Grand F, Kulkarni S, Chase A, Goldman J M, Gordon M, Cross N C
Department of Haematology, Imperial College School of Medicine, Hammersmith Hospital, London, United Kingdom.
Cancer Res. 1999 Aug 15;59(16):3870-4.
During routine two-fusion fluorescence in situ hybridization analysis of patients with blast crisis of chronic myeloid leukemia (CML), we observed that yeast artificial chromosome 29GD7, which is distal to BCR at 22q11, failed to hybridize to the 9q+ derivative chromosome in 3 of 11 (27%) cases. This deleted region is close to hSNF5/INI1 (SMARCB1), a gene that encodes a widely expressed component of the SWI/SNF chromatin remodeling complex and that suffers biallelic mutations in malignant rhabdoid tumors. To determine whether hSNF5/INI1 was also deleted in patients with CML, we performed fluorescence in situ hybridization analysis with a specific cosmid probe. Deletion of hSNF5/INI1 on the 9q+ chromosome was found in 9 of 25 (36%) cases in blast crisis (lymphoid, n = 3; myeloid, n = 6). For the three of these nine patients for whom material was available prior to transformation, deletions were also seen in chronic phase, indicating that they are early events. Analysis of an additional 21 patients in chronic phase revealed heterozygous loss of hSNF5/INI1 in 5 (24%) cases. Of the 14 patients who had hSNF5/INI1 deletions, 7 showed a mosaic pattern of hybridization in which only a proportion of CML cells that harbored both the t(9;22) derivative chromosomes had a deletion, indicating that loss of hSNF5/INI1 was acquired during the course of the disease. Single-strand conformation polymorphism analysis of all nine hSNF5/INI1 exons and splice junctions failed to reveal any mutations for 31 patients in transformation, including 8 who had deletions, although two polymorphisms were identified. We conclude that deletions of hSNF5/INI1 are frequent in patients with CML. Such deletions may be associated with reduced levels of hSNF5/INI1 expression, which could contribute to leukemogenesis by altering chromatin-mediated transcriptional control. Alternatively, the deletions could target another unidentified gene at 22q11 that plays a role in the pathogenesis of CML.
在对慢性髓性白血病（CML）急变期患者进行常规双融合荧光原位杂交分析时，我们观察到，位于22q11上BCR远端的酵母人工染色体29GD7，在11例患者中有3例（27%）未能与9q+衍生染色体杂交。该缺失区域靠近hSNF5/INI1（SMARCB1），该基因编码SWI/SNF染色质重塑复合物中广泛表达的一个组分，且在恶性横纹肌肉瘤中发生双等位基因突变。为确定hSNF5/INI1在CML患者中是否也缺失，我们用一种特异性黏粒探针进行了荧光原位杂交分析。在25例急变期患者中有9例（36%）（淋巴细胞性，n = 3；髓细胞性，n = 6）被发现9q+染色体上存在hSNF5/INI1缺失。对于这9例患者中在转变前有可用材料的3例，在慢性期也观察到了缺失，表明它们是早期事件。对另外21例慢性期患者的分析显示，有5例（24%）存在hSNF5/INI1杂合性缺失。在14例有hSNF5/INI1缺失的患者中，7例显示杂交的嵌合模式，即只有一部分携带t(9;22)衍生染色体的CML细胞存在缺失，这表明hSNF5/INI1的缺失是在疾病过程中获得的。对所有9个hSNF5/INI1外显子和剪接位点进行单链构象多态性分析，未能发现31例处于转变期患者（包括8例有缺失的患者）有任何突变，不过鉴定出了两个多态性位点。我们得出结论，hSNF5/INI1缺失在CML患者中很常见。这种缺失可能与hSNF5/INI1表达水平降低有关，这可能通过改变染色质介导的转录调控而促进白血病发生。或者，这些缺失可能靶向22q11上另一个未鉴定的基因，该基因在CML发病机制中起作用。
