Brain-Specific Regulator of G-Protein Signaling 9-2 Selectively Interacts with α-Actinin-2 to Regulate Calcium-Dependent Inactivation of NMDA Receptors

Abstract

Regulator of G-protein signaling 9-1 (RGS9-1) and RGS9-2 are highly related RGS proteins with distinctive C termini arising from alternative splicing of RGS9 gene transcripts. RGS9-1 is expressed in photoreceptors where it functions as a regulator of transducin. In contrast, RGS9-2 is abundantly expressed in the brain, especially in basal ganglia, where its specific function remains poorly understood. To gain insight into the function of RGS9-2, we screened a human cDNA library for potential interacting proteins. This screen identified a strong interaction between RGS9-2 and alpha-actinin-2, suggesting a possible functional relationship between these proteins. Consistent with this idea, RGS9-2 and alpha-actinin-2 coimmunoprecipitated after coexpression in human embryonic kidney 293 (HEK-293) cells. Furthermore, endogenous RGS9-2 and alpha-actinin-2 could also be coimmunoprecipitated from extracts of rat striatum, an area highly enriched in both these proteins. These results supported the idea that RGS9-2 and alpha-actinin-2 could act in concert in central neurons. Like alpha-actinin-2, RGS9-2 coimmunoprecipitated NMDA receptors from striatal extracts, suggesting an interaction between RGS9-2, alpha-actinin-2, and NMDA receptors. Previous studies have shown that alpha-actinin mediates calcium-dependent inactivation of NMDA receptors. In HEK-293 cells expressing NMDA receptors, expression of RGS9-2 significantly modulated this form of NMDA receptor inactivation. Furthermore, this modulation showed remarkable preference for NMDA receptor inactivation mediated by alpha-actinin-2. Using a series of deletion constructs, we localized this effect to the RGS domain of the protein. These results identify an unexpected functional interaction between RGS9-2 and alpha-actinin-2 and suggest a potential novel role for RGS9-2 in the regulation of NMDA receptor function.

Gβ5-RGS complexes are gatekeepers of hyperactivity involved in control of multiple neurotransmitter systems

“…Thus, our results reinforce the central role of glutamate signaling via NMDA receptors in setting the level of motor activity and provide evidence that Gβ5-RGS complexes play important role in dopamine-NMDA receptor cross-talk. This hypothesis is further supported by findings that implicate RGS9, a member of the R7 RGS family that forms complexes with Gβ5 in the striatum, as a possible regulator of NMDA receptor signaling (Bouhamdan et al 2006; Kovoor et al 2005). However, it is likely that other Gβ5-binding RGS proteins also contribute to this process since elimination of RGS9 alone is not sufficient to trigger hyperactive behavior (Rahman et al 2003; Zachariou et al 2003).…”

Accelerators, Brakes, and Gears of Actin Dynamics in Dendritic Spines

“…Both Ca 2+ /calmodulin and Ca 2+ /calmodulin-dependent protein kinase II (CaMKII) compete with α-actinin for binding of the NR1 subunit of the NMDA receptor [162, 163]. While α-actinin binding to the NMDA receptor increases the receptor open probability, Ca 2+ /calmodulin interaction with the NMDA receptor reduces it, resulting in NMDA receptor inactivation [164–167]. The role of α-actinin in enhancing NMDA receptor activity is consistent with its ability to induce dendritic filopodia-like protrusions, as NMDA receptor activation also leads to spine remodeling.…”

The R7 RGS Protein Family: Multi-Subunit Regulators of Neuronal G Protein Signaling

“…This interaction that was shown to result in the enhancement of neurite outgrowth when studied in transfected cells (117). Similarly, RGS9-2 was reported to be associated with another cytoskeletal protein, α-actinin-2 (118). In transfected cells, this interaction was demonstrated to link RGS9-2 to the regulation of NMDA receptor function (118).…”

“…Similarly, RGS9-2 was reported to be associated with another cytoskeletal protein, α-actinin-2 (118). In transfected cells, this interaction was demonstrated to link RGS9-2 to the regulation of NMDA receptor function (118). Finally, RGS7 was found to bind a component of the synaptic fusion complex, snapin, leading to the hypothesis that R7 RGS proteins can also regulate exocytosis (93, 119).…”