Both carboxy-terminus NES motif and mutated tryptophan(s) are crucial for aberrant nuclear export of nucleophosmin leukemic mutants in NPMc+ AML.
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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ABSTRACT: NPM1 mutations represent frequent genetic alterations in patients with acute myeloid leukemia (AML) associated with a favorable prognosis. Different types of NPM1 mutations have been described. The purpose of our study was to evaluate the relevance of different NPM1 mutation types with regard to clinical outcome. Our analyses were based on 349 NPM1-mutated AML patients treated in the AMLCG99 trial. Complete remission rates, overall survival and relapse-free survival were not significantly different between patients with NPM1 type A or rare type mutations. The NPM1 mutation type does not seem to play a role in risk stratification of cytogenetically normal AML.PLoS ONE 01/2014; 9(10):e109759. · 3.53 Impact Factor
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ABSTRACT: The aim of this study was to quantify the copies of circulating nucleophosmin (NPM) mutations DNA in the plasma of patients with acute myeloid leukemia (AML) and to explore the association of circulating NPM mutation levels with clinical characteristics. The presence of NPM mutations in 100 Chinese patients newly diagnosed with AML were identified by RT-PCR and sequencing analysis. Copies of circulating NPM mutation A (NPM mut.A) DNA in the plasma of mutation-positive cases were quantified by real-time quantitative PCR (qRT-PCR). Furthermore, the association of circulating NPM mutation levels and clinical characteristics was analyzed. NPM mutations were identified in 37 of the 100 patients and all cases were NPM mut.A. The circulating NPM mut.A levels ranged from 0.35×10(8) copies/ml to 6.0×10(8) copies/ml in the 37 mutation-positive cases. The medium and quartile M (P25, P75) of the circulating NPM mut.A levels in patients classified as M2, M4 and M5 morphological subtypes were 1.35×10(8) (0.76×10(8), 1.91×10(8)) copies/ml, 1.81×10(8) (1.47×10(8), 2.2×10(8)) copies/ml and 2.50×10(8) (2.42×10(8), 3.05×10(8)) copies/ml, respectively. Circulating NPM mut.A levels were significantly higher in patients with the M5 subtype of AML compared to patients with the M2 and M4 subtypes (p=0.000, p=0.046). In addition, circulating NPM mut.A copies were significantly associated with a higher white blood cell count, platelet count and bone marrow blast percentage (p<0.05). Our results suggest that circulating NPM mutations DNA assay serves as a complementary to the routine investigative protocol of NPM-mutated leukemia.International journal of medical sciences 01/2015; 12(1):17-22. · 1.55 Impact Factor
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ABSTRACT: Myelodysplastic syndromes (MDS) are rare in children and only a few studies have analyzed their molecular mechanisms. The NPM1 gene encodes for nucleophosmin (NPM) which regulates hematopoiesis. Mutations in exon 12 of the NPM1 cause the nucleophosmin cytoplasmic dislocation and disrupt its functions. We have analyzed mutations of the NPM1 gene in archival bone marrow samples from 17 children with MDS and detected, in one patient, transition C to T in codon 293. To the best of our knowledge, this is the first analysis of NPM1 mutations in childhood MDS and the very first missense mutation of the NPM1 gene reported so far.Archives of Biological Sciences 01/2011; 63(3). · 0.61 Impact Factor