Qi Y, Liu J, Saadat S, Tian X, Han Y, Fong G-H, Pandolfi P P, Lee L Y, Li S
Department of Surgery, Rutgers University Robert Wood Johnson Medical School, 125 Paterson Street, New Brunswick, NJ 08093, USA.
Shenyang Northern Hospital, Shenyang, China.
Cell Death Differ. 2015 May;22(5):875-84. doi: 10.1038/cdd.2014.185. Epub 2014 Nov 14.
The tumor suppressor phosphatase and tensin homolog (PTEN) dephosphorylates PIP3 and antagonizes the prosurvival PI3K-Akt pathway. Targeted deletion of PTEN in mice led to early embryonic lethality. To elucidate its role in embryonic epithelial morphogenesis and the underlying mechanisms, we used embryonic stem cell-derived embryoid body (EB), an epithelial cyst structurally similar to the periimplantation embryo. PTEN is upregulated during EB morphogenesis in parallel with apoptosis of core cells, which mediates EB cavitation. Genetic ablation of PTEN causes Akt overactivation, apoptosis resistance and cavitation blockade. However, rescue experiments using mutant PTEN and pharmacological inhibition of Akt suggest that the phosphatase activity of PTEN and Akt are not involved in apoptosis-mediated cavitation. Instead, hypoxia-induced upregulation of Bnip3, a proapoptotic BH3-only protein, mediates PTEN-dependent apoptosis and cavitation. PTEN inactivation inhibits hypoxia- and reactive oxygen species-induced Bnip3 elevation. Overexpression of Bnip3 in PTEN-null EBs rescues apoptosis of the core cells. Mechanistically, suppression of Bnip3 following PTEN loss is likely due to reduction of hypoxia-inducible factor-2α (HIF-2α) because forced expression of an oxygen-stable HIF-2α mutant rescues Bnip3 expression and apoptosis. Lastly, we show that HIF-2α is upregulated by PTEN at both transcriptional and posttranscriptional levels. Ablation of prolyl hydroxylase domain-containing protein 2 (PHD2) in normal EBs or inhibition of PHD activities in PTEN-null EBs stabilizes HIF-2α and induces Bnip3 and caspase-3 activation. Altogether, these results suggest that PTEN is required for apoptosis-mediated cavitation during epithelial morphogenesis by regulating the expression of HIF-2α and Bnip3.
肿瘤抑制因子磷酸酶和张力蛋白同源物（PTEN）使磷脂酰肌醇-3,4,5-三磷酸（PIP3）去磷酸化，并拮抗促生存的磷脂酰肌醇-3激酶（PI3K）-蛋白激酶B（Akt）信号通路。在小鼠中靶向缺失PTEN会导致早期胚胎致死。为了阐明其在胚胎上皮形态发生中的作用及潜在机制，我们使用了胚胎干细胞来源的胚状体（EB），这是一种结构上与着床前胚胎相似的上皮囊肿。在EB形态发生过程中，PTEN与核心细胞凋亡同时上调，核心细胞凋亡介导EB空泡化。PTEN的基因敲除导致Akt过度激活、凋亡抵抗和空泡化受阻。然而，使用突变型PTEN的挽救实验和Akt的药理学抑制表明，PTEN的磷酸酶活性和Akt并不参与凋亡介导的空泡化。相反，缺氧诱导的促凋亡的仅含BH3结构域的蛋白Bnip3的上调介导了PTEN依赖的凋亡和空泡化。PTEN失活抑制缺氧和活性氧诱导的Bnip3升高。在PTEN缺失的EB中过表达Bnip3可挽救核心细胞的凋亡。从机制上讲，PTEN缺失后Bnip3的抑制可能是由于缺氧诱导因子-2α（HIF-2α）减少，因为强制表达氧稳定的HIF-2α突变体可挽救Bnip3表达和凋亡。最后，我们表明HIF-2α在转录和转录后水平均被PTEN上调。在正常EB中敲除含脯氨酰羟化酶结构域蛋白2（PHD2）或在PTEN缺失的EB中抑制PHD活性可使HIF-2α稳定并诱导Bnip3和半胱天冬酶-3激活。总之，这些结果表明PTEN通过调节HIF-2α和Bnip3的表达，是上皮形态发生过程中凋亡介导的空泡化所必需的。
