Department of Human Genetics, Academic Medical Center, Amsterdam, the Netherlands.
Mol Cancer Res. 2010 Oct;8(10):1344-57. doi: 10.1158/1541-7786.MCR-09-0546. Epub 2010 Sep 13.
The transcription factor orthodenticle homeobox 2 (OTX2) has been implicated in the pathogenesis of medulloblastoma, as it is often highly expressed and sometimes amplified in these tumors. Little is known of the downstream pathways regulated by OTX2. We therefore generated MED8A and DAOY medulloblastoma cell lines with doxycycline-inducible OTX2 expression. In both cell lines, OTX2 inhibited proliferation and induced a senescence-like phenotype with senescence-associated β-galactosidase activity. Expression profiles of time series after OTX2 induction in MED8A showed early upregulation of cell cycle genes related to the G(2)-M phase, such as AURKA, CDC25C, and CCNG2. Paradoxically, G(1)-S phase genes such as MYC, CDK4, CDK6, CCND1, and CCND2 were strongly downregulated, in line with the observed G(1) arrest. ChIP-on-chip analyses of OTX2 binding to promoter regions in MED8A and DAOY showed a strong enrichment for binding to the G(2)-M genes, suggesting a direct activation. Their mRNA expression correlated with OTX2 expression in primary tumors, underscoring the in vivo relevance of this regulation. OTX2 induction activated the P53 pathway in MED8A, but not in DAOY, which carries a mutated P53 gene. In DAOY cells, senescence-associated secretory factors, such as interleukin-6 and insulin-like growth factor binding protein 7, were strongly upregulated after OTX2 induction. We hypothesize that the imbalance in cell cycle stimulation by OTX2 leads to cellular senescence either by activating the P53 pathway or through the induction of secretory factors. Our data indicate that OTX2 directly induces a series of cell cycle genes but requires cooperating genes for an oncogenic acceleration of the cell cycle.
转录因子同源异型盒 2（OTX2）已被牵连到成神经管细胞瘤的发病机制中，因为它在这些肿瘤中经常高度表达，有时甚至扩增。关于 OTX2 调节的下游途径知之甚少。因此，我们生成了具有可诱导 OTX2 表达的多柔比星诱导 MED8A 和 DAOY 成神经管细胞瘤细胞系。在这两种细胞系中，OTX2 抑制增殖并诱导具有衰老相关β-半乳糖苷酶活性的衰老样表型。OTX2 诱导后 MED8A 时间序列的表达谱显示，与 G2-M 期相关的细胞周期基因（如 AURKA、CDC25C 和 CCNG2）早期上调。矛盾的是，G1-S 期基因（如 MYC、CDK4、CDK6、CCND1 和 CCND2）被强烈下调，与观察到的 G1 期阻滞一致。OTX2 与 MED8A 和 DAOY 启动子区域结合的 ChIP-on-chip 分析显示，与 G2-M 基因的结合强烈富集，表明直接激活。它们的 mRNA 表达与原发性肿瘤中的 OTX2 表达相关，突出了这种调节的体内相关性。OTX2 诱导在 MED8A 中激活了 P53 途径，但在携带突变 P53 基因的 DAOY 中没有。在 DAOY 细胞中，细胞衰老相关的分泌因子，如白细胞介素 6 和胰岛素样生长因子结合蛋白 7，在 OTX2 诱导后强烈上调。我们假设，OTX2 通过激活 P53 途径或通过诱导分泌因子，导致细胞周期刺激失衡，从而导致细胞衰老。我们的数据表明，OTX2 直接诱导一系列细胞周期基因，但需要协同基因来加速细胞周期的致癌作用。
