NQO1 in Protection Against Benzene Toxicicity

描述（由申请人提供）：由于突变体NQO1*2蛋白被泛素/蛋白酶体途径加速降解，导致NQO1*2纯合子多态性完全缺乏NQO1活性。NQO1*2多态性已被发现是苯诱导的髓系毒性的危险因素，也是儿童和成人因化疗引起的新生白血病和继发性白血病的危险因素。NQO1对苯诱导的骨髓毒性以及新生白血病和继发性白血病的保护作用机制尚不清楚，因为NQO1在抽吸的人骨髓细胞或人骨髓CD34+祖细胞（诱导再生障碍性贫血和白血病的靶细胞）中不表达。然而，我们观察到NQO1存在于人骨髓内皮细胞（HBMEC）中，这些细胞不是通过骨髓抽吸获得的。在目前的应用中，我们希望探索NQO1在HBMEC中保护苯诱导再生障碍性贫血的潜在作用，并为此目的在我们的实验室建立了HBMEC培养物。我们提出了一种机制，即暴露于苯代谢物的HBMEC产生内皮il - 8 （elL8）的数量增加，导致邻近造血细胞和髓系祖细胞凋亡，导致再生障碍性贫血。我们还将通过描述顺式作用的DNA序列和调节NQO1表达的反式作用的核蛋白-DNA相互作用，在转录水平上研究NQO1在人髓细胞中缺乏表达的机制。哺乳动物系统中主要的肿瘤抑制基因之一是p53，高比例的白血病包含p53的突变或等位基因丢失。在初步数据中，我们证明NQO1与野生型p53形成蛋白复合物。我们打算研究NQO1和p53的相互作用是否对野生型p53具有特异性，以及它是否对p53的稳定性和下游基因的p53依赖性转录激活有影响。如果NQO1稳定了p53，并且这种相互作用具有功能性后果，这将为不同来源的白血病发病率增加提供一种机制，这种白血病的发病率增加与NQO1*2多态性导致的NQO1蛋白缺乏有关。

DESCRIPTION (provided by applicant): The homozygous NQO1*2 polymorphism results in a total lack of NQO1 activity due to accelerated degradation of the mutant NQO1*2 protein by the ubiquitin/proteasomal pathway. The NQO1*2 polymorphism has been found to be a risk factor for benzene-induced myeloid toxicity but also for childhood and adult de-novo leukemias and secondary leukemias arising as a result of chemotherapy. The mechanisms underlying the protective effects of NQO1 against benzene-induced myelotoxicity and both de-novo and secondary leukemias were puzzling since NQO1 was not expressed in aspirated human bone marrow cells or human bone marrow CD34+ progenitor cells, the target cell for induction of both aplastic anemia and leukemia. However, we observed that NQO1 was present in human bone marrow endothelial cells (HBMEC), which are not harvested by bone marrow aspiration. In the present application, we wish to explore the potential role of NQO1 in HBMEC in protection against benzene induced aplastic anemia and have established HBMEC cultures in our lab for this purpose. We propose a mechanism whereby HBMEC exposed to benzene metabolites produce increasing amounts of endothelial IL8 (elL8) which results in apoptosis of neighboring hematopoietic cells and myeloid progenitor cells resulting in aplastic anemia. We will also examine the mechanism underlying the lack of expression of NQO1 in human myeloid cells at the transcriptional level by characterizing cis acting DNA sequences and trans acting nuclear protein-DNA interactions that modulate NQO1 expression. One of the major tumor suppressor genes characterized in mammalian systems is p53 and a high percentage of leukemias contain mutations or allelic losses of p53. In preliminary data, we demonstrate that NQO1 forms a protein complex with wild type p53. We propose to examine whether the interaction of NQO1 and p53 is specific for wild type p53 and whether it has consequences for p53 stability and p53-dependent transcriptional activation of downstream genes. If NQO1 stabilizes p53 and the interaction has functional consequences, this would provide a mechanism for the increased incidence of leukemia of diverse origin that has been associated with a lack of NQO1 protein due to the NQO1*2 polymorphism.