Abstract
The mammalian mediator complex subunit 28 (MED28) is overexpressed in a variety of cancers and it regulates cell migration/invasion and epithelial-mesenchymal transition. However, transcription factors that increase MED28 expression have not yet been identified. In this study, we performed a luciferase reporter assay to identify and characterize the prospective transcription factors, namely E2F transcription factor 1, nuclear respiratory factor 1, E-26 transforming sequence 1, and CCAAT/enhancer-binding protein β, which increased MED28 expression. In addition, the release from the arrest at the G1−S or G2−M phase transition after cell cycle synchronization using thymidine or nocodazole, respectively, showed enhanced MED28 expression at the G1−S transition and mitosis. Furthermore, the overexpression of MED28 significantly decreased the duration of interphase and mitosis. Conversely, a knockdown of MED28 using si-RNA increased the duration of interphase and mitosis. Of note, the overexpression of MED28 significantly increased micronucleus and nuclear budding in HeLa cells. In addition, flow cytometry and fluorescence microscopy analyses showed that the overexpression of MED28 significantly increased aneuploid cells. Taken together, these results suggest that MED28 expression is increased by oncogenic transcription factors and its overexpression disturbs the cell cycle, which results in genomic instability and aneuploidy.
Highlights
The mediator complex is known to serve as an intermediary between transcription factors and RNA polymerase II for the transmission of intracellular signals
We found putative binding sites for transcription factors, including E2F transcription factor 1 (E2F-1; −44 to −37 bp), nuclear respiratory factor 1 (NRF-1; −39 to −28 bp), E-26 transforming sequence 1 (ETS-1; −43 to −37 bp and −10 to −3 bp), and CCAAT/enhancer-binding protein β (C/EBPβ; −16 to −13 bp and −6 to −3 bp; Figure 1B)
We evaluated whether E2F-1, National Research Foundation of Korea (NRF)-1, ETS-1, and C/EBPβ could affect the transcription of mediator complex subunit 28 (MED28)
Summary
The mediator complex is known to serve as an intermediary between transcription factors and RNA polymerase II (pol II) for the transmission of intracellular signals. After the recruitment to DNA through the mediator-transcription complex, the mediator complex controls a variety of processes that are critical for transcription, including the reorganization of chromatin architecture and the regulation of pol II-mediated preinitiation, initiation, and elongation [3] in transcription. When considering that the essential role of the mediator complex in transcriptional control, genetic variation, or change in the expression of the mediator complex subunits that affect the pol II activity could lead to a variety of diseases. Mutations in MED12, MED17, and MED23 are associated with X-linked mental retardation syndrome, infantile cerebral atrophy, and intellectual disability, respectively [2,4,5,6,7]. Mutational analysis of the mediator complex subunits can provide valuable insights that could be useful in the development of novel drugs against critical human diseases [8]
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