Characterization of a Novel Translocation Product in APL

描述(由申请人提供)：急性早幼粒细胞白血病(APL)的特征是骨髓前体细胞在早幼粒细胞水平成熟停滞。APL在白血病中是独一无二的，因为维甲酸诱导原始细胞分化，并诱导患者缓解。我们一直在探索APL的分子机制，长期目标是开发其他恶性肿瘤的分化治疗策略。我们是第一个克隆APL t(5；17)(q35；q21)变异体的小组。这种易位产生了核磷蛋白(NPM)的N端117个氨基酸与维甲酸受体α(RARA)的C端403个氨基酸的框内融合。NPM-RAR是一种独特的“自然实验”，可以用来确定APL的常见分子机制。我们发现，无论是在细胞模型中还是在转基因动物中，NPM-RAR的表达都可以阻止髓系分化。其他研究表明，仅含有RARA的C-末端403个氨基酸的截短的RARA不足以引起APL。事实上，我们的初步研究表明，NPM-RAR可能结合了不与RARA相互作用的蛋白质。在本提案中，我们将确定NPM对NPM-RAR蛋白功能的贡献。我们将检验这一假设，即NPM-RAR中的NPM序列对于其产生APL表型的能力是必不可少的。我们的具体目标是1)确定NPM-RAR是否作为蛋白质相互作用结构域；2)确定NPM改变RARA转录活性的机制；3)确定NPM-RAR是否抑制野生型NPM功能。这些研究将确定RARA融合伙伴在t(5；17)APL中的作用，并将有助于确定APL表型的共同途径。急性髓系白血病(AML)是一个重要的公共卫生问题。了解NPM-RAR融合蛋白表达导致APL的详细机制可能有助于更深入地理解分化治疗的成功，并产生可应用于其他白血病的新的治疗策略。此外，最近在大多数正常细胞遗传学AML患者中发现的NPM重排增加了这些突变NPM研究的意义，超出了在其中发现NPM-RAR的APL变体。

DESCRIPTION (provided by applicant): Acute Promyelocytic Leukemia (APL) is characterized by a maturational arrest of bone marrow progenitors at the level of the promyelocyte. APL is unique amongst the leukemias in that retinoic acid induces differentiation of the blasts, and induces remissions in patients. We have been exploring the molecular mechanism underlying APL, with the long-term goal of developing strategies of differentiation therapy for other malignancies. We were the first group to clone the t(5; 17)( q35;q21) variant of APL. This translocation generates an in-frame fusion of the N-terminal 117 amino acids of nucleophosmin (NPM) with the C-terminal 403 amino acids of the retinoic acid receptor alpha (RARa). NPM-RAR serves as a unique "experiment of nature" with which to identify the common molecular mechanisms underlying APL. We have found that NPM- RAR expression can block myeloid differentiation, both in cell models and in transgenic animals. Others have shown that a truncated RARa that harbors just the C-terminal 403 amino acids of RARa is insufficient to cause APL. Indeed, our preliminary studies suggest that NPM-RAR may bind proteins that do not interact with RARa. In this proposal we will determine the contribution of NPM to the function of the NPM-RAR protein. We will test the hypothesis that the NPM-sequences within NPM-RAR are essential for its ability to generate the APL phenotype. Our Specific Aims are 1) to determine whether the NPM-sequences serves as a protein-interaction domain for NPM-RAR; 2) to determine the mechanism whereby NPM alters RARa transcriptional activity; 3) to determine whether NPM-RAR inhibits wild-type NPM function. These studies will identify the role of the RARa fusion partner in t(5; 17) APL, and will help identify common pathways that underlie the APL phenotype. Acute Myeloid Leukemia (AML) is a significant public health issue. Understanding the detailed mechanism whereby expression of the NPM-RAR fusion protein leads to APL may lead to deeper understanding of the success of differentiation therapy, and generate novel therapeutic strategies that can be applied to other leukemias. In addition, the recent finding of NPM-rearrangements in the majority of normal-cytogenetic AML patients increases the significance of these studies of mutated NPM beyond the variant APL in which NPM- RAR is found.