Institute of Bioscience and Biotechnology, National Taiwan Ocean University, Keelung, Taiwan, ROC.
Cell Death Differ. 2011 Nov;18(11):1757-70. doi: 10.1038/cdd.2011.44. Epub 2011 May 6.
Hypoxia-inducible factor (HIF) 1α and HIF2α and the inhibitor of apoptosis survivin represent prominent markers of many human cancers. They are also widely expressed in various embryonic tissues, including the central nervous system; however, little is known about their functions in embryos. Here, we show that zebrafish HIF2α protects neural progenitor cells and neural differentiation processes by upregulating the survivin orthologues birc5a and birc5b during embryogenesis. Morpholino-mediated knockdown of hif2α reduced the transcription of birc5a and birc5b, induced p53-independent apoptosis and abrogated neural cell differentiation. Depletion of birc5a and birc5b recaptured the neural development defects that were observed in the hif2α morphants. The phenotypes induced by HIF2α depletion were largely rescued by ectopic birc5a and birc5b mRNAs, indicating that Birc5a and Birc5b act downstream of HIF2α. Chromatin immunoprecipitation assay revealed that HIF2α binds to birc5a and birc5b promoters directly to modulate their transcriptions. Knockdown of hif2α, birc5a or birc5b reduced the expression of the cdk inhibitors p27/cdkn1b and p57/cdkn1c and increased ccnd1/cyclin D1 transcription in the surviving neural progenitor cells. The reduction in elavl3/HuC expression and enhanced pcna, nestin, ascl1b and sox3 expression indicate that the surviving neural progenitor cells in hif2α morphants maintain a high proliferation rate without terminally differentiating. We propose that a subset of developmental defects attributed to HIF2α depletion is due in part to the loss of survivin activity.
缺氧诱导因子 (HIF) 1α 和 HIF2α 以及凋亡抑制剂 survivin 是许多人类癌症的重要标志物。它们也广泛表达于各种胚胎组织中，包括中枢神经系统；然而，它们在胚胎中的功能知之甚少。在这里，我们发现斑马鱼 HIF2α 通过在胚胎发生过程中上调 survivin 同源物 birc5a 和 birc5b 来保护神经祖细胞和神经分化过程。使用 morpholino 介导的 hif2α 敲低会降低 birc5a 和 birc5b 的转录，诱导 p53 非依赖性凋亡并破坏神经细胞分化。birc5a 和 birc5b 的耗竭回收了在 hif2α 形态发生体中观察到的神经发育缺陷。HIF2α 耗竭诱导的表型在很大程度上被外源性 birc5a 和 birc5b mRNA 挽救，表明 Birc5a 和 Birc5b 是 HIF2α 的下游作用物。染色质免疫沉淀检测显示 HIF2α 直接结合到 birc5a 和 birc5b 启动子上，调节它们的转录。hif2α、birc5a 或 birc5b 的敲低降低了 cdk 抑制剂 p27/cdkn1b 和 p57/cdkn1c 的表达，并增加了存活的神经祖细胞中 ccnd1/cyclin D1 的转录。elavl3/HuC 表达的降低和 pcna、nestin、ascl1b 和 sox3 表达的增强表明 hif2α 形态发生体中的存活神经祖细胞在没有终末分化的情况下保持高增殖率。我们提出，归因于 HIF2α 耗竭的一部分发育缺陷是由于 survivin 活性的丧失。
