Glutamate is an essential neurotransmitter regulating brain functions. Excitatory amino acid transporter (EAAT)-2 is one of the major glutamate transporters primarily expressed in astroglial cells. Dysfunction of EAAT2 is implicated in acute and chronic neurological disorders, including stroke/ischemia, temporal lobe epilepsy, amyotrophic lateral sclerosis, Alzheimer disease, human immunodeficiency virus 1-associated dementia, and growth of malignant gliomas. Ceftriaxone, one of the β-lactam antibiotics, is a stimulator of EAAT2 expression with neuroprotective effects in both in vitro and in vivo models based in part on its ability to inhibit neuronal cell death by glutamate excitotoxicity. Based on this consideration and its lack of toxicity, ceftriaxone has potential to manipulate glutamate transmission and ameliorate neurotoxicity. We investigated the mechanism by which ceftriaxone enhances EAAT2 expression in primary human fetal astrocytes (PHFA). Ceftriaxone elevated EAAT2 transcription in PHFA through the nuclear factor-κB (NF-κB) signaling pathway. The antibiotic promoted nuclear translocation of p65 and activation of NF-κB. The specific NF-κB binding site at the -272 position of the EAAT2 promoter was responsible for ceftriaxone-mediated EAAT2 induction. In addition, ceftriaxone increased glutamate uptake, a primary function of EAAT2, and EAAT2 small interference RNA completely inhibited ceftriaxone-induced glutamate uptake activity in PHFA. Taken together, our data indicate that ceftriaxone is a potent modulator of glutamate transport in PHFA through NF-κB-mediated EAAT2 promoter activation. These findings suggest a mechanism for ceftriaxone modulation of glutamate transport and for its potential effects on ameliorating specific neurodegenerative diseases through modulation of extracellular glutamate.

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-κB (NF-κB) signaling pathway. The present studies elucidate the domains of AEG-1 important for mediating its function. Serial NH₂-terminal and COOH-terminal deletion mutants were constructed and functional analysis revealed that the NH₂-terminal 71 amino acids were essential for invasion, migration, and NF-κB–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-κB, CBP, and the basal transcription machinery. Chromatin immunoprecipitation assays showed that AEG-1 is associated with the NF-κB binding element in the interleukin-8 promoter. Thus, AEG-1 might function as a coactivator for NF-κB, 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. [Cancer Res 2008;68(5):1478–84]

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

It is well established that Ha- ras and c- myc genes collaborate in promoting transformation, tumor progression, and metastasis. However, the precise mechanism underlying this cooperation remains unclear. In the present study, we document that astrocyte elevated gene-1 ( AEG-1 ) is a downstream target molecule of Ha- ras and c- myc , mediating their tumor-promoting effects. AEG-1 expression is elevated in diverse neoplastic states, it cooperates with Ha-ras to promote transformation, and its overexpression augments invasion of transformed cells, demonstrating its functional involvement in Ha-ras-mediated tumorigenesis. We now document that AEG-1 expression is markedly induced by oncogenic Ha-ras, activating the phosphatidylinositol 3-kinase signaling pathway that augments binding of c-Myc to key E-box elements in the AEG-1 promoter, thereby regulating AEG-1 transcription. In addition, Ha-ras-mediated colony formation is inhibited by AEG-1 siRNA. This is a demonstration that Ha-ras activation of a tumor-promoting gene is regulated directly by c-Myc DNA binding via phosphatidylinositol 3-kinase signaling, thus revealing a previously uncharacterized mechanism of Ha-ras-mediated oncogenesis through AEG-1.