Mechanisms of HOX Protein Mediated Transformation

描述（由申请人提供）：同源盒基因HOXA9的过表达是骨髓发育不良和急性淋巴细胞和髓细胞白血病中生长失调的重要机制。HOXA9在伴有MLL重排的急性白血病、骨髓增生异常疾病和高风险AMI中高水平表达。HOXA9本身是一个弱致癌基因。然而，在肿瘤中，HOXA9几乎总是与HOX辅助因子MEIS1共表达。此外，HOXA9和MEIS1在动物模型中强烈合作产生白血病。了解这种协同作用的分子基础对于开发靶向治疗至关重要。两种一般的合作机制是可能的。其中之一涉及HOXA9和MEIS1之间的直接物理相互作用。这可能导致HOXA9定位或稳定性的改变，或改变HOXA9与转录靶标结合的亲和力或特异性。另外，HOXA9和MEIS1可能调节在白血病发生中合作的不同途径。由于缺乏对HOXA9相关蛋白的了解以及对HOXA9和MEIS1下游靶点的了解，这一目标的进展受到阻碍。本研究将采用两种策略来鉴定HOXA9转化细胞中与HOXA9相关的蛋白。我们将确定白血病细胞中是否存在一个以上的HOXA9复合体，以及大量表达的HOXA9T异构体在转化中的作用。我们将确定MEIS1过表达是否会影响HOXA9复合物的定位和组成，以及减少HOXA9或MEIS1表达是否会阻碍转化。具有条件形式HOXA9和MEIS1或敲低的细胞系将用于识别HOXA9的直接和间接靶标。利用生物信息学工具，我们将识别和表征造血细胞中响应HOXA9的调控元件。总的来说，这项工作将为HOXA9介导的转化提供机制见解，并可能发现骨髓增生异常和白血病中有希望的新治疗靶点。

DESCRIPTION (provided by applicant): Overexpression of the homeobox gene HOXA9 is emerging as an important mechanism of deregulated growth in both myelodysplasia and acute lymphoid and myeloid leukemias. HOXA9 is expressed at high levels in acute leukemias with MLL rearrangements, in myelodysplastic disorders and in high risk AMI. By itself, HOXA9 is a weak oncogene. However, in tumors, HOXA9 is almost always coexpressed with MEIS1, a HOX cofactor. Furthermore, HOXA9 and MEIS1 strongly cooperate to produce leukemia in animal models. Understanding the molecular basis for this cooperativity is pivotal for developing targeted therapy. Two general mechanisms of cooperativity are possible. One involves direct physical interaction between HOXA9 and MEIS1. This could result in altered HOXA9 localization or stability or change the affinity or specificity of HOXA9 in binding to transcriptional targets. Alternatively, HOXA9 and MEIS1 may regulate distinct pathways that cooperate in leukemogenesis. Progress toward this goal has been hampered by lack of knowledge of the proteins associated with HOXA9 and lack of insight into downstream targets of HOXA9 and MEIS1. In this proposal, two strategies would be pursued for identifying proteins associated with HOXA9 in cells transformed by HOXA9. We will determine if more than one HOXA9 complex exists in leukemia cells and what the role of the abundantly expressed HOXA9T isoform is on transformation. We will determine if MEIS1 overexpression affects the localization and composition of HOXA9 complexes and if reducing HOXA9 or MEIS1 expression blocks transformation. Cell lines with conditional forms of HOXA9 and MEIS1 or knock down will be used to identify direct and indirect targets of HOXA9. Using bioinformatics tools, we will identify and characterize regulatory elements responsive to HOXA9 in hematopoietic cells. Overall, this work will provide mechanistic insights into HOXA9 mediated transformation and is likely to uncover promising new therapeutic targets in myelodysplasia and leukemia.