Oncogene database

92140

MTDH

metadherin;MTDH;metadherin

3D3/LYRIC|astrocyte elevated gene 1|astrocyte elevated gene-1 protein|lysine-rich CEACAM1 co-isolated protein|metastasis adhesion protein|protein LYRIC

8q22.1

protein-coding

Astrocyte elevated gene-1 (AEG-1) displays oncogenic properties. Its expression is elevated in diverse neoplastic states and it cooperates with Ha-ras to promote cellular transformation. Overexpression of AEG-1 augments invasion and anchorage-independent growth of transformed cells, while AEG-1 siRNA inhibits Ha-ras-mediated colony formation, supporting a potential functional role in tumorigenesis. Additionally, oncogenic Ha-ras induces AEG-1 expression through the phosphatidylinositol 3-kinase (PI3K)-Akt signaling pathway. In the present study, we investigated whether AEG-1 could induce serum-independent cell growth, another property of oncogenes. Overexpression of AEG-1 inhibited serum starvation-induced apoptosis through activation of PI3K-Akt signaling, one of the effector pathways induced by activated Ras. AEG-1 also affected the phosphorylation state of Akt substrates that are implicated in apoptosis suppression, including glycogen synthase kinase 3beta, c-Myc, murine double minute 2, p53, p21/mda-6 and Bad. Additionally, AEG-1 blocked the activity of serum starvation-induced caspases. Taken together, these observations provide evidence that AEG-1 is an oncogene cooperating with Ha-ras as well as functioning as a downstream target gene of Ha-ras and may perform a central role in Ha-ras-mediated carcinogenesis. Activation of survival pathways may be one mechanism by which AEG-1 exerts its oncogenic properties.

Astrocyte-elevated gene-1 (AEG-1) expression is increased in multiple cancers and plays a central role in Ha-ras-mediated oncogenesis through the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. Additionally, overexpression of AEG-1 protects primary and transformed human and rat cells from serum starvation-induced apoptosis through activation of PI3K/Akt signaling. These findings suggest, but do not prove, that AEG-1 may function as an oncogene. We now provide definitive evidence that AEG-1 is indeed a transforming oncogene and show that stable expression of AEG-1 in normal immortal cloned rat embryo fibroblast (CREF) cells induces morphological transformation and enhances invasion and anchorage-independent growth in soft agar, two fundamental biological events associated with cellular transformation. Additionally, AEG-1-expressing CREF clones form aggressive tumors in nude mice. Immunohistochemistry analysis of tumor sections demonstrates that AEG-1-expressing tumors have increased microvessel density throughout the entire tumor sections. Overexpression of AEG-1 increases expression of molecular markers of angiogenesis, including angiopoietin-1, matrix metalloprotease-2, and hypoxia-inducible factor 1-alpha. In vitro angiogenesis studies further demonstrate that AEG-1 promotes tube formation in Matrigel and increases invasion of human umbilical vein endothelial cells via the PI3K/Akt signaling pathway. Tube formation induced by AEG-1 correlates with increased expression of angiogenesis markers, including Tie2 and hypoxia-inducible factor-alpha, and blocking AEG-1-induced Tie2 with Tie2 siRNA significantly inhibits AEG-1-induced tube formation in Matrigel. Overall, our findings demonstrate that aberrant AEG-1 expression plays a dominant positive role in regulating oncogenic transformation and angiogenesis. These findings suggest that AEG-1 may provide a viable target for directly suppressing the cancer phenotype.

Our microRNA (miRNA) expression signatures of hypopharyngeal squamous cell carcinoma, maxillary sinus squamous cell carcinoma and esophageal squamous cell carcinoma revealed that miR-375 was significantly reduced in cancer tissues compared with normal epithelium. In this study, we focused on the functional significance of miR-375 in cancer cells and identification of miR-375-regulated novel cancer networks in head and neck squamous cell carcinoma (HNSCC). Restoration of miR-375 showed significant inhibition of cell proliferation and induction of cell apoptosis in SAS and FaDu cell lines, suggesting that miR-375 functions as a tumor suppressor. We adopted genome-wide gene expression analysis to search for miR-375-regulated molecular targets. Gene expression data and luciferase reporter assays revealed that AEG-1/MTDH was directly regulated by miR-375. cancer cell proliferation was significantly inhibited in HNSCC cells transfected with si-AEG-1/MTDH. In addition, expression levels of AEG-1/MTDH were significantly upregulated in cancer tissues. Therefore, AEG-1/MTDH may function as an oncogene in HNSCC. The identification of novel tumor suppressive miRNA and its regulated cancer pathways could provide new insights into potential molecular mechanisms of HNSCC oncogenesis.

Aggressive tumor growth, diffuse tissue invasion, and neurodegeneration are hallmarks of malignant glioma. Although glutamate excitotoxicity is considered to play a key role in glioma-induced neurodegeneration, the mechanism(s) controlling this process is poorly understood. Astrocyte elevated gene-1 (AEG-1) is an oncogene that is overexpressed in several types of human cancers, including more than 90% of brain tumors. In addition, AEG-1 promotes gliomagenesis, particularly in the context of tumor growth and invasion, 2 primary characteristics of glioma. In the present study, we investigated the contribution of AEG-1 to glioma-induced neurodegeneration. Pearson correlation coefficient analysis in normal brain tissues and samples from glioma patients indicated a strong negative correlation between expression of AEG-1 and a primary glutamate transporter of astrocytes EAAT2. Gain- and loss-of-function studies in normal primary human fetal astrocytes and T98G glioblastoma multiforme cells revealed that AEG-1 repressed EAAT2 expression at a transcriptional level by inducing YY1 activity to inhibit CBP function as a coactivator on the EAAT2 promoter. In addition, AEG-1-mediated EAAT2 repression caused a reduction of glutamate uptake by glial cells, resulting in induction of neuronal cell death. These findings were also confirmed in samples from glioma patients showing that AEG-1 expression negatively correlated with NeuN expression. Taken together, our findings suggest that AEG-1 contributes to glioma-induced neurodegeneration, a hallmark of this fatal tumor, through regulation of EAAT2 expression.

Metadherin (MTDH), the newly discovered gene, is overexpressed in more than 40% of breast cancers. Recent studies have revealed that MTDH favors an oncogenic course and chemoresistance. With a number of breast cancer cell lines and breast tumor samples, we found that the relative expression of MTDH correlated with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) sensitivity in breast cancer. In this study, we found that knockdown of endogenous MTDH cells sensitized the MDA-MB-231 cells to TRAIL-induced apoptosis both in vitro and in vivo. Conversely, stable overexpression of MTDH in MCF-7 cells enhanced cell survival with TRAIL treatment. Mechanically, MTDH down-regulated caspase-8, decreased caspase-8 recruitment into the TRAIL death-inducing signaling complex, decreased caspase-3 and poly(ADP-ribose) polymerase-2 processing, increased Bcl-2 expression, and stimulated TRAIL-induced Akt phosphorylation, without altering death receptor status. In MDA-MB-231 breast cancer cells, sensitization to TRAIL upon MTDH down-regulation was inhibited by the caspase inhibitor Z-VAD-fmk (benzyloxycarbonyl-VAD-fluoromethyl ketone), suggesting that MTDH depletion stimulates activation of caspases. In MCF-7 breast cancer cells, resistance to TRAIL upon MTDH overexpression was abrogated by depletion of Bcl-2, suggesting that MTDH-induced Bcl-2 expression contributes to TRAIL resistance. We further confirmed that MTDH may control Bcl-2 expression partly by suppressing miR-16. Collectively, our results point to a protective function of MTDH against TRAIL-induced death, whereby it inhibits the intrinsic apoptosis pathway through miR-16-mediated Bcl-2 up-regulation and the extrinsic apoptosis pathway through caspase-8 down-regulation.

MicroRNAs (miRNAs) play critical roles in tumorigenesis by modulating the expression of target gene mRNAs. However, their role in cell signaling is not well defined. In this study, we identified miR-30d as a downstream effector of the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway in renal cell carcinoma (RCC) cells. We show that Akt inhibition transcriptionally up-regulates miR-30d expression through activation of the transcription factor forkhead box O (FOXO) 3A. Functional analysis revealed that miR-30d overexpression suppresses cell proliferation and induces apoptosis in RCC cells, suggesting that miR-30d acts as a tumor suppressor. In searching for downstream targets of miR-30d, we found that miR-30d post-transcriptionally suppresses expression of the oncoprotein metadherin (MTDH) by destabilizing its mRNA. Furthermore, we found that FOXO down-regulates MTDH expression through up-regulating expression of miR-30d. Thus, our findings reveal a new Akt/FOXO/miR-30d/MTDH signaling transduction pathway and identify miR-30d as a tumor suppressor, providing a new potential target for the treatment of RCC.

The pivotal role of LYRIC/AEG-1 in malignant transformation, tumourigenesis and chemo-resistance has previously been demonstrated in different cell types and sub-cellular compartments. The localisation of LYRIC/AEG-1 appears crucial to its function and is regulated by three lysine-rich nuclear localisation signal regions, one of which was previously demonstrated to be modified by ubiquitin. Here we show that mutation of LYRIC/AEG-1 at K486 and K491 results in a loss of ubiquitination. A K486/491R double mutant that is incapable of ubiquitination shows reduced binding to the NFkappaB subunit p65 or importin-beta resulting in a distinctive peri-nuclear localisation of LYRIC/AEG-1. We also provide evidence to suggest that TOPORS, an E3 ligase that also regulates p53 modification may be responsible for LYRIC/AEG-1 ubiquitin modification. Overall we demonstrate that specific sites of LYRIC/AEG-1 ubiquitination are essential for regulating LYRIC/AEG-1 localisation and functionally interacting proteins.

The Metadherin gene (MTDH) is prevalently amplified in breast cancer and associated with poor prognosis; however, its functional contribution to tumorigenesis is poorly understood. Using mouse models representing different subtypes of breast cancer, we demonstrated that MTDH plays a critical role in mammary tumorigenesis by regulating oncogene-induced expansion and activities of tumor-initiating cells (TICs), whereas it is largely dispensable for normal development. Mechanistically, MTDH supports the survival of mammary epithelial cells under oncogenic/stress conditions by interacting with and stabilizing Staphylococcal nuclease domain-containing 1 (SND1). Silencing MTDH or SND1 individually or disrupting their interaction compromises tumorigenenic potential of TICs in vivo. This functional significance of MTDH-SND1 interaction is further supported by clinical analysis of human breast cancer samples.

The hepatitis B viral X protein (HBx) has been established to implicate in the development of HBV-related hepatocellular carcinoma (HCC) via multiple pathways. The oncoprotein astrocyte elevated gene-1 (AEG-1) is overexpressed in various tumors, including HCC, and plays critical roles in promoting cell migration and invasion. However, the mechanisms for AEG-1 upregulation in tumors are largely unknown. In this study, we found that HBx could elevate AEG-1 protein level without altering its mRNA level. When blocking AEG-1 expression with siRNA in HBx-transfected cells, the HBx-induced cell migration was significantly suppressed. Further study indicated that miR-375 and miR-136 that targeted AEG-1 were downregulated with HBx expression. Overexpressing miR-375 and miR-136 could effectively attenuate HBx-mediated AEG-1 elevation and cell migration. These results demonstrated that HBx enabled to increase oncoprotein AEG-1 expression to promote cell migration via downregulating miR-375 and miR-136. Our findings provide a novel insight into AEG-1 upregulation in HCC and shed new light on HBx promoting HCC progression. Meanwhile, our results also suggest that miR-375 and miR-136 may have the miRNA-based therapeutic potential in HBV-associated HCC.

MicroRNAs (miRNAs) have been suggested to play critical roles in tumorigenesis as well as in the development of therapies for the treatment of cancers. However, the tumor-associated miRNAs in gastric cancers remain poorly understood. Here, we report on miR-542-3p in gastric cancers, which has been widely studied in other cancers as a tumor suppressor. Real-time quantitative PCR analysis demonstrated that miR-542-3p was significantly down-regulated in gastric cancer tissues (p < 0.0001) and cell lines (p < 0.001). Overexpression of miR-542-3p significantly inhibited cell growth of gastric cancer cells both in vitro (p < 0.01) and in vivo (p < 0.01). Notably, overexpression of miR-542-3p apparently reduced the protein expression of astrocyte-elevated gene-1 (AEG-1) (p < 0.01). The dual-luciferase reporter assay validated that miR-542-3p directly bound the 3 -untranslated region (UTR) of AEG-1, which could be abolished by mutation of the predicted miR-542-3p binding site. Furthermore, overexpression of miR-542-3p markedly inhibited the activation of oncogenic signaling pathways including the Akt, beta-catenin and nuclear factor-kappaB pathways. Additionally, overexpression of AEG-1 without the 3 -UTR partially reversed the cell growth arrest induced by miR-542-3p overexpression in gastric cancer cells (p < 0.05). Taken together, these data suggest that miR-542-3p might function as a tumor suppressor in gastric cancer, potentially by targeting the oncogene AEG-1, implying a potential role for miR-542-3p in the development of therapeutic methods for gastric cancer.