Rui Caixia, Li Changyan, Xu Wangxiang, Zhan Yiqun, Li Yonghui, Yang Xiaoming
Beijing Institute of Radiation Medicine, 27 Taiping Road, Beijing 100850, P.R. China.
Biochem J. 2008 Apr 15;411(2):379-86. doi: 10.1042/BJ20071343.
Steroid 5alpha-reductase 1 (5alpha-R1), a key enzyme in the conversion of steroids into their respective 5alpha-reduced derivatives, plays a key role in some hormone-dependent tumours and is abundant in the liver, although it is also widely distributed throughout the body. HGF (hepatocyte growth factor) is a pleiotropic cytokine/growth factor involved in the progression of hepatocellular carcinoma. In the present paper, we report the stimulatory effect of HGF on human 5alpha-R1 transcription in hepatocellular carcinoma cells. Pre-treatment with actinomycin D or cycloheximide blocked the up-regulation of 5alpha-R1 mRNA expression by HGF, indicating that the increased level of 5alpha-R1 mRNA expression is regulated by transcriptional activation and was dependent on de novo protein synthesis. Functional analysis of the 5'-flanking region of the 5alpha-R1 gene by transfection analysis showed that the -79 to -50 region functioned as the HGF-responsive region. Mutagenesis and electrophoretic mobility-shift assays demonstrated that induction of 5a-R1 by HGF is mediated by an Egr-1 (early growth-response gene 1)-binding site at -60/-54. In addition, overexpression of Egr-1 was sufficient to transactivate 5alpha-R1 promoter activity, and knockdown of Egr-1 with gene-specific small interfering RNA resulted in inhibition of HGF-induced up-regulation of endogenous 5alpha-R1 expression. These data provide the first evidence that HGF stimulates 5alpha-R1 expression through up-regulation of the transcription factor Egr-1, thus suggesting the possibility that regulation of steroid metabolism by HGF represents a mechanism for high risk of hepatocellular carcinogenesis in males.
类固醇5α-还原酶1（5α-R1）是将类固醇转化为其各自5α-还原衍生物的关键酶，在一些激素依赖性肿瘤中起关键作用，在肝脏中含量丰富，尽管它也广泛分布于全身。肝细胞生长因子（HGF）是一种多效性细胞因子/生长因子，参与肝细胞癌的进展。在本文中，我们报道了HGF对肝癌细胞中人类5α-R1转录的刺激作用。用放线菌素D或环己酰亚胺预处理可阻断HGF对5α-R1 mRNA表达的上调，表明5α-R1 mRNA表达水平的升高受转录激活调节且依赖于从头合成蛋白质。通过转染分析对5α-R1基因5'侧翼区域进行功能分析表明，-79至-50区域作为HGF反应区域发挥作用。诱变和电泳迁移率变动分析表明，HGF对5α-R1的诱导是由-60/-54处的早期生长反应基因1（Egr-1）结合位点介导的。此外，Egr-1的过表达足以反式激活5α-R1启动子活性，用基因特异性小干扰RNA敲低Egr-1导致HGF诱导的内源性5α-R1表达上调受到抑制。这些数据提供了首个证据，即HGF通过上调转录因子Egr-1刺激5α-R1表达，从而提示HGF对类固醇代谢的调节可能是男性肝细胞癌高风险的一种机制。
