Astrocyte elevated gene-1 (AEG-1) is a target gene of oncogenic Ha-ras requiring phosphatidylinositol 3-kinase and c-Myc

Astrocytic AEG-1 drives neuroinflammation and enhances seizure susceptibility

Astrocyte-elevated gene-1 (AEG-1), also known as metadherin (MTDH) has emerged as a potent oncogene expressed in cancers. An increasing body of evidence indicates AEG-1 plays a pivotal role in various brain pathophysiological processes. Abnormal expression of AEG-1 in astrocytes has been correlated with inflammatory response, suggesting a possible role of AEG-1 in the pathogenesis of inflammatory encephalopathy. Here, we analyzed single-cell RNA sequencing data to explore the heterogeneity of astrocyte subpopulations in a mouse model induced by lipopolysaccharide (LPS), and investigated the effect of astrocytic AEG-1 on lipopolysaccharide (LPS)-induced inflammatory response and seizure susceptibility in mice, as well as in an in vitro astrocyte culture model. Our single-cell RNA sequencing analysis reveals that AEG-1-expressing astrocyte subpopulation is associated with inflammatory responses. LPS-induced inflammatory response is accompanied by increased AEG-1 expression in astrocytes. Depletion of astrocytic AEG-1, however, suppressed LPS-induced neuroinflammation and high seizure susceptibility both in vivo and in vitro. Furthermore, we find that AEG-1 induces neuroinflammatory cytokine expression and enhances seizure susceptibility, which is dependent on NF-κB signaling pathway. These data identify an important role of astrocytic AEG-1 in LPS-induced neuroinflammation and high seizure susceptibility, demonstrating that AEG-1 mediates downstream neuroinflammatory and epileptic effect via NF-κB signaling pathway.

Astrocyte Elevated Gene-1/Metadherin (AEG-1/MTDH): A Promising Molecular Marker and Therapeutic Target for Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related deaths. The 5-year survival rate has been estimated to be less than 20% while its incidence rates have more than tripled since the 1980s. Astrocyte elevated gene-1/Metadherin (AEG-1/MTDH) has been demonstrated to have an influential role in HCC progression and the development of an aggressive phenotype. AEG-1 has been shown to be upregulated in many cancers, including HCC. Studies have shown that it plays a crucial role in the proliferation, invasion and metastasis, and evasion of apoptosis in HCC. Its relationship with proteins and pathways, such as MYC, SND1, PI3K/AKT, and other signaling pathways demonstrates its pertinent role in oncogenic development and relevance as a biomarker and therapeutic target. Recent studies have shown that AEG-1 is present in tumor tissues, and the anti-AEG-1 antibody is detected in the blood of cancer patients, demonstrating its viability as a diagnostic/prognostic marker. This review paper shines light on recent findings regarding the molecular implications of AEG-1, with emphasis on its role of regulating metabolic dysfunction-associated steatohepatitis (MASH), a key predisposing factor for HCC, new treatment strategies targeting AEG-1, and challenges associated with analyzing this intriguing molecule.

Discovery of Novel Small-Molecule Inhibitors Disrupting the MTDH-SND1 Protein-Protein Interaction

MTDH-SND1 protein-protein interaction (PPI) plays an important role in the initiation and development of tumors, and it is a target for the treatment of breast cancer. In this study, we identified and synthesized a series of novel small-molecule inhibitors of MTDH-SND1 PPI. The representative compound C19 showed potent activity against MTDH-SND1 PPI with an IC50 of 487 ± 99 nM and tight binding to the SND1-purified protein with a Kd value of 279 ± 17 nM. Compound C19 significantly degraded SND1 and downregulated downstream at the protein level. Further biological evaluations suggested that compound C19 exhibited potent activity against the proliferation of breast cancer MCF-7 cells with an IC50 value of 626 ± 27 nM, significantly inhibited invasion and migration, and induced cell apoptosis. In addition, compound C19 exhibited promising tumor growth inhibition in the xenograft model. Our study provides a potential candidate targeting MTDH-SND1 PPI for the treatment of breast cancer.

Metadherin orchestrates PKA and PKM2 to activate β-catenin signaling in podocytes during proteinuric chronic kidney disease

Podocyte damage is the major cause of glomerular injury and proteinuria in multiple chronic kidney diseases. Metadherin (MTDH) is involved in podocyte apoptosis and promotes renal tubular injury in mouse models of diabetic nephropathy and renal fibrosis; however, its role in podocyte injury and proteinuria needs further exploration. Here, we show that MTDH was induced in the glomerular podocytes of patients with proteinuric chronic kidney disease and correlated with proteinuria. Podocyte-specific knockout of MTDH in mice reversed proteinuria, attenuated podocyte injury, and prevented glomerulosclerosis after advanced oxidation protein products challenge or adriamycin injury. Furthermore, specific knockout of MTDH in podocytes repressed β-catenin phosphorylation at the Ser675 site and inhibited its downstream target gene transcription. Mechanistically, on the one hand, MTDH increased cAMP and then activated protein kinase A (PKA) to induce β-catenin phosphorylation at the Ser675 site, facilitating the nuclear translocation of MTDH and β-catenin; on the other hand, MTDH induced the deaggregation of pyruvate kinase M2 (PKM2) tetramers and promoted PKM2 monomers to enter the nucleus. This cascade of events leads to the formation of the MTDH/PKM2/β-catenin/CBP/TCF4 transcription complex, thus triggering TCF4-dependent gene transcription. Inhibition of PKA activity by H-89 or blockade of PKM2 deaggregation by TEPP-46 abolished this cascade of events and disrupted transcription complex formation. These results suggest that MTDH induces podocyte injury and proteinuria by assembling the β-catenin-mediated transcription complex by regulating PKA and PKM2 function.

Metadherin inhibits chemosensitivity of triple-negative breast cancer to paclitaxel via activation of AKT/GSK-3β signaling pathway

Triple-negative breast cancer (TNBC) has an aggressive clinical course, and paclitaxel (PTX)-based chemotherapy remains the main therapeutic drug. Metadherin (MTDH) acts as an oncogene that regulates proliferation, invasion, metastasis, and chemoresistance. This study aimed to investigate whether TNBC chemosensitivity to PTX was related to the MTDH/AKT/glycogen synthase kinase-3beta (GSK-3β) pathway. Clinical baseline characteristics and immunohistochemistry (IHC) were used to evaluate the expression and prognosis of MTDH and AKT (protein kinase B, PKB) in TNBC patient samples. MTDH shRNA, MTDH overexpression vector, MK-2206, and PTX intervention were used in cell models and mouse tumor-bearing models. Afterwards, mRNA and protein levels were assessed using quantitative real-time polymerase chain reaction and Western blot. Evaluate the level of tumor cell apoptosis and cell cycle using flow cytometry. Cell viability was detected using Cell Count Kit 8. The in vivo imaging system is used to analyze the growth of tumors. We found that higher expression of MTDH or AKT resulted in poorer disease-free survival and a lower Miller-Payne grade. MTDH promotes cell proliferation and increases p-AKT and p-GSK-3β expression in TNBC cells. Notably, suppression of AKT terminated MTDH overexpression-induced cell proliferation and apoptosis. MTDH knockdown or the AKT inhibitor MK2206 reduced the p-AKT and p-GSK-3β ratio, reduced cell viability and proliferation, increased cell apoptosis, and increased chemosensitivity to PTX. In vivo, xenograft tumors of an MTDH knockdown+MK2206 group treated with PTX were the smallest compared to other groups. In short, MTDH inhibits TNBC chemosensitivity to PTX by activating the AKT/GSK-3β signaling pathway.

AEG-1 as a Novel Therapeutic Target in Colon Cancer: A Study from Silencing AEG-1 in BALB/c Mice to Large Data Analysis

BACKGROUND

Astrocyte elevated gene-1 (AEG-1) is overexpressed in various malignancies. Exostosin-1 (EXT-1), a tumor suppressor, is an intermediate for malignant tumors. Understanding the mechanism behind the interaction between AEG-1 and EXT-1 may provide insights into colon cancer metastasis.

METHODS

AOM/DSS was used to induce tumor in BALB/c mice. Using an in vivo-jetPEI transfection reagent, transient transfection of AEG-1 and EXT-1 siRNAs were achieved. Histological scoring, immunohistochemical staining, and gene expression studies were performed from excised tissues. Data from the Cancer Genomic Atlas and GEO databases were obtained to identify the expression status of AEG-1 and itsassociation with the survival.

RESULTS

In BALB/c mice, the AOM+DSS treated mice developed necrotic, inflammatory and dysplastic changes in the colon with definite clinical symptoms such as loss of goblet cells, colon shortening, and collagen deposition. Administration of AEG-1 siRNA resulted in a substantial decrease in the disease activity index. Mice treated with EXT-1 siRNA showed diffusely reduced goblet cells. In vivo investigations revealed that PTCH-1 activity was influenced by upstream gene AEG-1, which in turn may affect EXT-1 activity. Data from The Cancer Genomic Atlas and GEO databases confirmed the upregulation of AEG-1 and downregulation of EXT-1 in cancer patients.

CONCLUSIONS

This study revealed that AEG-1 silencing might alter EXT-1 expression indirectly through PTCH-1, influencing cell-ECM interactions, and decreasing dysplastic changes, proliferation and invasion.

Using the metabolite alterations monitoring the AEG-1 expression level and cell biological behaviour of U251 cell in vitro

Astrocyte elevated gene-1 (AEG-1) is an important oncogene that overexpresses in gliomas and plays a vital role in their occurrence and progression. However, few reports have shown which biomarkers could reflect the level of AEG-1 expression in vivo so far. In recent years, intracellular metabolites monitored by proton magnetic resonance spectroscopy (1H MRS) as non-invasive imaging biomarkers have been applied to the precise diagnosis and therapy feedback of gliomas. Therefore, understanding the correlation between 1H MRS metabolites and AEG-1 gene expression in U251 cells may help to identify relevant biomarkers. This study constructed three monoclonal AEG-1-knockout U251 cell lines using the clustered regularly interspaced short palindromic repeat (CRISPR) /Cas9 technique and evaluated the biological behaviors and metabolite ratios of these cell lines. With the decline in AEG-1 expression, the apoptosis rate of the AEG-1-knockout cell lines increased. At the same time, the metastatic capacities decreased, and the relative contents of total choline (tCho) and lactate (Lac) were also reduced. In conclusion, deviations in AEG-1 expression influence the apoptosis rate and metastasis capacity of U251 cells, which the 1H MRS metabolite ratio could monitor. The tCho/creatinine(Cr) and Lac/Cr ratios positively correlated with the AEG-1 expression and malignant cell behavior. This study may provide potential biomarkers for accurate preoperative diagnosis and future AEG-1-targeting treatment evaluation of gliomas in vivo.

Expression patterns of AEG-1 in the normal brain

Astrocyte elevated gene-1 (AEG-1) is a well-known oncogene implicated in various types of human cancers, including brain tumors. Recently, AEG-1 has also been reported to play pivotal roles in glioma-associated neurodegeneration and neurodegenerative diseases like Parkinson's disease and amyotrophic lateral sclerosis. However, the normal physiological functions and expression patterns of AEG-1 in the brain are not well understood. In this study, we investigated the expression patterns of AEG-1 in the normal mouse brain and found that AEG-1 is widely expressed in neurons and neuronal precursor cells, but little in glial cells. We observed differential expression levels of AEG-1 in various brain regions, and its expression was mainly localized in the cell body of neurons rather than the nucleus. Additionally, AEG-1 was expressed in the cytoplasm of Purkinje cells in both the mouse and human cerebellum, suggesting its potential role in this brain region. These findings suggest that AEG-1 may have important functions in normal brain physiology and warrant further investigation. Our results may also shed light on the differential expression patterns of AEG-1 in normal and pathological brains, providing insights into its roles in various neurological disorders.

Metadherin Regulates Inflammatory Breast Cancer Invasion and Metastasis

Inflammatory breast cancer (IBC) is one of the most lethal subtypes of breast cancer (BC), accounting for approximately 1-5% of all cases of BC. Challenges in IBC include accurate and early diagnosis and the development of effective targeted therapies. Our previous studies identified the overexpression of metadherin (MTDH) in the plasma membrane of IBC cells, further confirmed in patient tissues. MTDH has been found to play a role in signaling pathways related to cancer. However, its mechanism of action in the progression of IBC remains unknown. To evaluate the function of MTDH, SUM-149 and SUM-190 IBC cells were edited with CRISPR/Cas9 vectors for in vitro characterization studies and used in mouse IBC xenografts. Our results demonstrate that the absence of MTDH significantly reduces IBC cell migration, proliferation, tumor spheroid formation, and the expression of NF-κB and STAT3 signaling molecules, which are crucial oncogenic pathways in IBC. Furthermore, IBC xenografts showed significant differences in tumor growth patterns, and lung tissue revealed epithelial-like cells in 43% of wild-type (WT) compared to 29% of CRISPR xenografts. Our study emphasizes the role of MTDH as a potential therapeutic target for the progression of IBC.

DOT1L regulates MTDH-mediated angiogenesis in triple-negative breast cancer: intermediacy of NF-κB-HIF1α axis

DOT1L, a specific H3K79 methyltransferase, has a tumour-promoting role in various cancers, including triple-negative breast cancer (TNBC). However, the molecular mechanism by which the deregulated DOT1L promotes cancer progression is unclear. Herein, we show that a significantly higher basal level of DOTL1 strongly correlates with MTDH, an oncogene, in clinical TNBC patient cohorts and mediates TNBC progression by enhancing MTDH-induced angiogenesis. In parallel, severe combined immunodeficiency mice-bearing MDA-MB-231 cells with MTDH-Wt or MTDHΔ7 (spliced isoform of MTDH) overexpression constructs showed enhanced blood vessel formations at the tumour site in comparison with control groups. Selective inhibition of DOT1L by EPZ004777, a specific DOT1L inhibitor, or siDOT1L, significantly impaired MTDH-induced proliferation, invasion and angiogenic markers expression in TNBC cells. ChIP assay revealed that Dot1L promotes MTDH-Wt/Δ7 transcription by increasing H3K79me3 levels on its promoter. Dot1L depletion reversed this effect. Mechanistically, DOT1L-induced MTDH caused enhanced nuclear factor kappa B (NF-κB) occupancy on the hypoxia-inducible factor1α (HIF1α) promoter and increased its transcription, leading to elevated levels of proangiogenic mediators in TNBC cells. Moreover, the condition media obtained from MDA-MB-231 cells stably expressing either MTDH-Wt or MTDHΔ7 treated with EPZ004777 or Bay-11-7082 (NF-κB inhibitor) or FM19G11 (HIF1α inhibitor) significantly inhibited MTDH-induced tube formation in human umbilical vein endothelial cells, rat aortic ring sprouting and vessel formations by chick chorioallantoic membrane assay mimicking physiological angiogenic vasculature. Collectively, our findings reveal a novel epigenetic regulation of MTDH by DOTL1, which drives angiogenesis, and that the therapeutic disruption of the DOT1L-MTDH-NF-κB-HIF1α axis may have usefulness in the management of TNBC.

The absence of cellular glucose triggers oncogene AEG-1 that instigates VEGFC in HCC: A possible genetic root cause of angiogenesis

BACKGROUND AND OBJECTIVE

Astrocyte Elevated Gene-1 (AEG-1) is the master and multi-regulator of the various transcriptional factor primarily regulating chemoresistance, angiogenesis, metastasis, and invasion under the pathological condition, including liver cancer. This study was focused on investigating the process of tumor angiogenesis in liver carcinoma by studying the role of AEG-1 under GD/2DG conditions.

METHOD AND RESULTS

The PCR and western blot analysis revealed that glucose depletion (GD) induces the overexpression of AEG-1. Further, it leads to the constant expression of VEGFC through the activation of HIF-1α/CCR7 via the stimulations of PI3K/Akt signaling pathways. GLUT2 is the major transporter of a glucose molecule that is highly participating under GD through the expression of AEG-1 and constantly expresses glucokinase (GCK). The obtained data suggest that AEG-1 act as an angiogenesis and glycolysis regulator by modulating the expression of GCK through HIF-1α and GLUT2. 2-deoxy-D-glucose (2DG) is a glycolysis inhibitor that induces impaired glycolysis and cellular apoptosis by cellular oxidative stress. The administration of 2DG has led to the chemoresistance of AEG-1.

CONCLUSION

The total findings of the study judged that disruption of cellular energy metabolism induced by the absence of glucose or the presence of mutant glucose moiety (2DG) promotes the overexpression of AEG-1. The GD/2DG activates the VEGFC by inducing the HIF-1α and CCR7. Moreover, AEG-1 induces the expression of OPN, which regulates metastasis, angiogenesis, and actively participates in protective autophagy by promoting LC3 a/b.

Metadherin-mediated mechanisms in human malignancies

Metadherin (MTDH) has been recognized as a novel protein that is critical for the progression of multiple types of human malignancies. Studies have reported that MTDH enhances the metastatic potential of cancer cells by regulating multiple signaling pathways. miRNAs and various tumor-related proteins have been shown to interact with MTDH, making it a potential therapeutic target as well as a biomarker in human malignancies. MTDH plays a critical role in inflammation, angiogenesis, hypoxia, epithelial-mesenchymal transition and autophagy. In this review, we present the function and mechanisms of MTDH for cancer initiation and progression.

Expression of astrocyte-elevated gene-1 indicates prognostic value of fluoropyrimidine-based adjuvant chemotherapy in resectable stage III colorectal cancer

It is unclear which prognostic factor such as pathological features and gene mutation are majorly relevant for stage III disease and whether they aid in determining patients who will be benefit from postoperative adjuvant chemotherapy. The expression of astrocyte-elevated gene-1 (AEG-1), thymidylate synthase (TS), excision repair cross-complementation group 1 (ERCC1), epidermal growth factor receptor (EGFR), and vascular endothelial growth factor (VEGF) was examined to investigate their role in adjuvant chemotherapy for patients with resectable stage III colorectal cancer (CRC). A significant positive correlation was observed between AEG-1, TS, ERCC1, EGFR, and VEGF gene expression levels in CRC cell lines, and low AEG-1 and TS expression were highly sensitive to 5-fluorouracil treatment. Our results showed that AEG-1 expression was high in T4 and caused CRC recurrence or metastasis. Patients with T4, high AEG-1, TS and VEGF expression had a significantly short disease-free survival and overall survival. In multivariate Cox regression analysis, high AEG-1 expression could be an independent prognostic factor indicating poor survival in patients with resectable stage III CRC treated with adjuvant chemotherapy. In conclusion, AEG-1 expression and tumor grade are potential prognostic factors for recurrence and survival in patients with stage III CRC receiving adjuvant fluoropyrimidine-based chemotherapy.

Astrocyte elevated gene-1 (AEG-1): A key driver of hepatocellular carcinoma (HCC)

An array of human cancers, including hepatocellular carcinoma (HCC), overexpress the oncogene Astrocyte elevated gene-1 (AEG-1). It is now firmly established that AEG-1 is a key driver of carcinogenesis, and enhanced expression of AEG-1 is a marker of poor prognosis in cancer patients. In-depth studies have revealed that AEG-1 positively regulates different hallmarks of HCC progression including growth and proliferation, angiogenesis, invasion, migration, metastasis and resistance to therapeutic intervention. By interacting with a plethora of proteins as well as mRNAs, AEG-1 regulates gene expression at transcriptional, post-transcriptional, and translational levels, and modulates numerous pro-tumorigenic and tumor-suppressive signal transduction pathways. Even though extensive research over the last two decades using various in vitro and in vivo models has established the pivotal role of AEG-1 in HCC, effective targeting of AEG-1 as a therapeutic intervention for HCC is yet to be achieved in the clinic. Targeted delivery of AEG-1 small interfering ribonucleic acid (siRNA) has demonstrated desired therapeutic effects in mouse models of HCC. Peptidomimetic inhibitors based on protein-protein interaction studies has also been developed recently. Continuous unraveling of novel mechanisms in the regulation of HCC by AEG-1 will generate valuable knowledge facilitating development of specific AEG-1 inhibitory strategies. The present review describes the current status of AEG-1 in HCC gleaned from patient-focused and bench-top studies as well as transgenic and knockout mouse models. We also address the challenges that need to be overcome and discuss future perspectives on this exciting molecule to transform it from bench to bedside.

Emerging Role and Clinicopathological Significance of AEG-1 in Different Cancer Types: A Concise Review

Tumor breakthrough is driven by genetic or epigenetic variations which assist in initiation, migration, invasion and metastasis of tumors. Astrocyte elevated gene-1 (AEG-1) protein has risen recently as the crucial factor in malignancies and plays a potential role in diverse complex oncogenic signaling cascades. AEG-1 has multiple roles in tumor growth and development and is found to be involved in various signaling pathways of: (i) Ha-ras and PI3K/AKT; (ii) the NF-κB; (iii) the ERK or mitogen-activated protein kinase and Wnt or β-catenin and (iv) the Aurora-A kinase. Recent studies have confirmed that in all the hallmarks of cancers, AEG-1 plays a key functionality including progression, transformation, sustained angiogenesis, evading apoptosis, and invasion and metastasis. Clinical studies have supported that AEG-1 is actively intricated in tumor growth and progression which includes esophageal squamous cell, gastric, colorectal, hepatocellular, gallbladder, breast, prostate and non-small cell lung cancers, as well as renal cell carcinomas, melanoma, glioma, neuroblastoma and osteosarcoma. Existing studies have reported that AEG-1 expression has been induced by Ha-ras through intrication of PI3K/AKT signaling. Conversely, AEG-1 also activates PI3K/AKT pathway and modulates the defined subset of downstream target proteins via crosstalk between the PI3K/AKT/mTOR and Hedgehog signaling cascade which further plays a crucial role in metastasis. Thus, AEG-1 may be employed as a biomarker to discern the patients of those who are likely to get aid from AEG-1-targeted medication. AEG-1 may play as an effective target to repress tumor development, occlude metastasis, and magnify the effectiveness of treatments. In this review, we focus on the molecular mechanism of AEG-1 in the process of carcinogenesis and its involvement in regulation of crosstalk between the PI3K/AKT/mTOR and Hedgehog signaling. We also highlight the multifaceted functions, expression, clinicopathological significance and molecular inhibitors of AEG-1 in various cancer types.

Identification of Nucleolin as a Novel AEG-1-Interacting Protein in Breast Cancer via Interactome Profiling

Breast cancer is one of the most common malignant diseases worldwide. Astrocyte elevated gene-1 (AEG-1) is upregulated in breast cancer and regulates breast cancer cell proliferation and invasion. However, the molecular mechanisms by which AEG-1 promotes breast cancer have yet to be fully elucidated. In order to delineate the function of AEG-1 in breast cancer development, we mapped the AEG-1 interactome via affinity purification followed by LC-MS/MS. We identified nucleolin (NCL) as a novel AEG-1 interacting protein, and co-immunoprecipitation experiments validated the interaction between AEG-1 and NCL in breast cancer cells. The silencing of NCL markedly reduced not only migration/invasion, but also the proliferation induced by the ectopic expression of AEG-1. Further, we found that the ectopic expression of AEG-1 induced the tyrosine phosphorylation of c-Met, and NCL knockdown markedly reduced this AEG-1 mediated phosphorylation. Taken together, our report identifies NCL as a novel mediator of the oncogenic function of AEG-1, and suggests that c-Met could be associated with the oncogenic function of the AEG-1-NCL complex in the context of breast cancer.

Multifunctional Role of Astrocyte Elevated Gene-1 (AEG-1) in Cancer: Focus on Drug Resistance

Simple Summary

Chemotherapy is a major mode of treatment for cancers. However, cancer cells adapt to survive in stressful conditions and in many cases, they are inherently resistant to chemotherapy. Additionally, after initial response to chemotherapy, the surviving cancer cells acquire new alterations making them chemoresistant. Genes that help adapt the cancer cells to cope with stress often contribute to chemoresistance and one such gene is Astrocyte elevated gene-1 (AEG-1). AEG-1 levels are increased in all cancers studied to date and AEG-1 contributes to the development of highly aggressive, metastatic cancers. In this review, we provide a comprehensive description of the mechanism by which AEG-1 augments tumor development with special focus on its ability to regulate chemoresistance. We also discuss potential ways to inhibit AEG-1 to overcome chemoresistance.

Abstract

Cancer development results from the acquisition of numerous genetic and epigenetic alterations in cancer cells themselves, as well as continuous changes in their microenvironment. The plasticity of cancer cells allows them to continuously adapt to selective pressures brought forth by exogenous environmental stresses, the internal milieu of the tumor and cancer treatment itself. Resistance to treatment, either inherent or acquired after the commencement of treatment, is a major obstacle an oncologist confronts in an endeavor to efficiently manage the disease. Resistance to chemotherapy, chemoresistance, is an important hallmark of aggressive cancers, and driver oncogene-induced signaling pathways and molecular abnormalities create the platform for chemoresistance. The oncogene Astrocyte elevated gene-1/Metadherin (AEG-1/MTDH) is overexpressed in a diverse array of cancers, and its overexpression promotes all the hallmarks of cancer, such as proliferation, invasion, metastasis, angiogenesis and chemoresistance. The present review provides a comprehensive description of the molecular mechanism by which AEG-1 promotes tumorigenesis, with a special emphasis on its ability to regulate chemoresistance.

The Scope of Astrocyte Elevated Gene-1/Metadherin (AEG-1/MTDH) in Cancer Clinicopathology: A Review

Since its initial cloning in 2002, a plethora of studies in a vast number of cancer indications, has strongly established AEG-1 as a bona fide oncogene. In all types of cancer cells, overexpression and knockdown studies have demonstrated that AEG-1 performs a seminal role in regulating proliferation, invasion, angiogenesis, metastasis and chemoresistance, the defining cancer hallmarks, by a variety of mechanisms, including protein-protein interactions activating diverse oncogenic pathways, RNA-binding promoting translation and regulation of inflammation, lipid metabolism and tumor microenvironment. These findings have been strongly buttressed by demonstration of increased tumorigenesis in tissue-specific AEG-1 transgenic mouse models, and profound resistance of multiple types of cancer development and progression in total and conditional AEG-1 knockout mouse models. Additionally, clinicopathologic correlations of AEG-1 expression in a diverse array of cancers establishing AEG-1 as an independent biomarker for highly aggressive, chemoresistance metastatic disease with poor prognosis have provided a solid foundation to the mechanistic and mouse model studies. In this review a comprehensive analysis of the current and up-to-date literature is provided to delineate the clinical significance of AEG-1 in cancer highlighting the commonality of the findings and the discrepancies and discussing the implications of these observations.

A Review of AEG-1 Oncogene Regulating MicroRNA Expression in Colon Cancer Progression

MicroRNAs are a class of small non-coding RNAs that perform a crucial function in posttranscriptional gene regulation. Dysregulation of these microRNAs is associated with many types of cancer progression. In tumorigenesis, downregulated microRNAs might function as a tumour suppressor by repressing oncogenes, whereas overexpressed miRs might function as oncogenes by suppressing tumour suppressor. Similarly, Metadherin (also known as AEG-1/ LYRIC), is an oncogene, the levels of which are found to be very high in various cancers and play a crucial role in the proliferation of cells and invasion. Our review focuses on the study, which shows the alteration of microRNA expression profile and suppression of carcinogenesis when MTDH/AEG-1 is targeted. It summarises the studies where downregulation and upregulation of AEG-1 and microRNAs, respectively, alter the biological functions of the cell, such as proliferation and apoptosis. Studies have reported that AEG-1 can be direct or indirect target of microRNA, which could provide a new-insight to know the underlying molecular mechanism and might contribute to the progress of new therapeutic strategies for the disease.

ceRNA Networks: The Backbone Role in Neoadjuvant Chemoradiotherapy Resistance/Sensitivity of Locally Advanced Rectal Cancer

Approximately 40% of rectal cancers during initial diagnosis are identified as locally advanced rectal cancers (LARCs), for which the standardized treatment scenario is total mesorectal excision following neoadjuvant chemoradiotherapy (nCRT). nCRT can lead to discernible reductions in local relapse rate and distant metastasis rate in LARC patients, in whom previously inoperable tumors may potentially be surgically removed. However, only 4% to 20% cases can attain pathological complete response, and the remaining patients who are unresponsive to nCRT have to suffer from the side effects plus toxicities and may encounter poor survival outcomes due to the late surgical intervention. As such, employing potential biomarkers to differentiate responders from nonresponders before nCRT implementation appears to be the overarching goal. Well-defined competing endogenous RNA (ceRNA) networks include long noncoding RNA (lncRNA)-microRNA (miRNA)-mRNA and circRNA-miRNA-mRNA networks. As ceRNAs, lncRNAs, and circRNAs sponge miRNAs to indirectly suppress miRNAs downstream of oncogenic mRNAs or tumor-suppressive mRNAs. The abnormal expression of mRNAs regulates the nCRT-induced DNA damage repair process through pluralistic carcinogenic signaling pathways, thereby bringing about alterations in the nCRT resistance/sensitivity of tumors. Moreover, many molecular mechanisms relevant to cell proliferation, metastasis, or apoptosis of cancers (eg, epithelial-mesenchymal transition and caspase-9-caspase-3 pathway) are influenced by ceRNA networks. Herein, we reviewed a large group of abnormally expressed mRNAs and noncoding RNAs that are associated with nCRT resistance/sensitivity in LARC patients and ultimately pinpointed the backbone role of ceRNA networks in the molecular mechanisms of nCRT resistance/sensitivity.

Metadherin-PRMT5 complex enhances the metastasis of hepatocellular carcinoma through the WNT-β-catenin signaling pathway

Accumulating data suggest that metadherin (MTDH) may function as an oncogene. Our previous study showed that MTDH promotes hepatocellular carcinoma (HCC) metastasis via the epithelial-mesenchymal transition. In this study, we aim to further elucidate how MTDH promotes HCC metastasis. Using Co-immunoprecipitation (co-IP) and mass spectrometry, we found that MTDH can specifically bind to protein arginine methyltransferase 5 (PRMT5). Further functional assays revealed that PRMT5 overexpression promoted the proliferation and motility of HCC cells and that knockout of PRMT5 impeded the effect of MTDH. The immunohistochemistry assay/tissue microarray results showed that when MTDH was overexpressed in HCC cells, PRMT5 translocated from the nucleus to the cytoplasm, with the subsequent translocation of β-catenin from the cytoplasm to the nucleus and upregulation of the WNT-β-catenin signaling pathway. Further in vivo experiments suggested that PRMT5 and β-catenin played a pivotal role in MTDH-mediated HCC metastasis. We therefore concluded that the MTDH-PRMT5 complex promotes HCC metastasis by regulating the WNT-β-catenin signaling pathway.

Role of serum Metadherin mRNA expression in the diagnosis and prediction of survival in patients with colorectal cancer

Early diagnosis and treatment of colorectal cancer (CRC) are important for improving patients' survival. Metadherin is an oncogene that plays a pivotal role in carcinogenesis and can be suggested as a cancer biomarker. This study aimed to elucidate the efficacy of serum Metadherin mRNA expression as a potential non-invasive biomarker for early diagnosis of CRC in relation to other screening markers as carcinoembryonic antigen (CEA), carbohydrate antigen 19.9 (CA19.9) and Fecal occult blood (FOB) and also to assess its relationship with the tumor stage and survival rate. A convenience series of 86 CRC cases (group I) were recruited with 78 subjects as controls (group II). Serum Metadherin mRNA expression level was determined using reverse transcription polymerase chain reaction (RT-PCR). Serum Metadherin mRNA expression level was significantly elevated in CRC cases when compared with controls (P < 0.001). For CRC diagnosis; Receiver operator characteristic (ROC) analyses revealed that the diagnostic accuracy of serum Metadherin mRNA (AUC = 0.976) was significantly higher than other routine CRC screening markers as CEA, CA19.9 and FOB. The combined accuracy of these markers (AUC = 0.741) was increased when used with serum Metadherin mRNA (AUC = 0.820). High serum Metadherin mRNA expression was associated with poorly differentiated histological grade, advanced tumor stage and lower survival rate. AUC of Metadherin was 0.820 for differentiating advanced versus early tumor stages. Serum Metadherin mRNA expression is a useful non-invasive biomarker for CRC. It can be used for screening and early diagnosis of CRC and can increase the efficacy of other routine CRC screening markers when it is estimated in CRC patients with them. It is also associated with advanced tumor stage and a lower survival rate.

Elevated expression of MTDH predicts better prognosis of locally advanced HER-2 positive breast cancer patients receiving neoadjuvant chemotherapy plus trastuzumab

Metadherin (MTDH), also known as astrocyte elevated gene-1 (AEG-1), is an oncoprotein closely related to the development of breast cancer. However, few studies have been done on the expression and clinical significance of MTDH in human epidermal growth factor receptor-2 (HER-2) positive breast cancer patients.This study aimed to investigate the expression of MTDH in locally advanced HER-2 positive breast cancer, and evaluate the clinical significance of MTDH in predicting the prognosis of patients with HER-2 positive advanced breast cancer who received the neoadjuvant chemotherapy plus trastuzumab.In 144 HER-2 positive breast cancer tissues, 79 cases showed high expression of MTDH and 65 cases showed low expression. The expression of MTDH in locally advanced HER-2 positive breast cancer tissues was correlated with TNM stage, lymph node metastasis, Miller-Payne (MP) grade, and pathologic complete response (pCR) status (P < .05), but was not correlated with patient age, estrogen receptor (ER) expression level, progesterone receptor (PR) expression level, and Ki-67 expression level (P > .05). Kaplan-Meier univariate analysis revealed a negative correlation between MTDH expression and the disease-free survival (DFS) and overall survival (OS) in the post-operative patients with locally advanced HER-2 positive breast cancer (log rank test: P < .001). By using the COX proportional hazard regression model, it was found that MTDH expression, TNM stage, lymph node metastasis, and Ki-67 expression were closely related to DFS in patients. The hazard ratio (HR) of high MTDH expression was 1.816 (95% CI: 1.165-2.829). In addition, MTDH expression, TNM stage, and lymph node metastasis were also closely related to the OS of patient. The HR of the high expression of MTDH was 2.512 (95% CI: 1.472-4.286). The expression of MTDH in tumor tissues of patients with HER2-positive locally advanced breast cancer was significantly elevated, which was related to the poor pathological features.High MTDH expression was closely correlated with poor prognosis of patients and was an important factor affecting tumor progression.

AEG-1 promotes the growth of gastric cancer through the upregulation of eIF4E expression

Background: AEG-1 has been proven to be tumor enhancer in gastric cancer. However, its mechanism has not yet been fully clarified. Methods: Gain-of-function and loss-of-function experiments were conducted to determine the role of eIF4E in AEG-1-induced growth of gastric cancer cells and xenografts of a nude mouse model. Western blot analysis and SRB assay were used to determine the protein expression levels and survival cell numbers. Results: Silencing the expression of AEG-1 inhibited the growth of gastric cancer cells in parallel with a decreased eIF4E and cyclin D1 expression; however, the overexpression of AEG-1 promoted cell growth and increased eIF4E and cyclin D1 expression. Moreover, the overexpression of eIF4E partially reversed the AEG-1 silencing-induced reduction of cyclin D1 and the inhibition of cell growth. An eIF4E knockdown also partially reversed the AEG-1 overexpression-induced upregulation of cyclin D1 and cell growth. Notably, manipulating the expression of eIF4E did not affect the expression of AEG-1. Finally, the silencing of AEG-1 expression inhibited the growth of SGC-7901 xenografts in parallel with the downregulation of eIF4E and cyclin D1 expression in the nude mouse model. Conclusion: AEG-1 promoted the growth of gastric cancer through upregulation of eIF4E/cyclin D1 signaling pathway.

Metadherin Is a Prognostic Apoptosis Modulator in Mesothelioma Induced via NF-κB-Mediated Signaling

Therapies against malignant pleural mesothelioma (MPM) have yielded disappointing results, in part, because pathologic mechanisms remain obscure. In searching for rational molecular targets, we identified metadherin (MTDH), a multifunctional gene associated with several tumor types but previously unrecognized in MPM. Cox proportional hazards regression analysis delineated associations between higher MTDH expression and lower patient survival from three independent MPM cohorts (n = 349 patients). Through in vitro assays with overexpression and downregulation constructs in MPM cells, we characterized the role of MTDH. We confirmed in vivo the phenotype of altered MTDH expression in a murine xenograft model. Transcriptional regulators of MTDH were identified by chromatin immunoprecipitation. Overexpression of both MTDH mRNA (12-fold increased) and protein levels was observed in tumor tissues. MTDH stable overexpression significantly augmented proliferation, invasiveness, colony formation, chemoresistance, and an antiapoptosis phenotype, while its suppression showed opposite effects in MPM cells. Interestingly, NF-κB and c-Myc (in a feed-forward loop motif) contributed to modulating MTDH expression. Knockdown of MTDH expression profoundly retarded xenograft tumor growth. Thus, our findings support the notion that MTDH integrates upstream signals from certain transcription factors and mediates pathogenic interactions contributing to MPM traits. MTDH represents a new MPM-associated gene that can contribute to insights of MPM biology and, as such, suggest other treatment strategies.

Roles of microRNA-22 in Suppressing Proliferation and Promoting Sensitivity of Osteosarcoma Cells via Metadherin-mediated Autophagy

Objective

To analyze the effect of microRNA‐22 on autophagy and proliferation and to investigate the underlying molecular mechanism of osteosarcoma cell chemotherapy sensitivity.

Methods

MG‐63 cells were divided into four groups, including a control group, a negative control (NC) group, a cisplatin group, and a cisplatin + miR‐22 group. Proliferation of MG‐63 cells that had been treated with cisplatin and transfected with miR‐22 mimics was determined using MTT assay and colony formation assay. We assessed the degree of autophagy using flow cytometry through cellular staining of the autophagy lysosomal marker monodansylcadaverine (MDC). The effect of microRNA‐22 on autophagy was observed along with the expression levels of Beclin1, LC3, metadherin (MTDH) and ATG5 by western blot and quantitative reverse transcription polymerase chain reaction (qRT‐PCR). Luciferase reporter assay revealed the targeted binding site between miR‐22 and the 3′‐untranslated region (3′‐UTR) of MTDH mRNA. Western blot and qRT‐PCR were used to explore the level of MTDH in the control group, the NC group, the cisplatin group, and the miR‐22 group for 6, 12, and 24 h.

Results

In the in vitro study, the MTT results indicated that the MG‐63 cells with overexpression of miR‐22 exhibited a significant decline in the proliferation capacity compared with the control group (0.513 ± 0.001, P < 0.0005). Similar to the MTT results, MG‐63 cells that were transfected with miR‐22 mimic (101.0 ± 10.58) formed fewer colonies compared with the cisplatin group (129.7 ± 4.163). MDC staining revealed that miR‐22‐overexpressing osteosarcoma (OS) cells treated with cisplatin showed a significant decrease in the expression of autophagy (7.747 ± 0.117, P < 0.0001). Our data revealed that miR‐22 could regulate not only autophagy but also proliferation in the chemosensitivity of osteosarcoma cells. We found that miR‐22 sensitized osteosarcoma cells to cisplatin treatment by regulating autophagy‐related genes. In addition, Luciferase Reporter Assay revealed that miR‐22 negatively regulated autophagy through direct targeting of MTDH. We performed western blot analysis to detect the MTDH expression level. The results revealed that the overexpression of miR‐22 obviously decreased the expression of MTDH (1.081 ± 0.023, P < 0.001).

Conclusion

Inhibition of miR‐22 ameliorated the anticancer drug‐induced cell proliferation decrease in osteosarcoma cells. MTDH was identified as the miR‐22 target in OS cells and MTDH‐triggered autophagy played a key function in the miR‐22‐associated chemotherapy sensitivity.

CCL18 promotes the metastasis of squamous cell carcinoma of the head and neck through MTDH-NF-κB signalling pathway

Metastasis is one of the primary causes for high mortality in patients with squamous cell carcinoma of the head and neck (SCCHN). Our previous study showed that chemokine (C‐C motif) ligand 18 (CCL18), derived from tumour‐associated macrophages (TAMs), regulates SCCHN metastasis by promoting epithelial‐mesenchymal transition (EMT) and preserving stemness. However, the underlying mechanism needs to be further investigation. Interestingly, metadherin (MTDH) expression was induced when SCCHN cells were stimulated with recombinant CCL18 protein in this study. Suppressing MTDH expression reversed CCL18‐induced migration, invasion and EMT in SCCHN cells. Furthermore, the NF‐κB signalling pathway was involved in the MTDH knock‐down cells with CCL18 stimulation. We performed ELISA to evaluate the CCL18 levels in the serums of 132 treatment‐naive SCCHN patients, 25 patients with precancerous lesion and 32 healthy donors. Our results demonstrated that serum CCL18 levels were significantly higher in SCCHN patients than patients with precancerous lesion and healthy individuals. CCL18 levels were found to be significantly correlated with tumour classification, clinical stage, lymph node metastasis and histological grade in SCCHN patients. Thus, our findings suggest that CCL18 may serve as a potential biomarker for diagnosis of SCCHN and promote SCCHN invasion, migration and EMT by MTDH‐NF‐κB signalling pathway.

Interaction with AEG-1 and MDM2 is associated with glioma development and progression and correlates with poor prognosis

Glioma is the most common central nervous system tumor with poor prognosis. The AEG-1 (Astrocyte Elevated Gene 1) gene displays oncogenic characteristics, including proliferation, metastasis, chemoresistance, invasion, and evasion of apoptosis, and is strongly linked to the occurrence of glioma. Here, we elucidated the potential contribution of AEG-1 in human glioma pathogenesis. In glioma cells, AEG-1 could directly interact with Murine Double Minute-2 (MDM2) protein resulting in MDM2-p53-mediated cell proliferation and apoptosis. MDM2 is being revealed as an oncoprotein, which is involved in many human cancers progression. By immunohistochemical and a multivariate analysis, expressions of AEG-1 and MDM2 were elevated in glioma and high AEG-1 and MDM2 expressions were showed to be correlated with poor prognosis. AEG-1-MDM2 interaction prolonged stabilization of MDM2 where AEG-1 inhibited ubiquitination and subsequent proteasome-mediated degradation of MDM2 protein. Moreover, slicing AEG-1 blocked MDM2 expression and then impacted MDM2-p53 pathway that influenced cell proliferation and apoptosis. These findings uncover a novel AEG-1-MDM2 interplay by which AEG-1 augments glioma progression and reveal a viable potential therapy for the treatment of glioma patients.

A Preliminary Study on Metadherin as a Potential Marker for Progression of Diffuse Large B Cell Lymphoma

AIMS

To determine if Metadherin (MTDH) expression levels are positively correlated with the clinical stage of diffuse large B-cell lymphoma (DLBCL) based on MTDH being highly expressed in other type of tumors including melanoma, malignant glioma, breast cancer, and hepatocellular carcinoma. In this study, we investigated the pathologic significance of MTDH and its potential in predicting DLBCL outcomes.

MATERIALS AND METHODS

Tissue samples from 50 patients with DLBCL and 22 patients with lymph node reactive hyperplasia were collected and evaluated using immunohistochemical staining, microscopy, and western blotting. The Kaplan-Meier method and Cox regression model were used for survival analysis of patients.

RESULTS

Our results show that the overexpression of the MTDH protein in tissues was observed in 66% of patients with DLBCL, whereas it was not overexpressed in the patients with reactive hyperplastic lymph nodes. While there was no correlation between MTDH overexpression with age, sex, presence of B symptoms, and lactate dehydrogenase (LDH) levels in patients with DLBCL, this parameter was positively correlated with clinical stages. Moreover, MTDH-negative patients had significantly better prognoses compared with the MTDH-positive patients.

CONCLUSION

Our preliminary study indicates that MTDH may play an important role in the development of DLBCL, and that MTDH overexpression is potentially associated with the clinical progression of DLBCL. In addition, high expression levels of MTDH in tissues was correlated with a poorer prognosis for patients with DLBCL. As such, MTDH may be a potential therapeutic target for specific therapy. However, research on a larger group of patients is needed to verify these preliminary results.

microRNA-1471 suppresses glioma cell growth and invasion by repressing metadherin expression

microRNA-1471 (miR-1471) is a newly identified miRNA that is downregulated in breast cancer. However, its biological roles in human tumors are largely unknown. This study aimed to investigate the clinical significance and functions of miR-1471 in glioma. We found miR-1471 expression was significantly reduced in glioma tissues and cell lines. Forced expression of miR-1471 remarkedly suppressed glioma cell proliferation and invasion. Notably, metadherin (MTDH) was validated as a direct target of miR-1471 and the restoration of MTDH expression reversed the inhibitory effects of miR-1471 on glioma cell proliferation and invasion. Also, low miR-1471 expression was a predictor for worse 5-year overall survival of glioma patients. Overall, these results reveal the tumor suppressive role of miR-1471 in glioma, highlighting the potential to consider miR-1471/MTDH axis as a therapeutic target for the treatment of glioma in the near future.

LINC01638 lncRNA activates MTDH-Twist1 signaling by preventing SPOP-mediated c-Myc degradation in triple-negative breast cancer

Breast cancer is a heterogeneous disease, and triple-negative breast cancer (TNBC) continues to be a serious health problem. The potential involvement of lncRNAs in TNBC progression remains unexplored. Here, we demonstrated that LINC01638 is highly expressed in TNBC tissues and cells. LINC01638 maintains the mesenchymal traits of TNBC cells, including an enriched epithelial-mesenchymal transition (EMT) signature and cancer stem cell-like state. LINC01638 knockdown suppresses tumor proliferation and metastasis both in vitro and in vivo. LINC01638 overexpression predicts a poor outcome of breast cancer patients. Mechanistically, LINC01638 interacts with c-Myc to prevent SPOP-mediated c-Myc ubiquitination and degradation. C-Myc transcriptionally enhances MTDH (metadherin) expression and subsequently activates Twist1 expression to induce EMT. Our findings describe LINC01638-mediated signal transduction and highlight the crucial role of LINC01638 in TNBC progression.

Astrocyte elevated gene-1 is a novel regulator of astrogliosis and excitatory amino acid transporter-2 via interplaying with nuclear factor-κB signaling in astrocytes from amyotrophic lateral sclerosis mouse model with hSOD1G93A mutation

AEG-1 has received extensive attention on cancer research. However, little is known about its roles in astrogliosis of Amyotrophic lateral sclerosis (ALS). In this study, we detected AEG-1 expression in hSOD1G93A-positive (mut-SOD1) astrocytes and wild type (wt-SOD1) astrocytes, and intend to elucidate its potential functions in ALS related astrogliosis and the always accompanied dysregulated glutamate clearance. Results showed elevated protein and mRNA levels of AEG-1 in mut-SOD1 astrocytes; Also, NF-κB signaling pathway related proteins and inflammatory cytokines were upregulated in mut-SOD1 astrocytes; AEG-1 knockdown attenuated astrocytes proliferation and pro-inflammatory release; also we found that AEG-1 silence inhibited translocation of p65 from cytoplasma to nuclear, which was associated with inhibited NF-κB signaling. Besides, excitatory amino acid transporter-2 (EAAT2) expression levels were significantly decreased, accompanied by impaired glutamate clearance ability, in mut-SOD1 astrocytes; yin yang 1 (YY1), a transcriptional inhibitor for EAAT2, increased in nucleus of mut-SOD1 astrocytes. AEG-1 silence inhibited translocation of YY1 to nucleus, increased EAAT2 expression levels, and enhanced astrocytic ability of glutamate clearance, ultimately exerted the neuronal protection. Findings from this study implicate potential function of AEG-1 in mut-SOD1 related astrogliosis and the accompanied excitatory cytotoxic mechanism in ALS.

Upregulation of neuronal astrocyte elevated gene-1 protects nigral dopaminergic neurons in vivo

The role of astrocyte elevated gene-1 (AEG-1) in nigral dopaminergic (DA) neurons has not been studied. Here we report that the expression of AEG-1 was significantly lower in DA neurons in the postmortem substantia nigra of patients with Parkinson’s disease (PD) compared to age-matched controls. Similarly, decreased AEG-1 levels were found in the 6-hydroxydopamine (6-OHDA) mouse model of PD. An adeno-associated virus-induced increase in the expression of AEG-1 attenuated the 6-OHDA-triggered apoptotic death of nigral DA neurons. Moreover, the neuroprotection conferred by the AEG-1 upregulation significantly intensified the neurorestorative effects of the constitutively active ras homolog enriched in the brain [Rheb(S16H)]. Collectively, these results demonstrated that the sustained level of AEG-1 as an important anti-apoptotic factor in nigral DA neurons might potentiate the therapeutic effects of treatments, such as Rheb(S16H) administration, on the degeneration of the DA pathway that characterizes PD.

AEG-1 Contributes to Metastasis in Hypoxia-Related Ovarian Cancer by Modulating the HIF-1alpha/NF-kappaB/VEGF Pathway

Objective

Ovarian carcinoma represents one of the deadliest malignancies among female cancer patients. Astrocyte-elevated gene-1 (AEG-1) participates in the ontogenesis of multiple human malignant diseases. Here we evaluated AEG-1, hypoxia-inducible factor- (HIF-) 1α, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and vascular endothelial growth factor (VEGF) amounts in hypoxia induced ovarian carcinoma cells. This study aimed to explore the mechanism by which AEG-1 regulates metastasis in hypoxia induced ovarian carcinoma.

Patients and Methods

AEG-1, HIF-1α, and VEGF protein amounts were evaluated by immunohistochemistry in 40 and 170 normal ovary and ovarian cancer tissue specimens, respectively. In addition, AEG-1, HIF-1α, NF-κB, and VEGF mRNA and protein levels were determined by reverse quantified RT-PCR and WB, respectively, at different time periods (0–24 h) in epithelial ovarian cancer (EOC) SKOV3 cells treated in a hypoxia incubator. Furthermore, NF-κB and VEGF gene and protein expression levels in AEG-1 knockdown EOC cells were quantitated by RT-PCR and WB, respectively.

Results

AEG-1, HIF-1α, and VEGF amounts were significantly elevated in EOC tissue samples compared with normal ovary specimens (p < 0.001). Positive expression of HIF-1α and AEG-1 was associated with higher metastatic rate (p < 0.01), lower FIGO stage (p < 0.001), and degree of differentiation (p < 0.001). Meanwhile, EOC SKOV3 cells grew upon exposure to hypoxia for 8 h (p < 0.001); at this time point, AEG-1, HIF-1α, NF-κB, and VEGF amounts peaked (p < 0.001), at both the gene and the protein levels. After AEG-1 knockdown, HIF-1α, NF-κB, and VEGF amounts were significantly decreased in EOC SKOV3 cells, also under hypoxic conditions (p < 0.01).

Conclusions

As an independent prognostic factor, AEG-1 was found to be significantly associated with hypoxia in ovarian cancer by regulating the HIF-1alpha/NF-kappaB/VEGF pathway. Therefore, AEG-1 may be useful in determining disease stage and prognosis in ovarian cancer.

Metadherin: An emerging key regulator of the malignant progression of multiple cancers

We and others recently identified the gene metadherin (MTDH) as a functional driver in multiple aspects of cancer progression. It is overexpressed in cancer cells originating from a variety of tissues, partially due to DNA amplification of the chromosomal 8q22 region where this gene resides. The rapidly accumulated data from MTDH studies of the past several years have documented its role in tumorigenesis, angiogenesis, cell proliferation, survival, anchorage-independent growth, metastasis and chemoresistance. In particular, it simultaneously helps the primary tumor cells to survive conventional chemotherapy and spread to distant organs, both of which are major contributors to cancer therapy failure and ultimately patient death. The efforts to elucidate the molecular mechanism of MTDH functions led to observations indicating its involvement in several prominent cancer-related signaling pathways including Ras, c-Myc, PI3K/AKT, NF-κB, Wnt/β-catenin, and more recently, microRNA machinery. Herein we will briefly summarize the studies that establish MTDH as a promising target for cancer therapeutics.

AEG-1 knockdown in colon cancer cell lines inhibits radiation-enhanced migration and invasion in vitro and in a novel in vivo zebrafish model

Background

Radiotherapy is a well-established anti-cancer treatment. Although radiotherapy has been shown to significantly decrease the local relapse in rectal cancer patients, the rate of distant metastasis is still very high. The aim of this study was to evaluate whether AEG-1 is involved in radiation-enhanced migration and invasion in vitro and in a novel in vivo zebrafish model.

Results

Migration and invasion were decreased in all the AEG-1 knockdown cell lines. Furthermore, we observed that radiation enhanced migration and invasion, while AEG-1 knockdown abolished this effect. The results from the zebrafish embryo model confirmed the results obtained in vitro. MMP-9 secretion and expression were decreased in AEG-1 knockdown cells.

Materials and Methods

We evaluated the involvement of AEG-1 in migration and invasion and, radiation-enhanced migration and invasion by Boyden chamber assay in three colon cancer cell lines and respective stable AEG-1 knockdown cell lines. Furthermore, we injected those cells into zebrafish embryos and evaluated the amount of disseminated cells into the tail.

Conclusion

AEG-1 knockdown inhibits migration and invasion, as well as radiation-enhanced invasion both in vitro and in vivo. We speculate that this is done via the downregulation of the intrinsic or radiation-enhanced MMP-9 expression by AEG-1 in the cancer cells. This study also shows, for the first time, that the zebrafish is a great model to study the early events in radiation-enhanced invasion.

Depletion of astrocyte elevated gene-1 suppresses tumorigenesis through inhibition of Akt activity in bladder cancer cells

Astrocyte elevated gene-1 (AEG-1) has been reported to promote tumorigenesis, however the molecular mechanisms by which AEG-1-induced bladder cancer progression has remained elusive. Here, we identified that depletion of AEG-1 in bladder cancer cells suppressed cell growth. Moreover, we observed that down-regulation of AEG-1 induced apoptosis and inhibited cell migration and invasion. Furthermore, depletion of AEG-1 inhibited Akt activity and suppressed Bcl-2 expression, but upregulated the levels of p21 and p27. Our findings reveal that AEG-1 carries out its oncogenic function via activation of the Akt pathway. Therefore, inhibition of AEG-1 could be a novel treatment approach for bladder cancer.

AEG-1/MTDH-activated autophagy enhances human malignant glioma susceptibility to TGF-β1-triggered epithelial-mesenchymal transition

Autophagy is a tightly regulated process activated in response to metabolic stress and other microenvironmental changes. Astrocyte elevated gene 1 (AEG-1) reportedly induces protective autophagy. Our results indicate that AEG-1 also enhances the susceptibility of malignant glioma cells to TGF-β1-triggered epithelial-mesenchymal transition (EMT) through induction of autophagy. TGF-β1 induced autophagy and activated AEG-1 via Smad2/3 phosphorylation in malignant glioma cells. Also increased was oncogene cyclin D1 and EMT markers, which promoted tumor progression. Inhibition of autophagy using siRNA-BECN1 and siRNA-AEG-1 suppressed EMT. In tumor samples from patients with malignant glioma, immunohistochemical assays showed that expression levels of TGF-β1, AEG-1, and markers of autophagy and EMT, all gradually increase with glioblastoma progression. In vivo siRNA-AEG-1 administration to rats implanted with C6 glioma cells inhibited tumor growth and increased the incidence of apoptosis among tumor cells. These findings shed light on the mechanisms underlying the invasiveness and progression of malignant gliomas.

MicroRNA-384 represses the growth and invasion of non-small-cell lung cancer by targeting astrocyte elevated gene-1/Wnt signaling

Dysregulation of microRNA (miRNA) expression is a critical event in the development and progression of non-small-cell lung cancer (NSCLC). miR-384 has been identified as a novel cancer-related miRNA in numerous cancers, but little is known about its role and functional mechanism in NSCLC. In this study, we found that miR-384 was significantly downregulated in NSCLC tissues and cell lines. The overexpression of miR-384 repressed the growth and invasion of NSCLC cells, whereas its suppression showed the opposite effect. Moreover, astrocyte elevated gene-1 (AEG-1) was identified as a target gene of miR-384. The overexpression of miR-384 significantly decreased AEG-1 expression and Wnt signaling, whereas its suppression promoted this pathway. Furthermore, miR-384 was inversely correlated with AEG-1 expression in NSCLC tissues. Additionally, restoration of AEG-1 expression in miR-384-overexpressing cells significantly reversed the antitumor effects of miR-384. Taken together, these results reveal that miR-384 represses the growth and invasion of NSCLC cells by targeting AEG-1. Our study suggest that miR-384 and AEG-1 may serve as potential targets for the diagnosis and treatment of NSCLC.

MicroRNA-202 inhibits cell proliferation, migration and invasion of glioma by directly targeting metadherin

Glioma is the most common and aggressive type of primary malignant brain tumour. Increasing evidence has revealed that microRNAs play important roles in multiple biological processes related to glioma occurrence, development, diagnosis, treatment and prognosis. MicroRNA-202 (miR-202) has been studied in several types of human cancer, whereas the biological roles of miR-202 in glioma remain unknown. The present study, aimed to investigate the expression, clinical significance and biological roles of miR-202 in glioma, as well as its underlying molecular mechanism. We found that miR-202 was significantly downregulated in glioma tissues and cell lines. Low miR-202 expression was associated with Karnofsky performance status (KPS) score and World Health Organization (WHO) grade of glioma patients. Functional assays revealed that ectopic expression of miR-202 inhibited cell proliferation, migration and invasion of glioma. In addition, metadherin (MTDH) was identified as a direct target gene of miR-202 in glioma through bioinformatic analysis, luciferase reporter assay, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting. Furthermore, MTDH expression was upregulated and negatively correlated with miR-202 expression in clinical glioma tissues. MTDH knockdown had similar roles to miR-202 overexpression in glioma cells. Rescue experiments revealed that upregulation of MTDH reversed the suppression of glioma cell growth and metastasis by miR-202. Moreover, miR-202 impaired the PI3K/Akt and Wnt/β-catenin pathways. These results highlight the tumour-suppressive effect of miR-202 in glioma, thereby suggesting that miR-202 may be a potential therapeutic target for the treatment of patients with this malignancy.

The role of toll-like receptor 4 in tumor microenvironment

Tumors are closely related to chronic inflammation, during which there are various changes in inflammatory sites, such as immune cells infiltration, pro-inflammation cytokines production, and interaction between immune cells and tissue cells. Besides, substances, released from both tissue cells attacked by exogenous etiologies, also act on local cells. These changes induce a dynamic and complex microenvironment favorable for tumor growth, invasion, and metastasis. The toll-like receptor 4 (TLR4) is the first identified member of the toll-like receptor family that can recognize pathogen-associated molecular patterns (PAMPs) and damage-associated molecular pattern (DAMPs). TLR4 expresses not only on immune cells but also on tumor cells. Accumulating evidences demonstrated that the activation of TLR4 in tumor microenvironment can not only boost the anti-tumor immunity but also give rise to immune surveillance and tumor progression. This review will summarize the expression and function of TLR4 on dendritic cells (DCs), tumor-associated macrophages (TAMs), T cells, myeloid-derived suppressor cells (MDSCs), tumor cells as well as stromal cells in tumor microenvironment. Validation of the multiple role of TLR4 in tumors could primarily pave the road for the development of anti-tumor immunotherapy.

AEG-1 induces gastric cancer metastasis by upregulation of eIF4E expression

Gastric cancer is the third leading cause of cancer-related deaths worldwide, and patients with lymph node, peritoneal and distant metastasis have a poor prognosis. Overexpression of Astrocyte-elevated gene-1 (AEG-1) has been reported to be correlated with the progression and metastasis of gastric cancer. However, its mechanisms are quite unclear. In this study, we found that elevated expression of AEG-1 was correlated with metastasis in human gastric cancer tissues. Moreover, gain- or loss-of-function of AEG-1, respectively, promoted or suppressed epithelial-mesenchymal transition (EMT), migration and invasion of gastric cancer cells. AEG-1 positively regulated eIF4E, MMP-9 and Twist expression. Manipulating eIF4E expression by transfection of overexpression constructs or siRNAs partially eliminated AEG-1-regulated EMT, cell migration and invasion. In addition, overexpression or knockdown of eIF4E promoted or suppressed EMT, cell migration and invasion in parallel with upregulation of MMP-9 and Twist expression, while manipulating eIF4E expression partially abrogated AEG-1-induced MMP-9 and Twist. Finally, silencing of AEG-1 expression not only inhibited tumour growth in parallel with downregulation of eIF4E, MMP-9 and Twist expression in a xenograft nude mouse model, but also suppressed lymph node and peritoneal metastasis of gastric cancer in an orthotopic nude mouse model. These findings suggest that AEG-1 promotes gastric cancer metastasis through upregulation of eIF4E-mediated MMP-9 and Twist, which provides new diagnostic markers and therapeutic targets for cancer metastasis.

Astrocyte-elevated gene-1 confers resistance to pemetrexed in non-small cell lung cancer by upregulating thymidylate synthase expression

Previous studies have suggested that astrocyte-elevated gene-1 (AEG-1) contributes to the mechanisms of resistance to various chemotherapeutics. In this study, we investigated whether AEG-1 expression level correlated with that of thymidylate synthase (TS), as higher TS expression is known to be associated with the resistance to pemetrexed chemotherapy in patients with advanced lung adenocarcinoma. Using pemetrexed-resistant lung adenocarcinoma PC-9 cell line, we demonstrated that transfection of AEG-1 siRNA lowered TS expression and decreased pemetrexed IC₅₀ value. In contrast, overexpression of AEG-1 was associated with increased expression of TS and higher pemetrexed IC₅₀ value. Immunohistochemical staining of clinical biopsy samples showed that patients with lower AEG-1 expression had longer overall survival time. Moreover, analysis of repeated biopsy samples revealed that an increase in the TS level from baseline to disease progression was significantly associated with the elevation of AEG-1 expression. In conclusion, our data demonstrated that TS expression might be regulated by AEG-1 and that increased expression of these proteins contributes to lung cancer disease progression and may be associated with the development of resistance to pemetrexed.

Novel Thiosemicarbazones Inhibit Lysine-Rich Carcinoembryonic Antigen-Related Cell Adhesion Molecule 1 (CEACAM1) Coisolated (LYRIC) and the LYRIC-Induced Epithelial-Mesenchymal Transition via Upregulation of N-Myc Downstream-Regulated Gene 1 (NDRG1)

Tumor necrosis factor α (TNFα) plays a vital role in cancer progression as it is associated with inflammation and promotion of cancer angiogenesis and metastasis. The effects of TNFα are mediated by its downstream target, the oncogene lysine-rich CEACAM1 coisolated protein (LYRIC, also known as metadherin or astrocyte elevated gene-1). LYRIC plays an important role in activating the nuclear factor-ĸB (NF-κB) signaling pathway, which controls multiple cellular processes, including proliferation, apoptosis, migration, etc. In contrast, the metastasis suppressor N-myc downstream regulated gene 1 (NDRG1) has the opposite effect on the NF-κB pathway, being able to inhibit NF-κB activation and reduce angiogenesis, proliferation, migration, and cancer cell invasion. These potent anticancer properties make NDRG1 an ideal therapeutic target. Indeed, a novel class of thiosemicarbazone anticancer agents that target this molecule has been developed; the lead agent, di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone, has recently entered clinical trials for advanced and resistant cancers. To further elucidate the interaction between NDRG1 and oncogenic signaling, this study for the first time assessed the effects of NDRG1 on the tumorigenic properties of TNFα and its downstream target, LYRIC. We have demonstrated that NDRG1 inhibits the TNFα-mediated epithelial-to-mesenchymal transition. Further, NDRG1 also potently inhibited LYRIC expression, with a negative feedback loop existing between these two molecules. Examining the mechanism involved, we demonstrated that NDRG1 inhibited phosphatidylinositol 3-kinase/AKT signaling, leading to reduced levels of the LYRIC transcriptional activator, c-Myc. Finally, we demonstrated that novel thiosemicarbazones that upregulate NDRG1 also inhibit LYRIC expression, further highlighting their marked potential for cancer treatment.