Involvement of ATBF1 in liver regeneration and hepatocarcinogenesis

AT基序结合因子1（ATBF 1）cDNA首先从HuH-7人肝癌细胞中分离，基于其产物与人甲胎蛋白基因增强子中富含AT的元件结合的能力。ATBF 1蛋白属于一个含有同源结构域和锌指结构域的转录因子家族。ATBF 1的表达在神经元和肌源性分化过程中被诱导，并且还在绒毛基部的未成熟细胞中观察到。本研究旨在阐明ATBF 1在肝再生和肝癌发生中的作用。首先，我们建立了实时荧光定量PCR来测量ATBF 1 mRNA的表达水平，并研究了ATBF 1表达在肝细胞生长因子处理的原代培养大鼠肝细胞增殖过程中的连续变化。HGF处理后6小时ATBF 1的表达受到抑制，而cyclin D1的表达受到刺激。为了检测ATBF 1在肝祖细胞中的表达，对大鼠给予2-乙酰氨基芴（2-AAF），每周5次，持续2周，然后进行部分肝切除术（PH）。在该2-AAF/PH模型中，在汇管区旁边观察到肝祖细胞，所谓的“卵圆细胞”，并且HGF刺激这些细胞的增殖和肝分化。在成熟的肝细胞中，ATBF 1的表达在PH后8天的细胞核中，而ATBF 1在细胞核和细胞质中均被检测到。此外，虽然HGF处理降低了成熟肝细胞中ATBF 1的核表达，但该处理降低了卵圆细胞胞质中ATBF 1的表达。这些结果表明，HGF处理刺激卵圆细胞的增殖和肝分化，并且卵圆细胞的增殖逐渐终止并诱导向成熟肝细胞分化。ATBF 1可能通过其细胞内定位在肝祖细胞的增殖或分化中发挥重要作用。

AT motif-binding factor 1 (ATBF1) cDNA was first isolated from HuH-7 human hepatoma cells based on the ability of its products to bind to an AT-rich element in the enhancer of the human alpha-fetoprotein gene. ATBF1 protein belongs to a family of transcription factors containing both homeodomain and zinc finger motifs. Expression of ATBF1 is induced during neuronal and myogenic differentiation, and also observed in immature cells at the base of villi. This study aims to clarify a role of ATBF1 in liver regeneration and hepatocarcinogenesis. First, we have established real-time PCR to measure expression level of ATBF1 mRNA, and examined sequential changes in ATBF1 expression during proliferation of primary cultured rat hepatocytes treated with hepatocyte growth factor. Expression of ATBF1 was suppressed 6 hours after HGF treatment, while cyclin D1 expression was stimulated. To examine ATBF1 expression in hepatic progenitor cells, rats were administered 2-acetylaminofluorene (2-AAF) five times a week for two weeks, followed by partial hepatectomy (PH). In this 2-AAF/PH model, hepatic progenitor cells, so called "oval cells", are observed alongside of portal areas, and HGF stimulates proliferation and hepatic differentiation of these cells. In mature hepatocytes, ATBF1 expression was immunohistochemically observed in the nucleus eight days after PH, whereas ATBF1 was detected in both nucleus and cytoplasm. Additionally, Although HGF treatment decreased nuclear expression of ATBF1 in mature hepatocytes, and ATBF1 expression in the cytoplasm of oval cells was decreased by this treatment. These results suggest that HGF treatment stimulated proliferation and hepatic differentiation of oval cells, and that proliferation of oval cells gradually terminated and differentiation to mature hepatocytes was induced. ATBF1 may play an important role in proliferation or differentiation of hepatic progenitor cells via its intracellular localization.