Molecular diagnosis and theray of infantile acute leukemia carrying 11q23 translocations

染色体带11 q23是多种白血病和淋巴瘤如婴儿白血病和与表鬼臼毒素治疗相关的继发性白血病中染色体易位的常见断点。通常，携带1 lq 23易位的白血病预后不良。两组克隆了MLL，其涉及t（4 ; 11）（q21 ; q23）和t（11 ; 19）（q23 ; pl 3）。我们还克隆了在源自婴儿急性白血病的KOCL 33和KOCL 44细胞系中观察到的t（11 ; 19）（q23 ; pl 3）易位的断点，并发现MLL-LTG 19/ENL是由t（11 ; 19）易位形成的。此外，发现MLL参与t（11 ; 17）和t（11 ; 22）易位，并得出MLL负责主要11 q23易位的结论。测序研究表明，MLL与果蝇三胸基因相关，该基因编码一种含有两个DNA结合基序的蛋白质作为转录因子。MLL参与的11 q23易位中白血病发生的分子机制解释为MLL-伴侣基因的嵌合蛋白以非调控方式产生，导致MLL蛋白功能障碍，这可能是白血病发生的原因。我们合成了针对MLL-LTG 19嵌合转录物融合区的反义寡脱氧核苷酸（ODN），并用反义ODN处理具有t（11 ; 19）的KOCL 33细胞。反义ODN可抑制KOCL 33细胞的生长并诱导其凋亡，但对不含t（11 ; 19）的Daudi细胞无明显作用。RT-PCR和Western印迹分析显示，经反义ODN处理的KOCL 33细胞中MLL-LTG 19 mRNA和MLL-LTG 19蛋白水平随着时间的推移而下降。这些结果表明，MLL-LTG 19融合蛋白有助于具有t（11 ; 19）的婴儿急性白血病细胞的细胞增殖和恶性转化。

Chromosome band 11q23 is a common breakpoint of chromosome translocations in a variety of leukemias and lymphomas such as infantile leukemias and secondary leukemias associated with epipodophyllotoxin treatment. Generally, the leukemias carrying 1lq23 translocations have poor prognosis. Two groups cloned MLL which is involved in t(4 ; 11)(q21 ; q23) and t(11 ; 19)(q23 ; pl3). We also cloned the breakpoint of t(11 ; 19)(q23 ; pl3) translocations observed in KOCL33 and KOCL44 cell lines originated from infantile acute leukemias and found that the MLL-LTG19/ENL is formed by the t(11 ; 19) translocation. Further, it was found that MLL is involved in t(11 ; 17) and t(11 ; 22) translocations, and came to the conclusion that MLL is responsible for the major 11q23 translocations. A sequencing study demonstrated that MLL is related to the Drosophila trithorax gene encoding a protein containing two DNA-binding motifs as a transcriptional factor. The molecular mechanism of the leukemogenesis in 1lq23 translocations involving MLL is explained by the fact that the chimeric proteins from MLL-partner genes are produced in a nonregulated manner, resulting in the dysfunction of MLL protein, which could be the cause of leukemogenesis.To clarify the role of MLL-LTG19 protein in leukemogenesis, we synthesized the antisense oligodeoxyribonucleotide (ODN) against the fused region of MLL-LTG19 chimeric transcript and treated KOCL33 cells having t(11 ; 19) with the antisense ODN. The antisense ODN inhibited cell growth and induced apoptosis in KOCL33 cells, but not in Daudi cells, which have no t(11 ; 19). The levels of MLL-LTG19 mRNA and MLL-LTG19 protein in KOCL33 cells treated with antisense ODN were shown to decrease with time by RT-PCR and Western blot analysis. These results suggest that the MLL-LTG19 fusion protein contributes to cell proliferation and malignant transformation in infantile acute leukemia cells having t(11 ; 19).