Virgili Anna, Nacheva Elisabeth P
Academic Haematology, University College London Cancer Institute, Royal Free Campus, Rowland Hill Street, London, NW3 2PF, UK.
Mol Cytogenet. 2010 Sep 1;3:15. doi: 10.1186/1755-8166-3-15.
Chronic myeloid leukaemia (CML) is characterized by the expression of the BCR/ABL1 fusion gene, a constitutively activated tyrosine kinase that commonly results from the formation of the Philadelphia (Ph) chromosome after a t(9;22)(q34;q11) or variant rearrangement. The duplication of the Ph chromosome is a recurring abnormality acquired during disease progression, whereas intrachromosomal amplification of BCR/ABL1 is a rare phenomenon and has been associated with imatinib therapy resistance. Archival bone marrow chromosome suspensions from 19 CML patients known to carry more than 1 copy of BCR/ABL1 and 10 CML cell lines were analyzed by fluorescent in situ hybridization with a panel of probes from 9q34.1-qter to investigate whether they carried two identical copies of the Ph chromosome or, instead, one or both Ph contained cryptic imbalances of some regions.
A duplication of the entire Ph chromosome with no further events involving the derivative 22 was found in 12 patients. In contrast, a sideline with either 1 or 2 isochromosomes of the Ph chromosome was identified in 6 patients but none of the cell lines. In one of the patients a translocation between the distal end of one arm of the isoderivative chromosome 22 and a third chromosome was revealed. 2 patients were found to carry marker structures harbouring high copy number gains of BCR/ABL1 fusion along with a variable part of 9q34 region downstream of ABL1 breakpoint, similarly to the markers present in the imatinib resistant cell line K562. We identified the following regions of amplification: 9q34.1 → q34.2 and 9q34.1 → qter, with a common minimum amplified region of 682 Kb. One of the patients had 5 BCR/ABL1 positive clones with variable level of 9q34 amplifications on a variety of structures, from an isoderivative 22 to tandem duplications.
These data confirm that the intrachromosomal genomic amplification of BCR/ABL1 that occurs in some CML patients during disease progression also involves amplification of 9q34 gene-rich sequences downstream of ABL1 breakpoint. The variety of rearrangements identified in this relatively small cohort demonstrates that the Ph chromosome is not a stable structure but prone to further rearrangements during disease progression.
慢性髓性白血病（CML）的特征是BCR/ABL1融合基因的表达，这是一种组成性激活的酪氨酸激酶，通常由t(9;22)(q34;q11)或变异重排后形成的费城（Ph）染色体导致。Ph染色体的重复是疾病进展过程中反复出现的异常情况，而BCR/ABL1的染色体内扩增是一种罕见现象，并且与伊马替尼治疗耐药相关。对19例已知携带超过1份BCR/ABL1拷贝的CML患者的存档骨髓染色体悬液和10株CML细胞系，使用一组来自9q34.1-qter的探针进行荧光原位杂交分析，以研究它们是否携带两条相同的Ph染色体拷贝，或者相反，一条或两条Ph染色体是否包含某些区域的隐匿性失衡。
在12例患者中发现整个Ph染色体重复，且未发生涉及衍生22号染色体的其他事件。相比之下，在6例患者中鉴定出含有1条或2条Ph染色体等臂染色体的旁系，但在细胞系中均未发现。在其中1例患者中，发现等衍生22号染色体一条臂的远端与第三条染色体之间发生了易位。发现2例患者携带标记结构，其含有高拷贝数的BCR/ABL1融合基因以及ABL1断点下游9q34区域的可变部分，类似于伊马替尼耐药细胞系K562中存在的标记。我们确定了以下扩增区域：9q34.1→q34.2和9q34.1→qter，共同的最小扩增区域为682 Kb。其中1例患者有5个BCR/ABL1阳性克隆，在从等衍生22号染色体到串联重复的各种结构上具有不同水平的9q34扩增。
这些数据证实，在疾病进展过程中一些CML患者发生的BCR/ABL1染色体内基因组扩增也涉及ABL1断点下游9q34富含基因序列的扩增。在这个相对较小的队列中鉴定出的各种重排表明，Ph染色体不是一个稳定的结构，在疾病进展过程中容易发生进一步的重排。
