| Abstract |
In maturing postnatal cerebellar granule cells, the Etv1/Er81 transcription factor is induced by sequential activity-dependent mechanisms through stimulation of AMPA and NMDA receptors, voltage-dependent Nav1.2 Na(+) channels, and voltage-dependent Ca(2+) channels. Etv1 then up-regulates a battery of maturation genes involved in the cerebellar circuitry. In this process, BDNF is also induced and participates in the up-regulation of these maturation genes. Using cultures of granule cells, we addressed how the activity-dependent and BDNF signaling mechanisms converge on the regulation of the representative NR2C NMDA receptor and Tiam1 maturation genes. BDNF up-regulated both the NR2C and Tiam1 genes via the TrkB-Erk cascade and this up-regulation was blocked not only by inhibition of the activity-dependent signaling mechanisms but also by suppression of Etv1 expression with Etv1 siRNA. Importantly, Etv1 was selectively phosphorylated by Erk1/2 in the BDNF signaling cascade, and the inhibition of this phosphorylation abrogated the BDNF-induced up-regulation of the NR2C and Tiam1 genes. The luciferase reporter assays in combination with mutations of MEK and Etv1 indicated that the Erk-mediated, phosphorylated Etv1 interacted with the Ets motifs of the NR2C promoter sequence and that phosphorylation at both serine 94 and a cluster of threonines and a serine (Thr139, Thr143, and Ser146) of Etv1 was indispensable for the BDNF-mediated activation of the NR2C promoter activity. This study demonstrates that the NR2C and Tiam1 maturation genes are synergistically controlled by the activity-dependent induction of Etv1 and its phosphorylation by the BDNF signaling cascade.
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