白血病罕见染色体易位与相关新融合基因的鉴定及其发病机制研究

Chromosome translocations and their fusion genes are responsible for the development of leukemia. Compared with the gene mapping-based molecular cytogenetic techniques, next-generation sequencing techniques including whole genome sequencing and RNA sequencing provide a more efficient and precise strategy for identifying the genomic structural alterations and novel fusion genes. The aims of this study are to identify novel fusion genes and genomic structural alterations from a group of leukemia patients with rare chromosome translocations, and explore the potential function and role of the newly identified fusion genes in the development of leukemia. According to this strategy, a novel fusion gene KNASL1-MTCP1 was recently identified from an acute monocytic leukemia patient with the rare t(X;17)(q28;q21) translocation using RNA-seq in our lab. Both partners of this fusion gene have been suggested to play critical roles in the pathogenesis of leukemia. KANSL1 encodes a nuclear protein that is a subunit of two protein complexes involved with histone acetylation, the MLL1 complex and the NSL1 complex. MTCP1 has been reported to be associated with mature T-cell proliferations in t(X;14) (q28;q11) translocations. We will integrate the molecular biological technique with the next-generation sequencing platform to further study the biological characteristics and function of this KANSL1-MTCP1 fusion gene, and the effects of the wide-type counterparts, e.g. KANSL1 and MTCP1. Our work will be of help to reveal the mechanism underlying the newly identified structure alterations and fusion genes, especially KANSL1-MTCP1, in the pathogenesis of leukemia.

染色体易位及其产生的融合基因在白血病发病机制中至关重要，但新融合基因的发现和结构解析并不容易。相比于传统的候选基因定位克隆策略，基于二代测序的全基因组和转录组测序为识别染色体易位累及的基因组结构异常和融合基因提供了更高效和精准的策略。本项目运用该策略在一组伴有未见文献报道的罕见染色体易位白血病病例中进行基因组结构异常和新融合基因识别，并已通过RNA-seq在一例伴有罕见的t(X;17)(q28;q21)染色体易位的AML-M5初发白血病患者中发现了新融合基因KANSL1-MTCP1。KANSL1编码蛋白是MLL1复合物和NSL1复合物的重要亚基，参与组蛋白乙酰化修饰。MTCP1在伴t(X;14)(q28;q11)的T-PLL中受累，表达异常癌蛋白产物。本课题组将综合运用分子生物学和组学分析技术深入研究KANSL1-MTCP1融合基因的生物学特性与功能，揭示其在白血病发病机制中的作用。

染色体易位及相关融合基因对白血病发生发展具有至关重要，是白血病诊断分型的重要参考依据。本课题组在一例急性单核细胞白血病（AML-M5）患者骨髓样本中发现了新罕见染色体易位t(X;17)(q28;q21)，RNA-seq结果显示该易位导致患者位于17q21的KANSL1基因5’UTR区与位于Xq28的MTCP1/CMC4基因CDS区发生融合，产生两种不同的融合基因分别为KANSL1-MTCP1与KANSL1- CMC4。结构分析及实验证实，这两种融合基因并不形成融合蛋白，但导致MTCP1和CMC4基因异常高表达。进一步功能学实验证实MTCP1高表达能促进细胞克隆性增殖并部分抑制分化，而过表达CMC4并不显示上述效应，MTCP1异常高表达引起的克隆性增值优势是其参与白血病发病机制的关键因素。通过进一步文献整理与公共组学数据库中MTCP1高表达的AML病例筛查分析，我们的研究成果发现，引起MTCP1基因高表达的机制有多种，但MTCP1基因总体而言是通过异常高表达的方式参与白血病发病机制。..此外，本项目通过对急性T淋巴细胞白血病（T-ALL）进行大样本的转录组学研究，在成人与儿童T-ALL中发现了四大类36种融合基因，鉴定出重现性的新融合基因ZBTB16-ABL1、EVL-NKX2-1、TRA-SALL2、TRD-NKX2-1。进一步对新融合基因ZBTB16-ABL1进行生物功能学研究，证实ZBTB16-ABL1融合基因能导致明显的细胞增殖优势和周期阻滞，在骨髓移植小鼠模型中建立出类似慢性粒细胞白血病的骨髓增值性疾病表型。激酶（PTK）活性实验结果显示ZBTB16-ABL1能导致ABL1激酶活性异常增高，而且这种异常增高的激酶活性能被酪氨酸激酶抑制剂Imatinib和Dasatinib所抑制，提示这类白血病进行酪氨酸激酶抑制剂靶向治疗的潜在可能。. 本课题实施以来，已发表SCI论文5篇，中文核心期刊综述1篇，均已标注课题编号。