MicroRNA-193a represses c-kit expression and functions as a methylation-silenced tumor suppressor in acute myeloid leukemia
MicroRNA-193a represses c-kit expression and functions as a methylation-silenced tumor suppressor in acute myeloid leukemia
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MicroRNA-193a 抑制 c-kit 表达并在急性髓系白血病中充当甲基化沉默肿瘤抑制因子
作者：
Gao, X-N;Lin, J.;Yu, L.
c-kit原癌基因的异常激活通过改变酪氨酸激酶信号通路而导致细胞异常增殖，是白血病发生的重要动力。肿瘤抑制性微小RNA（miRNAs）的表观遗传沉默是肿瘤中癌基因激活的关键致癌机制。本研究利用荧光素酶报告基因技术筛选了几种可能与人c-kit mRNA 3′-非翻译区结合的miRNAs。在这些miRNAs中，miR-193 a嵌入在CpG岛中，并在急性髓性白血病（AML）细胞系和原发性AML母细胞中受到启动子超甲基化的表观遗传抑制，但在正常骨髓细胞中不受抑制。重要的是，miR-193 a水平与9种白血病细胞系和27种原发性AML样本中测量的c-kit水平呈负相关。通过合成的miR-193 a转染或DNA低甲基化剂5-氮杂胞苷（5-aza）处理，在携带c-kit突变和/或过表达的AML细胞中恢复miR-193 a表达，导致RNA和蛋白质水平的c-kit表达显著降低，并抑制细胞生长。miR-193 a的生长抑制活性与细胞凋亡和粒细胞分化相关。此外，5-aza诱导的c-kit减少可被miR-193 a抑制剂部分阻断，导致5-aza的抗增殖和促凋亡作用逆转。这些数据揭示了甲基化抑制的miR-193 a在髓性白血病发生中的关键作用以及上调miR-193 a表达对c-kit阳性AML的治疗前景。
Aberrant activation of c-kit proto-oncogene contributes to abnormal cell proliferation by altering the tyrosine kinase signaling and constitutes a crucial impetus for leukemogenesis. Epigenetic silencing of tumor-suppressive microRNAs (miRNAs) is a key oncogenic mechanism for the activation of oncogenes in tumors. In this study, several miRNAs potentially binding to the 3′-untranslated region of human c-kit mRNA were screened by luciferase reporter assays. Among these miRNAs, miR-193a was embedded in a CpG island and epigenetically repressed by promoter hypermethylation in acute myeloid leukemia (AML) cell lines and primary AML blasts, but not in normal bone marrow cells. Importantly, miR-193a levels were inversely correlated with c-kit levels measured in 9 leukemia cell lines and 27 primary AML samples. Restoring miR-193a expression in AML cells harboring c-kit mutation and/or overexpression, either by synthetic miR-193a transfection or by DNA hypomethylating agent 5-azacytidine (5-aza) treatment, resulted in a significant reduction in c-kit expression at both RNA and protein levels and inhibition of cell growth. The growth-inhibitory activity of miR-193a was associated with apoptosis and granulocytic differentiation. Moreover, 5-aza-induced c-kit reduction could be partially blocked by miR-193a inhibitor, leading to a reversal of antiproliferative and proapoptotic effects of 5-aza. These data reveal a critical role for methylation-repressed miR-193a in myeloid leukemogenesis and the therapeutic promise of upregulating miR-193a expression for c-kit-positive AML.