Regulation of GluR2 promoter activity by neurotrophic factors via a neuron-restrictive silencer element

The AMPA glutamate receptor subunit GluR2, which plays a critical role in r egulation of AMPA channel function, shows altered levels of expression in v ivo after several chronic perturbations. To evaluate the possibility that t ranscriptional mechanisms are involved, we studied a 1254-nucleotide fragme nt of the 5'-promoter region of the mouse GluR2 gene in neural-derived cell lines. We focused on regulation of GluR2 promoter activity by two neurotro phic factors, which are known to be altered in vivo in some of the same sys tems that show GluR2 regulation. Glial-cell line derived neurotrophic facto r (GDNF) and brain-derived neurotrophic factor (BDNF) both induced GluR2 pr omoter activity. This was associated with increased expression of endogenou s GluR2 immunoreactivity in the cells as measured by Western blotting. The effect of GDNF and BDNF appeared to be mediated via a NRSE (neuron-restrict ive silencer element) present within the GluR2 promoter. The response to th ese neurotrophic factors was lost upon mutating or deleting this site, but not several other putative response elements present within the promoter. M oreover, overexpression of REST (restrictive element silencer transcription factor; also referred to as NRSF or neuron restrictive silencer factor), w hich is known to act on NRSEs in other genes to repress gene expression, bl ocked the ability of GDNF to induce GluR2 promoter activity. However, GDNF did not alter endogenous levels of REST in the cells. Together, these findi ngs suggest that GluR2 expression can be regulated by neurotrophic factors via an apparently novel mechanism involving the NRSE present within the Glu R2 gene promoter.