7913

DEK

DEK proto-oncogene;DEK;DEK proto-oncogene

DEK oncogene (DNA binding)|protein DEK

6p22.3

protein-coding

The human DEK proto-oncogene is a nucleic acid binding protein with suspected roles in human carcinogenesis, autoimmune disease, and viral infection. Intracellular DEK functions, however, are poorly understood. In papillomavirus-positive cervical cancer cells, downregulation of viral E6/E7 oncogene expression results in cellular senescence. We report here the specific repression of DEK message and protein levels in senescing human papillomavirus type 16- (HPV16-) and HPV18-positive cancer cell lines as well as in primary cells undergoing replicative senescence. Cervical cancer cell senescence was partially overcome by DEK overexpression, and DEK overexpression was sufficient for extending the life span of primary keratinocytes, supporting critical roles for this molecule as a senescence regulator. In order to determine whether DEK is a bona fide HPV oncogene target in primary cells, DEK expression was monitored in human keratinocytes transduced with HPV E6 and/or E7. The results identify high-risk HPV E7 as a positive DEK regulator, an activity that is not shared by low-risk HPV E7 protein. Experiments in mouse embryo fibroblasts recapitulated the observed E7-mediated DEK induction and demonstrated that both basal and E7-induced regulation of DEK expression are controlled by the retinoblastoma protein family. Taken together, our results suggest that DEK upregulation may be a common event in human carcinogenesis and may reflect its senescence inhibitory function.

The human DEK proto-oncogene has been found to play an important role in autoimmune disease, viral infection and human carcinogenesis. Although it is transcriptionally up-regulated in cervical cancer, its intracellular function and regulation is still unexplored. In the present study, DEK and IkappaBalpha [inhibitor of NF-kappaB (nuclear factor kappaB) alpha] shRNAs (short hairpin RNAs) were constructed and transfected into CaSki cells using Lipofectamine. The stable cell line CaSki-DEK was obtained after G418 selection. CaSki-IkappaB cells were observed at 48 h after psiRNA-IkappaB transfection. The inhibitory efficiency of shRNAs were detected by RT (reverse transcription)-PCR and Western blot analysis. The proliferation activity of cells were measured using an MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay, cell apoptosis was measured using an Annexin V/PI (propidium iodide) kit, the cell cycle was analysed by flow cytometry and cell senescence was detected using senescence beta-galactosidase staining. The intracellular expression of NF-kappaB p65 protein was studied by cytochemistry. The expression levels of NF-kappaB p65, p50, c-Rel, IkappaBalpha and phospho-IkappaBalpha protein were analysed by immunoblotting in whole-cell lysates, cytosolic fractions and nuclear extracts. The protein expression and activity of p38 and JNK (c-Jun N-terminal kinase) were also assayed. In addition, the NF-kappaB p65 DNA-binding activity was measured by ELISA. Following the silencing of DEK and IkappaBalpha, cell proliferation was inhibited, apoptosis was increased, the cell cycle was blocked in the G0/G1-phase with a corresponding decrease in the G2/M-phase, and cell senescence was induced. ALL of these effects may be related to the up-regulation of NF-kappaB p65 expression and its nuclear translocation.