Goto T, Takano M, Albergaria A, Briese J, Pomeranz K M, Cloke B, Fusi L, Feroze-Zaidi F, Maywald N, Sajin M, Dina R E, Ishihara O, Takeda S, Lam E W-F, Bamberger A M, Ghaem-Maghami S, Brosens J J
1Institute of Reproductive and Developmental Biology, Imperial College London, Hammersmith Hospital, London, UK.
Oncogene. 2008 Jan 3;27(1):9-19. doi: 10.1038/sj.onc.1210626. Epub 2007 Jun 25.
The forkhead transcription factor FOXO1, a downstream target of phosphatidylinositol-3-kinase/Akt signalling pathway, regulates cyclic differentiation and apoptosis in normal endometrium, but its role in endometrial carcinogenesis is unknown. Screening of endometrial cancer cell lines demonstrated that FOXO1 is expressed in HEC-1B cells, but not in Ishikawa cells, which in turn highly express the FOXO1 targeting E3-ubiquitin ligase Skp2. FOXO1 transcript levels were also lower in Ishikawa cells and treatment with the proteasomal inhibitor was insufficient to restore expression. Lack of FOXO1 expression in Ishikawa cells was not accounted for by differential promoter methylation or activity, but correlated with increased messenger RNA (mRNA) turnover. Comparative analysis demonstrated that HEC-1B cells proliferate slower, but are more resistant to paclitaxel-mediated cell death than Ishikawa cells, which were partially reversed upon silencing of FOXO1 in HEC-1B cells or its re-expression in Ishikawa cells. We further show that FOXO1 is required for the expression of the growth arrest- and DNA-damage-inducible gene GADD45alpha. Analysis of biopsy samples demonstrated a marked loss of FOXO1 and GADD45alpha mRNA and protein expression in endometrioid endometrial cancer compared to normal endometrium. Together, these observations suggest that loss of FOXO1 perturbs endometrial homeostasis, promotes uncontrolled cell proliferation and increases susceptibility to genotoxic insults.
叉头转录因子FOXO1是磷脂酰肌醇-3-激酶/Akt信号通路的下游靶点，可调节正常子宫内膜的周期性分化和凋亡，但其在子宫内膜癌发生中的作用尚不清楚。对子宫内膜癌细胞系的筛选表明，FOXO1在HEC-1B细胞中表达，但在Ishikawa细胞中不表达，而Ishikawa细胞又高表达靶向FOXO1的E3泛素连接酶Skp2。Ishikawa细胞中的FOXO1转录水平也较低，用蛋白酶体抑制剂处理不足以恢复其表达。Ishikawa细胞中FOXO1表达的缺失并非由启动子甲基化或活性差异所致，而是与信使核糖核酸（mRNA）周转增加相关。比较分析表明，HEC-1B细胞增殖较慢，但比Ishikawa细胞对紫杉醇介导的细胞死亡更具抗性，在HEC-1B细胞中沉默FOXO1或在Ishikawa细胞中重新表达FOXO1后，这种差异部分得到逆转。我们进一步表明，生长停滞和DNA损伤诱导基因GADD45α的表达需要FOXO1。活检样本分析表明，与正常子宫内膜相比，子宫内膜样子宫内膜癌中FOXO1和GADD45α的mRNA及蛋白表达明显缺失。综上所述，这些观察结果表明，FOXO1的缺失扰乱了子宫内膜的稳态，促进了细胞的失控增殖，并增加了对基因毒性损伤的易感性。
