ROLE OF EDR3 IN NORMAL DEVELOPMENT AND TUMORIGENESIS

描述（由申请人提供）：我们在人类染色体3q26的一个区域筛选中发现了早期发育调节因子3 （EDR3）作为候选肿瘤抑制基因，该区域先前显示在骨肉瘤中发生LoH。我们发现EDR3基因的基因内缺失与骨肉瘤原发肿瘤和肿瘤细胞系的肿瘤抑制病因一致。对EDR3表达模式的检测显示，mRNA和蛋白在成人和胚胎组织中都表现出几乎普遍存在的表达模式。EDR3是果蝇多同源基因的同源物，也是Polycomb Group （PcG）蛋白家族的成员。PcG家族蛋白通过促进异染色质的形成和稳定传递而作为长期抑制因子。通过共免疫沉淀，我们发现EDR3蛋白与E2F6、Bmi1、YY1和M33结合，但不与pRB1或CtBP结合。这表明EDR3是先前描述的人类Polycomb抑制复合体（hPRC-H）的一部分，该复合体包含E2F6并在G0中活跃。与这一观察结果一致，我们发现当细胞进入G0时，EDR3在细胞核中的定位从弥漫性转变为高度间断的模式。这种转变与含有edr3的复合物结合YY1和E2F dna结合位点以及c-myc启动子的能力相吻合。当我们测试EDR3与E2F6和Bmi1的共定位时，我们发现当细胞进入G0时，EDR3和E2F6向间断定位模式的转变是由EDR3和E2F6共享的，而不是Bmi1。我们发现EDR3在约70%的骨肉瘤肿瘤中受到影响。对其他肿瘤的检查显示，EDR3蛋白在其他肿瘤中缺失，这表明这可能是一个检查点，在肿瘤发生过程中通常丢失。与该模型一致，我们发现EDR3在正常细胞中过表达或在肿瘤细胞中诱导表达时可以作为生长抑制因子。我们的假设是，EDR3蛋白作为抑制复合物的一部分，调节成骨细胞和间充质干细胞发育过程中G0的长期维持。一个必然的假设是，成骨细胞祖细胞中EDR3功能的丧失可能导致维持G0的能力丧失，从而有利于肿瘤的发生。为了验证我们的假设，我们提出了以下具体目标：1)研究EDR3在骨肉瘤肿瘤发生和成骨细胞分化中的作用；2)表征含EDR3和E2F6的PcG复合物的组分；3)确定EDR3调控的目标。

DESCRIPTION (provided by applicant): We identified Early Developmental Regulator 3 (EDR3), as a candidate tumor suppressor gene in a screen of a region of human chromosome 3q26 previously shown to undergo LoH in osteosarcoma. We found intragenic deletions in the EDR3 gene consistent with a tumor suppressor etiology in osteosarcoma primary tumors and tumor cell lines. Examination of the expression pattern of EDR3 revealed that both mRNA and protein showed a near ubiquitous pattern of expression in adult and embryonic tissues. EDR3 is a homolog of the Drosophila Polyhomeotic gene and a member of the Polycomb Group (PcG) family of proteins. The PcG family of proteins acts as long-term repressors by contributing to the formation and stable transmission of heterochromatin. By co-immunoprecipitation, we found that the EDR3 protein was bound to E2F6, Bmi1, YY1 and M33 but not pRB1 or CtBP. This suggested that EDR3 was part of a previously described human Polycomb repressive complex (hPRC-H), which contains E2F6 and is active in G0. Consistent with this observation, we found that as cells entered G0, EDR3 localization in the nucleus changed from a diffuse to a highly punctuate pattern. This shift coincided with the ability of the EDR3-containing complex to bind to YY1 and E2F DNA-binding sites and to the c-myc promoter. When we tested co-localization of EDR3 with E2F6 and Bmi1, we found that the shift to a punctuate pattern of localization as the cells entered G0, was shared by EDR3 and E2F6 but not Bmi1. We found that EDR3 was affected in >70% of osteosarcoma tumors. Examination of other tumors showed that EDR3 protein was absent in other tumors suggesting that this could be a checkpoint, which is commonly lost in tumorigenesis. Consistent with this model, we found that EDR3 could act as a growth suppressor when overexpressed in normal cells, or when inducibly expressed in tumor cells. Our hypothesis is that the EDR3 protein acts as part of a repressor complex to regulate long-term maintenance of G0 in developing osteoblasts and mesenchymal stem cells. A corollary hypothesis is that loss of EDR3 function in osteoblast progenitor cells could lead to a loss of the ability to maintain G0 and thus favor tumorigenesis. To test our hypotheses, we propose the following specific aims: 1) To examine the role of EDR3 in osteosarcoma tumorigenesis and osteoblastic differentiation; 2) To characterize the components of the PcG complex containing EDR3 and E2F6; and 3) To identify the targets of EDR3 regulation.