This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.This subproject will investigate the functions of a striatal specific protein, RGS9-2, a member of the RGS family of G GTPase accelerating proteins. Our previous data suggest that RGS9-2 is critical in the development of L-DOPA induced dyskinesia (LID) and tardive dyskinesia (TD). LID and TD are irreversible neurological motor toxicities of the pharmacotherapy of Parkinson's disease and psychotic disorders, respectively. While the etiology is unknown we have proposed a prelimainary molecular model: D2-dopamine receptors (D2DR) are a major target of both antipsychotic drugs and L-DOPA. RGS9-2 targets to D2DR via the RGS9 DEP domain and functionally compartmentalizes D2DR in striatal neurons to block D2DR-mediated inhibition of NMDA receptors and Ca2+ channels. Prolonged drug-treatment produces compensatory alterations that disrupt RGS9-2mediated cellular compartmentalization. These compensatory responses, lead to abnormal basal ganglia signal processing and to drug-induced abnormal involuntary movements. Determining how such compartmentalization is disrupted will require a better understanding of the D2DR-RGS9-2 interaction which has been suggested by our colocalization studies. Hence we will determine if the targeting of RGS9-2 to D2DR involves either a direct or indirect physical interaction. We will map and characterize the interacting surfaces and evaluate the effect of covalent modifications such as protein phosphorylation on the molecular interaction. We will in addition investigate the molecular mechanism for abnormal signaling between D2-like DR and NMDA-receptors observed in the absence of RGS9. We will test the hypothesis that coexpressed RGS9-2 can inhibit D2DR-NMDA-receptor coupling reconstituted in vitro. Parallel approaches will examine the role for RGS9-2 in the coupling between striatal D2DR and voltage-activated Ca2+ channels. Though the present proposal is restricted characterizing the cellular function of RGS9-2 it is my expectation that the effort will provide us with the tools to test, validate and expand our preliminary model for LID and TD, in subsequent studies.
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