Investigation of the Role of BAP1 in Normal and Malignant Hematopoiesis

描述(由申请人提供)： 本项目旨在研究BRCA1相关蛋白-1(BAP1)在正常和恶性造血中的作用。已发现BAP1在人类骨髓增生异常综合征(MDS)中发生突变和下调，这与BAP1作为一种新的肿瘤抑制因子在造血室发挥作用是一致的。作用机制(S)和BAP1的作用背景在很大程度上仍不清楚。我们的合作者最近发现，全身条件缺失BAP1的小鼠表现出全血细胞减少，这是人类MDS的特征。我们实验室和其他人之前的工作已经证明，BAP1是一种在组蛋白H2A赖氨酸119位脱泛素化过程中起作用的酶，它与ASXL1形成三元复合体。ASXL1在人类MDS中常见突变，急性髓系白血病(AML)和ASXL1突变是患者预后不良的预测因素。我们已经证明，虽然BAP1和ASXL1在造血细胞中确实相互作用，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。ASXL1缺失会导致HOXA簇表达上调，多梳抑制复合体2(PRC2)功能下降，而BAP1缺失会增加H3K27me3的整体表达，抑制HOXA基因的表达。我的中心假设是：(1)由于干细胞和/或祖细胞缺陷，BAP1基因缺失导致异常造血；(2)BAP1调节PRC2复合体，BAP1下调的MDS患者将对EZH2抑制剂敏感；(3)由于造血干/祖细胞染色质状态调节失调，BAP1可以与包括ASXL1在内的其他致癌等位基因协同作用。我的长期目标是了解MDS疾病的发病机制和MDS向AML转化的机制，并寻找新的靶向疗法来治疗人类MDS。第一个具体目标将是在一种新的小鼠模型中表征BAP1造血特异性丢失后的干细胞和祖细胞的表型，以及在体内表征BAP1在造血学中丢失的表观遗传表型。第二个具体目标将用于通过利用ASXL1和EZH2条件基因敲除模型和体外BAP1 shRNA系统来识别机制，以及评估BAP1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BAP1突变相当普遍的其他癌症相关，如葡萄膜黑色素瘤、间皮瘤和肾癌。此外，我们将建立新的MDS模型，以便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.