Brd4L启动子甲基化状态在B-ALL发生、发展和治疗中的机制探讨

This project is designed to study the role of Bromodomain-containing 4 Protein isoform long (or Brd4L) promoter hypomethylation in leukemogenesis, leukemia progress and treatment response of B-lineage acute lymphoblastic leukemia (B-ALL). Brd4 is a chromosome-regulating protein. Brd4 gene encodes two isoforms: Brd4L and isoform short (or Brd4S). Brd4L functions as a tumor suppressor gene and Brd4S serves as an oncogene during tumor progression. Brd4 is expressed in multiple types of cancers. Brd4 is involved in tumor initiation and progression by upregulation of expression and function of c-MYC and c-MYC downstream genes. We have found the clustering hypomethylation regions at Brd4L promoter in 67% of patients with B-ALL compared with methylation regions in normal subjects. Moreover, DNA and genome hypomethylation is tightly associated with tumor initiation and progression. Up to now, no study about Brd4L promoter methylation status and its role in the leukemogenesis, leukemia progress and treatment response has been reported. This project will study the interaction between Brd4L and Brd4S, the distinct regulation of c-MYC by Brd4L and Brd4S, and the influenence of Brd4L promoter hypomethylation on the interaction and the distinct regulation. This project will also study the coorrelation of Brd4L promoter hypomethylation with B-ALL treatment response and prognosis, with B-ALL cell survival and cell cycle, and with leukemogenesis, leukemia progress in mouse model.

Brd4是一个染色质调节蛋白。Brd4基因编码2个异构体：Brd4L和Brd4S；Brd4L是抑癌基因，Brd4S是癌基因。Brd4在多种肿瘤中表达，Brd4 通过上调MYC及其下游基因的表达和功能，参与肿瘤的发生和发展。前期我们发现Brd4L启动子在正常人中完全被甲基化，67% 的B系急性淋巴细胞白血病（B-ALL）病人的Brd4L启动子区域出现低甲基化的聚集区，而DNA或基因组低甲基化与肿瘤的发生和发展密切相关。目前未见有关Brd4甲基化状态改变及其在白血病发生和发展中作用的研究报道。本项目拟探讨Brd4L和Brd4S之间的相互作用以及对MYC的调节作用，研究Brd4L低甲基化对该作用的影响；研究Brd4L低甲基化与B-ALL病人治疗和预后、与B-ALL细胞存活和细胞周期改变、与B-ALL发生和发展的相关性，以明确Brd4L启动子低甲基化在B-ALL发生、发展和治疗中的作用。

应用BSP (Bisulfite sequencing PCR) 克隆测序法检测了120例初诊B细胞急性淋巴细胞白血病 (B-ALL) 病人BRD4启动子区域甲基化状态： 92例病人 (76.67%) 的甲基化率 ≥ 50% (高甲基化组)，28例病人 (23.33%) 的甲基化率 < 50% (低甲基化组)。高甲基化组病人的完全缓解率低于低甲基化组病人，其复发率高于低甲基化组病人，但差异均无统计学意义 (P> 0.05)。高甲基化组的总生存率和无病生存率均明显低于低甲基化组，其差异均有统计学意义 (P< 0.05)；提示BRD4启动子高甲基化状态是预测B-ALL病人预后不良的指标。