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: Clinical targeting of multi-dimensional proteins such as the proteasome has been efficacious in recent years. Inhibitors such as bortezomib and carfilzomib have been used successfully to treat multiple myeloma despite early skepticism surrounding unsubstantiated toxic side effects. Another target of this magnitude is ready to emerge as a clinically viable option for targeting various neoplasias. This target, XPO1 (exportin-1 also known as Chromosome Region Maintenance 1 (CRM1)), is the transport protein responsible for nuclear export of many of the major tumor suppressor proteins and cell growth regulators. Up-regulation of XPO1 protein, a common occurrence in a variety of cancers, can lead to aberrant cytoplasmic localization and degradation of tumor suppressors such as p53 and FOXO. Therefore, inhibition of XPO1 using specific small molecules collectively called Selective Inhibitors of Nuclear Export (SINE) could potentially restore normal tumor suppressor function and have universal application for the treatment of cancer. This review will discuss the current pre-clinical data on SINE compounds in both hematological and solid malignancies. Cancer treatment through direct inhibition of the proteasome and the nuclear export machinery should instill optimism for further targeting of critical cellular pathways.Seminars in Cancer Biology 04/2014; · 7.44 Impact Factor
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ABSTRACT: Acute myeloid leukemia (AML) is the most common form of acute leukemia affecting adults. Although it is a complex disease driven by numerous genetic and epigenetic abnormalities, nearly 50% of patients exhibit a normal karyotype (CN-AML) with an intermediate cytogenetic risk. However, a widespread genomic analysis has recently shown the recurrence of genomic aberrations in this category (mutations of FLT3, CEBPA, NPM1, RUNX1, TET2, IDH1/2, DNMT3A, ASXL1, MLL and WT1) thus revealing its marked genomic heterogeneity. In this perspective, a global gene expression analysis of AML patients provides an independent prognostic marker to categorize each patient into clinic-pathologic subgroups based on its molecular genetic defects. Consistently such classification, taking into account the uniqueness of each AML patient, furnishes an individualized treatment approach leading a step closer to personalized medicine. Overall the genome-wide analysis of AML patients, by providing novel insights into biology of this tumor, furnishes accurate prognostic markers as well as useful tools for selecting the most appropriate treatment option. Moreover it provides novel therapeutic targets useful to enhance efficacy of the current anti-AML therapeutics. Here we describe the prognostic relevance of such new genetic data and discuss how this approach can be used to improve survival and treatment of AML patients.Leukemia research 03/2014; · 2.36 Impact Factor