AMPA receptors generate the major depolarizing currents that trigger the formation of action potentials. Alterations of the rates of insertion and removal of receptors at synapses can modify receptor synaptic abundance and control synaptic strength. AMPA receptor C-terminal domain phosphorylation is thought to be a major regulator of receptor interaction with proteins that control trafficking. Synapses convert ionic fluxes associated with synapse activity into biochemical signals that control kinases and CTD phosphorylation. Phosphorylation of the GluR1 subunit on serine 845, which lies near the middle of the GluR1 CTD, by PKA has been correlated with the level of GluR1 at extrasynaptic sites in the plasma membrane. We will use molecular and electrophysiological approaches to investigate a new mechanism of serine 845 phosphorylation by the cyclic GMP regulated kinase cGKII. cGKII is under the control of the NMDA receptor through NMDAR activation of nNOS, leading to the production of nitric oxide, activation of soluble guanylate cyclase and production of cGMP, which induces cGKII.
The Aims of this project are:
Aim 1. To analyze the roles of cGKII myristoylation, dimerization and activation in GluR1 trafficking and physiology. We will analyze how the structure of cGKII contributes to GluR1 regulation.
Aim 2. To distinguish the mechanism of S845 phosphorylation in increasing GluR1 levels on the plasma membrane. We will determine the place within the cell that cGKII phosphorylates GluR1 and exerts its effect on GuR1 trafficking. We will attempt to distinguish whether cGKII regulates GluR1 exocytosis or if GluR1 delivered constitutively is stabilized on the plasma membrane by S845 phosphorylation. We will isolate factors that respond to S845 phosphorylation and control GluR1 surface levels.
Aim 3. To study the cGKII regulated trafficking of GluR4 and GluR2L. GluR4 and GluR2L are AMPAR subunits that are structurally related to GluR1 in ways that suggest that they may also be controlled by cGKII. We will analyze the role of cGKII in the trafficking of these subunits to determine if the NMDAR-nNOS-cGKII pathway is more generally employed. This project will provide new information about mechanisms of activity dependent control of synapse function and may help to define the role of nitric oxide in these mechanisms.
Learning and memory depend upon changes in the strength of connections between neurons in the brain. This project will study a new pathway that can allow neurons to respond to their own activity and change the strength of their connections. This work is relevant to mechanisms of memory formation and to the origin of learning disabilities. It can provide the basis for devising new drugs to help maintain memory or lessen learning disabilities.
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