Regulation of the α-fetoprotein gene by the isoforms of ATBF1 transcription factor in human hepatoma
Regulation of the α-fetoprotein gene by the isoforms of ATBF1 transcription factor in human hepatoma
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DOI：
10.1053/jhep.2002.30420
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发表时间：
2002-01-01
期刊：
影响因子：
13.5
通讯作者：
Tamaoki, T
中科院分区：
文献类型：
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作者：
Ninomiya, T;Mihara, K;Tamaoki, T
我们研究了 3 种人肝癌细胞系 HuH-7、HepG2 和 huH-1 中甲胎蛋白 (ATP) 表达的调节机制，分别产生高、中和低水平的 AFP。沉默子是 AFP 基因的负顺式作用元件，在 huH-1 和 HepG2 中高度激活，将 AFP 增强子活性抑制 91%，而在 HuH-7 中仅观察到 26% 的抑制。为了解释 HepG2 和 huH-1 之间 AFP 产生的差异，我们研究了 AT 基序结合因子 1 (ATBF1) 转录因子的两种亚型 ATBF1-A 和 -B 的作用。共转染测定表明，ATBF1 亚型在 HepG2 和 huH-1 中对 AFP 基因的调节不同。在 huH-1 和 HuH-7 中，两种 ATBF1 亚型均强烈抑制增强子活性和轻微抑制启动子活性。另一方面，在 HepG2 中，ATBF1-A 抑制增强子和启动子活性，但令人惊讶的是，ATBF1-B 被发现刺激增强子活性，但对启动子没有影响。所有 3 个细胞系中 ATBF1-A mRNA 的水平相似，而 ATBF1-B mRNA 的表达差异很大，其中 HepG2 中水平最高，其次是 huH-1 和 HuH-7。这些结果表明，在 HepG2 中，ATBF1-B 可能具有显性负效应，以减轻其亚型引起的转录抑制。为了支持这一观点，我们发现 ATBF1-A 分子特异的 N 末端区域具有转录抑制活性。因此，ATBF1 变体以及沉默子的使用可能提供一种独特的机制，有助于测定人肝癌细胞系中的 AFP 水平。
We investigated mechanisms regulating expression of alpha -fetoprotein (ATP) in 3 human hepatoma cell lines, HuH-7, HepG2, and huH-1, producing high, medium, and low levels of AFP, respectively. The silencer, a negative cis-acting element of the AFP gene, was highly activated in huH-1 and HepG2 to repress AFP enhancer activity by 91%,whereas only 26% repression was observed in HuH-7. To account for the difference in AFP production between HepG2 and huH-1, we investigated the roles of two isoforms of the AT motif-binding factor 1 (ATBF1) transcription factor, ATBF1-A and -B. Cotransfection assays showed that the ATBF1 isoforms regulated the AFP gene differently in HepG2 and huH-1. In huH-1 and HuH-7, both ATBF1 isoforms suppressed strongly enhancer activity and slightly promoter activity. In HepG2, on the other hand, ATBF1-A suppressed the enhancer and promoter activities, but surprisingly, ATBF1-B was found to stimulate enhancer activity while showing no effect on the promoter. Levels of ATBF1-A mRNA were similar in all 3 cell lines, whereas the expression ATBF1-B mRNA varied greatly, with the highest level seen in HepG2 followed by huH-1 and HuH-7. These results suggest that, in HepG2, ATBF1-B may have a dominant negative effect to relieve the transcriptional repression caused by its isoform. In support of this view, we found that the N-terminal region specific to the ATBF1-A molecule possessed transcriptional repressor activity. Thus, the use of the ATBF1 variants as well as the silencer may provide a unique mechanism that contributes to the determination of AFP levels in human hepatoma cell lines.