Piaggio G, Tomei L, Toniatti C, De Francesco R, Gerstner J, Cortese R
Istituto Regina Elena Centro Ricerca Sperimentale, Laboratorio Oncogenesi Molecolare, Rome, Italy.
Nucleic Acids Res. 1994 Oct 11;22(20):4284-90. doi: 10.1093/nar/22.20.4284.
LFB1/HNF1 is a hepatocyte-enriched trans-activator involved in the regulation of many liver-specific genes. We report the cloning and characterization of a rat genomic DNA fragment containing about 3.5 kb of the LFB1/HNF1 gene 5'-flanking region. This DNA segment is capable of directing the liver-specific expression of a reporter gene in transfection assays. More interestingly, the basal activity of the LFB1/HNF1 promoter in cultured hepatoma cell lines is down-regulated by exogenously added LFB1/HNF1 protein itself. The ability to repress transcription starting from its own promoter requires the integrity of the N-terminal LFB1/HNF1 DNA-binding domain. Contrary to the expectations, in vitro binding experiments failed to demonstrate any specific and functional interaction of purified LFB1/HNF1 with the -3.5 kb promoter sequence. In addition to the DNA-binding domain, a 60 aa region contained in the C-terminus of the protein and distinct from the previously characterized activation domains, is also required for the repressing function.
LFB1/HNF1是一种肝脏富集的反式激活因子，参与许多肝脏特异性基因的调控。我们报道了一个大鼠基因组DNA片段的克隆和特性分析，该片段包含约3.5 kb的LFB1/HNF1基因5'-侧翼区域。在转染实验中，该DNA片段能够指导报告基因的肝脏特异性表达。更有趣的是，在培养的肝癌细胞系中，外源性添加的LFB1/HNF1蛋白本身会下调LFB1/HNF1启动子的基础活性。从其自身启动子抑制转录的能力需要N端LFB1/HNF1 DNA结合结构域的完整性。与预期相反，体外结合实验未能证明纯化的LFB1/HNF1与-3.5 kb启动子序列有任何特异性和功能性相互作用。除了DNA结合结构域，该蛋白C端包含的一个60个氨基酸的区域，与先前鉴定的激活结构域不同，也是抑制功能所必需的。
