Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2016 Apr 26;7(17):23043-23055.
doi: 10.18632/oncotarget.8469.

Comprehensive analysis of the transcriptional profile of the Mediator complex across human cancer types

Affiliations

Comprehensive analysis of the transcriptional profile of the Mediator complex across human cancer types

Isabella Syring et al. Oncotarget. .

Abstract

The Mediator complex is a key regulator of gene transcription and several studies demonstrated altered expressions of particular subunits in diverse human diseases, especially cancer. However a systematic study deciphering the transcriptional expression of the Mediator across different cancer entities is still lacking.We therefore performed a comprehensive in silico cancer vs. benign analysis of the Mediator complex subunits (MEDs) for 20 tumor entities using Oncomine datasets. The transcriptional expression profiles across almost all cancer entities showed differentially expressed MEDs as compared to benign tissue. Differential expression of MED8 in renal cell carcinoma (RCC) and MED12 in lung cancer (LCa) were validated and further investigated by immunohistochemical staining on tissue microarrays containing large numbers of specimen. MED8 in clear cell RCC (ccRCC) associated with shorter survival and advanced TNM stage and showed higher expression in metastatic than primary tumors. In vitro, siRNA mediated MED8 knockdown significantly impaired proliferation and motility in ccRCC cell lines, hinting at a role for MED8 to serve as a novel therapeutic target in ccRCC. Taken together, our Mediator complex transcriptome proved to be a valid tool for identifying cancer-related shifts in Mediator complex composition, revealing that MEDs do exhibit cancer specific transcriptional expression profiles.

Keywords: MED8; Mediator complex; Pathology Section; cancer; oncomine; transcriptional profile.

PubMed Disclaimer

Conflict of interest statement

We declare no conflict of interest.

Figures

Figure 1
Figure 1. Transcriptional landscape of the Mediator complex in human cancers
The levelplots depict the frequencies (%) of A. over- and B. underexpression for the Mediator complex subunits in all analyzed tumor entities. Mediator subunits (MEDs) are color-coded based on the modules which they are part of (head, middle, tail, and kinase with the paralogs). While in some cancer entities (cervical, esophageal cancer, sarcoma, myeloma and leukemia) no differential MED expression was observed, other tumors exhibited altered MED expressions as compared to benign reference tissue (e.g. lung and breast cancer). Red = overexpression. Blue = underexpression.
Figure 2
Figure 2. MED8 in RCC
A. Representative IHC images from tissue of benign kidney, ccRCC and pRCC analysis of the MED8 protein expression with alkaline phosphatase as reporter dye (red), haematoxylin (blue) as counterstain. 5x (upper panel) and 40x (lower panel) objective magnification. B. MED8 protein expression profile of the total kidney cohort including benign tissue, ccRCC and pRCC. Boxplots of mean red chromogen intensity of the nucleus are shown. (Red reference line at y = 0.46 represents the cut-off for defining enhanced protein expression). C. Quantification of samples expressing MED8 in a normal and overexpressed range. D. Direct comparison between proportion of samples with a MED8 overexpression on mRNA (Oncomine) and protein level (IHC). (*** = p < 0.001, ccRCC = renal clear cell carcinoma, pRCC papillary renal cell carcinoma).
Figure 3
Figure 3. MED8 in ccRCC progression
A.+B. Significantly enhanced MED8 protein expression was observed in metastases derived from ccRCC. C. MED8 overexpression (z-score > 1.5) is associated with strongly reduced survival in ccRCC patients. D. MED8 knockdown led to significantly reduced proliferation in the ccRCC cell lines A-498 and ACHN. E. Migration was significantly impaired in MED8-deficient cells as compared to scrambled control cells.
Figure 4
Figure 4. MED12 in LCa
A. Representative IHC images from tissue of benign lung, AC and SCC analysis of the MED12 protein expression with haematoxylin. 5x (upper panel) and 40x (lower panel) objective magnification. B. MED12 protein expression profile of the total lung cohort including benign tissue, AC and SCC. Boxplots of mean brown chromogen intensity of the nucleus are shown. (Red reference line at y = 0.52 represents the cut-off for defining enhanced protein expression). C. Quantification of samples expressing MED12 in a normal and overexpressed range. D. Direct comparison between proportion of samples with a MED12 overexpression on mRNA (Oncomine) and protein level (IHC). (*** = p < 0.001, AC adenocarcinoma, SCC squamous cell carcinoma)

References

    1. Malik S, Roeder R. G. The metazoan Mediator co-activator complex as an integrative hub for transcriptional regulation. Nat Rev Genet. 2010;11:761–772. - PMC - PubMed
    1. Cai G, Imasaki T, Takagi Y, Asturias FJ. Mediator structural conservation and implications for the regulation mechanism. Structure. 2009;17:559–567. - PMC - PubMed
    1. Flanagan PM, Kelleher RJ, 3rd, Sayre MH, Tschochner H, Kornberg RD. A mediator required for activation of RNA polymerase II transcription in vitro. Nature. 1991;350:436–438. - PubMed
    1. Carlson M. Genetics of transcriptional regulation in yeast: connections to the RNA polymerase II CTD. Annu Rev Cell Dev Biol. 1997;13:1–23. - PubMed
    1. Daniels DL, Ford M, Schwinn MK, Benink H, Galbraith MD, Amunugama R, Jones R, Allen D, Okazaki N, Yamakawa H, Miki F, Nagase T, Espinosa JM, et al. Mutual Exclusivity of MED12/MED12L, MED13/13L, and CDK8/19 Paralogs Revealed within the CDK-Mediator Kinase Module. J Proteomics Bioinform. 2013;S2(004):1–7.