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J. Biol. Chem., Vol. 281, Issue 11, 7578-7582, March 17, 2006

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Age-dependent Participation of Ras-GRF Proteins in Coupling Calcium-permeable AMPA Glutamate Receptors to Ras/Erk Signaling in Cortical Neurons^*

From the Departments of Biochemistry and Neuroscience, Tufts University School of Medicine, Boston, Massachusetts 02111

-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors (AMPARs) are ligand-gated sodium channels. Through their ability to mediate the majority of rapid excitatory transmission in the central nervous system, these neurotransmitter receptors have been shown to influence synaptic plasticity. Some of these receptors are also calcium-permeable (CP), and they also have been implicated in regulating synaptic plasticity, particularly in interneurons where their concentration is highest. However, the biochemical pathways emanating from CP-AMPARs that mediate these effects have not been well characterized. In this paper, we show that CP-AMPARs are the predominant AMPAR class responsible for activating the Ras/Erk kinase signaling cascade and the cAMP-response element-binding protein (CREB) transcription factor in the cortex of mature mice. Activation of Ras and Erk, but not CREB, occurs through the calcium/calmodulin regulated Ras-GRF1 and Ras-GRF2 exchange factors, which form AMPA-induced complexes with CP-AMPARs but not calcium-impermeable (CI) AMPARs in vivo. Furthermore, we show that CP-AMPARs are also the major AMPAR type to activate Ras/Erk signaling in pubescent mice; however, at this developmental stage Ras-GRF (guanine nucleotide-releasing factor) proteins are not involved. Finally, in neonatal animals CI-AMPARs, but not CP-AMPARs, are the predominant AMPAR type that activates Ras-Erk signaling and CREB in cortical neurons. This occurs indirectly through activation of L-type voltage-dependent calcium channels, an event that is also Ras-GRF-independent. Thus, Ras/Erk signaling and CREB activity induced by AMPARs occur through age-dependent mechanisms that likely make unique developmentally dependent contributions to synaptic function.

Received for publication, November 9, 2005 , and in revised form, December 27, 2005.

^* This work was supported by Grant RO1CA47391 from NCI, National Institutes of Health (to L. A. F.) and Grant P3-DK3498 from the GRASP (gastrointestinal research on absorptive and secretory process) Digestive Disease Center. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Dept. of Biochemistry, Tufts University School of Medicine, 136 Harrison Ave., Boston, MA 02111. Tel.: 617-636-6956; E-mail: larry.feig{at}tufts.edu.

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