Falini Brunangelo, Bolli Niccolò, Shan Jing, Martelli Maria Paola, Liso Arcangelo, Pucciarini Alessandra, Bigerna Barbara, Pasqualucci Laura, Mannucci Roberta, Rosati Roberto, Gorello Paolo, Diverio Daniela, Roti Giovanni, Tiacci Enrico, Cazzaniga Giovanni, Biondi Andrea, Schnittger Suzanne, Haferlach Torsten, Hiddemann Wolfgang, Martelli Massimo F, Gu Wei, Mecucci Cristina, Nicoletti Ildo
Institute of Hematology, University of Perugia, 06122 Perugia, Italy.
Blood. 2006 Jun 1;107(11):4514-23. doi: 10.1182/blood-2005-11-4745. Epub 2006 Feb 2.
We recently identified aberrant cytoplasmic expression of nucleophosmin (NPM) as the immunohistochemical marker of a large subgroup of acute myeloid leukemia (AML) (about one-third of adult AML) that is characterized by normal karyotype and mutations occurring at the exon-12 of the NPM gene. In this paper, we have elucidated the molecular mechanism underlying the abnormal cytoplasmic localization of NPM. All 29 AML-associated mutated NPM alleles so far identified encode abnormal proteins which have acquired at the C-terminus a nuclear export signal (NES) motif and lost both tryptophan residues 288 and 290 (or only the residue 290) which determine nucleolar localization. We show for the first time that both alterations are crucial for NPM mutant export from nucleus to cytoplasm. In fact, the cytoplasmic accumulation of NPM is blocked by leptomycin-B and ratjadones, specific exportin-1/Crm1-inhibitors, and by reinsertion of tryptophan residues 288 and 290, which respectively relocate NPM mutants in the nucleoplasm and nucleoli. NPM leukemic mutants in turn recruit the wild-type NPM from nucleoli to nucleoplasm and cytoplasm. These findings indicate that potential therapeutic strategies aimed to retarget NPM to its physiological sites will have to overcome 2 obstacles, the new NES motif and the mutated tryptophan(s) at the NPM mutant C-terminus.
我们最近发现核磷蛋白（NPM）异常的细胞质表达是急性髓系白血病（AML）一个大亚组（约占成人AML的三分之一）的免疫组化标志物，该亚组的特征是核型正常且NPM基因第12外显子发生突变。在本文中，我们阐明了NPM异常细胞质定位的分子机制。迄今为止鉴定出的所有29个与AML相关的突变NPM等位基因均编码异常蛋白，这些蛋白在C末端获得了一个核输出信号（NES）基序，并丢失了决定核仁定位的色氨酸残基288和290（或仅残基290）。我们首次表明，这两种改变对于NPM突变体从细胞核输出到细胞质至关重要。事实上，NPM的细胞质积累被雷帕霉素B和大鼠茉莉酮阻断，这两种物质是特异性的输出蛋白1/Crm1抑制剂，同时也被色氨酸残基288和290的重新插入阻断，这分别使NPM突变体重定位到核质和核仁中。NPM白血病突变体进而将野生型NPM从核仁招募到核质和细胞质中。这些发现表明，旨在将NPM重新定位到其生理位点的潜在治疗策略将不得不克服两个障碍，即新的NES基序和NPM突变体C末端的突变色氨酸。
