Investigation of the Role of BAP1 in Normal and Malignant Hematopoiesis

描述（由申请人提供）： 该项目旨在描述BRCA 1相关蛋白-1（BAP 1）在正常和恶性造血中的作用。已经发现BAP 1在人骨髓增生异常综合征（MDS）中突变和下调，这与BAP 1在造血区室中作为新型肿瘤抑制剂起作用一致。BAP 1的作用机制和作用背景在很大程度上仍然未知。我们的合作者最近表明，全身条件性丧失BAP 1的小鼠表现出全血细胞减少症，这是人类MDS的特征。我们实验室和其他人以前的工作已经证明，BAP 1是一种在组蛋白H2 A赖氨酸119去泛素化中起作用的酶，与ASXL 1形成三元复合物。ASXL 1通常在人MDS和急性髓性白血病（AML）中突变，ASXL 1突变是患者预后不良的预测因子。我们已经表明，虽然BAP 1和ASXL 1在造血细胞中相互作用，但这些蛋白质对靶基因表达和全局组蛋白调控具有独立的影响。ASXL 1的缺失导致HOXA簇表达上调和多梳抑制复合物2（PRC 2）功能降低，而BAP 1缺失增加了整体H3 K27 me 3并抑制HOXA基因表达。我的主要假设是：（1）造血特异性区室中BAP 1的遗传缺失由于干细胞和/或祖细胞缺陷而导致异常造血，（2）BAP 1调节PRC 2复合体，并且具有BAP 1下调的MDS患者将对EZH 2抑制剂敏感，以及（3）由于造血干细胞和祖细胞中染色质状态的失调，BAP 1可以与包括ASXL 1在内的其他致癌等位基因协作。我的长期目标是了解MDS疾病的发病机制和MDS转化为AML的机制，并确定新的靶向治疗方法来治疗人类MDS。第一个具体的目的将是表征干细胞和祖细胞表型后BAP 1造血特异性损失在一种新的小鼠模型，除了表征体内表观遗传表型的BAP 1损失在造血。第二个具体目标将通过利用ASXL 1和EZH 2条件性敲除模型和体外BAP 1 shRNA系统来鉴定机制，以及评估BAP 1功能丧失模型系统对表观遗传疗法的敏感性。这意味着这些发现将与BAP 1突变相当普遍的其他癌症背景相关，如葡萄膜黑色素瘤，间皮瘤和肾细胞癌。此外，我们将建立新的MDS模型，用于未来在后续研究中测试新的治疗药物。

DESCRIPTION (provided by applicant): This project aims to characterize the role of BRCA1 associated protein-1 (BAP1) in normal and malignant hematopoiesis. BAP1 has been found to be mutated and downregulated in human myelodysplastic syndromes (MDS) consistent with BAP1 functioning as a novel tumor suppressor in the hematopoietic compartment. The mechanism(s) of action and the context in which BAP1 acts remains largely unknown. Our collaborators have recently shown that mice with whole body conditional loss of BAP1 manifest pancytopenia which is a characteristic of human MDS. Previous work by our lab and others has demonstrated that BAP1, an enzyme that has a role in deubiquitination of histone H2A at lysine 119, forms a ternary complex with ASXL1. ASXL1 is commonly mutated in human MDS and acute myeloid leukemia (AML) and ASXL1 mutations are predictors of poor patient outcome. We have shown that while BAP1 and ASXL1 do interact in hematopoietic cells, these proteins have independent effects on target gene expression and global histone regulation. Whereas loss of ASXL1 results in upregulation of expression HOXA cluster and decreased Polycomb Repressive Complex 2 (PRC2) function, BAP1 depletion increases global H3K27me3 and represses HOXA gene expression. My central hypotheses are: (1) Genetic deletion of BAP1 in the hematopoietic specific compartment causes abnormal hematopoiesis due to a stem and/or progenitor cell defect, (2) BAP1 regulates the PRC2 complex and MDS patients with BAP1 downregulation will be sensitive to EZH2 inhibitors, and (3) BAP1 could collaborate with other oncogenic alleles including ASXL1 due to dysregulation of the chromatin state in hematopoietic stem and progenitor cells. My long term goals are to understand MDS disease pathogenesis and mechanisms by which MDS transforms to AML and to identify novel targeted therapeutics to treat human MDS. The first specific aim will be to characterize the stem and progenitor cell phenotype following BAP1 hematopoietic-specific loss in a novel mouse model in addition to characterizing the in vivo epigenetic phenotype of BAP1 loss in hematopoiesis. The second specific aim will serve to identify mechanisms by utilizing ASXL1 and EZH2 conditional knockout models and in vitro BAP1 shRNA systems as well as to assess the sensitivity of BAP1 loss-of-function model systems to epigenetic therapies. The implications are that these findings will be relevant in other cancer contexts where BAP1 mutations are quite prevalent, such as uveal melanoma, mesothelioma, and renal cell carcinoma. Further, we will establish novel MDS models for future testing of novel therapeutic agents in subsequent studies.