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

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.

DEK, a nuclear protein, is chemotactic for hematopoietic stem/progenitor cells acting through CXCR2 and Gαi signaling

Few cytokines/growth modulating proteins are known to be chemoattractants for hematopoietic stem (HSC) and progenitor cells (HPC); stromal cell-derived factor 1α (SDF1α/CXCL12) being the most potent known such protein. DEK, a nuclear DNA-binding chromatin protein with hematopoietic cytokine-like activity, is a chemotactic factor attracting mature immune cells. Transwell migration assays were performed to test whether DEK serves as a chemotactic agent for HSC/HPC. DEK induced dose- and time-dependent directed migration of lineage negative (Lin- ) Sca-1+ c-Kit+ (LSK) bone marrow (BM) cells, HSCs and HPCs. Checkerboard assays demonstrated that DEK's activity was chemotactic (directed), not chemokinetic (random migration), in nature. DEK and SDF1α compete for HSC/HPC chemotaxis. Blocking CXCR2 with neutralizing antibodies or inhibiting Gαi protein signaling with Pertussis toxin pretreatment inhibited migration of LSK cells toward DEK. Thus, DEK is a novel and rare chemotactic agent for HSC/HPC acting in a direct or indirect CXCR2 and Gαi protein-coupled signaling-dependent manner.

DEK overexpression is predictive of poor prognosis in esophageal squamous cell carcinoma

INTRODUCTION

The DEK gene encodes a nuclear phosphoprotein which is involved in multiple cell metabolic processes, such as DNA damage repair, mRNA splicing, modifying chromatin structure and transcription regulation. DEK has been shown to be overexpressed in various solid human tumors and associated with patient prognosis. In this study, our aim was to investigate DEK protein expression and its relationship with clinicopathological parameters and prognosis in esophageal squamous cell carcinoma (ESCC).

MATERIAL AND METHODS

Tissue samples were collected from 120 routinely diagnosed ESCC patients who underwent surgical resection at the Zhongshan Hospital, Xiamen University in the period from June 2011 to May 2013. The expression of DEK was determined by immunohistochemistry.

RESULTS

DEK protein was ubiquitously distributed in the nucleus of ESCC cells, and its positive rate (71.7%) was significantly higher in cancer samples than those of para-carcinoma (21.4%) or normal esophageal (13.9%) tissues (p < 0.001). Similarly, significantly more cells overexpressing DEK were found in ESCC tissues (57.5%) in comparison with para-carcinoma samples (11.4%) and normal esophageal mucosa (0%, p < 0.001). The DEK overexpression rate was significantly different between patients with different tumor-node-metastasis (TNM) stages and differentiation degrees (p < 0.001). ESCC cases with elevated DEK amounts showed reduced disease-free and 5-year survival rates compared with those expressing low DEK amounts (p < 0.001). DEK overexpression was also confirmed to independently predict prognosis in ESCC (HR = 4.121, 95% CI: 1.803-9.42, p = 0.001).

CONCLUSIONS

DEK expression is positively correlated with reduced survival in ESCC patients. DEK has potential to be an independent biomarker in predicting prognosis of ESCC patients.

MiR-138-5p Inhibits the Proliferation of Gastric Cancer Cells by Targeting DEK

Background

Increasing evidence suggests that microRNAs (miRNAs) play critical roles in cancer progression. Therefore, investigating the function of miRNAs that are aberrantly expressed in gastric cancer (GC) and characterizing the involved underlying mechanism are essential for the treatment of gastric cancer. MiR-138-5p was found to be down-regulated in multiple cancers, which acted as a tumor suppressor in cancer progression; however, whether and how miR-138-5p regulates the malignant behaviors of GC has not been fully understood.

Methods

The level of miR-138-5p in GC tissues and cell lines was detected by RT-qPCR. The effects of miR-138-5p on the growth of GC cells were evaluated by the in vitro Cell Counting Kit-8 (CCK-8) assay, cell apoptosis, cell cycle analysis, wound-healing assay, and in vivo xenograft mice model. The targets of miR-138-5p were predicted using the miRDB online tool, confirmed by luciferase report assay and Western blot.

Results

MiR-138-5p was frequently decreased in GC tissues and cell lines. Decreased expression of miR-138-5p was significantly associated with the lymph node metastasis of GC patients. Overexpression of miR-138-5p suppressed GC cell proliferation, migration, increased cell apoptosis as well as inhibited the tumor growth in vivo. DEK oncogene was predicted as a potential target of miR-138-5p. MiR-138-5p bound the 3'-UTR of DEK and inhibited the level of DEK in GC cells. Restoration of DEK abrogated miR-138-5p overexpression-mediated suppression of GC cell proliferation and cell cycle arrest.

Conclusion

Our results demonstrated the anti-cancer role of miR-138-5p in GC by targeting DEK, which suggested miR-138-5p as a potential therapeutic target for the treatment of patient with GC.

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.

Loss of DEK induces radioresistance of murine restricted hematopoietic progenitors

Self-renewing hematopoietic stem cells and multipotent progenitor cells are responsible for maintaining hematopoiesis throughout an individual's lifetime. For overall health and survival, it is critical that the genome stability of these cells is maintained and that the cell population is not exhausted. Previous reports have indicated that the DEK protein, a chromatin structural protein that functions in numerous nuclear processes, is required for DNA damage repair in vitro and long-term engraftment of hematopoietic stem cells in vivo. Therefore, we investigated the role of DEK in normal hematopoiesis and response to DNA damaging agents in vivo. Here, we report that hematopoiesis is largely unperturbed in DEK knockout mice compared with wild-type (WT) controls. However, DEK knockout mice have fewer radioprotective units, but increased capacity to survive repeated sublethal doses of radiation exposure compared with WT mice. Furthermore, this increased survival correlated with a sustained quiescent state in which DEK knockout restricted hematopoietic progenitor cells (HPC-1) were nearly three times more likely to be quiescent following irradiation compared with WT cells and were significantly more radioresistant during the early phases of myeloid reconstitution. Together, our studies indicate that DEK functions in the normal hematopoietic stress response to recurrent radiation exposure.

Neuroanatomical Distribution of DEK Protein in Corticolimbic Circuits Associated with Learning and Memory in Adult Male and Female Mice

DEK, a chromatin-remodeling gene expressed in most human tissues, is known for its role in cancer biology and autoimmune diseases. DEK depletion in vitro reduces cellular proliferation, induces DNA damage subsequently leading to apoptosis, and down-regulates canonical Wnt/β-catenin signaling, a molecular pathway essential for learning and memory. Despite a recognized role in cancer (non-neuronal) cells, DEK expression and function is not well characterized in the central nervous system. We conducted a gene ontology analysis (ToppGene), using a cancer database to identify genes associated with DEK deficiency, which pinpointed several genes associated with cognitive-related diseases (i.e., Alzheimer's disease, presenile dementia). Based on this information, we examined DEK expression in corticolimbic structures associated with learning and memory in adult male and female mice using immunohistochemistry. DEK was expressed throughout the brain in both sexes, including the medial prefrontal cortex (prelimbic, infralimbic and dorsal peduncular). DEK was also abundant in all amygdalar subdivisions (basolateral, central and medial) and in the hippocampus including the CA1, CA2, CA3, dentate gyrus (DG), ventral subiculum and entorhinal cortex. Of note, compared to males, females had significantly higher DEK immunoreactivity in the CA1, indicating a sex difference in this region. DEK was co-expressed with neuronal and microglial markers in the CA1 and DG, whereas only a small percentage of DEK cells were in apposition to astrocytes in these areas. Given the reported inverse cellular and molecular profiles (e.g., cell survival, Wnt pathway) between cancer and Alzheimer's disease, these findings suggest a potentially important role of DEK in cognition.

A role for intracellular and extracellular DEK in regulating hematopoiesis

PURPOSE OF REVIEW

Hematopoietic stem/progenitor cell fate decision during hematopoiesis is regulated by intracellular and extracellular signals such as transcription factors, growth factors, and cell-to-cell interactions. In this review, we explore the function of DEK, a nuclear phosphoprotein, on gene regulation. We also examine how DEK is secreted and internalized by cells, and discuss how both endogenous and extracellular DEK regulates hematopoiesis. Finally, we explore what currently is known about the regulation of DEK during inflammation.

RECENT FINDINGS

DEK negatively regulates the proliferation of early myeloid progenitor cells but has a positive effect on the differentiation of mature myeloid cells. Inflammation regulates intracellular DEK concentrations with inflammatory stimuli enhancing DEK expression. Inflammation-induced nuclear factor-kappa B activation is regulated by DEK, resulting in changes in the production of other inflammatory molecules such as IL-8. Inflammatory stimuli in turn regulates DEK secretion by cells of hematopoietic origin. However, how inflammation-induced expression and secretion of DEK regulates hematopoiesis remains unknown.

SUMMARY

Understanding how DEK regulates hematopoiesis under both homeostatic and inflammatory conditions may lead to a better understanding of the biology of HSCs and HPCs. Furthering our knowledge of the regulation of hematopoiesis will ultimately lead to new therapeutics that may increase the efficacy of hematopoietic stem cell transplantation.

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.

An international effort to cure a global health problem: A report on the 19th Hemoglobin Switching Conference

Every 2 years since 1978, an international group of scientists, physicians, and other researchers meet to discuss the latest developments in the underlying etiology, mechanisms of action, and developmental acquisition of cellular and systemic defects exhibited and elicited by the most common inherited human disorders, the hemoglobinopathies. The 19th Hemoglobin Switching Conference, held in September 2014 at St. John's College in Oxford, once again exceeded all expectations by describing cutting edge research in cellular, molecular, developmental, and genomic advances focused on these diseases. The conference comprised about 60 short talks over 3 days by leading investigators in the field. This meeting report describes the highlights of the conference.