NQO1 in Protection Against Benzene Toxicicity

说明(申请人提供)：纯合的NQO1*2多态导致NQO1活性完全丧失，这是因为突变的NQO1*2蛋白通过泛素/蛋白酶体途径加速降解。已发现NQO1*2基因多态性是苯引起的髓系毒性的危险因素，也是儿童和成人新发白血病以及化疗引起的继发性白血病的危险因素。NQO1对苯诱导的骨髓毒性和初发及继发性白血病的保护作用机制令人费解，因为NQO1在抽吸的人骨髓细胞或人骨髓CD34+祖细胞中不表达，而CD34+祖细胞是诱导再生障碍性贫血和白血病的靶细胞。然而，我们观察到NQO1存在于人骨髓内皮细胞(HBMEC)中，而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HBMEC中NQO1在预防苯诱导的再生障碍性贫血中的潜在作用，并为此目的在我们的实验室建立HBMEC培养。我们提出了一种机制，即暴露于苯代谢物的HBMEC产生更多的内皮细胞白介素8(ElL8)，从而导致邻近造血细胞和髓系祖细胞的凋亡，从而导致再生障碍性贫血。我们还将通过鉴定调节NQO1表达的顺式作用DNA序列和反式作用核蛋白-DNA相互作用，在转录水平上研究NQO1在人类髓系细胞中缺乏表达的机制。哺乳动物系统中的主要抑癌基因之一是P53，很高比例的白血病含有P53突变或等位基因丢失。在初步数据中，我们证明了NQO1与野生型P53形成蛋白质复合体。我们建议检查NQO1和P53的相互作用是否是野生型P53所特有的，以及它是否对P53的稳定性和P53依赖的下游基因的转录激活有影响。如果NQO1稳定了P53，并且这种相互作用具有功能后果，这将为不同来源白血病发病率的增加提供一种机制，这种增加与NQO1*2基因多态导致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.