Sahlgrenska Cancer Center, University of Gothenburg , Box 425, SE 405 30 Gothenburg , Sweden ; Molecular Biology Research Center, School of Biological Science and Technology, Central South University , Changsha 410078 , China.
Biol Open. 2012 Jun 15;1(6):527-35. doi: 10.1242/bio.2012893. Epub 2012 Apr 18.
TLX is known as the orphan nuclear receptor indispensable for maintaining neural stem cells in adult neurogenesis. We report here that neuroblastoma cell lines express high levels of TLX, which further increase in hypoxia to enhance the angiogenic capacity of these cells. The proangiogenetic activity of TLX appears to be induced by its direct binding to the von Hippel-Lindau protein (pVHL), which stabilizes TLX. In turn, TLX competes with hydroxylated hypoxia-inducible factor (HIF-α) for binding to pVHL, which contributes to the stabilization of HIF-2α in neuroblastoma during normoxia. Upon hypoxia, TLX increases in the nucleus where it binds in close proximity of the HIF-response element on the VEGF-promoter chromatin, and, together with HIF-2α, recruits RNA polymerase II to induce VEGF expression. Conversely, depletion of TLX by shRNA decreases the expression of HIF-2α and VEGF as well as the growth-promoting and colony-forming capacity of the neuroblastoma cell lines IMR-32 and SH-SY5Y. On the contrary, silencing HIF-2α will slightly increase TLX, suggesting that TLX acts to maintain a hypoxic environment when HIF-2α is decreasing. Our results demonstrate TLX to play a key role in controlling angiogenesis by regulating HIF-2α. TLX and pVHL might counterbalance each other in important fate decisions such as self-renewal and differentiation, as well as angiogenesis and anti-angiogenesis.
TLX 被称为维持成体神经发生中神经干细胞所必需的孤儿核受体。我们在此报告，神经母细胞瘤细胞系表达高水平的 TLX，在低氧条件下进一步增加以增强这些细胞的血管生成能力。TLX 的促血管生成活性似乎是由其直接与 von Hippel-Lindau 蛋白（pVHL）结合诱导的，pVHL 稳定 TLX。反过来，TLX 与羟化的缺氧诱导因子（HIF-α）竞争与 pVHL 的结合，这有助于在正常氧条件下神经母细胞瘤中 HIF-2α 的稳定。在低氧条件下，TLX 增加到核内，在那里它与 VEGF 启动子染色质上的 HIF 反应元件紧密结合，并与 HIF-2α 一起募集 RNA 聚合酶 II 诱导 VEGF 表达。相反，通过 shRNA 耗尽 TLX 会降低 HIF-2α 和 VEGF 的表达以及神经母细胞瘤细胞系 IMR-32 和 SH-SY5Y 的促生长和集落形成能力。相反，沉默 HIF-2α 会略微增加 TLX，表明当 HIF-2α 减少时，TLX 作用于维持低氧环境。我们的结果表明 TLX 通过调节 HIF-2α 在控制血管生成中起关键作用。TLX 和 pVHL 可能在自我更新和分化以及血管生成和抗血管生成等重要命运决定中相互制衡。
