Expression Pattern of the Novel Gene EG-1 in Cancer

Identification of β-catenin target genes in colorectal cancer by interrogating gene fitness screening data

β-catenin regulates its target genes which are associated with proliferation, differentiation, migration and angiogenesis, and the dysregulation of Wnt/β-catenin signaling facilitates hallmarks of colorectal cancer (CRC). Identification of β-catenin targets and their potential roles in tumorigenesis has gained increased interest. However, the number of identified targets remains limited. The present study implemented a novel strategy, interrogating gene fitness profiles derived from large-scale RNA interference and CRISPR-CRISPR associated protein 9 screening data to identify β-catenin target genes in CRC cell lines. Using these data sets, pair wise gene fitness similarities were determined which highlighted a total of 13 genes whose functions were highly correlated with β-catenin. It was further demonstrated that the expression of these genes were altered in CRC, illustrating their potential roles in the progression of CRC. The present study further demonstrated that these targets could be used to predict disease-free survival in CRC. In conclusion, the findings provided novel approaches for the identification of β-catenin targets, which may become prognostic biomarkers or drug targets for the management of CRC.

MED28 Over-Expression Shortens the Cell Cycle and Induces Genomic Instability

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.

MED28 increases the colony-forming ability of breast cancer cells by stabilizing the ZNF224 protein upon DNA damage

The regulation of gene expression by transcription factors serves a critical function in cell proliferation. Zinc-finger protein 224 (ZNF224), a Krüppel-associated-box-containing zinc finger protein, is known to serve a crucial function in integrating the transcriptional co-factors that activate transcriptional regulation pathways in the cell. A previous study demonstrated that ZNF224 enhances cell proliferation by downregulating the expression of p21 and p53. The present study identified mediator complex subunit 28 (MED28) as a potential binding partner for ZNF224; this was confirmed by co-immunoprecipitation and a surface plasmon resonance assay. Additionally, the KRAB domain at the N-terminal of ZNF224 interacts with the MED domain of MED28. Bimolecular fluorescence complementation analysis revealed that ZNF224 associates with MED28 in the nucleus. In addition, ZNF224 was rapidly degraded upon treatment with the DNA-damaging agent camptothecin (CPT). Transient overexpression of MED28 inhibited the CPT-mediated degradation of ZNF224, resulting in increased colony formation by MCF-7 cells. The molecular mechanisms that underlie the biological outcomes of MED28 expression have not yet been fully elucidated. The present study provides molecular evidence for the function of ZNF224 and MED28 in the DNA-damage response.

Generation of med28 specific monoclonal antibodies

Med28 plays a role in transcription, signal transduction, and cell proliferation. The overexpression of med28 is associated with tumor progression in in vitro and in vivo models. Recently it has been reported that the elevated expression of med28 is associated with poor outcome in women with breast cancer. The expression level of med28 in in vitro and in vivo was examined by using anti-rabbit polyclonal antibody in previous reports. In this study, we report for the first time the generation and characterization of four monoclonal antibodies against med28 through immunoblotting, immunofluorescence microscopy, immunoprecipitation, and immunohistochemical analyses. These antibodies will be useful in detecting med28 in in vitro and in vivo.

Mediator Subunit Med28 Is Essential for Mouse Peri-Implantation Development and Pluripotency

The multi-subunit mammalian Mediator complex acts as an integrator of transcriptional regulation by RNA Polymerase II, and has emerged as a master coordinator of development and cell fate determination. We previously identified the Mediator subunit, MED28, as a cytosolic binding partner of merlin, the Neurofibromatosis 2 (NF2) tumor suppressor, and thus MED28 is distinct in having a cytosolic role as an NF2 interacting protein as well as a nuclear role as a Mediator complex subunit. Although limited in vitro studies have been performed on MED28, its in vivo function remains unknown. Employing a knockout mouse model, we describe for the first time the requirement for Med28 in the developing mouse embryo. Med28-deficiency causes peri-implantation lethality resulting from the loss of pluripotency of the inner cell mass accompanied by reduced expression of key pluripotency transcription factors Oct4 and Nanog. Further, overexpression of Med28 in mouse embryonic fibroblasts enhances the efficiency of their reprogramming to pluripotency. Cre-mediated inactivation of Med28 in induced pluripotent stem cells shows that Med28 is required for their survival. Intriguingly, heterozygous loss of Med28 results in differentiation of induced pluripotent stem cells into extraembryonic trophectoderm and primitive endoderm lineages. Our findings document the essential role of Med28 in the developing embryo as well as in acquisition and maintenance of pluripotency during reprogramming.

Involvement of Mediator complex in malignancy

Mediator complex (MED) is an evolutionarily conserved multiprotein, fundamental for growth and survival of all cells. In eukaryotes, the mRNA transcription is dependent on RNA polymerase II that is associated to various molecules like general transcription factors, MED subunits and chromatin regulators. To date, transcriptional machinery dysfunction has been shown to elicit broad effects on cell proliferation, development, differentiation, and pathologic disease induction, including cancer. Indeed, in malignant cells, the improper activation of specific genes is usually ascribed to aberrant transcription machinery. Here, we focus our attention on the correlation of MED subunits with carcinogenesis. To date, many subunits are mutated or display altered expression in human cancers. Particularly, the role of MED1, MED28, MED12, CDK8 and Cyclin C in cancer is well documented, although several studies have recently reported a possible association of other subunits with malignancy. Definitely, a major comprehension of the involvement of the whole complex in cancer may lead to the identification of MED subunits as novel diagnostic/prognostic tumour markers to be used in combination with imaging technique in clinical oncology, and to develop novel anti-cancer targets for molecular-targeted therapy.

Resveratrol modulates MED28 (Magicin/EG-1) expression and inhibits epidermal growth factor (EGF)-induced migration in MDA-MB-231 human breast cancer cells

Resveratrol and pterostilbene exhibit diverse biological activities. MED28, a subunit of the mammalian Mediator complex for transcription, was also identified as magicin, an actin cytoskeleton Grb2-associated protein, and as endothelial-derived gene (EG-1). Several tumors exhibit aberrant MED28 expression, whereas the underlying mechanism is unclear. Triple-negative breast cancers, often expressing epidermal growth factor (EGF) receptor (EGFR), are associated with metastasis and poor survival. The objective of this study is to compare the effect of resveratrol and pterostilbene and to investigate the role of MED28 in EGFR-overexpressing MDA-MB-231 breast cancer cells. Pretreatment of resveratrol, but not pterostlbene, suppressed EGF-mediated migration and expression of MED28 and matrix metalloproteinase (MMP)-9 in MDA-MB-231 cells. Moreover, overexpression of MED28 increased migration, and the addition of EGF further enhanced migration. Our data indicate that resveratrol modulates the effect of MED28 on cellular migration, presumably through the EGFR/phosphatidylinositol 3-kinase (PI3K) signaling pathway, in breast cancer cells.

Mediator and human disease

Since the identification of a metazoan counterpart to yeast Mediator nearly 15 years ago, a convergent body of biochemical and molecular genetic studies have confirmed their structural and functional relationship as an integrative hub through which regulatory information conveyed by signal activated transcription factors is transduced to RNA polymerase II. Nonetheless, metazoan Mediator complexes have been shaped during evolution by substantive diversification and expansion in both the number and sequence of their constituent subunits, with important implications for the development of multicellular organisms. The appearance of unique interaction surfaces within metazoan Mediator complexes for transcription factors of diverse species-specific origins extended the role of Mediator to include an essential function in coupling developmentally coded signals with precise gene expression output sufficient to specify cell fate and function. The biological significance of Mediator in human development, suggested by genetic studies in lower metazoans, is emphatically illustrated by an expanding list of human pathologies linked to genetic variation or aberrant expression of its individual subunits. Here, we review our current body of knowledge concerning associations between individual Mediator subunits and specific pathological disorders. When established, molecular etiologies underlying genotype-phenotype correlations are addressed, and we anticipate that future progress in this critical area will help identify therapeutic targets across a range of human pathologies.

Origins and activity of the Mediator complex

The Mediator is a large, multisubunit RNA polymerase II transcriptional regulator that was first identified in Saccharomyces cerevisiae as a factor required for responsiveness of Pol II and the general initiation factors to DNA binding transactivators. Since its discovery in yeast, Mediator has been shown to be an integral and highly evolutionarily conserved component of the Pol II transcriptional machinery with critical roles in multiple stages of transcription, from regulation of assembly of the Pol II initiation complex to regulation of Pol II elongation. Here we provide a brief overview of the evolutionary origins of Mediator, its subunit composition, and its remarkably diverse collection of activities in Pol II transcription.

Elevated MED28 expression predicts poor outcome in women with breast cancer

BACKGROUND

MED28 (also known as EG-1 and magicin) has been implicated in transcriptional control, signal regulation, and cell proliferation. MED28 has also been associated with tumor progression in in vitro and in vivo models. Here we examined the association of MED28 expression with human breast cancer progression.

METHODS

Expression of MED28 protein was determined on a population basis using a high-density tissue microarray consisting of 210 breast cancer patients. The association and validation of MED28 expression with histopathological subtypes, clinicopathological variables, and disease outcome was assessed.

RESULTS

MED28 protein expression levels were increased in ductal carcinoma in situ and invasive ductal carcinoma of the breast compared to non-malignant glandular and ductal epithelium. Moreover, MED28 was a predictor of disease outcome in both univariate and multivariate analyses with higher expression predicting a greater risk of disease-related death.

CONCLUSIONS

We have demonstrated that MED28 expression is increased in breast cancer. In addition, although the patient size was limited (88 individuals with survival information) MED28 is a novel and strong independent prognostic indicator of survival for breast cancer.

The merlin interacting proteins reveal multiple targets for NF2 therapy

The neurofibromatosis 2 (NF2) tumor suppressor protein merlin is commonly mutated in human benign brain tumors. The gene altered in NF2 was located on human chromosome 22q12 in 1993 and the encoded protein named merlin and schwannomin. Merlin has homology to ERM family proteins, ezrin, radixin, and moesin, within the protein 4.1 superfamily. In efforts to determine merlin function several groups have discovered 34 merlin interacting proteins, including ezrin, radixin, moesin, CD44, layilin, paxillin, actin, N-WASP, betaII-spectrin, microtubules, TRBP, eIF3c, PIKE, NHERF, MAP, RalGDS, RhoGDI, EG1/magicin, HEI10, HRS, syntenin, caspr/paranodin, DCC, NGB, CRM1/exportin, SCHIP1, MYPT-1-PP1delta, RIbeta, PKA, PAK (three types), calpain and Drosophila expanded. Many of the proteins that interact with the merlin N-terminal domain also bind ezrin, while other merlin interacting proteins do not bind other members of the ERM family. Merlin also interacts with itself. This review describes these proteins, their possible roles in NF2, and the resultant hypothesized merlin functions. Review of all of the merlin interacting proteins and functional consequences of losses of these interactions reveals multiple merlin actions in PI3-kinase, MAP kinase and small GTPase signaling pathways that might be targeted to inhibit the proliferation of NF2 tumors.

Mediator subunit MED28 (Magicin) is a repressor of smooth muscle cell differentiation

Magicin, a protein that we isolated earlier as an interactor of the neurofibromatosis 2 protein merlin, was independently identified as MED28, a subunit of the mammalian Mediator complex. Mediator complex is an evolutionarily conserved transcriptional cofactor, which plays an essential role in positive and negative gene regulation. Distinct Mediator subunit composition is thought to contribute to gene regulation specificity based on the interaction of specific subunits with subsets of transcription factors. Here we report that down-regulation of Med28 expression in NIH3T3 cells results in a significant induction of several genes associated with smooth muscle cell (SMC) differentiation. Conversely, overexpression of MED28 represses expression of SMC genes, in concordance with our knockdown data. More importantly, multipotent mesenchymal-derived murine precursors can transdifferentiate into SMCs when Med28 is down-regulated. Our data also show that Med28 functions as a negative regulator of SMC differentiation in concert with other Mediator subunits including Med6, Med8, and Med18 within the Mediator head module. Our results provide strong evidence that MED28 may function as a scaffolding protein by maintaining the stability of a submodule within the head module and that components of this submodule act together in a gene regulatory program to suppress SMC differentiation. The results presented here demonstrate for the first time that the mammalian Mediator subunit MED28 functions as a repressor of SMC differentiation, which could have implications for disorders associated with abnormalities in SMC growth and differentiation, including atherosclerosis, asthma, hypertension, and smooth muscle tumors.

Magicin associates with the Src-family kinases and is phosphorylated upon CD3 stimulation

We recently identified a novel actin cytoskeleton-associated protein magicin, for merlin and Grb2 interacting cytoskeletal protein. To unravel the cellular functions of magicin, we used a yeast two-hybrid system and identified Fyn tyrosine kinase as a specific binding partner for magicin. Fyn phosphorylates magicin in vitro. In addition to Fyn, Src and Lck also interact with magicin. Upon stimulation with anti-CD3 antibody, magicin is phosphorylated in the T lymphocyte leukemia Jurkat cell line. Magicin phosphorylation is not observed in an Lck-deficient line, J.CaM1.6, indicating that Lck is the major Src family kinase for phosphorylating magicin in Jurkat cells. Employing site-directed mutagenesis along with in vitro kinase assays, we found that Y64 of magicin is phosphorylated by Lck creating a SH2-Grb2 binding motif. Magicin has also been identified as a Mediator subunit (MED28) in the nucleus involved in transcriptional regulation, therefore we propose that magicin may serve as a multi-faceted adaptor/scaffold to relay cellular signaling to the cytoskeleton and from the cytoskeleton to the nucleus.

The novel gene EG-1 stimulates cellular proliferation

We recently discovered a novel gene and named it endothelial-derived gene 1 (EG-1). Previously, we have shown that the expression of EG-1 is significantly elevated in the epithelial cells of breast cancer, colorectal cancer, and prostate cancer. Here, we report that EG-1 can stimulate cellular proliferation. Transfection experiments which overexpressed the full-length EG-1 gene in human embryonic kidney HEK-293 cells or human breast cancer cell lines resulted in significantly increased in vitro proliferation, in comparison with transfection with empty vectors. On the other hand, small interfering RNA cotransfection resulted in inhibition of proliferation. S.c. xenograft assays were carried out in a severe combined immunodeficient mouse model. We found that injection of high EG-1 expressing HEK-293 clones resulted in significantly larger tumors, in comparison with clones carrying the empty vectors. To further clarify the function of this gene, we investigated its interaction with Src and members of the mitogen-activated protein kinase (MAPK) family. Immunoprecipitation with anti-Src antibody, followed by immunoblotting with anti-EG-1 antibody, showed an association between these two molecules. Overexpression of EG-1 was correlated with activation of the following kinases: extracellular signal-regulated kinases 1 and 2, c-jun-NH2-kinase, and p38. These observations collectively support the hypothesis that the novel gene EG-1 is a positive stimulator of cellular proliferation, and may possibly be involved in signaling pathways involving Src and MAPK activation.