Abstract
Addictive drugs usurp the brain's intrinsic mechanism for reward, leading to compulsive and destructive behaviors. In the ventral tegmental area (VTA), the center of the brain's reward circuit, GABAergic neurons control the excitability of dopamine (DA) projection neurons and are the site of initial psychostimulant-dependent changes in signaling. Previous work established that cocaine/methamphetamine exposure increases protein phosphatase 2A (PP2A) activity, which dephosphorylates the GABABR2 subunit, promotes internalization of the GABAB receptor and leads to smaller GABABR-activated G protein-gated inwardly rectifying potassium (GIRK) currents in VTA GABA neurons. How the actions of PP2A become selective for a particular signaling pathway is poorly understood. Here, we demonstrate that PP2A can associate directly with a short peptide sequence in the C terminal domain of the GABABR1 subunit, and that GABABRs and PP2A are in close proximity in rodent neurons (mouse/rat; mixed sexes). We show that this PP2A-GABABR interaction can be regulated by intracellular Ca2+. Finally, a peptide that potentially reduces recruitment of PP2A to GABABRs and thereby limits receptor dephosphorylation increases the magnitude of baclofen-induced GIRK currents. Thus, limiting PP2A-dependent dephosphorylation of GABABRs may be a useful strategy to increase receptor signaling for treating diseases.
Significance Statement:
Dysregulation of GABAB receptors underlie some of the altered neurotransmission in many neurological disorders. Protein phosphatase 2A (PP2A) is involved in dephosphorylating and subsequent internalization of GABAB receptors in models of addiction and depression. Here, we provide new evidence that PP2A B55 regulatory subunit interacts directly with a small region of the C-terminal domain of the GABABR1 subunit, and that this interaction is sensitive to intracellular Ca2+. We demonstrate that a short peptide corresponding to the PP2A interaction site on GABABR1 competes for PP2A binding, enhances phosphorylation GABABR2 S783, and affects functional signaling through GIRK channels. Our study highlights how targeting PP2A dependent dephosphorylation of GABABRs may provide a specific strategy to modulate GABABR signaling in disease conditions.
Footnotes
SJM serves as a consultant for AstraZeneca, and SAGE Therapeutics, relationships that are regulated by Tufts University. SJM holds stock in SAGE Therapeutics. No conflicts of interest for the other co-authors.
This work was supported in part by the National Institutes of Health (NIH)-- National Institute on Drug Abuse (DA037170) for PAS and SJM, the National Institute on Alcohol Abuse and Alcoholism (AA018734) to PAS, the National Institute of Neurological Disorders and Stroke (NS051195, NS056359, NS081735, R21NS080064 and NS087662) for SJM, the National Institute of Mental Health (MH097446) for SJM, a 2017 NARSAD Young Investigator Grant to XL, and the Yale/NIDA Neuroproteomics Center (P30 DA018343) for SJM and ACN. We thank the Slesinger and Moss laboratories for discussions on the experiments.
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