Identification of gene products suppressed by human immunodeficiency virus type 1 infection or gp120 exposure of primary human astrocytes by rapid subtraction hybridization

Noncanonical Functions and Cellular Dynamics of the Mammalian Signal Recognition Particle Components

The signal recognition particle (SRP) is a ribonucleoprotein complex fundamental for co-translational delivery of proteins to their proper membrane localization and secretory pathways. Literature of the past two decades has suggested new roles for individual SRP components, 7SL RNA and proteins SRP9, SRP14, SRP19, SRP54, SRP68 and SRP72, outside the SRP cycle. These noncanonical functions interconnect SRP with a multitude of cellular and molecular pathways, including virus-host interactions, stress response, transcriptional regulation and modulation of apoptosis in autoimmune diseases. Uncovered novel properties of the SRP components present a new perspective for the mammalian SRP as a biological modulator of multiple cellular processes. As a consequence of these findings, SRP components have been correlated with a growing list of diseases, such as cancer progression, myopathies and bone marrow genetic diseases, suggesting a potential for development of SRP-target therapies of each individual component. For the first time, here we present the current knowledge on the SRP noncanonical functions and raise the need of a deeper understanding of the molecular interactions between SRP and accessory cellular components. We examine diseases associated with SRP components and discuss the development and feasibility of therapeutics targeting individual SRP noncanonical functions.

The long non-coding RNA HCG18 promotes the growth and invasion of colorectal cancer cells through sponging miR-1271 and upregulating MTDH/Wnt/β-catenin

Long non-coding RNAs (lncRNAs) have recently emerged as key regulators of the occurrence and progression of various human cancers, including colorectal cancer. However, the regulatory mechanism of lncRNAs in the tumorigenesis of colorectal cancer remains poorly understood. In this study, we aimed to elucidate the potential role of lncRNA HCG18 in colorectal cancer. Herein, we found that HCG18 expression was significantly upregulated in colorectal cancer tissues and cell lines. Knockdown of HCG18 significantly inhibited the growth and invasion of colorectal cancer cells, while its overexpression had the opposite effect. Moreover, HCG18 was identified as a sponge of miR-1271. Our results showed that knockdown of HCG18 markedly upregulated miR-1271 expression in colorectal cancer cells. Notably, HCG18 expression was inversely correlated with miR-1271 expression in colorectal cancer specimens. Further investigation revealed that HCG18 contributed to the enhancement of MTDH/Wnt/β-catenin signalling in colorectal cancer cells. The antitumour effect of HCG18 inhibition was significantly reversed by miR-1271 inhibition or MTDH overexpression. Overall, the results of our study demonstrate that HCG18 exerts a potential oncogenic function in colorectal cancer by enhancing MTDH/Wnt/β-catenin signalling via sponging of miR-1271, highlighting the importance of HCG18/miR-1271/ MTDH/Wnt/β-catenin signalling in the progression of colorectal cancer.

Downregulation of microRNA-216b contributes to glioma cell growth and migration by promoting AEG-1-mediated signaling

Accumulating evidence indicates microRNA-216b (miR-216b) plays an important role in the development and progression of various cancers. However, little is known about the function of miR-216b in gliomas. In this study, we aimed to investigate the expression level and functional significance of miR-216b in gliomas. We found that miR-216b was significantly downregulated in glioma specimens and cell lines. Overexpression of miR-216b suppressed the growth and migration of glioma cells, while miR-216b inhibition showed the opposite effects. Astrocyte elevated gene-1 (AEG-1) was predicted as a potential target gene of miR-216b by bioinformatics analysis. A dual-luciferase reporter assay showed that miR-216b could directly target the 3'-untranslated region of AEG-1. RT-qPCR and western blot analysis showed that miR-216 negatively regulated AEG-1 expression in glioma cells. Correlation analysis revealed an inverse correlation between miR-216b and AEG-1 in clinical glioma specimens. miR-216b also regulated the activation of nuclear factor-κB and Wnt signaling in glioma cells. Moreover, restoration of AEG-1 expression partially reversed the inhibitory effect of miR-216b overexpression on glioma cell growth and migration. Overall, these results revealed a tumor suppressive role of miR-216b in glioma tumorigenesis, and identified AEG-1 as a target gene of miR-216b action. Our study suggests that miR-216b can be potentially targeted for the development of novel therapies for gliomas.

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.

Astrocyte elevated gene-1 promotes inflammation and invasion of fibroblast-like synoviocytes in rheumatoid arthritis

Astrocyte elevated gene-1 (AEG-1) was initially induced by HIV-1 infection and involved in tumor progression, migration and invasion as a nuclear factor-κB (NF-κB)-dependent gene. The present study we intended to investigate the protein expression of AEG-1 significantly associated with rheumatoid arthritis. Western blot analysis and immunohistochemistry demonstrated that AEG-1 was upregulated in synovial tissue of RA patients compared with the controls. Double immunofluorescent staining suggested that AEG-1 was expressed in fibroblast-like synoviocytes (FLS) of RA patients. Furthermore, the expression of AEG-1 in FLS was increased in time-dependent manner by TNF-α stimulation. Upon TNF-α-treated FLS, AEG-1 transferred from the cytoplasm to nucleus where it interacted with the p65 subunit of NF-κB, as examined by immunoprecipitation and immunofluorescent staining assay. Moreover, the inhibition of AEG-1 by RNA interference significantly suppressed TNF-α-induced IL-6 and MMP-3 expression, leading to attenuation of FLS migration and invasion and markedly decreased the phosphorylation of P65 and IκBα, as well as AKT in FLS. Collectively, Our findings provided evidence that AEG-1 contributed to the production of inflammatory cytokines, migration and invasion of RA FLS, and underscored the importance of AEG-1 in the inflammation process of RA.

MicroRNA-384 Inhibits the Growth and Invasion of Renal Cell Carcinoma Cells by Targeting Astrocyte Elevated Gene 1

MicroRNAs (miRNAs) are emerging as pivotal regulators in the development and progression of various cancers, including renal cell carcinoma (RCC). MicroRNA-384 (miR-384) has been found to be an important cancer-related miRNA in several types of cancers. However, the role of miR-384 in RCC remains unclear. In this study, we aimed to investigate the potential function of miR-384 in regulating tumorigenesis in RCC. Here we found that miR-384 was significantly downregulated in RCC tissues and cell lines. Overexpression of miR-384 significantly inhibited the growth and invasion of RCC cells, whereas inhibition of miR-384 had the opposite effects. Bioinformatic analysis and luciferase reporter assay showed that miR-384 directly targeted the 3′-untranslated region of astrocyte elevated gene 1 (AEG-1). Further data showed that miR-384 could negatively regulate the expression of AEG-1 in RCC cells. Importantly, miR-384 expression was inversely correlated with AEG-1 expression in clinical RCC specimens. Moreover, miR-384 regulates the activation of Wnt signaling. Overexpression of AEG-1 significantly reversed the antitumor effects of miR-384. Overall, these findings suggest that miR-384 suppresses the growth and invasion of RCC cells via downregulation of AEG-1, providing a potential therapeutic target for the treatment of RCC.

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.

HIF-1α binding to AEG-1 promoter induced upregulated AEG-1 expression associated with metastasis in ovarian cancer

Ovarian cancer with the highest mortality rate among gynecological malignancies is one of common cancers among female cancer patients. As reported in recent years, AEG‐1 was associated with the occurrence, development, and metastasis of ovarian cancer, but the mechanisms remain unclear. In the current study, invasion capabilities of ovarian cancer OVCAR3 cells were measured by viral infection and transwell assay. Western blot analysis was used to evaluate the expression levels of β‐catenin, E‐cadherin, MMP2, and MMP9. With qRT‐PCR analysis, AEG‐1 and HIF‐1α gene expression were detected. We used luciferase reporter gene to measure AEG‐1 promoter activity under normoxia/hypoxia in OVCAR3 cells. Our work demonstrated that AEG‐1 significantly enhanced invasion capabilities of OVCAR3 cells and the expression levels of β‐catenin, E‐cadherin, MMP2, and MMP9 associated with invasion capabilities of OVCAR3 cells were upregulated. Furthermore, hypoxia enhanced invasion capabilities of OVCAR3 cells and induced AEG‐1 high gene expression, which was reversed by AEG‐1 knockdown lentivirus. HIF‐1α expression upregulation was induced in OVCAR3 cells after hypoxia. HIF‐1α knockdown lentivirus induced downregulated expression of AEG‐1 and invasion capabilities of OVCAR3 cells were also inhibited. Wild‐type AEG‐1 promoter activity under hypoxic conditions was significantly higher than that AEG‐1 mutation under normoxic conditions in the absence of hypoxia response. Our results suggested that HIF‐1α binds to AEG‐1 promoter to upregulate its expression, which was correlated with metastasis in ovarian cancer by inducing the expression of MMP2 and MMP9 as well as inhibiting expression of E‐cadherin and β‐catenin.

Astrocyte Elevated Gene 1 Interacts with Acetyltransferase p300 and c-Jun To Promote Tumor Aggressiveness

Astrocyte elevated gene 1 (AEG-1) is an oncoprotein that strongly promotes the development and progression of cancers. However, the detailed underlying mechanisms through which AEG-1 enhances tumor development and progression remain to be determined. In this study, we identified c-Jun and p300 to be novel interacting partners of AEG-1 in gliomas. AEG-1 promoted c-Jun transcriptional activity by interacting with the c-Jun/p300 complex and inducing c-Jun acetylation. Furthermore, the AEG-1/c-Jun/p300 complex was found to bind the promoter of c-Jun downstream targeted genes, consequently establishing an acetylated chromatin state that favors transcriptional activation. Importantly, AEG-1/p300-mediated c-Jun acetylation resulted in the development of a more aggressive malignant phenotype in gliomas through a drastic increase in glioma cell proliferation and angiogenesis in vitro and in vivo Consistently, the AEG-1 expression levels in clinical glioma specimens correlated with the status of c-Jun activation. Taken together, our results suggest that AEG-1 mediates a novel epigenetic mechanism that enhances c-Jun transcriptional activity to induce glioma progression and that AEG-1 might be a novel, potential target for the treatment of gliomas.

Astrocyte elevated gene-1 (AEG-1) promotes osteosarcoma cell invasion through the JNK/c-Jun/MMP-2 pathway

Osteosarcoma is the most common primary malignant bone tumour in children and adolescents and is characterised by high malignant and metastatic potentials. However, the molecular mechanism underlying this invasiveness remains unclear. In this study, we determined that PD98059 and SP600125, the two mitogen-activated protein kinase (MAPK) family inhibitors, decreased the osteosarcoma cell U2OS-AEG-1 migration and invasion that was enhanced by astrocyte elevated gene-1 (AEG-1) in an in vitro wound-healing and Matrigel invasion assay independently of cell viability. These findings indicate that AEG-1 promoted osteosarcoma cell invasion is relevant to the MAPK pathways. The up-regulation of AEG-1 increased the levels of phosphor-c-Jun N-terminal kinase (JNK) and phosphor-c-Jun; however, there were no marked changes in the levels of phosphor-extracellular regulated kinase (ERK) 1/2 or phosphor-c-Fos due to the activation of AEG-1 in U2OS. SP600125 (a JNK inhibitor) decreased phosphor-c-Jun and MMP-2 in U2OS-AEG-1, while PD98059 (a ERK1/2 inhibitor) had no influence on the levels of phosphor-c-Jun or MMP-2 in U2OS-AEG-1. Further study revealed that the down-regulation of phosphor-c-Jun not only obviously decreased the MMP-2 protein level and the MMP-2 transcriptional activity that were up-regulated by AEG-1 in Western-blot and luciferase reporter assays, but also inhibited the migration and invasion abilities of the U2OS-AEG-1 cells, which suggests that AEG-1 mediated U2OS invasion at least partially via the JNK/c-Jun/MMP-2 pathway. Consistent with these observations, immunohistochemical (IHC) staining revealed that AEG-1 expression was associated with the protein levels of phosphor-c-Jun and MMP-2 in needle biopsy paraffin-embedded archival human osteosarcoma tissues. Taken together, our findings suggest that AEG-1 plays a crucial role in the aggressiveness of osteosarcoma via the JNK/c-Jun/MMP-2 pathway.

Expression of astrocyte elevated gene-1 (AEG-1) as a biomarker for aggressive pancreatic ductal adenocarcinoma

Background

Altered expression of astrocyte elevated gene-1 (AEG-1) is associated with tumorigenesis and progression. The present study aimed to investigate the clinical and prognostic significance of AEG-1 expression in pancreatic ductal adenocarcinoma (PDAC).

Methods

Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and Western blot analyses were employed to assess AEG-1 expression in three pancreatic cancer cell lines and normal pancreatic duct epithelial cells. qRT-PCR and immunohistochemical analyses were performed to detect AEG-1 expression in ten pairs of PDAC and normal pancreas tissues. Immunohistochemistry was then used to examine AEG-1 expression in paraffin-embedded tissues obtained from 105 patients, and its association with clinicopathological parameters including cancer classification was examined. Kaplan-Meier analysis was performed to study the survival rates of patients.

Results

Expression of AEG-1 mRNA and protein was markedly higher in pancreatic cancer cell lines than that in the normal pancreatic duct epithelial cells. AEG-1 expression was evidently upregulated in PDAC tissues compared to that of the matched distant normal pancreas tissues. qRT-PCR data revealed that the tumor/non-tumor ratio of AEG-1 expression was >1.5-fold (up to 6.5-fold). Immunohistochemical data showed that AEG-1 protein was detected in 98.09% (103/105) of PDAC tissues; and they were found to be associated with tumor size (P = 0.025), advanced clinical stage (P = 0.004), T classification (P = 0.006), N classification (P = 0.003), and M classification (P = 0.007). Furthermore, Kaplan-Meier analysis showed that patients with high AEG-1-expressed PDAC had shorter overall survival. A multivariate Cox regression analysis revealed that clinical stage, T classification, and AEG-1 expression were the independent prognostic predictors for PDAC.

Conclusions

This study suggests that AEG-1 protein was highly expressed in PDAC and associated with poor prognosis of the patients.

AEG-1/MTDH/LYRIC, the beginning: initial cloning, structure, expression profile, and regulation of expression

Since its initial identification as a HIV-1-inducible gene in 2002, astrocyte elevated gene-1 (AEG-1), subsequently cloned as metadherin (MTDH) and lysine-rich CEACAM1 coisolated (LYRIC), has emerged over the past 10 years as an important oncogene providing a valuable prognostic marker in patients with various cancers. Recent studies demonstrate that AEG-1/MTDH/LYRIC is a pleiotropic protein that can localize in the cell membrane, cytoplasm, endoplasmic reticulum (ER), nucleus, and nucleolus, and contributes to diverse signaling pathways such as PI3K-AKT, NF-κB, MAPK, and Wnt. In addition to tumorigenesis, this multifunctional protein is implicated in various physiological and pathological processes including development, neurodegeneration, and inflammation. The present review focuses on the discovery of AEG-1/MTDH/LYRIC and conceptualizes areas of future direction for this intriguing gene. We begin by describing how AEG-1, MTDH, and LYRIC were initially identified by different research groups and then discuss AEG-1 structure, functions, localization, and evolution. We conclude with a discussion of the expression profile of AEG-1/MTDH/LYRIC in the context of cancer, neurological disorders, inflammation, and embryogenesis, and discuss how AEG-1/MTDH/LYRIC is regulated. This introductory discussion of AEG-1/MTDH/LYRIC will serve as the basis for the detailed discussions in other chapters of the unique properties of this intriguing molecule.

Astrocyte elevated gene-1 (AEG-1) is a marker for aggressive salivary gland carcinoma

BACKGROUND

Astrocyte elevated gene-1 (AEG-1) is associated with tumorigenesis and progression in diverse human cancers. The present study was aimed to investigate the clinical and prognostic significance of AEG-1 in salivary gland carcinomas (SGC).

METHODS

Real-time PCR and western blot analyses were employed to examine AEG-1 expression in two normal salivary gland tissues, eight SGC tissues of various clinical stages, and five pairs of primary SGC and adjacent salivary gland tissues from the same patient. Immunohistochemistry (IHC) was performed to examine AEG-1 protein expression in paraffin-embedded tissues from 141 SGC patients. Statistical analyses was applies to evaluate the diagnostic value and associations of AEG-1 expression with clinical parameters.

RESULTS

AEG-1 expression was evidently up-regulated in SGC tissues compared with that in the normal salivary gland tissues and in matched adjacent salivary gland tissues. AEG-1 protein level was positively correlated with clinical stage (P < 0.001), T classification (P = 0.008), N classification (P = 0.008) and M classifications (P = 0.006). Patients with higher AEG-1 expression had shorter overall survival time, whereas those with lower tumor AEG-1 expression had longer survival time.

CONCLUSIONS

Our results suggest that AEG-1 expression is associated with SGC progression and may represent a novel and valuable predictor for prognostic evaluation of SGC patients.

Immunomodulatory properties of kappa opioids and synthetic cannabinoids in HIV-1 neuropathogenesis

Anti-retroviral therapy (ART) has had a tremendous impact on the clinical outcomes of HIV-1 infected individuals. While ART has produced many tangible benefits, chronic, long-term consequences of HIV infection have grown in importance. HIV-1-associated neurocognitive disorder (HAND) represents a collection of neurological syndromes that have a wide range of functional cognitive impairments. HAND remains a serious threat to AIDS patients, and there currently remains no specific therapy for the neurological manifestations of HIV-1. Based upon work in other models of neuroinflammation, kappa opioid receptors (KOR) and synthetic cannabinoids have emerged as having neuroprotective properties and the ability to dampen pro-inflammatory responses of glial cells; properties that may have a positive influence in HIV-1 neuropathogenesis. The ability of KOR ligands to inhibit HIV-1 production in human microglial cells and CD4 T lymphocytes, demonstrate neuroprotection, and dampen chemokine production in astrocytes provides encouraging data to suggest that KOR ligands may emerge as potential therapeutic agents in HIV neuropathogenesis. Based upon findings that synthetic cannabinoids inhibit HIV-1 expression in human microglia and suppress production of inflammatory mediators such as nitric oxide (NO) in human astrocytes, as well as a substantial literature demonstrating neuroprotective properties of cannabinoids in other systems, synthetic cannabinoids have also emerged as potential therapeutic agents in HIV neuropathogenesis. This review focuses on these two classes of compounds and describes the immunomodulatory and neuroprotective properties attributed to each in the context of HIV neuropathogenesis.

Gene expression profiles of HIV-1-infected glia and brain: toward better understanding of the role of astrocytes in HIV-1-associated neurocognitive disorders

Astrocytes are the major cellular component of the central nervous system (CNS), and they play multiple roles in brain development, normal brain function, and CNS responses to pathogens and injury. The functional versatility of astrocytes is linked to their ability to respond to a wide array of biological stimuli through finely orchestrated changes in cellular gene expression. Dysregulation of gene expression programs, generally by chronic exposure to pathogenic stimuli, may lead to dysfunction of astrocytes and contribute to neuropathogenesis. Here, we review studies that employ functional genomics to characterize the effects of HIV-1 and viral pathogenic proteins on cellular gene expression in astrocytes in vitro. We also present the first microarray analysis of primary mouse astrocytes exposed to HIV-1 in culture. In spite of different experimental conditions and microarray platforms used, comparison of the astrocyte array data sets reveals several common gene-regulatory changes that may underlie responses of these cells to HIV-1 and its proteins. We also compared the transcriptional profiles of astrocytes with those obtained in analyses of brain tissues of patients with HIV-1 dementia and macaques infected with simian immunodeficiency virus (SIV). Notably, many of the gene characteristics of responses to HIV-1 in cultured astrocytes were also altered in HIV-1 or SIV-infected brains. Functional genomics, in conjunction with other approaches, may help clarify the role of astrocytes in HIV-1 neuropathogenesis.

Proteomic modeling for HIV-1 infected microglia-astrocyte crosstalk

Background

HIV-1-infected and immune competent brain mononuclear phagocytes (MP; macrophages and microglia) secrete cellular and viral toxins that affect neuronal damage during advanced disease. In contrast, astrocytes can affect disease by modulating the nervous system's microenvironment. Interestingly, little is known how astrocytes communicate with MP to influence disease.

Methods and Findings

MP-astrocyte crosstalk was investigated by a proteomic platform analysis using vesicular stomatitis virus pseudotyped HIV infected murine microglia. The microglial-astrocyte dialogue was significant and affected microglial cytoskeleton by modulation of cell death and migratory pathways. These were mediated, in part, through F-actin polymerization and filament formation. Astrocyte secretions attenuated HIV-1 infected microglia neurotoxicity and viral growth linked to the regulation of reactive oxygen species.

Conclusions

These observations provide unique insights into glial crosstalk during disease by supporting astrocyte-mediated regulation of microglial function and its influence on the onset and progression of neuroAIDS. The results open new insights into previously undisclosed pathogenic mechanisms and open the potential for biomarker discovery and therapeutics that may influence the course of HIV-1-mediated neurodegeneration.

Modifications in the human T cell proteome induced by intracellular HIV-1 Tat protein expression

The effects of the human immunodeficiency virus type 1 (HIV-1) Tat protein on cellular gene expression were analysed using a Jurkat cell line that was stably transfected with tat gene in a doxycycline-repressible expression system. Expressed Tat protein (aa 1-101) was proved to present basically a nuclear localisation, and to be fully functional to induce HIV LTR transactivation. Tat expression also resulted in protection from Tunicamycin-induced apoptosis as determined by DNA staining and TUNEL assays. We applied proteomics methods to investigate changes in differential protein expression in the transfected Jurkat-Tat cells. Protein identification was performed using 2-D DIGE followed by MS analysis. We identified the down-regulation of several cytoskeletal proteins such as actin, beta-tubulin, annexin II, as well as gelsolin, cofilin and the Rac/Rho-GDI complex. Down-expression of these proteins could be involved in the survival of long-term reservoirs of HIV-infected CD4+ T cells responsible for continuous viral production. In conclusion, in addition to its role in viral mRNA elongation, the proteomic approach has provided insight into the way that Tat modifies host cell gene expression.

Cloning differentially expressed genes using rapid subtraction hybridization (RaSH)

Differential gene expression represents the entry point for comprehending complex biological processes. In this context, identification and cloning of differentially expressed genes represent critical elements in this process. Many techniques have been developed to facilitate achieving these objectives. Although effective in many situations, most currently described approaches are not trouble-free and have limitations, including complexity of performance, redundancy of gene identification (reflecting cloning biases) and false-positive gene identification. A detailed methodology to perform a rapid and efficient cloning approach, called rapid subtraction hybridization is described in this chapter. This strategy has been applied successfully to a number of cell culture systems and biological processes, including terminal differentiation and cancer progression in human melanoma cells, resistance or sensitivity to HIV-1 in human T cells and gene expression changes following infection of normal human fetal astrocytes with HIV-1 or treatment with neutrotoxic agents. Based on its simplicity of performance and high frequency of genuine differential gene identification, the rapid subtraction hybridization (RaSH) approach will allow wide applications in diverse systems and biological contexts.

N-acetylcysteine prevents HIV gp 120-related damage of human cultured astrocytes: correlation with glutamine synthase dysfunction

Background

HIV envelope gp 120 glycoprotein is released during active HIV infection of brain macrophages thereby generating inflammation and oxidative stress which contribute to the development of the AIDS-Dementia Complex (ADC). Gp120 has also been found capable to generate excitotoxic effect on brain tissue via enhancement of glutamatergic neurotransmission, leading to neuronal and astroglial damage, though the mechanism is still to be better understood.

Here we investigated on the effect of N-acetylcysteine (NAC), on gp120-induced damage in human cultured astroglial cells and the possible contribution of gp120-related reacting oxygen species (ROS) in the imbalanced activity of glutamine synthase (GS), the enzyme that metabolizes glutamate into glutamine within astroglial cells playing a neuroprotective role in brain disorders.

Results

Incubation of Lipari human cultured astroglial cells with gp 120 (0.1–10 nM) produced a significant reduction of astroglial cell viability and apoptosis as evaluated by TUNEL reaction and flow cytometric analysis (FACS). This effect was accompanied by lipid peroxidation as detected by means of malondialdehyde assay (MDA). In addition, gp 120 reduced both glutamine concentration in astroglial cell supernatants and GS expression as detected by immunocytochemistry and western blotting analysis. Pre-treatment of cells with NAC (0.5–5 mM), dose-dependently antagonised astroglial apoptotic cell death induced by gp 120, an effect accompanied by significant attenuation of MDA accumulation. Furthermore, both effects were closely associated with a significant recovery of glutamine levels in cell supernatants and by GS expression, thus suggesting that overproduction of free radicals might contribute in gp 120-related dysfunction of GS in astroglial cells.

Conclusion

In conclusion, the present experiments demonstrate that gp 120 is toxic to astroglial cells, an effect accompanied by lipid peroxidation and by altered glutamine release. All the effects of gp120 on astroglial cells were counteracted by NAC thus suggesting a novel and potentially useful approach in the treatment of glutammatergic disorders found in HAD patients.

Human immunodeficiency virus type 1 efficiently binds to human fetal astrocytes and induces neuroinflammatory responses independent of infection

BACKGROUND

HIV-1 infects human astrocytes in vitro and in vivo but the frequency of infected cells is low and its biological significance is unknown. In studies in vitro, recombinant gp120 alone can induce profound effects on astrocyte biology, suggesting that HIV-1 interaction with astrocytes and its functional consequences extend beyond the limited levels of infection in these cells. Here we determined the relative efficiencies of HIV-1 binding and infection in human fetal astrocytes (HFA), mainly at the single cell level, using HIV-1 tagged with green fluorescence protein (GFP)-Vpr fusion proteins, termed HIV-GFP, to detect virus binding and HIV-1 expressing Rev and NefGFP fusion proteins to detect productive infection.

RESULTS

Essentially all HFA in a population bound HIV-GFP specifically and independently of CCR5 and CXCR4. The dynamics of this binding at 37 degrees C resembled binding of an HIV fusion mutant to CD4-positive cells, indicating that most of HIV-GFP arrested infection of HFA at the stage of virus-cell fusion. Despite extensive binding, only about 1% of HFA were detectably infected by HIV-RevGFP or HIV-NefGFP, but this proportion increased to the majority of HFA when the viruses were pseudotyped with vesicular stomatitis virus envelope glycoprotein G, confirming that HFA impose a restriction upon HIV-1 entry. Exposure of HFA to HIV-1 through its native proteins rapidly induced synthesis of interleukin-6 and interleukin-8 with increased mRNA detected within 3 h and increased protein detected within 18 h of exposure.

CONCLUSION

Our results indicate that HIV-1 binding to human astrocytes, although extensive, is not generally followed by virus entry and replication. Astrocytes respond to HIV-1 binding by rapidly increased cytokine production suggesting a role of this virus-brain cell interaction in HIV-1 neuropathogenesis.

Astrocyte elevated gene-1: recent insights into a novel gene involved in tumor progression, metastasis and neurodegeneration

Tumor progression and metastasis are complex processes involving intricate interplay among multiple gene products. Astrocyte elevated gene (AEG)-1 was cloned as an human immunodeficiency virus (HIV)-1-inducible and tumor necrosis factor-alpha (TNF-alpha)-inducible transcript in primary human fetal astrocytes (PHFA) by a rapid subtraction hybridization approach. AEG-1 down-regulates the expression of the glutamate transporter EAAT2; thus, it is implicated in glutamate-induced excitotoxic damage to neurons as evident in HIV-associated neurodegeneration. Interestingly, AEG-1 expression is elevated in subsets of breast cancer, glioblastoma multiforme and melanoma cells, and AEG-1 cooperates with Ha-ras to augment the transformed phenotype of normal immortal cells. Moreover, AEG-1 is overexpressed in >95% of human malignant glioma samples when compared with normal human brain. Overexpression of AEG-1 increases and siRNA inhibition of AEG-1 decreases migration and invasion of human glioma cells, respectively. AEG-1 contains a lung-homing domain facilitating breast tumor metastasis to lungs. These findings indicate that AEG-1 might play a pivotal role in the pathogenesis, progression and metastasis of diverse cancers. Our recent observations indicate that AEG-1 exerts its effects by activating the nuclear factor kappa B (NF-kappaB) pathway and AEG-1 is a downstream target of Ha-ras and plays an important role in Ha-ras-mediated tumorigenesis. These provocative findings are intensifying interest in AEG-1 as a crucial regulator of tumor progression and metastasis and as a potential mediator of neurodegeneration. In this review, we discuss the cloning, structure and function(s) of AEG-1 and provide recent insights into the diverse actions and intriguing properties of this molecule.

Neuropathologic and neuroinflammatory activities of HIV-1-infected human astrocytes in murine brain

The balance between astrocyte and microglia neuroprotection and neurotoxicity defines the tempo of neuronal dysfunction during HIV-1-associated dementia (HAD). Astrocytes maintain brain homeostasis and respond actively to brain damage by providing functional and nutritive neuronal support. In HAD, low-level, continuous infection of astrocytes occurs, but the functional consequences of this infection are poorly understood. To this end, human fetal astrocytes (HFA) and monocyte-derived macrophages (MDM) were infected with HIV-1DJV and HIV-1NL4-3 (neurotropic and lymphotropic strains respectively) and a pseudotyped Vesicular Stomatitis Virus (VSV/HIV-1NL4-3) prior to intracranial injection into the basal ganglia of severe combined immunodeficient mice. Neuropathological and immunohistochemical comparisons for inflammatory and neurotoxic activities were performed amongst the infected cell types at 7 or 14 days. HIV-1-infected MDM induced significant increases in Mac-1, glial fibrillary acidic protein, ionized calcium-binding adapter molecule 1, and proinflammatory cytokine RNA and/or protein expression when compared with HSV/HIV-1- and HIV-1-infected HFA and sham-operated mice. Levels of neuron-specific nuclear protein, microtubule-associated protein 2, and neurofilament antigens were reduced significantly in the brain regions injected with human MDM infected with HIV-1DJV or VSV/HIV-1. We conclude that HIV-1 infection of astrocytes leads to limited neurodegeneration, underscoring the early and active role of macrophage-driven neurotoxicity in disease.

Plectin regulates the organization of glial fibrillary acidic protein in Alexander disease

Alexander disease (AxD) is a rare but fatal neurological disorder caused by mutations in the astrocyte-specific intermediate filament protein glial fibrillary acidic protein (GFAP). Histologically, AxD is characterized by cytoplasmic inclusion bodies called Rosenthal fibers (RFs), which contain GFAP, small heat shock proteins, and other undefined components. Here, we describe the expression of the cytoskeletal linker protein plectin in the AxD brain. RFs displayed positive immunostaining for plectin and GFAP, both of which were increased in the AxD brain. Co-localization, co-immunoprecipitation, and in vitro overlay analyses demonstrated direct interaction of plectin and GFAP. GFAP with the most common AxD mutation, R239C (RC GFAP), mainly formed abnormal aggregates in human primary astrocytes and murine plectin-deficient fibroblasts. Transient transfection of full-length plectin cDNA converted these aggregates to thin filaments, which exhibited diffuse cytoplasmic distribution. Compared to wild-type GFAP expression, RC GFAP expression lowered plectin levels in astrocytoma-derived stable transfectants and plectin-positive fibroblasts. A much higher proportion of total GFAP was found in the Triton X-insoluble fraction of plectin-deficient fibroblasts than in wild-type fibroblasts. Taken together, our results suggest that insufficient amounts of plectin, due to RC GFAP expression, promote GFAP aggregation and RF formation in AxD.

Molecular mechanisms of HIV-1 associated neurodegeneration

Since identification of the human immunodeficiency virus-1 (HIV-1), numerous studies suggest a link between neurological impairments, in particular dementia, with acquired immunodeficiency syndrome (AIDS) with alarming occurrence worldwide. Approximately, 60% of HIV-infected people show some form of neurological impairment, and neuropathological changes are found in 90% of autopsied cases. Approximately 30% of untreated HIV-infected persons may develop dementia. The mechanisms behind these pathological changes are still not understood. Mounting data obtained by in vivo and in vitro experiments suggest that neuronal apoptosis is a major feature of HIV associated dementia (HAD), which can occur in the absence of direct infection of neurons. The major pathway of neuronal apoptosis occurs indirectly through release of neurotoxins by activated cells in the central nervous system (CNS) involving the induction of excitotoxicity and oxidative stress. In addition a direct mechanism induced by viral proteins in the pathogenesis of HAD may also play a role. This review focuses on the molecular mechanisms of HIV-associated dementia and possible therapeutic strategies.

Methamphetamine stimulates interferon inducible genes in HIV infected brain

OBJECTIVE

To study the synergism of HIV and methamphetamine.

DESIGN AND METHODS

We undertook a microarray study using RNA from the frontal cortex of 15 individuals with HIV infection to initially identify genes that are differentially regulated by HIV encephalitis (HIVE). From the analysis of the microarray data, we identified candidate genes to be validated by quantitative real time PCR (qRT-PCR) and to assess if these genes were differentially modulated in individuals with HIVE and documented methamphetamine use.

RESULTS

Analysis of microarray data revealed that genes involved in several categories were dysregulated in HIVE. We then chose 15 candidate genes for validation by qRT-PCR and analyzed the tissue concentration of these genes across three groups: those with HIV infection and no brain pathology, those with HIVE, and those with both HIVE and a history of methamphetamine use. We noted that there was upregulation of interferon inducible genes in the HIVE with methamphetamine using group, which together as a gene group was highly statistically significant (p=0.0064).

CONCLUSION

These findings indicate that dysregulation of interferon inducible genes may underlie the pathogenic mechanism resulting in greater neurodegenerative and neurocognitive burden that occurs in methamphetamine using HIV infected individuals.

Cloning and characterization of HIV-1-inducible astrocyte elevated gene-1, AEG-1

We presently describe the full-length cloning and functional characterization of an HIV-1-inducible gene, astrocyte elevated gene (AEG)-1. Additionally, a novel method is outlined for producing tag-free recombinant protein in a baculovirus system and its use in producing AEG-1 protein. AEG-1 mRNA is expressed ubiquitously with higher expression in tissues containing muscular actin and its expression is increased in astrocytes infected with HIV-1 or treated with gp120 or tumor necrosis factor (TNF)-alpha. The mRNA encodes a single pass transmembrane protein of predicted molecular mass of 64-kDa and pI 9.3 that predominantly localizes in the endoplasmic reticulum and perinuclear region. Ectopic expression of AEG-1 inhibits excitatory amino acid transporter 2 (EAAT2) promoter activity with the potential to promote glutamate excitotoxicity and consequently HIV-1-associated dementia (HAD). AEG-1 expression is elevated in subsets of breast carcinomas, malignant gliomas and melanomas and it synergizes with oncogenic Ha-ras to enhance soft agar colony forming ability of non-tumorigenic immortalized melanocytes, documenting its tumor promoting activity. AEG-1 may affect tumor progression in multiple cell lineages by augmenting expression of the transformed phenotype and/or by inducing glutamate excitotoxicity in malignant glioma. In these contexts, an HIV-1-inducible gene, AEG-1, may contribute to multiple brain abnormalities, including HAD and tumor formation, by both common and distinct mechanisms.

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The RNA helicase DDX1 is involved in restricted HIV-1 Rev function in human astrocytes

Productive infection by human immunodeficiency virus type I (HIV-1) in the central nervous system (CNS) involves mainly macrophages and microglial cells. A frequency of less than 10% of human astrocytes is estimated to be infectable with HIV-1. Nonetheless, this relatively low percentage of infected astrocytes, but associated with a large total number of astrocytic cells in the CNS, makes human astrocytes a critical part in the analyses of potential HIV-1 reservoirs in vivo. Investigations in astrocytic cell lines and primary human fetal astrocytes revealed that limited HIV-1 replication in these cells resulted from low-level viral entry, transcription, viral protein processing, and virion maturation. Of note, a low ratio of unspliced versus spliced HIV-1-specific RNA was also investigated, as Rev appeared to act aberrantly in astrocytes, via loss of nuclear and/or nucleolar localization and diminished Rev-mediated function. Host cellular machinery enabling Rev function has become critical for elucidation of diminished Rev activity, especially for those factors leading to RNA metabolism. We have recently identified a DEAD-box protein, DDX1, as a Rev cellular co-factor and now have explored its potential importance in astrocytes. Cells were infected with HIV-1 pseudotyped with envelope glycoproteins of amphotropic murine leukemia viruses (MLV). Semi-quantitative reverse transcriptase-polymerase chain reactions (RT-PCR) for unspliced, singly-spliced, and multiply-spliced RNA clearly showed a lower ratio of unspliced/singly-spliced over multiply-spliced HIV-1-specific RNA in human astrocytes as compared to Rev-permissive, non-glial control cells. As well, the cellular localization of Rev in astrocytes was cytoplasmically dominant as compared to that of Rev-permissive, non-glial controls. This endogenous level of DDX1 expression in astrocytes was demonstrated directly to lead to a shift of Rev sub-cellular distribution dominance from nuclear and/or nucleolar to cytoplasmic, as input of exogenous DDX1 significantly altered both Rev sub-cellular localization from cytoplasmic to nuclear predominance and concomitantly increased HIV-1 viral production in these human astrocytes. We conclude that altered DDX1 expression in human astrocytes is, at least in part, responsible for the unfavorable cellular microenvironment for Rev function in these CNS-based cells. Thus, these data suggest a molecular mechanism(s) for restricted replication in astrocytes as a potential low-level site of residual HIV-1 in vivo.

Proteomic analysis of oxidatively modified proteins induced by the mitochondrial toxin 3-nitropropionic acid in human astrocytes expressing the HIV protein tat

The human immunodeficiency virus (HIV)-Tat protein has been implicated in the neuropathogenesis of HIV infection. However, its role in modulating astroglial function is poorly understood. Astrocyte infection with HIV has been associated with rapid progression of dementia. Intracellularly expressed Tat is not toxic to astrocytes. In fact, intracellularly expressed Tat offers protection against oxidative stress-related toxins such as the mitochondrial toxin 3-nitroproprionic acid (3-NP). In the current study, human astrocytes expressing Tat (SVGA-Tat) and vector controls (SVGA-pcDNA) were each treated with the irreversible mitochondrial complex II inhibitor 3-NP. Proteomics analysis was utilized to identify changes in protein expression levels. By coupling 2D fingerprinting and identification of proteins by mass spectrometry, actin, heat shock protein 90, and mitochondrial single-stranded DNA binding protein were identified as proteins with increased expression, while lactate dehydrogenase had decreased protein expression levels in SVGA-Tat cells treated with 3-NP compared to SVGA-pcDNA cells treated with 3-NP. Oxidative damage can lead to several events including loss in specific protein function, abnormal protein clearance, depletion of the cellular redox-balance and interference with the cell cycle, ultimately leading to neuronal death. Identification of specific proteins protected from oxidation is a crucial step in understanding the interaction of Tat with astrocytes. In the current study, proteomics also was used to identify proteins that were specifically oxidized in SVGA-pcDNA cells treated with 3-NP compared to SVGA-Tat cells treated with 3-NP. We found beta-actin, calreticulin precursor protein, and synovial sarcoma X breakpoint 5 isoform A to have increased oxidation in control SVGA-pcDNA cells treated with 3-NP compared to SVGA-Tat cells treated with 3-NP. These results are discussed with reference to potential involvement of these proteins in HIV dementia and protection of astrocytes against oxidative stress by the HIV virus, a prerequisite for survival of a viral host cell.

Identification and cloning of genes displaying elevated expression as a consequence of metastatic progression in human melanoma cells by rapid subtraction hybridization

Although extensively investigated, the complete repertoire of genes associated with and causative of metastasis remain largely unknown. We developed an efficient approach for identifying differentially expressed genes that involves rapid subtraction hybridization (RaSH) of cDNA clones prepared from two cell populations, a driver and a tester. This RaSH approach has previously documented high sensitivity and effectiveness in identifying genes that are differentially expressed as a function of induction of terminal differentiation in human melanoma cells, resistance or sensitivity to human immunodeficiency virus-1 (HIV-1) infection of human T cells and perturbation in gene expression in normal human fetal astrocytes infected with HIV-1 or treated with HIV-1 gp120 viral envelope glycoprotein or tumor necrosis factor-alpha (TNF-alpha). In the present study, RaSH has been applied to a metastatic melanoma model, which mimics the early events of metastasis in humans, comprising weakly metastatic vs. immunosuppressed newborn rat-selected highly metastatic variants. This has now resulted in the identification of eight genes displaying elevated expression in the high metastatic variants vs. normal immortal melanocytes or weakly metastatic parental clones. These include six known genes, 67-kDa laminin receptor (67LR), endothelin receptor B (ENDRB), Na+/K+-ATPase, Ku antigen, interleukin-receptor-associated kinase-1 (IRAK-1) and ribosomal protein RPLA, which may contribute to the complex process of melanoma metastasis. Additionally, two unknown genes (not reported in current databases) that may also impact on the metastatic phenotype have also been identified. These studies provide additional support of the use of the RaSH approach, in this application in the context of closely related variant cell lines with different metastatic potential, for effective differential gene identification and elucidate eight previously unrecognized genes whose role in melanoma progression to metastatic competence can now be scrutinized.

Proteomics analysis of human astrocytes expressing the HIV protein Tat

Astrocyte infection in HIV has been associated with rapid progression of dementia in a subset of HIV/AIDS patients. Astrogliosis and microglial activation are observed in areas of axonal and dendritic damage in HIVD. In HIV-infected astrocytes, the regulatory gene tat is over expressed and mRNA levels for Tat are elevated in brain extracts from individuals with HIV-1 dementia. Tat can be detected in HIV-infected astrocytes in vivo. The HIV-1 protein Tat transactivates viral and cellular gene expression, is actively secreted mainly from astrocytes, microglia and macrophages, into the extracellular environment, and is taken up by neighboring uninfected cells such as neurons. The HIV-1 protein Tat released from astrocytes reportedly produces trimming of neurites, mitochondrial dysfunction and cell death in neurons, while protecting its host, the astrocyte. We utilized proteomics to investigate protein expression changes in human astrocytes intracellularly expressing Tat (SVGA-Tat). By coupling 2D fingerprinting and identification of proteins by mass spectrometry, we identified phosphatase 2A, isocitrate dehydrogenase, nuclear ribonucleoprotein A1, Rho GDP dissociation inhibitor alpha, beta-tubulin, crocalbin like protein/calumenin, and vimentin/alpha-tubulin to have decreased protein expression levels in SVGA-Tat cells compared to the SVGA-pcDNA cells. Heat shock protein 70, heme oxygenase-1, and inducible nitric oxide synthase were found to have increased protein expression in SVGA-Tat cells compared to controls by slotblot technique. These findings are discussed with reference to astrocytes serving as a reservoir for the HIV virus and how Tat promotes survival of the astrocytic host.

Effects of human immunodeficiency virus type 1 on astrocyte gene expression and function: potential role in neuropathogenesis

Neurodegeneration and dementia caused by human immunodeficiency virus type 1 (HIV-1) infection of the brain are common complications of acquired immunodeficiency syndrome (AIDS). Introduction of highly active antiretroviral therapy (HAART) reduced the incidence of HIV-1-associated dementia, but so far had no effect on the high frequency of milder neurological disorders caused by HIV-1. This indicates that some neuropathogenic processes persist during limited HIV-1 replication in the central nervous system (CNS). The authors are evaluating the hypothesis that interaction of HIV-1 with astrocytes, which bind HIV-1 but support limited productive HIV-1 infection, may contribute to these processes by disrupting astrocyte functions that are important for neuronal activity or survival. Using laser-capture microdissection on brain tissue samples from HIV-1-infected individuals, we found that HIV-1 DNA can be detected in up to 1% of cortical and basal ganglia astrocytes, thus confirming HIV-1 infection in astrocytes from symptomatic patients. Using rapid subtraction hybridization, the authors cloned and identified 25 messenger RNAs in primary human fetal astrocytes either up-regulated or down-regulated by native HIV-1 infection or exposure to gp120 in vitro. Extending this approach to gene microarray analysis using Affymetrix U133A/B gene chips, the authors determined that HIV-1 alters globally and significantly the overall program of gene expression in astrocytes, including changes in transcripts coding for cytokines, G-coupled protein receptors, transcription factors, and others. Focusing on a specific astrocyte function relevant to neuropathogenesis, the authors showed that exposure of astrocytes to HIV-1 or gp120 in vitro impairs the ability of the cells to transport L-glutamate and the authors related this defect to transcriptional inhibition of the EAAT2 glutamate transporter gene. These findings define new pathways through which HIV-1 may contribute to neuropathogenesis under conditions of limited virus replication in the brain.

Customized rapid subtraction hybridization (RaSH) gene microarrays identify overlapping expression changes in human fetal astrocytes resulting from human immunodeficiency virus-1 infection or tumor necrosis factor-alpha treatment

Genes displaying altered expression as a function of human immunodeficiency virus (HIV)-1 infection of cultured primary human fetal astrocytes (PHFA) were previously identified using a rapid subtraction hybridization (RaSH) method. This scheme identified both known and novel genes displaying elevated expression, astrocyte elevated genes (AEG), and decreased expression, astrocyte suppressed genes (ASG), in PHFA as a consequence of infection with HIV-1 or treatment with HIV-1 envelope glycoprotein (gp120). RaSH also identified both known and novel genes displaying enhanced (HR) or reduced (HS) expression in HIV-1 resistant versus HIV-1 susceptible human T-cell clones. In the present study, a customized microarray approach employing these RaSH-derived genes was used to distinguish overlapping gene expression changes occurring in PHFA as a function of treatment with HIV-1 and the neurotoxic agent tumor necrosis factor (TNF)-alpha. RaSH cDNAs were spotted (microarrayed) on nylon membranes and probed with temporally isolated reverse transcribed cDNAs from HIV-1-infected and TNF-alpha-treated PHFA. This strategy identified genes displaying parallel changes after TNF-alpha treatment as observed following HIV-1 infection. Confirmation of genuine differential expression was achieved by Northern blotting. These studies document that TNF-alpha can induce a set of corresponding changes in specific AEGs and ASGs as does HIV-1 infection in PHFA. Furthermore, this customized microarray approach with RaSH-derived clones represents an efficient and sensitive methodology for elucidating molecular changes in PHFA occurring as a consequence of treatment with pharmacological agents affecting astrocyte physiology.