Falini B, Bolli N, Shan J, et al. Both carboxy-terminus NES motif and mutated tryptophan(s) are crucial for aberrant nuclear export of nucleophosmin leukemic mutants in NPMc+ AML

Sapienza University of Rome, Roma, Latium, Italy
Blood (Impact Factor: 10.43). 07/2006; 107(11):4514-23. DOI: 10.1182/blood-2005-11-4745
Source: PubMed

ABSTRACT 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.

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    • "This protein has been found over-expressed in tumors of different histological origins, including gastric, ovarian, bladder and prostate carcinomas and in various hematological malignancies [6] [7] [8] [9]. Notably, NPM1/ B23 has been identified as the most frequently mutated gene in acute myeloid leukemia (AML) patients, accounting for approximately 30% of cases [10] [11] [12] [13] [14]. NPM1/B23 belongs to the nucleophosmin/nucleoplasmin family of proteins [15]. "
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    ABSTRACT: Background Nucleophosmin (NPM1, B23) is a multifunctional protein that is involved in a variety of fundamental biological processes. NPM1/B23 deregulation is implicated in the pathogenesis of several human malignancies. This protein exerts its functions through the interaction with a multiplicity of biological partners. Very recently it is has been shown that NPM1/B23 specifically recognizes DNA G-quadruplexes through its C-terminal region. Methods Through a rational dissection approach of protein here we show that the intrinsically unfolded regions of NPM1/B23 significantly contribute to the binding of c-MYC G-quadruplex motif. Interestingly, the analysis of the ability of distinct NPM1/B23 fragments to bind this quadruplex led to the identifications of distinct NPM1/B23-based peptides that individually present a high affinity for this motif. Results These results suggest that the tight binding of NPM1/B23 to the G-quadruplex is achieved through the cooperation of both folded and unfolded regions that are individually able to bind it. The dissection of NPM1/B23 also unveils that its H1 helix is intrinsically endowed with an unusual thermal stability. Conclusions These findings have implications for the unfolding mechanism of NPM1/B23, for the G-quadruplex affinity of the different NPM1/B23 isoforms and for the design of peptide-based molecules able to interact with this DNA motif.
    Biochimica et Biophysica Acta (BBA) - General Subjects 06/2014; 1840(6). DOI:10.1016/j.bbagen.2014.02.017 · 3.83 Impact Factor
    • "Removal of the critical C-terminal tryptophan residues and generation of a new C-terminal NES motif dictate the localization of the mutated NPM1 protein in the cytoplasm, instead of in the nucleolus (Falini et al. 2006 "
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    ABSTRACT: The nucleophosmin (NPM)/nucleoplasmin family of nuclear chaperones has three members: NPM1, NPM2, and NPM3. Nuclear chaperones serve to ensure proper assembly of nucleosomes and proper formation of higher order structures of chromatin. In fact, this family of proteins has such diverse functions in cellular processes such as chromatin remodeling, ribosome biogenesis, genome stability, centrosome replication, cell cycle, transcriptional regulation, apoptosis, and tumor suppression. Of the members of this family, NPM1 is the most studied and is the main focus of this review. NPM2 and NPM3 are less well characterized, and are also discussed wherever appropriate. The structure–function relationship of NPM proteins has largely been worked out. Other than the many processes in which NPM1 takes part, the major interest comes from its involvement in human cancers, particularly acute myeloid leukemia (AML). Its significance stems from the fact that AML with mutated NPM1 accounts for ∼30% of all AML cases and usually has good prognosis. Its clinical importance also comes from its involvement in virus replication, particularly in the era of outbreaks of infectious diseases.
    The Nucleolus, 01/2011: pages 213-252; , ISBN: 978-1-4614-0513-9
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    • "B. Falini et al. | 442 | haematologica | 2008; 93(3) 2006). More recently, coexistence of JAK2V617F and BCR-ABL has also been reported in chronic myeloproliferative disorders 19,20 and association of JAK2V617F with t(8;21) in AML therapy-related 21 or secondary to a myeloproliferative syndrome. "
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    ABSTRACT: Acute myeloid leukemia carrying NPM1 mutations and cytoplasmic nucleophosmin (NPMc(+) acute myeloid leukemia) represents one-third of adult AML (50-60% of all acute myeloid leukemia with normal karyotype) and shows distinct biological, pathological and clinical features. We confirm in 2562 patients with acute myeloid leukemia our previous observation that NPM1 mutations and cytoplasmic nucleophosmin are mutually exclusive of recurrent genetic abnormalities. Taken together, these findings make NPMc+ acute myeloid leukemia a good candidate for inclusion in the upcoming World Health Organization classification.
    Haematologica 04/2008; 93(3):439-42. DOI:10.3324/haematol.12153 · 5.87 Impact Factor
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