Wnt/β-Catenin信号途径在难治性急性白血病中的作用及其机制

Wnt/β-catenin signaling plays an essential role in regulation of cellular survival and proliferation. It is one of essential pathways implicated in self-renewal regulation of hematopoietic stem cells. We found that expression of β-catenin and its target gene cyclin D1 were both upregulated in drug-resistant leukemic cell line HL60/DNR and K562/Adr. We hence postulate that aberrant activation of Wnt/β-catenin signaling is responsible for reduction in chemosensitivity of leukemic cells. To verify this hypothesis and to elucidate the significance and mechanism of Wnt/β-catenin signaling abnormality in pathogenesis of refractory acute leukemia, we propose present study, which will determine the expression and nuclear localization of β-catenin in refractory acute leukemia patients, investigate the modulation of chemosensitivity of HL60/DNR cells and possible mechanisms following shRNA knockdown of β-catenin, using both in vitro and in vivo experiments, and explore the expression of β-catenin in leukemic stem cells and its correlation with prognosis of acute leukemia. Our study therefore may provide novel molecular targets in an effort to improve chemosensitivity of patients with refractory acute leukemia.

Wnt/β-catenin信号途径在细胞生存、增殖的调节方面发挥着重要作用，也是参与造血干细胞胞自我更新调控的重要通路之一。我们发现，在耐药白血病细胞系HL60/DNR及K562/Adr中，β-catenin及下游基因cyclin D1过度表达。由此我们推测，Wnt/β-catenin信号途径的过度活化参与了白血病细胞药物敏感性的下调。为论证这一观点，同时明确Wnt/β-catenin信号途径在难治性急性白血病中的作用及机制，特提出此课题，检测β-catenin在难治性急性白血病患者中的表达及活化水平；应用RNAi技术靶向下调HL60/DNR细胞β-catenin基因表达后，研究该细胞在体外及NOD/SCID小鼠体内对化疗药物敏感性的改变及其机制；同时探讨该途径在白血病干细胞中的表达水平及其与患者预后之间的关系。本课题的开展将为改善难治性急性白血病患者化疗敏感性提供分子靶点。

为了明确在难治急性白血病中β-catenin信号途径过度活化是否参与了白血病细胞药物敏感性的下调： （1）我们比较了急性白血病患者与正常供者、难治组与化疗敏感组急性白血病患者，以及难治组白血病患者化疗前后骨髓中β-catenin mRNA水平的差异，结果显示急性白血病化疗难治组和之间的β-catenin表达水平高于化疗敏感组，但无统计学差异，需进一步扩大样本，延长随访时间；同一患者初治和化疗后缓解期的白血病细胞β-catenin表达水平相当，提示化疗并不能降低白血病细胞的β-catenin表达水平。（2）在耐药白血病细胞系K562/ADR，通过靶向下调β-catenin的表达，初步结果显示白血病细胞体外增殖减少、凋亡增加，对ADR药物敏感性有所增加。目前正在NOD/SCID小鼠体内进行成瘤实验。（3）用流式细胞术方法检测CD34+CD38-白血病干细胞群体中β-catenin的表达水平，结果显示白血病干细胞β-catenin的表达水平和患者化疗敏感性呈负相关。