Astrocyte Elevated Gene-1 Function Research Articles

Transcriptome analysis in an AEG‑1‑deficient neuronal HT22 cell line.

Astrocyte elevated gene-1 (AEG-1) is a key regulatory factor of progression in multiple types of tumor and neurodegenerative disease development. AEG-1 is associated with glutamate excitotoxicity due to its reported function of repressing excitatory amino acid transporter 2 expression in astrocytes. Although the function of AEG-1 has been demonstrated in neurological disorders, such as Alzheimer's disease and amyotrophic lateral sclerosis, the underlying mechanism of neuronal AEG-1 function remains unclear. The aim of the present study was to clarify the function and related mechanism of AEG-1 in neurons. A stable AEG-1-deficient HT22 neuronal cell line was constructed using CRISPR/Cas9 gene-editing technology. Reverse transcription-quantitative PCR and western blotting were carried out to analyze the knockdown efficiency of AEG-1-deficient HT22 cell line. RNA Sanger sequencing analysis was performed in AEG-1-deficient HT22 cells and wild-type HT22 cells without knockout (KO). Results from RNA sequencing revealed that AEG-1 modulated neuronal morphology and development by regulating the expression of numerous genes, such as ubiquitin C, C-X-C motif chemokine ligand 1, MMP9, Notch1, neuropilin 1 and ephrin type-A receptor 4. In addition, AEG-1 deficiency impacted several signaling pathways by mediating cell survival differentiation, apoptosis, and migration; this included the TNF-α pathway, the NF-κB pathway, the MAPK signaling pathway, the Notch signaling pathway and Axon guidance. Downregulation in cellular ion homeostasis, including ion channel function and neurotransmitter release, were observed after knocking out AEG-1 expression. Collectively, the present study provides insights into AEG-1-dependent gene regulation and signaling pathway transduction in neurons. The results of the present study may be applied for improving the understanding of AEG-1-associated central nervous system diseases.

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

Simple SummaryBreast cancer is one of the most common cancers affecting women today. Astrocyte Elevated Gene-1 (AEG-1) is elevated in breast cancer patients and is associated with metastasis and poor prognosis. However, the mechanisms by which AEG-1 promotes breast cancer are not fully understood. This report focuses on a novel AEG-1 interacting protein, nucleolin (NCL), which we identified via mass spectrometry-based interactome profiling. We found NCL to be important for the oncogenic function of AEG-1 in breast cancer. Further, c-Met was identified as a novel mediator of the oncogenic function of the AEG-1-NCL complex. Collectively, our study suggests that targeting the AEG-1-NCL protein complex could be an effective therapeutic approach for the treatment of some breast cancers.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.

In silico analysis and prediction of transcription factors of the proteins interacting with astrocyte elevated gene-1

Multifunctional in nature, the protein Astrocyte Elevated Gene-1 (AEG-1) controls several cancers through protein-protein interactions. Although, specific physiological processes and molecular functions linked with AEG-1 interactors remain unclear. In our present study, we procured the data of AEG-1 interacting proteins and evaluated their biological functions, associated pathways, and interaction networks using bioinformatic tools. A total of 112 proteins experimentally detected to interact with AEG-1 were collected from various public databases. DAVID 6.8 Online tool was utilized to identify the molecular functions, biological processes, cellular components that aid in understanding the physiological function of AEG-1 and its interactors in several cell types. With the help of integrated network analysis of AEG-1 interactors using Cytoscape 3.8.0 software, cross-talk between various proteins, and associated pathways were revealed. Additionally, the Enrichr online tool was used for performing enrichment of transcription factors of AEG-1 interactors’ which further revealed a closely associated self-regulated interaction network of a variety of transcription factors that shape the expression of AEG-1 interacting proteins. As a whole, the study calls for better understanding and elucidation of the pathways and biological roles of both AEG-1 and its interactor proteins that might enable their application as biomarkers and therapeutic targets in various diseases in the very near future.

AEG-1 promotes angiogenesis and may be a novel treatment target for tongue squamous cell carcinoma.

The study explored the potential function of astrocyte elevated gene-1 (AEG-1) on angiogenesis in tongue squamous cell carcinoma (TSCC) in TSCC cell lines. The different degrees of angiogenesis were detected in TSCC cell lines expressing different levels of AEG-1 by chick chorioallantoic membrane (CAM) experimental model. Next, we established xenografts of different TSCC cell lines with different expression levels of AEG-1 in nude mice and conducted immunohistochemistry to evaluate the expression of the angiogenesis-associated factor, that is, vascular endothelial growth receptor factor 2 (VEGFR-2) and microvessel density (MVD). Vascular endothelial growth factor (VEGF) was detected by ELISA. CAM assay showed that the number of vessels was significantly reduced in AEG-1-down um1 cell line (p<.05), whereas the number was significantly increased in AEG-1-over um2 cell line (p<.05). Moreover, up-regulated AEG-1 expression level was associated with higher tumor angiogenesis, which was reflected by augmented expression levels of VEGF (p<.01), VEGFR-2 (p<.05), and MVD counting (p<.01). This study demonstrated that AEG-1 can promote tumor angiogenesis in TSCC and inhibition of tumor angiogenesis by repressing the expression of AEG-1 may be a novel potential treatment approach for TSCC.

Astrocyte elevated gene-1 induces autophagy in diabetic cardiomyopathy through upregulation of KLF4.

Astrocyte elevated gene-1 (AEG-1), also known as metadherin, 3D3, and lysine-rich carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) coisolated, has emerged as an important oncogene that is overexpressed in a variety of cancers. Previous studies revealed that AEG-1 is also involved in multiple physiological and pathological processes, such as development, inflammation, neurodegeneration, migraine, and Huntington's disease. However, the function of AEG-1 in diabetic cardiomyopathy (DCM) has not been reported yet. Therefore, we conducted this study to characterize the potential role and mechanism of AEG-1 in DCM rats. DCM was induced by injections of streptozocin (STZ) in Wistar rats. Rats were randomized to be injected with lentivirus carrying AEG-1 small interfering RNA. Haemodynamic changes of Wistar rats, assessment of cardiac weight index, and the expression of AEG-1 and KLF4 were detected and compared among these three groups. The expressions of AEG-1 and KLF4 in the STZ group were significantly elevated in cardiac tissues compared with the control group. Knockdown of AEG-1 significantly increased the values of left ventricular ejection fraction, ±dp/dt max , repressed autophagy, as well as upregulated the expression of KLF4. Knockdown of AEG-1 suppresses autophagy in DCM by downregulating the expression of KLF4. This study provide first-notion evidence for the potential value of AEG-1 as a therapeutic target for the treatment of the patients with DCM.

Oncoprotein AEG-1 is an endoplasmic reticulum RNA-binding protein whose interactome is enriched in organelle resident protein-encoding mRNAs.

Astrocyte elevated gene-1 (AEG-1), an oncogene whose overexpression promotes tumor cell proliferation, angiogenesis, invasion, and enhanced chemoresistance, is thought to function primarily as a scaffolding protein, regulating PI3K/Akt and Wnt/β-catenin signaling pathways. Here we report that AEG-1 is an endoplasmic reticulum (ER) resident integral membrane RNA-binding protein (RBP). Examination of the AEG-1 RNA interactome by HITS-CLIP and PAR-CLIP methodologies revealed a high enrichment for endomembrane organelle-encoding transcripts, most prominently those encoding ER resident proteins, and within this cohort, for integral membrane protein-encoding RNAs. Cluster mapping of the AEG-1/RNA interaction sites demonstrated a normalized rank order interaction of coding sequence >5′ untranslated region, with 3′ untranslated region interactions only weakly represented. Intriguingly, AEG-1/membrane protein mRNA interaction sites clustered downstream from encoded transmembrane domains, suggestive of a role in membrane protein biogenesis. Secretory and cytosolic protein-encoding mRNAs were also represented in the AEG-1 RNA interactome, with the latter category notably enriched in genes functioning in mRNA localization, translational regulation, and RNA quality control. Bioinformatic analyses of RNA-binding motifs and predicted secondary structure characteristics indicate that AEG-1 lacks established RNA-binding sites though shares the property of high intrinsic disorder commonly seen in RBPs. These data implicate AEG-1 in the localization and regulation of secretory and membrane protein-encoding mRNAs and provide a framework for understanding AEG-1 function in health and disease.

AEG-1 associates with metastasis in papillary thyroid cancer through upregulation of MMP2/9.

Astrocyte elevated gene-1 (AEG-1), known as an oncogene, is overexpressed in various cancers and implicated in tumor progression and metastasis. However, its functional significance and underlying molecular mechanisms in thyroid cancer remain to be elucidated. In the present study, we detected the potential function of AEG-1 in papillary thyroid cancer (PTC). We also investigated the relation between AEG-1 and matrix metalloproteases (MMP)2 and 9 through immunohistochemistry, western blotting, real-time PCR, immunofluorescence staining, zymography and co-immunoprecipitation (Co-IP). We found that overexpression of AEG-1 in PTC was positively correlated with lymph node metastasis and MMP2/9 expression. Knockdown of AEG-1 reduced the capacity of migration and invasion through downregulation of MMP2/9 in thyroid cancer cells. Furthermore, we firstly found that AEG-1 interacted with MMP9 in thyroid cancer cells. AEG-1 was associated with the activation of the nuclear factor κB (NF-κB) signaling pathways in thyroid cancer cells. Overall, our results for the first time showed that AEG-1 interacted with MMP9 in thyroid cancer cells and AEG-1 expression was closely associated with progression and metastasis of papillary thyroid cancer. AEG-1 might be a potential therapeutic target in papillary thyroid cancer.

Lentivirus-Mediated Knockdown of Astrocyte Elevated Gene-1 Inhibits Growth and Induces Apoptosis through MAPK Pathways in Human Retinoblastoma Cells.

PurposeTo explore expression and function of astrocyte elevated gene-1 (AEG-1) in human retinoblastoma (RB).MethodsThe expression of AEG-1 in histological sections of human RBs and in RB cell lines was examined using immunohistochemical staining and RT-PCR and Western blotting respectively. We knocked down AEG-1 gene levels by AEG-1-siRNA lentivirus transfection of human RB cell lines SO-RB50 and Y79, and using an MTT assay, we assessed the role of AEG-1 on RB cell proliferation. The biological significance of lentivirus transfection induced AEG-1 down-regulation was examined by assessing the apoptosis rate in the transfected RB cells by Annexin V-APC staining and flow cytometry. We additionally measured the expression of Bcl-2, Bax, cleaved-caspase-3 and caspase-3, and the phosphorylation and non-phosphorylation alternation of MAPKs.ResultsAEG-1 expression was detected to be strongly positive in the histological slides of 35 out of 54 (65%) patients with RB. AEG-1 expression increased significantly (P<0.05) with tumor stage. In the RB cell lines SO-RB50, Y79 and WERI-RB1 as compared with retinal pigment epithelium cells, expression of AEG-1 mRNA and AEG-1 protein was significantly higher. In AEG-1-siRNA lentivirus transfected cell cultures as compared with negative control lentivirus transfected cell cultures, levels of AEG-1 mRNA and of AEG-1 protein (P<0.05) and cell growth rates (P<0.01) were significantly lower, and apoptosis rate (P<0.001), Bax/Bcl-2 ratio and cleaved-caspase-3 protein level were significantly increased. The P-ERK/ERK ratio was significantly decreased in the AEG-1-siRNA lentivirus transfected cell lines.ConclusionsExpression of AEG-1 was associated with RB, in histological slides of patients and in cell culture experiments. Lentivirus transfection induced knockdown of AEG-1 had a tumor suppressive effect, potentially by tumor cell apoptosis induction through inhibition of ERK.

Astrocyte Elevated Gene-1 (AEG-1) Regulates Lipid Homeostasis

Astrocyte elevated gene-1 (AEG-1), also known as MTDH (metadherin) or LYRIC, is an established oncogene. However, the physiological function of AEG-1 is not known. To address this question, we generated an AEG-1 knock-out mouse (AEG-1KO) and characterized it. Although AEG-1KO mice were viable and fertile, they were significantly leaner with prominently less body fat and lived significantly longer compared with wild type (WT). When fed a high fat and cholesterol diet (HFD), WT mice rapidly gained weight, whereas AEG-1KO mice did not gain weight at all. This phenotype of AEG-1KO mice is due to decreased fat absorption from the intestines, not because of decreased fat synthesis or increased fat consumption. AEG-1 interacts with retinoid X receptor (RXR) and inhibits RXR function. In enterocytes of AEG-1KO mice, we observed increased activity of RXR heterodimer partners, liver X receptor and peroxisome proliferator-activated receptor-α, key inhibitors of intestinal fat absorption. Inhibition of fat absorption in AEG-1KO mice was further augmented when fed an HFD providing ligands to liver X receptor and peroxisome proliferator-activated receptor-α. Our studies reveal a novel role of AEG-1 in regulating nuclear receptors controlling lipid metabolism. AEG-1 may significantly modulate the effects of HFD and thereby function as a unique determinant of obesity.

Astrocyte Elevated Gene-1 Is a Novel Modulator of HIV-1-associated Neuroinflammation via Regulation of Nuclear Factor-κB Signaling and Excitatory Amino Acid Transporter-2 Repression

Astrocyte elevated gene-1 (AEG-1), a novel human immunodeficiency virus (HIV)-1 and tumor necrosis factor (TNF)-α-inducible oncogene, has generated significant interest in the field of cancer research as a therapeutic target for many metastatic aggressive tumors. However, little is known about its role in astrocyte responses during HIV-1 central nervous system (CNS) infection and whether it contributes toward the development of HIV-associated neurocognitive disorders (HAND). Therefore, in this study, we investigated changes in AEG-1 CNS expression in HIV-1-infected brain tissues and elucidated a potential mechanism of AEG-1-mediated regulation of HAND. Immunoblotting and immunohistochemical analyses of HIV-1 seropositive and HIV-1 encephalitic human brain tissues revealed significantly elevated levels of AEG-1 protein. Immunohistochemical analyses of HIV-1 Tat transgenic mouse brain tissues also showed a marked increase in AEG-1 staining. Similar to in vivo observations, cultured astrocytes expressing HIV-1 Tat also revealed AEG-1 and cytokine up-regulation. Astrocytes treated with HAND-relevant stimuli, TNF-α, interleukin (IL)-1β, and HIV-1, also significantly induced AEG-1 expression and nuclear translocation via activation of the nuclear factor (NF)-κB pathway. Co-immunoprecipitation studies demonstrated IL-1β- or TNF-α-induced AEG-1 interaction with NF-κB p65 subunit. AEG-1 knockdown decreased NF-κB activation, nuclear translocation, and transcriptional output in TNF-α-treated astrocytes. Moreover, IL-1β treatment of AEG-1-overexpressing astrocytes significantly lowered expression of excitatory amino acid transporter 2, increased expression of excitatory amino acid transporter 2 repressor ying yang 1, and reduced glutamate clearance, a major transducer of excitotoxic neuronal damage. Findings from this study identify a novel transcriptional co-factor function of AEG-1 and further implicate AEG-1 in HAND-associated neuroinflammation.

Abstract 1324: Unraveling novel functions of the oncogene Astrocyte elevated gene-1 (AEG-1) contributing to hepatocarcinogenesis employing a transgenic mouse model

Abstract In vitro tissue culture and nude mice xenograft models have firmly established the role of Astrocyte elevated gene-1 (AEG-1) as a positive regulator of tumorigenesis, including hepatocarcinogenesis. To better appreciate the role of AEG-1 in hepatocarcinogenesis and to dissect the underlying molecular mechanism, we have created a transgenic mouse with hepatocyte-specific expression of AEG-1 (Alb/AEG1). Wild-type (WT) and Alb/AEG-1 mice were challenged with a hepatocarcinogen, N-nitrosodiethylamine (DEN), at 2 weeks of age. At 28 weeks of age, Alb/AEG-1 mice, but not WT mice, developed multinodular HCC with steatotic features and highly elevated serum liver enzymes. Affymetrix microarray analyses identified modulation of expression of genes associated with invasion, metastasis, angiogenesis and fatty acid synthesis in DEN-treated Alb/AEG-1 mice versus their WT counterparts. Hepatocytes isolated from Alb/AEG-1 mice demonstrated profound chemoresistance and dramatically evaded reduction in cell viability upon growth factor deprivation, which was associated with activation of multiple pro-survival signaling pathways. Compared to the WT hepatocytes, Alb/AEG-1 hepatocytes demonstrated marked resistance towards senescence, which was associated with abrogation of activation of a DNA damage response. Conditioned media (CM) from Alb/AEG-1 hepatocytes, but not form WT hepatocytes, induced marked angiogenesis. Mass spectrometric analysis of CM revealed noticeable increases in coagulation factors by AEG-1, which are known to play a significant role in regulating tumor invasion, angiogenesis and metastasis. siRNA-mediated knockdown of coagulation factor XII resulted in profound inhibition of AEG-1-induced angiogenesis. Our studies reveal novel aspects of AEG-1 functions, such as induction of steatosis, inhibition of senescence, a known anti-cancer mechanism, and activation of coagulation pathway to augment an aggressive hepatocarcinogenic phenotype. The Alb/AEG-1 mouse will be a useful model to decipher AEG-1 function in the context of hepatocarcinogenesis and to evaluate the efficacy of novel therapeutic strategies directed towards HCC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1324. doi:1538-7445.AM2012-1324

Overexpression of astrocyte-elevated gene-1 is closely correlated with poor prognosis in human non–small cell lung cancer and mediates its metastasis through up-regulation of matrix metalloproteinase-9 expression

Expression of astrocyte-elevated gene-1, a novel oncoprotein, is elevated in multiple cancers and plays a vital role in tumor cell growth, invasion, angiogenesis, and progression to metastasis. However, the functional significance of astrocyte-elevated gene-1 in non-small cell lung cancer still remains unclear. Our present study showed that the markedly up-regulated expression of astrocyte-elevated gene-1 was observed in non-small cell lung cancer cell lines and tissues at the level of both transcription and translation. Simultaneously, ectopic expression or small interfering RNA silencing of astrocyte-elevated gene-1 markedly enhanced or inhibited the invasive ability of non-small cell lung cancer cells, respectively. At the molecular level, we also revealed that the function of astrocyte-elevated gene-1 in promoting metastasis was associated with the activation of matrix metalloproteinase-9 expression. Consistent with these observations, immunostaining analysis revealed a significant positive correlation between astrocyte-elevated gene-1 and matrix metalloproteinase-9. Moreover, subcutaneous xenografts of non-small cell lung cancer cells engineered to express astrocyte-elevated gene-1 were highly invasive compared with the parental cells and expressed a high level of matrix metalloproteinase-9. In archival non-small cell lung cancer specimens, high astrocyte-elevated gene-1 expression correlated significantly with clinical staging (P = .048), differentiation (P = .023), and lymph node metastasis (P = .032). The overall survival time in patients with high astrocyte-elevated gene-1 expression was notably shorter than that in patients with low astrocyte-elevated gene-1 expression (P < .001). Taken together, our results indicate that astrocyte-elevated gene-1 plays a crucial role in the carcinogenesis and aggressiveness of non-small cell lung cancer, promoting its metastasis by modulating matrix metalloproteinase-9 expression and leading to a poor clinical prognosis.

Insulin-like Growth Factor–Binding Protein-7 Functions as a Potential Tumor Suppressor in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a highly virulent malignancy with no effective treatment, thus requiring innovative and effective targeted therapies. The oncogene astrocyte-elevated gene-1 (AEG-1) plays a seminal role in hepatocarcinogenesis and profoundly downregulates insulin-like growth factor-binding protein-7 (IGFBP7). The present study focuses on analyzing potential tumor suppressor functions of IGFBP7 in HCC and the relevance of IGFBP7 downregulation in mediating AEG-1 function. IGFBP7 expression was detected by immunohistochemistry in HCC tissue microarray and real-time PCR and ELISA in human HCC cell lines. Dual FISH was done to detect LOH at IGFBP7 locus. Stable IGFBP7-overexpressing clones were established in the background of AEG-1-overexpressing human HCC cells and were analyzed for in vitro proliferation and senescence and in vivo tumorigenesis and angiogenesis. IGFBP7 expression is significantly downregulated in human HCC samples and cell lines compared with normal liver and hepatocytes, respectively, and inversely correlates with the stages and grades of HCC. Genomic deletion of IGFBP7 was identified in 26% of patients with HCC. Forced overexpression of IGFBP7 in AEG-1-overexpressing HCC cells inhibited in vitro growth and induced senescence, and profoundly suppressed in vivo growth in nude mice that might be an end result of inhibition of angiogenesis by IGFBP7. The present findings provide evidence that IGFBP7 functions as a novel putative tumor suppressor for HCC and establish the corollary that IGFBP7 downregulation can effectively modify AEG-1 function. Accordingly, targeted overexpression of IGFBP7 might be a potential novel therapy for HCC.

Abstract 4706: Overexpression of the components of RNA-induced silencing complex: Contribution to hepatocellular carcinoma

Abstract Objectives: There is virtually no treatment for advanced hepatocellular carcinoma (HCC). As such novel targets need to be identified to develop effective therapies to combat this fatal disease. The oncogene Astrocyte elevated gene-1 (AEG-1) is overexpressed in more than 90% of human HCC patients and plays a seminal role in hepatocarcinogenesis. AEG-1 is localized on the cell membrane as well as in the cytoplasm, nucleus and endoplasmic reticulum. In each location AEG-1 interacts with specific proteins thereby modulating diverse intracellular processes which contributes pleotrophic oncogenic properties to AEG-1. Identification of AEG-1 interacting proteins would facilitate better understanding of AEG-1 function and help develop novel and targeted therapies for HCC. Methods: Yeast two-hybrid assay and co-immunoprecipitation (co-ip) followed by mass spectrometry were used to identify AEG-1-interacting proteins. Co-ip and double immunofluorescence analyses were performed to confirm protein-protein interaction. A Renilla luciferase reporter plasmid containing a miRNA-recognition site in the 3’-untranslated region was used in a transfection based assay to monitor RNA-induced silencing complex (RISC) activity. Immunohistochemistry in tissue microarray was performed to check protein expression. Nude mice xenograft studies were done to check tumorigenesis. Results: We identified Staphylococcal nuclease domain containing 1 (SND1), a nuclease functioning in the RNA-induced silencing complex (RISC), as an AEG-1 interacting protein. We documented that AEG-1 interacts with SND1 and Argonaute 2 (Ago2), the major nuclease in RISC, and thus AEG-1 itself is a component of RISC. Knocking down AEG-1 or SND1 abrogates and overexpression of AEG-1 or SND1 augments RISC activity in human HCC cells. In 109 human HCC samples SND1 was overexpressed in ∼74% cases compared to normal liver. Correspondingly, significantly higher RISC activity was observed in human HCC cells compared to normal hepatocytes. We hypothesized that increased RISC activity, conferred by AEG-1 or SND1 overexpression, might facilitate function of oncomiRs resulting in increased degradation of tumor suppressor mRNAs. Indeed, overexpression of AEG-1 or SND1 downregulated while knockdown of AEG-1 or SND1 upregulated the mRNA level of tumor suppressor PTEN, a target of several oncomiRs overexpressed in HCC. Inhibition of SND1 enzymatic activity significantly abrogated cell growth and proliferation of human HCC cells. Stable overexpression of SND1 augmented while stable knockdown of SND1 inhibited tumor growth by human HCC cells in nude mice xenograft assay. Conclusion: We unravel a novel mechanism that overexpression of AEG-1 and SND1 leading to increased RISC activity might contribute to hepatocarcinogenesis. Targeted inhibition of SND1 enzymatic activity might be developed as an effective therapy for HCC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4706. doi:10.1158/1538-7445.AM2011-4706

Astrocyte elevated gene-1 induces protective autophagy

Astrocyte-elevated gene-1 (AEG-1) expression increases in multiple cancers and plays a crucial role in oncogenic transformation and angiogenesis, which are essential components in tumor cell development, growth, and progression to metastasis. Moreover, AEG-1 directly contributes to resistance to chemotherapeutic drugs, another important hallmark of aggressive cancers. In the present study, we document that AEG-1 mediates protective autophagy, an important regulator of cancer survival under metabolic stress and resistance to apoptosis, which may underlie its significant cancer-promoting properties. AEG-1 induces noncanonical autophagy involving an increase in expression of ATG5. AEG-1 decreases the ATP/AMP ratio, resulting in diminished cellular metabolism and activation of AMP kinase, which induces AMPK/mammalian target of rapamycin-dependent autophagy. Inhibition of AMPK by siAMPK or compound C decreases expression of ATG5, ultimately attenuating AEG-1-induced autophagy. AEG-1 protects normal cells from serum starvation-induced death through protective autophagy, and inhibition of AEG-1-induced autophagy results in serum starvation-induced cell death. We also show that AEG-1-mediated chemoresistance is because of protective autophagy and inhibition of AEG-1 results in a decrease in protective autophagy and chemosensitization of cancer cells. In summary, the present study reveals a previously unknown aspect of AEG-1 function by identifying it as a potential regulator of protective autophagy, an important feature of AEG-1 that may contribute to its tumor-promoting properties.

Molecular Mechanism of Chemoresistance by Astrocyte Elevated Gene-1

Our recent findings show that astrocyte elevated gene-1 (AEG-1) is overexpressed in >90% of human hepatocellular carcinoma (HCC) samples, and AEG-1 plays a central role in regulating development and progression of HCC. In the present study, we elucidate a molecular mechanism of AEG-1-induced chemoresistance, an important characteristic of aggressive cancers. AEG-1 increases the expression of multidrug resistance gene 1 (MDR1) protein, resulting in increased efflux and decreased accumulation of doxorubicin, promoting doxorubicin resistance. Suppression of MDR1 by small interfering RNA or chemical reagents, or inhibition of AEG-1 or a combination of both genes, significantly increases in vitro sensitivity to doxorubicin. In nude mice xenograft studies, a lentivirus expressing AEG-1 short hairpin RNA, in combination with doxorubicin, profoundly inhibited growth of aggressive human HCC cells compared with either agent alone. We document that although AEG-1 does not affect MDR1 gene transcription, it facilitates association of MDR1 mRNA to polysomes, resulting in increased translation, and AEG-1 also inhibits ubiquitination and subsequent proteasome-mediated degradation of MDR1 protein. This study is the first documentation of a unique aspect of AEG-1 function (i.e., translational and posttranslational regulation of proteins). Inhibition of AEG-1 might provide a means of more effectively using chemotherapy to treat HCC, which displays inherent chemoresistance with aggressive pathology.

Over‐expression of AEG‐1 significantly associates with tumour aggressiveness and poor prognosis in human non‐small cell lung cancer

Astrocyte elevated gene 1 (AEG-1), a novel oncoprotein, has been implicated in oncogenesis and cancer progression in various types of human cancers. The clinical significance and biological role of AEG-1 in non-small cell lung cancer (NSCLC), however, remain unclear. In the present study, we found that the expression of AEG-1 was markedly up-regulated in NSCLC cell lines and NSCLC tissues at the level of both transcription and translation. Ectopically expressed AEG-1 enhanced the migratory and invasive abilities of NSCLC cells, whereas knockdown of endogenous AEG-1 by specific shRNAs significantly inhibited these abilities. The function of AEG-1 on metastasis modulation was associated with the activation of the PI3K-Akt and NF-kappaB signalling pathways. Furthermore, we showed high expression of AEG-1 in 99/200 (49.5%) paraffin-embedded archival NSCLC specimens. Moreover, statistical analysis displayed a significant correlation in AEG-1 expression with the clinical stage (p < 0.001), T classification (p = 0.001), N classification (p = 0.015), distant metastasis (p = 0.004) and differentiation (p = 0.027). Patients with higher AEG-1 expression had an overall shorter survival time, whereas patients with lower expression of AEG-1 had a better survival time. Multivariate analysis suggested that AEG-1 expression might be an independent prognostic indicator for the survival of NSCLC patients. Taken together, our results suggest that elevated expression of AEG-1 plays an important role in the aggressiveness of NSCLC, leading to a poor clinical outcome.

Astrocyte elevated gene-1 is a proliferation promoter in breast cancer via suppressing transcriptional factor FOXO1

We have previously reported that astrocyte elevated gene-1 (AEG-1) was upregulated in human breast cancer. However, the biological function of AEG-1 in the development and progression of breast cancer remains to be clarified. In this study, we examined the effect of AEG-1 on cell proliferation and found that AEG-1 upregulation was significantly linked to increased Ki67 (P<0.001). Ectopic expression of AEG-1 in MCF-7 and MDA-MB-435 breast cancer cells dramatically enhanced cell proliferation and their ability of anchorage-independent growth, whereas silencing endogenous AEG-1 with shRNAs inhibited cell proliferation and colony-forming ability of the cells on soft agar. Furthermore, these proliferative effects were significantly associated with decreases of p27Kip1 and p21Cip1 two key cell-cycle inhibitors. Moreover, we further demonstrated that AEG-1 could downregulate the transcriptional activity of FOXO1 by inducing its phosphorylation through the PI3K/Akt signaling pathway. These observations were further confirmed in clinical human primary breast cancer specimens, in which high-level expression of AEG-1 was inversely correlated with the expression of FOXO1. Taken together, our results provide the first demonstration of a novel mechanism by which AEG-1 induces proliferation of breast cancer cell, and our findings suggest that AEG-1 might play an important role in tumorigenesis of breast cancer.

Astrocyte elevated gene-1 regulates hepatocellular carcinoma development and progression.

Hepatocellular carcinoma (HCC) is a highly aggressive vascular cancer characterized by diverse etiology, activation of multiple signal transduction pathways, and various gene mutations. Here, we have determined a specific role for astrocyte elevated gene-1 (AEG1) in HCC pathogenesis. Expression of AEG1 was extremely low in human hepatocytes, but its levels were significantly increased in human HCC. Stable overexpression of AEG1 converted nontumorigenic human HCC cells into highly aggressive vascular tumors, and inhibition of AEG1 abrogated tumorigenesis by aggressive HCC cells in a xenograft model of nude mice. In human HCC, AEG1 overexpression was associated with elevated copy numbers. Microarray analysis revealed that AEG1 modulated the expression of genes associated with invasion, metastasis, chemoresistance, angiogenesis, and senescence. AEG1 also was found to activate Wnt/beta-catenin signaling via ERK42/44 activation and upregulated lymphoid-enhancing factor 1/T cell factor 1 (LEF1/TCF1), the ultimate executor of the Wnt pathway, important for HCC progression. Inhibition studies further demonstrated that activation of Wnt signaling played a key role in mediating AEG1 function. AEG1 also activated the NF-kappaB pathway, which may play a role in the chronic inflammatory changes preceding HCC development. These data indicate that AEG1 plays a central role in regulating diverse aspects of HCC pathogenesis. Targeted inhibition of AEG1 might lead to the shutdown of key elemental characteristics of HCC and could lead to an effective therapeutic strategy for HCC.

Molecular Basis of Nuclear Factor-κB Activation by Astrocyte Elevated Gene-1

Malignant glioma is a consistently fatal brain cancer. The tumor invades the surrounding tissue, limiting complete surgical removal and thereby initiating recurrence. Identifying molecules critical for glioma invasion is essential to develop targeted, effective therapies. The expression of astrocyte elevated gene-1 (AEG-1) increases in malignant glioma and AEG-1 regulates in vitro invasion and migration of malignant glioma cells by activating the nuclear factor-kappaB (NF-kappaB) signaling pathway. The present studies elucidate the domains of AEG-1 important for mediating its function. Serial NH(2)-terminal and COOH-terminal deletion mutants were constructed and functional analysis revealed that the NH(2)-terminal 71 amino acids were essential for invasion, migration, and NF-kappaB-activating properties of AEG-1. The p65-interaction domain was identified between amino acids 101 to 205, indicating that p65 interaction alone is not sufficient to mediate AEG-1 function. Coimmunoprecipitation assays revealed that AEG-1 interacts with cyclic AMP-responsive element binding protein-binding protein (CBP), indicating that it might act as a bridging factor between NF-kappaB, CBP, and the basal transcription machinery. Chromatin immunoprecipitation assays showed that AEG-1 is associated with the NF-kappaB binding element in the interleukin-8 promoter. Thus, AEG-1 might function as a coactivator for NF-kappaB, consequently augmenting expression of genes necessary for invasion of glioma cells. In these contexts, AEG-1 represents a viable potential target for the therapy of malignant glioma.