Li Jun, Kretzner Leo
Department of Cellular and Molecular Biology, Division of Basic Biomedical Sciences, University of South Dakota School of Medicine, Vermillion, SD, USA.
Mol Cell Biochem. 2003 Aug;250(1-2):91-105. doi: 10.1023/a:1024918328162.
A major prognostic marker for neuroblastoma (Nb) is N-myc gene amplification, which predicts a poor clinical outcome. We sought genes differentially expressed on a consistent basis between multiple human Nb cell lines bearing normal versus amplified N-myc, in hopes of finding target genes that might clarify how N-myc overexpression translates into poor clinical prognosis. Using differential display, we find the previously described growth-inhibitory gene Ndrg1 is strongly repressed in all tested Nb cell lines bearing N-myc amplification, as well as in a neuroepithelioma line with amplified c-myc. Overexpression of N-myc in non-amplified Nb cells leads to repression of Ndrg1, as does activation of an inducible c-myc transgene in fibroblasts. Conversely, N-myc downregulation in N-myc-amplified Nb cells results in re-expression of the Ndrg1, and stimuli known to induce Ndrg1 do so in Nb cells while simultaneously down-regulating N-myc. Relevant to these results, we demonstrate an in vitro interaction of Myc protein with the Ndrg1 core promoter. We also find that Ndrg1 levels increase dramatically during in vitro differentiation of two cell lines modeling neural and glial development, while c- and N-myc levels decline. Our results combined with previous information on the Ndrg1 gene product suggest that downregulation of this gene is an important component of N-Myc effects in neuroblastomas with poor clinical outcome. In support of this notion, we find that re-expression of Ndrg1 in high-Myc Nb cells results in smaller cells with reduced colony size in soft-agar assays, further underscoring the functional significance of this gene in human neuroblastoma cells.
神经母细胞瘤（Nb）的一个主要预后标志物是N-myc基因扩增，它预示着临床预后不良。我们寻找在携带正常与扩增N-myc的多个人类Nb细胞系之间持续差异表达的基因，希望找到可能阐明N-myc过表达如何转化为不良临床预后的靶基因。使用差异显示技术，我们发现先前描述的生长抑制基因Ndrg1在所有测试的携带N-myc扩增的Nb细胞系以及一个具有c-myc扩增的神经上皮瘤细胞系中均被强烈抑制。在未扩增的Nb细胞中过表达N-myc会导致Ndrg1的抑制，在成纤维细胞中诱导性c-myc转基因的激活也会如此。相反，在N-myc扩增的Nb细胞中下调N-myc会导致Ndrg1的重新表达，已知能诱导Ndrg1的刺激物在Nb细胞中也能诱导其表达，同时下调N-myc。与这些结果相关，我们证明了Myc蛋白与Ndrg1核心启动子之间的体外相互作用。我们还发现，在模拟神经和胶质细胞发育的两个细胞系的体外分化过程中，Ndrg1水平显著增加，而c-myc和N-myc水平下降。我们的结果与先前关于Ndrg1基因产物的信息相结合，表明该基因的下调是临床预后不良的神经母细胞瘤中N-Myc效应的一个重要组成部分。支持这一观点的是，我们发现在高Myc的Nb细胞中重新表达Ndrg1会导致在软琼脂试验中细胞变小且集落大小减小，进一步强调了该基因在人类神经母细胞瘤细胞中的功能意义。
