Nucleophosmin 1 (NPM1) is an oligomeric, nucleolar phosphoprotein that functions as a molecular chaperone for both proteins and nucleic acids. NPM1 is mutated in approximately one-third of patients with AML. The mutant NPM1c؉ contains a 4-base insert that results in extra C-terminal residues encoding a nuclear export signal, which causes NPM1c؉ to be localized in the cytoplasm. Here, we determined the effects of targeting NPM1 in cultured and primary AML IntroductionNucleophosmin (NPM1 or B23.1) is a ubiquitously expressed, nucleolar phosphoprotein that functions as a molecular chaperone, shuttling between the nucleolus and the cytoplasm. 1-3 NPM1 plays multiple roles in cell growth and proliferation by participating in diverse biologic processes, including ribosome biogenesis and transport, centrosome duplication, DNA repair, transcriptional regulation and histone chaperoning. 4-7 Intracellular NPM1 is predominantly oligomeric and binds to other proteins, including the tumor suppressor proteins p14ARF and p53. 1,[8][9][10] Multifunctional characteristic of NPM1 appears to be dictated not only by its sub-cellular localization and its binding partners, but is also influenced by the various post translational modifications in NPM1, including acetylation, phosphorylation, poly-ubiquitination and sumoylation. [11][12][13][14] Wild-type (WT) NPM1 contains distinct structural domains that account for its ability to act as a multifunctional protein. 1,15 NPM1 has an N-terminal conserved, hydrophobic, oligomerization domain (residues, 1-110), which is common to all isoforms of NPM1 and critical for its chaperone activity. [1][2][3] Recently, NSC348884 was identified as a small molecule inhibitor that disrupts NPM1 dimer/oligomer formation, inducing apoptosis of cancer cells. 16 Oncogenic fusion proteins created by chromosomal translocation involving NPM1 gene, or mutations in NPM1 are observed in leukemia and lymphoma. 17 Notably, NPM-ALK fusion protein is found in CD30ϩ anaplastic large-cell lymphoma, 18 while leukemia related NPM1 fusion proteins include NPM-MLF1 and NPM-RAR␣. 17,19,20 These chimeric fusion proteins contain the N-terminal NPM1 oligomerization domain and a C-terminal fragment of the other protein. 17 NPM1 gene is also mutated in one third of adult acute myeloid leukemia (AML), especially those with the normal karyotype. 21 NPM1 mutations are heterozygous and, in the majority, localized to exon 12 of the gene. 21,22 Approximately 50 different types of mutations have been found, all creating the cytoplasm-dislocated mutant (Mt) NPM1 (NPM1cϩ) protein. 21,22 The most common is the type-A mutation, accounting for 75% of cases, which consists of TCTG tetranucleotide tandem duplication at position 956-959 of the NPM1 coding sequence. [22][23][24] This mutation causes the loss of tryptophans 288 and 290 (or 290 alone) from the carboxy-terminus and the creation of an additional leucine-rich nuclear export motif in the NPM1 protein, which causes the aberrant cytoplasmic dislocation of NPM1cϩ. [22][23][24] Knock...

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It is commonly believed that paragangliomas are rare tumors arising from the neural crest-derived chromaffin cells. Although it has been speculated that paraganglioma is related to stem cell origin, there has been lack of direct evidence demonstrating the presence of (neural) stem cells in these tumor tissues. In this study, we found a subgroup of human paraganglioma from ten clinical samples displayed definitive markers of CD133 and/or nestin, the fundamental features of neural stem cell capable of self-renewal and differentiation. A panel of lineage-specific markers was also manifest in some of these tumors, consistent with the hierarchical and heterogeneous nature of these tumors. These observations strongly suggest that at least some forms of paraganglioma maintain tumor stem-like cells (TSCs) that potentially contribute to the histologic complexity of human paraganglioma. Finally, we found that the genomic DNA structure becomes highly unstable in tumor cells of paraganglioma, indicating the loss of tight control of genomic surveillance system be an important transitory event from normal multi-potent tissue stem cells to TSCs.

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