Glutamate Promotes Cell Growth by EGFR Signaling on U-87MG Human Glioblastoma Cell Line

Abstract

Accumulating evidences suggest that glutamate plays a key role in the proliferation and invasion of malignant glioblastoma (GBM) tumors. It has been shown that GBM cells release and exploit glutamate for proliferation and invasion through AMPA glutamate receptors. Additionally, amplification of the epidermal growth factor receptor (EGFR) gene occurs in 40-50% of GBM. Since, PI3K/Akt is considered one of the main intracellular pathways involved in EGFR activation, AKT functions could trigger EGFR signaling. Thus, we investigated whether EGFR-phospho-Akt pathway is involved on the glutamate inducing U-87MG human GBM cell line proliferation. For these purpose, we treated the U-87MG cell line with 5 to 200 mM of glutamate and assessed the number of viable cells by trypan blue dye exclusion test. An increase in cell number (50%) was found at 5 mM glutamate, while the addition of DNQX (500 microM), an antagonist of AMPA receptor, inhibited the effect of glutamate on the U87-MG cells proliferation. Also, at 5 mM glutamate we observed an increase on the EGFR and phospho-Akt contents evaluated by immunohistochemistry. Moreover, U-87MG cells treated with glutamate exhibited an increase about 2 times in the EGFR mRNA expression. While, in the presence of the anti-EGFR gefitinib (50 muM) or the PI3K inhibitor wortmannin (5 muM), the U-87MG proliferation was restored to control levels. Together, our data suggest that glutamate signaling mediated by AMPA receptor induces U-87MG human GBM cell line proliferation via EGFR-phospho-Akt pathway.

Use of in Vivo Two-dimensional MR Spectroscopy to Compare the Biochemistry of the Human Brain to That of Glioblastoma

“…The (glutamate-glutamine)-to-creatine ratio in patients with GBM agrees with reports of higher levels of glutamate in the tumor than in peritumoral tissue ( 5 ), which is consistent with reports that GBM secretes large amounts of glutamate ( 38,39 ).…”

Neuroepithelial stem cell marker nestin regulates the migration, invasion and growth of human gliomas

“…Moreover, recurrent glioblastomas are resistant to conventional radiotherapy and chemotherapy. Many cell adhesion proteins, cytoplasmic proteins and growth factor receptors, including the neural cell adhesion molecule (NCAM), matrix metalloproteinase (MMP), integrin, CD44 and epidermal growth factor receptor (EGFR), play important roles in glioblastoma cell migration and invasion (4)(5)(6). These factors affect the intracellular states of tumor cells and induce their migration and invasion.…”

The Role of Inflammation in Brain Cancer

“…AMPA receptors on BTICs are comprised of GluR1 and GluR4 subunits (Oh et al 2012), whereas AMPA receptors on the glioblastoma cell line U87MG contain the GluR2 subunit and are Ca 2+ impermeable (Ekici et al 2012). Human surgical glioma tissues contain Ca 2+ permeable AMPA receptors, and glutamate activation promotes cell growth and mobility (Lyons et al 2007) by activation of the Akt pathway (Ishiuchi et al 2007;Schunemann et al 2010). …”