Defects in dopamine signaling have been linked to schizophrenia, drug addiction, depression and Parkinson's Disease. However, the incredible complexity of the human brain has left the physiological basis and molecular mechanisms underlying these complex diseases largely unknown. One way in which signal transduction pathways can be regulated is via the post-translational modification of signaling proteins. Post-translational modifications are covalent processing events that change the properties of a protein after its synthesis, such as its activity state, localization, turnover or interactions wit other proteins. Recently, methylation of the amino acid arginine (catalyzed by protein arginine methyltransferases/PRMTs) has begun to emerge as an important regulator of protein function. Our experiments in the small round worm (nematode) C. elegans have revealed a role for a PRMT in regulating endogenous dopamine signaling, and we corroborated this finding using the human D2 dopamine receptor in human cell culture. C. elegans is the only organism for which the developmental lineage, physical positions and synaptic connectivity of the entire nervous system (302 neurons) are known. Importantly, C. elegans behaviors are modulated by many of the same chemicals that affect human nervous system function, including the neurotransmitter dopamine. As an important step towards our long-term goal of understanding how diverse regulatory mechanisms coordinate to regulate G protein-coupled signaling, the overall objective of this application is to determine specifically the mechanism by which arginine methylation regulates human D2 G protein-coupled receptor (GPCR) function. Herein we propose to use biochemical, proteomic, and cell biological approaches to understand how arginine methylation regulates dopaminergic signal transduction. We will: (1) determine the effect of methylation on D2 - Galphai/o association, activation and signaling through adenylyl cyclase, and (2) identify methylated arginines in human D2 and establish their functional significance. Together, these studies will define a new means of regulating G protein-coupled signal transduction and thus are expected to lead to the identification of novel therapeutic approaches to selectively treat neurological and psychiatric disorders that are associated with dysregulation of dopamine signaling.
Aberrant dopamine signaling has been linked to several human neurological disorders, including schizophrenia, depression, drug addiction and Parkinson's disease. The goal of our research is to understand, for preventative and therapeutic purposes, how dopamine signaling is regulated in the brain.
|Likhite, Neah; Jackson, Christopher A; Liang, Mao-Shih et al. (2015) The protein arginine methyltransferase PRMT5 promotes D2-like dopamine receptor signaling. Sci Signal 8:ra115|