, cholesterol, and fatty acid metabolism and in determining the hepatic phenotype. We have previously shown that HNF-4 contains transcription activation functions at the N terminus (AF-1) and the C terminus (AF-2) which work synergistically to confer full HNF-4 activity. Here, we show that HNF-4 recruits the CREB-binding protein (CBP) coactivator on promoters of genes that contain functional HNF-4 sites. HNF-4 interacts with the N-terminal region of CBP (amino acids 1-771) and the C-terminal region of CBP (amino acids 1812-2441). The two activating functions of HNF-4, AF-1 and AF-2, interact with the N terminus and the N and C terminus of CBP, respectively. In addition, we show that in contrast to the other nuclear hormone receptors the interaction between HNF-4 and CBP is ligand-independent. Recruitment of CBP by HNF-4 results in an enhancement of the transcriptional activity of the latter. CBP does not activate gene expression in the absence of HNF-4, and dominant negative forms of HNF-4 prevent transcriptional activation by CBP, suggesting that the mere recruitment of CBP by HNF-4 is not sufficient for enhancement of gene expression. These findings demonstrate that CBP acts as a transcriptional coactivator for HNF-4 and provide new insights into the regulatory function of HNF-4.
肝细胞核因子4（HNF-4）是一种肝脏富集转录因子，对调控大量参与葡萄糖、胆固醇和脂肪酸代谢的基因以及决定肝脏表型起着关键作用。我们之前已经表明，HNF-4在N端（AF-1）和C端（AF-2）含有转录激活功能，二者协同作用赋予HNF-4完整活性。在此，我们发现HNF-4在含有功能性HNF-4位点的基因启动子上募集CREB结合蛋白（CBP）共激活因子。HNF-4与CBP的N端区域（氨基酸1-771）和C端区域（氨基酸1812-2441）相互作用。HNF-4的两个激活功能，即AF-1和AF-2，分别与CBP的N端以及N端和C端相互作用。此外，我们还发现，与其他核激素受体不同，HNF-4与CBP之间的相互作用不依赖配体。HNF-4对CBP的募集导致后者转录活性增强。在没有HNF-4的情况下，CBP不会激活基因表达，而HNF-4的显性负性形式会阻止CBP的转录激活，这表明仅HNF-4对CBP的募集不足以增强基因表达。这些发现证明CBP作为HNF-4的转录共激活因子发挥作用，并为HNF-4的调控功能提供了新的见解。
