WT1低表达致t(8;21)急性髓性白血病预后不良的机制研究

RUNX1-RUNX1T1 (AML1-ETO) fusion gene is the common molecular characteristic of t(8;21) acute myeloid leukemia (AML), however, their prognosis were heterogeneous. We reported firstly in the world that low WT1 expression of bone marrow samples collected at diagnosis is an independent poor prognostic factor in t(8;21)AML. Its mechanism remains unknown to date. Previous studies showed that WT1 regulated the methylation status and the expression of downstream molecules through WIT (WT1-IDH1/2-TET2) pathway; WT1 inhibited tumor growth through negatively regulating Wnt signal pathway. According to these studies and our preliminary work, we put forward the following hypothesis: in t(8;21)AML, low WT1 expression inhibits WIT pathway activation and increases methylation levels of CXXC5, CXXC5 expression is decreased and Wnt signal pathway is activated. As a result, cell proliferation and self-renewal capacity are promoted, which result in poor prognosis; and hypomethylation agent may improve prognosis. We will use t(8;21)AML cell lines and primary leukemia cells to perform in vitro and mouse leukemia model studies, and conduct clinical cohort study in order to clarify the association between WT1 expression, WIT pathway and Wnt signal pathway, demonstrate its impact on the characteristics of leukemia cells and investigate the efficacy of demethylation treatment on t(8;21)AML leukemia cells with low WT1 expression. The current project will illustrate the mechanism of the poor prognostic impact of low WT1 expression in t(8;21)AML and provide preliminary evidence for the combined treatment with hypomethylation agents.

RUNX1-RUNX1T1融合基因是t(8;21)急性髓性白血病（AML）共有分子特征，但该病预后具有异质性。我们在国际上首次报道初诊WT1低表达是该病独立预后不良因素，但机制尚不清楚。有研究发现WT1通过WIT通路影响甲基化调控靶分子表达；WT1通过负调控Wnt通路抑制肿瘤生长。我们在预实验基础上提出科学假说：t(8;21)AML中，WT1低表达抑制WIT通路引起甲基化水平升高，下调CXXC5表达，活化Wnt信号通路，促进细胞增殖和自我更新造成预后不良；去甲基化药物有望改善预后。为此，我们将采用细胞株和原代白血病细胞进行体外和小鼠模型研究，并开展临床病例队列研究，以明确WT1表达和WIT通路及Wnt信号通路的关系，证实其对白血病细胞生物学特征的影响；研究去甲基化药物对WT1低表达细胞的作用。本研究将阐明WT1低表达致t(8;21)AML预后不良的分子机制并为联合去甲基化治疗提供初步依据。

急性髓系白血病（AML）是起源于骨髓造血干祖细胞的恶性克隆性肿瘤，具有高度异质性，不同亚型的预后因素及相同预后因素在不同亚型中的预后意义可能不同。AML患者初诊时普遍过表达Wilms肿瘤基因1（WT1），且患者之间表达水平差异很大，提示WT1是潜在的预后因素。本项目组前期已报道初诊WT1低表达是t(8;21) AML患者独立预后不良因素。为探讨WT1的作用机制，本课题组利用t(8;21)AML和非t(8;21) AML患者数据和细胞株进行了临床队列和实验研究。取得研究成果如下：1）初诊WT1mRNA水平在t(8;21) AML及非t(8;21) AML患者中的预后意义相反，WT1低表达是t(8;21) AML患者复发和生存的独立预后不良因素得到验证，而初诊WT1高表达是不具有RUNX1-RUNX1T1的中高危核型AML患者诱导完全缓解的独立预后不良因素；2）WT1抑制t(8;21) AML细胞株增殖，增强其对阿糖胞苷的药物敏感性，并降低小鼠皮下成瘤性；对于非t(8;21) AML细胞株WT1则表现为促增殖和鼠皮下成瘤以及降低对阿糖胞苷的敏感性。t(8;21) AML患者初诊WT1mRNA水平与CD34+细胞增殖活性负相关。WT1不影响AML细胞株的凋亡和分化；3）t(8;21) AML中，在辅因子（cofactor）RUNX1-RUNX1T1的辅助下，WT1作为转录因子靶向调控双特异性磷酸酶（DUSP）家族成员DUSP6的表达，降低ERK磷酸化水平,抑制MAPK信号通路活化，发挥抑制增殖的作用。不具有RUNX1-RUNX1T1的 AML细胞中，DUSP6不是WT1的靶基因。本研究阐明了t(8;21) AML中WT1发挥抑癌基因作用的分子机制，为具有与不具有RUNX1-RUNX1T1的AML患者之间WT1预后意义相反提供了一项理论依据。