Cleavage of the MLL gene by activators of apoptosis is independent of topoisomerase II activity
Cleavage of the MLL gene by activators of apoptosis is independent of topoisomerase II activity
复制标题
DOI：
10.1038/sj.leu.2403966
复制
发表时间：
2005-12-01
期刊：
影响因子：
11.4
通讯作者：
Vaughan, ATM
中科院分区：
文献类型：
--
作者：
Betti, CJ;Villalobos, MJ;Vaughan, ATM
暴露于拓扑异构酶II抑制剂与白血病的发生有关，涉及MLL基因的易位，通常限制在8.3KBP的区域，即断点簇区(BCR)。通过体外试验，包括辐射和抗CD95抗体在内的凋亡激活剂可以触发MLL BCR内第12外显子附近的定点特异性切割，并促进MLL基因在能够存活的细胞中的易位。为了更详细地探索切割和重排的机制，将整个MLL BCR插入到pREP4外体载体中，并将其导入人淋巴母细胞样TK6细胞。含有MLL BCR或367bp或更大缺失结构的Episome在暴露于凋亡刺激后与基因组MLL相同的位置被切割。进一步分析MLL裂解区周围的序列基序表明，预测的核基质附着序列和潜在的拓扑异构酶II的强结合部位都存在于裂解部位的两侧。催化抑制剂Merbarone对拓扑异构酶II的失活不能抑制MLL的裂解，提示MLL重排的起始裂解步骤不是由拓扑异构酶II介导的。
Exposure to topoisomerase II inhibitors is linked to the generation of leukemia involving translocations of the MLL gene, normally restricted to an 8.3 kbp tract, the breakpoint cluster region (BCR). Using an in vitro assay, apoptotic activators, including radiation and anti-CD95 antibody, trigger site-specific cleavage adjacent to exon 12 within the MLL BCR and promote translocation of the MLL gene in cells that can survive. To explore the mechanism of cleavage and rearrangement in more detail, the entire MLL BCR was placed into the pREP4 episomal vector and transfected into human lymphoblastoid TK6 cells. Episomes containing either the MLL BCR, or deletion constructs of 367 bp or larger, were cleaved at the same position as genomic MLL after exposure to apoptotic stimuli. Further analysis of sequence motifs surrounding the cleaved region of MLL showed the presence of both a predicted nuclear matrix attachment sequence and a potential strong binding site for topoisomerase II, flanking the site of cleavage. Inactivation of topoisomerase II by the catalytic inhibitor merbarone did not inhibit MLL cleavage, suggesting that the initial cleavage step for MLL rearrangement is not mediated by topoisomerase II.