Inoue K, Tamaki H, Ogawa H, Oka Y, Soma T, Tatekawa T, Oji Y, Tsuboi A, Kim E H, Kawakami M, Akiyama T, Kishimoto T, Sugiyama H
Department of Medicine III, Osaka University Medical School, Osaka, Japan.
Blood. 1998 Apr 15;91(8):2969-76.
The WT1 gene is a tumor-suppressor gene that was isolated as a gene responsible for Wilms' tumor, a childhood kidney neoplasm. We have previously reported that the WT1 gene is strongly expressed in leukemia cells with an increase in its expression levels at relapse and an inverse correlation between its expression levels and prognosis, thus making it a novel tumor marker for leukemic blast cells. Furthermore, WT1 antisense oligomers have been found to inhibit the growth of leukemic cells. These results strongly suggested the involvement of the WT1 gene in human leukemogenesis. The present study was performed to prove our hypothesis that the WT1 gene plays a key role in leukemogenesis and performs an oncogenic function in hematopoietic progenitor cells, rather than a tumor-suppressor gene function. 32D cl3, an interleukin-3-dependent myeloid progenitor cell line, differentiates into mature neutrophils in response to granulocyte colony-stimulating factor (G-CSF). However, when transfected wild-type WT1 gene was constitutively expressed in 32D cl3, the cells stopped differentiating and continued to proliferate in response to G-CSF. As for signal transduction mediated by G-CSF receptor (G-CSFR), Stat3alpha was constitutively activated in wild-type WT1-infected 32D cl3 in response to G-CSF, whereas, in WT1-uninfected 32D cl3, activation of Stat3alpha was only transient. However, most interesting was the fact that G-CSF stimulation resulted in constitutive activation of Stat3beta only in wild-type WT1-infected 32D cl3, but not in WT1-uninfected 32D cl3. Thus, WT1 expression constitutively activated both Stat3alpha and Stat3beta. A transient activation of Stat1 was detected in both wild-type WT1-infected and uninfected 32D cl3 after G-CSF stimulation, but no difference in its activation was found. No activation of MAP kinase was detected in both wild-type WT1-infected and uninfected 32D cl3 after G-CSF stimulation. These results demonstrated that WT1 expression competed with the differentiation-inducing signal mediated by G-CSFR and constitutively activated Stat3, resulting in the blocking of differentiation and subsequent proliferation. Therefore, the data presented here support our hypothesis that the WT1 gene plays an essential role in leukemogenesis and performs an oncogenic function in hematopoietic progenitor cells and represent the first demonstration of an important role of the WT1 gene in signal transduction in hematopoietic progenitor cells.
WT1基因是一种肿瘤抑制基因，最初是作为与儿童肾肿瘤——威尔姆斯瘤相关的基因被分离出来的。我们之前报道过，WT1基因在白血病细胞中强烈表达，在复发时其表达水平升高，且表达水平与预后呈负相关，因此它成为白血病原始细胞的一种新型肿瘤标志物。此外，已发现WT1反义寡聚物可抑制白血病细胞的生长。这些结果强烈提示WT1基因参与了人类白血病的发生。本研究旨在证实我们的假设，即WT1基因在白血病发生中起关键作用，并且在造血祖细胞中发挥致癌功能，而非肿瘤抑制基因功能。32D cl3是一种依赖白细胞介素-3的髓系祖细胞系，在粒细胞集落刺激因子（G-CSF）作用下可分化为成熟的中性粒细胞。然而，当转染的野生型WT1基因在32D cl3中组成性表达时，细胞停止分化，并在G-CSF作用下继续增殖。至于由G-CSF受体（G-CSFR）介导的信号转导，在野生型WT1感染的32D cl3中，G-CSF可使Stat3α组成性激活，而在未感染WT1的32D cl3中，Stat3α的激活只是短暂的。然而，最有趣的是，G-CSF刺激仅在野生型WT1感染的32D cl3中导致Stat3β组成性激活，而在未感染WT1的32D cl3中则不会。因此，WT1的表达可组成性激活Stat3α和Stat3β。在G-CSF刺激后，野生型WT1感染和未感染的32D cl3中均检测到Stat1的短暂激活，但在其激活方面未发现差异。在G-CSF刺激后，野生型WT1感染和未感染的32D cl3中均未检测到丝裂原活化蛋白激酶的激活。这些结果表明，WT1的表达与G-CSFR介导的分化诱导信号相互竞争，并组成性激活Stat3，从而导致分化受阻并随后增殖。因此，本文提供的数据支持了我们的假设，即WT1基因在白血病发生中起重要作用，并且在造血祖细胞中发挥致癌功能，这也是WT1基因在造血祖细胞信号转导中重要作用的首次证明。
