Identification of a novel and myeloid specific role of the leukemia-associated fusion protein DEK-NUP214 leading to increased protein synthesis

An evolutionary dynamics analysis of the plant DEK gene family reveals the role of BnaA02g08940D in drought tolerance

DEK is a chromatin protein that interacts with DNA to influence chromatin formation, thereby affecting plant growth, development, and stress response. This study investigates the molecular evolution of the DEK family in plants, with a particular focus on the Brassica species. A total of 127 DEK genes were identified in 34 plants and classified into seven groups based on the phylogenetic analysis. The distribution of motifs and gene structure is similar within each group, indicating a high degree of conservation. The results of the collinearity analysis indicated that the DEK protein has undergone a certain degree of evolutionary conservation. The expansion of the DEK family is primarily attributable to whole-genome duplication (WGD) or segmental duplication events. The DEK protein has undergone purification during its evolutionary history, and several positively selected sites have been identified. Moreover, the examination of cis-acting elements and expression patterns revealed that the BnDEKs play a significant role in plant growth and stress response. The protein-protein interaction network identified several noteworthy proteins that interact with DEK. These analyses enhance our comprehension of the DEK gene family and establish the foundation for additional validation of its function. Further research demonstrated that the overexpression of one DEK family member, BnaA02g08940D, enhanced the transgenic Arabidopsis tolerance to drought and osmosis. This indicates that the DEK family may respond when plants are subjected to drought stress, thereby strengthening the plant's resilience.

XPO1-dependency of DEK::NUP214 leukemia

The nuclear export protein XPO1 interacts with nucleoporin 214 (NUP214) and has been implicated in the pathogenesis of SET::NUP214 acute myeloid leukemia (AML). We evaluated DEK::NUP214 (DN), characterizing a distinct AML entity, for its dependency on XPO1 in human AML models. Deletion of XPO1 in DN-positive FKH-1 cells revealed a strong dependency on XPO1. Pharmacologic inhibition of XPO1 by the second-generation selective inhibitor of nuclear export, eltanexor, in primary human and FKH-1 cells reduced XPO1 expression, disrupted co-localization of XPO1 and DN, and induced apoptosis and cell cycle arrest. Functionally, XPO1 and DN co-localized at chromatin, and this co-localization was strongly reduced by XPO1 inhibition. Loss of chromatin binding resulted in downregulation of DN target genes and pathways related to cell cycle and self-renewal. Eltanexor treatment of a patient-derived DN-AML xenograft model disrupted leukemia development, showing molecular clearance in bone marrow after a median of 377 days in eltanexor-treated mice, while control mice succumbed after a median of 244 days. In summary, XPO1 stabilizes DN at chromatin to allow the activation of its oncogenic gene signature, while targeting XPO1 treats leukemia successfully in vivo. These findings establish XPO1 as a molecular target in DEK::NUP214 AML.

Advances in the understanding of nuclear pore complexes in human diseases

BACKGROUND

Nuclear pore complexes (NPCs) are sophisticated and dynamic protein structures that straddle the nuclear envelope and act as gatekeepers for transporting molecules between the nucleus and the cytoplasm. NPCs comprise up to 30 different proteins known as nucleoporins (NUPs). However, a growing body of research has suggested that NPCs play important roles in gene regulation, viral infections, cancer, mitosis, genetic diseases, kidney diseases, immune system diseases, and degenerative neurological and muscular pathologies.

PURPOSE

In this review, we introduce the structure and function of NPCs. Then We described the physiological and pathological effects of each component of NPCs which provide a direction for future clinical applications.

METHODS

The literatures from PubMed have been reviewed for this article.

CONCLUSION

This review summarizes current studies on the implications of NPCs in human physiology and pathology, highlighting the mechanistic underpinnings of NPC-associated diseases.

NUP214 fusion genes in acute leukemias: genetic characterization of rare cases

Introduction

Alterations of the NUP214 gene (9q34) are recurrent in acute leukemias. Rearrangements of chromosomal band 9q34 targeting this locus can be karyotypically distinct, for example t(6;9)(p22;q34)/DEK::NUP214, or cryptic, in which case no visible change of 9q34 is seen by chromosome banding.

Methods

We examined 9 cases of acute leukemia with NUP214 rearrangement by array Comparative Genomic Hybridization (aCGH), reverse-transcription polymerase chain reaction (RT-PCR), and cycle sequencing/Sanger sequencing to detect which fusion genes had been generated.

Results

The chimeras DEK::NUP214, SET::NUP214, and NUP214::ABL1 were found, only the first of which can be readily detected by karyotyping.

Discussion

The identification of a specific NUP214 rearrangement is fundamental in the management of these patients, i.e., AMLs with DEK::NUP214 are classified as an adverse risk group and might be considered for allogenic transplant. Genome- and/or transcriptome-based next generation sequencing (NGS) techniques can be used to screen for these fusions, but we hereby present an alternative, step-wise procedure to detect these rearrangements.

Regulation of HOX gene expression in AML

As key developmental regulators, HOX cluster genes have varied and context-specific roles in normal and malignant hematopoiesis. A complex interaction of transcription factors, epigenetic regulators, long non-coding RNAs and chromatin structural changes orchestrate HOX expression in leukemia cells. In this review we summarize molecular mechanisms underlying HOX regulation in clinical subsets of AML, with a focus on NPM1 mutated (NPM1mut) AML comprising a third of all AML patients. While the leukemia initiating function of the NPM1 mutation is clearly dependent on HOX activity, the favorable treatment responses in these patients with upregulation of HOX cluster genes is a poorly understood paradoxical observation. Recent data confirm FOXM1 as a suppressor of HOX activity and a well-known binding partner of NPM suggesting that FOXM1 inactivation may mediate the effect of cytoplasmic NPM on HOX upregulation. Conversely the residual nuclear fraction of mutant NPM has also been recently shown to have chromatin modifying effects permissive to HOX expression. Recent identification of the menin-MLL interaction as a critical vulnerability of HOX-dependent AML has fueled the development of menin inhibitors that are clinically active in NPM1 and MLL rearranged AML despite inconsistent suppression of the HOX locus. Insights into context-specific regulation of HOX in AML may provide a solid foundation for targeting this common vulnerability across several major AML subtypes.

Rare Hematologic Malignancies and Pre-Leukemic Entities in Children and Adolescents Young Adults

There are a variety of rare hematologic malignancies and germline predispositions syndromes that occur in children and adolescent young adults (AYAs). These entities are important to recognize, as an accurate diagnosis is essential for risk assessment, prognostication, and treatment. This descriptive review summarizes rare hematologic malignancies, myelodysplastic neoplasms, and germline predispositions syndromes that occur in children and AYAs. We discuss the unique biology, characteristic genomic aberrations, rare presentations, diagnostic challenges, novel treatments, and outcomes associated with these rare entities.

Application of Super-resolution SPEED Microscopy in the Study of Cellular Dynamics

Super-resolution imaging techniques have broken the diffraction-limited resolution of light microscopy. However, acquiring three-dimensional (3D) super-resolution information about structures and dynamic processes in live cells at high speed remains challenging. Recently, the development of high-speed single-point edge-excitation subdiffraction (SPEED) microscopy, along with its 2D-to-3D transformation algorithm, provides a practical and effective approach to achieving 3D subdiffraction-limit information in subcellular structures and organelles with rotational symmetry. One of the major benefits of SPEED microscopy is that it does not rely on complex optical components and can be implemented on a standard, inverted epifluorescence microscope, simplifying the process of sample preparation and the expertise requirement. SPEED microscopy is specifically designed to obtain 2D spatial locations of individual immobile or moving fluorescent molecules inside submicrometer biological channels or cavities at high spatiotemporal resolution. The collected data are then subjected to postlocalization 2D-to-3D transformation to obtain 3D super-resolution structural and dynamic information. In recent years, SPEED microscopy has provided significant insights into nucleocytoplasmic transport across the nuclear pore complex (NPC) and cytoplasm-cilium trafficking through the ciliary transition zone. This Review focuses on the applications of SPEED microscopy in studying the structure and function of nuclear pores.

The impact of the chromatin binding DEK protein in hematopoiesis and acute myeloid leukemia

Hematopoiesis is an exquisitely regulated process of cellular differentiation to create diverse cell types of the blood. Genetic mutations, or aberrant regulation of gene transcription, can interrupt normal hematopoiesis. This can have dire pathological consequences, including acute myeloid leukemia (AML), in which generation of the myeloid lineage of differentiated cells is interrupted. In this literature review, we discuss how the chromatin remodeling DEK protein can control hematopoietic stem cell quiescence, hematopoietic progenitor cell proliferation, and myelopoiesis. We further discuss the oncogenic consequences of the t(6;9) chromosomal translocation, which creates the DEK-NUP214 (aka: DEK-CAN) fusion gene, during the pathogenesis of AML. Combined, the literature indicates that DEK is crucial for maintaining homeostasis of hematopoietic stem and progenitor cells, including myeloid progenitors.

Myelodysplastic syndrome with t(6;9)(p22;q34.1)/DEK-NUP214 better classified as acute myeloid leukemia? A multicenter study of 107 cases

t(6;9)(p22;q34.1)/DEK-NUP214 is a recurrent genetic abnormality that occurs in 1-2% of patients with acute myeloid leukemia (AML), and rarely in myelodysplastic syndrome (MDS). It has been suggested by others that all myeloid neoplasms with t(6;9)/DEK-NUP214 may be considered as AML, even when blast count is <20%. In this study, we compared the clinicopathologic features of 107 patients with myeloid neoplasms harboring t(6;9)/DEK-NUP214: 33 MDS and 74 AML. Compared with patients with AML, patients with MDS were older (p = 0.10), had a lower white blood cell count (p = 0.0017), a lower blast count in the peripheral blood (p < 0.0001) and bone marrow (p < 0.0001), a higher platelet count (p = 0.022), and a lower frequency of FLT3-ITD mutation (p = 0.01). In addition, basophilia was not a common feature in the patients of this cohort. Although there was no difference in overall survival between MDS and AML patients (p = 0.18) in the entire cohort, the survival curves did show a trend toward favorable survival in MDS patients. Multivariate analyses showed that initial diagnosis of MDS vs. AML and allogeneic hematopoietic stem cell transplantation were prognostic factors for survival of patients with t(6;9)/DEK-NUP214 (p = 0.008 and p < 0.0001, respectively). Our data suggest that MDS with t(6;9)/DEK-NUP214 is prognostically not equivalent to AML with t(6;9)/DEK-NUP214. These data also show that stem cell transplantation greatly improves the survival of MDS and AML patients with myeloid neoplasms associated with t(6;9)/DEK-NUP214.

Allogeneic hematopoietic cell transplantation improves outcome of adults with t(6;9) acute myeloid leukemia: results from an international collaborative study

Acute myeloid leukemia (AML) with t(6;9)(p22;q34) is a distinct entity accounting for 1-2% of AML cases. A substantial proportion of these patients have a concomitant FLT3-ITD. While outcomes are dismal with intensive chemotherapy, limited evidence suggests allogeneic hematopoietic cell transplantation (allo-HCT) may improve survival if performed early during first complete remission. We report on a cohort of 178 patients with t(6;9)(p22;q34) within an international, multicenter collaboration. Median age was 46 years (range: 16-76), AML was de novo in 88%, FLT3-ITD was present in 62%, and additional cytogenetic abnormalities in 21%. Complete remission was achieved in 81% (n=144), including 14 patients who received high-dose cytarabine after initial induction failure. With a median follow up of 5.43 years, estimated overall survival at five years was 38% (95%CI: 31-47%). Allo-HCT was performed in 117 (66%) patients, including 89 in first complete remission. Allo-HCT in first complete remission was associated with higher 5-year relapse-free and overall survival as compared to consolidation chemotherapy: 45% (95%CI: 35-59%) and 53% (95%CI: 42-66%) versus 7% (95%CI: 3-19%) and 23% (95%CI: 13-38%), respectively. For patients undergoing allo-HCT, there was no difference in overall survival rates at five years according to whether it was performed in first [53% (95%CI: 42-66%)], or second [58% (95%CI: 31-100%); n=10] complete remission or with active disease/relapse [54% (95%CI: 34-84%); n=18] (P=0.67). Neither FLT3-ITD nor additional chromosomal abnormalities impacted survival. In conclusion, outcomes of t(6;9)(p22;q34) AML are poor with chemotherapy, and can be substantially improved with allo-HCT.

NUP214 in Leukemia: It's More than Transport

NUP214 is a component of the nuclear pore complex (NPC) with a key role in protein and mRNA nuclear export. Chromosomal translocations involving the NUP214 locus are recurrent in acute leukemia and frequently fuse the C-terminal region of NUP214 with SET and DEK, two chromatin remodeling proteins with roles in transcription regulation. SET-NUP214 and DEK-NUP214 fusion proteins disrupt protein nuclear export by inhibition of the nuclear export receptor CRM1, which results in the aberrant accumulation of CRM1 protein cargoes in the nucleus. SET-NUP214 is primarily associated with acute lymphoblastic leukemia (ALL), whereas DEK-NUP214 exclusively results in acute myeloid leukemia (AML), indicating different leukemogenic driver mechanisms. Secondary mutations in leukemic blasts may contribute to the different leukemia outcomes. Additional layers of complexity arise from the respective functions of SET and DEK in transcription regulation and chromatin remodeling, which may drive malignant hematopoietic transformation more towards ALL or AML. Another, less frequent fusion protein involving the C terminus of NUP214 results in the sequestosome-1 (SQSTM1)-NUP214 chimera, which was detected in ALL. SQSTM1 is a ubiquitin-binding protein required for proper autophagy induction, linking the NUP214 fusion protein to yet another cellular mechanism. The scope of this review is to summarize the general features of NUP214-related leukemia and discuss how distinct chromosomal translocation partners can influence the cellular effects of NUP214 fusion proteins in leukemia.

Clinical implications of molecular markers in acute myeloid leukemia

The recently updated World Health Organization (WHO) Classification of myeloid neoplasms and leukemia reflects the fact that research in the underlying pathogenic mechanisms of acute myeloid leukemia (AML) has led to remarkable advances in our understanding of the disease. Gene mutations now allow us to explore the enormous diversity among cytogenetically defined subsets of AML, particularly the large subset of cytogenetically normal AML. Despite the progress in unraveling the tumor genome, only a small number of recurrent mutations have been incorporated into risk-stratification schemes and have been proven to be clinically relevant, targetable lesions. We here discuss the utility of molecular markers in AML in prognostication and treatment decision making, specifically highlighting the aberrations included in the current WHO classification.

Molecular Malfeasance Mediating Myeloid Malignancies: The Genetics of Acute Myeloid Leukemia

A remarkable number of different, but recurrent, structural cytogenetic abnormalities have been observed in AML, and the 2016 WHO AML classification system incorporates numerous distinct entities associated with translocations or inversions, as well as others associated with single gene mutations into a category entitled "AML with recurrent genetic abnormalities." The AML classification is heavily reliant on cytogenetic and molecular information based on conventional genetic techniques (including karyotype, fluorescence in situ hybridization, reverse transcriptase polymerase chain reaction, single gene sequencing), but large-scale next generation sequencing is now identifying novel mutations. With targeted next generation sequencing panels now clinically available at many centers, detection of mutations, as well as alterations in epigenetic modifiers, is becoming part of the routine diagnostic evaluation of AML and will likely impact future classification schemes.

DEK-NUP214-Fusion Identified by RNA-Sequencing of an Acute Myeloid Leukemia with t(9;12)(q34;q15)

BACKGROUND/AIM

Given the diagnostic, prognostic, biologic, and even therapeutic impact of leukemia-associated translocations and fusion genes, it is important to detect cryptic genomic rearrangements that may exist in hematological malignancies.

CASE REPORT

RNA-sequencing was performed on an acute myeloid leukemia case with the bone marrow karyotype 45,X,-Y,t(9;12) (q34;q15)[16].

RESULTS

The DEK-NUP214 and PRRC2B-DEK fusion genes were found. Reverse transcriptase polymerase chain reaction together with direct sequencing verified the presence of both. Fluorescence in situ hybridization showed that the DEK-NUP214 fusion gene was located on the 6p22 band of a seemingly normal chromosome 6.

CONCLUSION

RNA-sequencing proved to be a valuable tool for the detection of a fusion of genes DEK and NUP214 in a leukemia that showed cryptic cytogenetic rearrangement of chromosome band 9q34.

ASXL2 mutations are frequently found in pediatric AML patients with t(8;21)/ RUNX1-RUNX1T1 and associated with a better prognosis

ASXL2 is an epigenetic regulator involved in polycomb repressive complex regulation or recruitment. Clinical features of pediatric acute myeloid leukemia (AML) patients with ASXL2 mutations remain unclear. Thus, we investigated frequencies of ASXL1 and ASXL2 mutations, clinical features of patients with these mutations, correlations of these mutations with other genetic alterations including BCOR/BCORL1 and cohesin complex component genes, and prognostic impact of these mutations in 369 pediatric patients with de novo AML (0-17 years). We identified 9 (2.4%) ASXL1 and 17 (4.6%) ASXL2 mutations in 25 patients. These mutations were more common in patients with t(8;21)(q22;q22)/RUNX1-RUNX1T1 (ASXL1, 6/9, 67%, P = 0.02; ASXL2, 10/17, 59%, P = 0.01). Among these 25 patients, 4 (27%) of 15 patients with t(8;21) and 6 (60%) of 10 patients without t(8;21) relapsed. However, most patients with relapse were rescued using stem cell transplantation irrespective of t(8;21). The overall survival (OS) and event-free survival (EFS) rates showed no differences among pediatric AML patients with t(8;21) and ASXL1 or ASXL2 mutations and ASXL wild-type (5-year OS, 75% vs. 100% vs. 91% and 5-year EFS, 67% vs. 80% vs. 67%). In 106 patients with t(8;21) AML, the coexistence of mutations in tyrosine kinase pathways and chromatin modifiers and/or cohesin complex component genes had no effect on prognosis. These results suggest that ASXL1 and ASXL2 mutations play key roles as cooperating mutations that induce leukemogenesis, particularly in pediatric AML patients with t(8;21), and these mutations might be associated with a better prognosis than that reported previously.

Leukemia-Associated Nup214 Fusion Proteins Disturb the XPO1-Mediated Nuclear-Cytoplasmic Transport Pathway and Thereby the NF-κB Signaling Pathway

Nuclear-cytoplasmic transport through nuclear pore complexes is mediated by nuclear transport receptors. Previous reports have suggested that aberrant nuclear-cytoplasmic transport due to mutations or overexpression of nuclear pore complexes and nuclear transport receptors is closely linked to diseases. Nup214, a component of nuclear pore complexes, has been found as chimeric fusion proteins in leukemia. Among various Nup214 fusion proteins, SET-Nup214 and DEK-Nup214 have been shown to be engaged in tumorigenesis, but their oncogenic mechanisms remain unclear. In this study, we examined the functions of the Nup214 fusion proteins by focusing on their effects on nuclear-cytoplasmic transport. We found that SET-Nup214 and DEK-Nup214 interact with exportin-1 (XPO1)/CRM1 and nuclear RNA export factor 1 (NXF1)/TAP, which mediate leucine-rich nuclear export signal (NES)-dependent protein export and mRNA export, respectively. SET-Nup214 and DEK-Nup214 decreased the XPO1-mediated nuclear export of NES proteins such as cyclin B and proteins involved in the NF-κB signaling pathway by tethering XPO1 onto nuclear dots where Nup214 fusion proteins are localized. We also demonstrated that SET-Nup214 and DEK-Nup214 expression inhibited NF-κB-mediated transcription by abnormal tethering of the complex containing p65 and its inhibitor, IκB, in the nucleus. These results suggest that SET-Nup214 and DEK-Nup214 perturb the regulation of gene expression through alteration of the nuclear-cytoplasmic transport system.

Nucleoporin genes in human diseases

Nuclear pore complexes (NPCs) are large channels spanning the nuclear envelope that mediate nucleocytoplasmic transport. They are composed of multiple copies of ~30 proteins termed nucleoporins (NUPs). Alterations in NUP genes are linked to several human neoplastic and non-neoplastic diseases. This review focuses on NUPs, their genes, localization, function in the NPC and involvement in human diseases.

Nuclear Pore Complexes and Nucleocytoplasmic Transport: From Structure to Function to Disease

Nucleocytoplasmic transport is an essential cellular activity and occurs via nuclear pore complexes (NPCs) that reside in the double membrane of the nuclear envelope. Significant progress has been made during the past few years in unravelling the ultrastructural organization of NPCs and their constituents, the nucleoporins, by cryo-electron tomography and X-ray crystallography. Mass spectrometry and genomic approaches have provided deeper insight into the specific regulation and fine tuning of individual nuclear transport pathways. Recent research has also focused on the roles nucleoporins play in health and disease, some of which go beyond nucleocytoplasmic transport. Here we review emerging results aimed at understanding NPC architecture and nucleocytoplasmic transport at the atomic level, elucidating the specific function individual nucleoporins play in nuclear trafficking, and finally lighting up the contribution of nucleoporins and nuclear transport receptors in human diseases, such as cancer and certain genetic disorders.

The DEK oncoprotein and its emerging roles in gene regulation

The DEK oncogene is highly expressed in cells from most human tissues and overexpressed in a large and growing number of cancers. It also fuses with the NUP214 gene to form the DEK-NUP214 fusion gene in a subset of acute myeloid leukemia. Originally characterized as a member of this translocation, DEK has since been implicated in epigenetic and transcriptional regulation, but its role in these processes is still elusive and intriguingly complex. Similarly multifaceted is its contribution to cellular transformation, affecting multiple cellular processes such as self-renewal, proliferation, differentiation, senescence and apoptosis. Recently, the roles of the DEK and DEK-NUP214 proteins have been elucidated by global analysis of DNA binding and gene expression, as well as multiple functional studies. This review outlines recent advances in the understanding of the basic functions of the DEK protein and its role in leukemogenesis.

DEK oncogene expression during normal hematopoiesis and in Acute Myeloid Leukemia (AML)

DEK is important in regulating cellular processes including proliferation, differentiation and maintenance of stem cell phenotype. The translocation t(6;9) in Acute Myeloid Leukemia (AML), which fuses DEK with NUP214, confers a poor prognosis and a higher risk of relapse. The over-expression of DEK in AML has been reported, but different studies have shown diminished levels in pediatric and promyelocytic leukemias. This study has characterized DEK expression, in silico, using a large multi-center cohort of leukemic and normal control cases. Overall, DEK was under-expressed in AML compared to normal bone marrow (NBM). Studying specific subtypes of AML confirmed either no significant change or a significant reduction in DEK expression compared to NBM. Importantly, the similarity of DEK expression between AML and NBM was confirmed using immunohistochemistry analysis of tissue mircorarrays. In addition, stratification of AML patients based on median DEK expression levels indicated that DEK showed no effect on the overall survival of patients. DEK expression during normal hematopoiesis did reveal a relationship with specific cell types implicating a distinct function during myeloid differentiation. Whilst DEK may play a potential role in hematopoiesis, it remains to be established whether it is important for leukemagenesis, except when involved in the t(6;9) translocation.

Nucleoporin Gene Fusions and Hematopoietic Malignancies

Nuclear pore complexes (NPCs) are the sole gateways between the nucleus and the cytoplasm of eukaryotic cells and they mediate all macromolecular trafficking between these cellular compartments. Nucleocytoplasmic transport is highly selective and precisely regulated and as such an important aspect of normal cellular function. Defects in this process or in its machinery have been linked to various human diseases, including cancer. Nucleoporins, which are about 30 proteins that built up NPCs, are critical players in nucleocytoplasmic transport and have also been shown to be key players in numerous other cellular processes, such as cell cycle control and gene expression regulation. This review will focus on the three nucleoporins Nup98, Nup214, and Nup358. Common to them is their significance in nucleocytoplasmic transport, their multiple other functions, and being targets for chromosomal translocations that lead to haematopoietic malignancies, in particular acute myeloid leukaemia. The underlying molecular mechanisms of nucleoporin-associated leukaemias are only poorly understood but share some characteristics and are distinguished by their poor prognosis and therapy outcome.

t(6;9)(p22;q34)/DEK-NUP214-rearranged pediatric myeloid leukemia: an international study of 62 patients

Acute myeloid leukemia with t(6;9)(p22;q34) is listed as a distinct entity in the 2008 World Health Organization classification, but little is known about the clinical implications of t(6;9)-positive myeloid leukemia in children. This international multicenter study presents the clinical and genetic characteristics of 62 pediatric patients with t(6;9)/DEK-NUP214-rearranged myeloid leukemia; 54 diagnosed as having acute myeloid leukemia, representing <1% of all childhood acute myeloid leukemia, and eight as having myelodysplastic syndrome. The t(6;9)/DEK-NUP214 was associated with relatively late onset (median age 10.4 years), male predominance (sex ratio 1.7), French-American-British M2 classification (54%), myelodysplasia (100%), and FLT3-ITD (42%). Outcome was substantially better than previously reported with a 5-year event-free survival of 32%, 5-year overall survival of 53%, and a 5-year cumulative incidence of relapse of 57%. Hematopoietic stem cell transplantation in first complete remission improved the 5-year event-free survival compared with chemotherapy alone (68% versus 18%; P<0.01) but not the overall survival (68% versus 54%; P=0.48). The presence of FLT3-ITD had a non-significant negative effect on 5-year overall survival compared with non-mutated cases (22% versus 62%; P=0.13). Gene expression profiling showed a unique signature characterized by significantly higher expression of EYA3, SESN1, PRDM2/RIZ, and HIST2H4 genes. In conclusion, t(6;9)/DEK-NUP214 represents a unique subtype of acute myeloid leukemia with a high risk of relapse, high frequency of FLT3-ITD, and a specific gene expression signature.

The Challenge of t (6;9) and FLT3-Positive Acute Myelogenous Leukemia in a Young Adult

Translocation t(6;9) is a rare cytogenetic abnormality found in fewer than 5% of pediatric and adult cases of acute myelogenous leukemia (AML). The outcomes of t(6;9) AML are generally poor, with low five-year overall survival and increased risk for relapse. Furthermore, FLT3-ITD is one of the most common molecular abnormalities found in AML that is associated with increased risk of treatment failure and mortality. Allogeneic hematopoietic cell transplantation (HCT) with the best available donor is a standard treatment option for these cases once remission is achieved. We report a challenging case of t(6;9) and FLT3-positive AML in a young adult male. After failing multiple standard induction regimens, morphologic remission was eventually achieved with a FLT3 inhibitor (sorafenib) and a hypomethylating agent (azacytidine). However, despite allogeneic HCT and re-initiation of sorafenib in the post-HCT setting, he experienced early relapse with the original [FLT3-ITD and t(6;9)] and new (FLT3-D835 and +8) molecular and cytogenetic markers, respectively. This case highlights the need for improved strategies in the post-HCT setting for high-risk AML.

Forced expression of the DEK-NUP214 fusion protein promotes proliferation dependent on upregulation of mTOR

BACKGROUND

The t(6;9)(p23;q34) chromosomal translocation is found in 1% of acute myeloid leukemia and encodes the fusion protein DEK-NUP214 (formerly DEK-CAN) with largely uncharacterized functions.

METHODS

We expressed DEK-NUP214 in the myeloid cell lines U937 and PL-21 and studied the effects on cellular functions.

RESULTS

In this study, we demonstrate that expression of DEK-NUP214 increases cellular proliferation. Western blot analysis revealed elevated levels of one of the key proteins regulating proliferation, the mechanistic target of rapamycin, mTOR. This conferred increased mTORC1 but not mTORC2 activity, as determined by the phosphorylation of their substrates, p70 S6 kinase and Akt. The functional importance of the mTOR upregulation was determined by assaying the downstream cellular processes; protein synthesis and glucose metabolism. A global translation assay revealed a substantial increase in the translation rate and a metabolic assay detected a shift from glycolysis to oxidative phosphorylation, as determined by a reduction in lactate production without a concomitant decrease in glucose consumption. Both these effects are in concordance with increased mTORC1 activity. Treatment with the mTORC1 inhibitor everolimus (RAD001) selectively reversed the DEK-NUP214-induced proliferation, demonstrating that the effect is mTOR-dependent.

CONCLUSIONS

Our study shows that the DEK-NUP214 fusion gene increases proliferation by upregulation of mTOR, suggesting that patients with leukemias carrying DEK-NUP214 may benefit from treatment with mTOR inhibitors.

DEK expression in Merkel cell carcinoma and small cell carcinoma

BACKGROUND

The chromatin architectural factor DEK maps to chromosome 6p and is frequently overexpressed in several neoplasms, including small cell lung carcinoma, where it is associated with poor prognosis, tumor initiation activity and chemoresistance. DEK expression has not been studied in cutaneous Merkel cell carcinoma.

METHODS

We applied a DEK monoclonal antibody to 15 cases of Merkel cell carcinoma and 12 cases of small cell carcinoma. DEK nuclear immunoreactivity was scored based on percentage (0, negative; 1+, <25%; 2+, 25-50%; 3+, >50%) and intensity (weak, moderate or strong).

RESULTS

All 15 Merkel cell carcinoma cases (100%) showed diffuse (3+) nuclear positivity (14 strong, 1 weak). Six of 12 small cell carcinoma cases (50%) showed diffuse (3+) and strong nuclear positivity, while one case exhibited focal (1+) weak nuclear positivity. The remaining five cases were negative for DEK expression.

CONCLUSIONS

Our results suggest that DEK may be involved in the pathogenesis of Merkel cell carcinoma and therefore may provide therapeutic implications for Merkel cell carcinomas. In addition, the difference in DEK expression between Merkel cell carcinoma and small cell carcinoma suggests possible separate tumorigenesis pathways for the two tumors.

Unfavorable-risk cytogenetics in acute myeloid leukemia

Cytogenetic analysis at diagnosis is one of the most significant prognostic factors in acute myeloid leukemia (AML). AML patients with unfavorable-risk cytogenetic abnormalities account for 16-30% of younger adult patients and have poor response to standard treatment, with only 32-55% achieving a complete response. Overall survival is also extremely poor with only 5-12% patients alive at 5-10 years after diagnosis. Owing to the poor response in this subset of patients, risk-adapted treatment has been investigated. Allogeneic stem cell transplant has been shown to provide a survival benefit in patients with unfavorable-risk cytogenetic abnormalities in complement receptor 1. Other risk-adapted treatment strategies, such as reduced-intensity conditioning regimens prior to allogeneic stem cell transplant for older patients with AML, have also shown some survival benefit, without increasing treatment-related toxicities. Risk-stratification models that include cytogenetic abnormalities, as well as other molecular markers, are being developed to allow for individualized risk-adapted treatment for patients with AML. Prospective multicenter trials will be needed to validate these prognostic models.

Control of tumorigenesis and chemoresistance by the DEK oncogene

Slight modifications of chromatin dynamics can translate into small- and large-scale changes in DNA replication and DNA repair. Similarly, promoter usage and accessibility are tightly dependent on chromatin architecture. Consequently, it is perhaps not surprising that factors controlling chromatin organization are frequently deregulated (directly or indirectly) in cancer cells. DEK is emerging as a novel class of DNA topology modulators that can be both targets and effectors of protumorigenic events. The locus containing DEK at chromosome 6p22.3 is amplified or reorganized in multiple cancer types. In addition, DEK can be subject to a variety of tumor-associated transcriptional and post-translational modifications. In turn, DEK can favor cell transformation, at least in part by inhibiting cell differentiation and premature senescence. More recently, DEK has also been linked to the resistance of malignant cells to apoptotic inducers. Interestingly, a fraction of DEK can also bind RNA and affect alternative splicing, further illustrating the pleiotropic roles that this protein may exert in cancer cells. Here we will summarize the current literature about the regulation and function(s) of DEK as a proto-oncogene. In addition, the translational relevance of DEK as a putative diagnostic marker and candidate for drug development will be discussed.

The C. elegans homolog of nucleoporin Nup98 is required for the integrity and function of germline P granules

C. elegans P granules are conserved cytoplasmic ribonucleoprotein complexes that are unique to the germline and essential for fertility. During most of germline development, P granules are perinuclear and associate with clusters of nuclear pores. In an RNAi screen against nucleoporins, we have identified a specific nucleoporin essential for P granule integrity and function. The C. elegans homolog of vertebrate Nup98 (CeNup98) is enriched in P granules and associates with the translationally repressed, P granule-enriched mRNA nos-2 (nanos homolog). Loss of CeNup98 causes P granules to disperse in the cytoplasm and to release nos-2 mRNA. Embryos depleted for CeNup98 express a nos-2 3'UTR reporter prematurely. In the mouse, Nup98 immunoprecipitates with the germ granule component MVH. Our findings suggest that, in germ cells, the function of Nup98 extends beyond transport at the nuclear pore to include mRNA regulation in the cytoplasm.

Progress in studies on the DEK protein and its involvement in cellular apoptosis

DEK protein is an ubiquitous phosphorylated nuclear protein. Specific binding of DEK to DNA could change the topology of DNA and then affect the gene activity of the underlying DNA sequences. It is speculated that there might be some potential relationship between the stress reaction of cells and DEK proteins. The phosphorylation status of DEK protein is altered during death-receptor-mediated cell apoptosis. Both phosphorylation and poly(ADP-ribosyl)ation could promote the release of DEK from apoptotic nuclei to extracellular environment, and in this case DEK becomes a potential autoantigen of some autoimmune diseases. The available evidence powerfully suggests that DEK protein is closely relevant to apoptosis. The overexpression of DEK protein has dual function in cell apoptosis, in terms of inhibiting or triggering cell apoptosis.

Nuclear pore proteins and cancer

Nucleocytoplasmic trafficking of macromolecules, a highly specific and tightly regulated process, occurs exclusively through the nuclear pore complex. This immense structure is assembled from approximately 30 proteins, termed nucleoporins. Here we discuss the four nucleoporins that have been linked to cancers, either through elevated expression in tumors (Nup88) or through involvement in chromosomal translocations that encode chimeric fusion proteins (Tpr, Nup98, Nup214). In each case we consider the normal function of the nucleoporin and its translocation partners, as well as what is known about their mechanistic contributions to carcinogenesis, particularly in leukemias. Studies of nucleoporin-linked cancers have revealed novel mechanisms of oncogenesis and in the future, should continue to expand our understanding of cancer biology.