Direct interaction of GABAB receptors with M2 muscarinic receptors enhances muscarinic signaling

Abstract

Downregulation of G-protein-coupled receptors (GPCRs) provides an important mechanism for reducing neurotransmitter signaling during sustained stimulation. Chronic stimulation of M2 muscarinic receptors (M2Rs) causes internalization of M2R and G-protein-activated inwardly rectifying potassium (GIRK) channels in neuronal PC12 cells, resulting in loss of function. Here, we show that coexpression of GABAB R2 receptors (GBR2s) rescues both surface expression and function of M 2R, including M2R-induced activation of GIRKs and inhibition of cAMP production. GBR2 showed significant association with M 2R at the plasma membrane but not other GPCRs (M1R, μ-opioid receptor), as detected by fluorescence resonance energy transfer measured with total internal reflection fluorescence microscopy. Unique regions of the proximal C-terminal domains of GBR2 andM2R mediate specific binding between M2R and GBR2. In the brain, GBR2, but not GBR1, biochemically coprecipitates with M2R and overlaps with M 2R expression in cortical neurons. This novel heteromeric association between M2R and GBR2 provides a possible mechanism for altering muscarinic signaling in the brain and represents a previously unrecognized role for GBR2. Copyright © 2009 Society for Neuroscience.