Oncogene DEK is highly expressed in lung cancerous tissues and positively regulates cell proliferation as well as invasion

Proto-oncogene DEK binds to pre-mRNAs and regulates the alternative splicing of Hippo signaling genes in HeLa cells

Our study aimed to explore how DEK, a carcinogenic protein with chromatin architectural function, genome-widely binds to RNA and affects the alternative splicing in cancer cells to decipher its molecular functions. To achieve this goal, cell phenotype experiments, RNA sequencing (RNA-seq), and improved RNA immunoprecipitation sequencing (iRIP-seq) were conducted to identify the function and regulated targets of DEK in HeLa cells. The results showed DEK overexpression promoted cell proliferation and invasion of HeLa cells. Meanwhile, DEK hardly affected transcript level expression of those high expressed genes, but splicing pattern of 411 genes was regulated by DEK in HeLa cells, which were enriched in Hippo signaling pathway. Moreover, DEK broadly bind the RNA of a total of 11, 112 genes, with a biased binding the 5' splice site (5'SS) consensus GGUAA motifs at the CDS and intronic regions. In addition, 297 DEK-binding genes showed different splicing pattern after DEK overexpression in HeLa cells. These genes were enriched in Hippo signaling pathway including CSNK1D. The RT-qPCR and RIP-PCR confirmed that DEK can bind to CSNK1D to regulate its alternative splicing in HeLa cells. In summary, our results indicated DEK could broadly bind and regulate the pre-mRNA splicing process, which provide new insights of mechanisms that DEK functions in various biological processes including cancer.

p21-activated kinase 2 binds to transcription factor SOX2 and up-regulates DEK to promote the progression of lung squamous cell carcinoma

Lung squamous cell carcinoma (LSCC) is a prevalent and progressive subtype of lung cancer. This study aimed to substantiate the regulatory effect of the PAK2/SOX2/DEK axis on the LSCC development. LSCC tissues (n = 83) and adjacent normal tissues were collected and SOX2 expression was determined by qRT-PCR and Western blotting. Correlation between SOX2 expression and the prognosis of LSCC patients was then explored utilizing Kaplan-Meier analysis. Co-immunoprecipitation and glutathione-S-transferase pull-down assays were conducted to validate the binding of SOX2 to DEK. Gain- and loss- of function assays were then performed on LSCC cells, with CCK-8 and Transwell assays applied to detect the malignant behaviors of cells. A mouse xenograft model of LSCC was further established for in vivo validation. The expression levels of SOX2, PAK2 and DEK were up-regulated in LSCC tissues and cells. SOX2 overexpression was correlated with poor prognosis of LSCC patients. Knockdown of SOX2 weakened the viability and the migratory and invasive potential of LSCC cells. Further, PAK2 directly interacted with SOX2. PAK2 overexpression accelerated the malignant phenotypes of LSCC cells through interplay with SOX2. Moreover, SOX2 activated the expression of DEK, and silencing DEK attenuated the malignant behaviors of LSCC cells. In conclusion, PAK2 could bind to the transcription factor SOX2 and thus activate the expression of DEK, thereby driving the malignant phenotypes of LSCC cells both in vivo and in vitro.

Gigantol inhibits cell proliferation and induces apoptosis by regulating DEK in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is a common type of cancer, with a mortality of >80% worldwide. Gigantol is a bibenzyl compound that displays anticancer activity. The aim of the present study was to determine the biological activity of gigantol in NSCLC and to elucidate the underlying molecular mechanism of its action. The expression of DEK proto-oncogene (DEK) was measured in NSCLC tissues and cell lines by reverse transcription-quantitative PCR (RT-qPCR). The results suggested that DEK levels were significantly increased in NSCLC tissues and cell lines compared with adjacent non-tumor tissues and BEAS-2B normal bronchial epithelial cells, respectively. A549 cells were exposed to a series of gigantol concentrations (0, 25, 50 and 100 µM) and transfected with DEK small interfering RNA. The results of cell viability measured by MTT assay indicated that gigantol significantly decreased cell viability. Additionally, cell proliferation was assessed by CCK-8 and apoptosis was measured by flow cytometry. In comparison with the control group, gigantol treatment inhibited cell proliferation and promoted apoptosis, whereas DEK knockdown increased gigantol-induced suppression of proliferation and acceleration of apoptosis. Additionally, DEK overexpression reversed gigantol-induced effects on proliferation and apoptosis. Moreover, compared with the control group, gigantol treatment decreased Ki-67 and Bcl-2 expression levels, increased Bax expression levels and inactivated the Wnt/β-catenin signaling pathway, as assessed by RT-qPCR and/or western blot. DEK knockdown further increased gigantol-induced effects, but DEK overexpression reversed gigantol-induced effects. To conclude, the results of the present study suggested that gigantol inhibited cell proliferation and induced apoptosis by decreasing Ki-67 and Bcl-2 expression, increasing Bax expression and activating the Wnt/β-catenin signaling pathway by regulating DEK. The present study indicated the therapeutic potential of gigantol in patients with NSCLC. In addition, DEK may serve as a novel therapeutic target to enhance the effects of gigantol treatment.

DEK is highly expressed in breast cancer and is associated with malignant phenotype and progression

DEK proto-oncogene (DEK) has been demonstrated as an oncogene and is associated with the development of many types of tumor; however, the expression and role of DEK in breast cancer remain unknown. The present study aimed to determine the role of DEK in the progression of breast cancer. The expression of DEK in 110 breast cancer tissues and 50 adjacent normal breast tissues was examined using immunohistochemistry. Furthermore, DEK expression was upregulated by DEK transfection or downregulated by DEK shRNA interference in MCF7 cells. Proliferative and invasive abilities were examined in MCF7 cells using MTT assay, colony-formation assay and transwell invasion assays. The results demonstrated that DEK expression level was significantly increased in breast cancer tissues compared with normal breast tissues. Furthermore, high DEK expression was associated with high histological grade, lymph node metastasis, advanced Tumor-Node-Metastasis stage and high Ki-67 index; however, DEK expression was not associated with the expression level of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. High DEK expression indicated poor prognosis in patients with breast cancer. DEK overexpression upregulated the protein expression of β-catenin and Wnt and increased the proliferative and invasive abilities of breast cancer cells. DEK downregulation had the opposite effect. Taken together, the results from the present study demonstrated that high expression of DEK was common in patients with breast cancer and was associated with progression of the disease and poor prognosis, and that DEK overexpression promoted the proliferative and invasive abilities of breast cancer cells.

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.

The oncoprotein DEK affects the outcome of PARP1/2 inhibition during mild replication stress

DNA replication stress is a major source of genomic instability and is closely linked to tumor formation and progression. Poly(ADP-ribose)polymerases1/2 (PARP1/2) enzymes are activated in response to replication stress resulting in poly(ADP-ribose) (PAR) synthesis. PARylation plays an important role in the remodelling and repair of impaired replication forks, providing a rationale for targeting highly replicative cancer cells with PARP1/2 inhibitors. The human oncoprotein DEK is a unique, non-histone chromatin architectural protein whose deregulated expression is associated with the development of a wide variety of human cancers. Recently, we showed that DEK is a high-affinity target of PARylation and that it promotes the progression of impaired replication forks. Here, we investigated a potential functional link between PAR and DEK in the context of replication stress. Under conditions of mild replication stress induced either by topoisomerase1 inhibition with camptothecin or nucleotide depletion by hydroxyurea, we found that the effect of acute PARP1/2 inhibition on replication fork progression is dependent on DEK expression. Reducing DEK protein levels also overcomes the restart impairment of stalled forks provoked by blocking PARylation. Non-covalent DEK-PAR interaction via the central PAR-binding domain of DEK is crucial for counteracting PARP1/2 inhibition as shown for the formation of RPA positive foci in hydroxyurea treated cells. Finally, we show by iPOND and super resolved microscopy that DEK is not directly associated with the replisome since it binds to DNA at the stage of chromatin formation. Our report sheds new light on the still enigmatic molecular functions of DEK and suggests that DEK expression levels may influence the sensitivity of cancer cells to PARP1/2 inhibitors.