CALCIUM INFLUX VIA THE NMDA RECEPTOR INDUCES IMMEDIATE-EARLY GENE-TRANSCRIPTION BY A MAP KINASE ERK-DEPENDENT MECHANISM/

The regulation of gene expression by neurotransmitters is likely to pl ay a key role in neuroplasticity both during development and in the ad ult animal. Therefore, it is important to determine the mechanisms of neuronal gene regulation to understand fully the mechanisms of learnin g, memory, and other long-term adaptive changes in neurons. The neurot ransmitter glutamate stimulates rapid and transient induction of many genes, including the c-fos proto-oncogene. The c-fos promoter contains several critical regulatory elements, including the serum response el ement (SRE), that mediate glutamate-induced transcription in neurons; however, the mechanism by which the SRE functions in neurons has not b een defined. In this study, we sought to identify transcription factor s that mediate glutamate induction of transcription through the SRE in cortical neurons and to elucidate the mechanism(s) of transcriptional activation by these factors. To facilitate this analysis, we develope d an improved calcium phosphate coprecipitation procedure to transient ly introduce DNA into primary neurons, both efficiently and consistent ly. Using this protocol, we demonstrate that the transcription factors serum response factor (SRF) and Elk-1 can mediate glutamate induction of transcription through the SRE in cortical neurons. There are at le ast two distinct pathways by which glutamate signals through the SRE: an SRF-dependent pathway that can operate in the absence of Elk and an Elk-dependent pathway. Activation of the Elk-dependent pathway of tra nscription seems to require phosphorylation of Elk-1 by extracellular signal-regulated kinases (ERKs), providing evidence for a physiologica l function of ERKs in glutamate signaling in neurons. Taken together, these findings suggest that SRF, Elk, and ERKs may have important role s in neuroplasticity.