Jin Guilan, Matsushita Hiromichi, Asai Satomi, Tsukamoto Hideo, Ono Ryoichi, Nosaka Tetsuya, Yahata Takashi, Takahashi Shinichiro, Miyachi Hayato
Department of Laboratory Medicine, Tokai University School of Medicine, 143 Shimokasuya, Isehara, Kanagawa 259-1193, Japan.
Biochem Biophys Res Commun. 2009 Dec 18;390(3):1001-6. doi: 10.1016/j.bbrc.2009.10.094. Epub 2009 Oct 22.
Fms-related tyrosine kinase 3-internal tandem duplications (FLT3-ITD) are strongly associated with the refractory nature of acute myeloid leukemia (AML) by the standard combined chemotherapy. FLT3-ITD-expressing murine and human myeloid cell lines, HF6/FLT3-ITD and K562/FLT3-ITD cells, respectively, were developed in order to clarify whether FLT3-ITD is involved in the resistance to cytotoxic agents in AML. Both of these cell lines were specifically resistant to the pyrimidine analogue cytosine arabinoside (ara-C), an essential agent for AML, accompanied by the downregulation of equilibrative nucleoside transporter 1 (ENT1), a transporter responsible for the cellular uptake of ara-C. The ENT1 promoter activity and the cellular uptake of ara-C were reduced in K562/FLT3-ITD cells, and rescued by pretreating the cells with PKC412, a FLT3 inhibitor. In addition, the expression of hypoxia inducible factor 1 alpha subunit (HIF1A) transcripts was upregulated in K562/FLT3-ITD cells, and the induction of HIF-1alpha reduced the promoter activity of ENT1 gene in K562 cells. Taken together, these findings suggest that FLT3-ITD specifically induces ara-C resistance in leukemic cells by the repression of ENT1 expression, possibly through the upregulation of HIF-1alpha, while also partially accounting for the poor prognosis of AML with FLT3-ITD due to resistance to the standard chemotherapy protocols which include ara-C.
Fms相关酪氨酸激酶3内部串联重复（FLT3-ITD）与急性髓系白血病（AML）经标准联合化疗后的难治性密切相关。为了阐明FLT3-ITD是否参与AML细胞对细胞毒性药物的耐药性，分别构建了表达FLT3-ITD的小鼠和人髓系细胞系HF6/FLT3-ITD和K562/FLT3-ITD细胞。这两种细胞系对嘧啶类似物阿糖胞苷（ara-C）均具有特异性耐药性，ara-C是AML治疗的重要药物，同时伴随着平衡核苷转运体1（ENT1）的下调，ENT1是负责细胞摄取ara-C的转运体。K562/FLT3-ITD细胞中ENT1启动子活性和ara-C的细胞摄取减少，用FLT3抑制剂PKC412预处理细胞可使其恢复。此外，K562/FLT3-ITD细胞中缺氧诱导因子1α亚基（HIF1A）转录本的表达上调，HIF-1α的诱导降低了K562细胞中ENT1基因的启动子活性。综上所述，这些发现表明，FLT3-ITD可能通过上调HIF-1α抑制ENT1表达，从而特异性诱导白血病细胞对ara-C耐药，这也部分解释了伴有FLT3-ITD的AML患者因对包括ara-C在内的标准化疗方案耐药而预后不良的原因。
