Inhibition of mitogen-activated protein kinase kinase blocks proliferation of neural progenitor cells

Nestin-expressing neural progenitor (NP) cells have been isolated from the subventricular zone (SVZ) of the brain and propagated with epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF). In other neural cell types it has been shown that EGF and bFGF activate cell surface receptors involved in the mitogen-activated protein kinase (MAPK) signal pathway. To examine this issue in NP cells, we isolated primary SVZ cells and stimulated them with EGF and bFGF and then used a phosphorylation-specific antibody to detect activated MAPK by immunofluorescent staining or Western blotting. The addition of growth factors activated MAPK transiently in cells that co-expressed nestin. A distinct phospho-MAPK signal was also detected in nestin-positive cells with mitotic chromosomes. A novel MAPK kinase (MEK1) inhibitor U0126 blocked the activation of MAPK and the proliferation of primary cells more effectively than the same concentration of PD98059. After exposure of cells to U0126 for 10 days, we noted that there was a significant reduction in the number of cells that expressed nestin and an increase in the percentage of apoptotic cells. These data provide evidence that activation of MAPK by MEK1 is important for the proliferation of NP cells.