In silico gene expression and pathway analysis of DEK in the human brain across the lifespan.

DEK, a chromatin-remodelling phosphoprotein, is associated with various functions and biological pathways in the periphery, including inflammation, oncogenesis, DNA repair, and transcriptional regulation. We recently identified an association between DEK loss and central nervous system diseases, such as Alzheimer's. To understand DEK's potential role in disease, it is critical to characterize DEK in healthy human brain to distinguish between neural DEK expression and function in healthy versus diseased states like dementia. We utilized two public databases, BrainCloud and Human Brain Transcriptome, and analysed DEK mRNA expression across the lifespan in learning and memory relevant brain regions. Since DEK loss induces phenotypes associated with brain ageing (e.g., DNA damage and apoptosis), we hypothesized that neural DEK expression may be highest during foetal development and lower in elderly individuals. In agreement with this hypothesis, DEK was most prominently expressed during foetal development in all queried forebrain areas, relative to other ages. Consistent with its roles in the periphery, pathways related to DEK in the brain were associated with cellular proliferation, DNA replication and repair, apoptosis, and inflammation. We also found novel neural development-relevant pathways (e.g., synaptic transmission, neurite outgrowth, and myelination) to be enriched from genes correlated with DEK expression. These findings suggest that DEK is important for human brain development. Overall, we highlight age-related changes in neural DEK expression across the human lifespan and illuminate novel biological pathways associated with DEK that are distinct from normal brain ageing. These findings may further our understanding of how DEK impacts brain function and disease susceptibility.

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.

Novel molecular mechanisms in Alzheimer's disease: The potential role of DEK in disease pathogenesis.

Alzheimer's disease and age-related dementias (AD/ADRD) are debilitating diseases that exact a significant physical, emotional, cognitive, and financial toll on the individual and their social network. While genetic risk factors for early-onset AD have been identified, the molecular and genetic drivers of late-onset AD, the most common subtype, remain a mystery. Current treatment options are limited for the 35 million people in the United States with AD/ADRD. Thus, it is critically important to identify novel molecular mechanisms of dementia-related pathology that may be targets for the development of new interventions. Here, we summarize the overarching concepts regarding AD/ADRD pathogenesis. Then, we highlight one potential molecular driver of AD/ADRD, the chromatin remodeling protein DEK. We discuss in vitro, in vivo, and ex vivo findings, from our group and others, that link DEK loss with the cellular, molecular, and behavioral signatures of AD/ADRD. These include associations between DEK loss and cellular and molecular hallmarks of AD/ADRD, including apoptosis, Tau expression, and Tau hyperphosphorylation. We also briefly discuss work that suggests sex-specific differences in the role of DEK in AD/ADRD pathogenesis. Finally, we discuss future directions for exploiting the DEK protein as a novel player and potential therapeutic target for the treatment of AD/ADRD.

Drug resistance mechanisms create targetable proteostatic vulnerabilities in Her2+ breast cancers.

Oncogenic kinase inhibitors show short-lived responses in the clinic due to high rate of acquired resistance. We previously showed that pharmacologically exploiting oncogene-induced proteotoxic stress can be a viable alternative to oncogene-targeted therapy. Here, we performed extensive analyses of the transcriptomic, metabolomic and proteostatic perturbations during the course of treatment of Her2+ breast cancer cells with a Her2 inhibitor covering the drug response, resistance, relapse and drug withdrawal phases. We found that acute Her2 inhibition, in addition to blocking mitogenic signaling, leads to significant decline in the glucose uptake, and shutdown of glycolysis and of global protein synthesis. During prolonged therapy, compensatory overexpression of Her3 allows for the reactivation of mitogenic signaling pathways, but fails to re-engage the glucose uptake and glycolysis, resulting in proteotoxic ER stress, which maintains the protein synthesis block and growth inhibition. Her3-mediated cell proliferation under ER stress during prolonged Her2 inhibition is enabled due to the overexpression of the eIF2 phosphatase GADD34, which uncouples protein synthesis block from the ER stress response to allow for active cell growth. We show that this imbalance in the mitogenic and proteostatic signaling created during the acquired resistance to anti-Her2 therapy imposes a specific vulnerability to the inhibition of the endoplasmic reticulum quality control machinery. The latter is more pronounced in the drug withdrawal phase, where the de-inhibition of Her2 creates an acute surge in the downstream signaling pathways and exacerbates the proteostatic imbalance. Therefore, the acquired resistance mechanisms to oncogenic kinase inhibitors may create secondary vulnerabilities that could be exploited in the clinic.

Loss of DEK Expression Induces Alzheimer's Disease Phenotypes in Differentiated SH-SY5Y Cells.

Alzheimer's disease (AD) is the most common cause of dementia and is characterized by the buildup of ß-amyloid plaques and neurofibrillary Tau tangles. This leads to decreased synaptic efficacy, cell death, and, consequently, brain atrophy in patients. Behaviorally, this manifests as memory loss and confusion. Using a gene ontology analysis, we recently identified AD and other age-related dementias as candidate diseases associated with the loss of DEK expression. DEK is a nuclear phosphoprotein with roles in DNA repair, cellular proliferation, and inhibiting apoptosis. Work from our laboratory determined that DEK is highly expressed in the brain, particularly in regions relevant to learning and memory, including the hippocampus. Moreover, we have also determined that DEK is highly expressed in neurons. Consistent with our gene ontology analysis, we recently reported that cortical DEK protein levels are inversely proportional to dementia severity scores in elderly female patients. However, the functional role of DEK in neurons is unknown. Thus, we knocked down DEK in an in vitro neuronal model, differentiated SH-SY5Y cells, hypothesizing that DEK loss would result in cellular and molecular phenotypes consistent with AD. We found that DEK loss resulted in increased neuronal death by apoptosis (i.e., cleaved caspases 3 and 8), decreased ß-catenin levels, disrupted neurite development, higher levels of total and phosphorylated Tau at Ser262, and protein aggregates. We have demonstrated that DEK loss in vitro recapitulates cellular and molecular phenotypes of AD pathology.

Sex differences in DEK expression in the anterior cingulate cortex and its association with dementia severity in schizophrenia.

DEK is a chromatin-remodeling phosphoprotein found in most human tissues, but its expression and function in the human brain is largely unknown. DEK depletion in vitro induces cellular and molecular anomalies associated with cognitive impairment, including down-regulation of the canonical Wnt/ß-catenin signaling pathway. ToppGene analyses link DEK loss to genes associated with various dementias and age-related cognitive decline. To examine the role of DEK in cognitive impairment in severe mental illness, DEK protein expression was assayed by immunoblot in the anterior cingulate cortex (ACC) of subjects with schizophrenia. Cognitive impairment is a core feature of schizophrenia and cognitive function in subjects was assessed antemortem using the clinical dementia rating (CDR) scale. DEK protein expression was not significantly altered in schizophrenia (n = 20) compared to control subjects (n = 20). Further analysis revealed significant reduction in DEK protein expression in women with schizophrenia, and a significant increase in expression in men with schizophrenia, relative to their same-sex controls. DEK protein expression levels were inversely correlated with dementia severity in women. Conversely, in men, DEK protein expression and dementia severity were positively correlated. Notably, there was no sex difference in DEK protein expression in the control group, suggesting that this sex difference is specific to schizophrenia and not due to inherent differences in DEK expression between males and females. These results suggest a novel, sex-specific role for DEK in cognitive performance and highlight a putative sex-specific link between central nervous system DEK protein expression and a neuropsychiatric disease that is commonly associated with cognitive impairment.

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.

Defects in the Fanconi Anemia Pathway in Head and Neck Cancer Cells Stimulate Tumor Cell Invasion through DNA-PK and Rac1 Signaling.

PURPOSE: Head and neck squamous cell carcinoma (HNSCC) remains a devastating disease, and Fanconi anemia (FA) gene mutations and transcriptional repression are common. Invasive tumor behavior is associated with poor outcome, but relevant pathways triggering invasion are poorly understood. There is a significant need to improve our understanding of genetic pathways and molecular mechanisms driving advanced tumor phenotypes, to develop tailored therapies. Here we sought to investigate the phenotypic and molecular consequences of FA pathway loss in HNSCC cells. EXPERIMENTAL DESIGN: Using sporadic HNSCC cell lines with and without FA gene knockdown, we sought to characterize the phenotypic and molecular consequences of FA deficiency. FA pathway inactivation was confirmed by the detection of classic hallmarks of FA following exposure to DNA cross-linkers. Cells were subjected to RNA sequencing with qRT-PCR validation, followed by cellular adhesion and invasion assays in the presence and absence of DNA-dependent protein kinase (DNA-PK) and Rac1 inhibitors. RESULTS: We demonstrate that FA loss in HNSCC cells leads to cytoskeletal reorganization and invasive tumor cell behavior in the absence of proliferative gains. We further demonstrate that cellular invasion following FA loss is mediated, at least in part, through NHEJ-associated DNA-PK and downstream Rac1 GTPase activity. CONCLUSIONS: These findings demonstrate that FA loss stimulates HNSCC cell motility and invasion, and implicate a targetable DNA-PK/Rac1 signaling axis in advanced tumor phenotypes.

Stacking the DEK: from chromatin topology to cancer stem cells.

Stem cells are essential for development and tissue maintenance and display molecular markers and functions distinct from those of differentiated cell types in a given tissue. Malignant cells that exhibit stem cell-like activities have been detected in many types of cancers and have been implicated in cancer recurrence and drug resistance. Normal stem cells and cancer stem cells have striking commonalities, including shared cell surface markers and signal transduction pathways responsible for regulating quiescence vs. proliferation, self-renewal, pluripotency and differentiation. As the search continues for markers that distinguish between stem cells, progenitor cells and cancer stem cells, growing evidence suggests that a unique chromatin-associated protein called DEK may confer stem cell-like qualities. Here, we briefly describe current knowledge regarding stem and progenitor cells. We then focus on new findings that implicate DEK as a regulator of stem and progenitor cell qualities, potentially through its unusual functions in the regulation of local or global chromatin organization.

The DEK oncogene is a target of steroid hormone receptor signaling in breast cancer.

Expression of estrogen and progesterone hormone receptors indicates a favorable prognosis due to the successful use of hormonal therapies such as tamoxifen and aromatase inhibitors. Unfortunately, 15-20% of patients will experience breast cancer recurrence despite continued use of tamoxifen. Drug resistance to hormonal therapies is of great clinical concern so it is imperative to identify novel molecular factors that contribute to tumorigenesis in hormone receptor positive cancers and/or mediate drug sensitivity. The hope is that targeted therapies, in combination with hormonal therapies, will improve survival and prevent recurrence. We have previously shown that the DEK oncogene, which is a chromatin remodeling protein, supports breast cancer cell proliferation, invasion and the maintenance of the breast cancer stem cell population. In this report, we demonstrate that DEK expression is associated with positive hormone receptor status in primary breast cancers and is up-regulated in vitro following exposure to the hormones estrogen, progesterone, and androgen. Chromatin immunoprecipitation experiments identify DEK as a novel estrogen receptor α (ERα) target gene whose expression promotes estrogen-induced proliferation. Finally, we report for the first time that DEK depletion enhances tamoxifen-induced cell death in ER+ breast cancer cell lines. Together, our data suggest that DEK promotes the pathogenesis of ER+ breast cancer and that the targeted inhibition of DEK may enhance the efficacy of conventional hormone therapies.