Identification of alpha-fetoprotein silencer and analysis of its regulatory mechanisms

a-胎蛋白（AEP）消声器活性与出生后AFP表达的抑制有关。此外，沉默子活性的下调会导致AFP基因在肝癌发生过程中的重新表达。在本研究中，AFP屏蔽剂与其增强子相互作用，导致增强子活性受到抑制。此外，AFP增强子活性的抑制抑制了AFP和白蛋白基因的表达。在hh -7人肝癌细胞中转染视网膜母细胞瘤（retinoblastoma, Rb）基因或ras基因后，Rb基因的转导上调肝细胞核因子-1 （hepatocyte nuclear factor-1, HNF-1）基因的表达，HNF-1是一种肝脏特异性转录因子，通过激活其启动子刺激AFP和白蛋白基因的转录。ras基因的转导导致AFP增强子活性的抑制和AFP基因转录的抑制。此外，在hh -7细胞中Rb基因的转导不仅刺激了HNF-1的表达，还促进了细胞生长的接触抑制。因此，Rb基因被认为是一种分化诱导剂，尽管它不能直接诱导AFP消音器的活性。HMGI-C是参与DNA环形成的关键因子，在胎儿器官或某些恶性细胞中高度表达。采用RT-PCR方法分析人肝癌细胞株中HMGI-C的表达。其在产afp细胞中的表达明显高于非产afp细胞。这表明HMGI-C的表达与人肝癌细胞中AFP消音器的活性有关。

The a-fetoprotein (AEP) silencer activity is relevant to repression of AFP expression after birth. Moreover, down-regulation of the silencer activity would lead to re-expression of the AFP gene in the hepatocarcinogenetic process. In the present study, the AFP silecer interacted with its enhancer, resulting in the inhibition of the enhancer activity. Furthermore, repression of the AFP enhancer activity depressed both the AFP and albumin gene expression. When retinoblastoma (Rb) gene or ras gene were transduced in HuH-7 human hepatoma cells, transduction of Rb gene up-regulated expression of the hepatocyte nuclear factor-1 (HNF-1) gene, a liver-specific transcriptional factor, which stimulated both the AFP and albumin gene transcription through activation of their promoters. Transduction of ras gene induced the suppression of the AFP enhancer activity and repressed the AFP gene transcription. In addition, the Rb gene transduction in HuH-7 cells not only stimulated HNF-1 expression but also promoted contact inhibition of cell growth. Thus the Rb gene was considered to function as a differeatiation inducer, although it did not directly induce the AFP silencer activity.HMGI-C is a key factor involved in DNA loop formation and expressed highly in fetal organs or certain malignant cells. Expression of HMGI-C was analyzed in human hepatoma cell lines by means of RT-PCR.Its expression was apparenty higher in AFP-producing cells than nonproclucing cells. This would suggest the association of HMGI-C expression with the AFP silencer activity in human hepatoma cells.