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

染色体带11q23是各种白血病和淋巴瘤，如婴儿白血病和继发性白血病与表鬼臼毒素治疗相关的染色体易位的常见断裂点。一般来说，携带1lq23易位的白血病预后较差。两组克隆了涉及t(4；11)(q21；q23)和t(11；19)(q23；pl3)的MLL。我们还克隆了婴儿急性白血病KOCL33和KOCL44细胞系中观察到的t(11；19)(q23；pl3)易位断裂点，发现MLL-LTG19/enl是由t(11；19)易位形成的。进一步发现MLL参与了t(11；17)和t(11；22)易位，并得出MLL是11q23易位的主要原因的结论。一项测序研究表明，MLL与果蝇三胸基因有关，该基因编码一个含有两个DNA结合基序的蛋白质作为转录因子。为了阐明MLL-LTG19蛋白在白血病发生中的作用，我们合成了针对MLL-LTG19融合转录本融合区域的反义寡核苷酸(ODN)，并用反义ODN处理t(11；19)的KOCL33细胞。反义ODN抑制KOCL33细胞生长，诱导细胞凋亡，但对不含t(11；19)的Daudi细胞无明显影响。RT-PCR和Western印迹分析显示，反义ODN处理KOCL33细胞后，MLL-LTG19mRNA和MLL-LTG19蛋白的表达水平随时间的延长而降低。这些结果提示MLL-LTG19融合蛋白有助于t(11；19)急性白血病细胞的增殖和恶性转化。

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).