Asgar Zaheer, Mark A. Yorek, Ramon Lim

Using the replication-defective adenovirus vector, we overexpressed rat glia maturation factor (GMF) in primary astrocyte cultures derived from embryonic rat brains. Among the three isoforms of MAP kinase, there was a big increase in the phosphorylation of p38, as detected with Western blotting using the phosphospecific antibody. Likewise, there was a substantial increase in the phosphorylation of the transcription factor CREB. Using the electrophoretic mobility shift assay (EMSA), we found a stimulation in the transcription factor NF-kappaB. The activations of CREB and NF-kappaB were blocked by inhibitors of either p38 (SB-203580) or MEK (PD-098059), suggesting that they were events downstream of MAK kinase. There was an increased secretion of BDNF and NGF into the conditioned medium, along with an increase in their messenger RNA. The inductions of BDNF and NGF were also blocked by inhibitors of p38 and MEK, as well as by the inhibition of NF-kappaB with a decoy DNA sequence. Taken together, the results suggest that GMF functions intracellularly in astrocytes as a modulator of MAP kinase signal transduction, leading to a series of downstream events including CREB and NF-kappaB activation, resulting in the induction and secretion of the neurotrophins.