Nerve Growth Factor Stimulates Glioblastoma Proliferation through Notch1 Receptor Signaling

Notch receptors are heterodimeric transmembrane proteins that regulate cell fate, such as differentiation, proliferation, and apoptosis. Dysregulated Notch pathway signaling has been observed in glioblastomas, as well as in other human malignancies. Nerve growth factor (NGF) is essential for cell growth and differentiation in the nervous system. Recent reports suggest that NGF stimulates glioblastoma proliferation. However, the relationship between NGF and Notch1 in glioblastomas remains unknown. Therefore, we investigated expression of Notch1 in a glioblastoma cell line (U87-MG), and examined the relationship between NGF and Notch1 signaling.

We evaluated expression of Notch1 in human glioblastomas and normal brain tissues by immunohistochemical staining. The effect of NGF on glioblastoma cell line (U87-MG) was evaluated by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. To evaluate the relationship between NGF and Notch1 signaling, Notch1 and Hes1 expression were evaluated by reverse transcription polymerase chain reaction (RT-PCR) and Western blot analysis, respectively. To confirm the effects of NGF on Notch1 signaling, Notch1 and Hes1 small interfering RNAs (siRNAs) were used.

In immunohistochemistry, Notch1 expression was higher in glioblastoma than in normal brain tissue. MTT assay showed that NGF stimulates U87-MG cells in a dose-dependent manner. RT-PCR and Western blot analysis demonstrated that Notch1 and Hes1 expression were increased by NGF in a dose-dependent manner. After transfection with Notch1 and Hes1 siRNAs, there was no significant difference between controls and 100 nM NGF-β, which means that U87-MG cell proliferation was suppressed by Notch1 and Hes1 siRNAs.

These results indicate that NGF stimulates glioblastoma cell proliferation via Notch1 signaling through Hes 1.