Investigation into the mechanism for expansion of abnormal clone in paroxysmal nocturnal hemoglobinuria

探讨GPI阴性造血干细胞良性肿瘤样增殖的机制我们分析了两例PNH患者，他们表现出完全扩增的GPI缺陷克隆，具有相似的染色体异常。高迁移率族蛋白A2（HMGA 2）定位于断点处，并且在两个患者中HMGA 2的3' UTR被截短（我们未发表的数据）。截短形式的HMGA 2在肿瘤组织中异位表达，在正常状态下不表达，并使细胞像良性肿瘤一样生长。我们认为，异位表达的截短HMGA 2或上调该靶基因与PIG-A突变一起导致GPI缺陷干细胞的扩增。事实上，HMGA 2仅在两名患者的骨髓细胞的GPI阴性群体中高度表达。然而，与正常个体相比，包括上述两名患者在内的PNH患者的外周血细胞中HMGA 2表达没有显著上调。我们将进一步分析骨髓样本中HMGA 2的表达。我们也已经制造了HMGA 2截短型的转基因小鼠，并且已经证实其在骨髓细胞中表达，因此我们计划研究其与PNH细胞克隆扩增的关系。我们已经克隆了PIG-Y，它是GPI生物合成的第一步酶复合物的重要组成部分。PIG-Y是酵母Eri 1 p的同源物，但在酵母系统中未检测到PIG-Y与Ras家族蛋白活性形式的相互作用。

Investigation into the mechanism for the benign tumor like proliferation of GPI negative hematopoietic stem cells.We have analyzed two PNH patients who showed fully expanded GPI-deficient clones with similar chromosomal abnormalities. The high-mobility group protein A2 (HMGA2) is localized at the breakpoint and 3' UTR of HMGA2 is truncated in both patients (our unpublished data). The truncated form of HMGA2 is ectopically expressed in tumor tissues, unexpressed in normal state, and making cells grow like a benign tumor. We suggest that ectopic expression of this truncated HMGA2 or up-regulation of this target gene together with a PIG-A mutation result in expansion of GPI-deficient stem cells. In fact, HMGA2 was highly expressed only in the GPI negative populations of the bone marrow cells in both patients. However, HMGA2 expression was not significantly up-regulated in the peripheral blood cells in PNH patients including two patients mentioned above compared to normal individuals. We will further analyze the HMGA2 expression in the bone marrow samples. We have also made the transgenic mice of truncated form of HMGA2 and already confirmed its expression in bone marrow cells, so we are planning to investigate its relation to clonal expansion of PNH cells.We have cloned PIG-Y, which is important for the first step enzyme complex in GPI biosynthesis. PIG-Y is the homologue of Eri1p of yeast, but we could not detect the interactions between PIG-Y and active form of Ras family proteins, which was proved in yeast system.