Epigenetic regulation of transcription by mixed lineage leukemia protein MLL1

描述（由申请人提供）：MLL1（混合谱系白血病）蛋白通过调节一组特定基因的表达，在正常和恶性造血中发挥重要作用。已经提出MLL1通过影响组蛋白H3对赖氨酸4的甲基化，以及通过与其他染色质修饰活性如组蛋白乙酰转移酶的相互作用来影响基因表达。本研究的目的是了解MLL1如何通过不同染色质重塑活动的协同作用实现致密染色质介导的转录激活的基本机制，并研究其对Polycomb组蛋白的拮抗作用的分子基础，Polycomb组蛋白是基因抑制表观遗传调控的关键成分。拟开展的研究重点是复合物中MLL1酶活性的调控，MLL1复合物靶向启动子的募集机制，以及通过下游效应物的特异性对接，将组蛋白修饰转化为转录激活的下游事件。我们将从靶基因的结构分析和基因组定位结果中获取线索，采用成熟的方法，如MLL1复合体重构和重组染色质模板体外转录分析，对导致转录激活的一系列事件进行详细的机制解剖。体外研究将与体内方法相辅相成，旨在指导和验证从无细胞系统获得的结果。这项工作将大大提高我们对MLL1在胚胎发育、造血、细胞命运决定和细胞周期控制等重要过程中的功能的认识，这些过程是通过转录调控特定基因来实现的。鉴于MLL1突变常见于人类髓系和淋巴系急性白血病，本研究对阐明白血病发生机制也具有重要意义，从而为疾病的诊断、治疗和预防奠定基础。该项目最符合国家普通医学研究所的使命，五年期预算为1 250 000美元。

DESCRIPTION (provided by applicant): MLL1 (mixed lineage leukemia) protein plays important roles in normal and malignant hematopoiesis by regulating the expression of a specific group of genes. It has been proposed that MLL1 affects gene expression through effecting histone H3 methylation on lysine 4, and through interactions with other chromatin modifying activities such histone acetyltransferases. The objectives of the proposed research are to understand the fundamental mechanisms of how MLL1 mediated transcription activation from compacted chromatin is achieved through concerted actions of different chromatin remodeling activities and to study the molecular basis for its well-described antagonism against Polycomb group proteins, which are critical components for epigenetic regulation of gene repression. The proposed research emphasizes on the regulation of MLL1 enzymatic activities in the complex, on the recruitment mechanism targeting MLL1 complex to promoters, and on downstream events that transduce the histone modifications to transcription activation, through the specific docking of downstream effectors. We will take clues from the structural analyses and the genomic mapping results of target genes, employ well-established methods such as MLL1 complex reconstitution and the recombinant chromatin-templated in vitro transcription assays for detailed mechanistic dissection of the series events leading to transcriptional activation. The in vitro studies will be complemented with in vivo approaches designed to guide and validate results obtained from cell-free system. The proposed work will significantly advance our knowledge for the functions of MLL1 in important processes such as embryonic development, hematopoiesis, cell fate determination and cell cycle control through transcriptional regulation of specific genes. Given that MLL1 mutations are commonly found in human myeloid and lymphoid acute leukemias, the proposed study also bears significance in elucidating mechanisms for leukemogenesis and thus, lays the foundation for advances in disease diagnosis, treatment, and prevention. This project matches best with the mission of national institute of general medical science (NIGMS) and is budgeted at $1,250,000 for a five-year period. PUBLIC HEALTH RELEVANCE: Genetic changes of mixed lineage leukemia protein (MLL1) account for ~10% acute leukemia in adult and for ~70% infant leukemia in the population. The most notable signature for MLL-related leukemia is the change of specific gene expression pattern. This project is to understand the fundamental mechanism for these changes and thus, the cause of the disease. It will set up the foundation for potential medical interference in the future.