DEK Expression Level And Mechanism In Lung Cancer Cells

PURPOSE:DEK is a ubiquitous protein in multicellular organisms as well as in some unicellular organisms. DEK is over-expressed in various malignant tumor cells, while remaining in a low level or is even undetectable in quiescent and terminally differentiated cells. DEK can regulate proliferation, differentiation, migration, apoptosis, senescence, self-renewal and DNA repairing of cells by means of altering chromatin structure, involving in signal transduction pathways, or acting as a transcription factor. Therefore, DEK is closely linked to the carcinogenesis process. Yet few researches are concentrated in DEK expression and mechanism in lung cancer. This research studies the expression level, function, mechanism as well as transcriptional regulation of DEK in lung cancer, thus reveal the connection between DEK and tumor formation.METHODS:Reverse Transcription Polymerase Chain Reaction (RT-PCR) and Immunohistochemistry (IHC) are performed to detect DEK expression level in tissues of lung cancer patients. DEK expression level in lung cancer cell line A549is altered by transfecting siRNA and DEK over-expression plasmid. Downstream effects to cell function and expression level of related genes are detected. Specifically, MTT assay and colony formation assay are performed to detect cell proliferation; Annexin V-PE cell apoptosis detection kit is applied to detect cell apoptosis; Matrigel invasion assay is performed to detect cell invasion. Meanwhile, by performing bisulfite sequencing PCR (BSP) using lung cancer patient’s genomic DNA, connection between methylation level of DEK promoter region and its transcriptional regulation is studied.RESULTS:Over-expression of DEK mRNA is detected in51.7%of lung cancerous tissues compared to corresponding normal tissues using RT-PCR. Among those,87.5%of the adenocarcinoma tissues show over-expression of DEK mRNA, which is higher than those of other histopathological types.81.5%of the lung cancerous tissues show positive expression of DEK protein detected by IHC, while39.5%show strong positive expression of DEK protein, which is higher than the strong positive rate in normal tissues. By regulating the DEK expression level of A549lung cancer cell line using siRNA and DEK over-expression plasmid, positive correlations between DEK expression level and cell proliferation as well as cell invasion are detected. Moreover, negative correlations between DEK expression level and cell apoptosis as well as expression level of p53, p65and ATM are also discovered. Lastly, decrease of over-all methylation level of CpG islands as well as methylation level of CpGs on a number of transcriptional factor binding sites (such as E2F and YYl) of DEK promoter region in lung cancerous tissues are detected. The results indicate that the over-expression of DEK in lung cancers is likely to be strongly connected with the function of DEK as an oncogene. The carcinogenesis process regulated by DEK may involve the p53, p65and ATM pathways. Loss of methylation level in DEK promoter region is also likely to be closely related to the transcriptional activation of DEK as well as tumor formation.