Identification of genes conferring resistance to 5-fluorouracil. Proc Natl Acad Sci U S A. 2009;106:12938-12943. [PMID: 19622726 DOI: 10.1073/pnas.0901451106]

Epigenetics and chemoresistance in colorectal cancer: an opportunity for treatment tailoring and novel therapeutic strategies

Colorectal cancer is the second leading cause of cancer-related deaths in the world. Despite many therapeutic opportunities, prognosis remains dismal for patients with metastatic disease, and a significant portion of early-stage patients develop recurrence after chemotherapy. Epigenetic gene regulation is a major mechanism of cancer initiation and progression, through the inactivation of several tumor suppressor genes. Emerging evidence indicates that epigenetics may also play a key role in the development of chemoresistance. In the present review, we summarize epigenetic mechanisms triggering resistance to three commonly used agents in colorectal cancer: 5-fluorouracil, irinotecan and oxaliplatin. Those epigenetic biomarkers may help stratify colorectal cancer patients and develop a tailored therapeutic approach. In addition, epigenetic modifications are reversible through specific drugs: histone-deacetylase and DNA-methyl-transferase inhibitors. Preclinical studies suggest that these drugs may reverse chemoresistance in colorectal tumors. In conclusion, an epigenetic approach to colorectal cancer chemoresistance may pave the way to personalized treatment and to innovative therapeutic strategies.

Insulin-like growth factor-binding protein-7 functions as a potential tumor suppressor in hepatocellular carcinoma

PURPOSE

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.

EXPERIMENTAL DESIGN

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.

RESULTS

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.

CONCLUSION

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.

Expression of astrocyte elevated gene-1: a novel marker of the pathogenesis, progression, and poor prognosis for endometrial cancer

OBJECTIVE

To assess the expression of astrocyte elevated gene-1 (AEG-1) in different endometrial specimens and to investigate its relationship with clinicopathological features and its impact on patient outcome.

MATERIALS AND METHODS

By Western blot analysis, we investigated AEG-1 expression in paired endometrial tissues and adjacent nontumor tissues of the same patients (n = 4). Immunohistochemistry analysis was used to determine the expression levels of AEG-1 protein in 35 normal endometrium, 40 atypical endometrial hyperplasia, and 174 endometrial cancers. The correlation between AEG-1 expression and various clinicopathological characteristics of endometrial cancer patients was analyzed.

RESULTS

Western blot analysis showed that AEG-1 expression levels were up-regulated in all 4 human primary endometrial cancer tissues compared with their matched adjacent noncancerous tissues. The frequent and strong expression of AEG-1 was gradually elevated in normal endometrial tissue, atypical hyperplasia, and endometrial cancers (P < 0.001). Although AEG-1 staining mainly emerged in the cytoplasm, a nuclear distribution was observed in both invasive and advanced endometrial cancer cells. The Ki67 (a proliferation marker) was frequently expressed in the high AEG-1-expressed area, whereas areas with low AEG-1 levels showed weak Ki67 expression. Astrocyte elevated gene-1 overexpression was positively correlated with the International Federation of Gynecology and Obstetrics stage, depth of myometrial invasion, lymph node metastasis, lymph vascular space invasion, and recurrence but not with age or histological type. Patients with high AEG-1 expression had significantly poor overall survival and disease-free survival compared with patients with AEG-1 low expression (both P < 0.001). Multivariate Cox proportional hazards regression demonstrated that high AEG-1 expression was an independent prognostic factor for both the overall survival and disease-free survival of patients with endometrial cancer (P = 0.002 and P = 0.004, respectively).

CONCLUSION

Astrocyte elevated gene-1 overexpression may be associated with carcinogenesis and tumor progression in endometrial cancer. Moreover, it may be a new prognostic marker or a target for improving the treatment efficiency of patients with endometrial cancer.

Knockdown of MTDH sensitizes endometrial cancer cells to cell death induction by death receptor ligand TRAIL and HDAC inhibitor LBH589 co-treatment

Understanding the molecular underpinnings of chemoresistance is vital to design therapies to restore chemosensitivity. In particular, metadherin (MTDH) has been demonstrated to have a critical role in chemoresistance. Over-expression of MTDH correlates with poor clinical outcome in breast cancer, neuroblastoma, hepatocellular carcinoma and prostate cancer. MTDH is also highly expressed in advanced endometrial cancers, a disease for which new therapies are urgently needed. In this present study, we focused on the therapeutic benefit of MTDH depletion in endometrial cancer cells to restore sensitivity to cell death. Cells were treated with a combination of tumor necrosis factor-α-related apoptosis-inducing ligand (TRAIL), which promotes death of malignant cells of the human reproductive tract, and histone deacetylase (HDAC) inhibitors, which have been shown to increase the sensitivity of cancer cells to TRAIL-induced apoptosis. Our data indicate that depletion of MTDH in endometrial cancer cells resulted in sensitization of cells that were previously resistant in response to combinatorial treatment with TRAIL and the HDAC inhibitor LBH589. MTDH knockdown reduced the proportion of cells in S and increased cell arrest in G2/M in cells treated with LBH589 alone or LBH589 in combination with TRAIL, suggesting that MTDH functions at the cell cycle checkpoint to accomplish resistance. Using microarray technology, we identified 57 downstream target genes of MTDH, including calbindin 1 and galectin-1, which may contribute to MTDH-mediated therapeutic resistance. On the other hand, in MTDH depleted cells, inhibition of PDK1 and AKT phosphorylation along with increased Bim expression and XIAP degradation correlated with enhanced sensitivity to cell death in response to TRAIL and LBH589. These findings indicate that targeting or depleting MTDH is a potentially novel avenue for reversing therapeutic resistance in patients with endometrial cancer.

MTDH/AEG-1-based DNA vaccine suppresses lung metastasis and enhances chemosensitivity to doxorubicin in breast cancer

The gene MTDH/AEG-1 is overexpressed in more than 40% of breast cancer patients, and it is associated with poor clinical outcomes. Previous studies have indicated that MTDH/AEG-1 could promote metastatic lung-seeding and enhance chemoresistance. Therefore, MTDH/AEG-1 could be a candidate target against breast cancer lung metastasis. We demonstrated that MTDH/AEG-1-based DNA vaccine, delivered by attenuated Salmonella typhimurium, could evoke strong CD8(+) cytotoxic-T-cell mediated immune responses against breast cancer. This vaccine showed anti-tumor growth and metastasis efficacy in a prophylactic setting. Importantly, in a therapeutic model, MTDH/AEG-1 vaccine was proved to increase chemosensitivity to doxorubicin and inhibit breast cancer lung metastasis. This vaccine could also prolong the life span of tumor-bearing mice without significant side effects in vivo. These results suggested that this novel DNA vaccine was effective in the inhibition of breast cancer growth and metastasis, and this vaccine in combination with chemotherapies offered new strategies for the clinical therapeutics of breast cancer metastasis.

Thymidylate synthase expression and genotype have no major impact on the clinical outcome of colorectal cancer patients treated with 5-fluorouracil

BACKGROUND AND OBJECTIVES

Thymidylate synthase (TS) expression levels appear to be related to response to 5-fluorouracil-(5-FU)-based chemotherapy in colorectal cancer (CRC) patients. Three polymorphisms have been proposed as modulators of TS expression: a tandemly repeated sequence (2R/3R) in the 5' UTR, a SNP (G>C) within the 3R allele and a 6bp deletion in the 3' UTR. To evaluate the influence of TS expression and polymorphisms on clinical outcome of 5-FU-treated patients we performed a comprehensive genetic analysis on 63 CRC patients.

METHODS

TS expression levels were analyzed in normal and tumor tissues. TS coding sequence and UTR polymorphisms were investigated on DNA from normal tissue. LOH analysis was performed to determine tumor genotype.

RESULTS

A difference in disease-free survival (DFS), although not statistically significant, was observed between high and low mRNA expression levels: patients with low levels showed longer DFS. The 2R2R genotype showed significantly lower expression than the 3R3R and 2R3R genotypes in normal tissue. No other TS polymorphism was associated with mRNA expression or clinical outcome.

CONCLUSIONS

The results obtained in this pilot study indicate that the number of 5' UTR repeats is the major genetic determinant of TS expression. The lack of association with other polymorphisms might be partially explained by the existence of linkage disequilibrium in the TS gene. Our data support the growing evidence that TS control may require multiple mechanisms acting in close coordination with one another and suggest that TS genotyping alone in tumor samples is not sufficient to accurately predict response to 5-FU.

Identification of staphylococcal nuclease domain-containing 1 (SND1) as a Metadherin-interacting protein with metastasis-promoting functions

Metastasis is the deadliest and most poorly understood feature of malignant diseases. Recent work has shown that Metadherin (MTDH) is overexpressed in over 40% of breast cancer patients and promotes metastasis and chemoresistance in experimental models of breast cancer progression. Here we applied mass spectrometry-based screen to identify staphylococcal nuclease domain-containing 1 (SND1) as a candidate MTDH-interacting protein. After confirming the interaction between SND1 and MTDH, we tested the role of SND1 in breast cancer and found that it strongly promotes lung metastasis. SND1 was further shown to promote resistance to apoptosis and to regulate the expression of genes associated with metastasis and chemoresistance. Analyses of breast cancer clinical microarray data indicated that high expression of SND1 in primary tumors is strongly associated with reduced metastasis-free survival in multiple large scale data sets. Thus, we have uncovered SND1 as a novel MTDH-interacting protein and shown that it is a functionally and clinically significant mediator of metastasis.

Astrocyte elevated gene-1 and breast cancer (Review)

Astrocyte elevated gene-1 (AEG-1), also known as MTDH and Lyric, is a novel gene that was first cloned by subtraction hybridization in 2002 and has recently been shown to play a role as a crucial oncogene that acts as a promoter of tumor malignancy. Overexpression and inhibition studies both in in vitro and in vivo models have partly shown the oncogenic roles of AEG-1 in a number of crucial aspects of tumor development and progression, including transformation, evasion of apoptosis, proliferation, cell survival, migration, invasion, metastasis, angiogenesis and chemoresistance through the activation of numerous signaling pathways, such as the nuclear factor κB, PI3K/AKT, Wnt/β-catenin and mitogen-activated protein kinase signaling pathways. However the potential roles of AEG-1, particularly in specific organs or tissues, such as breast tissue, require further clarification. Studies have found that in normal human breast tissue, AEG-1 is always expressed at low levels or is absent, while it is widely overexpressed in many breast cancer cell lines and breast tumors. The present review evaluates the current literature with regards to AEG-1 relative to breast cancer development and progression and highlights new perspectives relative to this molecule, indicating its potential to become a new target for the clinical treatment of breast cancer.

Astrocyte elevated gene-1 (AEG-1): A multifunctional regulator of normal and abnormal physiology

Since its initial identification and cloning in 2002, Astrocyte Elevated Gene-1 (AEG-1), also known as metadherin (MTDH), 3D3 and LYsine-RIch CEACAM1 co-isolated (LYRIC), has emerged as an important oncogene that is overexpressed in all cancers analyzed so far. Examination of a large cohort of patient samples representing diverse cancer indications has revealed progressive increase in AEG-1 expression with stages and grades of the disease and an inverse relationship between AEG-1 expression level and patient prognosis. AEG-1 functions as a bona fide oncogene by promoting transformation. In addition, it plays a significant role in invasion, metastasis, angiogenesis and chemoresistance, all important hallmarks of an aggressive cancer. AEG-1 is also implicated in diverse physiological and pathological processes, such as development, inflammation, neurodegeneration, migraine and Huntington's disease. AEG-1 is a highly basic protein with a transmembrane domain and multiple nuclear localization signals and it is present in the cell membrane, cytoplasm, nucleus, nucleolus and endoplasmic reticulum. In each location, AEG-1 interacts with specific proteins thereby modulating diverse intracellular processes the combination of which contributes to its pleiotrophic properties. The present review provides a snapshot of the current literature along with future perspectives on this unique molecule.

Astrocyte elevated gene-1 (AEG-1): A multifunctional regulator of normal and abnormal physiology

Since its initial identification and cloning in 2002, Astrocyte Elevated Gene-1 (AEG-1), also known as metadherin (MTDH), 3D3 and LYsine-RIch CEACAM1 co-isolated (LYRIC), has emerged as an important oncogene that is overexpressed in all cancers analyzed so far. Examination of a large cohort of patient samples representing diverse cancer indications has revealed progressive increase in AEG-1 expression with stages and grades of the disease and an inverse relationship between AEG-1 expression level and patient prognosis. AEG-1 functions as a bona fide oncogene by promoting transformation. In addition, it plays a significant role in invasion, metastasis, angiogenesis and chemoresistance, all important hallmarks of an aggressive cancer. AEG-1 is also implicated in diverse physiological and pathological processes, such as development, inflammation, neurodegeneration, migraine and Huntington's disease. AEG-1 is a highly basic protein with a transmembrane domain and multiple nuclear localization signals and it is present in the cell membrane, cytoplasm, nucleus, nucleolus and endoplasmic reticulum. In each location, AEG-1 interacts with specific proteins thereby modulating diverse intracellular processes the combination of which contributes to its pleiotrophic properties. The present review provides a snapshot of the current literature along with future perspectives on this unique molecule.

Effect of small interfering RNA 3'-end overhangs on chemosensitivity to thymidylate synthase inhibitors

Background

Small interfering RNAs (siRNAs) are double-stranded RNAs that effectively inhibit expression of its complimentary target mRNA. Standard siRNAs contain two nucleotide overhangs on their 3' end. While these overhangs are usually comprised of deoxythymidines (dT), it has been shown that any nucleotide can be used on the 3' end without affecting RNAi silencing.

Results

It was recently shown that extension of the 3' end to five or eight dT molecules allows siRNAs to be effectively complexed with linear polyethylenimine (PEI), leading to enhanced cellular uptake and intracellular release. Here, we provide further evidence that only extended or 'sticky' siRNAs complexed with PEI result in significant target knockdown. However, when investigating the potential effects of these extended siRNAs on growth of human colon cancer RKO cells, we observed a dose-dependent reversal of cytotoxicity of a thymidylate synthase-targeted siRNA. In contrast, siRNAs with uridine overhangs maintained their growth inhibitory effects. We further demonstrated that dT-containing siRNAs prevented the cytotoxic effects of thymidylate synthase (TS) inhibitor compounds, such as ZD1694 and 5'-fluoro-deoxyuridine, while having no deleterious effect on cisplatin toxicity. We show that this rescue effect results from the rapid degradation of the siRNA.

Conclusions

Given that TS is an important enzyme for cell growth and proliferation and that its expression is controlled by multiple pathways, the rescue of its growth inhibitory effects may have unintended consequences. As siRNAs are being developed as therapeutic molecules, it will be important to avoid such off-target effects due to dT release. Hence, siRNAs should contain only uridine residues in their 3'-end overhangs.

Astrocyte-elevated gene-1 (AEG-1) induction by hypoxia and glucose deprivation in glioblastoma

Glioblastomas continue to carry poor prognoses for patients despite advances in surgical, chemotherapeutic, and radiation regimens. One feature of glioblastoma associated with poor prognosis is the degree of hypoxia and expression levels of hypoxia-inducible factor-1 α (HIF-1α). HIF-1α expression allows metabolic adaptation to low oxygen availability, partly through upregulation of VEGF and increased tumor angiogenesis. Here, we demonstrate an induced level of astrocyte-elevated gene-1 (AEG-1) by hypoxia in glioblastoma cells. AEG-1 has the capacity to promote anchorage-independent growth and cooperates with Ha-ras in malignant transformation. In addition, AEG-1 was recently demonstrated to serve as an oncogene and can induce angiogenesis in glioblastoma. Results from in vitro studies show that hypoxic induction of AEG-1 is dependent on HIF-1α stabilization during hypoxia and that PI3K inhibition abrogates AEG-1 induction during hypoxia through loss of HIF-1α stability. Furthermore, we show that AEG-1 is induced by glucose deprivation and that prevention of intracellular reactive oxygen species (ROS) production prevents this induction. Additionally, AEG-1 knockdown results in increased ROS production and increased glucose deprivation-induced cytotoxicity. On the other hand, AEG-1 overexpression prevents ROS production and decreases glucose deprivation-induced cytotoxicity, indicating that AEG-1 induction is necessary for cells to survive this type of cell stress. These observations link AEG-1 overexpression in glioblastoma with hypoxia and glucose deprivation, and targeting these physiological pathways may lead to therapeutic advances in the treatment of glioblastoma in the future.

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.

Prognostic significance of AEG-1 expression in colorectal carcinoma

BACKGROUND

Astrocyte elevated gene-1 (AEG-1), as an HIV-1 or TNF-alpha-inducible transcript, is associated with various aspects of tumor malignancy. However, relatively little knowledge is available related to the role of AEG-1 in colorectal carcinoma.

METHODS

By immunohistochemical and western blot analysis, we investigated AEG-1 expression in normal mucosa, adenomas, and carcinomas of colorectum. By statistical analysis, we determined its relationship with clinicopathological parameters and overall survival in colorectal carcinoma.

RESULTS

We found that AEG-1 expression levels were gradually elevated in normal tissues, low-grade adenoma, high-grade adenoma, and colorectal carcinoma, respectively. Though AEG-1 staining mainly emerged in the cytoplasm, we observed that nuclear staining of AEG-1 tends to become more common in lesions from patients with more advanced disease stages. Furthermore, there was a similar trend for Ki67 expression (as a proliferative index) from normal mucous to adenoma and carcinoma. Statistical analysis revealed that AEG-1 expression was markedly correlated with the UICC stage (P < 0.001), T classification (P = 0.002), N classification (P = 0.015), M classification (P = 0.010), Ki67 expression (P = 0.012), and histological differentiation (P = 0.037) in the colorectal cancer patients. Besides, those patients with high AEG-1 levels had shorter survival time (P < 0.001).

CONCLUSIONS

High AEG-1 expression correlates with poor overall survival in the colorectal carcinoma patients. In addition, AEG-1 expression in colorectal carcinoma may be associated with tumor progression, indicating that AEG-1 may be a potential preventive and chemotherapeutic target in the patients.

Prolyl isomerase Pin1 regulates transcription factor LSF (TFCP2) by facilitating dephosphorylation at two serine-proline motifs

Transcription factor LSF is essential for cell cycle progression, being required for activating expression of the thymidylate synthase (Tyms) gene at the G1/S transition. We previously established that phosphorylation of LSF in early G1 at Ser-291 and Ser-309 inhibits its transcriptional activity and that dephosphorylation later in G1 is required for its reactivation. Here we reveal the role of prolyl cis-trans isomerase Pin1 in activating LSF, by facilitating dephosphorylation at both Ser-291 and Ser-309. We demonstrate that Pin1 binds LSF both in vitro and in vivo. Using coimmunoprecipitation assays, we identify three SP/TP motifs in LSF (at residues Ser-291, Ser-309, and Thr-329) that are required and sufficient for association with Pin1. Co-expression of Pin1 enhances LSF transactivation potential in reporter assays. The Pin1-dependent enhancement of LSF activity requires residue Thr-329 in LSF, requires both the WW and PPiase domains of Pin1, and correlates with hypophosphorylation of LSF at Ser-291 and Ser-309. These findings support a model in which the binding of Pin1 at the Thr-329-Pro-330 motif in LSF permits isomerization by Pin1 of the peptide bonds at the nearby phosphorylated SP motifs (Ser-291 and Ser-309) to the trans configuration, thereby facilitating their dephosphorylation.

Transcription factor Late SV40 Factor (LSF) functions as an oncogene in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a highly aggressive cancer with no currently available effective treatment. Understanding of the molecular mechanism of HCC development and progression is imperative for developing novel, effective, and targeted therapies for this lethal disease. In this article, we document that the cellular transcription factor Late SV40 Factor (LSF) plays an important role in HCC pathogenesis. LSF protein was significantly overexpressed in human HCC cells compared to normal hepatocytes. In 109 HCC patients, LSF protein was overexpressed in >90% cases, compared to normal liver, and LSF expression level showed significant correlation with the stages and grades of the disease. Forced overexpression of LSF in less aggressive HCC cells resulted in highly aggressive, angiogenic, and multiorgan metastatic tumors in nude mice. Conversely, inhibition of LSF significantly abrogated growth and metastasis of highly aggressive HCC cells in nude mice. Microarray studies revealed that as a transcription factor, LSF modulated specific genes regulating invasion, angiogenesis, chemoresistance, and senescence. The expression of osteopontin (OPN), a gene regulating every step in tumor progression and metastasis, was robustly up-regulated by LSF. It was documented that LSF transcriptionally up-regulates OPN, and loss-of-function studies demonstrated that OPN plays an important role in mediating the oncogenic functions of LSF. Together, these data establish a regulatory role of LSF in cancer, particularly HCC pathogenesis, and validate LSF as a viable target for therapeutic intervention.

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.

Astrocyte-elevated gene-1 overexpression is associated with poor prognosis in gastric cancer

Astrocyte-elevated gene-1 (AEG-1) plays an important role in diverse cancers and its up-regulation is associated with poor survival of patients. However, the status of AEG-1 expression and its significance in gastric cancer are still unclear. In this study, the expression of AEG-1 was studied in different gastric cancer cell lines and gastric cancer tissues. Expression of AEG-1 was significantly higher in gastric cancer tissues than that in normal tissues. Overexpression of AEG-1 was found in 62.9% of gastric cancers and significantly associated with TNM stage and Ki-67 proliferation index (P < 0.01). For survival study, overexpression of AEG-1 was significantly associated with poor survival (P < 0.01). Further multivariate analysis suggested that AEG-1 overexpression was an independent prognostic factor for the disease. We demonstrated that inhibition of AEG-1 expression by specific siRNA clearly inhibited SGC-7901 cell growth and enhanced cell apoptosis (P < 0.01). Inhibition of AEG-1 reduced phosphorylation of AKT and glycogen synthase kinase (GSK)-3β (Ser 9) and decreased the level of β-catenin, lymphoid enhancer binding factor 1 (LEF1), and Cyclin D1. This indicated that AEG-1 may play a role in Wnt/β-catenin-mediated cancer progression. Taken together, overexpression of AEG-1 could be a useful prognostic factor in patients with gastric cancer. Targeted inhibition of AEG-1 may provide a novel therapeutic strategy for gastric cancer.

Astrocyte elevated gene-1: a novel target for human glioma therapy

Malignant gliomas including glioblastoma multiforme (GBM) and anaplastic astrocytomas are the most common primary brain tumors. Despite multimodal treatment including surgery, chemotherapy, and radiation, median survival for patients with GBMs is only 12 to 15 months. Identifying molecules critical for glioma progression is crucial for devising effective targeted therapy. In the present study, we investigated the potential contribution of astrocyte elevated gene-1 (AEG-1) in gliomagenesis and explored the possibility of AEG-1 as a therapeutic target for malignant glioma. We analyzed the expression levels of AEG-1 in 9 normal brain tissues and 98 brain tumor patient samples by Western blot analysis and immunohistochemistry. AEG-1 expression was significantly elevated in >90% of diverse human brain tumor samples including GBMs and astrocytic tumors, and also in human glioma cell lines compared with normal brain tissues and normal astrocytes. Knockdown of AEG-1 by small interfering RNA inhibited cell viability, cloning efficiency, and invasive ability of U87 human glioma cells and 9L rat gliosarcoma cells. We also found that matrix metalloproteases (MMP-2 and MMP-9) are involved in AEG-1-mediated invasion of glioma cells. In an orthotopic nude mouse brain tumor model using primary human GBM12 tumor cells, AEG-1 small interfering RNA significantly suppressed glioma cell growth in vivo. Taken together, these provocative results indicate that AEG-1 may play a crucial role in the pathogenesis of glioma and that AEG-1 could represent a viable potential target for malignant glioma therapy.

Astrocyte elevated gene-1: far more than just a gene regulated in astrocytes

Since its original cloning by subtraction hybridization in 2002, it is now evident that Astrocyte elevated gene-1 (AEG-1) is a key contributor to the carcinogenic process in diverse organs. AEG-1 protein expression is elevated in advanced stages of many cancers, which correlates with poor survival. In specific cancers, such as breast and liver cancer, the AEG-1 gene itself is amplified, further supporting a seminal role in tumorigenesis. Overexpression and inhibition studies both in in vitro and in in vivo models reveal the importance of AEG-1 in regulating multiple physiologically and pathologically relevant processes including proliferation, invasion, metastasis, and gene expression. AEG-1 is a single-pass transmembrane protein with multiple nuclear localization signals and no known domains or motifs. Although pertinent roles of AEG-1 in the carcinogenic process are established, its potential function (promotion of metastasis only versus functioning as a bona fide oncogene) as well as localization (cell surface versus nucleus) remain areas requiring further clarification. The present review critically evaluates what is currently known about AEG-1 and provides new perspectives relative to this intriguing molecule that may provide a rational target for intervening in the cancer phenotype.