Lu Zhengfei, Lieber Michael R, Tsai Albert G, Pardo Carolina E, Müschen Markus, Kladde Michael P, Hsieh Chih-Lin
USC Norris Comprehensive Cancer Ctr., Los Angeles, California, USA.
USC Norris Comprehensive Cancer Ctr., Los Angeles, California, USA
Mol Cell Biol. 2015 Apr;35(7):1209-22. doi: 10.1128/MCB.01085-14. Epub 2015 Jan 26.
Chromosomal translocations are a hallmark of hematopoietic malignancies. CG motifs within translocation fragile zones (typically 20 to 600 bp in size) are prone to chromosomal translocation in lymphomas. Here we demonstrate that the CG motifs in human translocation fragile zones are hypomethylated relative to the adjacent DNA. Using a methyltransferase footprinting assay on isolated nuclei (in vitro), we find that the chromatin at these fragile zones is accessible. We also examined in vivo accessibility using cellular expression of a prokaryotic methylase. Based on this assay, which measures accessibility over a much longer time interval than is possible with in vitro methods, these fragile zones were found to be more accessible than the adjacent DNA. Because DNA within the fragile zones can be methylated by both cellular and exogenous methyltransferases, the fragile zones are predominantly in a duplex DNA conformation. These observations permit more-refined models for why these zones are 100- to 1,000-fold more prone to undergo chromosomal translocation than the adjacent regions.
染色体易位是造血系统恶性肿瘤的一个标志。易位脆性区域（通常大小为20至600碱基对）内的CG基序在淋巴瘤中易于发生染色体易位。在这里，我们证明人类易位脆性区域中的CG基序相对于相邻DNA是低甲基化的。使用对分离细胞核的甲基转移酶足迹分析（体外），我们发现这些脆性区域的染色质是可及的。我们还使用原核甲基化酶的细胞表达来检测体内可及性。基于该分析方法，其测量可及性的时间间隔比体外方法长得多，发现这些脆性区域比相邻DNA更易及。由于脆性区域内的DNA可被细胞和外源性甲基转移酶甲基化，脆性区域主要处于双链DNA构象。这些观察结果为这些区域为何比相邻区域发生染色体易位的倾向高100至1000倍提供了更精细的模型。
