DEK Proto-Oncogene Expression Interferes with the Normal Epithelial Differentiation Program

Abstract

Overexpression of the DEK gene is associated with multiple human cancers, but its specific roles as a putative oncogene are not well defined. DEK transcription was previously shown to be induced by the high-risk human papillomavirus (HPV) E7 oncogene via E2F and Rb pathways. Transient DEK overexpression was able to inhibit both senescence and apoptosis in cultured cells. In at least the latter case, this mechanism involved the destabilization of p53 and the decreased expression of p53 target genes. We show here that DEK overexpression disrupts the normal differentiation program in a manner that is independent of either p53 or cell death. DEK expression was distinctly repressed upon the differentiation of cultured primary human keratinocytes, and stable DEK overexpression caused epidermal thickening in an organotypic raft model system. The observed hyperplasia involved a delay in keratinocyte differentiation toward a more undifferentiated state, and expansion of the basal cell compartment was due to increased proliferation, but not apoptosis. These phenotypes were accompanied by elevated p63 expression in the absence of p53 destabilization. In further support of bona fide oncogenic DEK activities, we report here up-regulated DEK protein levels in both human papilloma virus-positive hyperplastic murine skin and a subset of human squamous cell carcinomas. We suggest that DEK up-regulation may contribute to carcinoma development at least in part through increased proliferation and retardation of differentiation. The human DEK protein was originally identified as a fusion with the NUP214/CAN nucleoporin in a subset of patients with acute myeloid leukemia 1 and was independently purified as a protein that modulates the topology of SV40 minichromosomes.2 DEK is abundantly expressed in proliferating cells, and a majority of the protein is bound to chromatin, whereas a small fraction is bound to RNA.3 The 43-kDa nuclear phosphoprotein is the only member of its family, and contains a conserved central SAP DNA binding domain with homology to SAF-A/B, acinus, and PIAS, 4 and a second DNA binding motif within the C-terminus.5,6 DNA binding as well as DEK self-association can be regulated by C-terminal phosphorylation and N-terminal acetylation. 7,8 Preferential DEK association with structured DNA templates and its ability to induce positive supercoils into circular DNA templates in vitro have led to the notion that DEK serves as an architectural protein.9 -12 Multiple reports have implicated DEK in replication, 2 positive and negative regulation of transcription [13][14][15][16][17][18][19] as well as mRNA processing. 20 -22 How these activities translate into putative oncogenic DEK functions is presently unclear.

DEK oncoprotein regulates transcriptional modifiers and sustains tumor initiation activity in high-grade neuroendocrine carcinoma of the lung

“…Thus, DEK may maintain the tumor-initiating activity of solid tumors, at least partly through modulation of these transcriptional regulators, suggesting that a common molecular pathway functions in the maintenance of both liquid and solid CSCs. It has been shown that DEK overexpression interferes with differentiation and expands the population of undifferentiated keratinocytes (Wise-Draper et al, 2009b), supporting the contention that DEK also has a significant role in normal epithelial stem cell maintenance.…”

DEK over-expression promotes mitotic defects and micronucleus formation

“…To explore this, we used immunofluorescence to determine DEK localization throughout mitosis in NIKS cells, a near-diploid spontaneously immortalized keratinocyte cell line that harbors low DEK expression levels. 30 While DEK is known to bind chromatin constitutively during interphase, we noted its marked absence from DNA during certain phases of mitosis ( Fig. 1B and 1C).…”

“…30 Primary antibodies used for DEK were as follows: DEK (1:1000; http://www.bdbiosciences.com/us/reagents/research/antibodiesbuffers/cell-biology-reagents/cell-biology-antibodies/purifiedmouse-anti-human-dek-2dek/p/610948), DEK-Aviva (1:1000; http://www.avivasysbio.com/dek-antibody-n-terminal-regionp100637-t100.html), DEK antibody K-877 (1:10,000, a polyclonal antibody; gift from Ferdinand Kappes), a DEK cocktail including the 3 described antibodies and DEK polyclonal rabbit from Proteintech (1:1000; http://www.ptglab.com/Products/ DEK-Antibody-16448-1-AP.htm). Other antibodies include a tubulin (1:5000; http://www.sigmaaldrich.com/catalog/product/ sigma/t9026), pH3-S10 (1:1000; http://www.cellsignal.com/ product/productDetail.jsp?productIdD9701), H3 (1:1000; http://www.cellsignal.com/products/primary-antibodies/9715), pan-actin (1:20,000; a gift from James Lessard, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA).…”

“…26,27 DEK overexpression can inhibit cell death and differentiation as well as promote proliferation, and invasion in multiple types of cancer. [28][29][30][31][32] During interphase, DEK plays a role in numerous nuclear processes including transcription, RNA processing, DNA repair, and chromatin organization. 20,[33][34][35][36][37] DEK is a highly modified protein, containing 57 potential phosphorylated sites and over 70 lysine residues with the potential to be poly ADPribosylated and ubiquitinated.…”

Construction and analysis of a subtractive cDNA library of early embryonic development in duck

“…Differentiation results in DEK downregulation in human promyelocytic HL-60 cells and in human foreskin keratinocytes, and in turn, overexpression of DEK counteracts cell differentiation (Savli et al, 2002;Wise-Draper et al, 2009b) and promotes proliferation and transformation of epithelial cells (Wise-Draper et al, 2009a). The DEK gene was originally described during early embryonic development, but is preferentially expressed in actively proliferating cells and can inhibit cell differentiation, senescence, and apoptosis.…”