RGS14:14-3-3 Complex Effect on Signaling in Hippocampal CA2 Synaptic Plasticity

Emory University, Atlanta GA

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Abstract

Project Summary/Abstract The hippocampus is essential for multiple aspects of learning and memory. Within the hippocampus, the projection of Schaffer collaterals from the CA3 to CA1 region as part of the hippocampal trisynaptic circuit has been of particular interest due to the display of robust long-term potentiation (LTP) at these synapses. LTP is a persistent, activity-dependent increase in synaptic strength that has been referred to as a cellular correlate of learning and memory. Notably, CA3 projections to the hippocampal CA2 region are incapable of eliciting LTP under the same conditions that successfully provoke LTP in CA1 neurons. CA2 is differentiated from the surrounding regions in part by differential expression of multiple genes. One of these genes encodes regulator of G protein signaling 14 (RGS14). Recently, our lab discovered that knockout (lack of expression) of RGS14 not only relieves the suppression of synaptic plasticity in CA2 hippocampal neurons, but also enhances performance in hippocampal-dependent tasks of learning and memory as compared to wild type mice. However, the cellular mechanism by which RGS14 suppresses LTP in CA2 neurons is unknown. RGS14 is a multifunctional protein scaffold that is known to interact with active G?i/o via its RGS domain, Raf and active H-Ras via its R1 Ras binding domain (RBD), and inactive G?i1/3 via its G protein regulatory (also known as GoLoco) motif. My preliminary data indicate that RGS14 also interacts with the phospho-serine/threonine binding protein, 14-3-3, and this interaction is enhanced by H-Ras-GTP and G?i1, both of which are RGS14 binding partners. Furthermore, I have found that this interaction requires phosphorylation at serine 218, within a conserved 14-3-3 binding motif, in the linker region between the RGS and R1 domains of RGS14. 14-3-3 proteins are well known modulators of intracellular signaling and are most highly expressed in brain, including the CA2 hippocampal region. These proteins have a variety of functions including modulating of subcellular localization and protein interactions. Notably, both H-Ras-GTP and G?i1 are capable of recruiting RGS14 to the plasma membrane of the cell where it can modulate intracellular signaling. This may be prevented or enhanced by association with 14-3-3. Additionally, 14-3-3 proteins are known to modulate Raf activity upstream of Erk, and both Raf and 14-3-3 have been shown to be necessary for hippocampal LTP. Based on these findings, my working hypothesis is that RGS14 interaction with 14-3-3 modulates RGS14?s interactions with H-Ras and Raf, working to inhibit H-Ras/Raf/MEK/Erk signaling and thereby suppressing LTP in CA2 hippocampal neurons. I will test this hypothesis with the following aims: 1. Determine the effect of 14-3-3 binding to RGS14 in relation to known binding partners. 2. Determine the effect of 14-3-3 association with RGS14 in modulating LTP in CA2 hippocampal neurons.