Nucleophosmin (NPM1) is a nucleolar protein and one of the most frequently mutated genes in acute myeloid leukemia (AML). In addition to the commonly detected frameshift mutations in exon12 (NPM1c), previous studies have identified NPM1 gene rearrangements leading to the expression of NPM1-fusion proteins in pediatric AML. However, whether the NPM1-fusions are indeed oncogenic and how the NPM1-fusions cause AML have been largely unknown. In this study, we investigated the subcellular localization and leukemogenic potential of two rare NPM1-fusion proteins, NPM1::MLF1 and NPM1::CCDC28A. NPM1::MLF1 is present in both the nucleus and cytoplasm and occasionally induces AML in the mouse transplantation assay. NPM1::CCDC28A is more localized to the cytoplasm, immortalizes mouse bone marrow cells in vitro and efficiently induces AML in vivo. Mechanistically, both NPM1-fusions bind to the HOX gene cluster and, like NPM1c, cause aberrant upregulation of HOX genes in cooperation with XPO1. The XPO1 inhibitor selinexor suppressed HOX activation and colony formation driven by the NPM1-fusions. NPM1::CCDC28A cells were also sensitive to menin inhibition. Thus, our study provides experimental evidence that both NPM1::MLF1 and NPM1::CCDC28A are oncogenes with functions similar to NPM1c. Inhibition of XPO1 and menin may be a promising strategy for the NPM1-rearranged AML.

核磷蛋白 （NPM1） 是一种核仁蛋白，是急性髓性白血病 （AML） 中最常见的突变基因之一。除了外显子 12 （NPM1c） 中常见检测到的移码突变外，以前的研究还确定了导致儿科 AML 中 NPM1 融合蛋白表达的 NPM1 基因重排。然而，NPM1 融合是否确实致癌以及 NPM1 融合如何导致 AML 在很大程度上尚不清楚。在这项研究中，我们研究了两种罕见的 NPM1 融合蛋白 NPM1：：MLF1 和 NPM1：：CCDC28A 的亚细胞定位和白血病发生潜力。NPM1：：MLF1 存在于细胞核和细胞质中，偶尔在小鼠移植试验中诱导 AML。NPM1：：CCDC28A 更定位于细胞质，在体外使小鼠骨髓细胞永生化，并在体内有效诱导 AML。从机制上讲，两种 NPM1 融合都与 HOX 基因簇结合，并且与 NPM1c 一样，与 XPO1 合作导致 HOX 基因异常上调。XPO1 抑制剂塞利尼索抑制了 NPM1 融合驱动的 HOX 活化和集落形成。NPM1：：CCDC28A 细胞对 menin 抑制也敏感。因此，我们的研究提供了实验证据，证明 NPM1：：MLF1 和 NPM1：：CCDC28A 都是功能类似于 NPM1c 的癌基因。抑制 XPO1 和 menin 可能是 NPM1 重排 AML 的一种有前途的策略。